A POWER PLANT AND METHOD FOR INCREASING THE EFFICIENCY OF THE POWER PLANT

Abstract

 A coal fired power plant 10 includes a boiler 20 having a combustion chamber 30 to carry out combustion of fuel 40 to generate heat, ash 50 and flue gas 60 in the combustion chamber 30. The boiler 20 is connected to an energy recovery system 70. The energy recovery systems 70 recovers heat of the ash 50 and utilize the recovered heat to increase the efficiency of the power plant 10. The recovered heat is transferred to a working fluid 130 for example feed water 132 and steam 135 which is fed to the boiler 20.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a power plant, and more specifically, to a coal fired power plant where hot ash is stored and utilized for heat recovery and a method for recovering heat of the ash and utilize the recovered heat to increase the efficiency of the power plant.

BACKGROUND

[0002] In currently pulverized coal fired power plants flue gas passes the rotary air preheater where the flue gas heat transfer to access air takes place. The flue gas is loaded with fly ash which will be separated downstream in the electrostatic precipitator. After electrostatic precipitator the ash is discharged to a fly ash silo for further utilization or back to the mine. In other types of boiler for example circulating fluidized bed boiler hot bed ash is also cooled down and discharged to the mine.

[0003] Currently available pulverized coal fired and circulating fluidized bed power plants are not able to of use heat of the ash when it is just come out of combustion chamber and yet to reach the rotary air preheater and this heat is wasted. Also a portion of useful steam is extracted from a steam turbine during expansion and is utilize to preheat feedwater which is further sent to a boiler. The use of useful steam reduces efficiency of the steam turbine.

[0004] It is important that any solution to use the heat of the ash is capable of implementation within the current power plants.

[0005] Accordingly, any solution must be able to be used as "retrofitted" to fit within existing power plants.

SUMMARY OF THE INVENTION

[0006] The present disclosure relates to a power plant and more specifically, to a coal fired power plant where hot ash is stored and utilized for heat recovery and a method for recovering heat of the ash and utilize the recovered heat to increase the efficiency of the power plant. The recovered heat of the hot ash improves cycle efficiency replacing the steam extraction from steam turbine. The solution of the present disclosure can be used as "retrofit" within existing power plants.

[0007] Accordingly, the present disclosure a power plant comprising a boiler including a combustion chamber configured to carry out combustion of fuel to form ash and flue gas. An energy recovery system connected to the boiler to recover heat of the ash and utilize the recovered heat to increase the efficiency of the power plant and save steam extraction from the steam turbine for feedwater heating.

[0008] In another embodiment the energy recovery system comprising ash storage to receive and store the ash, a heat exchanger fluidically connected to the ash storage and the ash which is stored in the ash storage is passed through the heat exchanger to extract the heat of the ash.

[0009] In another the energy recovery system further comprising an ash discharge system connected to the heat exchanger to discharge the ash.

[0010] In another embodiment the ash is a fly ash from a pulverized coal fired boiler or a bed ash or a mixture of the fly ash and the bed ash in CFB arrangement.

[0011] In another embodiment the recovered heat of the ash is provided to heat a working fluid being fed to the boiler.

[0012] In another embodiment the boiler is a pulverized coal boiler and in that the energy recovery system is connected to the pulverized coal boiler through a separator.

[0013] In another embodiment the recovered heat of the fly ash is provided to heat the working fluid, the heated working fluid being fed at startup to the pulverized coal boiler.

[0014] In another embodiment the recovered heat of the fly ash is used to heat a plurality of tubes of the combustion chamber of the pulverized coal boiler in case of a part load change of the pulverized coal boiler.

[0015] In another embodiment the boiler is a circulating fluidized bed boiler and in that the energy recovery system is connected to the circulating fluidized bed boiler through an ash discharge screw.

[0016] In another embodiment stored bed ash in the ash storage is provided to fluidize circulating bed at startup of the circulating fluidized bed boiler.

[0017] In yet another embodiment a method for increasing efficiency of a power plant comprising providing a boiler including a combustion chamber , the boiler being in connection with an energy recovery system and configured so that ash and flue gas are produced during combustion of fuel inside the combustion chamber , recovering heat of the ash through the energy recovery system and utilizing the recovered heat to increase the efficiency of the power plant.

[0018] In another embodiment the energy recovery system comprises an ash storage and a heat exchanger which are fluidically connected with each other and recovery of heat of the ash comprising the steps of receiving and storing the ash in the ash storage , passing the ash through the heat exchanger recovering the heat of the ash.

