WO2024013695A1

WO2024013695A1 - Method for generating steam in combination with a power generation process as well as plant to this end

Info

Publication number: WO2024013695A1
Application number: PCT/IB2023/057188
Authority: WO
Inventors: Renaat De Proft; Giovanni Nizzola; Benoit Englebert; Rudolf PITTOORS; Tom CROYMANS; Gerben TIMMER; Goof HOLTZER
Original assignee: Keppel Seghers Belgium Nv
Priority date: 2022-07-13
Filing date: 2023-07-13
Publication date: 2024-01-18
Also published as: BE1030715B1; BE1030715A1

Abstract

The invention relates to a method for generating steam in combination with a power generation process, comprising the following steps: guiding hot flue gas formed during the combustion past at least one preheater and at least one steam superheater, feed water being passed through a preheater and steam through a steam superheater; heating steam in a steam superheater to superheated steam with a temperature of at least 400°C and a pressure of at least 100 bar; feeding the superheated steam to a turbine; wherein the steam is reheated after leaving a stage of the turbine and is added to at least one subsequent stage of the turbine, this steam being reheated by means of heat from steam originating from a steam vessel, wherein this steam is also reheated by means of heat from hot flue gas before being added to a next stage of the turbine. The invention also relates to a waste incineration plant.

Description

METHOD FOR GENERATING STEAM IN COMBINATION WITH A POWER GENERATION PROCESS AS WELLAS PLANT TO THIS END

TECHNICAL FlELD

In a first aspect, the invention relates to a method for generating steam in combination with a power generation process. i n a second aspect, the invention relates to a waste incineration plant for generating steam in combination with a power generation process.

PRIOR ART

Waste incineration plants are known per se in the prior art. In a waste incineration plant, hot flue gas from the combustion of waste is used to produce steam by heating water.

The steam is used to drive turbines or used for other energy processes such as cogeneration with the aim of recovering energy. The recovery of thermal energy from the flue gas generated during the combustion process is currently carried out by traditional boilers that usually consist of a water-walled combustion chamber, as well as evaporators, preheaters and steam superheaters that use the heat of the hot flue gas as an energy source.

In the preheater, the feed water is heated before being fed to an evaporator. The evaporator produces steam by converting the heated feed water into wet steam . The wet steam is then converted to dry steam and brought to a useful tem perature by the steam superheater. The dry, heated steam from the superheater is used to produce useful work in the form of electricity and/or heat. The water wails of the combustion chamber also absorb the heat released during combustion. This heat is also used to evaporate the feed water into steam , which is then directed to the steam superheater.

The steam is generally superheated to a temperature of about 400°C, a maximum of 450°C, and a pressure of about 40 bar. Higher temperatures and pressures are used in a number of installations. However, boilers for steam generation suffer from thermal power fluctuations because waste incineration is characterized by high variability in net calorific value. This leads to a number of technical problems that limit the maximum net electrical efficiency that can be achieved in existing waste incineration plants. In general, the reason for this lies in the fact that the low joule “fuel”, the waste material, leads to corrosion in those parts of the plant that come into contact with the flue gases. The measures taken to combat this corrosion (low temperature of both the surface of the heat exchanger and the flue gases that come into contact with it) are at the expense of the overall efficiency of the plant, A problem is therefore that the maximum steam temperature that can be reached by the steam superheater is limited due to corrosion.

An additional problem is that conventional waste incineration plants use steam superheaters with a large superheating surface. The superheating surface of such steam superheaters is currently provided with a nickel alloy that protects the surface against high temperatures and corrosion as a result of these high temperatures. Such a nickel alloy is expensive and detrimental to the cost of a waste incineration plant. The present invention aims to solve at least some of the problems mentioned above.

While attempts have heretofore been made to improve the final net electrical efficiency of these known installations, this has not yet been achieved. The net electrical efficiency for large modern installations is approximately 25% .

The invention contemplates a waste incineration plant with a higher net electrical efficiency in which steam parameters such as steam pressure and steam temperature remain within a range so that corrosion risks are limited. SUMMARY OF THE INVENTION

In a first aspect, the invention relates to a method for generating steam in combination with a power generation process according to claim 1 . More specifically, the method according to the first aspect of the invention comprises reheating the steam after leaving a stage of the turbine and adding it to at least one subsequent stage of the turbine, this steam being reheated by means of heat from steam originating from a steam vessel, wherein this steam is also reheated by means of heat from the flue gas before being added to a next stage of the turbine. An advantage of a method according to the first aspect is that an increased net electrical efficiency is obtained compared to known methods for generating steam in combination with a power generation process. In particular, this increased net electrical efficiency is achieved without high steam parameters being required, such as for instance temperature and pressure of the steam .

