Power plants – Motor having exhaust fluid treating or handling means – Motor and indirect heat exchanger
Patent
1990-07-09
1991-10-22
Ostrager, Allen M.
Power plants
Motor having exhaust fluid treating or handling means
Motor and indirect heat exchanger
60670, F01K 900
Patent
active
050583867
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a power generation plant, and in particular to an electrical power generation plant which includes a steam-driven turbine.
The advantages of an electrical power generation plant which includes a steam-driven turbine have been well documented. A steam turbine coupled to a generator for generating electricity, typically to supply a national electric grid, can provide an output substantially exceeding that of a gas turbine, oil engine or petrol engine, for instance over 1200 Megawatts (MW) for a single turbine; it can use a variety of fuels; a typical power-station steam turbine is designed to run for over 200,000 hours, which is many times the life of currently-available gas turbines. Whilst steam-driven turbines are without serious competition for high-power production, they are also widely used in low and medium power production plants.
Despite however the skills and efforts of successive generations of steam engineers, the efficiency of modern steam plant is still low, and steam usage high, and improvements are greatly needed; few commercial steam turbines convert more than 50% of the available fuel energy into useful work. In order to keep to a minimum the cost of each unit of electricity generated, it is the constant endeavour of steam engineers and plant designers both to minimise the specific steam consumption, and to maximise the thermal efficiency of the plant.
One known efficiency-improving technique is to operate with high-pressure steam cycles, but even the known practice of superheating the steam up to the metallurgical limit will not alone maintain turbine exhaust dryness fractions above 0.9, as is desirable if last row turbine blade erosion is to be kept within acceptable limits. Many existing plants therefore incorporate re-heat i.e. the high-pressure (superheated) steam is fed to a high pressure turbine, and expands to an intermediate pressure, whereupon the steam is re-heated at near-constant pressure back to a higher temperature, usually the original temperature, whereafter the steam is further expanded within a low-pressure turbine; since each kilogram of the steam does more work, less steam has to be used, whilst plant efficiency can be improved by up to 10%. Systems using re-heat typically use the highest possible turbine inlet pressure.
Even at atmospheric pressure, steam contains substantial energy. Thus many power generation plants are designed to exhaust the steam from the turbine outlet to a vacuum, for instance one created by a condenser using a coolant to take out most of the residual heat, with the steam re-appearing as water. Nevertheless, a main source of inefficiency in the steam cycle is still the heat thrown away in the spent steam, so it is important design consideration to keep this loss down by using as low an exhaust pressure as possible, including using as low a coolant temperature as possible.
Once the spent steam has been condensed, significant pumping power is required to bring the water up to boiler pressure, and this power is conventionally subtracted as "parasitic power" from that generated by the turbine.
One prior proposal to increase the efficiency of power generation plant which includes a steam-driven turbine is the 1892 German Pat. No. 70286 to Burnham. Exhaust steam from the steam turbine is condensed, and returned to the boiler by a stand pipe of height sufficient for the water pressure to equal the pressure in the boiler, whereby a lower boiler pressure can be used. A similar proposal is that of the 1982 Japanese patent application No. 59-119073 to Toshiba, wherein the condenser is at a height above the boiler sufficient for the water to flow to the boiler by gravity, thus obviating the need for a water pump and lowering the construction cost of the power plant. Another proposal was shown in the 1928 German Pat. No. 498700 to Schultz, wherein an underground boiler is warmed by geothermal heat, as a disclosed means of utilising the earth's heat; in response to fluid level gauges in the boiler and condenser, liquid is pumped from
REFERENCES:
patent: 3393515 (1968-07-01), Tabor et al.
patent: 3820334 (1974-06-01), Heller et al.
Kasper Horst M.
Ostrager Allen M.
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