Furnaces – Process – Burning pulverized fuel
Patent
1991-07-09
1992-10-20
Favors, Edward G.
Furnaces
Process
Burning pulverized fuel
110263, 110264, F23D 100
Patent
active
051561000
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a method for starting the boiler of a solid-fuel fired power plant and for ensuring the burning process of the fuel.
The invention also concerns an apparatus used for the implementation of the method.
DESCRIPTION OF THE BACKGROUND ART
Solid-fuel fired boilers of power plants are provided with several burners. The primary proportion of the boiler energy output is produced by main burners which deliver the major quantity of fuel used for firing the boiler. In boilers fired with a low-grade solid fuel, the continuous combustion of the fuel must be ensured, since extinction of the fire causes an explosion hazard through the gasification of the fuel in the hot boiler into a gas containing explosion-susceptible carbon monoxide. The continuous combustion of fuel is ensured by means of auxiliary torches. The auxiliary torches typically are different kinds of oil or gas torches.
A boiler fired with a solid fuel such as coal or peat is started (also called "warm-up") by heating the boiler to a sufficient heat by the igniting torches, after which the feed of the solid fuel into the boiler can be initiated. The capacity of the igniting torches necessary in the process must be relatively high in relation to the total capacity of the boiler in order to make the starting operation possible. As a rule, the igniting torches are dimensioned so that their capacity is approx. 25 . . . 50% of the total capacity of the boiler.
The igniting burners conventionally used are gas or oil torches, which simultaneously function as combustion supporting torches. The main burner in the boiler is mounted to an opening in the boiler wall, while the igniting auxiliary torch is placed in the center of the main burner. During the warm-up phase the boiler is heated by the auxiliary torch flame. When required, the igniting torch is used in the steady-state operation of the boiler as an auxiliary burner in the purpose of ensuring the continuous combustion of the main fuel. The function and construction of different kinds of gas and oil torches is well known in the art.
The use of plasma torches as auxiliary and/or igniting burners has been investigated, yet wider use of these apparatuses is still unseen. Further, the direct use of arc-ignited pulverized coal for the ignition and auxiliary firing of the boiler is also being investigated, but equipment based on this idea is neither yet applicable at the scale of power plants. The state of the art is elucidated in the following publications Melilli, W. H. Reed, Energy, Iron and Steel International, December 1983, pp. 207 . . . 211. Industrial opportunities for plasma technology, Symposium in Toronto, Oct. 21, 1982, D-2, 15 pp. fuel handling, Power, May 1983, pp. 111 . . . 113.
In addition to the above described implementations, an auxiliary burner based on multistage firing is known in the art in which the coal acting as the auxiliary fuel is delivered into the flame of a gas torch. The fuel mix delivered into the torch flame is air-deficient, whereby the auxiliary air required for complete combustion is fed into the stream of the auxiliary fuel through a separate adapter. Conventionally used ignitor and auxiliary burner constructions based on oil or gas torches have a simple structure and achieve a well-behaved control of the combustion process by means of these burners. The disadvantage of these systems is, however, that the torch uses a different fuel from that used for firing the boiler, whereby a separate fuel feed and storage system must be constructed for the torch. Oil and gas are priced above conventionally used solid fuels, and since the capacity of ignitors and auxiliary burners must be relatively high in relation to the total capacity of the boiler, they consume the high-priced fuels in abundance, thereby raising the operating costs of the plant. The combustion of large quantities of oil in conjunction with the use of a solid fuel appreciably increases the sulfur release rate of the plant, since the oil grades conventional
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ASME article "Plasma Arc Ignition of Pulverized Coal", Cioffi et al., pp. 1-5.
ASME article "Plasma Arc Pulverized Coal Ignition Demonstration Tests", Paley et al., pp. 1-7.
Article "Get Oil and Gas Out of Pulverized-Coal Firing" John Reason.
Article "Plasma Totch Boiler Ignition", pp. D.2-1 to D.2-10; Oct. 1982.
Article "Plasma Torches as Replacement for Oil Burners" Thunberg et al., pp. 207-211 from Iron and Steel International Dec. 1983.
Favors Edward G.
Imatran Voima Oy
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