TURBINE SYSTEM AND METHOD

Abstract

A power generating system includes a condensing steam turbine fed with steam from a boiler, wherein the air supply for the boiler combustion process is preheated by means of a heat pump system comprising at least one heat pump with at least one compressor, before entry to the boiler. A method for generating power using the power generating system is also described. A method and apparatus for extracting heat from the gases of a combustion process are also described.

Claims

1. A power generating system comprising; a condensing steam turbine fed with steam from a boiler, wherein the air supply for the boiler combustion process is preheated by means of a heat pump system comprising at least one heat pump, before entry to the boiler.

2. The power generating system of claim 1 wherein the heat pump system extracts heat from the cooling system employed to condense the steam from the condensing steam turbine.

3. The power generating system of claim 1, wherein the heat pump system extracts heat from a flue gas cooling and condensation process of the power generating system.

4. The power generating system of claim 1, wherein the heat pump system extracts heat from at least one of: waste heat from rotating equipment; waste heat from transformation equipment; waste heat from cooling the steam turbine or waste heat from ash disposal.

5. The power generating system of claim 1, wherein the heat pump system or other heat exchange system extracts heat from at least one of: an energy source or sources selected from the group consisting of a solar energy source, a geothermal energy source or a factory process energy source.

6. The power generating system of claim 1, wherein at least one variable drive heat pump is employed in the heat pump system.

7. The power generating system of claim 6, wherein all the heat pumps of the heat pump system employ variable drive compressors.

8. The power generating system of claim 1, wherein the boiler is a biomass burning boiler.

9. The power generating system of claim 8, wherein the boiler is a fluidized bed biomass burning boiler.

10. The power generating system of claim 9, wherein the boiler is a fluidized bed biomass burning boiler and the combustion temperature is controlled, to minimize NOx formation.

11. The power generating system of claim 1, wherein the heat of the flue gas from the boiler is used to heat the boiler feed water.

12. The power generating system of claim 8, wherein the condensing steam turbine is not provided with a steam extraction facility for the purpose of boiler feed water pre-heating.

13. The power generating system of claim 11, wherein water in the flue gas is condensed by cooling from the boiler feed water and/or by the cooling, heat extraction, side of a heat pump or a heat pump of the heat pump system.

14. The power generating system of claim 13, wherein the water in the flue gas is substantially fully condensed.

15. The power generating system of claim 13, wherein water in the flue gas is condensed in a two stage arrangement wherein condensate returning from the condensing steam turbine first exchanges heat in a condenser/scrubber arrangement for the flue gas, directly or via a heat pump arrangement, and then exchanges heat with the flue gas exiting from the boiler in a pre-cooler for the condenser/scrubber.

16. The power generating system of claim 15, wherein heat from at least one of the gas and water from the flue gas, after the pre-cooler and condenser/scrubber, is used to dry or heat the fuel supplied to the boiler.

17. The power generating system of 1, wherein the condensing steam turbine is coupled to an electrical generator for generating electricity.

18. The power generating system of claim 17, wherein a transformer is connected to the electrical generator for supply of electricity to a grid.

19. The power generating system of claim 1, wherein condensate returning from the condensing steam turbine is heated only by heat from the flue gas from the boiler before being fed to the boiler.

20. The power generating system of claim 17, wherein energy provided from at least one of cooling the electrical generator and cooling the transformer is used to pre-heat condensate returning from the condenser turbine, by direct heat exchange or via a heat pump of the heat pump system.

21. The power generating system of claim 1, wherein more than one condensing steam turbine is provided.

22. The power generating system of claim 1, wherein more than one boiler is provided.

23. The power generating system of claim 1, further comprising a carbon capture unit.

24. The power generating system of claim 1, further comprising a generator powered by an engine or other means, for starting up and/or augmenting the power generating system.

25. The power generating system of claim 1, wherein the working fluid for heat pumps of the heat pump system is selected from the group consisting of carbon dioxide, ammonia, organic fluids and halocarbons,.

26. A method for generating power, the method comprising: operating a power generating system comprising a condensing steam turbine fed with steam from a boiler, wherein the air supply for the boiler combustion process is preheated by means of a heat pump system comprising at least one heat pump, before entry to the boiler.

27. The method for generating power according to claim 26, wherein at least one heat pump of the heat pump system also provides active cooling to any equipment within the power generating system that benefits from being operated at a regulated temperature.

28. The method for generating power according to claim 27, wherein the active cooling is supplied to at least one of: the condensing steam turbine, a generator, a transformer or other rotating equipment of the power generating system.

29. A method for extracting heat from the gases of a combustion process, the method comprising: cooling the gases by heat exchange to condense the water present and upgrading the heat extracted from at least the condensation phase change by means of a heat pump.

