EP1563224B1 - Continuous steam generator with circulating atmospheric fluidised-bed combustion - Google Patents

Description

The invention relates to a continuous steam generator with circulating atmospheric fluidized bed combustion.

In addition to natural circulation and forced circulation steam generators are Zwangdurchlauf- or. Continuous steam generator for generating electrical energy by burning of, for example, fossil fuels known. The latter are used in particular in modern or large power plants. In the process, the heat released during the combustion of the fuel in the combustion chamber of the continuous-flow steam generator flows through heating surfaces through which working medium flows, consisting of, for example, steam. B. combustion chamber surrounding walls, radiation or. Convective heating surfaces, the continuous steam generator delivered. The working medium is incorporated into a water / steam cycle of a steam turbine in which it passes on the absorbed thermal energy.

Such continuous steam generators, in which the working medium is preheated substantially in one pass of the steam generator, evaporated, superheated and possibly reheated, have long been known and usually equipped with burners for the combustion of fossil fuels. From the publication " Forced-circulation boiler for sliding pressure operation with vertical combustion chamber bore ", VGB Kraftwerkstechnik 64, Issue 4, April 1984, H. Juzi, A. Salem and W. Stocker a conventional coal-fired continuous-flow steam generator has become known. As a rule, the combustion chamber surrounding walls of the continuous steam generators are formed from welded tube-web-tube evaporator heating surfaces. To ensure sufficient cooling of the containment tube walls, either sloped smooth tubes (ie tubes with smooth inner walls that slope within the containment tube walls), internally ribbed vertical tubes, or drop / riser systems (ie Surround pipe walls are divided into several wall sections, which are flowed through successively, see also Figure 2c of the above document).

In recent years, it has also gone to train continuous steam generator with circulating fluidized bed combustion (ZWSF). As with all fossil fuel-fired power plants, attempts are made to minimize the emissions produced by combustion to protect the environment. This can be accomplished by increasing power plant process efficiency and the concomitant reduction in fuel. Part of the increase in efficiency takes place by generating steam with high steam parameters (high steam pressures and temperatures). So that the power plant blocks operate economically within a large load range, the steam generators are operated in sliding pressure. At the same time to meet the various requirements (constant high steam temperature, sliding vapor pressure, high load change rate), only the above-mentioned forced-circulation steam generator systems are used or in question.

For reasons of erosion, the combustion chamber enclosing walls of continuous steam generators with circulating fluidized bed combustors can not be inclined or inclined as in conventionally pulverized coal continuous steam generators, but must be bored vertically. The circulating fluidized bed combustors have therefore been predominantly combined with evaporator systems which operate in recirculating or forced circulation operation and are therefore equipped with vertically bored containment walls. A few circulating fluidized bed combustors also produce the steam with a forced flow system, but as a downcomer system and at low vapor pressures (eg, KW Moabit). Considerations have already been made to use the once-through steam generator with ZWSF even in the pressure range from 100 to 300 bar, and thus more economically, ie with less fuel to operate. Because of the need to form combustor confinement walls from vertical evaporator tubes, internally ribbed tubes have been proposed for cooling the evaporator walls (see above reference).

• ZWSF-Durchlaufdampferzeuger, die mit unterkritischen Dampfdrücken betrieben werden, benötigen im Vergleich zu überkritischen Dampfdrücken bei gleicher Dampferzeugerleistung einen höheren Brennstoffeinsatz und erzeugen dadurch mehr schädliche Emissionen.
• Vertikal berohrte Zwangdurchlaufdampferzeuger besitzen im Gegensatz zu geneigten Rohren den Nachteil, dass die Anzahl der Rohre bei einer gegebenen Brennkammergeometrie größer ist und damit die Massenstromdichte (Maß des Arbeitsmediumstromes in kg pro m2 Durchströmungsquerschnitt und pro Sekunde) pro Rohr abnimmt. Um trotzdem eine ausreichende Kühlung der Rohre sicherzustellen, werden innenberippte Rohre eingesetzt oder die einzelnen Wände der Brennkammerumfassungswände hintereinander durchströmt.
• Die Aufteilung des gesamten Verdampferstromes auf mehrere in Serie geschaltete Wände besitzt mehrere Nachteile :
  1. 1) Die einzelnen Wände müssen über Fallrohre verbunden werden.
  2. 2) Bei der erneuten Verteilung des Verdampferstromes treten Entmischungsvorgänge auf (unterschiedliche Dampfgehalte), die am Austritt des Verdampfers als Temperaturschieflagen sichtbar werden und infolge behinderter Wärmedehnung zu Rissen in den Wänden führen können.
  3. 3) Höherer Druckverlust infolge höherer Massenstromdichte. - Innenberippte Rohre besitzen größere Reibungsdruckverluste und haben den Nachteil einer Sonderfertigung und einen erhöhten Fertigungsaufwand beim Zusammensetzen von Teilflächen.

