GB2065231A - Gas turbine installations - Google Patents

Abstract

The main air flow from compressor (11) is fed to a heat exchanger (13) from which the air heated by turbine exhaust is fed to a combustion chamber (12) a secondary air steam (21) being passed through pump (22) to an adjustable proportioning valve (23) in which the secondary stream is divided in dependence on operating power requirements into a stream (24) which is mixed with and conveys pulverised fuel to combustion chamber (12) and a residual stream (25) which is fed to the combustion chamber. <IMAGE>

Description

SPECIFICATION gas turbine installations The invention relates to a method of operating a gas turbine installation and a gas turbine installation operated by this method. The installation basically comprises a gas turbine, to the combustion chamber of which air which has been compressed and heated in a heat exchanger and fuel are fed. Hitherto such methods have related generally to the operation of gas turbines using liquid fuels. The object underlying the invention is to disclose a method which makes reliable and economic operation of a gas turbine installation possible by also using fine-grained or dust-like fuels.According to this invention, there is provided a method of operating a gas turbine installation, to the combustion chamber of which air which has been compressed and heated in a heat exchanger and fuel are fed, wherein the method comprises diverting a secondary stream of air from a main stream of air from the compressor and leading to the heat exchanger, compressing the secondary stream still further and dividing the secondary stream, depending on output, into a conveying air stream for a flowable solid fuel and into a residual air stream, fuel being added by mixing to the conveying air stream in a volume corresponding to the volume of the air and the fuel/air mixture thus formed being fed to the combustion chamber.This division of the air into two streams permits reliable operation of the gas since the solid fuel, for example pulverised coal, is fed, according to the required power output, safely and without risk of spontaneous ignition in the combustion chamber by the conveying air which is relatively cool and under relatively high pressure, whilst a highly efficient combustion is maintained by heating the greater part of the air which is fed to the combustion chamber in the heat exchanger.

In one embodiment of the invention the residual air is added to the mixture consisting of conveying air and fuel before the said mixture enters the combustion chamber. By this means the relatively high pressure of the residual air is used for feeding the mixture to the combustion chamber.

In another embodiment of the invention the residual air is added to the main stream of air before the said main stream enters the heat exchanger. As a result, the temperature of the residual air in the heat exchanger is raised and the economy of the method is therefore increased.

The invention also provides a gas turbine installation comprising a combustion chamber to which air is supplied from a compressor and a heat exchanger, wherein the installation comprises means for directing a secondary stream of air from the stream of air delivered by the compressor, means for further compressing said secondary stream and means for dividing the secondary stream into an air stream for conveying a flowable solid fuel to the combustion chamber and a residual air stream, the residual air stream being mixed with the fuel-conveying air stream in proportion to the required power output of the turbine, and wherein the secondary stream is conducted along a duct containing a controllable pump the output of which is connected to a controllable valve in which said secondary stream is proportionally divided into the fuel-conveying air stream and the residual air stream, the fuel conveying air stream passing through a fluidised bed in which said air stream entrains and mixes with the fuel to form a fuel-air mixture which is conveyed to the combustion chamber, the residual air stream being conveyed from the valve along a line by-passing the fluidised bed to the combustion chamber.

Particularly through the provision of a fluidised bed influenced by a control valve, such a plant enables the method of operation to be rapidly adapted to sudden changes in load, as occur in small gas turbines and particularly in gas turbines for motor vehicles.

Two embodiments of the invention will now be described by way of example and with reference to the accompanying drawings, in which: Figure 1 is a diagram of a fuel system of a gas turbine operated by pulverised coal, and Figure 2 is a diagram of a part of a modified fuel system.

The fuel system shown in Figure 1 serves to operate a gas turbine of a motor vehicle using pulverised coal. The gas turbine consists of the customary components, of which only tne compressor 11, the combustion chamber 12 and a heat exchanger 13 are shown.

A line 14 leads from the outlet of the compressor 11 to the heat exchanger 13 and, from there, a line 1 5 leads to the combustion chamber 12 in which the line 1 5 leads into an annular space 16 between a flame tube 17 and a chamber wall 1 8. A line 1 9 conducts hot exhaust gases from the gas turbine to the heat exchanger 1 3 and continue flowing through a line 20 to the exhaust (not shown).

Branching off the line 14 is a line 21, in which a controllable air pump 22 is located and which leads to an adjustable control valve 23, from which a line 24 for a conveying air flow and a line 25 for a residual air flow extend. The line 24 leads from the valve 23 to a fluidised bed 26 from which a line 27 extends to the inlet 28 of the combustion chamber 12. The line 25 by-passes the fluidised bed 26 and leads into the line 27 upstream of the inlet 28.

The fluidised bed 26, which serves to admix the pulverised coal with the conveying air, is a cylindrical container in which a fine-meshed grating 30 is arranged at a distance from its bottom 29. The lines 24 and 27 are connected to, respectively, the bottom 29 and the cover 31 of the fluidised bed 26. In addition, a line 32 which connects the fluidised bed 26 to a pulverised coal store 33, is connected to the cover 31. A screw conveyor 34 located in the line 32 serves to feed the pulverised coal to the fluidised bed 26.

