EP2412943B1 - Device and method for generating hot gas with integrated heating of a heat distribution medium - Google Patents

Description

The invention relates to a steam generator comprising a first train with a combustion chamber and an evaporator and at least a second train with at least one superheater and / or at least one economizer. Furthermore, the invention relates to a plant for steam generation and a steam power plant. Such steam generators are from the publications US7229833 B1 . US2003 / 185718 A1 . DE202007005195 U1 and US2008 / 251952 A1 known. Steam generators are used in various industrial applications where steam is needed to drive machinery, generate electrical energy, heat transfer medium or process steam. In a steam generator pressure, temperature and amount of steam produced are designed so that they can be applied to the steam consumer, z. As a power plant turbine are tuned. Essential components of a steam generator are the evaporator for generating the steam, the superheater, in which the steam is heated to the temperature required for the consumer, the feedwater and air preheater, in which water and combustion air are preheated and the firing, the for the Consumers needed heat generated with fuels such as coal, oil or gas.
From practice, various designs for steam generators are known. A known steam generator includes a first train with a combustion chamber with grate firing and evaporator arranged above. The upward flowing through the evaporator flue gases of grate firing to 180 ° in the second train of the steam generator deflected ("Leerzug"), they flow through downwards. At the lower end of the flue gases are redirected in a Umlenkabscheider, in which coarse particles are deposited, again by 180 ° in a third train of the steam generator. In this, the flue gases flow upwards through a plurality of superheaters and are then redirected a final 180 ° in a fourth train of the steam generator, where they flow through a plurality of economizers in the downward direction.

The steam generator described above has a total of technically very complicated to implement construction. In particular, it is not possible with the proposed Umlenkabscheider in addition to coarse ash particles also deposit aerosols from the flue gases that condense predominantly on the tubes / harden and thus pollute them in a problematic way (caking, glazing, ..). The non-deposited fine ash particles have to be removed from the flue gas stream consuming, for example, by arranged downstream of the steam generator in the flow direction. By contrast, the components present in the steam generator, such as superheaters and economizers, are permanently exposed to the damaging effect of non-deposited aerosols.

Proceeding from this, the present invention seeks to provide a steam generator of the type mentioned above, which is characterized by a simplified construction as well as the ability to remove even the smallest particles, especially aerosols and fine fly ash particles from the flue gas stream, characterized.

The object is achieved with a steam generator according to claim 1. The particular advantage of the steam generator according to the invention is that it is possible by the integration of a cyclone between the first and the second train, coarse as well as very fine particles or aerosols already deposited in the steam generator from the flue gas and thus an approximately particle-free gas for more Applications, such as use in a dryer, provide. Furthermore, the almost complete cleaning of the flue gases also proves to be advantageous in that, for example, in the second train built evaporator, superheater, economizer and Luftvorwärmerbündel which use the heat of the flue gases for feedwater and / or air preheating, in ribbed construction and thus can be made much more compact, since the cleaned flue gases do not burden the surfaces of the superheater and / or economizer.
Overall, the steam generator according to the invention is characterized by a very simple and compact and thus inexpensive to be realized construction.
According to a first embodiment of the invention, the evaporator of the first train of the steam generator comprises a water / steam-permeable pipe-web-pipe construction. This construction, also referred to as "membrane wall", allows efficient utilization of the maximum temperature of the flue gases, so that a maximum amount of feed water can be converted to steam.
Constructively, the steam generator according to the invention can be realized, for example, that the first and the second train of the steam generator with the interposed separator take the form of an inverted U, such that the first train is flowed through by the flue gases from the grate furnace and the second train of the flue gases are flowed through downwards.

According to the steam generator according to the invention, the outflow region of the second train is connected via a Rezirkulationsgasleitung with the combustion chamber, so that at least a portion of the cooled in the second train of the steam generator flue gases is recirculated as recirculation gas in the combustion chamber of the first train. This allows a precise adjustment of the combustion chamber temperature and thus an optimized combustion process.
With regard to the combustion performance of the steam generator this is preferably designed such that the firing capacity is ≤ 100 MW. Above this power range, steam generators known from the prior art are usually operated with a fluidized bed furnace, in which such a "hot gas" cyclone belongs to the process concept.
The grate firing of the steam generator is supplied during operation with combustion air, preferably with primary and secondary combustion air. In the combustion air supply for grate firing, at least one heat exchanger for preheating the combustion air is preferred thermal energy of the steam generated in the steam generator and / or provided to the steam generator recycled feedwater. This achieves a further increase in efficiency through optimized process heat utilization.