In the transition from natural circulation to (supercritical) forced circulation steam generators with high steam parameters (typically 250 to 300 bar, 560 to 620 C) in the power range of 300 to 600 MWel, the following problems or disadvantages arise with the prior art:

• ZWSF Continuous Steam Generators operating at subcritical vapor pressures require higher fuel input compared to supercritical vapor pressures with the same steam generator output, thereby producing more harmful emissions.
• Vertical-bore forced-circulation steam generators have the disadvantage, in contrast to inclined pipes, that the number of pipes is greater for a given combustion chamber geometry and thus the mass flow density (measure of the working medium flow in kg per m2 flow cross section and per second) per pipe decreases. Nevertheless, in order to ensure sufficient cooling of the tubes, inside ribbed tubes are used or the individual walls of the combustion chamber surrounding walls flow one behind the other.
• The distribution of the entire evaporator flow to several walls connected in series has several disadvantages:
  1. 1) The individual walls must be connected via downpipes.
  2. 2) In the redistribution of the evaporator stream segregation occur (different levels of steam), which are visible at the outlet of the evaporator as temperature imbalances and can lead to cracks in the walls due to impaired thermal expansion.
  3. 3) Higher pressure loss due to higher mass flow density. - Internal ribbed tubes have greater friction pressure losses and have the disadvantage of a special production and increased manufacturing costs in the assembly of partial surfaces.

By publication EP 1 030 150 A1 has become known as a fluidized bed combustion chamber for the gasification and combustion of combustibles. The heat released in the combustion chamber is dissipated on all sides of the heat exchanged heat exchanger heating surfaces, either immersed in the fluidized bed of a heat recovery chamber or come into contact with the gas stream above the combustion chamber. The walls of the combustion chamber are formed of a sheet steel housing or the like instead of one side of the heat-exposed and the combustion chamber comprising Heizflächenrohren. In the used and series-connected heat exchanger heating surfaces circulates a heat transfer medium operated by a circulation pump forced circulation steam generator in which, in contrast to a forced flow steam generator, the heat transfer medium flows several times in the circuit through the heat generator.

By publication EP 0 882 872 A2 For example, there is known a pressurized fluidized bed boiler with internal circulating, i.e., stationary fluidized bed for combustion of fuel, operating at much higher pressure than the atmospheric pressure, in which the exhaust gas produced during combustion is fed to a gas turbine. In order to control the operating load of such a boiler without having to vary the height of the fluidized bed within the cylindrical combustion chamber, the combustion chamber located in a pressure vessel is formed with a main combustion chamber and with a thermal energy recovery chamber. For combustion technology and process side separation of these two chambers, the main combustion chamber is centrally located in the middle and the thermal energy recovery chamber includes the main combustion chamber outside, a walled partition is arranged, which is fixed by individual, not interconnected by webs water pipes in position. Due to the conical design of the masonry partition in the upper part, the solid particles within the stationary fluidized bed in the main combustion chamber are directed into the energy recovery chamber such that the height of the stationary fluidized bed remains the same. The heat generated in the combustion chamber in the field of stationary fluidized bed is thereby within the thermal energy recovery chamber to the immersed in the fluidized bed and a working medium, for example, water or steam-conducting Heizflächenrohre and to the water pipes of the outside and the combustion chamber bounding surrounding wall delivered. The forming the partition wall and immersed in the stationary fluidized bed water pipes take due to the surrounding outer wall no or only a negligible amount of heat and thus do not participate in this area in the energy production. The water pipes and the pipes of the heating surfaces are part of an unspecified steam generator or boiler type.

Out Goidich, Lundqvist, "The utility CFB boiler - Present status short and long term feature with super-critical and super-critical steam parameters" Power Gen Conference Europe, Milan, June 11-13, 2002 , a fluidized bed steam generator is known, which is designed as a continuous steam generator. The tubes of the enclosure walls are vertical. In addition, an evaporator heating surface may be present in the combustion chamber to reduce the height of the combustion chamber.

