EP2423584B1 - Steam unit for generating superheated steam in a waste incineration unit - Google Patents

Description

The invention relates to a steam generator for generating superheated steam in a waste incineration plant according to the preamble of claim 1.

Waste incinerators are state of the art and are particularly prevalent in Western Europe. In most plants, the waste is burnt by means of grate firing. The energy released during combustion is usually used to generate high-pressure steam, which is used in a steam turbine to generate electricity. Furthermore, plants are known in which in addition to power generation, part of the energy is converted into process steam or district heating. However, the boundary conditions for such a type of heat utilization are possible only in a limited number of locations.

In the plants used in Central Europe, boilers are preferably used as steam generators, in which the flue gas produced by the combustion process flows through a second down-draft train into a third up-flow train and then into a horizontal bundle train after leaving the combustion chamber, the latter often also is called convection part.

However, plants are also known in which the gases flow directly into the horizontal convection pass after leaving the combustion chamber. The previously described boilers with horizontally extending convection parts are referred to in professional circles as Horizontalzugkessel.

In the waste incinerators described above, the convection part comprises an evaporator, end superheater, superheater and a first economizer, which are housed in the convection part in the above order and are flowed through by the flue gas in order to extract thermal energy from the resulting convection.

This arrangement of the heating surfaces in the convection part, at which the thermal energy of the flue gas is transmitted primarily by convection, is preferably at a Pressure of the superheated steam of up to about 40 bar and a temperature thereof of up to about 400 ° C used, which represent the usual steam parameters today.

The efficiency of the plants is known to be greatly influenced by the temperature and the pressure of the live steam, with a high steam temperature leads to a high efficiency, which is in the existing systems in terms of the electrically generated energy in the range of about 25%.

Although it is desirable to increase the efficiency of the waste incineration plants to increase the steam temperature to a value of more than 400 ° C, this is usually not realized in the known waste incineration plants for corrosion reasons, since steam temperatures> 400 ° C and associated pipe outside wall temperatures of> 430th - 450 ° C at the final superheater used in the convection part of the systems to increase the efficiency disadvantageously lead to an increased occurrence of corrosion. These corrosions are caused by the fact that the aggressive pollutants entrained by the exhaust gas precipitate on the hot tubes of the heat exchangers of the final superheaters as encrustations, which, in combination with the high temperatures, after a short time lead to corrosion-induced destruction of the components.

In order to protect the walls of the combustion chamber of waste incineration plants upstream of the convection part from corrosion by the flue gases resulting from the combustion process, plates or ramming masses with a high thermal conductivity are often applied to the walls of the combustion chamber, e.g. made of silicon carbide or ceramic. These plates are sometimes also placed at a certain distance from the tube wall, so that between the inside of the plates and the outside of the tube wall, a gap is formed, which is preferably applied to a non-corrosive gas atmosphere, e.g. with air. By this measure it is achieved that the corrosive flue gases, which can diffuse through cracks or pores in the plates or the Bestampfung, do not lead to damage to the water leading high-pressure lines in the walls of the combustion chamber.

From the EP 0 981 015 B1 is a waste incinerator with a steam generator is known in which a wall superheater is used in the form of a final superheater, which is arranged together with the evaporator in the lower part of the combustion chamber of the boiler is, in which the heat transfer takes place primarily by the heat radiation generated during the combustion process. In order to prevent corrosion of the horizontal superheater tubes of the final superheater as well as the outer wall of the combustion chamber, the superheater tubes are covered towards the inside of the combustion chamber by plates of ceramic material which are spaced from the tubes. The space between the inside of the combustion chamber wall and the plates is thereby filled with a gas which has a slightly higher pressure than the pressure of the combustion gases in the combustion chamber in order to prevent the combustion gases from penetrating into the gap.

By directly juxtaposed tubes of the final superheater and the evaporator results in the steam generator described the problem that the steam-conducting superheater tubes by the contrast significantly cooler water leading evaporator tubes are cooled again, which increases the required heat exchange surface and limits the achievable steam temperature in the superheater becomes.