Consequently, the invention has the additional advantage that extreme corrosion risks are avoided since the temperature and pressure of the steam remain iimited. Another additional advantage of avoiding corrosion risks is that maintenance costs are saved for, for example, replacing steam superheaters or other components.

An additional advantage of a method according to the first aspect is that a high thermal efficiency of the steam superheaters is achieved through less superheating surface, compared to the required superheating surface of known methods to obtain a comparable thermal efficiency. In this way an economic advantage is obtained through the increased thermal efficiency, but there is also an advantage in the form of a cost saving since less superheating surface has to be covered with an expensive nickel alloy.

An additional advantage of a method according to the first aspect is that more energy is recovered per ton of processed waste compared to known methods.

Preferred embodiments of the first aspect of the invention are described in claims 2-10.

In a second aspect, the invention relates to a waste incineration plant for generating steam in combination with a power generation process according to claim 11. More specifically, the waste incineration plant according to the second aspect also comprises at least one steam reheater and a reheat line, as well as a second steam vessel for reheating steam from a first stage of the turbine, a steam reheater being located in a pass of the combustion chamber for absorbing heat from the hot flue gas and wherein at least part of the reheat line passes through the second steam vessel to absorb heat from steam present in the second steam vessel. An advantage of a waste incineration plant according to the second aspect is that the waste incineration plant in an active state achieves an increased net electrical efficiency compared to known waste incineration plants. In particular, this increased net electrical efficiency is achieved without high steam parameters being required, such as temperature and pressure of the steam , so that corrosion risks remain lim ited.

An additional advantage of avoiding corrosion risks is that maintenance costs are saved, for example for replacing steam superheaters or other components. Preferred embodiments of the second aspect of the invention are described in claims 12- 15. A particular embodiment relates to a waste incineration plant according to claim 13. This embodiment has the advantage that optimum heat transfer takes place between, on the one hand, steam originating from a stage of the turbine and steam originating from a steam vessel. This allows to realize the heat transfer with a minim um temperature difference.

DESCRIPTION OFTHE FlGURES Fig. 1 illustrates a schematic representation of a waste incineration plant having a plurality of vertical passes according to preferred embodiments of the invention.

Fig. 2 illustrates a process diagram for generating steam in combination with a power generation process according to preferred embodiments of the invention, wherein a pump is placed between a second and a first steam vessel.

Fig. 3 illustrates a process diagram for generating steam in combination with a power generation process according to preferred embodiments of the invention, wherein no pump is placed between a second and a first steam vessel.

Fig. 4 illustrates a schematic representation of a waste incineration plant having a plurality of horizontal passes according to preferred embodiments of the invention.

DETAILED DESCRIPTION

The invention relates to a method for generating steam in combination with a power generation process. The invention further relates to a waste incineration plant for generating steam . Unless otherwise defined, ail terms used in the description of the invention, including technical and scientific terms, have the meanings com m only understood by those skilled in the art of the invention. For a better understanding of the description of the invention, the following terms are explained explicitly. The term “steam vessel” in this text comprises a container containing both water and steam . A steam vessel acts as a phase separator for the steam/water mixture. The term “preheater” or “economizer” in this text comprises a heat exchanger that receives heat from fine gas and transfers it to the feed water of a steam vessel.

In this docum ent, “a” and “the” refer to both the singular and the plural, unless the context presupposes otherwise. For example, “a segment” means one or more segments.

When the term “around” or “about” is used in this document with a measurable quantity, a parameter, a duration or moment, and the like, then variations are meant of approx. 20% or less, preferably approx. 10% or less, more preferably approx, 5% or less, even more preferably approx. 1 % or less, and even more preferably approx. 0.1 % or less than and of the quoted value, insofar as such variations are applicable in the described invention. However, it m ust be understood that the value of a quantity used where the term “about" or “around” is used, is itself specifically disclosed.

