Experimental Study And Numerical Simulation Of Coal Partial Gasification In Pressurized Fluidized Bed With A Jet

The second generation pressurized fluidized bed combined cycle based on coal partial gasification andresidual char combustion is one of the promising technologies in 21st century. Coal partial gasification inpressurized fluidized bed is a key technology. This thesis is focused on coal partial gasification behavior inthe bench-scale test equipment and the pilot-scale pressurized fluidized bed with a jet. The aim of the studyis to understand the coal partial gasification behavior at elevated pressure for developing a industry-scalecoal partial gasifier.The high temperature air/steam as gasifying agent gasification of coal was applied successfully the firsttime in a 0.1MW thermal input pressurized fluidized bed with a jet, and the inlet temperature of air/steamreached 700℃. The experimental results indicated that the gas heating value increased by more than 20%with the temperature of air/steam increasing from 300℃ to 700℃. Effect of operating parameters such astemperature, pressure, equilibrium ratio, and the ratio of steam to coal on coal partial gasificationcharacteristics were also studied. The results show that gasification temperature is the most important factor.With the temperature increasing, the concentration of combustible gas and carbon conversion are increased.The fluidization and the concentration of reactant are both improved at the elevated pressure, therefore thegasification reaction is also improved. The equilibrium ratio and the ratio of steam to coal are twoimportant parameters for optimizing gasification conditions.Based on the tests of the lab-scale, a 2MW thermal input pilot-scale coal partial gasification system wasconstructed. Three tests were carried out successfully, and the longest durable time was 12 hours. Thedeep-bed-height gasification technology was applied in No.3 test. The results show that the gas heatingvalue approaches to the calculated heating value (8%-12% lower than the theory calculated value), higherthan those of same pilot-scale coal gasifier (The HHV of fuel gas of U.K. CRE was 3.7-3.9 MJ/Nm3 whilethe LHV of fuel gas of Japanese PDU was 3.3-4.02 MJ/Nm3), and close to the HHV (4.85 MJ/Nm3) of fuelgas of American PSDF. The carbon conversion is higher apparently than that in shallow-bed-heightgasification, and the operating temperature is nearly uniform in the whole fluidized bed. The maximumdeviation of bed temperature is only 30℃ in the range of 0.86m and 5.26m above the air inlet nozzle.Comparison of coal partial gasification in the lab-scale and pilot-scale gasifier show that the coalgasification characteristics behaved differently when the spout-fluid bed or jetting fluidized bed scaled up.The mixing of solid and gas become worse and the heat loss is decreased after the reactor scale-up. Twomethods for scale-up were proposed and discussed in this thesis.In order to study coal partial gasification process at elevated pressure, a nonisothermal model ofpressurized fluidized bed with a jet was constructed. The volatile of coal and gasification of char areconsidered using the reaction equilibrium and dynamics theory, respectively. The effect of pressure onhydrodynamics, combustion and gasification was taken into account. Compared the calculated values withexperimental ones show that the calculated values are consistent with the experimental values.