Out Goidich, "Integration of the BENSON vertical OTU technology and the compact CFB boiler", Power Gen International, Orlando, Florida, November 2000 is a continuous steam generator with Umfassungswänden known, the tubes are vertical and flowed through in parallel. Additional evaporator heating surfaces within the combustion chamber are not mentioned.

Out EP 0 025 975 A2 is a continuous steam generator with Umfassungswänden known having vertically extending tubes. Within the combustion chamber partitions are arranged, which are connected to the Umfassungswänden. The tubes of the intermediate walls are heated on both sides. At least in sections, the tubes are provided on their inner surfaces with ribs or other elements for swirling the flow to ensure adequate cooling.

A circulating fluidized bed reactor with heat exchange surface extensions is known in DE 694 04 423 T2 described. Inside the combustion chamber, the surrounding walls are provided with extensions extending transversely thereto, which are heated on both sides. The spaces between the extensions are to form channels or shafts through which the solids fall into the fluidized bed to increase the rate of sinking solids to the fluidized beds.

US 6 470 833 Bl describes a fluidized bed steam generator with vertically drilled Umfassungswänden. In the combustion chamber chambers are arranged, which have vertically extending tubes. These chambers are supplied with secondary air and fuel. The chambers are spaced from the enclosure walls.

• Einsatz von wirtschaftlicheren und ökologischeren Durchlaufdampferzeugern mit ZWSF im Leistungsbereich von etwa 300 bis 600 MWel und in einem Druckbereich von etwa 100 bis 300 bar,
• Erzielung einer effizienten Brennkammerauslegung für einen derartigen Durchlaufdampferzeuger unter Berücksichtigung von innerhalb bzw. ggf. außerhalb der Brennkammer zusätzlich installierter Heizflächen.

The object of the invention is now to provide a continuous steam generator with circulating atmospheric fluidized bed combustion, in which the aforementioned disadvantages are avoided or the following criteria are met or respected.

• Use of more economical and ecological continuous flow steam generators with ZWSF in the power range of about 300 to 600 MWel and in a pressure range of about 100 to 300 bar,
• Achieving an efficient combustion chamber design for such a continuous steam generator taking into account additionally installed inside or outside the combustion chamber heating surfaces.

The above object is solved by the characterizing features of claim 1.

Advantageous embodiments of the invention can be found in the dependent claims.

• Durch die Kombination von Brennkammerumfassungswänden und zusätzlicher, in der Brennkammer angeordneter, Heizflächen als Verdampferheizflächen und paralleler Arbeitsmittel-durchströmung dieser Verdampferheizheizflächen kann die Wirbelbrennkammer und somit auch der Durchlaufdumpferzeuger in den baulichen Ausmaßen wesentlich niedriger und damit kostengünstiger ausgebildet werden.
• Durch die Verwendung von Glattrohren, d. h. Rohre mit auf der Innenseite glatten Oberflächen, in den Umfassungswänden des Durchlaufdampferzeugers ergeben sich wirtschaftliche Vorteile, da sie gegenüber innenberippten Rohren billiger sind und auch keine Sonderanfertigungen nötig sind. Glattrohr werden im Gegensatz zu innenberippten Rohren von vielen Herstellern in einer großen Vielfalt produziert.
• Durch den Einsatz von Glattrohren in den Umfassungswänden des Durchlaufdampferzeugers ergibt sich ein niedrigerer Druckverlust in der Verdampferheizfläche im Vergleich zu einer mit innenberippten Rohren ausgebildeten Verdampferheizfläche.
• Durch die parallele Durchströmung der Umfassungswände und der in der Wirbelbrennkammer zusätzlich angeordneten Heizflächen ergeben sich wirtschaftliche Vorteile, da der Einbau von Zwischensammlern (Misch- oder Druckausgleichsammler) nicht mehr erforderlich ist.
• Der Zusammenbau der Heizflächen, die aus Glattrohren hergestellt sind, ist wirtschaftlicher (Keine Anpassung der Innenberippung erforderlich, dadurch weniger Rohrverluste bei der Montage).
• Die Länge bzw. Höhe der vertikalen, in der Wirbelbrennkammer zusätzlich angeordneten Heizflächen ist der Höhe und Bauweise (unterschiedliche Trichter im unteren Bereich der Brennkammer) der Wirbelbrennkammer angepasst. Daraus resultieren Vorteile bei der Montage der Heizflächen, da sie effizient in den Brennkammerboden bzw. in die Trichteroberkante sowie in die Brennkammerdecke eingebunden werden können.
• Die in der Wirbelbrennkammer zusätzlich angeordneten Heizflächen sind als einseitig beheizte zu Kasten verschweißte Heizflächen ausgeführt.
• Durch die Integration beheizter zusätzlicher Heizflächen wird die gewünschte Massenstromdichte eingestellt, die erforderlich ist, um Massenstrom- und Beheizungsunterschiede auszugleichen und annähernd gleiche Austrittstemperaturen zu erzielen.
• Die Brennkammerabmessungen (Querschnitt, Höhe) und die integrierten Heizflächen sind so bemessen, dass die wirksamen Wärmestromdichten den Einsatz vertikaler Glattrohr in den Umfassungswänden bei kleinen Massenstromdichten zulassen.