The terms “comprise," “comprising,” “consist of," “consisting of,” “provided with,” “have,” “having," “include,” “including,” “contain,” “containing” are synonyms and are inclusive or open terms that indicate the presence of what follows, and which do not exclude or prevent the presence of other components, characteristics, elements, members, steps, as known from or disclosed in the prior art.

Quoting numeric intervals by the endpoints includes all integers, fractions, and/or real numbers between the endpoints, including those endpoints.

In a first aspect, the invention relates to a method for generating steam in combination with a power generation process, comprising the following steps:

- guiding hot flue gas formed during the combustion past at least one preheater and at least one steam superheater, feed water being passed through a preheater and steam through a steam superheater: - heating steam in a steam superheater to superheated steam with a temperature of at least 400°C and a pressure of at least 100 bar:

- feeding the superheated steam to a turbine; wherein the steam is reheated after leaving a stage of the turbine and is added to at least one subsequent stage of the turbine, this steam being reheated by means of heat from steam originating from a steam vessel, and wherein this steam is also reheated by means of heat from hot flue gas before being added to a next stage of the turbine. In this process, the steam is reheated using heat from steam originating from a steam vessel through a heat exchanger, without mixing the steam . The steam and the steam from the steam vessel are not mixed, Combustion refers to the incineration of waste. In a preferred embodiment, the combustion does not involve incineration of fossil fuels.

Fossil fuels refer to a group of naturally occurring carbon-containing compounds derived from the remains of ancient plants and animals, such as coal, lignite, petroleum , and natural gas.

Examples of waste include sludge, biomass, chemicai waste, medical waste, and municipal waste.

In one embodiment, the flue gas comprises a concentration of hydrogen chloride of at least 10 mg/Nm³ , preferably at least 100 mg/Nm³ , more preferably at least 200 mg/Nm³ , even more preferably at least 300 mg/Nm³ , and even more preferably at least 500 mg/Nm³.

In one embodiment, the flue gas comprises a concentration of hydrogen chloride ranging from 10 mg/Nm³ to 10,000 mg/Nm³ , preferably ranging from 100 mg/Nm³ to 7,000 mg/Nm³ , more preferably at least 200 mg/Nm³ to 5,000 mg/Nm³ , and even more preferably at least 300 mg/Nm³ to 3,000 mg/Nm³.

In one embodiment, the flue gas comprises a concentration of sulfur dioxide of at least 1 mg/Nm³ , preferably at least 10 mg/Nm³ , more preferably at least 50 mg/Nm³ , and even more preferably at least 100 mg/Nm³.

In one embodiment, the flue gas comprises a concentration of sulfur dioxide ranging from 1 mg/Nm³ to 10,000 mg/Nm³ , preferably ranging from 10 mg/Nm³ to 5,000 mg/Nm³ , more preferably at least 50 mg/Nm³ to 2,000 mg/Nm³ , and even more preferably at least 100 mg/Nm³ to 1 ,000 mg/Nm³.

The term 'Nm³ ' refers to the normal cubic meter, where a normal cubic meter is a quantity of gas that occupies a volume of 1 cubic meter (m³) at 0°C, 1 .01325 bar, and 0% relative humidity, according to DINN 1343: 1990-01 . An advantage of a method according to the first aspect is that an increased net electrical efficiency is obtained compared to known methods for generating steam in combination with a power generation process. In particular, this increased net electrical efficiency is achieved without high steam parameters being required, such as for instance temperature and pressure of the steam .

Consequently, the invention has the additional advantage that extreme corrosion risks are avoided since the temperature and pressure of the steam remain limited. Another additional advantage of avoiding corrosion risks is that maintenance costs are saved for, for example, replacing steam superheaters or other components.

In a preferred embodiment of the present invention, the steam is heated to a temperature in the range of 400-450°C, preferably in the range of 400-440°C. If the steam is heated to a temperature higher than this range, considerable corrosion occurs on parts of the waste incineration plant, resulting in high maintenance costs. If the steam is heated to a temperature lower than this range, the steam contains too low an amount of energy, which can be converted into electrical energy by means of a turbine, to obtain an econom ically relevant net electrical efficiency. This embodiment therefore has the advantage that the steam is heated to a temperature in an optimum range.