In the fluidised bed 26 a lower lever sensor 35 and an upper lever sensor 36, which are connected to the switch 39 of the screw conveyor 34 by electrical leads 37 and 38, respectively, are located in the region of the minimum permitted level and the maximum level in the bed. When the level falls below the minimum or exceeds the maximum value, the switch 39 switches the screw conveyor 34 on or off so that there is always an adequate supply of pulverised coal in the fluidised bed 26. It is also possible to provide a circuit which adapts the quantity conveyed by the screw conveyor 34 to the current consumption of pulverised coal of the gas turbine by varying the rotational speed.

During operation of the gas turbine the compressor 11 delivers compressed air, which flows through the line 14 to the heat exchanger 13 and is heated therein indirectly by the hot exhaust gases of the gas turbine which are fed through the line 1 9. The heated air flows through the line annular space 1 6 of the combustion chamber 12.

A small portion of the compressed air, which is for example, five per cent, is bled off through the branch line 21 to the air pump 22 and is further compressed at this point. Frnm the air pump 22 the air continues to flow through the line 21 to the control valve 23 and is divided at this point into conveying air for the coal dust and into residual air. The quantitative proportion of the two partial streams of air is varied depending on the output required of the gas turbine. Thus, the proportion of fuel-conveying air in the line 24 increases constantly from the idle running state of the gas turbine up to full load, whilst the residual air in the line 25 decreases to the same extent.In the case of full load, virtually all the air delivered by the air pump 22 flows through the line 24 to the fluidised bed 26 whilst no, or hardly any, compressed air continues to flow through the line 25. In the case of the vehicle gas turbine, for example, the control valve 23 can be adjusted indirectly or directly by the accelerator pedal.

Depending on the quantity of air delivered, the conveying air flowing through the fluidised bed 26 entrains more or less of the pulverised coal supply which is constantly held in suspension above the grating 30 in the fluidised bed. The mixture of conveying air and pulverised coal which is formed as a result is fed through the line 27 to the combustion chamber 12. The residual air, which is diverted from the control valve 23 into the line 25 and which does not entrain any'pulverised coal, is added to the mixture flowing through the line 27 to the combustion chamber 12.

The compression of the air which is increased by the air pump 22, compensates for the flow losses which occur particularly in the control valve 23 and in the fluidised bed 26 and ensures that the conveying air and residual air, which flow through the line 27 to the combustion chamber 12 and act as primary air, have, when compared with the air which comes from the heat exchanger 13 and is introduced into the combustion chamber 12 as secondary air, a higher pressure which facilitates the inflow of the mixture at the inlet 28 of the combustion chamber 12. The mixture ignites in the combustion chamber 12 and the pulverised coal is burned.

The modified fuel system, part of which is shown in Figure 2, corresponds in the main to the fuel system schematically illustrated in Figure 1. It differs merely in that a return line 40, which branches off the control valve 23 and is intended for conveying the residual air, is connected to the line 14 between the compressor 11 and the heat exchanger 13. In contrast to the embodiment shown in Figure 1 , the residual air is thereby fed back to the main stream of the air and heated together with this main stream in the heat exchanger 13 and fed through the line 1 5 to the combustion chamber (not shown).

Claims (7)

1. A method of operating a gas turbine installation, to the combustion chamber of which air which has been compressed and heated in a heat exchanger and fuel are fed, wherein the method comprises diverting a secondary stream of air from a main stream of air from the compressor and leading to the heat exchanger, compressing the secondary stream still further and dividing the secondary stream, depending on output, into a conveying air stream for a flowable solid fuel and into a residual air stream, fuel being added by mixing to the conveying air stream in a volume corresponding to the volume of the air and the fuel/air mixture thus formed being fed to the combustion chamber.

2. A method according to Claim 1, wherein the method comprises mixing the residual air stream with the mixture consisting of conveying air and fuel before the said mixture enters the combustion chamber.

3. A method according to Claim 1, wherein the method comprises mixing the residual air stream with the main stream of air before the said main stream enters the heat exchanger.

4. A gas turbine installation including a combustion chamber to which air is supplied from a compressor and a heat exchanger, wherein the installation comprises means for directing a secondary stream of air from the stream of air delivered by the compressor, means for further compressing said secondary stream and means for dividing the secondary stream into an air stream for conveying a flowabie solid fuel to the combustion chamber and a residual air stream, the residual air stream being mixed with the fuelconveying air stream in proportion to the required power output of the turbine, and wherein the secondary stream is conducted along a duct containing a controllable pump the output of which is connected to a controllable valve in which said secondary stream is proportionally divided into the fuel-conveying air stream and the residual air stream, the fuel conveying air stream passing through a fluidised bed in which said air stream entrains and mixes with the fuel to form a fuel-air mixture which is conveyed to the combustion chamber, the residual air stream being conveyed from the valve along a line bypassing the fluidised bed to the combustion chamber.

5. An installation according to Claim 4, wherein a mechanical conveyor for the fuel is arranged upstream from the fluidised bed, the quantity of fuel conveyed being regulated in dependence on the level of fuel in the fluidised bed.

6. A method of operating a gas turbine installation, substantially as hereinbefore described with reference to the accompanying drawings.

7. A gas turbine installation, substantially as hereinbefore described with reference to the accompanying drawings.