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Technical Series

Steam boilers

L.I.F.E. pharmaceutical plant, part of B. Braun Melsungen AG Two Vitomax 200-HS high pressure steam boilers deliver up to 40 tonnes of steam per hour for the production of infusion solutions.



Page 1 1.1 1.2 2 2.1 2.2 2.3 3 3.1 3.2 3.3 4 4.1 4.2 4.3 4.4 4.5 4.5.1 4.5.2 4.5.3 4.6 4.7 5 5.1 5.2 5.3 5.4 5.5 6 6.1 6.2 6.3 6.4 7 7.1 7.2 7.3 8 8.1 8.2 9 10 Introduction Aim of this technical series Steam ­ a brief history General principles Heat content of steam Application areas for steam What is steam? Steam generation Steam boilers Legal framework Components of a boiler house Components of a steam boiler system Steam boilers Burner Feedwater preheaters/Eco Flue gas system Water treatment Chemical water treatment Osmosis systems Thermal water treatment Condensate treatment Regulating and control systems Sizing Pressure and output Primary energy demand of a steam boiler system Boiler feedwater level control Application procedure for steam boiler systems in Germany Multi-boiler systems Positioning Location Noise emissions Transport Handling Operation Operating modes Standards and regulations governing operation Service Special types Waste heat boilers Steam boilers with superheaters Reference systems Advanced design and production methods ensure high quality 4








51 54


1 Introduction

1.1 Aim of this technical series It is the aim of this technical series to provide an insight into the basic aspects of steam utilisation and its generation in steam boilers. The properties of steam differ considerably from those of the more frequently utilised heat transfer medium water. Consequently, we will first turn to some fundamental considerations regarding the medium "steam" and steam generation. We will then introduce the individual components of a steam boiler and provide information regarding the sizing, positioning and operation of steam boiler systems. This technical series considers only the generation of steam and does not, in any detail, concern itself with "hot water boilers". The content refers to "land-based steam"; in other words, stationary steam generation (Fig. 1). The particular features associated with mobile generation, e.g. on board ships, are excluded here. Where reference is made to standards and Acts of Parliament, we refer exclusively to European rules. By way of example, considerations are taken into account that are based on German regulations. These cannot necessarily be applied to other countries.

Fig. 1: Stationary steam engine

Fig. 2: Geysers and volcanoes are natural steam generators

1.2 Steam ­ a brief history Steam has been known since man first used fire; it was and is created unintentionally when a fire is put out with water or during cooking. Archimedes (287 to 212 BC) is considered to have first studied the technical utilisation of steam, i.e. in the design of a steam canon. Leonardo da Vinci (1452 to 1519) first made calculations on the subject, according to which an 8 kilogram shot would be propelled 1250 metres if fired from such a canon.

Denis Papin is credited with the practical execution of the steam cooker (circa 1680). This first pressure vessel was already equipped with a safety valve, after a prototype exploded during initial experiments. The utilisation of the steam engine from circa 1770 made it essential, to take a closer look at the process medium water, both theoretically and in practical terms. Practitioners included James Watt and Carl Gustav Patrik de Laval, both of whom became wealthy men from marketing their machines.


2 General principles

2.1 Heat content of steam The benefit of steam as a heat transfer medium is its considerably higher thermal capacity compared to water (Fig. 3). With identical mass and temperature, the heat content of steam is more than 6 times as high as that of water. The reasons for this phenomenon lie in the substantial evaporation energy required to evaporate water; that energy is then contained in the steam that has been created and is released again upon condensation. This characteristic is well-known from boiling water (Fig. 4): To evaporate the content of a pan, a considerable period of time is required for heat absorption via the hot plate of a cooker. The energy transferred during that time serves exclusively to evaporate the water; the temperature of the water or steam remains constant (under atmospheric pressure 100 °C) (Fig. 5). This gives steam a substantial advantage as a heat transfer medium: Compared with water, only one sixth of the mass needs to be moved for the transfer of the same heat volume.


Calorific content, water vapour: 2675.4 kJ (1 kg, 100 °C, 1 bar)

Calorific content, water: 417.5 kJ (1 kg, 100 °C)

Calorific content [kJ]

Fig. 3: Calorific content of water and steam


Boiling temperature

Boiling x = 1 Time

Fig. 4: Boiling water

Fig. 5: Boiling characteristics


General principles

2.2 Application areas for steam Steam is used in many industrial processes as an energy medium and as a medium for carrying chemical substances. Typical application areas are, amongst others, the paper and building material industry, refineries, the pharmaceutical industry and processing of food on an industrial scale. Steam drives turbines for the generation of power, vulcanises rubber products and sterilises packaging.

Liquification of ice under pressure

Critical isotherms


Critical point

Melting point 1 Pressure [bar] 0.006 Triple point Normal boiling point

Typical applications for stationary steam production:

­ Steam turbines, ­ Steam heating systems (medium for transferring the thermal energy), ­ Chemical processes: as energy carrier and carrier of active agents, ­ Food processing industry (fruit juice production, breweries, pasta and cheese production, dairies, large bakeries); also for sterilising ­ Fertiliser industry, ­ Vulcanising rubber products, ­ Pharmaceutical industry for sterilisation purposes and as carrier of therapeutic agents, ­ Building material industry, ­ Paper industry, ­ Refineries (cracking crude oil), ­ Wood processing (forming wood), ­ For the generation of a vacuum by replacing air and subsequent condensation. The generation of steam for industrial purposes and its "handling" differ significantly in some points from conventional heat generation in heating technology using water as the heat transfer medium. In particular, the high pressure steam generation in the higher output range requires special equipment for the systems concerned.

0.01 Temperature [°C]



Fig. 6: Physical characteristics

2.3 What is steam? Within the context of this technical series, we are not talking about mixtures of air and steam but exclusively about dry steam generated in sealed systems (steam boilers). Steam is created from the liquid or solid phase through evaporation or sublimation. In the physical sense, steam is gaseous water. With time, the evaporation of water generates a dynamic equilibrium, at which point the same number of particles of the liquid or solid phase transfer into the gaseous phase and vice-versa from the gaseous into the solid/liquid phase. At this point, the steam is saturated. How many particles change from the one into the other phase is largely dependent on the pressure and temperature of the system concerned.

Physical characteristics (Fig. 6): Density at 100 °C and 1.01325 bar: 0.598 kg/m3 Spec. thermal capacity: cp= 2.08 kJ/(kg·K) Thermal conductivity: > 0.0248 W/(m·K) Triple point: 0.01 °C corresponding to 273.165 K at 0.00612 bar Critical point: 374.15 °C at 221.2 bar


General principles

Wet steam, superheated steam, saturated steam

When evaporating water in a colder ambience whilst adding heat, particles of the gaseous water condense again into fine droplets. At this point, the steam consists of a mixture of fine droplets and gaseous, invisible water. This mixture is described as wet steam (Fig. 7). In the T-s diagram (Fig. 8), the range of wet steam extends to the critical point at 374 °C and 221.2 bar. Above this temperature, steam and liquid water can no longer be distinguished in their density, which is why that state is referred to as "supercritical". This state is irrelevant to the application of steam boilers. Supercritical water has, from a chemical viewpoint, particularly aggressive properties. Below the critical point, steam is obviously "subcritical" and in equilibrium with the liquid water. "Superheated steam" is created if it is heated further in this range via the associated evaporation temperature, after the liquid has been fully evaporated. This form of steam contains no water droplets and is, in its physical characteristics, also a gas and is invisible. The border region between the wet and superheated steam is referred to as "saturated steam"; in the border towards wet steam it is also known as "dry steam". Most tabular values regarding steam refer to this state.


Wet steam


Cylinder boiling

Heat supply Convection inside the steam boiler x=0 x>0 x = 0.2 x = 0.8 x<1 x=1

e.g.: x = 0.8 = : 80% of the water is present as steam volume

Fig. 7: Wet steam, superheated steam, saturated steam


Critical point x = Percentage by mass, steam [%]


x = 40%



0% =

x = 60%

x =









0 Evaporation heat: 2250 kJ/kg Temperature [°C] ­100

­200 ­273 0.0







Entropy [kJ/(kg · K)] Change of state of water at 100 °C and 1 bar pressure

Fig. 8: T-s diagram for water


General principles

Condensation and defervescence

When the steam is cooled down, at some point the dew point is reached, where the steam is saturated again; cooling it down further condenses the steam to a liquid. In the case of a direct change from the gaseous to the solid state, in other words during resublimation, this point is referred to as the frost point. Supersaturation is reached if the steam is cooled down below the dew point without condensation occurring. The reason for this condition is the absence of condensation nuclei, e.g. dust or ice particles. Defervescence can occur in the "opposite direction": Water without dust particles or gas bubbles can also be heated beyond the boiling temperature without boiling. The smallest of faults, such as shocks as a result of mixing, can lead to an explosive separation between the liquid and vapour phase; this is described as defervescence.


Critical point

Liquid Superheated steam 300 400

1 Steam

Pressure [bar]


Triple point 0 100 200

Temperature [°C]

Fig. 9: Boiling point curve of steam

Risks caused by steam

A small amount of steam can transport a large amount of heat and therefore energy. For this reason, the destructive potential associated with equipment handling steam, such as steam boilers and pipework, is substantial. A conventional steam boiler for industrial applications is a sealed vessel. This means that the steam is generally under pressure higher than atmospheric pressure. At ambient pressure, one litre of water turns into 1700 litres of steam; at 7 bar, this volume is reduced to 240 litres. It is easy to see that, should the vessel be opened, the volume would violently expand with resulting dangers. Steam (in the "superheated" state) escaping at a high temperature and pressure from a faulty pipe is invisible and can form a beam of considerable length. Contact with such a beam over a larger area would be lethal due to instant scalding.


3 Steam generation

3.1 Steam boilers A steam boiler is a sealed vessel designed for the purpose of generating steam pressure at a higher level than atmospheric pressure. "Harnessing" the steam raises the pressure and consequently the boiling temperature. This also increases the energy content of the resulting steam (Fig. 10). Different boiler types can be differentiated either according to their design, method of combustion or type of fuel. Steam boilers are defined by their design, steam output and permissible operating pressure. Essentially, two designs are offered to generate high pressure steam with a higher output range: The water tube boiler and the flame tube/smoke tube boiler (also referred to as boiler with large water chamber). With the former type, the water is held inside tubes that are surrounded by hot gas. This design is conventionally used as a quick steam boiler up to approx. 30 bar or as a water tube boiler up to approx. 300 bar. Flame tube/smoke tube boilers cannot, on account of their design principles, be operated at such pressure. With this design, the hot gas (flue gas) flows through tubes that are surrounded by water (Fig. 11). Subject to size, these boilers can be operated with a permissible pressure of approx. 25 bar and deliver, for example, 25 tonnes of steam per hour. The design of the flame tube/smoke tube boiler is suitable to cover the demands for steam generation ­ in particular regarding pressure and steam volume ­ safely and economically. Where low pressure steam (up to 1 bar) is required, this design is also the conventional choice.