In a preferred embodiment of the present invention, after leaving a stage of the turbine, the steam is reheated to a temperature of at least 300°C, preferably in the range 310- 450°C, more preferably in the range of 320- 450°C and most preferably in the range of 350-450°C. An advantage of this embodiment is that the steam is reheated to a temperature of at least 300°C, resulting in an increased net electrical efficiency that cannot be achieved with known waste incineration plants without taking considerable risks of corrosion. In a preferred embodiment of the present invention, the pressure of the superheated steam is supplied to a first stage of the turbine in a range of 100-180 bar, preferably in a range of 110-170 bar and most preferably in the range of 110-150 bar. A pressure lower than the aforementioned range is too low to achieve an increase in net electrical efficiency. A pressure higher than the aforementioned range results in too high an operational cost to achieve such pressures. An advantage of this embodiment is that the pressure of the superheated steam is delivered to a first stage of the turbine in an econom ically relevant range and an increased net electrical efficiency is achieved.

In a preferred embodiment of the present invention, the pressure of the reheated steam is supplied to a next stage of the turbine in a range of 15-70 bar, preferably 20-50 bar and most preferably in a range of 25-45 bar. A pressure lower than the aforementioned range is too low to achieve an increase in net electrical efficiency. A pressure higher than the aforementioned range results in the need to closely control the temperature of the reheated steam to avoid corrosion of parts. An advantage of this embodiment is therefore that there is no need to control the temperature of the reheated steam , so that some variability in temperature is allowed, and yet an increase in net electrical efficiency is achieved.

In a preferred embodiment of the present invention, the velocity of the flue gas during heat exchange with a preheater and/or steam superheater is 3-6 m/s, preferably the velocity is 4-5.5 m/s. A speed in such a range has the advantage that a uniform temperature reduction of the flue gas is obtained. A steam superheater substantially comprises a heat exchanger comprising a bundle of evaporator tubes that further heat saturated steam to superheated steam beyond the saturated steam point. In this way, superheated steam has a higher temperature and lower density than saturated steam at the same pressure.

In a preferred embodiment of the present invention, a steam superheater comprises at least two rows of evaporator tubes, each row comprising a plurality of evaporator tubes, preferably 50-100 evaporator tubes per row. In a further embodiment, the diameter of an evaporator tube of a steam superheater comprises 30-75 m m , preferably 35-60 m m and most preferably 40-50 mm . Such an embodiment has the advantage that an optimal and uniform heat exchange is achieved. In a preferred embodiment, at least one steam superheater is positioned countercurrent to the flow direction of the flue gas and at least one other steam superheater is positioned co-current to the flow direction of the flue gas.

In a preferred embodiment, a preheater comprises at least two rows of evaporator tubes, each row comprising a plurality of evaporator tubes, preferably 50-100 evaporator tubes per row. In a further embodiment, the diameter of an evaporator tube of a preheater comprises 30-75 m m , preferably 35-60 m m and most preferably 40-50 mm . Such an embodiment has the advantage that an optimal and uniform heat exchange is achieved.

In a preferred embodiment, a preheater is positioned countercu rrent to the flow direction of the flue gas. Such an embodiment has the advantage that the heat from the flue gas is absorbed optimally by feed water in the preheater. In another embodiment, a preheater is positioned co-current to the direction of flow of the flue gas since this makes the plant less susceptible to corrosion on the flue gas side.

In a second aspect, the invention relates to a waste incineration plant for generating steam , comprising: a combustion chamber in which waste is burned, hot flue gas being released during combustion, the combustion chamber comprising a number of passes: at least one preheater to heat feed water using heat from the hot flue gas; at least one evaporator to produce steam from the heated feed water using heat from the hot flue gas; a first steam vessel configured to receive the heated feed water from at least one preheater and act as a supply of heated feed water, the at least one steam vessel being further configured to receive the steam from at least one evaporator and act as a supply of steam ; at least one steam superheater to receive the steam from at least one steam vessel and further heat the steam to superheated steam using heat from the hot flue gas; at least one turbine to receive superheated steam from at least one steam superheater and convert the steam to electricity; wherein the waste incineration plant also comprises at least one steam reheater, a reheat line, as well as a second steam vessel for reheating steam from a first stage of the turbine, a steam reheater being located in a pass of the combustion chamber for absorbing heat from the hot flue gas and wherein at least part of the reheat line passes through the second steam vessel to absorb heat from steam present in the second steam vessel. An advantage of a waste incineration plant according to the second aspect is that the waste incineration plant in an active state achieves an increased net electrical efficiency compared to known waste incineration plants. In particular, this increased net electrical efficiency is achieved without high steam parameters being required, such as temperature and pressure of the steam , so that corrosion risks remain limited.

