Furnaces – Combined – With boiler
Patent
1991-03-06
1992-09-15
Favors, Edward G.
Furnaces
Combined
With boiler
34 10, 34 57A, 110224, 110245, 110347, F23B 700
Patent
active
051468573
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a procedure for the production of electrical energy and/or heating and operational heat by utilizing combustion heat from fossil fuels, dried in an indirectly heated fluidized bed dryer prior to burning, especially of crude lignite. The resultant flue gases are cooled to an interstage temperature in a heat exchange between the working materials and the combustion air, are freed from dust and, if necessary, are freed from other damaging substances and, subsequently, discharged into the atmosphere.
In power plants in which fossil fuels with a high content of moisture are used as, for example, crude brown coal with a water content of 50% or more, a considerable portion, up to 25% of the utilized fuel, must be used for the vaporization of the water which then, as steam together with the flue gas, leaves the power plant. According to that method, the heat required for the vaporization demands an unnecessarily high temperature level.
To improve the level of effectiveness of such power plants, drying the fuel prior to its combustion has already been suggested in indirectly heated fluidized bed dryers utilizing the vapor stream deriving from the drying process as a support medium for the fluidized bed. The disadvantage of such a procedure is that, based on the pure steam atmosphere in the dryer, i.e. of the high partial pressure of the steam, the heat required for the drying process must be produced at a relatively high temperature level. Besides, an additional expenditure in equipment is necessary, for example, for special parts such as a vapor cleaning device, evaporator, condenser and preparer for the vapor condensation which, even in a close inclusion into the generator process, cannot be reduced essentially.
SUMMARY OF THE INVENTION
The invention has the object of further developing a process of the above-mentioned type in such a manner that, without considerably limiting the availability of the power plant process, the predrying of the utilized fuel can be accomplished with the lowest possible energy and equipment expenditure.
The object, based on this invention, is solved in that a partial flue gas stream is used as a carrier medium for the fluidized bed dryer, and that the mixture of fumes and steam, obtained during the drying process after an intermediate treatment, can be removed with the main flue gas stream.
The proposal based on this invention renders the energetically favorable integration of the drying of fuel in the existing power plant possible, without a considerable additional expenditure. In using a partial flue gas stream as a support medium for the fluidized bed of the dryer, the residual heat, normally removed as waste heat, can be utilized in a simple manner for the drying process. Furthermore, the mixing of the vapors developing in the dryer with the flue gas effects a considerable partial reduction of the steam pressure, so that the drying heat can be made available at a relatively low temperature level. For example, a low temperature residual bleeder steam from the water-steam circulation process of the power plant can be reused. To control the respective temperature level in the dryer, the pressure of the steam used as a heating medium can be adjusted, for example, through integration of a counter-pressure turbine into the water-steam circulation process of the power plant or an adjustable condensation extraction turbine.
It is of advantage if at least a part of the mixture of flue gas and steam developing in the dryer is returned to the furnace for the fossil fuels, without first removing the dust. Thereby the necessary dust removal of this gas stream is eliminated and, on the other hand, the energy content of the fuel particles carried along can, in a simple manner, be utilized in the power plant process.
The gas amount introduced from the fluidized bed dryer into the furnace depends on the type of fuel used, as well as on the respective load condition of the power plant process. Thereby it can be expected that, during the utiliza
REFERENCES:
patent: 4311103 (1982-01-01), Hirose
patent: 4359006 (1982-11-01), Have
patent: 4627173 (1986-12-01), O'Hagan et al.
patent: 4970803 (1990-11-01), Keller
patent: 4976107 (1990-12-01), Korpela
Moller Burkhard
Spliethoff Heinz
Wolf Bodo
Creighton Wray James
Favors Edward G.
Saarberg-Interplan Gesellschaft fur Rohstoff-, Energie- und
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