[0019] In another embodiment the recovery of heat of the ash by the energy recovery system further comprising discharging the ash through an ash discharge system.

[0020] In another embodiment the ash is a fly ash or a bed ash or a mixture of the fly ash and the bed ash.

[0021] In another embodiment the method further including step of providing the recovered heat of the ash to heat a working fluid being fed to the boiler.

[0022] In another embodiment the method further including step of providing the recovered heat of the fly ash to heat a plurality of tubes of the combustion chamber of a pulverized coal boiler during a load change of the pulverized coal boiler.

[0023] In another embodiment the method further including step of providing the recovered heat of the fly ash to heat the working fluid and feeding the heated working fluid at startup of the pulverized coal boiler.

[0024] In another embodiment the method further including step of providing stored bed ash of the ash storage to fluidize circulating bed of a circulating fluidized bed boiler at startup of the circulating fluidized bed boiler.

[0025] The present disclosure offers a technical solution for power plants which are hard coal fired units with pulverized coal fired boiler as well as lignite fired units and circulating fludized bed boiler. The technical solution is achieved by providing intermediate hot ash storage to store hot ash and utilize inherent heat on demand in the power plant particularly for feed water heating during startup of the boiler. The inherent heat is also used to heat saturated steam in tubes of combustion chamber of the pulverized coal fired boiler in case of a load change. In case of the circulating fluidized bed boiler the inherent heat is also used to heat fluidized bed at the starting time. The hot ash is a fly ash or a bed ash or a mixture of the fly ash and the bed ash. The ash is the fly ash from the pulverized coal fired boiler or a bed ash or a mixture of the fly ash and the bed ash in circulating fluidized bed boiler.

[0026] The technical solution provides several advantages like application of a smaller electrostatic precipitator in power plants as ash is dealt with earlier. Recovered heat utilization leads to less power consumption of steam and electric power in the power plants as well as savings on start-up fuels. A reduction in CO2 emission as the ash is separated and captured efficiently at a very early stage and a constant feed water temperature is provided during the operation of the boiler.

[0027] These together with the other aspects of the present disclosure, along with the various features of novelty that characterize the present disclosure, are pointed out with particularity in the present disclosure. For a better understanding of the present disclosure, its operating advantages, and its uses, reference should be made to the accompanying drawings and descriptive matter in which there are illustrated exemplary embodiments of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The advantages and features of the present disclosure will be better understood with reference to the following detailed description and claims taken in conjunction with the accompanying drawings, wherein like elements are identified with like symbols, and in which:

FIG. 1 is a schematic illustrating a power plant according to present disclosure;

Fig.2 illustrates a power plant having a pulverized coal fired boiler according to present disclosure;

Fig.2a illustrates a plurality of tubes forming walls of combustion chamber of the pulverized coal boiler; and

Fig. 3 illustrates a power plant having a circulating fluidized bed boiler according to present disclosure;

DETAILED DESCRIPTION OF THE PRESENT DISCLOSURE

[0029] In reference to FIG. 1, a schematic of a coal fired power plant 10 is shown. The power plant 10 includes a boiler 20 having a combustion chamber 30 to carry out combustion of fuel 40 to generate heat, ash 50 and flue gas 60 in the combustion chamber 30. The coal is stored in a silo 104. The boiler 20 is connected to an energy recovery system 70. The energy recovery systems 70 recovers heat of the ash 50 and utilize the recovered heat to increase the efficiency of the power plant 10. The recovered heat is transferred to a working fluid 130 for example feed water 132 and steam 135 which is fed to the boiler 20. The working fluid 130 is further heated in the boiler 20 from the heat generated during the combustion and used to drive a steam turbine or a series of steam turbines 100. The boiler 20 is connected to the energy recovery system 70 through a separator 110. The energy recovery system 70 may include an ash storage 80 and a heat exchanger 90 fluidically connected to the ash storage 80. The ash storage 80 may receive and store the ash 50 generated in the boiler 20. The ash 50 may be passed through the heat exchanger 90 to extract the heat of the ash 50. The energy recovery system 70 further includes an ash discharge system 95 which is connected to the heat exchanger 90 to discharge the ash 50 in to ash silo 105.

