Furnaces – Process – Burning pulverized fuel
Patent
1989-09-13
1991-02-19
Favors, Edward G.
Furnaces
Process
Burning pulverized fuel
110204, 110232, 110245, 110263, F23D 100
Patent
active
049933329
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention concerns a hybrid fluidized bed and pulverized coal combustion system which as a consequence of the combination of fluidized bed combustion and the conventional pulverized coal combustion has at least one coal grinding plant(coal mill), at least one pulverized coal burner, an air distributor required for realizing fluidized bed combustion, a device for blowing in secondary air, a slag removal device as well as an ignition device. Furthermore the invention concerns a process for converting the already available pulverized coal boilers (furnaces) to the hybrid fluidization bed and pulverized coal combustion system.
BACKGROUND OF THE INVENTION
In the known solutions of pulverized coal firing the pulverized coal ground to the required fineness in a pulverized coal preparation system and dried therein is fed to a pulverized coal burner where the pulverized coal is mixed with the combustion air. The mixture ignites in the combustion chamber and burns at a high temperature. A part of the released heat quantity is radiated at the cooled wall of the furnace chamber while the remaining part will be utilized at the other surfaces of the boiler (super-heater, feed water preheater, air heater).
This known mode of combustion and the plant serving for its realization are disadvantageous from several points of view. It is disadvantageous that in order to obtain practically complete combustion of the combustible part of the pulverized coal, the coal must be ground to the required fineness. Grinding involves a significant expenditure of energy and costs. Even despite this measure, one must reckon with ignition problems and with extinction of the fire when the quality of the coal is poorer than planned. A further disadvantage is that the still tolerable partial load (without auxiliary combustion with gas or oil) amounts to approximately 60 to 70% of the nominal load. It is also disadvantageous that due to the high temperature prevailing in the furnace chamber, the emission of environmentally harmful materials, particularly of NO.sub.x, has an extremely high value and the basic additive for use for binding the SO.sub.2 is not sufficiently effective so that a supplementary, expensive flue gas purification must be carried out.
In the per se also known solutions of fluidized bed combustion, the unground coal introduced e.g. via an air distributor assuring uniform distribution is combusted completely or partially with the combustion air flowing through the air distributor at a relatively low temperature of between 750.degree. and 950.degree. C.
In this case, the grinding process producing the pulverized coal is obviated. Thereby the costs of grinding are saved, the glowing fluidized bed of high mass assures an insensitivity to changes in the quality of the coal and at the same time the combustion temperature, being restricted to the temperature range of between 750.degree. and 950.degree. C., also restricts environmental pollution caused by NO.sub.x and SO.sub.2.
The known mode of using fluidized bed combustion nevertheless brings also certain disadvantages with it.
In a variant of fluidized bed combustion, a full combustion of the coal is realized in the fluidized bed and the overwhelming part of the released heat is abstracted by way of cooling surfaces immersed into the fluidized bed. In another version the coal is only partially combusted in the fluidized bed whereafter the gases leaving the fluidized bed are combusted with air passed over the fluidized bed. In this solution the cooling surfaces immersed into the fluidized bed are mostly dispensed with.
In both cases the flow velocity of the air supplied to maintain the fluidized state and also to promote the combustion process is relatively low (it is, in general, below a velocity of 4 m/s). Consequently it is necessary to overdimension the cross-section of the fluidized bed transversely of the direction of air flow in relation to the dimensions of the pulverized coal combustion systems wherein the velocity of the pulverized coal supp
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Boross Laszlo
Gerlai Tibor
Horvath Ferenc
Kovacs Sandor
Remenyi Karoly
Dubno Herbert
Favors Edward G.
Tatabanyai Hoeromu Vallalat
Villamosenergiapari Kutato Intezet
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