WO2002090721A1

WO2002090721A1 - Power generation apparatus

Info

Publication number: WO2002090721A1
Application number: PCT/GB2002/002127
Authority: WO
Inventors: Alexander Kenworth Molyneaux; David Ainsworth; Clive Anthony Davies
Original assignee: Bowman Power Systems Limited
Priority date: 2001-05-09
Filing date: 2002-05-09
Publication date: 2002-11-14
Also published as: GB0111301D0

Abstract

A power generation apparatus (100) includes a gas turbine (106) and generator (136). The generator (136) is cooled by bleeding air from a main compressor (108) of the gas turbine and through a heat exchanger (102) and secondary turbine (134). The secondary turbine (134) drives a secondary compressor (142) which compresses natural gas fuel to be delivered to a combustor (110) of the gas turbine.

Description

POWER GENERATION APPARATUS

The present application relates to power generation apparatus, for example to micro-turbines, particularly but not exclusively being of the cogen type being adapted to produce power in the form of electricity and thermal energy.

A known power generation apparatus includes an electrical generator driven by a turbine of a gas turbine. The generator is cooled by passing air through a gap between a rotor and a stator of the generator, this cooling airflow being driven by a fan driven by an electric motor. Additionally, the stator is surrounded by a water radiator and a flow of cooling water is driven by a pump driven by an electric motor through the water radiator. Fuel is provided to a combustor of the gas turbine by a pump which is driven by an electric motor in association with a pressure return valve for returning excess fuel to the low pressure side of the fuel pump and a fuel control valve. The configuration of the various ancillary pumps and fan with associated motors in the prior art means that this type of apparatus is rather complicated, as well as time consuming and expensive to make.

US-A-5329757 and US-A-5488823 disclose an apparatus in which gas is taken from a high pressure section of a gas turbine engine to a turbine which drives a compressor to supply fuel to a fuel system of the gas turbine.

The engine is a complicated high pressure machine, appearing to have a pressure ratio in excess of 10 to 1.

The present invention aims to alleviate at least some of the problems of the prior art.

According to the present invention a power generation apparatus comprises; a gas turbine, the gas turbine including a main compressor and a main turbine; and a generator, wherein the generator is cooled by cooling gases taken from a bleed point in a flow path through the gas turbine. Accordingly, one or more of the generator air cooling fan and water radiator cooling pump with associated motor(s) may, in preferred embodiments be omitted, as may be the water radiator in some preferred embodiments, thereby saving substantial complexity and cost in the apparatus.

The bleed point may be located at a pressurised location on the main compressor and/or downstream of the main compressor in a gas turbine main working fluid flow path. The bleed point may be located on a high pressure side of the main compressor or downstream of the main compressor. The bleed point is preferably located upstream of a combustor of the gas turbine. A plurality of said bleed points may be provided. Said bleed points may be located at different points along the main working fluid flow path.

Preferably, the power generation apparatus is provided with a secondary turbine in a cooling flow path from the bleed point to the generator. Accordingly, the turbine may be adapted to remove energy from the gases in the cooling flow path so as to cool said gases on the way to the generator. A heat exchanger may be provided in the cooling flow path. The heat exchanger may be located between the bleed point and the secondary turbine in the cooling flow path. The heat exchanger may be arranged for cooling the gases in the cooling flow path. The heat exchanger may alternatively be arranged for heating the gases in the cooling flow path. The heat exchanger may be arranged to be capable of heating or cooling the gases in the cooling flow path as selected by a control device of the apparatus. Preferably, the power generation apparatus includes a control device which is operational for controlling the cooling or heating of the gases in the cooling flow path. The control device may comprise a valve which is variably operable for varying the cooling or heating of the gases in the cooling flow path.

The apparatus may include a cooling flow path control device for controlling the flow of gases along the cooling flow path. The cooling flow path control device may comprise a valve which is located in the cooling flow path. The valve located in the cooling flow path may be operable in response to signals received from a control unit of the apparatus.