[0030] Referring now to Figure 2 in an exemplary embodiment the boiler 20 of the power plant 10 may be a pulverized coal boiler, such as pulverized coal boiler 200, herein after 'boiler 200'. The boiler 200 may include a combustion chamber 202 to carry out combustion of fuel to generate heat, ash and flue gas in the combustion chamber 202. In one embodiment, the boiler 200 includes a silo 204 that stores coal to be burned to produce heat, ash 50 and flue gas 60 in the combustion chamber 202. In this embodiment, the coal from the silo 204 may be sent to a pulverizer (not shown) to be crushed in to a powder form. The coal powder is mixed with air that is induced by a fan 205 to produce fuel 206. The fuel 206 may be supplied in to the combustion chamber 202 through burners 207. During combustion of the fuel 206 heat, ash 50 and flue gas 60 are produced. The ash 50 may be a fly ash 52 or a bed ash 55 or a mixture of the fly ash 52 and the bed ash 55.

[0031] The boiler 200 may be connected to an energy recovery system 270 through a separator 210. The energy recovery system 270 may include an ash storage 280 and a heat exchanger 290 fluidically connected to the ash storage 280. The ash storage 280 may receive and store the ash 50 generated in the boiler 200. The ash 50 may be passed through the heat exchanger 290 to extract the heat of the ash 50.

[0032] One part of the ash 50, which is heavy, may be settled in bottom of the combustion chamber 202, and the other part which is lighter may be moved up in the combustion chamber 202. In one form, heavy ash may be the bed ash 55 and the lighter ash may be the fly ash 52. The separator 210 which is connected to the combustion chamber 202 receives the fly ash 52 and the flue gas 60 and separates fly ash 52 from the flue gas 60. For coal fired plants, for example, where bituminous coal is used, the fly ash 52 leaves the separator 210 with a temperature range of 410 °C to 450 °C, and more particularly at 430 °C, is stored in the ash storage 80 and for example lignite coal with a temperature range of 280 °C - 320 °C and more particularly at 300 °C is stored in an ash storage 80. The stored fly ash 52 is discharged through the heat exchanger 290 where inherent heat of the fly ash 52 is utilized to heat the working fluid 130 for example feed water 132 or steam 135 which is supplied to the boiler 200.

[0033] The energy recovery system 270 further includes an ash discharge system 295 which is connected to the heat exchanger 290 to discharge the fly ash 52 in to ash silo 237. As the fly ash 52 is very much fluid, the energy recovery system 270 is arranged in such a way that a gravimetric flow is realized. The recovered heat of the fly ash 52 is further utilized to heat the working fluid 130 for example steam 135 being fed at startup to the boiler 200. Also the recovered heat of the fly ash 52 is utilized to heat a plurality of tubes 230 forming walls of the combustion chamber 202 of the boiler 200 in case of a part load change of the boiler 200 so that the working fluid 130 is flowing though the plurality of tubes 230 is also heated and converted to steam with high temperature to be supplied immediately to the steam turbine 100. The bed ash 55 may also be supplied through a conduit 240 or any other suitable means to the ash storage 80. The fly ash 52 or the bed ash 55 or the mixture of the fly ash 52 and the bed ash 55 may also be discharged directly through the heat exchanger 90 to recover the heat of the ash 50. The ash storage 280 may be covered by an insulated layer to stop the loss of the heat during storage. A controlled valve 260 is provided to control flow of the fly ash 52 to the heat exchanger 290.

[0034] A series of heat transfer surfaces 250 are also provide in the combustion chamber 202 in form of super heater, reheater and economizer which are arranged as per the requirements of the boiler 200. The heat transfer surfaces 250 further heated the working fluid 130 into super-heated steam, reheated steam.

[0035] Referring now to Figure 3 in an exemplary embodiment the boiler 20 of the power plant 10 may be a circulating fluidized bed boiler, such as circulating fluidized bed boiler 300, herein after 'boiler 300'. The boiler 300 may include a combustion chamber 302 to carry out combustion of fuel to generate heat, ash and flue gas in the combustion chamber 302. In one embodiment, the boiler 300 includes a silo 304 that stores crushed coal to be burned to produce heat, ash 50 and flue gas 60 in the combustion chamber 302. In this embodiment, the crushed coal as a fuel 306 from the silo 304 may be supplied in to the combustion chamber 302 at its bottom. A bed 307 of inert material for example sand is formed at the bottom of the combustion chamber 302. The bed 307 is where the crushed coal or fuel 306 spreads. Preheated primary air 309 supply is from under the bed 307 at high pressure through primary air fans (not shown). This lifts the bed 307 material and fuel particles 308 and keeps the fuel particles 308 in suspension. The combustion of the fuel particles 308 takes place in this suspended condition. The lifted bed 307 and suspended fuel particles 308 forms a fluidized circulating bed which is maintained at range of 850 °C - 900 °C. Secondary air 314 provides pre-heated combustion air. Nozzles 341 in the combustion chamber 302 walls at various levels distribute the preheated combustion air in the combustion chamber 302.

