Fire-tube boiler

The water-tube boiler is a steam boiler and is used to generate steam or hot water in industrial enterprises and on board of steamboats and steam locomotives. Characteristic of the boiler design is a cylindrical water-steam room with flat or gekrempten floors. The lighting was originally from outside. In current designs, the heating occurs exclusively from the inside through the flame tube and flue pipes. In contrast to the water -tube boiler, the flue gas is led into the tubes.

• 3.1 Fossil Fuels
• 3.2 Power

Historical development

Suitcase boiler

The first steam boiler in the overpressure range to the end of the 18th century, the steam with a pressure of 0.5-1 bar produced, were riveted boiler case.

Rolling boiler

This was followed by the rolling boiler, as the prototype of the low- voltage design with a cylindrical shell and dished ends. In general, the boiler was operated horizontally. But there were standing models that have been used in metallurgical plants and were heated with the departing gases from flames and annealing furnaces.

The boiler was walled and was fired from below. The flue gases were passed around the outer walls of the boiler. In the masonry features were immured in order to use the heat of the flue gas as well as possible. Often below the boiler 2 separate channels had been created. The boiler was installed with a slight slope to the rear, so that the sludge formed is derived backwards to blowdown and the heat transfer from the boiler base is not further restricted.

The diameter of the roller boiler was up to 1.5 m, with a length up to 10 m. With this dimensioning achieves a heating surface of 25 m². The area- specific steam capacity is 10-12 kg of steam per square meter and hour; so that the steam output of the boiler is limited to a roller 300 kg / h.

The roll kettle was a cost-effective design. The scale could be easily solved with the Scaling hammer, since no installations hinder this work. The heat efficiency is very unfavorable and the boiler requires a very long heating time and was therefore suitable only for continuously operating companies.

Multiple rolling boiler

The multiple roll boiler consists of the overlying main boiler or boiler and the upper underlying smaller boilers, which are referred to as a kettle. Among the boilers have approximately 2/3 of the diameter of the main vessel. The diameter of the lower boiler but should not be less than 55 cm to the part and ride and clean the scale to be able to. The partial shells are joined together by socket. There were two sub- arrays with boilers which have been juxtaposed. There have been over interconnected depending on the steam demand even more partial boiler; They were then designated as a battery vessel. The furnace was placed under the steam drum, in which case plan or oblique gratings were used. The flue gases are then passed to the boiler bottom. The sludge settled out in the lower tank.

The roll kettle with a lower boiler has a heating surface to 50 m; with 2 sub boilers is 70 m². Battery boiler heating surfaces reached to 150 m². The heat flux is comparable to that of the simple rolling boiler.

Flammrohr-/Rauchrohrkessel

As a further development step was 1811 firetube. This consisted of a cylindrical jacket and a flame tube, which was riveted between the boiler surfaces. The first vessel of this type were operated at a pressure up to 7 bar. The boiler type already set higher requirements on the manufacturer. The firing was carried out exclusively with solid fuels. A flat grate is installed either in the flame tube and the furnace is operated in an upstream combustion chamber, which can be designed as an inclined grate.

The heat transfer by radiation was carried out in the region of flame formation and convection. These boilers were walled and the flue gases have been passed through a brick-built partition wall to the outer wall so that the heat content of the flue gas could be used as well as possible. A further development of the formed double -flue boiler. This design was widely used in industrial establishments where steam was needed with pressures up to 16 bar. These boilers were often used in boiler plants of mining, to generate steam for the carriers or in industrial plants, the steam engine to drive a transmission (mechanical engineering) inserting. An important aspect in the sizing was sufficient free space in the boiler to remove scale by händisches pecking can. Fire-tube boilers were always equipped with a steam dome.

Riveted boiler were built until about 1945. Disadvantage of the fire-tube boiler was not optimum use of the heat content of the flue gases, as an enlargement of the heating surface by design the boiler itself is not possible. An optimized utilization of flue gas heat was only possible by the incorporation of adjuncts that can be used as a superheater and / or feedwater.