Accordingly, it is an object of the present invention to provide a steam generator for a waste incineration plant, with which the efficiency in the production of superheated superheated steam can be further increased, without the life of the overheated live steam components leading to corrosion is adversely affected.

This object is achieved by the features of claim 1.

Further features of the invention are described in the subclaims.

According to the invention, a steam generator for generating superheated steam in a waste incineration plant comprises a boiler containing a combustion chamber, the walls of which have an evaporator with water-flowing pipelines, which are exposed to thermal energy for the production of superheated steam the combustion chamber is generated. The steam generator according to the invention further has a wall superheater, which is preferably designed as a final superheater, which comprises a plurality of housed in the wall of the boiler casing pipes, which are flowed through by the in the evaporator and preferably in the convection part arranged superheater superheated steam generated by the temperature of the superheated steam to more than 470 ° C, wherein the pressure is at least 60 bar. In order to protect the superheated steam pipes of the wall superheater from the flue gas produced during the combustion process, the pipes are protected by a refractory lining, in particular in the form of ventilated, plate-shaped elements made of a corrosion-resistant material, such as silicon carbide or other ceramic material, wherein the gap between Pipe wall and refractory lining is filled with a non-corrosive gas or is acted upon.

The steam generator according to the invention is characterized in that the boiler housing comprises an evaporator housing part containing the evaporator and a spatially separated, the wall superheater containing wall superheater housing part, wherein the wall superheater housing part is considered downstream of the evaporator housing part in the flow direction of the flue gas and the two housing parts are separated and designed to be movable relative to each other to allow a thermally induced different expansion of the materials. After the wall superheater housing part, one or more further evaporator housing parts can be arranged to improve the overall efficiency of the system, which are flowed through by the flue gas.

The inventive design of the steam generator has the advantage that compared to conventional steam generators in waste incineration plants significantly higher superheater temperatures can be driven without it comes after a short time to a corrosion-related destruction of the pipes of the superheater. The temperatures can be up to 550 ° C in the case of an embodiment of the wall superheater as a final superheater, which heated the hot steam for the last time before it is fed to a turbine waste incineration plant to drive an electric generator, wherein the vapor pressure can be up to 150 bar.

According to a first embodiment of the invention, the boiler housing comprises a first vertical train containing the combustion chamber and a second train for the flue gas connected thereto, the flue gas flowing in the first train in the upward direction and in the second train in the downward direction. The wall super heater housing part in this case has the shape of a hood closed to the outside or a cap which is placed on the first train and the second train and this gas-tight at the top, so that the emerging from the first train flue gas in the second train is diverted. This embodiment of the invention has the advantage that the base area required for the boiler does not increase despite the improved efficiency.

Due to the inventive spatial separation between the comparatively cool evaporator housing part and compared to this much hotter wall superheater housing part in the form of the first and second train patch hood also results in the advantage that the radiation part of the boiler, i. in particular, the combustion chamber wall can be designed in a cost effective manner as an evaporator wall, which consists of a plurality of juxtaposed, preferably in the vertical direction extending pipes. These pipelines, which carry the water supplied for generating the superheated steam, are preferably connected to one another via webs and form an outwardly closed circumferential wall which absorbs the thermal energy from the combustion chamber primarily via the resulting heat radiation.

The wall superheater housing part is supported in this embodiment of the invention preferably on the boiler frame and is connected by compensators smoke gas tight with the evaporator housing part, whereby a temperature-induced displacement of the wall superheater housing part relative to the evaporator housing part is made possible. This results in particular when using an evaporator housing part with a tube-web tube evaporator wall, the advantage that the two housing parts manufactured inexpensively and thermal expansion of the tubes of the evaporator wall and the tubes of the wall superheater in the vertical direction without complex measures by the Compensators known in the art can be compensated.

According to another underlying idea of the invention, the boiler housing has a first, the combustion chamber-containing vertical train and at this fluidly adjacent further vertical train for the flue gas, the flue gas in the first train in the upward direction and in the further train, the following also is referred to as a second train, flows in the downward direction and is deflected in a known manner by a deflection from the first train in the second train. The first train contains in this embodiment of the invention, only the evaporator housing part and the second train exclusively the wall superheater housing part, wherein the first train and the second train form independent units which are movable in the vertical direction relative to each other. To a free movement of the two housing parts in the vertical direction and Also to allow each other in the horizontal direction, the outer walls of the housing parts are preferably arranged at a distance from each other.