The solution according to the invention provides a circulating atmospheric fluidized bed continuous-flow steam generator which has the following advantages:

• By combining Brennkammerumfassungswänden and additional, arranged in the combustion chamber, heating surfaces as Verdampferheizflächen and parallel working medium flow through this Verdampferheizheizflächen the vortex combustion chamber and thus the Durchlaufdumpferzeuger in the structural dimensions are much lower and thus cheaper.
• The use of smooth tubes, ie tubes with smooth surfaces on the inside, in the surrounding walls of the continuous steam generator, there are economic benefits, since they are cheaper than internally ribbed tubes and no special designs are needed. Smooth pipe, in contrast to internally ribbed pipes, is produced in many varieties by many manufacturers.
• The use of smooth tubes in the surrounding walls of the continuous-flow steam generator results in a lower pressure loss in the evaporator heating surface in comparison to an evaporator heating surface formed with internally ribbed tubes.
• The parallel flow through the enclosing walls and the additional arranged in the fluidized combustion chamber heating surfaces have economic benefits, since the installation of intermediate collector (mixing or pressure compensation collector) is no longer required.
• The assembly of the heating surfaces, which are made of smooth tubes, is more economical (no adjustment of the internal ribbing required, thereby less pipe losses during assembly).
• The length or height of the vertical heating surfaces additionally arranged in the fluidized-bed combustion chamber is adapted to the height and construction (different funnels in the lower region of the combustion chamber) of the fluidized-bed combustion chamber. This results in advantages in the installation of the heating surfaces, as they can be efficiently integrated into the combustion chamber floor or in the upper edge of the funnel and in the combustion chamber ceiling.
• The additionally arranged in the fluidized combustion chamber heating surfaces are designed as unilaterally heated to box welded heating surfaces.
• By integrating heated additional heating surfaces, the desired mass flow density is set, which is necessary to compensate for mass flow and heating differences and to achieve approximately the same outlet temperatures.
• The combustion chamber dimensions (cross-section, height) and the integrated heating surfaces are dimensioned such that the effective heat flux densities make the use of vertical Allow smooth tube in the enclosure walls at low mass flow densities.

the invention The invention provides to heat the heating surface according to the invention on one side and form the one side heated heating surface with smooth tubes. As a result, as already mentioned in the smooth tubes of Umfassungswand a significant economic advantage achieved because smooth-tube are much cheaper, easier to assemble and cause a lower friction pressure loss.

In an advantageous embodiment of the heating surface heated on one side, this is designed as a box-shaped heating surface with a box-shaped cross-section. Due to the box-shaped design, the heating surface receives great stability, which makes it possible to form combustion chambers of the largest continuous steam generators with heating surfaces. In a further advantageous embodiment, the cross section of the box-shaped heating surface is rectangular.

In order to achieve a uniform heating of the working medium within the tubes of the enclosure walls, it is advantageous that these tubes have substantially the same heated length. The same effect on the pipes of the heating surfaces To transfer it is also advantageous that the tubes of the heating surfaces have the same heated length as the tubes of Umfassungswänden.

Embodiments of the invention with reference to the drawings and the description are explained in more detail below.