Calorific content, water vapour: 2777.0 kJ (1 kg, 180 °C, 10 bar)

Calorific content, water vapour: 2675.4 kJ (1 kg, 100 °C, 1 bar)

Calorific content [kJ]

Fig. 10: Calorific content of steam

Fig. 11: Vitomax 200-HS ­ High pressure steam boiler

Fig. 12: Vitomax 200-HS ­ High pressure steam boiler type M237; steam output: 0.5 to 3.8 t/h

Fig. 13: Vitomax 200-HS ­ High pressure steam boiler type M235; steam output: 4.0 to 25.0 t/h


Steam generation

As early as 1985, there was a call for uniform technical rules to achieve an internal European market without trade barriers. However, different regulations concerning the manufacture of pressure equipment, and consequently steam boilers, still applied to the countries of the European Union until 1997. The "Directive 97/23/EC of the European Parliament and Council dated the 29.05.1997 on the assimilation of the legal requirements for pressure equipment in Member States" (PED) came into force on the 29.05.1997, granting a transition period of five years for member states. This Directive applies to all steam boilers with a permissible operating pressure above 0.5 bar or an operating temperature higher than 110 °C and a volume in excess of 2 litres. For content details it should be noted that the total steam boiler volume must be taken into account. This Directive does not apply to steam boilers with an operating pressure below 0.5 bar and an operating temperature lower than 110 °C. For systems of that type, the Gas Equipment Directive applies, for example. The PED regulates all processes up to the point of bringing the pressure equipment into circulation. Apart from the pressure equipment itself, all equipment components with safety functions and all pressurised equipment parts fall into the scope of this Directive. Appendix II of the PED splits combustion pressure equipment (steam boilers) into different categories (Fig. 14).

PS [bar]


100 32 25 10 3 1 0.5 I II III

Article 3, paragraph 3

3.2 Legal framework


PS = 32 PS ·V ·V = = 20 50







V = 1000


PS = 0.5




6.25 10


400 1000

10 000 V [Litre]

Fig. 14: Diagram of the PED, modified according to the EHI (Association of the European Heating Industry, guideline regarding the application of the Pressure Equipment Directive 97/23/EC)

The high pressure steam boiler of the Viessmann series Vitomax 200-HS, as well as the low pressure steam boiler Vitomax 200-LS, on account of the formula: Pressure · Content fall into category IV of the diagram. Only the Vitoplex 100-LS boiler series (steam boilers with a permissible operating pressure of 1 bar) with a content of less than 1000 litres fall into category III. The possible module categories according to the PED are derived from categories III and IV.

The module categories regulate which tests the manufacturer can carry out and which tests must be performed by an independent test body ("named institute" according to the PED). Viessmann high pressure steam boilers to category IV are preferably tested in accordance with module G. This means that a "named institute" charged with the testing by the manufacturer carries out all boiler tests. These tests comprise checking the design (checking the pressure part calculation and construction in accordance with standard specifications), checking the production processes, monitoring the build, strength test (pressure test) and a final inspection.


Steam generation

The institute charged with carrying out the tests issues a Declaration of Conformity after a successful final inspection in accordance with module G. The manufacturer states in the Declaration of Conformity (Fig. 17) that the steam boiler meets the current requirements according to the PED or other applicable Directives. As a symbol that these requirements have been met, the manufacturer affixes the CE symbol to the boiler. Standard boilers can be manufactured to module B (EC type testing). With this module, the manufacturers themselves carry out the tests on each standard boiler. One condition for this is that the manufacturer operates an approved quality assurance system for the manufacture, final inspection and all inspections/ tests associated with the manufacture, subject to monitoring by a named institute. By the manufacturer affixing the CE symbol and issuing the Declaration of Conformity, as well as providing verification of tests having been carried out in accordance with the module derived from Fig. 14, the boiler can be brought into circulation without any trade barriers anywhere in the territory of the EU member states. EU member states must assume that the boiler meets all regulations of current Directives, e.g. the PED (assumption of conformity). For countries outside the EU that do not recognise the PED, specific arrangements will need to be made between the manufacturer and the supervisory body of the country concerned.

Fig. 15: System comprising three Vitoplex 100-LS ­ one low pressure steam boiler and two hot water boilers

Fig. 16: Vitoplex 100-LS low pressure steam boiler, 260 to 2200 kg/h

Fig. 17: Declaration of Conformity for boilers


Steam generation

Steam to consumers


Control panel

Top-up water

Steam boiler with combustion system

Thermal water treatment (full aeration)

Blow-down valve

Feed water control valve with spillback

Boiler feedwater pump

Chemical water treatment (softening)

Untreated water

Cooling water

Condensate cylinder

T.D.S. expander

Mixing cooler


Condensate from consumers

Fig. 18: Components of a steam boiler system

3.3 Components of a boiler house A well functioning boiler system comprises not only the steam boiler with its safety, control, indication and shut-off equipment, but also additional assemblies required for the operation of such systems (see Fig. 63, page 32/33). This chapter should provide an overview and illustrate the interaction of the different assemblies. The details of these assemblies are described in the following chapters. A typical boiler system comprises the following main components:

Fig. 19: Vitomax 200-HS High pressure steam boiler type M237; steam output: 0.5 to 3.8 t/h

Fig. 20: Vitomax 200-HS High pressure steam boiler type M235; steam output: 4.0 to 25.0 t/h

1. Boiler house/boiler room

The structural layout of the boiler house is subject to the Building Regulations of the respective country. The requirements for the boiler positioning inside the boiler room and in connection with the surrounding areas and their use is regulated [in Germany] by the TRD 403 (technical rules for steam).


Steam generation

The ventilation apertures to supply the combustion air and equipment for lighting the boiler system are considered to be part of the boiler house, as is any method of communication with the outside.

2. Steam boilers

Steam boilers are defined by their design, their steam output and their permissible operating pressure. The safety equipment, control, display and shut-off equipment, the feedwater module, the combustion system (burner) and the control system are considered to be part of the steam boiler. The selection of the individual components is governed by the system operating mode and the fuel preferred by the user.

3. Economiser

To raise the boiler efficiency level, a feedwater preheater (economiser ­ ECO) in the shape of an integral assembly or one installed downstream of the boiler is added to the steam boiler. Inside the ECO, the feedwater is heated by the flue gas, thereby cooling the flue gas (Fig. 21).

Fig. 21: Vitomax 200-HS oil/gas fired high pressure steam boiler with ECO integrated into the flue gas chamber; steam output: 4.0 to 25.0 t/h

4. Fuel supply

In Germany and in neighbouring states the predominant fuel types have been fuel oil EL and natural gas. Alternative types of fuel, such as heavy fuel oil, waste oil, LPG, biogas, blast furnace gas etc. are restricted to individual cases. Heating with fuel oil requires storage tanks, filling facilities, intermediate storage tanks, fuel oil pumps (Fig. 22), fuel lines with oil fittings and safety shut-off valves are part of the fuel supply system. Gas combustion requires a quickacting gas shut-off valve, gas lines inside the boiler room, ventilation apertures and the gas train, all of which are part of the fuel supply system (Fig. 23).

Fig. 22: Twin oil pump unit (source: Weishaupt)

Fig. 23: Gas train


Steam generation

5. Flue gas system

The flue pipes between the boiler/ economiser and the chimney, the flue gas silencer and the chimney are considered to be part of this system.

6. Chemical water treatment

The type of treatment process is subject to the following: ­ Chemical consistency of the untreated water ­ Quality of the condensate ­ Volume of the condensate that is returned ­ Requirements regarding the steam quality ­ T.D.S. rate of the steam boiler The process for treating the water is selected on the basis of these criteria. Equipment for conditioning the feedwater are also part of the area of water treatment.

Fig. 24: Flue gas system (source: ASETEC)

Fig. 25: Chimney foot

7. Thermal water treatment

Removing the solute gases from the feedwater, such as oxygen and carbon dioxide that are detrimental to the boiler operation, requires equipment for thermal deaerating. Increasing the temperature reduces the solubility of the water for these gases, thereby reducing the gas content in the feedwater.

9. Superheaters

Superheaters are designed to superheat the steam beyond the saturation temperature (see also page 50, point 8.2: Steam boilers with superheaters).

10. Pipework

All pipework, fittings, steam distributors and dewatering lines required for the transportation of the different media, are also considered to be part of the boiler house components.

8. Thermal equipment

Part of thermal water treatment facilities is equipment for expelling the gases contained in the water, such as a full deaerating system, tanks for cooling the blow-down and desalination water from the steam boiler, heat exchangers for recovering energy from the desalination of the water, and condensate containers, including the associated condensate pumps.

All the above components are considered by the supervisory body when assessing a boiler system.


4 Components of a steam boiler system

4.1 Steam boilers In Germany, more than 50% of operational high pressure steam boilers are boilers with large water chambers of the three-pass design; this description also applies to the Vitomax 200-HS (Fig. 26 and 27). The three-pass design enables a particularly clean and consequently a very environmentally responsible combustion to be achieved. At the end of the combustion chamber, the hot gases flow through a watercooled reversing chamber into the second flue (pass). In a further reversing chamber in the area of the front boiler door, the hot gases reach the third flue (pass) that is designed as a convection heating surface. The hot gases leave the combustion chamber through the rear reversing chamber and include no returning hot gases; consequently the flame can transfer more heat and is therefore cooled down more thoroughly. This circumstance, combined with the reduced dwell time of the hot gases in the reaction zone, reduces the formation of nitrogen oxide. The design principle of boilers which have a large water chamber is characterised by their large water volume, a large steam chamber and the resulting excellent storage capacity. Consequently, this type of boiler safeguards a stable steam delivery, even where loads fluctuate strongly or briefly. The large evaporator surface, in conjunction with the favourably laid out steam chamber and the integral demister ensure a delivery of dry steam. High steam output with short heatup times are a guaranteed feature of the three passes.

