Fluidized Bed Powerplant With Helium Circuit, Indirect Heat Exchange And Compressed Air Bypass Control

Abstract

A power unit consists basically of two gas turbine engines. In the first which is a closed cycle the working fluid (helium) is heated by passing it through a duct embedded in a fluidized bed. The exhaust gas is passed through a conventional heat exchanger before being returned to the compressor. In the second engine, consisting of a compressor and a turbine, air from the compressor is passed through the particulate material of the fluidised bed with fuel which maintains combustion in the fluidised bed. The exhaust gas from the turbine of the second engine is passed through a conventional heat exchanger and then to atmosphere. The two engines each drive an alternator.

Description

This invention relates to power plants, and is particularly but not exclusively concerned with a closed cycle gas turbine engine power plant.

According to the present invention, a power plant comprises fluidised bed combustion means connected to receive a working fluid in heat exchange relationship with the fluidised bed, turbine means connected to receive and be driven by the working fluid heated by the fluidised bed combustion means, compressor means connected to supply compressed air to the fluidised bed combustion means to support the combustion therein, further turbine means which is connected to receive and be driven by the combustion products from the fluidised bed combustion means and which is drivingly connected to the compressor means, and control valve means operative to permit at least a part of the compressed air compressed by the compressor means to by-pass the fluidised bed combustion means and flow to the inlet of the further turbine means.

There may be provided throttle valve means connected between the outlet of the compressor means and the fluidised bed combustion means so as to control the quantity of compressed air supplied to the latter.

In a preferred embodiment of the invention, the power plant additionally comprises auxiliary combustion means connected between the throttle valve means and the fluidised bed combustion means so as to heat the compressed air supplied to the latter prior to its entry therein.

There may also be provided further auxiliary combustion means adapted to heat the combustion products from the fluidised bed combustion means prior to their entry into the further turbine means.

The power plant may also comprise further control valve means operative to permit at least a part of the compressed air compressed by the compressor means to by-pass the fluidised bed combustion means and flow to the inlet of the further auxiliary combustion means.

The fluidised bed combustion means and the firstmentioned turbine means may be arranged to form a closed cycle for the working fluid thereof.

Thus there may be provided condenser means and pump means connected in series between the outlet of the firstmentioned turbine means and the fluidised bed combustion means so as to form a closed steam cycle.

Alternatively, there may be provided further compressor means connected in series between the outlet of the firstmentioned turbine means and the fluidised bed combustion means so as to form a closed cycle gas, e.g. helium, cycle.

Preferably there is provided heat exchange means connected to receive exhaust gases from the further turbine means in heat exchange relationship with the working fluid compressed by the further compressor means prior to its heating by the fluidised bed combustion means: additionally or alternatively there may be provided further heat exchange means connected to receive exhaust gases from the further turbine means in heat exchange relationship with the air compressed by the firstmentioned compressor means.

The heat exchange means and the further feat exchange means may be connected in flow series or in parallel.

There may also be provided a recuperator connected to receive the working fluid expanded in the firstmentioned turbine means in heat exchange relationship with the working fluid compressed by the further compressor means prior to its heating by the fluidised bed combustion means, the recuperator preferably being connected between the compressor means and the firstmentioned heat exchange means.

The invention will now be described, merely by way of example, with reference to the accompanying drawing, which is a schematic block diagram of a gas turbine engine power plant in accordance with the invention.

The gas turbine engine power plant shown in the drawing comprises, in flow series, a low pressure compressor 10, a high pressure compressor 12, a fluidised bed combustion apparatus 14, a compressor-driving turbine 16 drivingly connected to the compressors 10 and 12 by a shaft 18 and a free power turbine 20 which is drivingly connected to an alternator 22, the compressors 10, 12, the combustion apparatus 14 and the turbine 16, 20 being connected to form a closed cycle flow path for the working fluid of the power plant. The working fluid is preferably helium.