The last-described embodiment has the advantage that the heat-transferring surface of the wall superheater housing part can be increased in total compared with the hood-type embodiment described first without increasing the overall height. Optionally, further vertical trains, e.g. a third and a fourth train can be provided with the steam-carrying pipelines which are protected against corrosion by plates of ceramic material. At least a portion of the steam-carrying pipelines may in this case also be assigned to a superheater, which additionally overheats the steam generated in the evaporator before it is fed to the final heater, thereby further increasing the efficiency.

In the same way as in the first embodiment described with a hood-like end superheater, the water-carrying piping of the evaporator housing part are preferably connected to each other in this embodiment via webs and form a circumferential, outwardly closed pipe-web tube evaporator wall. This has the advantage that the lower part of the boiler can be manufactured in a cost effective manner according to the proven pipe-web-tube principle.

In the above-described embodiments of the invention, the superheater casing passages through which superheated steam flows are preferably received in a space formed between the inner wall of the corrosion-resistant material plates and the outer wall of the wall superheater case, which is charged with a gas such that an overpressure arises in the intermediate space, which prevents penetration of the flue gas into the intermediate space. The gas is preferably air or recirculated clean gas, e.g. via a fan with an overpressure of e.g. 0.005 bar can be blown into the space between the outer wall of the wall superheater housing part and the plate-shaped elements.

The invention will be described below with reference to the drawings with reference to the two preferred embodiments.

Fig. 1

eine schematische Darstellung der ersten Ausführungsform der Erfindung, bei der das Wandüberhitzer-Gehäuseteil nach Art einer Haube auf den ersten und zweiten, als Verdampferwand ausgestalteten Gehäuseteil aufgesetzt ist, und

Fig. 2

eine zweite Ausführungsform der Erfindung, bei der der erste Zug vollständig als Verdampfer-Gehäuseteil und der sich daran anschließende zweite Zug als Wandüberhitzer-Gehäuseteil ausgestaltet sind.

In the drawings show:

Fig. 1

a schematic representation of the first embodiment of the invention, in which the wall superheater housing part is placed in the manner of a hood on the first and second, designed as an evaporator wall housing part, and

Fig. 2

a second embodiment of the invention, in which the first train are designed completely as an evaporator housing part and the adjoining second train as a wall super heater housing part.

As in Fig. 1 is shown, a steam generator 1 comprises in a not completely shown illustrative reasons waste incineration plant, a boiler housing 2, in which a combustion chamber 4 is formed in the not shown in detail waste z. B. is burned on a grate 6 to produce a flame 8.

The resulting during the combustion process highly corrosive flue gas 13 flows along the arrows in a first train 10 in the upward direction, which is also referred to as a radiation part, since in this the released thermal energy is transmitted primarily by thermal radiation.

In the upper region of the first train 10, the flue gas 13 is deflected into a parallel to the first train 10 extending second train 12, in which the flue gas 13 flows in the downward direction, from where it flows thereafter via a subsequent third train 14 in turn in the upward direction and from there into a horizontally extending fourth train 16 enters, from where it is then passed to a cleaning device of the waste incineration plant not shown in detail. The fourth train is also referred to below as the convection part.

At the in Fig. 1 In the embodiment of the invention shown, the walls of the combustion chamber 4 are designed as an evaporator wall 18, which contains a plurality of mutually parallel, extending in the vertical direction pipes, which are interconnected by webs shown in dashed lines and form a circumferential closed gas-tight wall, in the water fed in the pipes to the Generation of steam is heated by the released during combustion heat radiation.

Like the presentation of Fig. 1 can still be removed, made according to the pipe-web-tube principle evaporator wall 18 with the evaporator tubes 20 contained therein an independent evaporator housing part 24, the walls due to the guided through the pipes 20 during operation of the steam generator 1 depending on depending Steam pressure assume a temperature in the range of about 300 ° Celsius.

