KUMPULAINEN, Mauri (Kämnerinkuja 2 B 11, Helsinki, FI-00750, FI)
RAIKO, Markku (Rajalantie 223, Hyvinkää, FI-05800, FI)
JANKA, Pentti (Jänislamminkatu 9, Tampere, FI-33410, FI)
KUMPULAINEN, Mauri (Kämnerinkuja 2 B 11, Helsinki, FI-00750, FI)
RAIKO, Markku (Rajalantie 223, Hyvinkää, FI-05800, FI)
Claims
1. A combustion plant (10), which comprises a boiler (13) of solid fuel in which, in the combustion process, at the heat surfaces of the boiler (13) is directed a danger of corrosion from the components of the combusted material causing corrosion, which boiler (13) comprises for combustion air a inlet fitting (14) and which steam boiler (13) comprises a steam generator (18) inside it from a steam generator circuit of which steam is transferred to a superheater (24) in the steam boiler (13) of the combustion plant via a fitting (23), from which superheater (24) superheated steam is transferred to a steam turbine (100) which is arranged to rotate an electric generator (G) for generating electricity, characterised in that the steam turbine (100) is two-piece comprising a low-pressure turbine section (100a) and a high-pressure turbine section (100b), whereby from the steam boiler (13) is conveyed from the first superheater (24) a fitting (25) first to the high- pressure turbine section (100b), from which is conveyed a bled steam fitting (26) back to the steam boiler (13) to a second superheater (27) located in it, from which via a fitting (28) superheated steam is transferred to the low-pressure turbine section (100a) of the steam turbine (100).
2. A combustion plant (10) according to claim 1, characterised in that from the bled steam fitting (26) there is a branch point (Cl) from which there is a fitting (29) to a combustion air preheater (15) by means of which combustion air is heated and from which combustion air preheater there is a fitting (16) to a feed water tank (17).
3. A combustion plant (10) according to any one of preceding claims, characterised in that from the bled steam fitting (26) of the high-pressure turbine section (100b) of the combustion plant (10) there is a branch point (C2) and from it a branch fitting (30) to a feed water steam preheater (31), which branch fitting (30) advantageously comprises a valve (38) for ad- justing the flow of bled steam to the steam preheater (31) for adjusting the temperature of feed water.
4. A combustion plant (10) according to any one of preceding claims, char- acterised in that the steam preheater (31) is arranged to heat feed water which is conveyed from the feed water tank (17) and so that from the feed water tank (17) is conveyed a fitting (33) to a two-piece feed water preheater (46) located in connection with the steam boiler (13) which preheater comprises a first feed water preheater section (46a) and a second feed wa- ter preheater section (46b) being in series in relation to it which are arranged to be located in a flue gas passage (34) or a flue gas duct (35) of the steam boiler (13) and that the first preheater section (46a) of the feed water preheater (46) is bypassable with a bypass flow (S 2 ), whereby the bypass flow (S 2 ) in question comprises a fitting (36) for conveying the flow (S 2 ) as a bypass into connection with the second feed water preheater section (46b), whereby in the bypass fitting (36) is located the feed water steam preheater (31) by means of which the temperature of the bypassed feed water (S 2 ) can be adjusted by adjusting the bled steam flow conveyed to the steam preheater (31).
5. A combustion plant (10) according to claim 1, characterised in that from the feed water tank (17) is conveyed feed water to the at least two-piece feed water preheater (46) in the steam boiler (13) and that between the first preheater section (46a) and the second preheater section (46b) of the two- piece preheater (46) is located the feed water steam preheater (31) in which steam is conveyed from the high-pressure turbine section (100b) of the steam turbine (100) and that feed water is conveyed from the feed water tank (17) to the fitting (33) and flowed to the feed water preheater (46) and from there to the steam generator (18) in its boiler drum (21), whereby from the boiler drum (21) there is the fitting (23) to the first superheater
(24) in the steam boiler (13).
6. A combustion plant (10) according to any one of preceding claims, characterised in that from the low-pressure turbine section (100a) there is a bled steam fitting (40) to the feed water tank (17) and a steam fitting (41) to a condenser (42) to which there is a cooling water fitting (43) and from which there is an outlet fitting (44) for conveying the heated water in question for utilisation.
7. A combustion plant according to any one of preceding claims, character- ised in that at least one superheater (24, 27) comprises spray water cooling
(50, 51) for decreasing the temperature of steam conveyed via the superheater (24, 27) when required by spraying feed water from a jet pipe to cool steam in connection with the superheater (24, 27).