Fig. 27: Three-pass boiler Vitomax 200-HS

Fig. 26: Vitomax 200-HS oil/gas fired high pressure steam boiler with ECO integrated into the flue gas chamber; steam output: 4.0 to 25.0 t/h

Combustion chamber (pass 1) Hot gas flue (pass 2)

Hot gas flue (pass 3)


Components of a steam boiler system

The heat transfer within the flues is split as follows: ­ Pass 1 and reversing chamber approx. 35% ­ Pass 2 and 3/smoke tube flue approx. 65%. The Vitomax 200-HS design is characterised by the following special features: ­ Clean combustion with low nitrogen oxide emissions through low combustion chamber loading ­ Large steam chamber and large evaporator surface as well as an integral demister improve the steam quality ­ High level of serviceability through water-cooled rear reversing chamber without lining ­ Large cleaning door ­ A stable cover on top of the boiler is part of the standard delivery ­ this simplifies installation and protects the thermal insulation against accidental damage (Fig. 28) ­ High level of operational reliability and a long service life through wide water galleries and large distances between the hot gas tubes ­ Large water content ensures excellent natural circulation and a reliable heat transfer ­ Low radiation losses through 120 mm thick composite thermal insulation and water-cooled front ­ Low pressure drop on the hot gas side through convection heating surfaces with large hot gas tubes. The maximum steam boiler output is governed by the European standard EN 12953, compulsory for manufacturers. When using gas, boilers can be built up to an output of 25 t/h; for fuel oil, the maximum rating is 19 t/h. Subject to boiler output, the permissible operating pressure may be up to 25 bar.

Fig. 28: Stable boiler cover ­ part of the standard delivery of the Vitoplex boilers from 575 kW and for the Vitomax boilers

Fig. 29: Steam boiler system

The approval bodies in some countries require test points for monitoring the flame tube temperature for boiler output ratings from 12 MW when using fuel oil or from 15.6 MW for gas fired boilers. Such test ports can be easily integrated into the Vitomax 200-HS.

Fig. 30: Steam distribution


Components of a steam boiler system

The safety equipment, control, display and shut-off equipment, feedwater module, combustion system (burner) and a control panel for regulating all boiler-specific control equipment are considered to be part of the steam boiler. The selection of the individual components to be added to the steam boiler is governed by the system operating mode and the fuel preferred by the user. Blow-down and T.D.S. valves on the steam boiler are of particular importance. They are required to ensure consistently reliable operation of the steam boiler. During operation, sludge deposits are created inside the boiler that must be removed regularly. The so-called blow-down valve is designed for this purpose (Fig. 31); it drains boiler water from the lower boiler zone. If that valve is opened suddenly, the quick flow of water effectively removes the sludge from the lower boiler zone. During steam generation, the solute salts in the water originating from dosing remain in the water and increase the salt concentration of the boiler water. An excessively high salt concentration results in the formation of a solid crust, reduces the heat transfer and leads to corrosion and foaming, enabling the foam in the water to enter the steam system. This leads to reduced steam quality and water backup; both put additional strain on the fittings. In addition, the function of the water level controllers that safeguard the adequate water level in the boiler would be impaired. For this reason, T.D.S. valves have the task of preventing an excess of permissible salt concentration. The salt content is measured by a T.D.S. electrode fitted inside the boiler; it triggers the opening of the T.D.S. valve (Fig. 32) when the set level is exceeded.

Fig. 31: Automatic valve for regularly draining the sludge from the boiler

Fig. 32: T.D.S. valve


Components of a steam boiler system

4.2 Burner It is the task of burners to make the energy content of fuel available as thermal energy. Conventionally, boilers with large water chambers burn liquid and/or gaseous fuels. In rare cases, coal dust or wood is also combusted; however, due to their rarity we shall not discuss these in detail here.

Combustion air

Gas and oil can only be combusted by adding oxygen (air). For this reason, every burner is fitted with a combustion air fan. Subject to arrangement, we differentiate between mono and dual-block burners. (Mono-block: the fan is fitted to the burner; dual-block: the fan is fitted on its own.) The combustion air fan is designed to deliver the stoichiometrically required air volume plus the approximate supplement of 10% required in practice to bridge the system-specific pressure drop. This may, amongst others, comprise that of the boiler, burner, economiser and flue gas silencer. To safeguard clean combustion and a long service life of the boiler and burner, the temperature of the inrushing combustion air should be between 5 °C and 40 °C. In addition, the air should be free from corrosive elements, such as chlorine or halogen compounds.

Fig. 33: Pressure pulveriser (source: Weishaupt)

Fig. 34: Sectional view of a pressure pulveriser (source: Weishaupt)

Fig. 35: Rotary pulveriser (source: Saacke)

Fuel oil

Fuel oil is categorised as follows: HEL: Extra light fuel oil Hu = 42.7 MJ/kg S Oil: Heavy fuel oil Hu = 40.2 MJ/kg Oils may have a different consistency from country to country. The DIN 51603 T1 and T3 describe the minimum requirements for the above fuel oils. In addition there are oils, particularly outside Europe, that cannot be allocated to the above categories but that are conventionally used in boilers. Different burner versions are offered for the various oil types. These burners are differentiated as pressure pulverisers, steam pressure pulverisers and rotary pulverisers.

Pressure pulveriser

This burner pulverises the oil into an oil fog using pump pressure and a nozzle. These burners are primarily used to pulverise light fuel oil (Fig. 33 and 34).


Components of a steam boiler system

Steam pressure pulveriser

The oil is pulverised in the burner head with the aid of steam. This process is conventionally used only for very high output ranges.

Rotary pulveriser

This process sees the oil placed into a quickly rotating cup. The rotation and conical shape of the cup interior let the oil drift towards the combustion chamber, and it is finely pulverised at the edge of the cup through the centrifugal effect and pulverising air that is expelled at high velocity. Rotary pulverisers are preferred in the combustion of heavy fuel oil (Fig. 35). They are also suitable for the combustion of light fuel oil, oil residues, such as oil:grease mixtures or degreasing residues, for animal or chip fat as well as for rape seed oil.

Fig. 36: Gas burner (source: Weishaupt)

Gaseous fuels

We are considering here the natural gas group. LPG and town gas are not highlighted here due to their minor relevance. Natural gas is a gas consisting mainly of methane (CH4). Its consistency may differ, subject to its origin. Normally, natural gas contains, amongst others, inert gases (noncombustible constituents) and possibly heavy hydrocarbons. Natural gas is heavier than town gas, but lighter than air. Natural gas H: Natural gas L: Hu = 36 MJ/kg Hu = 32 MJ/kg

Fig. 37: Dual-fuel burner (source: Weishaupt)

Fig. 38: Dual-fuel burner for oil and gas on the Vitomax 200 HS

In many cases, biogas or sewer gas can be mixed with natural gas; frequently both gases can be used without mixing them with natural gas. The change in calorific value must be observed when mixing gases so that it is noted if the burner needs to be adjusted or a special burner is required.

Generally speaking, observe the sulphur content when designing a system, as high-grade materials, such as stainless steel, may be required for those fittings that are in contact with gas.

Dual-fuel burner

Conventionally, these are burners that can combust gas and oil. The changeover between these fuels can be manual or automatic, e.g. based on OFF periods prescribed by the gas supplier that require a changeover to oil. This version is preferred for larger systems to safeguard continuity of supply.


Components of a steam boiler system

4.3 Feedwater preheater/Eco An economiser is a flue gas/water heat exchanger that is integrated into the steam boiler (Fig. 26, page 15) or installed as a separate assembly behind the boiler. With steam boilers, such economisers are used to preheat the feedwater. The flue gas temperatures at the boiler outlet are approx. 50 K higher than the temperature of the saturated steam. Because of the laws of physics, this value cannot be further reduced economically during the heat transfer. This comparatively high flue gas temperature is used to calculate a combustion efficiency of 89 to 91%. Consequently, the flue gas loss can be as high as 11%. The German Immissions Act (BImSchV) specifies a maximum flue gas loss of 9%. Therefore, in many cases feedwater preheaters (economisers ­ ECO) are used to achieve values lower than that limit. Generally, the ECO are installed downstream of the third flue (pass) in boilers with large water chambers. There, the flue gas is further cooled by the boiler feedwater flowing in countercurrent fashion through the exchanger. The thermal sizing is established in accordance with the fixed parameters flue gas volume and temperature, feedwater volume and temperature and the required flue gas temperature downstream of the ECO. Subject to the size of the heating surface area, the flue gas is cooled to approx. 130 °C. Economisers in two sizes for the Vitomax steam boilers, to cool flue gases to approx. 180 °C or 130 °C, are offered as standard products. The feedwater is heated from 102 °C (inlet temperature) to approx. 135 °C (with a flue gas temperature of 130 °C). Upon customer request, different values are calculated and offered. This can enable a combustion efficiency of 95% to be achieved.

93.0 92.5 92.0 91.5 91.0 90.5 90.0 89.5

Boiler efficiency [%]




Boiler efficiency [%] Boiler output [%] relative to rated output

89.0 88.5 88.0 87.5


Boiler output [%] relative to rated output


Operating pressure 5 bar Operating pressure 7 bar Operating pressure 9 bar Operating pressure 12 bar Operating pressure 15 bar Operating pressure 17 bar Operating pressure 19 bar Operating pressure 21 bar Operating pressure 24 bar


Operating pressure 5 bar Operating pressure 7 bar Operating pressure 9 bar Operating pressure 12 bar Operating pressure 15 bar Operating pressure 17 bar Operating pressure 19 bar Operating pressure 21 bar Operating pressure 24 bar

Fig. 39-1: Boiler efficiency subject to operating pressure without economiser (average value for all boiler sizes, residual oxygen content in the flue gas 3%, feedwater temperature 102 °C)

Fig. 39-2: Boiler efficiency subject to operating pressure with economiser 200 (average value for all boiler sizes, residual oxygen content in the flue gas 3%, feedwater temperature 102 °C)

Venting via the roof

Blow-off line




Vitomax 200-HS


Fig. 40: Control diagram for an ECO that can be shut off with valves and bypass


Components of a steam boiler system

The experience gained from economisers leads to the conclusion that a reduction of the flue gas temperature by 20 °C raises the efficiency by approx. 1%. The integral ECO comprises stainless steel tubes that may, for example, be fitted with fully welded spiral fins (Fig. 41 and 42). The complete connection between the fin and the tube ensures an optimum heat transfer between the flue gas and the feedwater, and also results in a very compact ECO assembly. In practical applications, two versions of ECO arrangements have found prevalence. The preferred version is the "integral ECO". With this version, the ECO is factory-fitted inside the flue gas collector of the boiler. In this form, the ECO cannot be shut off and is therefore permanently connected with the boiler via the feedwater line. Consequently, the boiler and the ECO are a joint component that is approved as combined assembly; additional shut-off valves and safety equipment are not required. A flue gas hood, provided with a flue gas connection and clean-out apertures for the ECO tube pack in accordance with customer requirements, is fitted on top of the ECO. The second version is a downstream ECO (Fig. 43) that can be installed in accordance with the physical conditions in the boiler house. Generally, this form of ECO can be shut off at the water side and equipped with a bypass on the flue gas side. This is done in the following cases: ­ To avoid the flue gas temperature falling below the dew point ­ When using different fuel types with varying consistencies (e.g. natural gas and sulphurous heavy fuel oil)

With this version, the flue gas temperature can also be regulated downstream of the ECO via the bypass position. The ECO downstream requires additional shut-off valves for the feedwater inlet and outlet, a drain valve, safety valve and pressure gauge. According to the PED, it must be considered as a separate component. To achieve optimum utilisation of the thermal energy in the flue gases, steam boilers with ECO should use modulating burners and a constant feedwater control. This ensures that the thermal energy released during burner operation is constantly used to preheat the feedwater. New systems should always be equipped with an ECO, given the improvement in boiler efficiency and the resulting fuel cost savings this can achieve.

