Power plants – Utilizing natural heat – Geothermal
Reexamination Certificate
1997-07-28
2001-10-09
Nguyen, Hoang (Department: 3745)
Power plants
Utilizing natural heat
Geothermal
C060S641500
Reexamination Certificate
active
06298663
ABSTRACT:
DESCRIPTION
1. Technical Field
This invention relates to a method of and apparatus for producing power from geothermal fluid, and more particularly, from geothermal fluid comprising a two-phase mixture of geothermal steam and brine.
2. Background of the Invention
Geothermal steam and brine produced by some newly discovered geothermal fields are at relatively high pressure and temperature (e.g., about 200 psia., and about 400° F.) permitting economical power generation using steam turbines. The conventional approach has been to drill a number of production wells in a field, and to construct a power plant containing steam turbines at a central location in the field convenient to a source of water for the steam condensers associated with the steam turbines. Input conduits can be many hundreds of meters in length, and would carry the geothermal fluid from the production wells to a separator located at the power plant which functions to separate the geothermal fluid into geothermal steam and geothermal brine. After heat had been extracted from the geothermal steam by the steam turbines in the power plant plant, the heat depleted steam and the brine would be disposed of in re-injection wells located away from the production wells thereby preventing the release into the atmosphere of noxious gases present in the geothermal fluid.
While the resources of a geothermal field are enormous, they are nevertheless finite; and an objective of the design of a geothermal power plant is not only to extract heat economically, taking the finite nature of the resource into account, but to extract heat as efficiently as possible from the geothermal fluid. A number of problems have consistently arisen in designing geothermal power plants using high pressure geothermal fluid that is a two-phase mixture of steam and brine. One is the pressure loss in the input conduit that connects a production well that is remote from the separator of the power plant. The pressure of the steam separated at the power plant will be considerably lower than the steam at the well head by reason of the friction losses in the input conduit due to the two-phase nature of the flow in this conduit. As a consequence, the power output of the plant is penalized even before the plant is designed.
Another problem is the reduction in well head pressure with aging of the field. The capital costs for design, construction, and operation of a medium sized geothermal power plant presently exceeds $1000 per installed kilowatt based on power production at a design level for the life of the plant. However, there is no guarantee that the resources of a field under development will actually produce at its design rate for the life of the plant; and, in fact, it is not unusual for the well head pressure to begin to drop after a period of use. Particularly when condensing steam turbines are involved, a reduction in well head pressure results in a reduction in electrical output which reduces the financial return below its contemplated level, and increases the cost of power production.
It is therefore an object of the present invention to provide a new and improved method of and apparatus for producing power from geothermal fluid which overcomes, or substantially ameliorates, the prior art problems summarized above.
BRIEF DESCRIPTION OF THE INVENTION
Apparatus according to the present invention for producing power utilizing geothermal fluid comprising a two-phase mixture of geothermal steam and brine produced by a production well, includes an input conduit connecting the production well with a separator which separates the geothermal fluid into high pressure geothermal steam and geothermal brine. A connecting conduit carrying the separated high pressure steam connects the separator to a geothermal power plant which produces power from the high pressure geothermal steam. The input conduit is shorter than said connecting conduit to reduce pressure losses due to two-phase flow in the input conduit.
The geothermal power plant includes a topping steam turbine coupled to a generator, and a flow control mechanism for applying the high pressure geothermal steam to the topping steam turbine which is constructed and arranged to drive the generator and produce exhaust steam at a pressure greater than atmospheric pressure. A secondary separator receives the exhaust steam and produces steam condensate and dry low pressure steam which is applied to a condensing steam turbine coupled to a generator for producing power and exhaust steam that is below atmospheric pressure. The flow control system is effective to maintain a substantially constant flow rate of geothermal steam through the power plant in the face of decreasing pressure of the geothermal fluid such that the inlet pressure of the condensing steam turbine remains substantially constant.
A power plant utilizing a geothermal fluid comprising a mixture of steam and brine at a pressure that decreases with time is operated, according to the present invention, by separating the geothermal fluid into two channels, one containing steam and the other containing brine. The steam is expanded in a plurality of topping steam turbines, each of which is coupled to a generator and has inlet nozzles and a plurality of stages, for producing power and exhaust steam at a pressure above atmospheric pressure. The exhaust steam is dried and applied to a condensing steam turbine that drives a generator producing power, and produces exhaust steam that is condensed at a pressure below atmospheric pressure. Decreases in pressure of the geothermal fluid are compensated for by changing the extent of admission of the inlet nozzles, the number of stages of the topping turbines, or the number of topping steam turbines on-line in order to maintain a substantially constant flow rate of geothermal fluid through the power plant.
REFERENCES:
patent: 4127989 (1978-12-01), Mickelson
patent: 4576006 (1986-03-01), Yamaoka
patent: 4996846 (1991-03-01), Bronicki
patent: 5497624 (1996-03-01), Amir et al.
ECNZ Geothermal Group Annual Environmental Report 1993-94, “Future Options”, Taupo, 1994.
“Geothermal Energy”, in: Hearings before the Subcommittee on Energy of the Committee on Science and Astronautics U.S. House of Representatives Ninety-Third Congress First Session on H.R. 8628, H.R. 9658, No. 21, Sep. 11, 13 and 18, 1973.
Proceedings of the 11thNew Zealand Geothermal Workshop 1989, pp. 9, 13, 14, 19, Electricity Corporation of New Zealand Ltd., 1989.
Bronicki Lucien Y.
Kaplan Uri
Meyer Jerald L.
Nath Gary M.
Nath & Associates PLLC
Nguyen Hoang
Ormat Industries Ltd.
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