8. A combustion plant according to any one of preceding claims, characterised in that the first superheater (24) comprises a spray cooling device (50, 51) and that also the second superheater (27) comprises a spray cooling device (51) to which cooling water is taken from the feed water tank (17).
9. A combustion plant according to any one of preceding claims, characterised in that the combustion plant comprises a sensor device (Mi) either for defining the quality of fuel directly before the combustion process or a sensor device (M 2 ) for defining the quality of fuel in the boiler (13) or a sensor device (M 3 ) for defining the quality of fuel from flue gases whereby, based on the quality of fuel measured with the sensor device or based on a chemical analysis of fuel, the temperature of steam flowed via the superheaters is adjusted either in one of the superheaters (24 or 27) or in both superheaters (24 and 27).
10. A combustion plant according to any one of preceding claims, characterised in that the combustion plant comprises the first superheater (24) which is two-piece (24a, 24b) and comprises in its connection the cooling water jet apparatus (51) and that there is the second superheater (27) which is also two-piece (27a, 27b) and comprises in its connection the cooling water jet apparatus (51).
11. A combustion plant according to the previous claim, characterised in that for the jet apparatus (51) cooling water is conveyed from the feed water tank (17).
12. A combustion plant according to any one of preceding claims, characterised in that the combustion plant comprises the sensor device (M 1 , M 2 , M 3 ) for defining the quality or composition of the material being combusted whereby, based on the composition or quality, the cooling water volume conveyed to the jet (51) is adjusted by adjusting a valve (52, 53).
13. A combustion plant according to any one of preceding claims, characterised in that the steam generator circuit of the steam generator (18) includes the boiler drum (21) in which water is transferred from the steam generator (18) and from the boiler drum steam is transferred to the first superheater (24).
14. A combustion plant according to any one of preceding claims, characterised in that the combustion plant is a waste incineration plant and the fuel is material containing substances causing corrosion.
15. A method in the combustion of solid fuel causing corrosion of heat surfaces, characterised in that the fuel is brought to a combustion plant (10) and conveyed to a steam boiler (13) for fuel, whereby to the steam boiler (13) is conveyed an inlet fitting (14) for air and that the boiler (21) com- prises a steam generator (18) from a steam generator circuit of which steam is conveyed further to a first superheater (24) inside the boiler (13) and from it to a steam turbine (100) for rotating an electricity generator (G) and for producing electricity, and that in the combustion plant (10) the steam produced in the first superheater (24) of the steam boiler (13) is conveyed via a fitting (25) to a high-pressure section (100b) of the steam turbine (100) and from it bled steam is conveyed via a fitting (26) back to the steam boiler (13) to its second superheater (27) from which the steam is conveyed to a low-pressure section (100a) of the steam turbine (100).
16. A method in combustion according to the previous claim, characterised in that, according to the moisture content or quality of waste, the preheating of feed water is adjusted by bled steam, the combustion plant (10) comprising a sensor device (Mi, M 2 , M 3 ) measuring the quality of fuel and/or sensor devices measuring the temperature of feed water, whereby it is possible to adjust the optimum use of the combustion plant and the tem- perature of feed water especially in the superheaters (24, 27) by adjusting the temperature of steam in the superheater (24, 27) based on the quality/composition measurement of fuel.
17. A method according to any one of preceding claims 15 or 16, character- ised in that in the combustion plant (10) from its steam boiler (13) is conveyed bled steam of the high-pressure turbine section (100b) to a combustion air preheater (15) in which the combustion air can be preheated.
18. A method according to any one of claims 15-17, characterised in that in the method bled steam is flowed from the low-pressure turbine section
(100a) of the steam turbine (100) to the feed water tank (17) and bled steam from the low-pressure turbine section (100a) is also conveyed to a condenser (42) via which cooling water is cycled and heated for utilisation.
19. A method according to any one of preceding claims 15-18, characterised in that, in the method, feed water is flowed via an at least two-piece feed water preheater (46) which is located in a flue gas passage (34) or a flue gas duct (35) in the steam boiler (13) and that, in the method, feed water is flowed via a steam preheater (31) to which steam preheater (31) the flow of steam can be adjusted by a valve (38) and to which steam preheater (31) the steam is conveyed from the high-pressure section (100b) of the steam turbine (100).