Fig. 41: Complete connection of the fin and heat transfer (source: Rosink)

Fig. 42: Eco tubes with fully welded steel fins (example)

Fig. 43: Vitomax 200-HS steam boiler with economiser downstream (r.h. side)


Components of a steam boiler system

4.4 Flue gas system Carbon and hydrogen are essential components of liquid and solid types of fuel. After complete combustion, the flue gases contain carbon dioxide (CO2), nitrogen (N2) and water (H2O).


There are two pressure conditions relevant for the expulsion of flue gases. Accordingly, we differentiate between the type of flue gas system. When expelling flue gas with positive pressure, the burner pushes the flue gases through the steam boiler and the flue gas system right to the flue terminal. When expelling flue gas under negative pressure, the burner pressure only takes the gases to the flue outlet. Downstream of the outlet, the chimney takes over the expulsion, i.e. the flue gas system is under negative pressure. This negative pressure is created by the thermal buoyancy of the warm flue gas and the static height differential between the inlet and the terminal, as air pressure decreases with increasing height. The pipe friction and pressure drop of the integrated components, such as bends and silencers, counteract this buoyancy. Consequently, the pipe dimensions for every flue gas system must be sized in accordance with EN 13384.

Fig. 44: Flue gas silencer

Fig. 45: Flue gas system (source: ASETEC)

Flue gas systems operated with negative pressure require only a system resistant to condensate that need not be gas-tight to positive pressure, as the flue gases cannot escape at joints on account of the negative pressure. The flue must protrude at least one metre above the roof, and for systems in excess of 1 MW at least ten metres above the ground and three metres above the roof ridge. Generally speaking, consider the buildings in the surrounding area to prevent negative influences through the flue gas system. Also take into consideration any existing loading regarding emissions and noise pollution through existing flues. Frequently, such details are regulated on a regional basis; refer to the relevant authority in your country.


Today, the vertical part of the flue gas system is conventionally made from stainless steel. In some cases, fire clay is also used in steam boiler systems. The flue connection pieces (between the chimney and the steam boiler) are also mostly made from stainless steel; less frequently from mild steel (St. 37.2). Plastic flue pipes are not commonly used with industrial/commercial boiler systems.


Generally speaking, smaller pipe diameters are required when flue gas is routed through systems with positive pressure than through those with negative pressure. The flue gas system must be gas-tight if operated with positive pressure. This is achieved with welded pipes or plugin systems with seals, primarily with "older" chimney stacks or when utilising condensing technology.

Observe the fire risk

The supporting outer casing can be made from different materials. It must only meet the static requirements and, for systems inside buildings, the fire protection requirements. Consequently, the chimney inside the building has a rating of F90. For chimneys outside buildings, the outer casing simply supports the internal flue. In most cases, steel with a surface coating or brickwork/concrete are used.


Components of a steam boiler system

4.5 Water treatment The purest form of natural water is rainwater. However, rainwater contains gaseous (solute) elements picked up from the atmosphere. Essentially, these are oxygen, nitrogen, carbon dioxide and, increasingly, sulphur compounds ("acid rain"). When rainwater soaks away into the ground, further substances are added, e.g. iron and lime. The consistency of water therefore depends also on what path the water takes getting into the ground. For the operation of steam boilers, the TRD [Germany] and EN 12953 require "appropriate treatment and monitoring of the feed and boiler water". The feed and boiler water requirements are detailed in the EN 12953 part 10, the TRD 611 and the Viessmann technical guide "Water quality" (Fig. 46 and 47).

Fig. 46: Table 5-1 of the EN 12953-10 feedwater for steam boilers

The purpose of water treatment is the provision of treated water that has no detrimental effect on the boiler operation. This means constituents in the water that could result in a fault are bound, for example by adding chemicals. For boiler operation, untreated water could be surface water, well water or treated potable water. Surface or well water could contain constituents, such as suspended matter, matter that makes water opaque, organic contaminants, or iron:manganese compounds that need to be removed in the water treatment stages. These pre-treatments are not required for potable water. In boiler systems with boilers that have a large water chamber, generally two different treatment processes are applied in parallel (e.g. ion exchange and thermal water treatment).

Fig. 47: Table 5-2 of the EN 12953-10 boiler water for steam boilers and hot water boilers


Components of a steam boiler system

4.5.1 Chemical water treatment

Softening through ion exchange

The alkaline earths calcium and magnesium are solute in water in the form of ions. These elements are referred to as scale formers. These compounds would, under the influence of heat during boiler operation, form scale that settles as a solid deposit on the heating surfaces. This coating would prevent the heat transfer from the combustion to the water side. Initially, this would result in higher flue gas temperatures and in consequently reduced efficiency. As the scale thickens, the absence of cooling of the heating surfaces would lead to their destruction. For this reason, standards specify softened feedwater. Process of scale formation CaCO3 under the influence of heat: Ca(HCO3)2 ----> CaCO3 + H2O + CO2 Systems with ion exchange resin are used for softening the water. Ion exchangers are spherical resins with absorbed active groups. As an active group, ion exchangers for softening water have absorbed sodium ions. When the hard water runs over the ion exchanger, the absorbed sodium ions are exchanged for calcium and magnesium ions that are solute in the water. The scale formers that are detrimental to the boiler operation are thereby removed from the water.

Once the ion exchanger is exhausted, i.e. all sodium ions have been exchanged for calcium and magnesium ions, it will be regenerated with a sodium solution (rock salt). The sodium ions are channelled over the ion exchange mass in the surplus and replace the settled scale formers. The ion exchanger is then operational again. This process can be repeated without limit.

Loading: 2R ­ Na+ + Ca++/Mg++ ---> R2 ­ Ca++/Mg++ + 2 Na+ Regeneration: R2 ­ Ca++/Mg++ + 2 Na+ ---> 2 R ­ Na+ + Ca++/Mg++

Fig. 48: Double pendulum softening system from Viessmann

R...ion exchanger (radicals)

Generally speaking, we differentiate between three operating modes: ­ Time-controlled: Operates at set times ­ Volume controlled: Operates to set delivery volumes ­ Quality-regulated: Continually monitors the quality of the feedwater. These systems can be in the form of single or duplex systems. Single systems are designed for intermittent operation, i.e. no pure water is available during the regeneration phase (several hours). Double pendulum softening systems are compulsory for continual operation.

Viessmann offers this volume controlled, double pendulum softening system in different output sizes. The softening module comprises a completely fitted system with two columns of ion exchangers, a salt solvent and the control unit, and can be used without any additional installation effort (Fig. 48 and 49). The soft water capacity between two regenerations is selected during commissioning and results from the system size and the hardness of the untreated water. The system operates automatically and must only be replenished with rock salt to achieve regeneration. One exchanger is always available as there are two columns of ion exchangers. The second column is regenerated, and is afterwards put on standby.


Components of a steam boiler system

Dosing corrective chemicals

To maintain the alkaline level of the feedwater, to bind the residual hardness and to bind the residual oxygen, corrective chemicals are added to the feedwater after the ion exchange or osmosis. A number of products are offered by water treatment companies to achieve this. Always consult the water treatment companies regarding the application conditions.

4.5.2 Osmosis systems In the past few years, osmosis systems have been increasingly used to desalinate water. Osmosis is a natural process that operates without chemicals, and is therefore very environmentally friendly. The yield of desalinated water (permeate) is approx. 80% of the water used (Fig. 50). For osmosis, the untreated water is pushed through a diaphragm with a pressure of approx. 30 bar. The pores of the semi-permeable diaphragm allow the water molecules to pass through (diffusion); the solute salt remains on the entry side and is channelled out of the system. It should be noted that the untreated water must not contain any solids prior to entering the osmosis system, and that the scale formers are stabilised before entry (via fine filters and dosing). Solids would block the diaphragm pores and consequently rapidly reduce the system performance. Osmosis systems should be operated as continually as possible and are therefore frequently equipped with a buffer tank for the permeate.

Fig. 50: Osmosis system

Fig. 49: Setting parameters for the ion exchanger system


Components of a steam boiler system



d 1 Steam boiler with integral economiser and combustion equipment Thermal full deaerating system T.D.S. expander with heat recovery Dosing stations Feedwater pumps Mixing cooler Chemical water treatment

d b h 2 a 4 5 6 7 c 4 4 6 5 5 a b c d e f g h i 3 2


1 c c


c i

g 7

Steam to the consumer Safety valve blow-off line Air vent and drain line Vapour line Condensate feed Fuel feed Untreated water inlet Soft water Feedwater



Fig. 51: Steam boilers with thermal equipment

4.5.3 Thermal water treatment Water can only store a limited amount of gas. The storage capacity can be calculated according to Henry's law (English chemist, 1775 to 1836), subject to the partial pressure of the gas and the water temperature. For example, water contains approx. 8 mg O2/kg at a temperature of 25 °C. The solubility of gas reduces as the water temperature rises. In extreme cases, i.e. when water evaporates (the situation in a steam boiler), all solute gases are released. The gases frequently form other compounds. The free oxygen can, for example, link up with the ferrous steel of the boiler. With steam boilers, these compounds result in the dreaded pitting. Dotted abrasions can form incredibly quickly, particularly within the area of the feedwater tank.

It is therefore vital to extract the solute gases from the boiler feedwater. One proven method for this is thermal feedwater deaerating. In the deaerating system, the feedwater is largely freed from all gasses by heating it to almost boiling point. Parallel to the removal of the solute gases, the water is also held with a low steam pressure at a temperature of 80 to 105 °C (subject to the equipment selection) to prevent a renewed absorption of gases. It should be noted that, apart from fresh water, condensate too can be fed into the system. This also must be deaerated. Subject to the requirements for feedwater quality, different types of thermal deaerating units can be applied.

Information regarding the condition of boiler water is contained in the TRD 611, the EN 12953 and the codes of practice issued by the VdTÜV [Germany]. Observation of the limits stated in these documents are a prerequisite for the reliable and economical operation of a boiler system. We recommend for boilers with large water chamber to use feedwater with an O2 content of < 0.05 mg/kg.

Partial deaerating

Partial deaerating is deaerating effected under atmospheric pressure. Partial deaerators are permanently connected with the atmosphere via a ventilation line. Partial deaerating is the simplest form of thermal feedwater treatment. The partial deaerator is equipped with inserts for the distribution and irrigation of the fresh water supplied and the returning condensate.


