Power plants – Motive fluid energized by externally applied heat – Noncommunicating heat transferring motive fluid system
Patent
1995-05-16
1997-05-13
Lazarus, Ira S.
Power plants
Motive fluid energized by externally applied heat
Noncommunicating heat transferring motive fluid system
60682, 60719, F01K 2304
Patent
active
056281919
DESCRIPTION:
BRIEF SUMMARY
The invention is directed to a natural gas expansion plant provided to expand natural gas supplied at high pressure and to be fed at a lower pressure into a distribution supply network leading to the end users.
In long-distance pipelines, natural gas is subjected to a relatively high pressure of about 55 bar, whereas a lower pressure, e.g. 9 bar, prevails in the end user network. At the junction from the long-distance pipeline network to the distribution supply network, natural gas expansion plants are required for reducing the pressure. During the pressure reduction process, energy is released which can be used to generate electricity. In natural gas expansion plants, it is known to use piston expansion engines, operating as volumetric displacement engines, for driving a generator. In further known expansion plants, expansion turbines are used. In these plants, oil is used for lubricating the bearings. Since the natural gas will cool down during expansion, the natural gas is heated up prior to expansion to such an extent that the temperature will not cool down to a value below the critical range of 0.degree. C. This requirement provides that the plant is insensitive to humidity contained in the natural gas. The heating process requires the provision of thermal energy. Normally, this thermal energy is generated by heating boiler plants.
A gas expansion plant known from EP-A-0 004 398 comprises a power plant consisting of a motor and a power generator. The waste heat of the motor is supplied to a heat exchanger for preheating the gas flowing to an expansion turbine. The amount of heat transmitted to the gas cannot be changed without abandoning the full-load operation of the motor.
It is an object of the invention to provide a natural gas expansion plant which, irrespective of the present need for expanded natural gas, always operates with high efficiency and, respectively, good utilization of energy.
According to the invention, the above object is solved by the features indicated in claim 1.
According to the invention, the energy supplied to the heat exchanger connected upstream of the turbo generator is generated by at least one block-type thermal power station comprising a gas-fired internal combustion engine and a generator for electric power generation. For preheating the natural gas, the waste heat of the block-type thermal power station is used which is driven in full-load operation. A block-type thermal power station has its highest efficiency in full-load operation, whereas the efficiency is considerably reduced in part-load operation. According to the invention, the block-type thermal power station is either run in full-load operation or is switched off, as required by the natural gas network. Thus, operation is always performed with high efficiency, with the generator of the block-type thermal power station generating electric energy which can be fed into the power supply network. Also on cold winter days, when the demand for natural gas is high, the block-type thermal power stations will produce considerable electric power, which contributes to meet the likewise increased electric power requirement.
According to the invention, the heat supplied to the natural gas prior to expansion of the gas is generated by respective limited, relatively small units, i.e. the block-type thermal power stations, which also release, in form of electric power, a part of the energy received by them. This generation of electric power is obtained as a sort of by-product, but is appreciated because it occurs in situations when the power requirement is particularly high.
Preferably, the increase in temperature of the natural gas caused by the heat exchangers will raise the gas temperature to a temperature below 100.degree. C., thus allowing the use of gas motors--wherein the cooling water is below 100.degree. C.--in the block-type thermal power stations. On the other hand, due to the enthalpy/entropy diagram for natural gas, the above low preheating temperatures allow only pressure ratios of up to about 2-3,5 to be reduc
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Canders Wolf-Ruediger
Kueck Elmar
Siefen Heinz
Energieversorgung Leverkusen GmbH
Lam Nhat-Hang H.
Lazarus Ira S.
Piller GmbH
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