Fig. 1

schematisch dargestellt einen Durchlaufdampferzeuger mit zirkulierender atmosphärischer Wirbelschichtfeuerung im Längsschnitt

Fig. 2

schematisch dargestellt eine Wirbelbrennkammer eines Wirbelschicht-Durchlaufdampferzeugers mit einem Brennkammertrichter im Längsschnitt,

Fig. 3

wie Figur 2, jedoch Wirbelbrennkammer mit zwei Brennkammertrichter ("Pant leg") im Längsschnitt,

Fig. 4

schematisch dargestellt eine Brennkammer eines Wirbelschicht- Durchlaufdampferzeugers (mit einem Brennkammertrichter) im Querschnitt gemäß Schnitt A-A der Figur 2, Schnitt um 90 gedreht,

Fig. 5

schematisch dargestellt eine Brennkammer eines Wirbelschicht-Durchlaufdampferzeugers (mit zwei Brennkammertrichter) im Querschnitt gemäß Schnitt B-B der Figur 3, Schnitt um 90 ° gedreht,

Fig.6

schematischer Querschnitt einer alternativen kastenförmigen Heizfläche (Kastenschott) gemäß Detail C der Figuren 4 und 5,

Fig.7

schematisch dargestellt eine kastenförmige Heizfläche mit vertikal fluchtendem Übergang von der Feuerfestauskleidung zur oberen Membranrohrwand im Längsschnitt, entspricht Schnitt A - A der Figur 8,

Fig.8

schematischer Querschnitt einer kastenförmigen Heizfläche gemäß Schnitt C - C der Figur 9,

Fig.9

schematischer Längsschnitt einer kastenförmigen Heizfläche gemäß Schnitt B - B der Figur 8.

It shows :

Fig. 1

schematically shows a continuous steam generator with circulating atmospheric fluidized bed combustion in longitudinal section

Fig. 2

schematically a vortex combustion chamber of a fluidized bed continuous steam generator with a combustion funnel in longitudinal section,

Fig. 3

as FIG. 2 , but vortex combustion chamber with two combustion chamber funnels ("pant leg") in longitudinal section,

Fig. 4

schematically shows a combustion chamber of a fluidized bed continuous steam generator (with a combustion chamber funnel) in cross section according to section AA of FIG. 2 , Cut at 90,

Fig. 5

schematically shows a combustion chamber of a fluidized bed continuous steam generator (with two combustion funnel) in cross section according to section BB of FIG. 3 , Section rotated 90 °,

Figure 6

schematic cross section of an alternative box-shaped heating surface (box bulkhead) according to detail C of FIGS. 4 and 5 .

Figure 7

schematically shows a box-shaped heating surface with vertically aligned transition from the refractory lining to the upper membrane tube wall in longitudinal section, corresponding section A - A of FIG. 8 .

Figure 8

schematic cross section of a box-shaped heating surface according to section C - C of FIG. 9 .

Figure 9

schematic longitudinal section of a box-shaped heating surface according to section B - B of FIG. 8 ,

In fossil-fired continuous steam generators of conventional power plants, it is known that the working medium, usually water / steam preheated substantially in one pass of a steam turbine cycle, evaporated, superheated and possibly reheated. The continuous steam generator including the associated furnace is described below.

FIG. 1 schematically shows a continuous steam generator 1 with circulating fluidized bed 2 (ZWSF) for the combustion of coal or other combustible materials. The material to be incinerated is introduced either together with an inert material or separately through the feed line 10 into the fluidized bed or fluidized-bed combustion chamber 3 of the continuous-flow steam generator 1 with ZWSF. To build up the fluidized bed and to burn the introduced substance within the combustion chamber 3, a fluidizing gas through the supply line 11 is usually the vortex combustion chamber 3 fed from below. The fluidizing gas is typically air and is thus used for combustion as the oxidant. The resulting during combustion exhaust gas or flue gas and carried along by the exhaust solids (inert material, ash particles and unburned) are in the upper part of the opening 12 from the. Combustion chamber 3 discharged and fed via an exhaust pipe 13 a separator, usually a centrifugal separator or cyclone 14. In the separator 14, the solids are largely separated from the exhaust gas and fed back to the combustion chamber 3 via the return line 15. The largely purified exhaust gas is supplied via the exhaust pipe 16 to a second flue 17, in which at least one economizer heating surface 18, at least one superheater heating surface 19 and possibly at least one reheater heating surface 20 is arranged for further use or decrease of the exhaust heat. The cross section of the combustion chamber 3 is generally rectangular. However, it can also be round or have a different shape.