Another aspect of the present invention relates to a plant for generating steam comprising at least one steam generator according to one of claims 1 to 6. The above-mentioned advantages apply in an analogous manner to the plant for generating steam.

According to one embodiment, the system comprises a drying device. With this, the residual heat of the purified flue gases for drying, for example, granular, fibrous or generally particulate material, in particular of chopped wood, sawdust, wood shavings, wood fibers, animal feed, cereals and the like can be used optimally. For this purpose, the outflow region of the second train of the steam generator is preferably connected to the drying device via a flue gas line.

According to a particularly advantageous embodiment, a task unit for discharging solid, particulate or fibrous fuel into the flue gas stream flowing into the drying device is provided on the hot gas line in front of the inlet opening of the drying device. The discontinued in the flue gas fuel is thus transported by this through the drying device and thereby dried. As a result, the residual heat of the flue gases is used to pre-dry the fuels used in the grate furnace and thus to optimize the energy input during operation of the plant for steam generation, as for the necessary drying of the fuel no separate energy must be expended.

This can be practically implemented by the fact that, viewed in the flow direction of the flue gases behind the drying device, a second separation device, in particular a cyclone, for separating the dried fuel and also a conveyor is provided, by means of which the dried fuel for grate firing of the steam generator can be transported. The conveyor may be formed for example as a pneumatic conveyor.

According to a further advantageous embodiment of the invention, the system comprises a condenser heat exchanger in which a further heat transfer medium, in particular thermal oil, is heated. This also contributes to optimized process heat utilization.

Another aspect of the present invention relates to a steam power plant comprising at least one steam turbine and a connected generator and a plant for generating steam according to one of claims 7 to 12. For the steam power plant according to the invention, the advantages mentioned above apply in an analogous manner.

According to one embodiment, the steam power plant additionally comprises at least one drying device of particulate material, in particular wood fibers and chips, wherein the at least one drying device can be heated by at least one heat exchanger through which steam can flow, in particular a condenser heat exchanger. As a result, the heat contained in the steam, for example the residual heat of the steam partially expanded in the turbine of the steam power plant, optimally used and the process efficiency thus further increased.

Fig. 1

einen Dampferzeuger mit ersten und zweiten Zug sowie zwischen erstem und zweitem Zug angeordnetem Zyklonabscheider in schematisierter Seitenansicht,

Fig. 2

eine Anlage zur Dampferzeugung mit einem Dampferzeuger aus Fig. 1 und

Fig. 3

ein Dampfkraftwerk mit einer Anlage zur Dampferzeugung aus Fig. 2.

The invention will be explained in more detail with reference to a drawing illustrating an exemplary embodiment. Show it:

Fig. 1

a steam generator with first and second train and between the first and second train arranged cyclone separator in a schematic side view,

Fig. 2

a plant for steam generation with a steam generator Fig. 1 and

Fig. 3

a steam power plant with a plant for steam generation Fig. 2 ,

The in Fig. 1 Steam generator shown in schematic form comprises a first train 1 and a second train 2. The first train 1 comprises a combustion chamber 11, which in turn has a grate furnace 12, and an evaporator 13. The evaporator 13 is present - as in the prior art known - as a water / steam flowed pipe-web-pipe construction executed in what Fig. 1 is schematically represented by a plurality of parallel tubes 13a. As a result of the very hot flue gases rising in the region of the evaporator 13, the feed water flowing through the tubes 13a is partly vaporized (~ 20%) and passed into a steam drum 14, where separation takes place between water and steam. In Fig. 1 as well as in the Fig. 2 and 3 Steam traversed lines are each shown as dashed lines, while the Feedwater flowing through lines are shown as solid lines.

The second train 2 of the steam generator the Fig. 1 In turn, it comprises two steam superheaters 21 arranged one below the other and two economizers 22 arranged underneath. It is understood that the number of superheaters 21 and economizers 22 can be varied depending on the particular application. In the superheaters 21, the steam generated in the evaporator is overheated by the flue gases flowing through the second train 2 of the steam generator to a temperature of typically 450 ° C - 540 ° C depending on the fuel quality.

Between the first and the second train 1, 2 a separating device is arranged for the particulate-laden flue gases flowing out of the first train 1 of the steam generator, which in the present case is designed as a separating cyclone 3. With the help of the separation cyclone, not only coarse particles but also aerosols can be effectively removed (up to 98%) from the flue gases, and the cyclone has a positive effect on burnout of co-flowing, unburnt particles and carbon monoxide (CO). As a result, the load on the heat exchanger surfaces of the superheater 21 and economizer 22 drops significantly during operation, resulting in a significantly increased service life of the components used. Furthermore, the proportion of unburned fuel in the ash decreases as well as the CO emissions.