In the middle of the 20th century, the welding technology used and the quality of the materials had developed so far that welds could be reliably produced for highly loaded components. In addition, seamless steel tubes since the late 19th century ( Mannesmann ) were available. There the flame tube smoke -tube boilers has been developed following the construction details are distinguished:

• All connections are welded,
• The boiler having a flame tube and the flue gases are diverted more than once in the longitudinal direction of the vessel. The boiler has a lot of trains (2-5 flues ), which are connected by reversing chambers at the rear and front floor.

About the flame tubes called flues for the further use of flue gas heat are fed, which are much smaller in diameter than the flame tubes. The convective heat transfer in a plurality of flue tubes is much better than a large diameter pipe at the smaller diameter due to the larger Reynolds number. Also for pipes of small diameter, a greater heating surface will be achieved in relation to the total cross sectional area of the tubes. The flame -tube smoke- tube boiler is heated only from the inside. It eliminates the masonry and the walls are thermally insulated from the outside.

Double -flue boiler of the Zeche Carl ( boiler house demolished)

Historic double flame - tube boilers

Modern open - water - space boiler with burner

Constructive details

Material stresses at the components to enter into the first vessel lines by the vapor pressure. The jacket is charged by the internal pressure, while the liner is exposed to a pressure load from the outside. Therefore, the flame tube must be designed to denting. Flame tube smoke -tube boilers with low stress often have a smooth flame tube and flat floors. Greater water boiler with higher operating pressures are designed with corrugated flame tubes (higher resistance to buckling ) and flat gekrempten floors. The advantage of soil gekrempten is the position of the weld in the cylindrical region prior to the brim, so that the seam is only loaded by tensile stresses. In flat disk floors in addition unfavorable bending stresses occur. In addition, contact stresses on temperature differences by heating. While the non-heated surfaces ( boiler shell ) have approximately saturated steam temperature, the temperature is higher at the heating surfaces. The difference in temperature is the boiler without water side surfaces to 50 ° C. In the case of scale deposits, this temperature difference can be much higher, causing cracks.

To maintain tension in the low boiler components as a result of thermal changes in the length, the smallest possible wall thickness of the vessel floor and the tube plates are used. The flame tube and the smoke pipes take the internal pressure load on the boiler ends up with. In the non- tubed areas of the jacket ( vapor space ) are also welded corner or tie rods, which receive the bending stress between the jacket and bottom part. These are the mechanical stress critical and damage prone components. The welds on the anchor must be welded through and by the shape of the anchor has a steady voltage flow to be guaranteed.

More than three trains are not common in today's shell boiler designs. The shell boilers are characterized by a high water content ( 1-30 t) and thus a high heat storage capacity of. By the re-evaporation of the saturated steam temperature under a short-term fluctuations in the water steam consumption can be equalized. The required wall thickness for the shell and the necessary anchorages soils limit the technically acceptable range of operating pressure (up about 38 bar). Due to its construction (large contiguous areas ) Shell boilers are sensitive to thermal stresses during heating and cooling. The boilers are therefore ramped up slowly to keep the temperature of the boiler components low.

In order to reduce fuel consumption further, an economiser ( Eco: feedwater preheater ) is nowadays, in most cases the vessel downstream. In the economizer, the boiler feed water is heated before it is passed into the boiler. The economiser is the shell boiler is a separate component, through which the discharged from the boiler flue gas at temperatures of 200 - 300 ° C is passed. It consists of a tube assembly, which is often also provided with ribs. If a lot of cold make-up water is fed in, you can switch also a second economizer according to which preheats the rinsing water to the feed water tank before entering. In these cases, however, the condensation of water vapor must be taken from the flue gas with formation of acid. The components must be made ​​of stainless steel or it is necessary to provide a flue gas temperature control to maintain a minimum temperature.

Energy supply

Fossil Fuels

The boilers were grown to mid-20th century mostly heated with solid fuel (coal, wood). In the 50s and 60s, the firing of many boiler was converted to fuel oil because of the ease of handling. The cheapest fuel was the heavy fuel oil S, which must be heated for promotion. Because of the emissions ( high sulfur, NOx and dust ) as well as the more expensive operation ( burner and boiler must be cleaned regularly, bonding of leads under failed trace heating ), the heavy fuel oil hardly ever used. Moreover, additional measures are required ( denitrification, dust ) to comply with the current emission limits. Therefore, almost only fuel oils of variety is EL ( extra light ) are used. With the proliferation of natural gas in the 60s of the 20th century, the gas is used for the firing of shell boilers, if it is available at the establishment. The advantage of the natural gas firing is in the low-emission combustion and it occurs at the correct burner settings, virtually no soot formation.