The FIGS. 2 to 5 The combustion chamber 3 is surrounded on all sides by Umfassungswände 4, the Umfassungswand 4 seen from bottom to top the combustion chamber 4.1, the combustion chamber side walls 4.2 and the combustion chamber ceiling 4.3 includes. The combustion chamber floor 4.1 is generally designed as a nozzle bottom, through which the fluidizing gas is introduced. FIG. 2 shows a combustion chamber 3 with a simple funnel 6 in the lower region of the combustion chamber 3, whereas FIG. 3 a combustion chamber 3 with double funnel 7, a so-called "pant leg" design shows. The combustion chamber surrounding walls 4 are designed as heating mediums through which working medium flows, these heating surfaces being formed from gas-tight membrane walls. Such membrane walls can be assembled by gas-tight welding of a pipe-web-tube combination. In general, the tube-web-tube combination comprises tubes 5, which are smooth on the outer circumference and which are each connected to separate webs 21. However, it is also possible fin tubes whose outer wall are already formed with webs and which are connected together.

The present invention is directed to continuous steam generator 1 with circulating fluidized bed 2 high power (about 300 to 600 Mwel) and high steam parameters (about 250 to 300 bar pressure and 560 to 620 ° C temperature) from. In order to achieve an efficient combustion chamber design in this power range, it is necessary to install additional heating surfaces 8, which for reasons of thermal engineering (uniform heat absorption) are preferably arranged inside the combustion chamber 3.

The continuous steam generator 1 according to the invention with ZWSF 2 provides that all the tubes 5, 9 of the enclosing walls 4 and lying within the combustion chamber 3 heating surfaces 8 are formed as Verdampferheizfläche and are connected in parallel for the flow of the entire working medium to be evaporated, that all tubes 5 of Surrounding walls 4 are formed with a smooth inner tube surface and the heating surfaces 8 extend between the combustion chamber bottom 4.1 or funnel top edge 24 and the combustion chamber ceiling 4.3. The parallel connection of the heating surfaces 8 and the heating surface of the enclosure wall 4 of the continuous steam generator 1 and the use of both heating surfaces as Verdampferheizfläche is achieved in an advantageous manner that on the one hand by means of adjusting the number of heating surfaces 8, the combustion chamber 3 can be designed efficiently. D. h., That with this measure the combustion chamber dimensions can be optimized, especially the combustion chamber height (distance between combustion chamber floor and ceiling) can be significantly reduced by the integration of the heating surfaces 8. On the other hand, the effective heat flux densities within the fluidized-bed combustion chamber 3 in the aforementioned circuit of the continuous steam generator 1 despite reduced working medium mass flow densities of about 400 to 1200 kg / m ² s allow for the tubes 5 of the enclosing walls 4 to use those inside smooth surface. Due to the reduced working medium mass flow densities, an improved natural circulation characteristic within the evaporator heating surfaces is achieved, which means that an increase in the working medium throughput also takes place in the event of a localized multiple heating, thus ensuring reliable tube cooling.

The use of tubes 5 with an inner smooth surface, also called smooth tubes for short, has several advantages over the inner-ribbed tubes otherwise used with such low mass flow densities. On the one hand, smooth tubes are much cheaper than internally ribbed tubes, have shorter delivery times, are available in much larger sizes and generally better available, since ribbed tubes are usually only available as custom-made, smooth tubes are also much easier to handle in terms of assembly. On the other hand, smooth tubes have a much smaller friction pressure loss of the working medium compared with internally ribbed tubes, which has a positive effect on the uniform distribution of the working fluid to the individual tubes 5 and a reduction of the feed pump power of the continuous steam generator 1.

In order to increase the continuous steam generator process efficiency, and thus to reduce harmful emissions to the atmosphere caused by the steam generator furnace, continuous steam generators 1 are increasingly being used in the supercritical range, i. H. operated at a vapor pressure of over 220 bar and in sliding pressure between supercritical and subcritical pressure (the operating pressure of the steam generator slides in the load range of the continuous steam generator, eg between 20 to 100% load). At a continuous steam generator operating pressure of, for example, 270 bar at full load, the steam generator reaches the critical pressure range at a partial load of about 70% and is operated subcritically below this partial load, ie. H. that in the partial load range approximately below 70% in the evaporator during the evaporation process, a two-phase mixture occurs. The abovementioned solution according to the invention ensures that no segregation of steam and water occurs within the evaporator heating surface (enclosing walls 4 and heating surfaces 8). This is further supported by the advantageous embodiment of the continuous steam generator 1 according to the invention that the working medium flow through the tubes 5, 9 of the enclosing walls 4 and the heating surfaces 8 takes place without the aid of intermediate collectors.