As in Fig. 1 As can be seen, the separation cyclone 3 is arranged between the upper outlet end of the first train 1 and the upper inlet of the second train 2, so that the first and the second train 1, 2 of the steam generator are interposed therebetween arranged Abscheidezyklon 3 take the form of an inverted U. Accordingly, the first train 1 flows through the flue gases of the grate firing upwards and the second train 2 flows through the flue gases downwards.

As mentioned, the combustion chamber 11 of the first train 1 comprises a grate furnace 12 for solid fuels. These are fed via the line 7 into the combustion chamber 11. The combustion air necessary for the combustion is injected as primary air via a line 15 into the combustion chamber 11 below the grate of the grate furnace 12 and introduced as secondary air via a line 16 into the combustion chamber 11 above the grate. As in Fig. 1 Recognizable, 15 heat exchangers 15a, b are provided in the primary air line, by means of which the primary air can be preheated. For example, in the heat exchanger 15a, the residual heat energy of the steam power plant connected downstream of the steam generator (cf. Fig. 3 ) condensed feed water can be used, while in the heat exchanger 15 b, the heat energy of a partial flow of teilentspannten steam is used to heat the primary air flow. In a very similar manner, the secondary air flow through heat exchangers 16a, b, which in turn are fed by water or partially expanded steam, are heated.

Finally, a (not shown in detail) burner is provided in the first train 1 of the steam generator, which is arranged in the region of the evaporator 13 and is fed via the line 13b with gaseous fuel. Likewise, a supply of this burner with dusty fuel is possible.

At the funnel-shaped outlet 2a of the second train 2, two lines 23, 24 are attached, via which by means of the blower 23a, 24a of the cooled to typically below 160 ° C flue gas stream from the second train 2 can be discharged. Specifically, it is possible to re-introduce a portion of the flue gas stream via line 23 as recirculation gas into the combustion chamber 11 in order to precisely adjust the combustion temperature there and in particular to avoid overheating. Via line 24 it is possible to supply the flue gases to further applications, as described below in connection with FIG Fig. 2 will be described in detail.

Fig. 2 shows a plant for steam generation in a schematic representation. This first comprises a steam generator, as described above in detail. As in Fig. 2 recognizable, the steam generated in the evaporator 13 is passed in part through the superheater 21, but in the present case supplied to another part of a heat exchanger 4, in which the steam, another heat transfer medium, in particular thermal oil, heated, wherein it condenses. The backflowing under very high pressure (eg 90 bar) standing water is then fed back to the steam drum 14.

The flue gases flowing out of the second train 2 of the steam generator via the line 24 in the present case flow through a drying device 5. In front of the front-side inlet opening of the cylindrical drying device 5, the particulate solid fuel provided for the grate firing 12 is conveyed via a Fig. 2 abandoned only as an arrow 5a task unit in the flue gas stream, whereupon it flows through the drying device 5 together with the flue gas stream and while releasing its residual moisture. After flowing out of the drying device 5, the now optimally dried fuel passes together with the flue gas stream in another cyclone separator 6, where it is separated from the flue gas stream and collected in a container 6 a. Then the separated dried fuel passes by means of a, preferably pneumatic, promotion (arrow 7) to the combustion chamber 11 to be abandoned there on the grate of the grate furnace 12. By means of this predrying of the fuel, the energy input during operation of the plant for steam generation can be further reduced because the necessary drying of the fuel no longer has to be done with separate energy input, but is carried out by utilizing the residual heat of the flue gases. The effluent from the cyclone 6 to typically cooled below 90 ° C flue gases are then a wet electrostatic filter 8 (see. Fig. 3 ).

Fig. 3 shows a steam power plant using the plant for steam generation described above in a schematic view. As shown, the superheated steam from the superheaters 21 of the steam generator flows to a steam turbine 9, which is driven by the very hot steam (about 470 ° C, 85 bar). The rotational energy of the steam turbine 9 is converted in a known manner via a connected generator 9a into electrical energy. The completely relaxed wet steam (0.2 bar, 60 ° C) is fed to an air condenser 90, where it condenses. Subsequently, the condensate passes into a feedwater tank 92. Parallel to the condenser 90, a heat exchanger 91 is arranged, in which the residual energy of the wet steam to a hot water flow (55 ° C) is discharged. This hot water flow can be used to heat the primary and Secondary air for the grate furnace 12 of the steam generator via the heat exchangers 15a, 16a serve, as in connection with Fig. 1 already described.

