Experimental Studies Of Low Calorific Premixed Gases Combustion In Porous Media With Reciprocating Flow System

Due to low heat value and complex composition, low calorific gases whose heat value is below 6.28MJ/m3 are not exploited and directly discharged. They contain large amounts of methane, greenhouse effects of which are 21 times more than carbon dioxide. The efficient transformation of methane to carbon dioxide will bring us huge environmental and economic benefits. In this thesis, combustion technology in porous media with reciprocating is used to deal with these low calorific gases, and some studies have been done to expend the system's flammability limit. Some low calorific gases are made up of combustible components and inert components, and don't contain oxygen. In order to study these gases'combustion and pollutant emission characteristics in porous media combustor with reciprocating flow, the mixture of nitrogen and natural gas is used to simulate these gases. The work done by this article mainly includes two parts:First, experimental studies of flammability limit of low calorific gases combustion in porous media with reciprocating flow system. Effects of regenerator section on temperature fluctuation and distribution, variation characteristics of axial temperature distribution and flammability limits were investigated experimentally. The results show that adding regenerative sections leads to reduction of temperature fluctuation amplitude and increase of combustion temperature and efficiency; With the increasing of equivalence ratio, the shape of axial temperature distribution has continuous changes, from saddle-shaped, ladder-shaped, oval-shaped to triangle-shaped when the system works on flammability limit; With the reducing of half-period, thermal load and inlet gas velocity, the system's flammability limit firstly decreases and then increases; With increasing of heat storage capacity of regenerator section, the flammability limit is slight lower. The flammability limit can be extended to the low equivalence ratio of 0.07, corresponding to the heat value of 264kJ/m3.Second, experimental studies of anaerobic gases in porous media with reciprocating flow system. The effects of the heat value of mixed fuel gases (the mixture of nitrogen and natural gases),oxygen content and air equivalence ratio on combustion and pollutant emission characteristics are investigated experimentally; Compared with simple porous media burner, analysis the advantages of reciprocating flow system. The results show that:With the reducing of heat value of mixed fuel gases, the length of high-temperature zone shortens, the average temperature and combustion temperature increases; with the reducing of oxygen content and air equivalence ratio, the combustion temperature firstly increases and then decreases, the exhaust gas temperature decreases, and oxygen contents of the maximum combustion temperature on certain air equivalence ratio are different, the air equivalence ratio higher, the oxygen content lower; Compared with simple porous media burner, the air equivalence ratio is lower when T/Tad=1, and the emission concentration of NOx and CO is lower; With the reducing of air equivalence ratio, the heat value of flammability mixed fuel gases firstly decreases and then increases, the oxygen content of flammability limit rise. The flammability limit can be extended to the mixed fuel gases heat value of 447.35kJ/m3, the oxygen content of the oxidizer of 3.5%, corresponding to the premixed gases heat value of 373.2 kJ/m3. In better combustion condition, the CO emission concentration is below 15ppm and the NOX mission concentration is below 5ppm.