Furnaces – Refuse incinerator – For liquid refuse
Patent
1995-05-23
1998-03-10
Kamen, Noah P.
Furnaces
Refuse incinerator
For liquid refuse
110251, F23G 704
Patent
active
057248958
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an arrangement and a device for distribution of oxygen-containing gas in a furnace, into which fuel is supplied as solid or fluid particles of such size and quality .that their trajectories are affected by gas flows. The oxygen-containing gas may be air, odorous gases (which will be converted to environmentally compatible gas in the combustion process) or flue gas. The intention is to establish such a flow pattern that intensifies the combustion process. As a typical application the invention relates to combustion of waste or residual products from pulp production.
2. Description of the Related Art
For the sake of clarity, the combustion of spent liquors from pulping processes utilizing organic fibrous material will be dealt with in the following. It shall not, however, be considered that the invention is limited to this particular area alone.
Spent liquors from pulping processes contain organic material which produces energy when burned and, additionally, inorganic chemicals, mainly sodium salts.
The spent liquor is sprayed into the furnace of the so-called black liquor recovery boiler with one or more liquor sprayers, which disperse the liquor into droplets of different size. Oxygen-containing gas--usually air--is in somewhat more than stoichiometric amount supplied into the furnace through special wall openings, so-called air ports. These air ports are usually arranged on three levels called primary, secondary and tertiary. Each of these levels consists of one or, sometimes, two (one lower and the other higher) horizontal or almost horizontal rows. Air or other oxygen-containing gas mixtures are fed into the air ports from one or, sometimes, two approximately horizontal ducts.
The function of the separate levels is explained in somewhat different ways. One of the most common explanations is presented below. The lowest level, i.e. primary, affects the so-called char bed on the furnace floor (2). The bed contains solid residues of the organic content of the fuel and the inorganic material which melts and flows out of the furnace.
The primary air oxidates the char, providing heat necessary for both melting of the inorganic salts and chemical reduction of sulphur into sulphide. The latter reaction is necessary to make sulphur recovery possible in a kraft pulping process. The area in which the drying and pyrolysis of the liquor droplets take place is provided with necessary oxygen from the secondary level. The ports for this air are usually located below the liquor sprayers. In boilers with a split secondary level, the upper level is sometimes located above the liquor sprayers.
Tertiary air burns out those combustible gases from fuel pyrolysis, which still are available in gases above the secondary air level. The tertiary ports are usually located on one level. Patent publication FI 85187, however, sets forth an application in which the secondary air ports are located on two levels. The patent application SE 467741 sets forth that "in the future, additional air supply over the tertiary level may be realized".
Kinetic energy of the supplied oxygen-containing gas is of importance. The primary and, to a certain extent, also the secondary flows affect the gas layer nearest the bed surface and consequently its burning. Secondary and tertiary air are given a high velocity in order to secure good mixing of oxygen with combustible gases. Besides, the jets often produce very complicated, stable or unstable flow patterns, which provide changing combinations of both favorable and unfavorable results.
Generally particle firing requires good mixing of oxygen-containing gas with fuel. Conveyance of fuel into the upper part of the furnace is not desirable. Combustion must take place rapidly and completely and, preferably, under a clearly stoichiometric oxygen deficit. Thus reduction or even entire removal of NO.sub.x (nitrogen oxides) in the flue gas would be achieved.
In this specific case concerning spent liquor combustion, more difficulties
Kamen Noah P.
Oy Polyrec AB
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