GB2249589A

GB2249589A - Combined heat and power turbine

Info

Publication number: GB2249589A
Application number: GB9021826A
Authority: GB
Inventors: Peter Torkington
Original assignee: ADVANCED TECHNOLOGY DESIGN Ltd
Current assignee: ADVANCED TECHNOLOGY DESIGN Ltd
Priority date: 1990-10-08
Filing date: 1990-10-08
Publication date: 1992-05-13
Anticipated expiration: 2010-10-08
Also published as: GB2249589B; GB9021826D0

Abstract

A combined heat and power installation comprising a gas turbine 1 providing shaft power, 18 the exhaust gases from the gas turbine 1 being directed to a heat utilisation system. The gas turbine 1 includes a recuperator 2 and means for varying the relative flow of exhaust gases to the heat utilisation system through the recuperator 2 or through a by-pass duct 22 which by-passes the recuperator 2. The heat utilization system 32, 34 may comprise two distinct heat demands. For example there may be relatively low temperature demand 32 for space heating purposes and a relatively high temperature demand 34 for process heat. Valves 38, 40 may be provided for distributing a lower temperature gas from the recuperator 2 and a higher temperature gas from the by-pass duct 22 between the two heat demands 32, 34. To boost the temperature of the higher temperature gas an afterburner 30 may be incorporated into the duct 22. <IMAGE>

Description

COMBINED HEAT AND POWER TURBINE The present invention relates to combined heat and power installations comprising a gas turbine providing shaft power, the exhaust gases from the gas turbine being directed to a heat utilization system.

Combined heat and power installations using gas turbines are already known. In order to achieve high fuel efficiency based on shaft power output, while retaining the simplicity of a relatively low pressure ratio gas turbine cycle, some such gas turbines use a gas turbine gas generator employing a recuperator (or heat exchanger) ahead of its combustion chamber. The recuperator extracts its heat from the exhaust of the power turbine before it is directed to the heat utilisation system. In this basic form, such systems provide a division of heat to electrical power of about two to one.

In such a known system, variation in the heat output to the heat utilisation system is an unavoidable consequence of a variation in the shaft power output.

Thus, changes in the ratio of heat demand to shaft power demand throughout the day and year cannot efficiently be accommodated.

According to the present invention there is provided a combined heat and power installation comprising a gas turbine providing shaft power, the exhaust gases in the gas turbine being directed to a heat utilisation system, the gas turbine including a recuperator and diverter means for directing exhaust gases to the heat utilisation system selectively through the recuperator or through a by-pass duct which by-passes the recuperator.

In a preferred embodiment, the power turbine is provided with variable nozzle guide vanes.

Preferably the diverter means comprises a continuously variable valve in the by-pass duct. The diverter means may also comprise a variable valve in the exhaust flow path through the recuperator. In order to further increase the overall heat output an afterburner may be provided in the by-pass duct.

The heat utilization system may comprise two distinct heat demands. For example there may be a relatively low temperature demand for space heating purposes and a relatively high temperature demand for process heat. Valves may be provided for distributing the lower temperature gas from the recuperator and the higher temperature gas from the by-pass duct between the two heat demands. Control means may be provided to control the operation of the valve means.

As a further means of increasing the heat output of the turbine at the expense of shaft power, a turbine bypass may be provided across the power turbine of the gas turbine.

For a better understanding of the present invention and to show how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 is a block diagram of a combined heat and power installation; and Figure 2 is a block diagram of an alternative combined heat and power installation.

Referring to the drawings, Figure 1 shows a gas turbine unit 1 having a gas generator 3, and a power turbine 16. The gas generator comprises a compressor 4 driven through a shaft 12 by a gas generator turbine 10, and a combustor 8. A recuperator 2 provides heat exchange between the exhaust gases from the power turbine 16 and the compressed air delivered by the compressor 4. The compressor 4 may, for example, be a centrifugal compressor with a 5:1 pressure ratio. The power turbine 16 is provided with variable nozzle guide vanes 14. The power turbine 16 drives an output shaft 18, which may, for example, be connected to a generator for electric power (not shown).

After passing through the power turbine 16, the exhaust gas enters a duct 20 which leads to the recuperator 2 and also to a by-pass duct 22. Exhaust gas which enters the recuperator 2 is cooled, transferring energy to the compressed air passing through the recuperator 2 on its way to the combustor 8 prior to combustion. The exhaust gas from the recuperator 2 passes into an outlet duct 24 leading to a heat utilization system 27. Exhaust gas which passes from the duct 20 into by-pass duct 22 passes directly to the heat utilization system.

A variable valve 26 is provided in the bypass duct 22 and a variable valve 28 is provided in the outlet duct 24.

In operation, the heat output and shaft power output of the gas turbine unit 1 can both be varied by varying the volume flow rate of fuel to the combustor 8. If the fuel flow rate is changed, the variable nozzle guide vanes 14 are rotated to vary the inlet area of the power turbine 16, so that an appropriate compressor running line is selected.

Where there is a requirement to vary the heat output independently of the shaft power, for instance to account for variations in instantaneous heat demand throughout a twenty four hour heating cycle, the degree of opening of the variable valves 26, 28 can be varied.

If the variable valve 26 is completely closed and the variable valve 28 is completely open, all the exhaust gas leaving the power turbine 16 passes directly into the recuperator 2 and energy from the exhaust gas passes via the recuperator 2 into the compressed air entering the combustor 8. Since the air entering the combustor 8 is then preheated, less fuel is required to be burnt in the combustor to provide the same shaft power from the gas turbine generator 10.