A precooler 24 is provided in flow series with the inlet of the compressor 10 while an intercooler 26 is provided between, and in flow series with, the compressors 10 and 12, the helium being passed in heat exchange relationship with cooling water in the coolers 24, 26. A recuperator 28 having two flow paths 30, 32 in heat exchange relationship is arranged so that the path 30 is connected in flow series between the outlet of the compressor 12 and the inlet of the fluidised bed combustion apparatus 14, and the path 32 is connected in flow series between the outlet of the turbine 20 and the inlet of the precooler 24.

The fluidised bed combustion apparatus 14 comprises a chamber 34 containing a particulate material 36 constituted by a particulate fuel such as granular coal or coke (about 1/8 inch diameter), although non-combustible particular material such as sand, soaked in or supplied with a light fuel such as kerosene or a gaseous fuel such as methane, may be used. The chamber 34 has an inlet 37 through which air compressed by a compressor 38 to a pressure of about six atmospheres enters the chamber and flows upwards through the particulate fuel 36. The particulate fuel 36 is thus fluidised, and burns continuously. The ash rises to the top, and is removed continuously by means not shown, while additional particulate fuel is continuously supplied by means not shown. Embedded in the particulate fuel 36 are a number of conduits (indicated diagrammatically at 39) through which the helium flows to be heated.

The combustion products resulting from the combustion of the particulate fuel 36 pass from the chamber 34 into a turbine 40 which is drivingly connected to the compressor 38 and to a further alternator 42. After being expanded in the turbine 40, the combustion products pass to atmosphere through a first flow path 44 of a heat exchanger 46 having a second flow path 48 connected, for the flow of helium, in series between the flow path 30 of the recuperator 28 and the inlet to the conduits 39 of the fluidised bed combustion apparatus 14. The considerable waste heat in the exhaust from the turbine 40 is thus injected into the closed helium cycle.

It will be appreciated that the flow path 48 may be arranged upstream of the flow path 30. Additionally, or alternatively, there may be provided a further heat exchanger (shown dotted at 50) having a first flow path 52 connected to receive the combustion products from the turbine 40 in heat exchange relationship with a second flow path 54 connected between the outlet of the compressor 38 and the inlet 37 of the chamber 34. The flow path 52 may be connected in series or in parallel with the flow path 44.

A throttle valve 56 and auxiliary combustion equipment 58 which is adapted to be supplied with liquid or gaseous fuel are connected in flow series between the outlet of the compressor 38 and the inlet 37 of the fluidised bed combustion apparatus 14, the throttle valve 56 being upstream of, and the combustion equipment 58 being downstream of, the flow path 54 if the flow path 54 is present. Further auxiliary combustion equipment 62 and a mixing chamber 64 are connected in flow series between the outlet of the chamber 34 of the fluidised bed combustion apparatus 14 and the inlet of the turbine 40, while a by-pass conduit 66 containing a by-pass control valve 68 is connected between the outlet of the compressor 38 and the mixing chamber 64. A further conduit 69 containing a shut-off valve 70 communicates between the outlet of the compressor 38 and the inlet of the combustion equipment 62.

The combustion equipment 58, 62 are preferably such that the gas passing therethrough (i.e. the compressed air or combustion products respectively) is indirectly heated, for example by passing through ducts in the combustion equipment 58, 62 which ducts are heated by the combustion of the fuel in the combustion equipment 58, 62.

When the power plant is to be started, the particulate fuel 36 in the fluidised bed combustion apparatus 14 is cold. The valve 56 is set fully open, the valves 68 and 70 are closed, and fuel is supplied to and burnt in the combustion equipment 58. Hot fluidising gas is thus supplied to the fluidised bed combustion apparatus 14, which hot gas rapidly heats the particulate fuel 36 to a temperature at which self-sustaining combustion can commence. At this point the supply of fuel to the combustion equipment 58 can be gradually reduced to zero. Before self-sustaining combustion of the particulate fuel 36 has commenced the temperature of the combustion products leaving the chamber 34 may be too low for satisfactorily driving the turbine 40. In this case, fuel may additionally be supplied to and burnt in the combustion equipment 62.

An alternative method of starting the power plant comprises adjusting the valves 56 and 68 so that only about 20 percent of the air compressed by the compressor 38 is supplied to the fluidised bed combustion apparatus 14. Fuel is supplied to the combustion equipment 58 and 62, and the very hot combustion products leaving the combustion equipment 62 are diluted and cooled in the mixing chamber 64 by air passing through the valve 68 to a temperature suitable for driving the turbine 40.

