EP0813650B1

EP0813650B1 - Power plant

Info

Publication number: EP0813650B1
Application number: EP96906961A
Authority: EP
Inventors: Rolf Kvamsdal
Original assignee: Kvaerner ASA
Current assignee: Kvaerner ASA
Priority date: 1995-03-10
Filing date: 1996-03-07
Publication date: 1998-10-21
Anticipated expiration: 2016-03-07
Also published as: DE69600843D1; NO300235B1; WO1996028650A1; DK0813650T3; EP0813650A1; NO950916D0; DE69600843T2; ATE172517T1; JPH11502580A; NO950916L

Abstract

A device for a power plant with a free piston device (1) which supplies gas for the operation of a turbine (20), and which has two pistons (3, 4) which via a synchronization device are moved in anti-phase. The exhaust gas from the turbine can be passed to a heat exchanger (38, 52), which is arranged for heating of either compressed air or water for the production of steam, in that the turbine device can comprise at least one additional turbine, which is driven by this air or steam. At least two separately driven compressors which are connected in series (11, 12, 13), between which an intermediate cooler (17, 18) is provided, supply compressed air to the cylinder's (2) air intake (6) and possibly to the heat exchanger. Between at least two compressors a bypass valve can be provided. Furthermore, the synchronization device can comprise an electronic device and be arranged to provide a phase shift between them.

Description

The invention concerns a device for power plants with a gas generator which supplies gas for the operation of a turbine device which has at least one first turbine, and a compressor device which has at least one first compressor which supplies air to the gas generator, wherein the gas generator is composed of a diesel free piston device with at least one cylinder, in which there are provided two pistons which together with the cylinder define respective cylinder end chambers, and which are controlled by a synchronization device and arranged for substantially synchronous forward and backward movement in anti-phase to each other in the cylinder.

Piston gas generators of the above-mentioned type can supply gas with a very high energy content, thus permitting the power plant to run with high thermal efficiency.

The development of new turbine engines such as gas turbines which are operated by the exhaust gases from the gas generator, and possibly turbo-compressors which supply compressed air to the free piston device, is extremely expensive. In order to prevent units of the above-mentioned type from becoming too expensive, designers are therefore obliged to employ turbine engines which are already on the market, but which only in exceptional cases are of a size and design which makes them wholly suitable for the requirement concerned. Even though the free piston device can be designed to suit this requirement, a power plant which is constructed from these components seldom has the efficiency which could have been achieved if all the plant's components had been fully adapted to suit one another and the requirement.

In addition the residual heat from the gas turbines is not fully exploited for a further increase in the efficiency.

Moreover the relative movement of the pistons of present gas generators is controlled by a substantially mechanical device which connects the pistons to each other and controls their anti-phase movement in such a manner that positions of one piston in relation to the cylinder at all times correspond to respective positions of the second piston in relation to the cylinder. Since opening and closing of the inlet and outlet ports in the cylinder are controlled by the respective pistons, it is thus only possible to achieve a high degree of efficiency for the gas generator in one specific, desired operating condition of the gas generator. In other operating conditions, e.g. with different piston frequencies, gas generator loads etc., the efficiency is reduced.

The object of the invention is to provide a device of the type mentioned in the introduction which permits optimum efficiency of the power plant.

The characteristics of the device according to the invention are presented in the characteristic features indicated in the claim.

The invention will now be described in more detail with reference to the drawing in which figs, 1 and 2 are schematic block diagrams which illustrate components of two respective embodiments of the device according to the invention.

For the sake of clarity, the construction and mode of operation of the known per se free piston gas generator which is illustrated in figs. 1 and 2 will be described first.

This

gas generator

31 and 71 respectively comprises a cylinder 2, in which two pistons 3,4 are freely movable towards and away from each other, being controlled by a synchronization device (not shown) which forces them to move in anti-phase to each other. Between them the pistons define a combustion chamber 5 which can be supplied with compressed air via an inlet manifold or air intake 6, which is provided around the cylinder 2 and communicates with one or more inlet ports (not shown) therein. Fuel can be supplied to the combustion chamber 5 via a fuel nozzle 7 as indicated by the arrow F. Exhaust is removed from the combustion chamber 5 via an outlet manifold 8 which is provided around the cylinder 2, and which communicates with one or more outlet ports (not shown) therein. One piston 3 is arranged to open or close the inlet port, and the other piston 4 is arranged to open or close the outlet port, this opening or closing occurring when the pistons pass the ports. Furthermore each piston and the respective, adjacent end bottom of the cylinder define closed

end chambers

9,10, where the air which is enclosed therein is progressively compressed when the pistons are moved away from each other, with the result that this air attempts to an increasing degree to force the pistons towards each other.