Current

A shell boilers can also be electrically heated. For this purpose heaters are used, which are usually used as a bundle in a piece of the boiler body. Due to the significantly higher specific costs of heating compared to the use of fossil fuels, the electrical heating is usually only for small steam output is (<1 t / h ) were used. The investment costs and the space requirements are low. It eliminates the exhaust system and the fuel supply and the boiler can be placed in sterile areas. To use the boiler is used in hospitals and in the pharmaceutical industry (steam for sterilization ) or in laboratories.

Feedwater

The feed water of shell boilers must be treated to prevent corrosion and scale deposition. As far as the additional water used does not have a particularly high hardness, it is sufficient in most cases to exchange the hardness of a regenerated with sodium chloride base exchanger by Na ions. The feed water should be thermally degassed. The feed water must conditioning agents (eg, sodium phosphate, sodium sulfite ) is added to prevent the loss of residual hardness, chemically ligate residual oxygen and to increase the pH. The feed water must also be oiled.

Ship steam boiler

In steamboats usually the Scottish boiler were used. These are two spacious shell boiler with one to four fire tubes and a Rauchrohrzug. To achieve the required steam output for larger vessels the number of boiler is increased accordingly. Thus, the RMS Titanic had a total of 29 Scottish marine steam boiler.

Plies the ships in the harbor, was heated at a wait time of up to 3 weeks, that is, at least one flame tube, usually of the so-called " monkey", so the flame tube at the lowest point of the boiler, was further fueled sparingly to the boiler water just in about 100 ° C and hold for about 1 bar pressure.

As long as steam ships had no desalination plants, reserve water had to be carried to compensate for unavoidable losses due to blowdown, steam leaks or the steam whistle.

Locomotive Boiler

A steam locomotive boiler is a design of mobile land-based steam boiler to generate steam to drive steam locomotives. Locomotive boilers are mostly tube boiler. But other types are also known.

Quality requirements

Shell boilers are pressure vessels according to the Pressure Equipment Directive 97/23/EC and may only be placed on the market if the manufacturer has demonstrated by a conformity assessment procedures involving a Notified Body that he has complied with the essential safety requirements of the Directive. The manufacturer must affix the CE mark and draw up a declaration of conformity. Harmonised product standards for shell boilers are:

• EN 12953-1 to 14: Shell boilers
• EN 14222: Stainless steel shell boilers

In applying this standard, the manufacturer may assume that it satisfies the fundamental safety requirements of the Directive ( presumption of conformity).

Manufacturer

Among the manufacturers of fire-tube boiler, there has been in recent decades a process of consolidation. One of the few remaining manufacturers include:

• APROVIS Energy Systems GmbH, Weidenbach ( waste heat boiler only )
• Bosch industrial boilers, Gunzenhausen
• Bosch thermal technology under the brand Buderus (only hot water boiler, no steam)
• Enkotherm GmbH, Merkendorf (only waste heat boiler )
• HKB KETELBOUW BV ( Venlo ) in the Netherlands
• Omnical boiler and Apparatus GmbH, Dietzhölztal
• SAACKE GmbH, Bremen
• Viessmann, Allendorf ( Eder)
• JCC Standardkessel Köthen GmbH, (2000 emerged from pre-heater and boiler Köthen GmbH and the standard boiler Lentjes Fasel GmbH)

Literature sources

• John Eug. Mayer: Paperback for the modern heater and boiler, Berlin 1912, Verlag Hermann Schran & Co.
• RE Th Schlippe: Steam boilers and their operation, 4th edition. Berlin 1923, Springer Verlag Julius.
• Wilhelm leather: Ship Machine Engineering Volume I: marine steam boiler, 1956, Fachbuchverlag Leipzig.
• Fritz Mayr: boiler operation engineering, 10th edition. Graefelfing 2009, Resch, ISBN 3-930039-13-3.

• Steam boiler