An additional advantage of avoiding corrosion risks is that maintenance costs are saved, for example for replacing steam superheaters or other components.

In a preferred embodiment of the present invention, the combustion chamber has four passes. In a further embodiment, at least one pass of the combustion chamber is positioned horizontally opposite at least one other pass. In another embodiment, at least one pass of the combustion chamber is positioned vertically opposite at least one other pass, preferably all four passes are positioned vertically. In another preferred embodiment, some passes are positioned horizontally.

In an embodiment, waste is burned in the combustion chamber by means of one of the following processes: pyrolysis, gasification, combustion by means of pure oxygen or another combustion process known in the art. Furthermore, examples of waste include: sludge, biomass, chem ical waste, medical waste and residual waste.

In some embodiments, the combustion chamber is a fluidized bed combustion chamber.

In another embodiment, the combustion chamber is a grate combustion chamber.

In a preferred embodiment, the temperature in the first pass is about 1200°C, in the second pass about 850°C, in the third pass about 650°C, and at the outlet of the fourth pass about 140°C.

In a preferred embodiment, the incineration plant comprises a total of 1 -20 steam superheaters, preferably 2-15 and more preferably 3-12. In a preferred embodiment, the incineration plant comprises a total of 1 -6 steam reheaters, preferably 1 -4 and more preferably 1 -3.

In a preferred embodiment, the steam reheater comprises a shell -and-tube heat exchanger. This embodiment has the advantage that optimum heat transfer takes place between, on the one hand, steam originating from a stage of the turbine and steam originating from a steam vessel. In particular, the outflow temperature of outgoing steam is approximately equal to the inflow temperature of incom ing steam . In a further embodiment, the steam reheater is a vertical shell-and-tube heat exchanger. In another embodiment, the steam reheater is a horizontal shell-and-tube heat exchanger,

In a preferred embodiment, the second steam vessel is directly connected to the first steam vessel without using a pump. In a further embodiment, the second steam vessel is placed on top of the first steam vessel. Such an embodiment has the advantage that condensate, i.e. water, flows back from the second steam vessel by gravity to the first steam vessel, making a pump superfluous and reducing operational and installation costs.

In a preferred embodiment, the reheat line also comprises a steam cooler. Such an embodiment has the advantage that the temperature of reheated steam can be lowered in order to avoid corrosion risks in the case of a highly variable temperature of reheated steam .

Examples for which the method according to the second aspect of the invention is suitable, in addition to processing waste for a power generation process, are: a carbon fixation process, a chemical process, a paper converting process; wherein the process supplies steam and/or heat to the processes mentioned above.

One skilled in the art will appreciate that a method according to the first aspect is preferably performed with a device according to the second aspect and that a device according to the second aspect is preferably configured for perform ing a method according to the first aspect. Each feature described in this document, both above and below, can therefore relate to any of the two aspects of the present invention.

Advantages associated with the method and waste incineration plant according to the present invention comprise, among others: more flexibility in the design because the temperature for reheating is not linked to the pressure of the steam : a lower superheating surface is required, which leads to a lower cost; maximum efficiency can be achieved without reduced availability and without an increased risk of corrosion ; maxim um efficiency can be achieved without excessively high maintenance and management costs (the superheater is not regarded as a part that is bound or designed to wear out or fail with repeated use) ; maximum efficiency can be achieved with predictable maintenance and management costs. In what follows, the Invention is described by way of non-lim iting figures illustrating the invention, and which are not intended to and should not be interpreted as lim iting the scope of the invention. FIGURES

Fig, 1 illustrates a schematic representation of a waste incineration plant 5. Waste is burned in a combustion chamber 6, releasing hot flue gas. The combustion chamber 6 comprises four vertical passes. The hot flue gas is fed to a first pass 1 . In the first pass 1 , the flue gas rises vertically upwards. At the start of the first pass 1 , the temperature of the flue gas is approximately 1200°C. The flue gas is then deflected to a second pass 2, where the flue gases are led downwards and deflected to a third pass 3. In the second pass 2, the temperature of the flue gas is approximately 850°C and in the third pass 650°C. Finally, the flue gas is deflected to a fourth pass 4. The temperature at the end of the fourth pass 4 is approximately 140°C. The velocity of the flue gases through the four passes is in the range of 3-6 m/s. A uniform temperature reduction is hereby obtained.