Components of a steam boiler system

The hot steam for driving out the gases is supplied via a lance installed centrally in the lower area of the container. The steam supply is, in its simplest form, matched by a mechanical thermostat and regulated to >90 °C. Fresh water is topped up via an electric level controller. Partial deaerators are predominantly used in boiler systems with low output and pressures. The slightly higher demand for oxygen binders associated with these deaerators (see chapter 4.5.1 ­ Chemical water treatment) is an acceptable feature.

Fig. 52: Deaerator for low pressure deaerating mounted on top of a feedwater tank Fig. 53: Irrigation deaerator (source: Powerline GmbH)

Full deaerating

Full thermal deaerating is the most effective method for removing solute gases from the feedwater. Here, we differentiate between high pressure, low pressure and vacuum deaerating.

16 14

­ High pressure deaerating

High pressure deaerating is used in processes that demand high thermal system efficiencies. However, they are rarely used due to their high investment outlay.

12 10 8 6 O2 [mg/l] 4 2 0 0 20 Temperature [°C] 40 60 80 100

­ Low pressure deaerating

In most cases, low pressure deaerating has proved to the best solution. The term "full deaerating" therefore always means deaerating with slight positive pressure (approx. 0.1 to 0.3 bar). The term "low pressure" therefore describes a process at slightly above ambient pressure. The operation with positive pressure ensures that contact between the feedwater and atmosphere and the re-solution of gases is prevented. Full deaerating comprises the deaerator and feedwater container assemblies. The deaerator, in the shape of a dome, is fitted immediately onto the feedwater tank (Fig. 52 and 53).

Fig. 54: Oxygen solubility subject to temperature at 1 bar in pure water

3500 3000 2500 2000 CO2 [mg/l] 1500 1000 500 0 0 20 Temperature [°C] 40 60 80 100

Fig. 55: Carbon dioxide solubility subject to temperature at 1 bar in pure water (source: TÜV Nord)


Components of a steam boiler system

The irrigation deaerator is the most commonly used form of deaerator. In the irrigation deaerator, the condensate fed into the system and the added fresh water are finely distributed over so-called cups, and brought together with the heating steam in stages by the irrigation process (hence the term "irrigation deaerator"). The water heating and expulsion of released gases also occurs in stages. The development of these deaerators into an irrigation deaerator with an integral re-boil facility (two-stage deaerating) has proved to be particularly effective. Today, deaerators are made completely from stainless steel, to prevent corrosion. The feedwater tank is designed to hold an adequate volume of boiler feedwater. The tank is connected to the deaerator via a so-called "tank neck". The feedwater tank is equipped with a heating lance to absorb and distribute the heating steam. That safeguards a temperature of 102 °C. The lance is permanently fitted centrally in the lower tank area. For single stage deaerating, the lance is sized for the throughput of the entire heating steam. For two-stage deaerating, the lance is designed to keep the stored water warm. Both versions prevent a partial cooling of the feedwater and the resulting re-solution of gases. The feedwater tank (Fig. 56) is equipped with fittings for the regulation of the heating steam, the fill level and safety, as well as the displays required for operation and monitoring.

Fig. 56: Feedwater tank with thermal deaerating

­ Vacuum deaerating

Vacuum deaerating is a method, used just like high pressure deaerating, to optimise the thermal efficiency of a heating system. However, the main benefit, i.e. that of an operation with low temperature, does not apply to boiler systems that generally operate with water and steam temperatures in excess of 100 °C.


Components of a steam boiler system

4.6 Condensate treatment Subject to the technical processes in the area of steam application, the steam can be channelled directly into the product or the process concerned. In such cases, condensate is not added. In the largest number of applications, the steam transfers its energy via a heating surface, where it condenses. The condensate is then channelled into the heating system for further utilisation. From a technical aspect, there are two different types of condensate return.

Monitoring the condensate for loss of conductivity Alarm output LRT 1-.. URS 2

Three-way diverter valve

1. Low pressure condensate

In 90% of all steam boiler systems, the condensate is returned via open condensate tanks. At operating temperatures in excess of 100 °C, this involves a re-evaporation. This creates, subject to the pressure stage, approx. 5 to 15% in weight of steam from the condensate volume. Naturally, apart from energy losses, this results in water losses that must be made good by topping-up with fresh water that has been subjected to the appropriate water treatment. Apart from these losses the condensate will, in open systems, also absorb oxygen that can then lead to oxygen corrosion in the area of the condensate system.

Fig. 57: Condensate monitoring (Gestra conductivity gauge) (source: Gestra)

2. High pressure condensate

With high pressure condensate systems, the condensate is returned via a sealed system (approx. 10% of steam boiler applications). These conditions prevent losses through re-evaporation. At the same time, the ingress of air-borne oxygen into the condensate system is also prevented.

Such systems are appropriate if they operate with a pressure of at least 5 bar. It should be noted that all pipework, fittings, pumps and containers must be suitable for this pressure. The container (e.g. condensate collector tank, feedwater tank) are pressure vessels that must be supervised in accordance with the PED, and are therefore subject to supervision by the appropriate authority. When engineering new systems or in the assessment of existing systems it must be decided which system to use. Substantial operating costs can be saved through an optimum condensate management and the utilisation of the re-evaporation steam.

Fig. 58: Mixing cooler


Components of a steam boiler system

Condensate treatment

Condensate may be loaded with foreign bodies on account of the technical processes it has gone through and with the products of corrosion. Water quality requirements must be met, however, since the condensate is to be used again as feedwater. Typical condensate contaminants are: ­ Mechanical contaminants (corrosion products) ­ Ingress of scale (potable or process water leakage in heat exchangers) ­ Ingress of acids and alkaline solutions (unintentional mixing during the heating of acid or alkaline baths) ­ Oil and grease (food processing industry, oil preheater). Subject to the degree of contamination, the required water treatment processes, such as filtration, degreasing, softening, desalination are provided. It should be noted during the design of such systems, that the boiler regulations provide for automatic analysis equipment for monitoring the condensate when operating boiler systems without supervision. When contaminants are detected in the condensate, the contaminated condensate must be removed from the water:steam cycle. Always arrange the sample extraction point in the condensate inlet, upstream of the collector tank to prevent contaminated condensate flowing into the tank. Remove the condensate from the cycle via three-way valves.

Monitoring the condensate for an ingress of oil

Delayed alarm output Transducer ORT 6 4 ­ 20 mA CANopen (option)

Three-way diverter valve Transducer ORG 12, 22

Fig. 59: Monitoring an ingress of oil (source: Gestra)

Fig. 60: Monitoring an ingress of oil (source: Gestra)


Components of a steam boiler system

4.7 Regulating and control systems The control system, e.g. the Vitocontrol control panel (Fig. 61), contains all components required for the regulation and control of the boiler-specific equipment of steam boiler systems. The control panel also contains the components required for fully automatic boiler operation without supervision over 24 or 72 hours according to TRD 604. These include "specially designed"* components required for the operation of a steam boiler system. The ideal would be a control of the regulating and control equipment by programmable logic control (PLC). The central, full graphic colour display (touch panel) (Fig. 62) is designed for the control and setting/ adjustment of system parameters. This display also shows all functions with the associated operating conditions, as well as all set and actual values. The PLC also records the hours run by the burner and the feedwater pumps. With dual-fuel burners, the hours run and starts made by each individual burner are recorded separately. All fault messages are recorded with the date and time. The fault messages are also stored as "history" to enable the occurrence of faults, their acknowledgement and removal to be documented.

* A special design means an electrical or mechanical part of any equipment that automatically implements regular tests (e.g. for electrode water level meters, the insulation resistance of which is monitored, for immersion equipment that implement an automatic function test, for external equipment that automatically blow through connecting lines).

Fig. 62: Display

Fig. 61: Vitocontrol control panel

Main functions: Burner output controller

The boiler pressure is captured by a probe and transferred to the PLC as an analog signal. The PLC regulates the pressure to a set value selected by the operator. Using the deviation between the set and the actual pressure, the output controller calculates the burner modulation level or the respective burner stage, subject to configuration.

Conductivity boiler water T.D.S. control

The T.D.S. function is optionally achieved through a continual regulation by the PLC. The water conductivity is captured by a probe and transferred to the PLC as an analog signal. The set value "salt content" and the control parameters are defaulted by the programming unit. When the salt content is too high, the T.D.S. valve opens to drain off the saline water.

Water level control

The level control of the steam boiler stored in the PLC can be achieved as two-point control by starting or stopping the feedwater pumps or as continual control via a feedwater valve. Starting and stopping the feedwater pump(s) or the additional regulation of the feedwater valve supplies the required volume of feedwater to the boiler to maintain the set water level inside the boiler. When two feedwater pumps are installed, the pumps are switched alternately and also if one of the pumps becomes faulty.

Blow-down control

As an option, the blow-down valve can be regulated by the PLC subject to the stored values for length of interval between two blow-down events and the duration of valve control. Additional functions, such as the control of a flue gas damper, control of a bypass damper, changeover to a second set value (pressure) are also integrated into the PLC.




Steam line to deaerating Steam line to the consumer

Blow-off lineSIV






Vitomax 200-HS






Venting via the roof


Venting via the roof at high pressure gas line

Vent via t Untreated water

Blow-off line Water level indicator




11.0 12.0


Line types

Steam Blow-off Feedwater Untreated water Soft water Gas Oil Waste water Condensate Dosing Control



BOILER ECONOMISER Sample cooler Control panel COMBUSTION


Gas train Oil train THERMAL WATER TREATMENT CHEMICAL WATER TREATMENT Double pendulum softening system


Hardness stabilisa Oxygen binder MIXING COOLER T.S.D. EXPANDER














Fig. 63: Components of a steam boiler system


Venting via the roof

Venting via the roof Condensate


Venting via the roof




Dosing connection



Soft water

Condensate return from the consumer


Dosing line









Untreated water


ing he roof




Brine container

Untreated water



to the duct

ID 1st letter C H I L M P Q S T V Z Temperature Valve safety-related control action


subsequent letter automatic control unit



High Display

This drawing is for information only. The layout of components not directly fitted to the boiler, components not supplied as standard by Viessmann and the pipe routing are shown for information only. This drawing does not represent an RI design and can, therefore, not be used as such.

Fill level Motor Pressure Quality, analysis


Circuit, control unit


Steam boiler system with dual-fuel burner and integral Eco



Date Name


Process flow chart Vitomax 200-HS


5 Sizing

5.1 Pressure and output In the technical application of steam, pressure is generally expressed as positive pressure in bar. The output of a steam boiler is quoted in kg/h or t/h. It represents the maximum possible continuous boiler output and is stated on the type plate (Fig. 65). Accessories are matched to that output. The minimum continuous boiler output is determined by the minimum burner output.