20. A method according to any one of preceding claims 15-20, characterised in that, in the method, a first feed water preheater section (46a) is bypassed via a bypass fitting (36, 37) in which is located the feed water steam preheater (31) after which feed water is conveyed into connection with a second feed water preheater section (46b) and the feed water preheater sec- tions (46a, 46b) are located in the steam boiler (13) in the flue gas passage
(34) or the flue gas duct (35) and that the feed water is conveyed to a boiler drum (21) and further to the first superheater (24) and that said first feed water preheater section (46a) is located in the flue gas passage (34) or the flue gas duct (35) in which the temperature of flue gases is lower than in the duct section in which the second preheater section (46b) of the feed water preheater (46) being in series in relation to the first preheater section (46a) is located.
21. A method according to any one of preceding claims 15-20, characterised in that, in the method, in accordance with the quality of waste, the temperature and steam pressure of the boiler (13) are adjusted and maintained at desired values based on the measurements of waste quality and that, in the method, from the high-pressure steam turbine section (100b) is conveyed bled steam to the second superheater (27) and the temperature of steam is observed by measurements with measurement data received from the temperature sensor based on which also the adjustment of the boiler (13) takes place.
22. A method according to any one of preceding claims 15-21, characterised in that, in the method, the quality of the fuel is observed and, based on the quality, the temperature of steam conveyed via the superheaters or via the superheater is adjusted by adjusting the volume of sprayed water conveyed into connection with the steam.
23. A method according to any one of preceding claims 15-22, characterised in that, in the method, spray water is conveyed from the feed water tank (17) into connection with steam flowed in the superheater (24 and/or 27) for cooling the steam, whereby is used the superheater (24a, 24b; 27a, 27b) which is two-piece, between the sections of which two-piece super- heater is conveyed a cooling- water spray pipe (50, 51) i.e. a spray water cooling apparatus.
24. A method according to any one of preceding claims 15-23, characterised in that waste is used as the fuel and that the boiler is a waste incineration boiler (13). |
Combustion plant and method for the combustion
The invention relates to a combustion plant and a method for the combustion.
Many fuels include substances which in hot conditions cause heavy corrosion and/or contamination. Such substances are, inter alia, chlorine, alkali metals and heavy metals separately or together. Above-mentioned substances particularly exist in municipal waste, black lye and many biofuels. In these plants, steam val- ues have to be defined low in order to avoid hot corrosion. Typical steam values in waste incineration plants are 40 bar, 420°C. Corrosion rate can be decelerated by using highly alloyed pipe materials. Even then, the steam values cannot be increased very much. A typical industrial power plant utilises the energy received from fuel as electricity and backpressure heat. When burning corrosive fuels, the yield of electricity remains small in about 20% and heat is obtained about 70%, the rest going to lost heat. Because electricity is notably more valuable as a product than backpressure heat, the sales revenues of the power plant from electricity and heat remain low. The situation is even worse with waste incineration plants which have to be situated outside population centres and heat utilisation of which is not cost-effective due to long distances. The plant consumes only a little backpressure heat. In condensate production, the expansion of the turbine has to be stopped at a considerably high pressure level when the moisture of steam limits decreasing the pressure. When the electricity efficiency of the condensate process remains low, revenues from electricity sales are small. In the method according to the invention, the steam of the boiler is run to the turbine and expanded in the high-pressure section of the turbine to a pressure in which steam is still dry. This steam reduced with the preheating steam volume of feed water is taken back to the boiler to be superheated and, after the superheating, steam is taken to the low- pressure section of the turbine. The steam can be expanded when dry to a very low pressure. The yield of electricity is substantially increased. The increase is dependent on the case. In the case of a waste incineration plant, the increase of
electricity can be even 50%.
The property of fuels causing corrosion varies naturally. For example, the maximum value of chlorine contained by waste can be several tenfolds compared with its average. From the viewpoint of corrosion, even short exposures cause the wearing of the material. Hence, the invention has an embodiment in which the temperature of the superheater of the steam boiler is adjusted lower when the component causing corrosion is larger than the average. The adjustment is thus based on the chemical or physical (amount etc.) measurement of the composition of the fuel or flue gases created in its combustion. By means of measuring data, temperature allowed for the superheating material is calculated or otherwise defined. For achieving this temperature, the temperature of the steam is adjusted in the superheaters by adjusting the spraying water flow.
The superheating temperature can, by means of the method in question, be kept considerably higher on average without the danger of the corrosion of the superheating pipes increasing. Thus, better efficiency of electricity production is gained. The combustion plant in this application is advantageously a waste incineration plant.