[0036] The ash 50 may be a fly ash 52 or a bed ash 55 or a mixture of the fly ash 52 and the bed ash 55.In boiler 300 the bed ash 55 is produced in the range of 35% to 45% of the ash 50 and settled in a lower portion of the combustion chamber 302. Fine particles of partly burned fuel particles 308, fly ash 52 and bed material 307 are carried along with the flue gas 60 to upper areas of the combustion chamber 302 and then into a separator 310 which is connected the combustion chamber 302. In the separator 310 fine particles of partly burned fuel particles 308, the fly ash 52 and the bed material 307 is captured and separated from the flue gas 60 and falls to a seal pot 312. The heavy particle of partly burned fuel particles 308, the fly ash 52 and the bed material 307 returns to the combustion chamber 302 for recirculation either directly through arm 316 or through another arm 317 after passing through a fluidized bed heat exchanger 318. These heavy particles keep on recirculating till they captured in the separator 310. The fly ash 52 keeps on adding with bed ash 55 in the lower portion of the combustion chamber 302.The flue gas 60 gases from the separator 310 pass to a series of heat transfer surfaces 350 and move out of the boiler 300.

[0037] The boiler 300 may be connected to an energy recovery system 370 through ash discharge screw 410. The energy recovery system 370 may include an ash storage 380 and a heat exchanger 390 fluidically connected to the ash storage 380. The ash storage 380 may receive and store the bed ash 55 particularly the mixture the fly ash 52 and the bed ash 55 generated in the boiler 300. The bed ash 55 particularly the mixture the fly ash 52 and the bed ash 55 may be passed through the heat exchanger 390 to extract the heat of the bed ash 55.

[0038] In the boiler 300 the bed ash 55 , particularly the mixture the fly ash 52 and the bed ash 55 leaves the boiler on a temperature range of 750 °C - 850 °C . Due to design constraints the bed ash 55 particularly the mixture the fly ash 52 and the bed ash 55 is supplied pneumatically through a conduit 375 to the ash storage 380 leads to a heat loss of in temperature range of 100 °C - 200 °C resulting in a final storage temperature of 600°C in the ash storage 380. The stored bed ash 55 particularly the mixture the fly ash 52 and the bed ash 55 is discharged through the heat exchanger 390 where inherent heat of the bed ash 55 particularly the mixture the fly ash 52 and the bed ash 55 is utilized to heat the working fluid 130 for example feed water 132 or steam 135 which is supplied to the boiler 300. The energy recovery system 370 further includes an ash discharge system 395 which is connected to the heat exchanger 390 to discharge the bed ash 55 particularly the mixture the fly ash 52 and the bed ash 55 in to a ash silo 420. As the bed ash 55 particularly the mixture the fly ash 52 and the bed ash 55 is very much fluidic, the energy recovery system 370 is arranged in such a way that a gravimetric flow is realized. The fly ash 52 or the bed ash 55 or the mixture of the fly ash 52 and the bed ash 55 may also be discharged directly through the heat exchanger 390 to recover the heat of the ash 50. The ash storage 380 may be covered by an insulated layer to stop the loss of the heat during storage. A controlled valve 430 is provided to control flow of the ash 50 particularly the mixture the fly ash 52 and the bed ash 55 to the heat exchanger 390. The stored bed ash 55 particularly the mixture the fly ash 52 and the bed ash 55 in the ash storage 380 is provided to fluidize bed 307 at startup of the boiler 300 through a conduit 450 . A controlled valve 440 is provided to control the flow of the stored bed ash 55 particularly the mixture the fly ash 52 and the bed ash 55 to the combustion chamber 302.

[0039] The foregoing descriptions of specific embodiments of the present disclosure have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present disclosure to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above examples teaching. The embodiments were chosen and described in order to best explain the principles of the present disclosure and its practical application, to thereby enable others skilled in the art to best utilize the present disclosure and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the claims of the present disclosure.