Preferably, the apparatus includes a secondary compressor, the secondary compressor being driven by the secondary turbine and being adapted to supply fuel to the gas turbine. Accordingly, the secondary turbine may advantageously serve two purposes, namely firstly being capable of reducing the temperature of gases on the way to the generator in the cooling flow path and secondly being the motive force for the fuel compressor. Accordingly, the electric motor-powered gas boost compressor normally used in the prior art, together with its associated pressure return valve and fuel control valve may, in preferred embodiments, be omitted, thus further saving on the complexity and cost of the power generation apparatus. Preferably, the secondary compressor and secondary turbine are each single stage, the secondary compressor being axial inlet flow/radial outlet flow pipe and the secondary turbine being radial inlet flow/axial outlet flow type. The secondary compressor may be adapted to supply gaseous fuel to the gas turbine. Preferably, at least the secondary compressor is single stage. Accordingly, in applications where the fuel is gaseous, such as natural gas, the gas may be boosted from mains pressure up to sufficient pressure for appropriate gas flow into any combustor of the gas turbine which may be provided.

Preferably, the gas turbine is configured such that in use the pressure ratio of the gas turbine (e.g. from fuel and/or air source to combustor, or across the main or secondary compressor) is less than 10 to 1, preferably less than 6 to 1 or 5 to 1, 4.3 to 1 being one example. Preferably, fuel delivery temperature to a combustor of the gas turbine is less than 200 °C, more preferably about 180°C. A fuel aftercooler may be provided downstream of the secondary compressor, especially when high pressure ratio is employed. Such an aftercooler may cool the fuel from about 179 to 200°C, to 200°F or below for delivery to the combustor, the aftercooler preferably using a water circuit such as a water circuit of a boiler of the apparatus for fuel cooling.

Preferably, a fuel control device is provided for controlling the mass flow rate of fuel delivered for combustion in the gas turbine from the secondary compressor. The fuel control valve may comprise a variable valve located in a fuel flow path leading from the secondary compressor to a combustor of the gas turbine, or may be on a low pressure side of the secondary compressor. A gas turbine speed sensor may be provided. A gas turbine exhaust gas temperature sensor may be provided. Each sensor may be adapted to send signals to a control unit of the power generation apparatus. The control unit may be adapted to send control signals to the variable valve for fuel control. The fuel control variable valve may be controlled open or closed loop based on one or more of the sensed speed or exhaust gas temperature of the gas turbine. Alternatively, the fuel control valve may be controlled open or closed loop based upon a turbine inlet temperature sensed by a turbine inlet temperature sensor of the gas turbine. Thus, the variable valve may be controlled for optimum thermal efficiency during part load conditions by mamtaining constant turbine inlet temperature or turbine exhaust gas temperature. Instead of or in addition to providing the variable valve in the path between the secondary compressor and the combustor of the gas turbine, fuel delivery to the gas turbine may be controlled open or closed loop based upon one or more of turbine speed, turbine inlet temperature or exhaust gas temperature, by varying flow with a valve in the cooling flow path, so as to vary the amount of work extracted by the secondary turbine from the gases in the cooling flow path and thereby vary the amount of work transferred by the secondary compressor to fuel, thus controlling fuel delivery.

Preferably, the main compressor is adapted to compress air for combustion with fuel in the gas turbine. When the bleed point is located between the main compressor and a combustor of the gas turbine, the bled cooling gases may therefore be air. Hence, the gases when exhausted from the cooling flow path will also be air, the apparatus therefore being relatively safe with it being envisaged therefore that the cooling flow exhaust path might be into a room, such as through a vent in a wall of a cabinet containing the power generation apparatus.

Preferably, the generator includes a rotor and stator. Preferably, a cooling flow path for at least some of the bled cooling gases passes between the rotor and stator. Preferably, the rotor has a cylindrical body and the stator has a larger generally cylindrical body surrounding the rotor, an annular elongate gap being provided between the rotor and stator for the through-flow of at least some of the bled cooling gases. Preferably, a stator outer cooling path is provided for at least some of the bled cooling gases, the stator outer cooling path at least partly surrounding the stator. The stator outer cooling path may be provided by an annular chamber surrounding the stator. The stator outer cooling path preferably includes at least one cooling fin for transferring heat from the stator to cooling gases in the stator outer cooling path. Thus, when part of the bled gas is passed between the rotor and stator and part of the bled gas is passed through a stator outer cooling path, good heat transfer from both of the rotor and stator may be achieved, so as to achieve sufficient cooling at moderate bled airflow rate, without necessarily requiring a water radiator and associated water cooling pipes and pump, or an additional motorised fan for blowing air to cool the stator and/or rotor.