Operating pressure

The pressure available at the boiler connector is described as the operating pressure. The level of that pressure is determined by the consumers to be supplied and the characteristics and layout of the steam network required for the steam distribution. In other words, the pressure at the boiler connector must always exceed that required by the consumer.

Fig. 64: High pressure steam boiler Vitomax 200-HS (4 t/h, commercial nurseries)


Hochdruckdampferzeuger mit ECO

Permissible operating pressure

The permissible operating pressure equals the response pressure of the safety valve and is specified on the type plate. It represents the maximum possible pressure with which the boiler can be operated. To enable as fault free an operation of the steam boiler as possible, the differential between the operating pressure and the permissible operating pressure for low pressure steam boilers must be at least 0.2 to 0.3 bar, and 1.5 bar for high pressure steam boilers.

High pressure steam boiler with heat exchanger Typ /Type Herstell-Nummer Serial number Baujahr Year of manufacture Zul. Betriebsdruck Permissible operating pressure Dampferzeugung Steam output Wasserinhalt gesamt / NW (LWL)


M235 122 ECO 187007480 2008


10 5 14050 / 11650 18.5

bar t/h l bar

mD =

V= PT=


Water capacity total / NW (LWL) Prüfdruck Test pressure Viessmann Werke GmbH & Co.KG D35107 Allendorf

- 0035



Fig. 65: Type plate

Categorisation into low pressure and high pressure steam boilers

Steam boilers with a permissible operating pressure up to 1 bar are described as low pressure steam boilers. Up to 0.5 bar, these boilers fall outside the Pressure Equipment Directive; they should be designed in accordance with "good engineering practice". Above 0.5 bar up to 1 bar, the design is subject to the Pressure Equipment Directive, but with lower 34

requirements than high pressure steam boilers operating above 1 bar. The equipment level and positioning can also be subject to less stringent conditions. Application areas for low pressure steam boilers are, for example: ­ Large bakeries ­ Butchers ­ Steam heating systems

High pressure steam boilers are constructed as boilers with large water chambers and a permissible operating pressure above 1 bar up to 25 bar. Application areas for high pressure steam boilers are, for example: ­ Food processing industry (breweries, dairies) ­ Paper industry ­ Pharmaceutical industry ­ Building material industry


Calculating the steam output

Water droplets will be extracted in increasing amounts if more steam is withdrawn from the boiler than the maximum permissible continuous output. This is not only detrimental to the steam quality, but also results in crusts forming on fittings and other equipment in the steam pipe. Furthermore, the steam pressure will fall and with it the boiler temperature. This might, under certain circumstances, put at risk the adequate supply of the consumers. It is therefore important to know, which consumers the boiler must supply and the extent of their respective steam demand. For this ensure that own consumption, too, is recorded, apart from the steam required for production purposes. This includes the demand for thermal water treatment or heating steam. Adding the partial loads, and possibly under consideration of the simultaneity factor, establishes the required steam output (Fig. 66). In addition, discuss with the future operator the question of availability or security of supply (ensuring a standard supply in case of faults or maintenance, backup boiler, etc.). This enables a sensible split over several boiler units.

Factor F

0.760 0.750 0.740 0.730 0.720 0.710 0.700 0.690 0.680 Operating pressure [bar] w/o flue gas/water heat exchanger (Economiser) with flue gas/water heat exchanger (Economiser), boiler efficiency: 94%

Fig. 66: Factor to determine the output of the combustion equipment via the steam output Combustion output in kW = Factor F · steam output in kg/h Example: Steam output: 10000 kg/h, operating pressure: 12 bar Operation without economiser: Factor F = 0.732 (see diagram) produces a combustion output of 7320 kW Operation with economiser (boiler efficiency 94%): Factor F = 0.697 (see diagram) produces a combustion output of 6970 kW

Boiler feed pumps for supplying the steam boilers with feedwater

The required drive output of the pump motors is determined subject to the permissible operating pressure of the steam boiler. The electrical primary demand of the pump is then determined by the steam output and the operating pressure of the steam boiler up to a specific time. It is calculated in accordance with the following equation:


·g·H·V = ­­­­­­­­­­­­ = = = = = Output demand [W] 1.25 x steam output [kg/h] Water density [kg/m3] Head [m] Pump efficiency


5.2 Primary energy demand of a steam boiler system The primary demand of the steam boiler systems is essentially determined by the electric power of all drive units of the individual main components. The main consumers are briefly described in the following.

P · V H

This shows that the pump rate demand is directly proportional to the pump head and the pump rate.



Burner system of the steam boiler

Different consumers may be included, subject to the type of fuel used: ­ The combustion air fan draws combustion air from the boiler room or directly through a duct system from outside the boiler room and supplies it to the burner. ­ With liquid fuels (e.g. HEL ­ light fuel oil), the high pressure oil pumps of the burner must also be supplied with electric power.

Further electrical consumers are the chemical water treatment, servomotors of shut-off valves and control valves, ring mains pumps in the fuel oil system, solenoid valves for regulating top-up water and small consumers, such as the control panel lighting, emergency lighting for the boiler house and system lighting. To minimise the primary energy demand, electric drives are frequently equipped with inverters. For example, if one divided the pump speed by half, to achieve 50% of the pump rate, the associated drive input for the pump would only be an eighth. As part of the engineering function, the analysis of the consumer system is an important pre-requisite for the application of inverters.

To summarise:

To calculate the primary demand of a system, always define the respective system output and the current system condition.

Additional electrical consumers

When the boiler system is shut down, some system users require that the flue gas duct is shut off using an electrically operated flue gas damper. This minimises the cooling of the boiler. The steam from the steam boiler is utilised to supply technical consumers and for heating purposes. In most cases, the condensate is collected in condensate tanks in the user system and is returned to the steam boiler system via electrically operated condensate pumps. The electrical output of the condensate pump is also calculated in accordance with the formula on page 35.

Primary steam demand

The consumption of heating steam for the supply of the thermal water treatment is also counted as primary energy demand. The top-up water from the chemical water treatment with a temperature of approx. 10 °C and the consumer condensate with approx. 85 °C are heated to 102 °C by steam to remove to atmosphere, via the deaerator, those gases that were originally solute in the water. The top-up water from the chemical water treatment makes up the water losses in the system, in other words the T.D.S. and blow-down losses and the condensate losses at the steam consumers. The higher the proportion of top-up water, the higher the primary demand for heat-up steam. The removed vapours are also losses that are compensated by top-up water.



5.3 Boiler feedwater level control The boiler feedwater pumps supply the steam boiler with feedwater in accordance with the required steam output. Experts differentiate between intermittent and continuous level control. For this, the relevant control magnitude is the steam boiler level.

Steam to consumers


Control panel

Top-up water

Steam boiler with conbustion system

Thermal water treatment (full aeration)

Boiler feedwater pump Blow-down valve

Chemical water treatment (softening)

Untreated water

Intermittent level control

The level is regulated between two adjustable switching points, i.e. "Pump ON" and "Pump OFF". The signal of the level electrode affects the pump (Fig. 67).

Cooling water

Condensate cylinder

T.D.S. expander

Mixing cooler


Condensate from consumers

Continuous level control via feedwater control valve

The control aims to maintain a near constant level inside the boiler that corresponds to the selected set value. The actual value is continuously monitored by a level probe and, in a controller, compared with the set value. Opening and closing the feedwater regulating valve regulates the set value in case of load fluctuations. A certain amount is returned to the feedwater tanks via an adjustable minimum volume line. The minimum pump rate ensures that the pump is cooled sufficiently (Fig. 68).

Fig. 67: Intermittent level control

Steam to consumers


Control panel

Top-up water

Steam boiler with combustion system

Thermal water treatment (full aeration)

Bypass Feedwater control valve Boiler feedwater pump

Chemical water treatment (softening)

Untreated water

Blow-down valve

Cooling water

Condensate cylinder

T.D.S. expander

Mixing cooler


Condensate from consumers

Fig. 68: Continuous level control via feed-water control valve



Continuous level control via feedwater control valve with spill back

Control panel

Steam to consumers


As soon as the main flow falls below a certain pump rate, the spill back non-return valve (bypass) opens enough to draw off the required minimum pump rate (for cooling purposes) (Fig. 69).

Top-up water

Steam boiler with combustion system

Thermal water treatment (full aeration)

Blow-down valve

Feedwater control valve with spill back

Boiler feedwater pump

Chemical water treatment (softening)

Untreated water

Continuous level control via variable speed pump control

The control aims to maintain a near constant level inside the boiler that corresponds to the selected set value. Load fluctuations result in the pump rate being adjusted through a variable speed control (in this case through an add-on inverter) to match the changing demand, until the set level has been achieved. This demand-dependent speed optimisation saves electrical power. This can also save the installation of control valves upstream of the boiler (Fig. 70).

Cooling water

Condensate cylinder

T.D.S. expander

Mixing cooler


Condensate from consumers

Fig. 69: Continuous level control via feedwater control valve with spill back

Steam to consumers


Control panel

Top-up water

Steam boiler with combustion system

Thermal water treatment (full aeration)

Bypass Boiler feedwater pump FU Blow-down valve

Chemical water treatment (softening)

Untreated water

Cooling water

Condensate cylinder

T.D.S. expander

Mixing cooler


Condensate from consumers

Fig. 70: Continuous level control via variable speed pump control



5.4 Application procedure for steam boiler systems in Germany Based on the legal framework "In the area of safety and Health & Safety at Work concerning the provision of equipment and their use, safety when operating systems subject to compulsory supervision and the organisation for safety in the workplace", the Health & Safety at Work Act applies [check local regulations]. Paragraph 13 determines the required steps to gain approval. The Health & Safety at Work Act determines the fundamental requirements for German law originating from the European Legislature. Boilers to category IV in accordance with the diagram of the PED (see Fig. 14, page 10) require permission for their assembly, installation and operation. As a first step, an assessment from the authorised institute selected by the user (up to the 31.12.2007, these are [in Germany] the local TÜV stations) must be sought. For this we recommend that a visit with an expert from the TÜV to the locality is arranged in advance to clarify all technical questions as part of the application process. This can reduce the time required for the process, possibly saving costs as well.

As a minimum, the following documentation is required for the professional assessment: ­ Installation drawings of the boiler system ­ Layout with boiler installation room ­ the purpose of the adjacent rooms must become apparent from the layout plan ­ Form describing the boiler system ­ Additional sheets describing the boiler system ­ Positioning ­ Gas supply ­ Oil storage ­ Flue gas heat exchanger ­ Combustion equipment ­ Unsupervised operation ­ Wiring diagrams for safety and combustion equipment

After the assessment by the responsible institute has been received, the user must apply for a permit of use at the relevant authority for the installation location [check with your local authority]. Together with the application, provide the documentation relating to the professional assessment and the assessment provided by the relevant institute. The authority must [in Germany] reach a decision within three months of application. The permit may be subject to conditions that must be observed during the installation. The assembly and installation can only commence after the authority has granted permission.