Example 1
Waste incineration plant 85,000 tons/waste/year Output to steam 32.5 MW Steam values: conventional process
Pressure 40 bar Temperature 420°C
Flow of high-pressure steam 12 kg/s Bled steam: 3.5 bar, 0.7 kg/s Condenser pressure: 1 bar, steam moisture 5% Electric power: 7.9 MW
Electricity efficiency 20.9%
Steam values: plant provided with intermediate superheater
Fuel and output the same as in the previous calculation Pressure 40 bar Temperature 42O 0 C
Flow of high-pressure steam 10.25 kg/s Bled steam: 3.5 bar, 0.7 kg/s Steam values after the high-pressure section:
Pressure 3.5 bar Temperature about 147°C
Intermediate superheated steam: Pressure 2.5 bar Temperature 420 0 C
Flow of intermediate superheated steam 8.25 kg/s Condenser pressure: 0.04 bar, steam moisture 0% Electric power: 11.1 MW Electricity efficiency 29.4%
A combustion plant and a method for the combustion according to the invention are characterised by what is presented in the claims.
The invention will now be described with reference to the accompanying figures and embodiments shown in them, to which the invention is, however, not intended to be solely defined.
Fig. IA shows a first advantageous embodiment of a waste incineration plant.
Fig. IB shows a second advantageous embodiment of a waste incineration plant.
Fig. IA illustratively and schematically shows a combustion plant 10, advantageously a waste incineration plant. Fittings in this application refer to pipes,
hoses, channels or equivalent. The waste incineration plant 10 comprises a waste reception location 11, waste sorting 12, a conveyor K for conveying sorted waste to a steam boiler 13. To the steam boiler 13, there is an inlet fitting 14 for combustion air. The inlet fitting 14 is conveyed from a combustion-air preheater 15 i.e. a so-called steam luvo. From the preheater 15, the mixture of steam and water is conveyed via a fitting 16 to a feed water tank 17. For the preheaters 15, combustion air is conveyed from outside, whereby air is heated in the preheater 15 in which heat energy is particularly brought from a high-pressure steam turbine section 100b via fittings 26 and 29.
The steam boiler 13 comprises a steam generator 18 inside the steam boiler. A steam generator circuit of the steam generator 18 comprises banks of tubes 19, manifolds Ji, J 2 , a boiler drum 21 and fittings between them; inlet fittings and outlet fittings. The steam generator 18 comprises the bank of tubes 19 i.e. pipes from the bottom of the boiler 13 to the top of the boiler from the manifolds Ji to the manifold J 2 . Water circulates as natural circulation from the top of the bank of tubes to its bottom and back to the top. From the manifold J 2 , the mixture of water and steam is conveyed via a fitting 20 to the boiler drum 21. There is water at the bottom of the boiler drum 21 and steam at the top. From the bottom of the boiler drum 21, there is a fitting 22 to the manifold J) below. From the top of the boiler drum 21, there is a fitting 23 to a steam superheater 24. The steam superheater 24 is at the top of the steam boiler 13. From the steam superheater 24 is conveyed a fitting 25 to a steam turbine 100. The steam turbine 100 comprises a low-pressure turbine section 100a and a high-pressure turbine section 100b coaxially and co- axially with a generator G generating electricity. The rotated steam turbine 100 rotates the generator G generating electricity. The fitting 25 is conveyed according to the invention to the high-pressure turbine section 100b and from the high- pressure turbine 100b there is a return steam fitting 26 back to the steam boiler 13 and its second superheater 27. From the second superheater 27 in question, there is a fitting 28 to the low-pressure turbine section 100a of the steam turbine 100. In the bled steam fitting 26, there is a branch point Cl from which there is a fitting
29 to the preheater 15 of combustion air as described above. From the bled steam fitting 26, there is via a second branch point C2 a branch fitting 30 to a feed-water steam preheater 31. From the steam preheater 31, there is a return fitting 32 to the feed water tank 17.
From the feed water tank 17, there is a fitting 33 for feed water to an at least two- piece preheater 46 of feed water in the steam boiler 13. The two-piece feed water preheater 46 comprises at least one first feed water preheater section 46a and at least one second feed water preheater section 46b in series in relation to it and the flow direction of water is shown with arrows Si and S 2 . The feed water preheaters 46a and 46b are located in a flue gas passage 34 or duct 35 conveying to the chimney. The first feed water preheater 46a is bypassable from the flow of feed water so that part of the feed water flow (flow arrow S 2 ) is directly transferrable to the second feed water preheater section 46b via branch points C3 and C4. From the branch point C3, a fitting 36 is conveyed to the feed water steam preheater 31 and from there a return fitting 37 via the branch point C4 to the second feed water preheater 46b from which feed water is advantageously conveyed to the boiler drum 21.