The additional heating surfaces 8 used in the fluidized-bed combustion chamber 3 are so-called Schott heating surfaces. Schott heating surfaces are self-contained and plate-like heating surfaces (ie the individual ones side by side arranged tubes 9 are connected to webs 22 - welded tube-web-tube combination - together to a bulkhead), which are in contrast to bundle heating surfaces that are open (ie, the individual juxtaposed tubes are not connected to each other with webs). The heating surfaces 8 are arranged substantially vertically within the combustion chamber 3 and the tubes 9 contained therein also extend substantially vertically.

According to the invention, the heating surfaces 8 extend, depending on the combustion chamber formation, either between the combustion chamber bottom 4.1 or the upper edge of the funnel 24 and the combustion chamber ceiling 4.3. As a result, they can be used together with the enclosure wall 4 fully for parallel flow through the entire working medium to be evaporated. The heating surfaces 8 thus spring in the lower region of the fluidized-bed combustion chamber 3 substantially at the combustion chamber bottom or at the funnel lower edge 4.1 in the case of a combustion chamber 3 with a funnel 6 (FIG. FIG. 2 ) and central arrangement of the heating surfaces 8 within the combustion chamber 3 or at the funnel upper edge 24 in a combustion chamber 3 with two funnels 7 (FIG. FIG. 3 ) and central arrangement of the heating surfaces 8 and ends in the upper region of the fluidized-bed combustion chamber 3 substantially at the combustion chamber ceiling 4.3. For attachment of the individual heating surfaces 8, these can be welded, for example, to the combustion chamber bottom 4.1 or upper edge of the funnel 24 and the combustion chamber ceiling 4.3. If more than two funnels are provided in the lower region of the combustion chamber 3, the integration of the heating surfaces 8 can take place analogously.

The parallel supply of the heating surfaces 8 and the enclosure wall 4 is effected by collectors, not shown, by means of which the above-mentioned heating surfaces, the working medium to be evaporated is supplied from below. The heating surfaces 8 start at a combustion chamber 3 with two hoppers 7 according to the FIG. 3 only at the upper edge of the funnel or on the funnel saddle 24, these heating surfaces 8 can be fed via the funnel enclosing walls 4 with working medium. A separate, parallel feed of the heating surfaces 8 is possible.

The solution according to the invention provides for heating the heating surfaces 8 arranged inside the fluidized-bed combustion chamber 1 on one side. FIG. 6 shows a heating surface 8 heated on one side. This heating surface 8 comprises an inner space 23 on the circumference and is box-shaped, which is why the heating surface 8 is also referred to in the following description as a box-shaped heating surface or as a box bulkhead (s) 8. The FIG. 6 shows an advantageous embodiment of the box-shaped heating surface 8 with a rectangular cross-section. The box bulkhead 8 according to the FIG. 6 has four sidewalls of welded membrane tube walls welded together at the corners, the membrane tube walls being formed of tubes 9 and lands 22. This results in a box in gas-tight welded tube-web-tube design or combination. Instead of in FIG. 6 cross-sectional side indicated rectangular design of the box-shaped heating surface 8, this may also be formed with a different cross-section, z. B-square (at least 3-sided), round, etc. D. h. in this case, the space 23 enclosed by the box-shaped heating surface 8 has an N-cornered cross section.

Due to the vertical arrangement of the heating surfaces 8 and thus also of the tubes 9 and the vertical tubes 5 of the enclosure walls 4, the tubes 5, 9 give the lowest possible erosion attack points in the combustion chamber 3 from the bottom upwards flowing gas and particle flow. In order to protect the tubes 5, 9 in the lower combustion chamber area or in the funnel area 6, 7 from the high transverse or turbulence flows of the gas and particle flow of the fluidized bed, these are provided with a refractory lining 25.

An advantageous embodiment of the invention provides according to the FIGS. 7 to 9 before, the tubes 9 of the combustion chamber in the hopper area 6, 7 with a refractory lining 25th provided box-shaped heating surface 8 in the transition region 26 between lined and non-lined Heizflächenbereich 27 inwardly into the region of the interior 23 and auszubilden the leading edges of the refractory lining 25 and the non-lined portion 27 of the heating surface 8 in the vertical direction aligned. This measure prevents 26 erosion attack points are given to the tubes 9 for turbulence flows of the gas and particle flow in the transition region.