5.5 Multi-boiler systems Multi-boiler systems are used for reasons of security of supply that must be guaranteed by the steam boiler system, e.g. in hospitals for sterilisation or when there is a varying demand for steam over a given period (day/night, summer/winter). The question as to how many boilers with what output should be installed as part of a single system is not a decision made from a safety aspect, but instead is a question of the security of supply whilst ensuring the lowest possible operating costs. With a single boiler system, consider that the boiler output range is only subject to the control range of the combustion equipment. Modern gas burners can be regulated down to 10% of boiler output. The boiler shuts down if the steam demand falls below that control range. That safeguards the demand-dependent steam supply. Systems comprising several boilers are predominantly operated with a sequential control. The sequential control enables only a boiler operation that covers the steam demand under the aspect of the most economical operating mode and a high security of supply. The economical operation results from the reduced number of starts and the boiler operation in the medium load range with low flue gas losses. Generally, each boiler is equipped with its own boiler control unit and can be regulated and operated on a stand-alone basis. We recommend the provision of a PLC for control purposes. The sequence control, also via a PLC, is higher ranking than the individual boiler control unit. The sequential control in the PLC

Fig. 71: Steam provision in the AMH Chorzow Hospital, Poland ­ three high pressure steam boilers Vitomax 200 HS with 2.4 t/h (8 bar) supply steam for the heating system, for the laundry and sterilisation

regulates which boiler is the lead boiler and the sequence of the lag boiler activation. Boilers that are currently undergoing modifications or those that are not required for a longer period of time because of a reduced steam demand, and that were consequently preserved, must be removed from the sequence control. The lead boiler is changed automatically according to the period and sequence programmed in the PLC. A backup boiler is added to the sequence if the operational boiler runs at an output level of approx. 80% over a programmed period. The lag boiler will be fired-up, and after the system pressure has been reached, the motorised steam valve opens, enabling the boiler to feed steam into the steam manifold.

The boiler will be shut down when its output falls to approx. 35%. At that point, the lag boiler shuts down and the motorised steam valve closes. The pressure in the backup boilers is maintained via a second control pressure that lies lower than the required steam system pressure. That control system ensures the rapid availability of the boiler when there is additional demand, and the pressure vessel is protected against corrosion occurring during idle periods. All specific adjustments for the sequence control must be determined on an individual system basis and must be defaulted via the PLC.




6.1 Location

Standard requirements


Boiler systems should always be installed in buildings that are free from the risk of frost, dust and dripping water. The temperature in the installation room should be between 5 and 40 °C. Safeguard adequate ventilation (combustion air supply). For this ensure, that no corrosive elements (e.g. chlorine or halogen compounds) are drawn in with the combustion air. Ensure the floor has sufficient load-bearing capacity and that it is level. For the load-bearing capacity, ensure that the maximum operating weight, in other words the wet weight and all fitted components, are taken into consideration. Boilers can be installed without special foundations. However, a plinth is advisable to enable the installation room to be cleaned.

14 3 1 12 6 1 2 3 4 5 6 7 8 9 10 11 12 13 14 High pressure steam boiler Burner Control panel Blow-down valve Feed pump (observe required feed height during installation) Flue Blow-down container Feedwater container with aeration (thermal water treatment) Steam distribution Dosing Chemical water treatment Flue gas system Extract air aperture Ventilation air aperture 4 5

2 7





Fig. 72: Example of a boiler installation room


The DDA information, issue 2.2002 [Germany] describes the "Installation and operation of land-based steam boiler systems with CE-designation". These rules are essentially drawn from the TRD 403 or, subject to the water volume and permissible operating pressure, from the TRD 702 for installations with lighter regulations [all Germany ­ check local regulations]. Also observe the relevant Building Regulations and Combustions Orders of the country of installation.

Apart from minimum clearances for the operation and maintenance, escape routes, flue gas routing, fuel storage and electrical equipment, these regulations determine the type of room where steam boilers can be installed. High pressure steam boilers (category IV to TRD) must not be installed in the following areas: ­ In, under, above or adjacent to living accommodation. ­ In, under and above assembly rooms (these are washrooms, changing rooms and rest areas) and workplaces.

These regulations also list lighter installation conditions, subject to the product of water content and permissible operating pressure, whilst considering the maximum steam output. However, the standards list different requirements, consequently requiring specific clarification in advance with the locally responsible authority.



6.2 Noise emissions

Sources of noise

Noise/sound is understood to mean mechanical vibrations and waves in flexible media, such as solid bodies (structure-borne noise), air (airborne noise) and liquids. These vibrations occur at certain frequencies (= number of vibrations per second). The human ear perceives vibrations from approx. 16 Hz (low notes) to approx. 16000 Hz (high notes). Any type of sound that man finds irritating or inconvenient is described as "noise". To prevent noise creating a nuisance, the legislature [in most countries] has issued regulations for the protection against noise. In Germany, for instance, these include the BImSchG, TA-Lärm, DIN 4109, DIN 45 680, VDI guideline 2058. Subject to the different environs and times of the day, limits and measuring/assessment criteria have been laid down in these standards.

Fig. 73: Structure-borne noise attenuation

The noise emanating from the boiler equipment is generally created by the following: ­ Combustion noise ­ Burner fan ­ Structure-borne noise transmission Airborne noise is predominantly created by the combustion process, and is transmitted by emission from the burner, boiler and flue gas path. Structure-borne noise is created by mechanical vibrations in the boiler system, and is generally transmitted through the foundations, walls and sides of the flue gas system. Subject to frequency, this can create sound pressure levels of 50 to 140 dB(A).

Selected attenuation measures

Up to a limited load-bearing degree, anti-vibration mounts can be supplied ex works. In addition, structural separation is one option, such as anti-vibration foundations.

1. Structure-borne noise attenuation

Anti-vibration boiler supports reduce the transmission of structure-borne noise to the support surface (Fig. 73).



2. Flue gas silencer

Flue gas silencers are used to attenuate combustion noises (Fig. 74). To ensure their effectiveness, these measures must be closely matched to the boiler/burner combination, the flue gas system and the chimney. When sizing the installation location please note that the flue gas silencer requires a considerable amount of space.

3. Flue expansion joints

Flue expansion joints prevent the transmission of structure-borne noise from the boiler/burner unit via the flue path to the building structure. In addition, they can compensate for the thermal expansion of the flue pipes (Fig. 75).

Fig. 74: Flue gas silencer

4. Burner fan ­ silencer hoods

Silencer hoods are used to attenuate the burner fan noise. Their main purpose is therefore to reduce the noise generated inside the installation room (Fig. 76).

5. Routing the ventilation air and flue gas

Balanced flues with silencers supply the burner specifically with combustion air and prevent the outward transmission of noise created inside the installation rooms via ventilation apertures (Fig. 77). We recommend you design your system with noise attenuation from the start to avoid costly retrofitting later. One pre-requisite for achieving an optimum solution is the close co-operation between architects, client, design engineer and contractors. Contact your local authority regarding emission requirements.

Fig. 75: Flue expansion joint

Fig. 76: Burner fan silencer hood

Fig. 77: Ventilation aperture of the installation room with silencer



6.3 Transport Boilers with large water chambers can be transported via road or rail as well as by sea. The packaging will be selected subject to the method of transportation; where necessary, the more fragile thermal insulation will be shipped separately. Accessories such as the burner, control equipment and fittings are packed separately to protect them during shipping. The option of minimised shipping dimensions are a further benefit of this methodology. Generally speaking, the accessories will be fitted only after the steam boiler has been installed in situ. The higher the steam output, the more involved will be the shipping. Where necessary, hauliers must select specific shipping routes (e.g. consideration of narrow passages or low/narrow bridges, the load-bearing capacity of passages) and arrange police escorts (special transports). The client must ensure that there is adequate access to the installation location at the place of installation. The access must offer sufficient load-bearing capacity (e.g. no tanks under ground or subterranean garages). In addition, sufficient room for manoeuvring must be available. Provide suitable lifting equipment for unloading the boiler and accessories and for handling the heavy equipment (e.g. burner, pumps, fittings and control panel) inside the boiler house.

Fig. 79: Transport by rail without thermal insulation

Fig. 78: Transporting a steam boiler



6.4 Handling Provide an adequately sized opening for bringing the boiler and the additional components into the boiler room. This opening may also be a hole in the boiler house roof or a duct. To reduce costs, the handling paths should be as short as possible and not be restricted through other structures. In this area too, ensure that there is sufficient load-bearing capacity. Lifting gear should be able to be positioned as close to the place of installation as possible. It must be of adequate lifting capacity and size to cope with the height and width to be covered. Lifting equipment needs a sufficiently large setdown area. Where required, access roads or road sections may need to be closed off for a time.

Fig. 80: Handling an industrial/commercial boiler requires experience and know-how

Fig. 81: Frequently, handling is precision work

Fig. 82: Handling without thermal insulation

Fig. 83: Sometimes the boiler needs to be brought in through the roof

Fig. 84: Delivery of a containerised steam boiler system in Estonia


7 Operation

7.1 Operating modes Subject to the respective equipment level, the TRD differentiates between several operating modes for high pressure steam boiler systems.

4. 24-hour operation without constant supervision (BosB 24h)

The boiler must be able to operate fully automatically and be equipped with two self-monitoring safety features, as water level limiter for the lowest possible water level. The combustion with additional safety features must also be approved for the unsupervised operation.

The operator must carry out the test procedures specified in the operational requirements, enter their completion in the operator's log and confirm the entry with their signature. A time switch for maintaining the test intervals is not compulsory. In addition, a contractor, such as the Viessmann customer service, must carry out an inspection every six months of those control and limiting facilities that are not subject to the regular checks by the operator. With this type of equipment, the operator's scope is extended to the maintenance and therefore requires a greater in-depth knowledge than is required for the operation of simpler systems. Modern control systems (e.g. PLC) enable a transfer of boiler details to a control centre. Control functions can also be triggered from this control centre. Furthermore, an automatic fuel changeover is also enabled for dual-fuel combustion systems. The boiler must always be manually reset at the boiler itself after a safety shutdown has been initiated.

1. Operation with constant immediate supervision

With this operating mode it will be necessary to subject the boiler operation to constant supervision by an operator. This makes automatic equipment for regulating the water and pressure levels superfluous. Such functions can be carried out by the operators.