If, however, the variable valve 26 is fully opened and the variable valve 28 is fully closed all the gas leaving the power turbine enters the by-pass duct 22 and passes directly to the heat utilization system 27.

Since the gas leaving the power turbine 16 does not pass through the recuperator 2 in this arrangement, it is not cooled and hence the energy supply to the heat utilization system 27 is greater than in the first example. However, since the air entering the combustor 8 is not preheated, more fuel is required to be burnt in the combustor 8 to provide the same shaft power.

By varying the relative opening of the variable valve 28 and the variable valve 26 the proportion of shaft power to heat can easily be varied.

In a system as described above, the ratio of heat output to shaft power with all the exhaust gas passing through the recuperator 2 may be in the range 1.5:1 to 2:1. If all of the exhaust gas is directed through the by-pass duct 22, this ratio may rise to a value in the range 3.5:1 to 4:1.

Figure 2 shows a further embodiment of a combined heat and power installation which includes a number of refinements over the basic combined heat and power installation shown in Figure 1. The layout of the gas turbine unit 1 of this embodiment is similar to that shown in Figure 1. However, an afterburner 30 is provided in the by-pass duct 22 downstream of the variable valve 26. In addition, the heat utilization system comprises two distinct heat demands 32 and 34.

The exhaust gas outlet 24 from the recuperator 2 in this embodiment is joined to the by-pass duct 22 via a connecting duct 36. Variable valves 38 and 40 are provided downstream of the duct 36 on the outlet duct 24 and the by-pass duct 22, respectively. A transfer valve 42 is provided in the connecting duct 36.

A further feature of the combined heat and power installation shown in Figure 2, is the provision of a power turbine by-pass across the power turbine 16. The power turbine by-pass 44 connects the inlet duct 46 of the power turbine 16 to the duct 20 which connects the gas output from the power turbine 16 to the recuperator 2 and the by-pass 22. A variable valve 48 is provided in the power turbine by-pass 44 and a variable valve 50 is provided in the outlet duct 20.

The operation of the combined heat and power installation of Figure 2 is similar to the operation of the first embodiment of the invention described above.

Thus, the heat available for the heat demands 32 and 34 can be adjusted by altering the by-pass ratio between the recuperator 2 and the by-pass duct 22. However, in the second embodiment, the heat output from the gas turbine unit 1 can be further boosted and the two separate heat demands 32 and 34 can be satisfied independently.

The further boosting of the heat output can be achieved in two ways.

Firstly, the variable valves 48 and 50 can be adjusted so that at least some gas from the gas generator turbine 10 bypasses the power turbine 16 along the power turbine by-pass 44 and is fed directly into the exhaust stream. Shaft power output is reduced in this way, and the heat output is boosted.

Secondly, the gas temperature in the bypass duct 22 can be boosted by burning fuel in the afterburner 30.

To increase the flexibility of the combined heat and power installation, provision is made for supplying two distinct heat demands 32 and 34, as mentioned above. For example, demand 32 may be for low grade heat to heat a factory building and demand 34 may be for high grade heat to generate steam for operating industrial processes in the factory.

The required heat supplies for the above example can be achieved by appropriate adjustment of the variable valves 38 and 40 and the transfer valve 42.

Thus, relatively cooler gas from the recuperator 2 can supply the low grade demand 32 and relatively hotter gas from the bypass duct 22 can supply the high grade demand 34.

Appropriate control systems may be provided for controlling the gas generator, the power turbine, the valves 26 and 28 governing the flow through the recuperator 2 and the by-pass duct 22, the power turbine by-pass valves 48 and 50, the fuel system of the after burner 30, and the valves 38, 40 and 42 distributing heat between the heat demands 32 and 34.

These control systems may be responsive to temperature and pressure sensors installed in the various ducts By controlling the above elements the temperature and flow rate of gas supplied to the heat demands 32 and 34 can be controlled with a high degree of flexibility.

It will be appreciated that, depending on the system requirements, the afterburner, the power turbine by-pass and/or the provision of two exhaust outlets of different grades of heat may be omitted.

Claims

1. A combined heat and power installation comprising a gas turbine providing shaft power, exhaust gases from the gas turbine being directed to a heat utilisation system the gas turbine including a recuperator and a by-pass duct which by-passes the recuperator, diverter means being provided for varying the relative flow of the exhaust gases to the heat utilisation system through the recuperator and through the by-pass duct.

2. A combined heat and power installation as claimed in claim 1 in which the power turbine is provided with variable nozzle guide vanes.

3. A combined heat and power installation as claimed in claim 1 or claim 2 in which the diverter means comprises a continuously variable valve in the by-pass duct.

4. A combined heat and power installation as claimed in any one of the-preceding claims, in which the diverter means comprises a variable valve in the exhaust flow path through the recuperator.

5. A combined heat and power installation as claimed in any one of the preceding claims in which an afterburner is provided in the by-pass duct.

6. A combined heat and power installation as claimed in any one of the preceding claims in which the heat utilization system comprises two distinct heat demands.

7. A combined heat and power installation as claimed in claim 6 in which the heat utilization system comprises a relatively low temperature demand and a relatively high temperature demand.

8. A combined heat and power installation as claimed in claim 6 or claim 7 in which valves are provided for distributing the lower temperature gas from the recuperator and the higher temperature gas from the by-bass duct between the two heat demands.

9. A combined heat and power installation as claimed in claim 8 in which control means is provided to control the operation of the valve means.

10. A combined heat and power installation as claimed in any one of the preceding claims in which a turbine by-pass is provided across the power turbine of the gas turbine.

11. A combined heat and power installation substantially as described herein, with reference to and as shown in Figure 1 or Figure 2 of the accompanying drawings.