In one example, the generator is adapted to produce up to a rated level of lOOKw of electricity under constant operation conditions and the total bled airflow rate may be about 50 litres per second. The temperature of gases in the cooling flow path downstream of the secondary turbine (when provided) and/or just upstream of the generator may be about 70°C. The temperature of the gases downstream of the generator in the cooling gases flow path in this embodiment may be about 140°C. Where a flow path between the rotor and stator is provided as well as an outer stator cooling flow path, the configuration of the gas conduits in the region of the generator is preferably such that about two-thirds of the mass flow rate of the cooling gases passes through the outer stator flow path and approximately one-third passes between the rotor and stator. Preferably, the apparatus includes a recuperator for recuperating heat exhausted from the main turbine. Preferably, the apparatus includes a boiler for transferring heat from gases exhausted from the main turbine, such as to produce hot water and/or steam.

In preferred embodiments, respective rotors of the main turbine, main compressor and generator may be mounted for rotation in unison on a common shaft.

The main compressor may comprise a single stage axial inlet flow/radial outlet flow type and the main turbine may comprise a single stage radial flow inlet/axial flow outlet type.

The present invention may take various forms and a preferred embodiment of a power generation apparatus in accordance with the invention will now be described with reference to the accompanying drawings, in which:

Fig.l shows schematically a prior art power generation apparatus; and Fig.2 shows a preferred embodiment of a power generation apparatus in accordance with a preferred embodiment of the present invention. As shown in Fig.l, a prior art power generation apparatus 10 includes a gas turbine 12 consisting of a compressor 14, combustor or burner 16 and turbine 18. A recuperator 20 and boiler 22 are provided. Air from an air source 24 is compressed in the compressor Ϊ , heated in the recuperator 20 then reacted with fuel in the combustor 16, then passed through the turbine 18 and back through the recuperator 20 and boiler 22 to an exhaust stack 24. Fuel is provided to the combustor 16 from a fuel source 26 by a pump 28 driven by an electric motor 30 in association with a pressure return valve 32 and fuel control valve 34. In addition to driving the compressor 14, the turbine 18 drives a rotor 36 of a generator 38 which also includes a stator 40 surrounding the rotor. A water radiator 42 surrounds the stator. Cooling air is blown through a radial gap 44 between the rotor 36 and stator 40 by a fan 46 driven by an electric motor 48. Cooling water is driven in a circuit 49 through the water radiator 42 from a reservoir 50 through a pump 52 driven by an electric motor 54. Fig.2 shows a preferred embodiment of a power generation apparatus

100 in accordance with the present invention. The power generation apparatus comprises a transportable cabinet 102 which is about 3m long, 2m high and 1.5m high. The cabinet may be supported on a floor by feet 104. The cabinet 102 has generally rectangular front and side elevations and top plan. A gas turbine 106 in the cabinet 102 comprises a main air compressor 108, a combustor 110 and a main turbine 112. Air from an air source 114 is compressed by the compressor 118, then heated in a recuperator 116 before reacting with fuel in a combustor 110, with the combusted gases from the combustor then passing through the main turbine 112, the recuperator 116 and then a boiler 118 to an exhaust stack 120. The boiler may convert relatively cold water 122 at a water source into hot water or steam at an outlet 124.

A bleed point 126 is provided at a high pressure side of the main compressor 108. The bleed point 126 allows bleed air to pass along a cooling flow path 128 through a control valve 130, heat exchanger 132, secondary turbine 134 and then past a generator 136 to an exhaust duct 138. The secondary turbine 134 is connected by a shaft 140 to a secondary compressor 142. The construction of the secondary compressor 142 and 134 may thus resemble that of a turbocharger. The secondary compressor may be a single stage axial inlet/radial outlet compressor and the secondary turbine 134 may comprise a radial inlet flow/axial outlet flow type turbine. The secondary compressor 142 is adapted to compress natural gas fuel emanating from a fuel source 144 and provide a fuel flow through a fuel flow control valve 146 to the combustor 110, for combustion with the air supplied by the main compressor 108. With the fuel control valve 146 on the high pressure side of the secondary compressor 142, a pressure relief/regulator valve 145 is preferably provided, having a return line 149 to the low pressure side of the secondary compressor. The valve 145 assists in preventing the secondary compressor 142 from entering a surge condition at low flows. Preferably, valves 145 and 146 and line 149 are omitted and, instead, a fuel flow control valve 147 is provided on the low pressure side of the secondary compressor 142.