30. An apparatus for extracting heat from gases of a combustion system comprising: a heat exchange system to cool the gases to the condensation temperature; and at least one heat pump for upgrading the heat extracted from at least the condensation phase change.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0074] FIG. 1 shows a power generating system in schematic view;

[0075] FIG. 2 shows a simplified schematic drawing of a power generating system as a block diagram; and

[0076] FIG. 3 shows a simplified schematic drawing of a power generating system as a block diagram, highlighting the recovery of low grade heat for upgrading in a heat pump system.

DETAILED DESCRIPTION OF THE INVENTION

[0077] FIG. 1 is a schematic illustration of a power generating system 1 that includes a condensing steam turbine arrangement 2 fed with steam from a boiler 4, in this example a fluidized bed boiler burning a biomass such as wood chips, at least as the primary fuel.

Steam cycle

[0078] The steam cycle operating in the system 1 can be described as follows. Biomass fuel from the fuel silo 6 is burned in air in the fluidized bed boiler 4. The heat is used in the boiler to boil water and generate high pressure steam which is fed from boiler 4 via line 8 to drive the high pressure turbine 10 (HP, TURB.) of the turbine 2. Used steam is returned to boiler 4 via line 12 for reheating in the conventional manner. The reheated steam is then supplied via line 14 to the low pressure turbine(s) 16 (LP. TURB.) of the turbine 2. Typically an intermediate and a low pressure turbine system is employed to maximize extraction of power. The steam exiting from the low pressure turbine(s) 16 is condensed in condenser 18 by use of a cooling water system indicated by line 20.

[0079] The condensed steam is pumped by condensate pump 22 through a preheating heat exchanger 24 that makes use of heat extracted from the cooling systems for electrical generator 26 and transformer 28, as suggested by lines 30,32.

[0080] The condensate is then fed via line 34 to be heated further in a heat recovery system 36 making use of flue gas from boiler 4 as described further hereafter under the heading Flue Gas. Finally the heated condensate is pressurized and returnedvia line 38, storage tank 39 (the drum), feed water pump 40, and line 42to boiler 4 for conversion back to steam. Any required make up water is delivered from the feed water treatment plant 44.

Fuel

[0081] The fuel supply in this example is wood chips. A fluidized bed combustion system is employed in boiler 4 that does not require special processing, such as milling, of the raw fuel. The raw fuel 46 is however dried in a fuel drying plant 48 before being fed to silo 6 that feeds the combustion process in boiler 4. A moisture content in the range of about 9 to 50% is suitable for the system envisaged, but is not critical.

Air Supply

[0082] The air supplied to boiler 4 via air heater 50. The air is heated in air heater 50 by meant of variable drive heat pump or pumps 52 which extracts heat from the cooling water system (line 20) for the condenser 18 of the turbine 2. The heated air is then pumped into boiler 4 via fan or fans 54. Other sources of relatively low grade heat may be employed alternatively or additionally. However use of the condenser turbine cooling water system increases the extraction of energy from the steam cycle improving efficiency. This arrangement allows the air to the boiler 4 to be supplied at a consistent temperature, essentially regardless of ambient air temperature and without requiring heat exchange inside the boiler, with exiting flue gas, as is typically employed.

Flue gas

[0083] The flue gas exits from boiler 4 via line 56 to heat recovery unit 36. As a consequence of the supply of heated air to boiler 4 the flue gas is consistent in temperature and somewhat hotter than in a conventional arrangement where ambient temperature air is fed into the boiler and heated by flue gas as it exits. The heat recovery unit 36 treats the flue gas in two stages. In stage I the flue gas exiting from the boiler 4 is pre-cooled by exchanging heat with the condensate returning to the boiler from the condenser turbine 18. In stage II a condenser scrubber unit condenses the steam in the flue gas and removes ash. The cooling and condensing of the flue gas in stage II of heat recovery unit 36 is obtained by heating the condensed steam returning to the boiler via line 34.

[0084] Thus the flue gas becomes two streams, gas and water. Both contain some low grade heat (having a temperature of about 40C for example) and either or both are fed to fuel drying unit 48 (via lines 58, 60 and pump 62) to dry the fuel supplied for the boiler.

Power output

[0085] In this example the condensing steam turbine 2 drives generator 26 to produce electricity, which is converted by transformer 28 to a suitable form for supply to the grid 64. A portion of the power generated is used for self-consumption 64 for example used to power pumps such as 22, 42, 54 and 62; and heat pump 52.

[0086] The energy efficiency and the lack of sensitivity to ambient conditions of the arrangement of FIG. 1 described above allows the use of a standardized and more compact power generating system to produce a given power output than can be realized with previous known arrangements.

[0087] FIG. 2 shows a power generating system akin to that of FIG. 1 as a schematic block diagram, generally indicating the mass and energy flows.

[0088] In FIG. 2 fuel 100 and heated air 101 is supplied to boiler 102. Steam 104 generated by burning the fuel in the boiler 102 is fed to the turbine 106. Mechanical power 108 from the turbine 106 drives generator to produce electricity 112 which is adjusted by transformer 114 to be suitable as electricity supply 116 to grid 118.

