Simulation of a catalytic coal gasification in elevated jetting fluidized bed

摘要

A number simulation study is conducted for catalytic coal gasification in pressured 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 takes account of pressured hydrodynamics, mass and heat transfers and catalytic reaction kinetics. The model is first validated by comparing predicted results with experimental data in a pressured electric-heated 1t/d PDU with 0.2m internal diameter, and 3m height. The calculated vales show good agreement with experimental results on the bed temperature and gas composition. The prediction presents that the temperature of particle in jet almost reaches the maximum value when the oxygen is introduced, then sharply decreases and levels off due to high reaction rate of catalytic char combustion and large heat transfer coefficients under high pressure. The gas concentration in the grid zone increase slowly due to low particle hold up and short resident time. With synthesis gas introduced to annulus from the distributor, H_2 and CO immediately appear in jet due to the fast gas exchange between jet and annuls. The way to promote methane production by increasing bed height is practicable, although increasing the risk 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 in bubble zone. Moreover, sensitivity analysis by this simulation for some operation conditions such as catalyst loading amount, oxygen and steam flow rates, bed temperatures and bed pressures on methane formation are carried out. The simulation results are shown that key operation parameters are steam flow rate and bed pressure.