During a start-up of the gas generator air is first supplied to the cylinder 2 via the inlet manifold 6, whereby the pistons are brought into a position in which they are at the greatest possible distance apart, whereupon by means of a start device (not shown), the pistons 3,4 are forcefully moved towards each other. The combustion compartment's connection with the

manifolds

6,8 is thereby broken and the air in the combustion chamber 5 is compressed. Fuel is then introduced into the combustion chamber 5 via the fuel nozzle 7. When the fuel/air mixture in the combustion chamber 5 has been compressed to such an extent that the temperature of this mixture has reached the self-ignition temperature, an ignition of the mixture occurs. The thereby increased pressure of the combusted mixture in the combustion chamber 5 forces the pistons 3,4 away from each other, thus causing the outlet port to be opened and exhaust to be released. After the inlet port is also opened, new compressed air is supplied to the combustion compartment, whereby the remainder of the exhaust is forced out of the cylinder 2. By means of this piston movement the air in the closed end chambers is compressed to an increasing degree, thus causing the pistons to be retarded. After the pistons have been brought to a standstill, they are once again moved towards each other due to the force which is exerted on the pistons by the compressed air in the enclosed end chambers, whereupon the gas generator's cycle is automatically repeated continuously. By adapting the mass of the moved components and the fluid forces which are exerted on the pistons to each other, the continued operation of the gas generator is ensured and the pistons' stroke frequency is determined.

According to the invention the synchronization device can comprise an electronic device which via a regulating device (not shown) controls the air pressure individually in the

end chambers

9,10. In addition to ensuring by very simple means the accurate relative synchronization of the pistons' anti-phase movement, by means of a suitable design, an equally very simple variation can also be obtained of the relative phase shift of the pistons 3,4 during their movement, dependent on the gas generator's operating conditions, thus increasing its efficiency. The design of such an electronic device and regulating device will be obvious to a person skilled in the art when the object of these is as described here.

As indicated in fig. 1 which illustrates a first embodiment of a device according to the invention, precompressed air is supplied to the inlet manifold 6 of the gas generator 31 from a first compressor 32. This compressor 32 is driven by a first gas turbine 33 via a drive shaft 37. The gas turbine 33 drives an electrical generator 40. The gas which flows out from the turbine 33 has a pressure which approximately corresponds to the pressure of the ambient air. The gas, however, has a temperature which is much greater than the temperature of the ambient air. In order to exploit the residual heat which thus exists in the gas, the gas is passed to a heat exchanger 38 for heating of compressed air from a second, third and

fourth compressors

34, 35 and 36 respectively, this air being passed on to a second turbine 39. In its turn this second turbine 39 drives a power generator 41 which can supply power to a consumer. Via a drive shaft 45 the second turbine 39 also drives the compressors 34 - 36. Between the second and

third compressors

34 and 35 respectively and between the third and

fourth compressors

35 and 36 respectively there is connected a first and a second

intermediate cooler

42 and 43 respectively, which are supplied with a suitable coolant, as indicated by the arrows A, for cooling of the air which is supplied from the compressor located upstream.

Fig. 2 illustrates a second embodiment of a device according to the invention, this being similar to the device which is illustrated in fig. 1. Here hot exhaust gases are supplied from a gas generator 71. In the device which is illustrated in fig. 2, however, between a high pressure turbine 50 which drives a power generator 51, and a heat exchanger 52, there is connected a low pressure turbine 53, which drives a power generator 54 which in turn can be supplied to a power consumer. Instead of the

turbines

51, 53 being arranged to supply energy to such a consumer, e.g. an electric motor for operation of a ship's propeller, they can of course be arranged to operate this in a directly mechanical fashion, possibly via an exchanger. The heat exchanger 52 is supplied with compressed air from a fifth and

sixth compressor

57 and 58 respectively either directly or via a seventh compressor 59. The seventh compressor 59 can be connected or disconnected by means of a bypass valve 56 and driven by a motor 68.