[0089] Spent steam from turbine 106 is condensed by cooling circuit 120 to provide condensate 122, which is returned to the boiler 102 via pre-heater 124 and flue gas heat recovery units II (126) and I (128). The condensate 120 will also be pressurized to provide a feed to the boiler that is at an appropriate temperature and pressure.

[0090] Cooling circuit 120 (typically a water cooling circuit) provides relatively low grade heat 130 which is used in a heat recovery unit 132 (by means of a heat pump arrangement) to heat incoming air 134 for the boiler 102, providing heated air 101. The heat 130 from cooling circuit 120 may also be employed as an external heat supply 136, for example for district heating. A yet further use of heat 130 may be to supply heat via heat recovery unit 138 to the pre-heater 124 which heats condensate 122 from the turbine 106. Heat recovery unit 138 may also be supplied with heat 140 from a cooling circuit for generator 110. In this example heat 142 is also recovered, from a cooling circuit used to cool transformer 114 and fed via another heat recovery unit 144 to pre-heater 124.

[0091] Flue gas 146 emanating from the boiler 102 is pre-cooled in heat recovery unit I (128) by the returning condensate 122. The pre-cooled flue gas 148 is then further cooled and water present in the stream condensed out in heat recovery unit II (126), which also makes use of the returning condensate 122 as coolant. The cooled dried flue gas 150 emanating from heat recovery unit II (126) may then be used further for drying fuel as shown in the arrangement of FIG. 1. The cooled dried flue gas 150 may then be processed in a carbon capture unit 151 to recover the carbon dioxide. Condensate 152 obtained from the flue gas may also be utilized, for example, for drying fuel as shown in FIG. 1.

[0092] In this example heat recovery in unit 132 is by means of a heat pump as part of a heat pump system. It will be understood that other heat recovery in systems of the invention may, in each instance, be by making use of heat exchangers, heat pumps or both heat exchangers and heat pumps in combination.

[0093] For example, the heat recovery units in any one of units 126, 128, 138 and 144 shown in FIG. 2 may use heat exchangers, heat pumps or both heat exchangers and heat pumps.

[0094] FIG. 3 shows in a simplified schematic block diagram features of a power generating system 200 of a general type similar that of FIG. 1. This illustration is focussed on the recovery of low grade energy for a heat pump system. In this example the heat pump system collects low grade heat from several sources and in turn uses heat pumps to upgrade the heat to perform several useful heating functions.

Steam Cycle

[0095] The power generating system includes a combustion boiler 201 fed with air 202, fuel 204 and heated pressurized water 206. Steam produced by the boiler 200 is fed by line 208 to the steam turbine 210. The spent steam is condensed in condenser 212 and returned by line 214, including compression pump 216 to the boiler 201 for reuse.

Flue gas

[0096] The flue gas (line 218) from the boiler 201 is cooled and condensed in a unit 220 such as the two stage heat recovery unit 36 described above with respect to FIG. 1. The remaining gases (mostly nitrogen and carbon dioxide) following condensation may progress to optional carbon capture unit 222.

Power output

[0097] In this example the condensing steam turbine 210 drives generator 224 to produce electricity, which is converted by transformer 226 to a suitable form for supply to the grid 228. A portion of the power generated is used for self-consumption 230, for example used to power pumps.

[0098] In this example a start-up motor and generator unit 232 is available for use in start-up of the system 200. The motor may be a gas piston engine or a gas turbine, for example. The motor and generator unit 232 may also be used more routinely to add to the output of the system 200, by being run, as required to generate electricity. This adds to the flexibility of system 200.

Heat Recovery and Heat Pump System

[0099] Dashed line 234 indicates the use of heat from the flue gas heat recovery and condensation unit to heat the condensate returning via line 214 to the boiler 201.

[0100] All the other dashed lines in the figure illustrate recovery of low grade heat from various sources, the upgrading of the heat by heat pumps of the heat pump system and the use of the upgraded heat for various duties.

[0101] Thus low grade heat is recovered as indicated by dashed lines 236, 238, 240, 242, 244, 248 and 250 from, respectively: the transformer 226; the generator 238; cooling the turbine 240; the condenser for the turbine 212; flue gas heat recovery and condensation 220, flue gas carbon capture 222; and the motor and generator unit 232.

[0102] In this example all the low grade heat recovery is pooled as suggested by linking line 252 as part of a heat pump system 254. The heat pump system includes optional heat storage 256, for example a tank of water.

[0103] The heat pump system includes variable drive compressor heat pumps. One or more heat pumps are employed for each duty as follows: at 258 for heating the air input 202 to the boiler; at 260 for heating the condensate returning to the boiler in line 214; and at 262 for drying the biomass fuel 204.

[0104] Also included in this figure is the optional use of another heat pump or pumps at 264 for supply of upgraded heat to a district heating system (DH grid 266), accessible if desired by control system 268.