Power plants – Combustion products used as motive fluid – With combustible gas generator
Reexamination Certificate
1998-08-13
2001-06-19
Freay, Charles G. (Department: 3746)
Power plants
Combustion products used as motive fluid
With combustible gas generator
C060S039463
Reexamination Certificate
active
06247301
ABSTRACT:
THE TECHNICAL FIELD OF THE INVENTION AND PRIOR ART
The present invention refers to a gasifier for producing a combustible gas, comprising a gasifying reactor in which a combustible gas is intended to be produced from a fuel, first conduit members arranged to supply an oxygen-containing gas necessary for the gasification to the gasifying reactor, and second conduit members arranged to discharge combustible gas from the gasifying reactor. Furthermore, the invention refers to a power plant comprising a combustion chamber in which the combustion of a combustible material is intended to be performed while forming hot combustion gases, a gas turbine device adapted to be driven by the combustion gases, a topping combustion device arranged to receive the combustion gases and raise the temperature thereof to a level suitable for the gas turbine device, a gasifying reactor arranged to produce a combustible gas for combustion in the topping combustion device to produce said temperature increase, first conduit members arranged to supply an oxygen-containing gas necessary for the gasification to the gasifying reactor, and second conduit members arranged to supply the combustible gas from the gasifying reactor to the topping combustion device. By combustible material or fuel is meant all fuels which may burn, such as for example pit coal, brown coal, peat, biofuel, oil shale, pet coke, waste, oils, hydrogen gas and other gases, etc.
The invention will now be discussed and illustrated in different applications in connection with a pressurized fluidized bed, a so called PFBC power plant (pressurized fluidized bed combustion). However, the invention is not limited to such applications but may be utilized in all conceivable power plants, especially gas turbine plants and also in connection with independent gasifying devices, so called gasifiers.
In a conventional PFBC power plant the bed is supplied with combustion air in the form of compressed air from the pressure vessel enclosing a combustion chamber in which the fluidized bed is housed, via fluidizing nozzles beneath the bed. The combustion gases formed during the combustion process pass a free board above the bed surface, whereafter they are purified and conveyed to a gas turbine. The combustion gases drive the gas turbine, which in turn drives on one hand an electric generator and on the other hand a compressor supplying the pressure vessel with compressed air. In the bed the fuel is combusted at a temperature in the order of 850° C. For generating steam a steam generator in the form of a tube arrangement is disposed in the bed. Energy is supplied by the bed via the steam turbines to which the steam is conveyed in a steam system. At full load the whole tube arrangement is disposed within the bed. A PFBC plant is characterized by a small plant volume in relation to the effect produced in comparison with other types of plants where the fuel is combusted in a fluidized bed at atmospheric pressure conditions. In addition, the efficiency of a PFBC plant is high. Furthermore, the combustion in a PFBC plant is performed at favourable conditions from an environmental and economical point of view.
One problem which is connected to the PFBC technique and which has prevented a substantially high efficiency is that the upper temperature limit at which the combustion of for example coal is performed in a fluidized bed, normally mounts to about 850 to 950° C. dependent on the coal quality. his means that the drive gas for the gas turbine of the PFBC power plant has a temperature which is about as high as the temperature in the fluidized bed. Since the turbine effect rises strongly with an increased temperature of the drive gas it is desirable to have a higher gas temperature, up to 1200 to 1500° C. in order to reach an optimal level of the effect from the gas turbine part of the plant. In order to remedy this disadvantage it has been suggested to raise the temperature of the gases leaving the PFBC combustion chamber by means of a topping combustion chamber in which a fuel is combusted. Since the drive gases pass the topping combustion chamber their temperature may be increased prior to being supplied to the gas turbine. Such technique is known from SE-B-458 995. Furthermore, in this document is described how the fuel for the topping combustion chamber may be produced by means of a gasifying reactor, in which coal at under-stoichiometric conditions is gasified while producing a combustible gas supplied to the topping combustion chamber.
The combustible gas produced in the gasifying reactor has a relatively high temperature, about 800 to 1000° C. as it leaves the gasifying reactor. Furthermore, the combustible gas leaving the gasifying reactor contains dust particles, which at such a high temperature may occur in a melted viscous form. Because thereof a possible purifying filter provided in the conduit member of the combustible gas will rapidly be stopped up. Furthermore, the hot dust containing combustible gas causes a problem in the regulating valves which may be provided for regulating the gas flow. In order to overcome this problem it is known to utilize expensive and complicated regulating valves to be cooled down by vaporizing of water and superheating of steam.
Furthermore, it should be noted that in the cases when the combustible gas is utilized for combustion in a power plant, for instance in a topping combustion chamber arranged prior to a gas turbine, such dust particles result in erosion and corrosion in the gas turbine leading to a premature wear. In order to purify the combustible gas it has been suggested to let the hot dust containing gas pass a cyclone separator at the outlet of the gasifying reactor. However, such a separator is not as effective as a filter and especially insufficient for the high purification level required of the gas to be supplied to a gas turbine.
JP-A-5/87315 discloses a power plant comprising a gasifying reactor having a fluidized bed, a combustion chamber with a fluidized bed and a topping combustion chamber. The combustion gases from the gasifying reactor and the combustion chamber are purified and supplied to the topping combustion chamber where a combustion takes place. The combustion gases from the topping combustion chamber drive a gas turbine which in turn drives a generator and a compressor compressing the air supplied to the gasifying reactor, the combustion chamber and the topping combustion chamber. The combustion air supplied to the topping combustion chamber is heat-exchanged by means of air tubes provided in the fluidized bed of the combustion chamber.
JP-A-5/93513 discloses a power plant having a gasifying reactor for producing a combustible gas. The combustible gas is purified and supplied to a topping combustion chamber. The solid rest products formed in the gasifying reactor are supplied to a combustion chamber comprising a fluidized bed where they are combusted. The combustion gases from the combustion chamber are also purified and supplied to the topping combustion chamber. Moreover, the topping combustion chamber is supplied with oxygen from outside and a combustion takes place so that the combustion gases formed in the topping combustion chamber are utilized for driving a gas turbine.
SUMMARY OF THE INVENTION
The object of the present invention is to remedy the problems mentioned above and to treat the gas leaving a gasifying reactor in such a manner that it may be utilized in a better way in the subsequent process stages.
This object is obtained by the gasifying device initially defined and characterized by a member arranged at the second conduit members and adapted to cool down the combustible gas leaving the gasifying reactor. By lowering the temperature of the combustible gas leaving the gasifying reactor in such a manner the stresses on the subsequent equipment decrease. Especially, it is possible to lower the temperature to under 600° C. so that the dust particles present in the gas will be in solid form and not stick to and stop up the subsequent equipment.
According to an embodiment
Brannstrom Roine
Lovgren Anders
Veenhuizen Dirk
ABB Carbon AB
Connolly Bove Lodge & Hutz
Freay Charles G.
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