The feedwater is finally returned via pumps 92a to the economizers 22 of the steam generator to be introduced from there into the evaporator, whereby the water vapor cycle is closed.

As in Fig. 3 Furthermore, partially expanded steam (255 ° C., 12 bar) can be taken off from the turbine 9, which is fed via a line 94 to the heat exchangers 95a, 95b of further drying devices 95 (in FIG Fig. 3 For the sake of clarity, only one is shown). The partially expanded steam condenses in the heat exchangers of the drying devices 95 and is subsequently fed back to the feedwater tank 12 via heat exchanger / expander registers 96, 97. A conveying air stream, which transports particulate material to be dried through the drying devices 95, preferably flows through the drying devices 95, the dried material then being fed to a separator column 98.

As in Fig. 3 also shown, the overheated steam flowing from the superheaters 21 can also be passed bypassing the turbine 9 in the heat exchangers 95a, 95b of the drying devices 95, where it must pass an expansion valve 940, for example, by a pressure of 85 bar to 12 bar relaxed to become. From the relaxed steam of the line 94, finally, a further partial flow can be branched off (not shown), which can be used to heat the feedwater in a further heat exchanger 93.

The steam power plant described above is characterized by a high process efficiency as a result of optimized utilization of the process heat. All specified process characteristics, in particular pressure and temperature specifications, are to be understood as examples only. It is understood that other parameter ranges can be chosen to achieve the advantages described.

Claims (12)

1. Steam generator comprising a first flue (1) with a combustion chamber (11) and a vaporiser (13) and at least one second flue (2) with at least one heat exchanger, in particular a vaporiser, superheater (21), air pre-heater and/or an economiser (22), wherein the combustion chamber (11) has a grate stoker furnace (12) and a separation device (3), in particular a cyclone is arranged between the first and the at least one second flue (1, 2) to separate particles and aerosols, characterised in that the outflow region of the second flue (1) is connected to the combustion chamber (11) via a recirculating gas line (23) such that at least one part of the flue gas cooled in the second flue (2) of the steam generate can be fed back into the combustion chamber (11) of the first flue (1) as recirculation gas.
2. Steam generator according to Claim 1, characterised in that the vaporiser (13) of the first flue (1) of the steam generator has a tube-web-tube construction (13) through which water/steam can flow.
3. Steam generator according to Claim 1 or 2, characterised in that the first and second flue (1, 2) of the steam generator adopt the shape of a rotated U with the separation device (3) arranged therebetween such that the flue gases from the grate stoker furnace (12) flow upwards through the first flue (1) and the flue gases flow downwards through the second flue (2).
4. Steam generator according to any one of Claims 1 to 3, characterised in that at least one heat exchanger (15a, 15b, 16a, 16b) is provided in the combustion air supply line (15, 16) for the grate stoker furnace (12) of the steam generator to pre-heat the combustion air via the thermal energy of the steam generated in the steam generator and/or of the feed water fed back to the steam generator.
5. Unit for generating steam comprising at least one steam generator according to any one of Claims 1 to 4.
6. Unit according to Claim 5, characterised in that the unit has a drying device (5).
7. Unit according to Claim 6, characterised in that the outflow region (2a) of the second flue (2) of the steam generator is connected to the drying device (5) via a flue gas line (24).
8. Unit according to Claim 7, characterised in that a feeding unit (5a) is provided at the hot gas line before the inlet opening of the drying device (5) to feed solid, particle or fibre-shaped fuel into the flue gas flow flowing into the drying device (5).
9. Unit according to Claim 8, characterised in that a second separation device (6), in particular a cyclone, is arranged behind the drying device (5) to separate the dried fuel and a delivery device is also provided by means of which the dried fuel can be transported to the grate stoker furnace of the steam generator.
10. Unit according to any one of Claims 5 to 9, characterised in that the unit has a condenser/heat exchanger (4) in which an additional heat-carrying medium, in particular thermal oil, is heated.
11. Steam power plant comprising at least one steam turbine (9) and a connected generator (9a) and a unit for generating steam according to any one of Claims 5 to 10.
12. Steam power plant according to Claim 11, characterised in that the steam power plant also has at least one drying device (95) for particle-shaped products, in particular wood fibres and shaving, wherein the at least one drying device (95) can be heated by at least one heat exchanger (95a, 95b) through which steam can flow, in particular a condenser/heat exchanger.

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