FI103905B - A method for feeding fuel to a recovery boiler - Google Patents

Description

Process for feeding waste into a soda boiler.

Menetelmä jäteliemen syöttämiseksi soodakattilaan.

The invention relates to a method of supplying fuel which operates as fuel in a furnace of a soda boiler which is supplied with oxygen for combustion in such a way that vertical mixing of the gas contents of the furnace is suppressed and horizontal mixing is amplified by at least a roughly vertical row of oxygen containing gas jets.

The state of the art.

Soda boilers, which are used for combustion of liquids which are produced in the production of cellulose from cellulosic plant parts, are in their conventional design having a number of process technical problems.

The fuel, which is supplied in a more or less atomized state, is easily seized by the flowing gases and transported out of the fireplace as so-called. carryover.

The combustion is then moved to the fireplace outlet, where the temperature rises higher than desired. The consequences will include: - Adequate heat release is not achieved in the lower part of the fireplace, where high temperature is required for good combustion stability and for good reduction of sulfur tili sulphide, which together with the rest of the fuel's inorganic chemicals should leave the fireplace as molten through openings 30 at the bottom level -high temperature at the outlet of the fireplace, the law provides thermal efficiency -the overburdened substance settles easily on the heat transfer surfaces after the fireplace 35 total clogging of the gas passage 2 The high gas temperature around the heat surfaces partially halves the overburden, causing the material to sticky and causing the coatings to sinter into a hard shell that is difficult to remove - both nitrogen oxides (NOx and SO becomes high Due to the above, in conventional soda boiler operation, it is necessary to concentrate the combustion as much as possible in the fireplace, in spite of this, there is usually an altogether too extensible combustion profile.

15 Loaning and benefits.

Thanks to the method described in application PCT / FI93 / 00488 to supply oxygen-containing gas to the fireplace, new possibilities are opened to combat the problems discussed in the preceding chapter. The arrangement of vertical rows of gas jets allows a concentration of combustion to the lower part of the fireplace to a greater extent than is necessary. Thus, there is a margin that can be utilized for further innovations.

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Since maximum concentration of combustion in the new situation is no longer necessary, the combustion capacity can be increased, the temperature peaks lowered and the heat load on the fireplace walls equalized by supplying the fuel at several levels. The combustion volume is thus increased in height. Lowering the maximum temperatures also reduces the risks of forming so-called. thermal NOx, i.e. oxidation of gaseous nitrogen at temperatures approaching 1300-1400 ° C.

The majority of NC., In flue gases from a boiler, originates from nitrogen in the fuel and is unlikely to be prevented from arising during combustion. However, different methods are available to remove existing NOx. Among other things, hydrocarbon radicals have been found to be effective in reducing nitrogen oxides in laboratory tests and in practical experiments. Said radicals arise during pyrolysis of hydrocarbons. Addition of hydrocarbon-containing material (fuel) at a suitable temperature level will therefore consume NOx.

Although a large amount of overburden for rapid coating formation and subsequent plugging of the flue gas paths, the other extreme condition with very small amounts of entrained fuel has in practice also posed problems. Probably fine dust is deposited over time on the heating surfaces, forming a slowly growing coating that sinters to a hardened surface which is very difficult to remove by conventional means. The supply of a small amount of effluent near the fireplace outlet makes the coating porous, which facilitates the pouring.

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application examples

An application utilizing all three aforementioned possibilities can be constructed as follows:

Tili a soda pan with, for example, a horizontal register near the bottom of the so-called. primary air and a similar horizontal register approx. chm above for so-called. high primary air, and with three vertical rows of air ports in one of the fireplace walls and two vertical rows in the opposite wall, the main amount of fire liquor with air syringes at levels 4, 6 and 8 m above the primary air level is supplied. This device strengthens the expanded combustion volume.

Approximately in the middle of the stove, an amount of fuel less than 101 of the total amount is added in the atomized state to remove NOx. Exact height position is preferably determined empirically by means of experiments.

4 103905

Finally, a very small amount of fuel is added about 2m below the fireplace outlet with the intention of making the coatings porous.

5 Figure description

Fig. 1 shows a side section of a soda boiler oven where the invention has been applied according to the preceding chapter. 1a, 1b and 1c denote the supply of the main quantity of lute, 6 denotes 10 supply of ΝΟ, reducing fuel and 7 denotes additive for unlocking coatings. Above the so-called. the bed 2 on the fireplace bottom 3 is supplied with air through air ports 4 in the two horizontal registers and the ports 5 thus give the vertical rows of oxygen-containing gas jets.

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Claims (4)

5 103905 1. A method of distributing waste in a furnace of a boiler to which oxygen necessary for combustion is supplied in gas jets which, with the intention of reinforcing horizontal and suppressing vertical mixing, are arranged in an at least a vertical row characterized therein that the waste is supplied at least two levels. 2. A method according to claim 1, characterized in that in order to reduce both local heat loads and local temperature peaks, the main part of the exhaust is supplied to the lower part of the fireplace ρέ at least two levels. 3. A process according to claim 1, characterized in that a smaller part of the effluent is supplied to the fireplace at such a level that due to the appropriate temperature the minsk, content of the flue gases is reduced. 4. A method according to claim 1, characterized in that a very small portion of the effluent is supplied in the vicinity of the fireplace outlet with the intention of making the coatings on subsequent heating surfaces porous and easy to remove. 6 103905