Combustion Characteristics Of Multi- Species Low Calorific Gaseous Fuels In A Two-layer Porous Burner

Porous media combustion is featured by high flame speed, low emission, and large operation range, due to the unique mechanism of internal heat recirculation, and thus provides great chances for clean utilization of low calorific gases. In the present thesis, combustion of three typical multi-species gases with low calorific value in a two-layer porous burner was experimentally and numerically studied. The investigation work is as follows.1. Lean combustion of multi-species gases with low calorific value in a two-layer burner was investigated experimentally. An experimental system with two-layer porous burner was developed. The temperature profiles, stability limits and pollutant emission for blast furnace gas, biogas gasified gas and landfill gas at lean conditions (φ=0.60～0.75) were investigated. Results show that the location of stabilized flame moved downward as the inlet velocity increases. For all equivalence ratios in the experiment, the maximum of upper stability limits for blast furnace gas was 24 cm/s, while that for biomass gasified gas was 50 cm/s. Landfill gas was able to stabilize between 14 cm/s and 30 cm/s. The results indicate that the stability limits are influenced by the heating values and the compositions of gas fuels. In terms of pollutant emissions, the maximum carbon monoxide (CO) emissions of blast furnace gas reached 303 mg/m3, while for landfill gas, the CO emissions were less than 15 mg/m3for all the operating conditions. Nitrogen oxide (NOx) emissions of the three types of premixed gases were below 2.67 mg/m3.2. Lean combustion of multi-species gases with low calorific value was numerically simulated using CFD software FLUENT 6.3. The simulation conforms to the two-layer porous burner prototype used in the lab. One-dimensional, two-energy model, while considering detailed chemical kinetics mechanism was developed to simulate the combustion of blast furnace gas, biogas gasified gas, and landfill gas at equivalence ratio 0.60 and inlet velocity 0.20 m/s. The general trends of temperature profiles and emission for various premixed gases are well predicted. The three gases stabilized at different locations. In the reaction zone, OH radical and O radical are most actively involved in combustion. OH-involved elementary reactions are significantly faster than O-involved elementary reactions. NO is the only NOx species that is significantly present in the exhaust gases. The concentrations of NO2 and N2O do not exceed 1 mg/Nm3.3. Property selection of the two sections of porous burner was investigated numerically. The model developed in Chapter 4 was used for the parametric analysis, in which the thermal conductivity and convective coefficient of upstream and downstream sections are perturbed separately. The results showed that the effect of solid conductivity on temperature profiles were closely associated with the reaction zone location. If the reaction zone of the premixed gas is in the downstream section, downstream solid conductivity has more influence on its temperature, and vice versa. In all cases investigated, perturbing upstream solid conductivity has most effect on the CO emissions. Among three types of gases, CO emission of blast furnace gas is most sensitive to the change in upstream solid conductivity.