Reference Numerals

[0040] 

10

Plant

20

Boiler

30, 202, 302

Combustion Chamber

40

Fuel

50

Ash

52

Fly Ash

55

Bed Ash

60

Flue Gas

70, 270, 370

Energy Recovery System

80, 280, 380

Ash Storage

90, 290, 390

Heat Exchanger

95, 295

Ash Discharge System

100

Steam Turbine

104, 204, 304

Silo

105, 237, 420

Ash Silo

110

Separator

130

Working Fluid

132

Feed Water

135

Steam

200

Pulverized coal boiler

202, 302

Combustion chamber

205

Fan

206, 306

Fuel

207

Burner

210, 310

Separator

230

Plurality of tubes

240

Conduit

250

Heat transfer surface

260

Controlled valve

270, 370

Energy recovery system

300

Circulating fluidized bed boiler

307

Bed

308

Fuel particles

309

Preheated primary air

312

Seal pot

314

Secondary air

316, 317

Arm

318

Fluidized bed heat exchanger

341

Nozzle

350

Heat transfer surface

370

Energy recovery system

375, 450

Conduit

395

Ash discharge system

410

Ash discharge screw

430, 440

Controlled valve

Claims

1. A power plant (10) comprising:

a boiler (20) including a combustion chamber (30) configured to carry out combustion of fuel (40) to form ash (50) and flue gas(60);

an energy recovery system (70) connected to the boiler (20) to recover heat of the ash (50).

2. The power plant (10) according to claim 1, wherein the energy recovery system (70) comprising:

an ash storage (80) to receive and store the ash (50);

a heat exchanger(90) fluidically connected to the ash storage (80) and wherein the ash (50) is passed through the heat exchanger to extract the heat of the ash (50).

3. The power plant (10) according to claim 2, wherein the energy recovery system (70) further comprising :

an ash discharge system (95) connected to the heat exchanger(90) to discharge the ash (50).

4. The power plant (10) according to claim 2, wherein the ash (50) is a fly ash (52) or a bed ash (55) or a mixture of the fly ash(52) and the bed ash (57).

5. The power plant (10) according to claim 4, wherein the recovered heat of the ash (50) is provided to heat a working fluid (130) being fed to the boiler (20).

6. The power plant (10) according to claim 1, wherein the boiler (20) is a pulverized coal boiler (200) and in that the energy recovery system (270) is connected to the pulverized coal boiler (200) through a separator (210).

7. The power plant (10) according to claim 4, wherein the recovered heat of the fly ash (52) is provided to heat the working fluid (130) and being fed at startup to the pulverized coal boiler (200).

8. The power plant (10) according to claim 4, wherein the recovered heat of the fly ash (52) is used to heat a plurality of tubes of the combustion chamber (202) of the pulverized coal boiler (200) in case of a part load change of the pulverized coal boiler (200).

9. The power plant (10) according to claim 1, wherein the boiler (20) is a circulating fluidized bed boiler (300) and in that the energy recovery system (370) is connected to the circulating fluidized bed boiler (300) through an ash discharge screw (410).

10. The power plant (10) according to claim 4, wherein stored bed ash (55) in the ash storage (380) is provided to fluidize circulating bed (370) at startup of the circulating fluidized bed boiler (300).

11. A method for increasing efficiency of a power plant (10) comprising:

providing a boiler (20) including a combustion chamber (30), the boiler (20) being in connection with an energy recovery system (70) and configured so that ash (50) and flue gas(60) are produced during combustion of fuel (40) inside the combustion chamber(30);

recovering heat of the ash (50) through the energy recovery system (70).

12. The method according to claim 11, wherein the energy recovery system (70) comprises an ash storage (80) and a heat exchanger (90) which are fluidically connected with each other and recovery of heat of the ash (50) comprising the steps of:

receiving and storing the ash (50) in the ash storage (80);

passing the ash (50) through the heat exchanger (90) recovering the heat of the ash (50).

13. The method according to claim 11, wherein the ash (50) is a fly ash (52) or a bed ash (55) or a mixture of the fly ash(52) and the bed ash (57).

14. The method according to claim 11, further including step of:

providing the recovered heat of the ash (50) to heat a working fluid(130) being fed to the boiler (20).

15. The method according to claim 11, further including step of:

providing the recovered heat of the fly ash (52) to heat a plurality of tubes (230) of the combustion chamber (202) of a pulverized coal boiler (200) during a load change of the pulverized coal boiler(200); or

providing the recovered heat of the fly ash (52) to heat the working fluid; and

feeding the heated working fluid at startup of the pulverized coal boiler(200).

16. The method according to claim 11, further including step of:

providing stored bed ash (55) of the ash storage (80) to fluidize circulating bed (307) of a circulating fluidized bed boiler (300) at startup of the circulating fluidized bed boiler(300).

Drawing