Power plants – Utilizing natural heat – Geothermal
Patent
1985-09-24
1987-12-15
Ostrager, Allen M.
Power plants
Utilizing natural heat
Geothermal
60715, F01K 700
Patent
active
047123800
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the utilization of thermal energy.
Over the past ten years considerable research has been carried out with a view to making use of thermal energy available from geological sources. It will be understood that many of these sources provide an inlet temperature/pressure which is too low to ensure satisfactory operation of most conventional power generating machines such as turbines. Moreover, even if these basic parameters are suitable for use in a turbine, the working fluid is frequently contaminated so that deposits are formed with resultant reduced efficiency and actual damage to the turbines.
With a view to overcoming the basic problems of relatively low grade heat, proposals have been put forward, for example in U.S. Pat. No. 3,751,653 and U.K. published Application No. 2114671, in which relatively low grade heat is utilized for the production of power with the aid of one or more helical screw expanders. Such expanders, initially developed by Lysholm, have the advantage that they can tolerate working fluids which are liable to cause deposits, because close tolerances are not critical to successful operation and deposits from the working fluid may even be beneficial. However, the use of geothermal water as proposed in the U.S. specification has the substantial disadvantage that the properties of water and steam necessitate the use of a very large machine in order to produce the required power. The specification of the published United Kingdom application is primarily concerned with the use of such machines, but employing in place of geothermal water a working fluid which has properties more suited to use in relatively small helical screw expanders.
In the cycle proposed in U.K. patent application No. 2114671, the inlet temperature of the working fluid is preferably fairly low, the geothermally-heated water being at a temperature of the order of 100.degree. C. Probably the greatest benefits will arise from use of geothermally heated water at temperatures of the order of 120.degree. C. At higher temperatures the efficiency advantage of the cycle disclosed in the United Kingdom published specification diminishes but is not eliminated because conventional supercritical Rankine cycles become more attractive in the matching of the boiler heating characteristics to the heat source at higher temperatures. Even at quite high temperatures, of the order of 300.degree. C., the advantage remains.
The general objective of the present invention is further to modify the prior proposals with a view to rendering possible more efficient use of geothermal and other low grade sources which enable higher inlet temperatures to be used than in hitherto proposed systems.
According to the present invention there is provided a method of utilizing thermal energy comprising the steps of heating a working fluid by pumping through a hot dry rock or other low grade heat source, supplying the heat from the working fluid to a more volatile, second, working fluid which passes through a trilateral cycle comprising substantially adiabatically pressurizing the said second working fluid, substantially adiabatically expanding the hot pressurized second working fluid by flashing in a helical screw expander or other expansion machine capable of operating effectively with wet working fluid and of progressively drying said fluid during expansion, passing the exhaust second working fluid through a turbine and condensing the second working fluid exhausted from the turbine.
The trilateral cycle referred to has been described and claimed in our co-pending published patent application No. 2114671. An important distinguishing aspect of the present invention as broadly defined is that the working fluid is chosen such that the expansion from saturated liquid to saturated vapour is carried out in a screw expander with or without preflashing and that further expansion of the saturated vapour is then carried out in a turbine of conventional design such as is used in Rankine systems. The second working fluid exhausted from the helical
REFERENCES:
patent: 3751673 (1973-08-01), Sprankle
patent: 3817038 (1974-06-01), Paull et al.
patent: 3977818 (1976-08-01), Sprankle
patent: 4063417 (1977-12-01), Shields
patent: 4201060 (1980-05-01), Outmans
patent: 4555905 (1985-12-01), Endou
Ostrager Allen M.
Solmecs Corporation N.V.
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