Simulation of a catalytic coal gasification in elevated jetting fluidized bed

摘要

A number simulation study is conducted for catalytic coal gasification inpressured jetting fluidized bed. The gasifier is divided into three parts: grid zone,bubble zone and freeboard zone. It is based on a steady-state model which takesaccount of pressured hydrodynamics, mass and heat transfers and catalytic reactionkinetics.The model is first validated by comparing predicted results with experimentaldata in a pressured electric-heated 1t/d PDU with 0.2m internal diameter, and 3mheight. The calculated vales show good agreement with experimental results on thebed temperature and gas composition. The prediction presents that the temperature ofparticle in jet almost reaches the maximum value when the oxygen is introduced, thensharply decreases and levels off due to high reaction rate of catalytic char combustionand large heat transfer coefficients under high pressure. The gas concentration in thegrid zone increase slowly due to low particle hold up and short resident time. Withsynthesis gas introduced to annulus from the distributor, H_2 and CO immediatelyappear in jet due to the fast gas exchange between jet and annuls. The way to promotemethane production by increasing bed height is practicable, although increasing therisk of slug. According to the calculated results, the maximum mean bubble size(0.1m) at 2.5MPa is less than about half of reactor diameter(0.2m), the bed operate inbubble zone. Moreover, sensitivity analysis by this simulation for some operationconditions such as catalyst loading amount, oxygen and steam flow rates, bedtemperatures and bed pressures on methane formation are carried out. The simulationresults are shown that key operation parameters are steam flow rate and bed pressure.