The temperature of the bypassed feed water S 2 can be adjusted by the feed water steam preheater 31 by adjusting the bled steam flow to the preheater in question with a valve 38.
From the second superheater 27, superheated steam is conveyed via the fitting 28 to the low-pressure turbine section 100a of the steam turbine 100. From the low- pressure turbine section, there is a bled steam fitting 40 to the feed water tank 17 and a bled steam fitting 41 to a condenser 42 from which there is a return fitting 45 to the feed water tank 17. To the condenser 42 is conveyed a cooling water fitting 43 and an outlet fitting 44 for different intended uses for utilisation e.g. as district heating water.
Fig. IB shows an embodiment of the invention in which the structure is otherwise equivalent to the embodiment of Fig. IA but in which arrangement the feed water preheater 46 is two-piece and such that, between the first and second feed water preheater section 46a, 46b, there is the feed water steam preheater 31. In the em- bodiment, the preheaters 46a and 46b are clearly in series and there is no bypass fitting in the embodiment.
Also in the embodiment of Fig. IB, from the steam generator 18, steam is conveyed to the superheater 24 and from there via the fitting 25 to the high-pressure turbine section 100b of the steam turbine 100 and, from the high-pressure turbine section, bled steam is conveyed via the fitting 26 back to the boiler 13 to its superheater 27 from which there is the fitting 28 back to the steam turbine 100 to its low-pressure turbine section 100a.
In the embodiments of Figs. IA and IB, feed water is flowed from the feed water tank 17 by means of a pump Pi to a fitting 33, such as a pipe, and further to the at least two-piece feed water preheater 46 advantageously in the flue gas passage 34 or the flue gas duct 35. Similarly, from the condenser 42 is conveyed via the fitting 45 feed water to the feed water tank 17 via a pump P 2 . In the invention, the two-piece feed water preheater 46 can comprise several preheater sections, but such an embodiment is advantageous in which there is the first preheater section 46a and the second preheater section 46b and thus, in the flue gas passage 34, the first preheater section 46a is located in the colder section of the flue gas passage 34 and the second preheater section 46b is located in the warmer section of the flue gas passage 34 in relation to the above-mentioned section. Then is always achieved the optimum and an advantageous temperature gradient and thermal transmission from flue gases to feed water and the temperature difference between flue gas and feed water is kept at its most advantageous value from the viewpoint of thermal transmission and efficiency.
As shown in the figure, the first superheater 24 is two-piece comprising superheater sections 24a and 24b and between them a cooling water spraying apparatus 50. Equivalently, the second superheater 27 is also advantageously two-piece and comprises between its pieces a cooling water spraying apparatus 51 i.e. a spray water cooling apparatus. The volume of spray water is adjusted with valves 52 and 53 in which is conveyed a fitting 54 from the feed water tank 17. A sensor device M 1 , M 2 , M 3 is advantageously located either directly in connection with brought fuel, whereby by means of the sensor device M] the quality/composition of the fuel and its tendency causing corrosion are observed. Equivalently, the sen- sor M 2 can be located directly inside the boiler 13 in the furnace measuring above- mentioned properties or the quality of the fuel can be measured from flue gases with the sensor M 3 , whereby the sensor device M 3 can be located in the flue gas duct 35 or in the chimney. Sensor data is controlled to a central processing unit (not shown in the figures) from which further the temperature of the steam flowed in the superheater is controlled based on the quality of the fuel and its property causing corrosion so that such optimum temperature can be adjusted for the steam that the corrosion of superheater pipes is avoided. There can be one of the sensors Mi, M 2 , M 3 or all the alternatives.
In the method, the quality of the fuel is observed and, based on the quality, the temperature of steam conveyed via the superheaters or via the superheater is adjusted by adjusting the volume of sprayed water conveyed into connection with the steam.
In the method, spray water is conveyed from the feed water tank 17 into connection with the steam flowed in the superheater 24 and/or 27 for cooling the steam, whereby the superheater 24a, 24b; 27a, 27b is used, which is two-piece, between the sections of which two-piece superheater is conveyed the cooling-water jet pipe 51 i.e. the spray water cooling apparatus.
For measuring the temperature of feed water, temperature sensors are used in feed water fittings.
Waste is used as the fuel and the boiler is a waste incineration boiler 13.
The adjustment of the superheating temperature and/or intermediate superheating temperature takes place by changing the volume of spray water for protecting the material of the superheater pipes against corrosion. The criterion of the adjustment is the measurement of the fuel corrosion tendency from the fuel (chlorine, Na, K Ca) or the flue gas (HCl).
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