WO1997004228A1

WO1997004228A1 - A thermodynamic conversion system

Info

Publication number: WO1997004228A1
Application number: PCT/NO1996/000183
Authority: WO
Inventors: John Lee Cotton; Ivar Helge Skoe
Original assignee: Kvaerner Energy A.S
Priority date: 1995-07-17
Filing date: 1996-07-16
Publication date: 1997-02-06
Also published as: NO952827D0; AU6633796A; NO300286B1; NO952827L; RU2158835C2

Abstract

A combined plant including a gas turbine (1) and an air bottoming gas turbine aggregate (2), which aggregate includes air compressors (8) and a drive connected turbine (9), where gas turbine outlet gas is in heat exchange with compressed air from the compressor. The heat exchanger (3) is dimensioned to take two gas flows having differing heat capacities resulting in maximum efficiency at part load conditions.

Description

A THERMODYNAMIC CONVERSION SYSTEM

The present invention relates to thermodynamic conversion apparatus.

5

US-PS 4.751.814 discloses an air cycle thermodynamic conversion system including a gas turbine providing a flow of heated gases from the gas turbine exhaust; at least one air compressor for compressing ambient air; a heat exchanger io including means for transferring heat from said flow of heated gas turbine exhaust gases to a compressed air from said air compressor to produce a heated compressed air; at least one air turbine connected to the heat exchanger responsive to said heated compressed air to drive said at

'5 least one compressor; said heated compressed air including an excess of energy beyond that required by said at least one air turbine to drive said at least one air compressor; and, means for delivering said excess of energy to a using process. By establishing the heated exhaust gas and the

20 compressed air flow in the heat exchanger such that they both have about equal heat capacities, a minimum temperature gradient is maintained between them. The use of compressed air provides an air bottoming cycle.

25 According to US-PS 4.751.814 there shall be a minimum temperature gradient across the heat exchanger and the two streams shall both have about equal heat capacities. This is to achieve maximum power.

J" Shaft power is extracted from both the parent gas turbine and the air bottoming cycle gas tubine. It is in the nature of the air bottoming cycle that the shaft power available from the air bottoming cycle gas turbine is significantly less than that from the parent gas turbine, approximately one

55 third, when the parent gas turbine is running at full power. At this condition, the mass flow and temperature of the exhaust from the parent gas turbine is known, and the air bottoming cycle gas turbine configuration and cycle para¬ meters can be chosen to give maximum air bottoming cycle gas turbine power and thus maximum overall plant power and efficiency.

In many possible applications of the air bottoming cycle, the combined plant will not be running continuously at full power. This is relevant where the plant is supplying a local grid where the load varies, for example on an offshore oil and gas production unit. In this type of application maximum power is only rarely required and for short periods. Under these circumstances, maximum efficiency at maximum power is not of prime importance.

We have now discovered that at part load conditions, where the overall power level, i.e. the combined parent gass turbine and air bottoming cycle gas turbine output power, is established by the demand, the maximum overall efficiency of the combined plant is achieved with the two gas streams having unequal heat capacities.

Thus, it is an object of the invention to provide means for achieving said maximum overall efficiency (shaft efficiency) at part loads.

Briefly stated, the present invention provides a thermodyn¬ amic conversion system including a gas turbine providing a flow of heated gases from the gas turbine exhaust, at least one air compressor for compressing ambient air; a heat exchanger including means for transferring heat from said flow of heated gas turbine exhaust gases to a compressed air from said air compressor to produce a heated compressed air; at least one air turbine connected to the heat exchanger responsive to said heated compressed air to drive said at least one compressor; said heated compressed air including an excess of energy beyond that required by said at least one air turbine to drive said at least one air compressor; and means for delivering said excess of energy to a using process; said heat exchanger having first conduits for the flow of turbine exhaust gas and second conduits for the flow of said compressed air, said first and second conduits being dimensioned to allow for flows with heat capacities differing substantially from each other.

The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction will the accompanying drawings, in which like reference numerals designate the same elements.

Figure 1 is a schematic diagram of a thermodynamic conversion system wherein the invention may be used.

Figure 2 depicts a diagram showing the shaft efficiency in Sέ related to the gas turbine rating in .

Referring to figure 1, there is shown a thermodynamic conversion system according to the prior art and including a parent gas turbine 1, an air bottoming cycle gas turbine 2 and a counterflow heat exchanger 3. The parent gas turbine comprises a compressor 4, a combustion chamber 5, and a turbine 6. The air bottoming cycle gas turbine 2 comprises a series of through intercoolers 7 connected air compressors 8 and an air turbine 9. The compressed air from the compressors 8 flows to the heat exchanger 3 and from there to the air turbine 9. Exhaust gases from the gas turbine 6 flow to the heat exchanger 3 for counterflow heat exchange with the compressed air from the air compressors 8. This known thermo¬ dynamic conversion apparatus is controlled by controlling the heat exchanger, as disclosed in US-PS 4.751.814, the content of which is hereby enclosed by reference.

Figure 2 depicts the overall efficiency related to the gas turbine rating. Figure 2 shows the effect on overall plant efficiency (shaft efficiency) of two different flows through the air bottoming cycle gas turbine compared to the parent gas turbine. These differences are approximately +1056(1) and -1056(2) of parent gas turbine flow at rated parent gas turbine power. Also plotted is the shaft efficiency of the parent gas turbine alone, i.e. without an air bottoming cycle gas turbine. It can clearly be seen that one flow (1) gives a higher overall efficiency or near full power, while the other (2) gives a higher overall efficiency at lower powers.

The cost of fuel and associated taxes is a major part of the overall costs of running a gas turbine plant to produce shaft power. This fuel cost will probably increase over time. It is thus of significant importance to an operator of such plant that the equipment can be chosen and configured to achieve an optimum for that operator's normal use.

Claims

C L I M S

1.

A method for achieving maximum overall efficiency in a thermodynamic conversion system including a gas turbine providing a flow of heated gases from the gas turbine exhaust; at least one air compressor for compressing ambient air; a heat exchanger including means for transferring heat from said flow of heated gas turbine exhaust gases to a compressed air from said air compressor to produce a heated compressed air; at least one air turbine connected to the heat exchanger responsive to said heated compressed air to drive said at least one compressor; said heated compressed air incuding an excess of energy beyond that required by said at least one air turbine to drive said at least one air compressor; and means for delivering said excess of energy to a using process, characterized in that the streams of turbine exhaust gases and compressed air from at least one air compressor have substantially differing heat capacities.

2.

A method according to claim 1, characterized in that relative different mass flows are directed through said heat ex¬ changer.

3.

A thermodynamic conversion system including a gas turbine providing a flow of heated gases from the gas turbine exhaust; at least one air compressor for compressing ambient air; a heat exchanger including means for transferring heat from said flow of heated gas turbine exhaust gases to a compressed air from said air compressor to produce a heated compressed air; at least one air turbine connected to the heat exchanger responsive to said heated compressed air to drive said at least one compressor, said heated compressed air including an excess of energy beyond that required by said at least one air turbine to drive said at least one air compressor; and means for delivering said excess of energy to a using process; c h a r a c t e r i z e d b y said heat exchanger having first conduits for the flow of turbine exhaust gas and second conduits for the flow of said compressed air, said first and second conduits being dimensioned to allow for flows with heat capacities differing substantially from each other.