During the normal running of the power plant, no fuel is supplied to the combustion equipment 56 or 62, the valve 56 is fully open and the valves 68 and 70 are closed. Should there be a sudden decrease in the load, by-pass valve 68 is rapidly opened while the throttle valve 56 is closed, thus rapidly reducing the temperature at the inlet of the turbine 40 and within the particulate fuel 36 of the fluidised bed combustion apparatus 14. Fine control of the overall power output of the power plant is exercised by adjusting the valve 68 alone or by simultaneously adjusting the valves 56 and 68 in opposite senses.

If it is desired to service or repair the main power producing part of the power plant, i.e. the compressors 10, 12 and their associated equipment, the turbines 16, 20, the alternator 22 and the fluidised bed combustion apparatus 14, the power plant can still be used to produce at least some power by closing the valves 56 and 68, opening the valve 70 and supplying fuel to the combustion equipment 62. The compressor 38, combustion equipment 62 and turbine 40 then act as an independently operable gas turbine engine to drive the alternator 42.

It will be appreciated that the invention is applicable to power plants other than gas turbine engine power plants. For example, the closed helium cycle part of the power plant could be replaced by a closed steam cycle. In this case the compressors 10, 12 and their associated equipment would be replaced by a condenser and a water pump, the turbines 16, 20 would be replaced by a steam turbine or turbines, and the fluidised bed combustion apparatus 14 would act as a boiler for the water supplied to the conduits 39.

Claims

We claim:

1. A gas turbine engine power plant comprising:

compressor means,

fluidised bed combustion means,

said fluidised bed combustion means being connected to receive working fluid compressed by said compressor means in heat exchange relationship with said fluidised bed,

turbine means,

said turbine means being connected to receive and be driven by said working fluid heated by said fluidised bed combustion means, said turbine means also being drivingly connected to said compressor means,

said turbine means and said compressor means being connected to form a closed cycle,

further compressor means,

said further compressor means being adapted to supply said fluidised bed combustion means with compressed air to support combustion therein,

further turbine means,

said further turbine means being connected to receive and be driven by the combustion products of the fluidised bed combustion means,

said further compressor means being connected to be driven by said further turbine means,

control valve means,

said control valve means being operative to permit at least a part of the compressed air compressed by said further compressor means to by-pass said fluidised bed combustion means and flow to said further turbine means,

auxiliary combustion means connected to receive and heat compressed air from said further compressor before said fluidised bed combustion means, and

further auxiliary combustion means connected to receive and heat combustion products from said fluidised bed combustion means before said further turbine.

2. A power plant as claimed in claim 1 having throttle valve means connected between the outlet of the further compressor means and the fluidised bed combustion means.

3. A power plant as claimed in claim 2 having further control valve means operable to permit at least a part of the compressed air compressed by the further compressor means to by-pass the fluidised bed combustion bed combustion means and flow to the inlet of the further auxiliary combustion means.

4. A power plant as claimed in claim 1 having condenser means and pump means connected in series between the outlet of the first mentioned turbine means and the fluidised bed combustion means.

5. A power plant as claimed in claim 1 in which the gas in the closed cycle is helium.

6. A power plant as claimed in claim 1 having heat exchange means connected to receive exhaust gases from the further turbine means in heat exchange relationship with the working fluid compressed by the further compressor means prior to its heating by the fluidised bed combustion means.

7. A power plant as claimed in claim 6 having further heat exchange means connected to receive exhaust gases from the further turbine means in heat exchange relationship with the air compressed by the first mentioned compressor means.

8. A power plant as claimed in claim 7 having a recuperator connected to receive the working fluid compressed by the further compressor means prior to its heating by the fluidised bed combustion means, the recuperator being connected between the compressor means and the first mentioned heat exchange means.

9. A power plant as claimed in claim 7 in which the heat exchange means and the further heat exchange means are connected in flow series.

10. A power plant as claimed in claim 7 in which the heat exchange means and the further heat exchange means are connected in parallel.