Power plants – Pressure fluid source and motor – Pneumatic motor with gas supply or removal device
Reissue Patent
2000-06-30
2002-03-26
Nguyen, Hoang (Department: 3748)
Power plants
Pressure fluid source and motor
Pneumatic motor with gas supply or removal device
C060S595000, C417S381000
Reissue Patent
active
RE037603
ABSTRACT:
This invention relates to gas compressors for supplying compressed gas and in particular to compressors for supplying compressed air or other gas turbine plants for the generation of electricity.
Compressors for producing hot compressed gas, such as air for burning with fuel in the combustion chamber of a gas turbine are well known. The gas produced by the compressor is heated as it is compressed by the adiabatic nature of the compression cycle. Because the gas is heated during compression, more energy is required to achieve the desired compression than if the temperature of the gas during compression was maintained constant, i.e. if the gas was compressed isothermally. It is also generally inefficient to use the mechanical energy of the compressor to heat the body of gas being compressed.
One example of a known apparatus designed to compress gas more efficiently is the hydraulic gas compressor in which gas is compressed in a downward moving column of liquid. The gas which is in the form of bubbles is cooled by the liquid during compression. The gas is then separated from the liquid at the bottom of the column where it is conveniently stored providing a supply of cool compressed gas which may subsequently be used for power generation.
A heat engine whose operation is based on the Carnot cycle is described in U.S. Pat. No. 3,608,311. Isothermal compression of the working fluid in the cycle is achieved by spraying a liquid into the chamber containing the working fluid so that the temperature of the gas is maintained constant during compression. However, this apparatus relates to heat engines and consists of a closed cycle heat engine in which each volume of working fluid remains permanently within a respective chamber. It is not concerned with gas compressors, which supply compressed gas.
In conventional gas turbine plants the exhaust gas from the gas turbine is generally much hotter than the ambient temperature of the surrounding atmosphere so that the excess heat of the exhaust gas may be wasted unless it can be converted back into useful energy for example to generate electricity. In one particular type of gas turbine plant, the combined-cycle gas turbine and steam plant (CCGT), the excess heat in the exhaust gas from the gas turbine is converted into steam to drive a second turbine. Although the CCGT is efficient, it does require additional plant such as a heat recovery steam generator and an associated steam turbine.
According to one aspect of the present invention there is provided a gas compressor comprising a chamber to contain gas to be compressed, a piston in the chamber and means to drive the piston into the chamber to compress the gas, means to form a spray of liquid in the chamber to cool the gas on compression therein, and valve means to allow compressed gas to be drawn from the chamber, wherein said means to drive the piston comprises means to deliver driving energy stored in a fluid directly to the piston.
Thus, the invention provides a useful source of compressed gas, in which the gas temperature is controlled by the liquid spray. The heat of compression is transferred to the droplets in the spray so that during compression, the gas temperature may be controlled to remain constant or to decrease. If the temperature of the gas is held constant, the energy required for compression is much less than it is if the temperature is allowed to rise. Advantageously, the piston is driven directly by the energy stored in a fluid, which may be the energy stored in a compressed gas or a combustible fuel/air mixture or the potential energy of a liquid. This enables the isothermal compression to be driven directly from a very high temperature heat source, while heat in the system is rejected at the lowest temperatures in the cycle. The piston enables large energies released from the fluid to be very efficiently converted into compression energy of the gas, and provides the opportunity of temporarily storing the energy released from the fluid as kinetic energy in such a way that large energies can be transferred to the piston, and therefore large volumes of gas can be compressed, but the rate at which the piston moves into the chamber can be controlled by the inertia of the piston so that the compression process is as near isothermal as possible. The invention also provides the opportunity of recovering excess heat released from the fluid to preheat the isothermally compressed gas. Furthermore, because the piston is driven directly, more complex mechanical arrangements involving rotating parts such as crankshafts are not required.
In a preferred embodiment, the compressor comprises kinetic energy storage means coupled to the piston and to which sufficient kinetic energy can be imparted to enable the piston to compress the gas. Advantageously, the kinetic energy storage means may comprise a mass arranged to move in phase with the piston, and in a preferred embodiment the mass may be provided by the piston itself. Advantageously, the kinetic energy storage means may have a large inertia to control the rate of compression to allow sufficient time for the heat of compression to be transferred to the spray so that the compression is isothermal. The kinetic energy storage means may comprise a rotatably mounted mass, e.g. a fly wheel, which is coupled to the piston so that rotational energy of the mass is converted into compression energy of the gas by the piston. The rotatable mass may be arranged to reverse direction with the piston or to rotate in one direction only, independently of the direction of movement of the piston. In the former case, the piston may be mounted on a rotatable disc, movement of the piston into the chamber being along an arc produced by rotation of the disc or along a linear path, with the piston being allowed to swivel relative to the disc.
Alternatively, a rack may be connected to the piston, the rack being arranged to drive a pinion, which either provides the rotating mass or to which a rotating mass is connected. In the latter case, the piston may be coupled to the rotating mass via a crankshaft. Advantageously, the compressor may include coupling means coupled to the piston to enable power to be drawn from or supplied to the piston directly. An output drive from the piston may be used to drive, for example, valves and liquid spray injection pumps associated with the compressor and mechanical compressors, supplying hot compressed gas to drive the compressor. Power from the piston may be extracted via any suitable mechanical coupling.
In a preferred embodiment, the compressor comprises means to impart kinetic energy to the kinetic energy storage means. If the kinetic energy storage means is provided by the mass of the piston, then the means to impart may be arranged to impart kinetic energy directly to the piston. The compressor may comprise means to convert the kinetic energy used to impart movement to the piston in one direction into kinetic energy to impart movemement to the piston in the other direction. The means to convert enables, for example, kinetic energy to be imparted to the kinetic energy storage means such that the piston moves out of the compression chamber and subsequently such that the piston moves into the compression chamber to compress the gas. Alternatively, the means to convert may be used to convert some of the kinetic energy used to drive the piston into the chamber to compress the gas, to drive the piston in the other direction out of the chamber. The means to convert may include means to convert the kinetic energy used to impart movement to the piston into potential energy. For example, the kinetic energy may be converted into potential energy by arranging a mass to displace vertically on movement of the piston. This could be a separate mass or the mass could be provided by the piston itself.
In a preferred embodiment, the compressor comprises a second chamber and a second piston, each arranged such that on movement of the piston into the chamber, the second piston moves out of the second chamber. The first and second pistons may
National Power PLC
Nguyen Hoang
LandOfFree
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