At least one steam superheater 8 and at least one steam reheater 11 are placed in the third pass 3. A steam superheater 8 and a steam reheater 11 comprise at least two rows of evaporator tubes through which steam flows. The steam superheater 8 and steam reheater 11 absorb heat from the hot flue gas rising through the third pass 3, thereby heating and raising the temperature of the steam in the evaporator tubes. The flue gas leaving the third pass 3 is passed on to at least one preheater 7, which is located in the fourth pass. A preheater 7 comprises at least two rows of evaporator tubes through which feed water flows. The preheater 7 absorbs heat from the hot flue gas flowing through the fourth pass 4, heating and increasing the temperature of the feed water in the evaporator tubes. The feed water comes from a first steam vessel 9.

The flue gas leaving the fourth pass 4 is partially filtered by means of a filter 19, after which the filtered flue gas is cooled and leaves the waste incineration plant 5 along a flue stack 18. The remaining part of the flue gas that is not filtered is fed back to the first pass 1 by means of a fan 15. The bottom ash leaves the combustion chamber 6 through an opening 17.

Fig. 2-3 illustrate a process diagram for steam generation combined with a power generation process. Fig. 2 illustrates a process diagram in which a pump 21 is placed between a second 10 and a first steam vessei 9. Fig. 3 illustrates a process diagram in which no pump 21 is placed between a second 10 and a first steam vessel 9. Ail other parts of both process diagrams are similar. Steam is fed from a first steam vessel 9 to at least one steam superheater 8 at a pressure in the range of 100-150 bar and a temperature of at least 300°C. By extracting heat from the hot flue gas, the steam is heated to a temperature of 400-450°C. This steam is fed to a first turbine stage 13 of a turbine, where it will exit the first turbine stage 13 at a pressure in the range of 20-50 bar and a temperature of about 180°C. The steam leaves the first turbine stage through a reheat line 12.

This steam is then reheated. On the one hand in a first step with the aid of steam from a second steam vessel 10, which steam initially originates from the first steam vessel 9. On the other hand, in a second step using at least one steam reheater 11 located in the third pass 3. In this way, the steam from the first turbine stage 13 is reheated by means of both heat from steam and heat from the hot flue gas.

The steam from the first turbine stage 13 is thus reheated to a temperature of at least 300°C. This reheated steam is then supplied to a second turbine stage 14 at a temperature of at least 300°C and a pressure in the range of 20-50 bar.

In Fig. 2, a pump 21 is provided which pumps condensate 22 from the second steam vessel 10 to the first steam vessei 9. In Fig. 3, the second steam vessel 10 is positioned relative to the first steam vessei 9 such that the condensate 22 will flow from the second steam vessel 10 to the first steam vessel 9 by gravity. As a result, a pump 21 is superfluous.

Fig. 4 illustrates a schematic representation of a waste incineration plant 5. Waste is burned in a combustion chamber 6, releasing hot flue gas. The combustion chamber 6 comprises three vertical passes (1 ,2,3) . The hot flue gas moves through the vertical passes as described in Figure 1 . Finally, the flue gas is deflected to a fourth pass 4, which is positioned horizontally.

At least one steam superheater 8 and at least one steam reheater 11 are placed in the fourth pass 4. A steam superheater 8 and a steam reheater 11 comprise at least two rows of evaporator tubes through which steam flows. The steam superheater 8 and steam reheater 11 absorb heat from the hot flue gas moving through the fourth pass 4, thereby heating and raising the temperature of the steam in the evaporator tubes. The flue gas leaving the fourth pass 4 is passed to at least one preheater 7, which is located in the fifth pass, the fifth pass 24 being positioned vertically. A preheater 7 comprises at least two rows of evaporator tubes through which feed water flows. The preheater 7 absorbs heat from the hot flue gas flowing through the fifth pass 24, heating and increasing the temperature of the feed water in the evaporator tubes. The feed water comes from a first steam vessel 9.

The flue gas leaving the fifth pass 24 is partially filtered by means of a filter 19, after which the filtered flue gas is cooled and leaves the waste incineration plant 5 along a flue stack 18. It is also possible to install a sixth, also vertical, pass with preheaters in between the fifth pass 24 and the filter 19. The remaining part of the flue gas that is not filtered is fed back to the first pass 1 by means of a fan 15. The bottom ash leaves the combustion chamber 6 through an opening 17.

