COMBUSTION METHOD

Abstract: The method relates to the control of the gasification process at the utilization of carboniferous fuel by gasification-combustion of the same in mixture with water in a reaction chamber, where the fuel first is partially gasified so that gas formed can be combusted at air deficit in order to gasify the remaining fuel. This method can now be improved so that soot formation and uncombusted residue are eliminated. The formation of nitrogen oxide and the formation of poorly combusted intermediate products of hydrocarbon nature is to be minimized. This is achieved in that a controlled amount of water is added to the fuel not later than at the beginning of the gasification phase so as hereby to control the temperature of the reactions as well as the time demand and the radiation pattern of the gas flames.

Description: Combustion method This invention relates to a method of controlling the gasification process when carboniferous fuel is utiliz¬ ed by gasi ication-combustion of the same in mixture with water in a reaction chamber, in which the fuel first is partially gasified so that gas formed can be combusted at air deficit in order to gasify the remain¬ ing fuel. The invention has the object to eliminate soot formati¬ on and uncombusted residue. The formation of nitrogen oxide and of poorly combusted intermediate products of hydrocarbon nature is to be minimized. The amount of said products must be reduced in order to satisfy the requirements of licensing authorities in respect of limit values for substances detrimental to environment. A study of desirable and non-desirable combustion products shows, that pure fuels, i.e. only coal or only oil, do not yield combustion products or emiss¬ ions, which are unobjectionable. In order to obtain unobjectionable results, it is a.o. necessary to relate the carbon content of the combust¬ ion material to he oxygen content of the air amount supplied, so that the combustion is close to stoichi- ometric and that the fuel material contains a suffic¬ ient amount of water. It was found that presence of water, for example at the combustion of pulverized coal, contributes to i part- ing to the coal fuel such properties, that the afore¬ said disadvantages can be minimized, and that the ignition can be facilitated and the combustion be intensified. In order to achieve the aforesaid object, the invention is characterized in that water in a controlled amount is added to the fuel not later than at the beginning of the gasification phase so as hereby to control the temperature of the reactions as well as the time demand and the radiation pattern of the gas flames. The method does not require the fuel to have a low total moisture content. It is an advantage, however, when the capillary and chemically bound water amount is small. At the addition of water the fuel must be prepared so that water does not penetrate into the fuel particles. A gasification/combustion process of solid fuels proc¬ eeds so that the lightest fractions of the fuel material are gasified first, whereafter the heavier particles are gasified in relation to the increased access to cleaving energy - heating. In a completed gasification process only incombus ible ash remains as solid residue product. The presence of water increases the reaction susceptibil¬ ity of the fuel material and the gasification speed due to the catalytic effect, which is obtained by the pres¬ ence of the atom groups - radicals of the type methyl- ene oxide and methylidyne oxide - which are formed and arise transiently. According to one theory, such pres¬ ence reduces the thickness of the diffusion layer about each coal grain. This in its turn increases the oxidat¬ ion speed and reduces soot formation and uneombusted residue. It is important that in the gasification phase air is supplied in deficit, thereby preventing that nitrogen oxide is formed earlier than in the combustion phase. The water present in the fuel material assists in the combustion process in such a manner, that it renders possible the formation of the aforementioned radical atom groups with catalytic effect. In the combustion the water vapour is re-formed. The method implies that pulverous solid fuel by the addit¬ ion of a suitable water amount not later than at the beginning of the gasification phase can be caused to react rapidly and completely, so that first gasificat¬ ion occurs which is followed by a partial combustion at air deficit of combustible gas formed. The presence of water at the gasification is a prerequis¬ ite for the water gas reaction, whereby carbon monoxide as well as a number of more or less well defined hydro¬ carbons are formed. The aforedescribed method at the gasification of solid fuel permits the gas formed to be combusted with a hot white flame in a fireplace. The hot flame in combination with optimum amount of water vapour and carbon monoxide yields optimum heat rediation to be absorbed by surrounding heat radiation absorbing surfaces, which renders possible increased effect output and boiler units of greater compactness. Summarizing, water assists in: o more rapid gasification-combustion reaction o increased capacity of controlling said reaction o more complete gasification o white heat radiating flame increasing the heat transfer in the fireplace o the occurrence of vapour in the combustion gases, which together with C0 ? increases the radiation effect in the fireplace.

Claims: Claims 1. A method of controlling the gasification process at the utilization of carboniferous fuel by gasificat¬ ion-combustion of the same In mixture with water in a reaction chamber, where the fuel first is partially gas¬ ified so that gas formed can be combusted at air deficit;; in order to gasify the remaining fuel, c h a r a c t e r i z e d i n that a controlled amount of water is added to the fuel not later than at the beginning of the gasification phase so as hereby to control the temperature of the reactions as well as the time demand and the radiation pattern of the gas flames. 2. A method as defined in claim 1, c h a r a c t e r¬ i z e d i that the water amount added Is such that the water amount is 10-40 per cent by weight of the fuel mixture weight.

Inventors: BOTHVIDSON ARNE, BOTHVIDSON, ARNE
Applicants: K KONSULT, K-KONSULT
Application year: 1984
Main classification: F23L7
IPC codes: F23C99, F23L7