Like the presentation of Fig. 1 In this case, further, the evaporator housing part 24 is closed at the top by a wall super heater housing part 26 which contains a plurality of pipes 28, which are preferably also connected to one another via webs 30. In these pipelines 28, the hot steam generated in a pre-superheater 48 - which is preferably in the horizontally extending fourth train - initiated to further overheat this before the steam is fed to a turbine not shown in detail.

Like the presentation of Fig. 1 can still be removed, the wall superheater housing part 26 has the shape of a hood closed to the outside, which engages over the first train 10 and the second train 12 and which deflects the flue gas 13 after its exit from the first train 10 in the second train 12 , In order to avoid corrosion of the pipes 28 in the wall superheater housing part 26, which would be destroyed in a short time due to the high temperature of the superheated steam of up to 550 ° C in the case of direct contact with the flue gas 13, the inside of Wandüberhitzer- Housing part 26 provided with a fire-resistant lining, which preferably consists of plate-shaped elements 32, which are made of a highly corrosion-resistant material, such as silicon carbide or other ceramic.

In order to additionally protect the pipe 28 from coming into contact with the flue gas 13 passing through cracks or gaps between the plate-shaped members 32, a space 34 is provided between the pipes 28 and the inside of the plate-shaped members 32 For example, via a not-shown blower with a gas is applied to within the space 34th to produce a pressure which is, for example, 0.005 bar higher than the pressure of the combustion gases within the combustion chamber 4. The gas is preferably air or other inert gas and may for example also be recirculated purified flue gas.

In order to compensate for the occurring between the comparatively cool evaporator housing part 24 and the hood-like, significantly hotter wall superheater housing part 26 thermal length expansions of the material, the wall superheater housing part 26 is gas-tightly connected to the evaporator housing part 24 via a Schiebestellte 38. The sliding point 38 comprises, for example, a plurality of projections 40 fastened to the outside of the wall superheater housing part 26, which are each supported via a schematically illustrated support 41 on a projection 43 of a boiler framework 42 which is shown only in sections. The projection 43 preferably also carries the evaporator housing part 24, which via corresponding, unspecified joints and e.g. rod-shaped connecting elements 45 is suspended on the underside of the respective projection 43. For sealing and to compensate for the thermally induced expansions between the wall superheater housing part 26 and the evaporator housing part 24, these two housing parts are coupled to each other via known compensators 44 which allow relative movement of the two housing parts 24, 26 in the horizontal and also in the vertical direction ,

At the in Fig. 2 shown further embodiment of the invention, the evaporator housing part 24 with the water-carrying pipes 20 containing evaporator wall 18 and the wall superheater housing part 26 with the superheated steam pipes 28 are juxtaposed, the evaporator housing part 24, the first train 10 and the Wandüberhitzer- Housing part 26 form the second train 12 of the boiler housing 2. In this embodiment of the invention, the evaporator housing part 24 are configured with the peripheral outwardly closed evaporator wall 18 and the wall superheater housing part 26 as self-contained units, as shown in FIG Fig. 2 at a distance of z. B. 0.5 m are arranged to each other, so that a relative movement of the two housing parts 24, 26 is made possible both in the vertical direction, as well as in the horizontal direction. The self-contained units are in this case in the upper region above the first train 10 via compensators 44 connected to the evaporator housing part 24 and in this embodiment preferably used horizontally extending portion 47 of the wall superheater housing part 26. The two Housing parts 24, 26 are in the same or similar manner as in the embodiment of Fig. 1 via sliding points on an in Fig. 2 Not shown boiler frame added, the components are sealed at the respective joints over compensators 44 against leakage of flue gas 13.

Also in this embodiment of the invention, the wall superheater housing part 26 is preferably connected as a final superheater, which in the same manner as in the embodiment of Fig. 1 completely lined with ventilated plate-shaped elements 32 made of corrosion-resistant material, such as silicon carbide, in order to prevent corrosion of the pipes 28.