The apparatus is configured for the secondary compressor 142 to run at a pressure ratio of 4.3 to 1. Thus, with natural gas as the fuel, with gamma = 1.304 (in one example), across the secondary compressor at ISO conditions (15 °C ambient) with the compressor having 70% efficiency: AT = (273 + 15) x (4.3Λ((gamma-l)/gamma)-l)/0.7 = 164 K. Thus, fuel delivery temperature to the combustor would be about 179°C in this example. If it is desired to reduce the fuel temperature further, using a water circuit (not shown) from boiler 118, the fuel may be cooled to about 200°F (94°C) or below prior to delivery to combustor 110.

An accumulator or plenum chamber 151 may be provided (or omitted as desired) at a location downstream of the secondary compressor 142. The heat exchanger 132 may be adapted to cool or heat, but preferably cool, the bled air in the cooling flow path 128, the heat exchange in the heat exchanger 132 being at least partly controlled by a cooling flow valve 148.

The generator 136 includes a cylindrical radial field rotor 150 surrounded by a stator 152 with an annular air gap 154 therebetween. The stator is surrounded by a finned chamber 156 including at least one fin 157 so as to provide an annular outer stator cooling flow path radially outside the stator, with an inner rotor cooling flow path being provided by virtue of the air gap 154. The stator 152 is connected by circuitry 158 to a power conditioning unit 160 including a rectifier 162, inverter 164 and filter 166 together with battery 168, the power conditioning unit being adapted to supply 3-phase AC to a load 170. The inverter may be PWM modulated in a known way in a generate mode to supply the load 170 or for operating the generator 136 as a motor for starting up the gas turbine, using the battery 168 as a power source.

The power conditioning unit 160 is connected to a microprocessor control unit 172 by a signal path 174. The microprocessor control unit 172 is connected by respective signal paths 176, 178, 180 and 182 to respective speed 184, EGT 186 and TIT 188 sensors, the sensors being adapted to provide signals representative of gas turbine shaft speed, exhaust gas temperature and turbine inlet temperature, respectively to the control unit 172. One or more of the EGT 186 and TIT 188 sensors may be omitted, if desired.

The control unit 172 is adapted to provide signals along flow paths 192, 194, 196 to the valves 146, 148 and 130, respectively.

In some embodiments, one of the fuel control valve 146 (or 147 where provided instead) and cooling gases control valve 130 may be omitted.

Preferably, one or both of the fuel control valve 146 and cooling gases flow control valve 130 is/are controlled by the control unit 172 based upon shaft speed sensed by the speed sensor 184 and/or EGT sensed by the EGT sensor

186, or perhaps TIT sensed by the TIT sensor 188, if turbine inlet temperature control is preferred over exhaust gas temperature control. Thus, one or more of the valves 146,130 may be controlled either open or closed loop based upon signals from the sensors 184,186,188, for example to provide sufficient fuel to run the gas turbine at constant or predetermined varying speed if desired or alternatively constant or predetermined varying EGT or TIT if desired.

Although the heat exchanger 132 may act as a heater for gases in the cooling gases flow path 128, the heat exchanger preferably acts as a cooler, the amount of cooling at the generator 136 being at least partly controlled by one or more of the valves 130,148, with cold water or cool gases being pumped from source 200 to return 202, for example, in a re-circulating circuit. The main compressor 108 comprises a single stage axial inlet/radial outlet type compressor and the main turbine 112 comprises a single stage radial inlet flow/axial outlet flow turbine. The rotors of the main compressor 108 and the main turbine 114 are mounted on a single shaft 204 with the rotor 150 of the generator 136, such that all three rotate in unison. The generator 136 is adapted to reach up to lOOkW at rated maximum operational conditions. The mass flow rate/airflow along the cooling flow path 128 to cool the generator 136 is about 50gms per second/50 litres per second. About two-thirds of the mass flow passes through the finned chamber 156 through the outer stator flow path and about one-third passes through the air gap 154 between the rotor 150 and stator 152.

The temperature of the cooling gases is controlled to be 70 °C downstream of the secondary turbine 134 and 140°C downstream of the generator, when the generator is operating at maximum rated power of lOOKw, the control being provided by operation of the various valves 148, 130,146.

Various modifications may be made to the embodiment described without departing from the scope of the invention as defined by the claims as interpreted under patent law.

Claims

1. A power generation apparatus comprising: a gas turbine, the gas turbine including a main compressor and a main turbine; and a generator, wherein the generator is cooled by cooling gases taken from a bleed point in a flow path through the gas turbine.