Below is an overview of the meaning of the numbers used in the figures:

1 first pass

2 second pass 3 third pass

4 fourth pass

5 waste incineration plant

6 combustion chamber

7 preheater 8 steam superheater

9 first steam vessel

10 second steam vessel 11 steam reheater

12 reheat line 13 first turbine stage

14 second turbine stage

15 fan

16 space

17 opening 18 flue stack

19 filter

20 condenser

21 pump 22 condensate

23 steam

24 fifth pass The present invention should not be construed as being lim ited to the embodiments described above and certain modifications or changes may be added to the figures described without having to re-evaluate the appended claims.

Claims

1 . Method for generating steam in combination with a power generation process, comprising the following steps: guiding hot flue gas formed during the combustion of waste past at least one preheater and at least one steam superheater, feed water being passed through a preheater and steam through a steam superheater; heating steam in a steam superheater to superheated steam with a temperature of at least 400ºC and a pressure of at least 100 bar; feeding the superheated steam to a turbine; characterized in that the steam is reheated after leaving a stage of the turbine and is added to at least one subsequent stage of the turbine, this steam being reheated by means of heat from steam originating from a steam vessel, wherein the steam passes through the steam vessel in a reheat line to absorb heat from steam present in the steam vessel, and wherein this stearn is also reheated by means of heat from hot flue gas before being added to a next stage of the turbine.

2. Method according to claim 1 , characterized in that the steam is heated to a temperature in the range of 400-450°C.

3. Method according to any of the preceding claims, characterized in that the steam is reheated to a temperature of at least 300°C after leaving a stage of the turbine.

4. Method according to any of the preceding claims, characterized in that the pressure of the superheated steam supplied to a first stage of the turbine is in the range of 100-180 bar.

5. Method according to any of the preceding claims, characterized in that the pressure of the reheated steam supplied to a subsequent stage of the turbine is in the range of 20-70 bar.

6. Method according to any of the preceding claims, characterized in that the velocity of the flue gas during the exchange of heat with a preheater and/or steam superheater is 3-6 m/s.

7. Method according to any of the preceding ciaims, characterized in that a steam superheater comprises at ieast two rows of evaporator tubes, each row comprising a plurality of evaporator tubes, preferably 50-100 evaporator tubes per row.

8. Method according to any of the preceding claims, characterized in that at least one steam superheater is positioned countercurrent to the flow direction of the flue gas and at least one other steam superheater is positioned co-current to the flow direction of the flue gas.

9. Method according to any of the preceding claims, characterized in that a preheater is positioned countercurrent to the flow direction of the fiue gas.

10. Method according to any of the preceding claims 1 -9, characterized in that a preheater is positioned co-current to the flow direction of the flue gas.

11 . Method according to any of the preceding claims, wherein the fiue gas comprises a concentration of hydrogen chloride of at least 10 mg/Nm³.

12. A waste incineration plant for generating steam , comprising: a combustion chamber in which waste is burned, hot flue gas being released during combustion, the combustion chamber comprising a number of passes; at least one preheater to heat feed water using heat from the hot flue gas; at least one evaporator to produce steam from the heated feed water using heat from the hot flue gas; a first steam vessel configured to receive the heated feed water from at least one preheater and act as a supply of heated feed water, the at least one steam vessel being further configured to receive the steam from at least one evaporator and act as a supply of steam ; at least one steam superheater to receive the steam from at least one steam vessel and further heat the steam to superheated steam using heat from the hot fiue gas; at least one turbine to receive superheated steam from at least one steam superheater and convert the steam to electricity; characterized in that the waste incineration plant also comprises at least one steam reheater, a reheat line, as well as a second steam vessel for reheating steam from a first stage of the turbine, a steam reheater being located in a pass of the combustion chamber for absorbing heat from the hot flue gas and wherein at least part of the reheat line passes through the second steam vessel to absorb heat from steam present in the second steam vessel.

13. A waste incineration plant according to the preceding claim 12, characterized in that the combustion chamber comprises four passes.

14. A waste incineration plant according to any of the preceding claims 12-13, characterized in that the steam reheater comprises a sheil-and-tube heat exchanger.

15. A waste incineration plant according to any of the preceding ciaims 12-14, characterized in that the second steam vessel is directly connected to the first steam vessel without using a pump.