MATHEMATICAL DESCRIPTION OF THE SOLID FUEL GASIFICATION PROCESS IN A FIXED BED: 2. THEORETICAL STUDY OF MULTI-STAGE PEAT PROCESSING IN THE AIR AND VAPOR-AIR MEDIUM AT DIFFERENT PRESSURE
Using the developed two-dimensional model presented in the first part of this work, the non-stationary process of peat gasification in a fixed bed in air and vapor-air medium at pressures of 1 MPa and 0,18 MPa, respectively, was theoretically investigated. A comparative analysis of the thermochemical processing of peat in the vapor-oxygen, air and vapor-air medium has been carried out. It was shown that: 1) in the oxidation zone with an air blast, the temperature of the dispersed phase turns out to be slightly higher than the temperature of the particles at a vapor-oxygen blast, despite the lower oxygen content in the gas. This is due to the intense endothermic reaction C+H2O=CO+H2 in the zone of maximum heat release; 2) the release of volatiles during vapor-oxygen gasification occurs much faster than with air due to the more rapid heating of the bed mass due to the higher rate of the maximum heat release zone movement along the height of the bed; 3) during air gasification in the oxidation zone, the temperature of the particles exceeds the temperature of the liquid-melting state of ash, which make it possible to organize a stable liquid slag removal from the reactor; 4) vapor gasification in a fixed bed is organized with dry slag removal, since the level of peat temperature in the zone of maximum heat generation does not exceed 1100 °C and is lower than the temperature of the onset of deformation of ash 1140 °C; 5) the generator gas composition at the outlet of the reactor at air gasification has a lower combustible part of CO = 34.33% and a higher content of ballast N2 = 65,67 %, in contrast to steam-oxygen one – CO2 = 1,5–2 %, H2O = 0,1–0,6 %, CO+H2 = 98 % and vapor-air – CO+H2 = 45,5 %, N2 = 53,3 % and CO2 = 1,2–2,13 %. It follows that the calorific value and quality of the generator gas at vapor-oxygen and vapor-air blast is higher than at air blast. An original method of supplying highly concentrated dust to the main burners at underpressure using a gas-jet ejector (working medium – synthetic gas Pg = 1-1,5 MPa) ensuring steady ignition and stabilization of a pulverized coal flame, is proposed. Ref. 4, fig.11, tables 1.
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