2. A power generation apparatus as claimed in claim 1 in which the bleed point is at a pressurised location on the main compressor.

3. A power generation apparatus as claimed in claim 1 or claim 2 in which the bleed point is on a high pressure side of or downstream of the main compressor.

4. A power generation apparatus as claimed in any preceding claim in which the bleed point is upstream of a combustor of the gas turbine.

5. A power generation apparatus as claimed in any preceding claim which includes a secondary turbine in a cooling flow path from the bleed point to the generator.

6. A power generation apparatus as claimed in claim 5 which includes a heat exchanger in the cooling flow path.

7. A power generation apparatus as claimed in claim 6 in which the heat exchanger is located between the bleed point and the secondary turbine in the cooling flow path.

8. A power generation apparatus as claimed in claim 6 or claim 7 in which the heat exchanger is arranged for cooling the gases in the cooling flow path.

9. A power generation apparatus as claimed in claim 6 or claim 7 in which the heat exchanger is arranged for heating the gases in the cooling flow path.

10. A power generation apparatus as claimed in claim 8 or claim 9 which includes a control device operative for controlling the cooling (or heating) of the gases in the cooling flow path.

11. A power generation apparatus as claimed in claim 9 in which the control device comprising valve which is variably operable for varying the cooling (or heating) of the gases in the cooling flow path.

12. A power generation apparatus as claimed in any one of claims 5 to 11 in which a cooling flow path control device is provided for controlling the flow of gases along the cooling flow path.

13. A power generation apparatus as claimed in claim 12 in which the cooling flow path control device comprises a valve which is located in the cooling flow path.

14. A power generation apparatus as claimed in any one of claims 5 to 13 which includes a secondary compressor, the secondary compressor being driven by the secondary turbine and adapted to supply fuel to the gas turbine.

15. A power generation apparatus as claimed in claim 14 in which the secondary compressor and secondary turbine are each single stage, the secondary compressor being axial inlet flow/radial outlet flow type and the second turbine being radial inlet flow/axial outlet flow type.

16. A power generation apparatus as claimed in claim 14 or claim 15 in which the secondary compressor is adapted to supply gaseous fuel to the gas turbine.

17. A power generation apparatus as claimed in any of claims 14 to 16 in which a fuel control device is provided for controlling the mass flow rate of fuel delivered for combustion in the gas turbine from the secondary compressor.

18. A power generation apparatus as claimed in claim 17 in which the fuel control device comprises a variable valve located in a fuel flow path on a low pressure side of the secondary compressor.

19. A power generation apparatus as claimed in any preceding claim in which the main compressor is adapted to compress air for combustion with fuel in the gas turbine.

20. A power generation apparatus as claimed in any preceding claim in which the generator includes a rotor and a stator.

21. A power generation apparatus as claimed in claim 20 in which a cooling flow path for at least some of the bled cooling gases passes between the rotor and stator.

22. A power generation apparatus as claimed in claim 21 in which the rotor has a cylindrical body and the stator has a larger generally cylindrical body surrounding the rotor, an annular elongate gap being provided between the rotor and stator for the through flow of the bled cooling gases.

23. A power generation apparatus as claimed in claim 20 or claim 21 or claim 22 in which a stator outer cooling path is provided for at least some of the bled cooling gases the stator outer cooling path at least partly surrounding the stator.

24. A power generation apparatus as claimed in claim 22 in which the stator outer cooling path is provided by an annular chamber surrounding the stator.

25. A power generation apparatus as claimed in claim 23 or claim 24 in which the stator outer cooling path includes at least one cooling fin for transferring heat from the stator to cooling gases in the stator outer cooling path.

26. A power generation apparatus as claimed in any preceding claim which includes a recuperator for recuperating heat exhausted from the main turbine.

27. A power generation apparatus as claimed in any preceding claim which includes a boiler for transferring heat from gases exhausted from the main turbine.

28. A power generation apparatus as claimed in any preceding claim in which respective rotors of the main turbine, main compressor and generator are mounted for rotation in unison on a common shaft.

29. A power generation apparatus as claimed in any preceding claim in which the main compressor is single stage axial inlet flow/radial outlet flow types and the main turbine is single stage radial flow inlet/axial flow outlet type.

30. A power generation apparatus substantially as described herein with reference to Figure 2 of the accompanying drawings.