Through the refractory lining 25 of the tubes 5, 9 in the funnel region 6, 7 results in substantially equal heated lengths of the tubes 5, 9 within the combustion chamber. 3

The box-shaped heating surfaces 8, which extend over a length L and over its cross-section over a width B and a depth T, have expediently dimensions of about 1.0 to 4.0 m over the width B, about 0, 1 to 1.0 m over the depth T and about 20 m to 50 m over the length L. This makes it possible to equip the combustion chamber 3 and the largest continuous steam generator 1.

The tubes 9 used for the box-shaped heating surfaces 8 have in an advantageous embodiment outer diameter between 20 mm and 70 mm. The production of the box-shaped heating surfaces 8 is possible with customary in steam generator construction materials and manufacturing processes. <B> LIST OF REFERENCES: </ b> 1 Through steam generator 2 Circulating fluidized bed firing 3 vortex combustion chamber 4 containment 4.1 Combustion chamber bottom or funnel bottom edge 4.2 Combustion chamber sidewall 4.3 combustion chamber ceiling 5 pipe 6 Funnel, easy 7 Funnel, double 8th heating surface 9 pipe 10 Feed fuel 11 Supply fluidizing gas 12 Opening or exit flue gas 13 exhaust pipe 14 cyclone 15 Return line 16 exhaust pipe 17 Second flue 18 Eco heating surface 19 Superheater heating surface 20 Intermediate superheater heating surface 21 Bridge surrounding wall 22 Bridge heating surface 23 inner space 24 funnel top edge 25 Refractory lining 26 Transition area 27 Non-lined area of the heating surface

Claims (7)

1. Once-through steam generator with circulating atmospheric fluidized-bed combustion, having a turbulence combustion chamber (3),
   wherein the turbulence combustion chamber (3) is bounded essentially on all sides by enclosure walls (4) and comprises gas-tight pipe walls, formed by essentially vertical pipes (5), and has at least one hopper (6, 7) in the lower region,
   and the turbulence combustion chamber (3) contains at least one essentially vertically arranged heating surface (8) provided with vertical pipes (9), wherein the heating surface (8) comprises a welded pipe-web-pipe combination,
   and wherein the pipes (5, 9) of the enclosure walls (4) and of the heating surface (8) have a water/steam working medium flowing through them,
   characterized in that all the pipes (5, 9) of the enclosure walls (4) and of the heating surface (8) are designed in the form of an evaporator heating surface and are connected in parallel for the throughflow of all working medium which is to be evaporated,
   in that all the pipes (5) of the enclosure walls (4) and of the heating surface (8) are formed with an internally smooth pipe surface,
   in that the heating surface (8) extends between the combustion-chamber floor (4.1) or upper hopper edge (24) and combustion-chamber ceiling (4.3),
   in that the heating surface (8) is designed in the form of a box which can be heated on one side and is of pipe-web-pipe configuration with gas-tight welding,
   and in that the flow of working medium through the pipes (5, 9) of the enclosure walls (4) and of the heating surface (8) takes place without the aid of intermediate collectors.
2. Once-through steam generator according to Claim 1, characterized in that the heating surface (8) has a box-like cross section with a width (B) and a depth (T), its circumference surrounds an interior (23), and it is closed over its circumference.
3. Once-through steam generator according to Claim 2, characterized in that the cross section of the box-like heating surface (8) is at least triangular or round.
4. Once-through steam generator according to Claim 2, characterized in that the cross section of the box-like heating surface (8) is rectangular.
5. Once-through steam generator according to Claim 2, characterized in that the pipes (9) of the box-like heating surface (8), which is provided with a refractory lining (25) in the hopper region (6, 7) of the combustion chamber, are curved out into the region of the interior (23) in the transition region (26) between the lined heating-surface region and non-lined heating-surface region (27), and the front edges of the refractory lining (25) and of the non-lined region (27) of the heating surface (8) are aligned in the vertical direction.
6. Once-through steam generator according to at least one of the preceding claims, characterized in that the pipes (5) of the enclosure walls (4) have essentially the same heated length.
7. Once-through steam generator according to at least one of the preceding claims, characterized in that the pipes (9) of the heating surface (8) have essentially the same heated length as the pipes (5) of the enclosure walls (4).

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