5. 72-hour operation without constant supervision (BosB 72h)

With this method, in addition to the requirements for 24 hour unsupervised operation, the high water level must also be limited via a special control amplifier. Added to this are limiters for the maximum conductivity of the boiler water, equipment for monitoring the water quality (top-up water, condensate) and additional control panel requirements. The current state of the art and the reliability of equipment enables new systems to be equipped for an unsupervised operation of over 24 or 72 hours. The tendency today is towards unsupervised operation over 72 hours. The operating modes described in points 1 to 3 are almost without relevance today. Observe the following conditions for an unsupervised operation:

2. Operation with limited supervision

An operator must personally verify the correct condition of the boiler system every two hours. The boiler must be equipped with control facilities for the water and pressure levels.

3. Temporary operation with lower operating pressure without supervision

During the unsupervised operation, the steam boiler is operated with a safety pressure of 1 bar. This operating mode requires additional boiler equipment (safety valve, pressure regulator, pressure limiter, pressure gauge).



7.2 Standards and regulations governing operation In Germany, the principle regulation for the operation is the BetrSichV [Health & Safety at Work Act]. Paragraph 12 specifies that the system must be operated in accordance with the rules formulated by the committee for Health & Safety at Work at the Federal Ministry for Labour (BMA) (Technical Instructions for Operational Safety). However, these rules are not as yet completed. Consequently, the transitional regulations for steam boilers still apply (TRD) [in Germany]. New systems may only be taken into use after the "Inspection prior to commissioning" has been carried out. For boilers in category III and IV, that inspection must be carried out by the relevant supervisory institute, that certifies the correct condition of the system. For commissioning, it is required that personnel trained in boiler operation are available. High pressure boilers must be operated by trained boilermen who have been trained as part of an approved training scheme for high pressure boilers [check local regulations]. Individuals who have the relevant technical know-how on account of their training are considered to be of equal status. Using the operator instructions is part of the operation. These instructions must contain all information required by the operator for operation, maintenance and inspection. This also includes a list of what actions operators must carry out at each individual part of the boiler equipment and at what intervals (Fig. 85).

Fig. 85: Extract from the check list for a steam boiler system (steam and hot water boiler)



An operator's log must be available for every boiler where all inspections are entered, and each entry is confirmed by the signature of the person carrying out the inspection. The log is verification of the correct operation and maintenance of the boiler system and may, on demand, need to be provided to the expert of the relevant supervisory body. Paragraph 3 of the [German] Health & Safety at Work Act makes it compulsory for employers to carry out a risk assessment. When carrying out an installation, risks must be avoided that could be created in the area of the steam boiler system. It is the aim of this assessment to provide and assess machinery without risk. High pressure steam vessels of category III (for a product of volume in litres and maximum permissible pressure in bar exceeding 1000) and IV, are subject to repeated inspections by the relevant supervisory institute. According to paragraph 15 of the [German] Health & Safety at Work Act, the user is obliged to notify the relevant authority of the test intervals he has determined within six months of commissioning. The relevant inspection institute must verify the calculated test intervals. The authority's decision is final and binding where there are discrepancies between the periods determined by the user and those set by the authority. The details provided by the boiler manufacturer, who makes relevant suggestions in the Declaration of Conformity, offer guidelines for these test intervals. In accordance with the [German] Health & Safety at Work Act, the maximum intervals are as follows: ­ External inspection annually ­ Internal inspection 3 years ­ Strength test 9 years Never exceed these intervals.

Fig. 86: Operator's log

Fig. 87: Vitomax 200-HS technical guide

Fig. 88: Viessmann brochures and datasheets

Fig. 89: Consultation

7.3 Service The industrial/commercial boiler department at Viessmann offers a comprehensive service for steam boilers and their periphery. Service starts with the provision of technical documentation, such as technical series, datasheets, technical guides, preservation information and operator logs.

Viessmann project engineers, located in the German sales offices, and the steam boiler specialists, located at the industrial/commercial boiler sales office in Berlin, are available to design engineers, investors and users for technical consultations. Consultation for new systems can take place at the design engineering office, in situ or at the local approval body.



Viessmann staff will generate the forms for the system description required for the permit procedure. A further field of consultation concerns existing systems, e.g. reduction of operating costs, improvements to system efficiency, system modernisation and a change in fuel. The members of the technical service for industrial and commercial boiler systems are available for many tasks that are covered by the Viessmann service.

­ Commissioning

All control and limiting equipment of the boiler system is adjusted and tested as part of the Viessmann commissioning service. The combustion is adjusted so that optimum combustion values are achieved and the warranted emission values are maintained. The operators are trained as part of the commissioning process. Upon customer request, the system will be run up by the inspecting institute as part of the inspections for commissioning in accordance with the Health & Safety at Work Act. Following the commissioning, the user will receive a test report with all actual values.

Fig. 90: Function test to EN 12953-6

­ Checking the system in accordance with TRD 604

One important task is the implementation of the bi-annual inspection of the high pressure steam boilers operated without permanent supervision for 24 or 72 hours, as specified by the TRD 604 [Germany]. As part of these checks, all control and limit equipment, the combustion, the water treatment, the quality of the feed and boiler water, as well as the general condition of the system, are inspected. The user and boilerman are immediately informed of any important items arising from the system inspection.

A report is produced containing the results that include all established data and any important information, and is handed to the user. The operator's log, too, will receive an entry confirming the inspection.

­ Maintenance steps

A further extensive area of activity for the technical service for industrial and commercial boilers is the implementation of maintenance work, such as the preparation of boilers for regular inspections (internal inspection and strength test ­ water pressure test) by the relevant inspection institute, troubleshooting and the replacement of assemblies. These maintenance tasks are not limited to the boiler and its equipment, but also extend to control systems and other boiler house assemblies.

The control panel section can produce advanced control panels for existing boilers, comprising the latest control and safety equipment. Where major modifications are required, the creation of the required permit documentation in accordance with the Health & Safety at Work Act can also be part of the standard delivery.

­ Repairs

The required repairs of faults on the pressure part are carried out in agreement with the relevant inspection institute. The required permits for welding on the pressure part that are a pre-requisite for repairs, are held by the service department for industrial/commercial boilers.


8 Special types

8.1 Waste heat boilers Waste heat boilers utilise the waste heat from flue gases generated during combustion processes or that from hot exhaust air from industrial processes to generate saturated steam. There are basically two forms of waste heat boiler: ­ Waste heat boiler without additional combustion: For this, the flue gas/exhaust air flow are used exclusively to generate saturated steam. ­ Hot water or steam boilers with waste heat utilisation: These are boilers with conventional combustion and additional waste heat utilisation.

8.2 Steam boilers with superheaters Many industrial applications demand specific requirements of the steam parameters. In some processes, steam with higher temperatures is used than those resulting from the saturated pressure. That requires that the steam is superheated. For that purpose, Viessmann has designed specific steam superheaters that are installed between the second and third flue pass of the Vitomax 200 HS. With this solution, the superheater can generate steam at a temperature which is approx. 50 K higher than the saturated steam temperature.

Fig. 92: Vitomax 200-HS with superheater Fig. 93: Vitomax 200-HS with superheater, 22 t/h at 10 bar, in production; used at Klaipedos Kartons AB (cardboard carton manufacturer at Klaipeda, Lithuania) Fig. 91: Vitomax 200-HS steam boiler with waste heat utilisation at the Maribor hospital, Slovenia (6 t/h, 13 bar saturated steam)


9 Reference systems

Beta Sentjernej Slovenia Vitomax 200-HS high pressure steam boiler, type M237; 10 bar, steam output: 1.15 t/h

Sanovel Istanbul Three Vitomax 200-HS high pressure steam boilers, type M235; 10 bar, steam output: 7 t/h each


Reference systems

General Hospital of the Peoples Liberation Army Beijing China Six Vitomax 200-HS, each producing 16 t/h, 10 bar

Listed hospital in Chorzów, Poland Three Vitomax 200-HS high pressure steam boilers provide the hospital with heat, DHW and process steam, each delivering 2.4 t/h, 8 bar


Reference systems

Emmi Dairy Lucerne Switzerland High pressure steam boiler Vitomax 200-HS 10 t/h, 13 bar

Textile plant Rivolta Carmignani Milan Italy Two high pressure steam boilers Vitomax 200-HS 4 t/h, 13 bar

Fiat Modena High pressure steam boiler system Vitomax 200-HS 2.9 t/h, 10 bar


10 Advanced design and production methods ensure high quality

State of the art processes are employed in the development of medium and industrial/commercial boilers from Viessmann. Stresses are analysed using the Finite Element Method, which also assists in optimising, for example, pipe arrangements or welded joints. The Vitoplex boilers are standard products, manufactured with a high degree of automation. The Vitomax series of commercial and industrial boilers are manufactured in smaller numbers or as bespoke boiler systems. At the end of production, the boilers are subjected to a pressure test at 1.57-times operating pressure, in accordance with the Pressure Equipment Directive. With high pressure steam and hot water boilers, welding seams are inspected in accordance with the country-specific regulations using ultrasound and X-ray procedures.

Assembly production

Welding the pressure body in the optimum welding position

Sub-arc welding (SAW)

SAW welding system

Boiler assembly


Advanced design and production methods ensure high quality

Boiler insulation applied at the factory

Assembly of the boiler casing with the flame tube Welding the smoke tube with mechanical welding equipment

CNC controlled oxy-acetylene cutter with thread cutter

Loading at the factory with a mobile crane

Standard shipping packaging


For three generations, the Viessmann family business has been committed to generating heat conveniently, economically, with environmental responsibility and in accordance with the prevailing demand. With a number of outstanding product developments and problem-solving solutions, Viessmann has created milestones which have frequently made them the pacemaker and trendsetter for their entire industry. With the current comprehensive range, Viessmann offers its customers a series of multi-stage products with output from 1.5 kW to 20000 kW: Freestanding and wall mounted boilers for oil and gas, either with conventional or condensing technology, plus systems using renewable energy, such as heat pumps, solar heating systems and boilers for sustainable fuel supplies. The product range further includes control technology and data communication, as well as the entire system periphery, down to radiators and underfloor heating systems. Viessmann is an international company with 13 plants in Germany, France, Canada, Poland, Hungary and China, sales organizations in Germany and 35 other countries and 119 sales branch offices.

Head Office Allendorf (Eder)

Commercial and industrial boiler manufacture at the Mittenwalde factory

Responsibility for the environment and society at large, fairness in dealing with business partners and employees as well as striving for perfection and the highest efficiency in all business processes are core values for Viessmann. This applies to every individual employee and therefore to the whole company. With its multitude of products and associated services, Viessmann offers its customers the particular benefit and added value of a strong brand.

Viessmann Werke 35107 Allendorf (Eder) Telephone 06452 70-0 Fax 06452 70-2780

Viessmann Werke Berlin Kanalstraße 13 D-12357 Berlin Telephone +49 30 6602-300 E-mail: [email protected]

Subject to technical modifications 9448 103 - 1 GB 06/2008


Technical Series

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