In both embodiments of the invention described above, further heat exchangers may further be arranged in the horizontally extending fourth train, for example, a superheater 48, which overheats the steam generated in the evaporator housing part 24 before being supplied to the wall superheater housing part 26, as well as a known from the prior art economizer 50 may be arranged to withdraw the flue gas 13 to increase the efficiency of further heat energy, which is transmitted in this part of the steam generator 1 primarily convective.

List of reference numbers

1

steam generator

2

boiler house

4

combustion chamber

6

rust

8th

flame

10

first train / radiation part

12

second train

13

flue gas

14

third train

16

fourth move

18

evaporator wall

20

water-bearing pipelines

22

Stege

24

Evaporator housing part

26

Wall superheater housing part

28

Superheated steam piping

30

Stege

32

plate-shaped elements

34

gap

38

sliding point

40

Projection on wall heater housing part

41

In stock

42

boiler frame

43

Lead on boiler frame

44

compensator

45

connecting element

47

horizontally extending section

48

pre-superheater

50

economizer

Claims (9)

1. Steam generator (1) for generating overheated steam in a waste incineration plant, with a boiler drum (2), comprising a combustion chamber (4), whose walls (18) comprise an evaporator with pipes (20) perfused by water, subjected to heat energy released during the combustion of waste for generating hot steam, as well as a wall superheater for increasing the temperature of the hot steam, the same comprising several pipes (28) perfused by hot steam, protected against flue gas (13) produced during the combustion process by plate-shaped elements (32) consisting of a corrosion resistant material,
   characterised in that
   the boiler drum (2) comprises an evaporator drum section (24) containing the pipes (20) perfused by water as well as a wall superheater drum section (26), spatially separate from the same and containing the pipes (28) perfused by hot steam, whereby the wall superheater drum section (26) is located downstream from the evaporator drum section (24) when viewed in flow direction of the flue gas (10) and is moveable relative to the same.
2. Steam generator according to claim 1,
   characterised in that
   the boiler drum (2) comprises a first vertical draught containing the combustion chamber (4) as well as a second draught (12) following the former in flow direction for the flue gas (13), whereby the flue gas (13) flows in a upward direction in the first draught (10) and in a downward direction in the second draught (12), and in that the wall superheater drum section (26) has the shape of an externally closed hood that closes the first draught (10) and the second draught (12) in a gas-tight way at the top and diverts flue gas (13) exiting from the first draught into the second draught (12).
3. Steam generator according to claim 2,
   characterised in that
   the wall superheater drum section (26) is designed as an end overheater, in which hot steam is heated prior to supply to a turbine.
4. Steam generator according to claim 2 or 3,
   characterised in that
   the wall superheater drum section (26) is supported on a boiler frame (42) in the area of its underside, and in that the evaporator drum section (24) is suspended from the boiler frame (42) in the area of its top.
5. Steam generator according to claim 1,
   characterised in that
   the boiler drum comprises a first vertical draught (10) containing the combustion chamber (4) as well as a further vertical draught (12) following the former in flow direction for the flue gas (13), and in that the first draught (10) comprises only the evaporator drum section (24) and the further draught the wall superheater drum section (26), whereby the first draught and the further draught form units that are moveable in a horizontal and vertical direction relative to each other.
6. Steam generator according to one of the preceding claims,
   characterised in that
   the evaporator drum section (24) and the wall superheater drum section (26) are displaceable relative to each other via compensators (44) and are externally coupled with each other in a gas-tight way.
7. Steam generator according to one of the preceding claims,
   characterised in that
   the same contains one or more further evaporator drum sections (24) and one or more further wall superheater drum sections (26).
8. Steam generator according to one of the preceding claims,
   characterised in that
   the water conveying pipes of the evaporator drum section (24) are connected with each other via bridges (22) and form a circumferential evaporator wall (18) that is closed on the outside.
9. Steam generator according to one of the preceding claims,
   characterised in that
   a gap (34), subjected to a gas in such a way that overpressure to prevent an ingress of flue gas (13) into the gap is created inside said gap (34), is envisaged between the hot steam perfused pipes (28) of the wall superheater drum section (26) and the interior wall of the plates (32) consisting of the corrosion resistant material.

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