The fifth, sixth and

seventh compressors

57, 58 and 59 respectively are driven by

respective motors

65, 66 and 68 respectively.

The compressed air which is supplied to the fifth and

sixth compressors

57 and 58 respectively and possibly the seventh compressor 59 is heated by the heat exchanger 52 and supplied to a turbine 63, which in turn drives a power generator 64.

An eighth compressor 60 is connected in series to the fifth and

sixth compressors

57 and 58 respectively, these three

compressors

57, 58, 60 together supplying compressed inlet air to the gas generator. The eighth compressor 60 is driven by a motor 67 with variable revolutions per minute.

Between the fifth and the

sixth compressors

57 and 58 respectively and between the sixth and the

eighth compressors

58 and 60 respectively there are provided

intermediate coolers

61 and 62 respectively.

The inlet pipe for the seventh compressor 59 is connected to the downstream side of the intermediate cooler 62.

The speed of revolution of each of the motors can be varied. The compressors' operating parameters can thereby be varied, thus enabling the compressors to be adapted to each other and to the gas generator, and thereby increasing the total efficiency. The aim of the intermediate coolers is to achieve an isothermal compression, thus further increasing the efficiency.

Instead of the gas turbines having separate output shafts, they can have one joint output shaft (not shown), which is driven by the turbines via, e.g., one or more exchangers, and which in turn drive one or more power generators. If separate output shafts are provided, however, the turbines' revolutions per minute can advantageously be varied in relation to each other, thus enabling the efficiency of each turbine and thereby the total efficiency of the plant to be more easily optimized.

Thus a great number of combinations of compressors with intermediate cooling are possible, especially when the residual heat in the exhaust gas from the turbine(s) is utilized. It can also be shown to be expedient for the compression to be carried out, e.g., partially by means of compressors of different types such as piston compressors.

The power plant according to the invention exploits the ability of the diesel process to handle high pressure and temperatures and the ability of the turbine engines to handle large volumes. According to the invention this exploitation is performed not only in connection with the expansion of the gases, but also during the compression, the first compression, e.g., being carried out by means of turbo-compressors.

Instead of exploiting the heat energy in the outlet gases from the turbine(s) for heating air from compressors, they can be used for heating a steam boiler (not shown). Steam from this boiler can be supplied to a steam turbine which in turn can drive a power generator.

It is stated above that a bypass valve is provided between the two compressors which are located immediately upstream in relation to the heat exchanger. It should be understood, however, that bypass valves can also be provided between other compressors of the device according to the invention.

By means of the device according to the invention, main components of a power plant of the type mentioned in the introduction can be adapted to the operating conditions of the gas generator during the operation of the plant, thus providing optimum total efficiency for the plant.

Claims

A device for power plants with a gas generator (31;71) which supplies gas for the operation of a turbine device (33,39;50;63) which has at least one first turbine (33;50), and a compressor device which has at least one first compressor (32;57,58,60) which supplies air to the gas generator (31;71), wherein the gas generator (31;71) is composed of a diesel free piston device with at least one cylinder (2), in which there are provided two pistons (3,4) which together with the cylinder (2) define respective cylinder end chambers (9,10), and which are controlled by a synchronization device and arranged for substantially synchronous forward and backward movement in anti-phase to each other in the cylinder (2),
characterized in that
the first compressor or each of the first compressors (32;57,58,60) is driven by a separate driving motor (65,66,67) whose rotary speed may be varied, that the first compressor (58) andior at least one additional compressor (34,35,36;59) of the compressor device supply air as the only driving fluid to at least one additional turbine (39;63) of the turbine device via a heat exchanger (38;52) for heating of this air from the compressor (34,35,36;57,58,59) by means of the exhaust from the gas generator (37;71).
A device according to claim 1,
characterized in that at least the compressors (34,35,36;57,58;59) which supply air for the operation of the additional turbine (39;63) are turbocompressors.
A device according to claim 1 or 2, where the synchronization device comprises an electronic device,
characterized in that the electronic device is arranged to control the air pressure in the end chambers via a regulating device.