Power plants – Combustion products used as motive fluid
Reexamination Certificate
1999-06-25
2001-10-09
Thorpe, Timothy S. (Department: 3746)
Power plants
Combustion products used as motive fluid
Reexamination Certificate
active
06298651
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a method and an apparatus for power generation, wherein a boiler-oriented fuel, such as coal and heavy oil is separated into a distillate and a residue by performing partial processing, and subsequently, a gas turbine fuel obtained from the distillate or a combination of the gas turbine fuel and another gas-turbine-oriented fuel is supplied to a gas turbine, the gas turbine fuel and the gas-turbine-oriented fuel are burned to generate electric power, on the other hand, a boiler fuel comprising the residue or a combination of the residue and the boiler-oriented-fuel and/or other boiler-oriented fuels are supplied to a boiler, these fuels are burned to generate steam, and power is generated by means of a steam turbine. The present invention further relates to a power generation method and apparatus for burning an exhaust gas again wherein an exhaust gas discharged from a gas turbine is supplied to a boiler and is utilized for burning boiler fuel.
There have been three kinds of power generation methods of converting energy produced by combustion into electrical energy through a motor such as a turbine, namely, a first method of generating electric power by means of a boiler and a steam turbine; a second method of generating electric power by means of a gas turbine; and a combined cycle method using the combination of the first and second methods.
In the method for generating electric power by means of a boiler and a steam turbine, fuel oil, crude oil, residue oil or coal is used as a fuel. Further, electric power is generated by driving the turbine by using steam of high-temperature and high-pressure produced by the boiler. However, the thermal efficiency is relatively low, namely, 38 to 40%/HHV basis (HHV: Higher Heating Value; the thermal efficiency of power generation is expressed on HHV basis, unless otherwise specified).
Further, in the method using the gas turbine, liquefied natural gas (LNG), kerosene (or kerosine) or light oil (gas oil) is used as a fuel. Furthermore, the fuel is burned in compressed air, and then burned by heating the compressed air by combustion heat. Electric power is generated by driving the gas turbine by the produced high-temperature and high-pressure gas. Although the thermal efficiency in this case is 20 to 35%, the temperature of the exhaust gas discharged from the gas turbine is high, for example, 450 to 700° C. and thus, the heat of this gas can be utilized.
Furthermore, in the case of using air-cooled fin turbine, the gas temperature can be raised to 1300 to 1500° C. Thus, the efficiency of power generation can be enhanced. Consequently, the exhaust gas can be utilized more effectively.
In the case of the combined cycle power generation method which is the combination of these power generation methods, LNG is used as the fuel. Electric power is generated by burning the fuel in compressed air and driving the gas turbine by the use of the high-temperature and high-pressure gas. Further, the exhaust gas is supplied to a heat recovery boiler to produce steam. Thus, the method of generating electric power by using the steam turbine is performed. Conventional gas turbine features high heat efficiency of 46 to 47%. Therefore, when a facility is newly established due to superannuation of the power generation facility, or when the increase of the ability of power generation by utilizing the existing facility is necessary, new facilities adopting the combined cycle power generation method by which high heat efficiency can be obtained have been constructed.
However, in the case of the combined cycle power generation method using LNG, the storage of the fuel, namely, LNG costs very much, and a problem in supplying LNG may occur.
Western countries have the experience of using crude oil and residue oil in addition to LNG and light oil as the fuel for a gas turbine. However, many troubles have occurred owing to impurities contained in crude oil and residue oil. Further, it is pointed out that the maintenance cost has amounted up to a larger sum in comparison with that in the case of using light oil and LNG. Incidentally, it is desirable that the contents of impurities in the fuel used in the gas turbine are limited as follows: a sum of a sodium content and a potassium content is not more than 0.5 ppm by weight; and a vanadium content is not more than 0.5 ppm by weight. Especially, a sodium salt component, a potassium salt component and a vanadium component affect one another. This results in drop of the melting point of metal used as the material of each blade of the gas turbine, and causes ash component to adhere to the blades.
On the other hand, in the case of thermal power generation, coal and heavy oil reserved in the nature in abundance are used as the raw fuel, in addition to petroleum and LNG. Further, it has been studied how the raw material and fuel are effectively used. For instance, integrated gasification combined cycle (IGCC) power generation, by which a furnace of the entrained (flow) bed gasification type is used as a gasification furnace and the net thermal efficiency of about 43 to 47% is obtained, has been studied. However, in the case of such techniques, it is necessary for utilizing coal and fuel oil in the combined cycle power generation method to convert the raw fuel into gas once and further refine the obtained gas.
Method of gasifying all of raw fuel has encountered the problems that excessive facilities are needed for pre-treatment of raw fuel, that a special type gasification furnace and a special type boiler to be combined with this gasification furnace are necessary, that operating conditions are severe, that as a result of gasifying all of the raw fuel, the quantity of the produced gas is large, that excessive facilities are needed for dust removal and purification of a gas, that the treatment of the remaining molten ash is needed, and that even a fuel to be used in a steam turbine is gasified and the obtained gas is purified.
Journal of Engineering for Gas Turbines and Power, vol. 118, October, 1996, p. 737 discloses the technique of a combined cycle power generation by which coal is gasified at high temperature in the presence of oxygen and water vapor, and in which the obtained gas is supplied to a gas turbine and is burned therein and subsequently, power generation is performed by driving the gas turbine by the use of the generated high-temperature combustion gas, and further, power generation is also performed by supplying char, which is left after the gasification of the coal, to a fluidized bed boiler, and by burning the char and driving a steam turbine by generated steam.
This technique, however, has the problem in that ingredients, such as Na salt, K salt and V compound, which corrode the turbine blades, are frequently included in the gas, because the gasification temperature is not lower than 1000° C., and thus there is the necessity for eliminating these ingredients. This technique further has the problem in that because a system constituted by the combination of a gasification device, a gas turbine and a fluidized bed boiler is peculiar, the extensive adjustment of the facility is needed in applying this technique to a boiler provided with a radiation heat transfer surface and a convention heat transfer surface, such as the existing boiler/steam turbine system, and thus, practically, this technique is subject to the constraint that this technique can be applied for establishing a new facility. This technique further has the problem in that the purification of the gas obtained at high temperature should be performed at low temperature and there is a great loss of energy, and that the cost of the entire facility becomes excessive.
SUMMARY OF THE INVENTION
An object of the present invention is to achieve power generation with high efficiency by using an inexpensive boiler-oriented fuel with low availability, which is a fuel that cannot be utilized for a gas turbine but can be utilized for a boiler, thereby effectively utilizing the fuel.
F
Mitsubishi Heavy Industries Ltd.
Myers Bigel Sibley & Sajovec P.A.
Rodriguez William H
Thorpe Timothy S.
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