Modeling,Simulation And Optimization Analysis For BGL Gasifier

Recently,BGL(British Gas Lurgi)gasification technology has attracted much attention thanks to its wide adaptability,high gasification efficiency,and environmental benefits.BGL gasifier adopts liquid-slagging processes,and the temperature near the slag discharging needs to be kept higher than the ash fusion point.The composition and the temperature profiles inside the reactor are extremely difficult to measure due to high operating temperature and pressure.Therefore,an accurate simulation and quantitative analysis of the BGL gasifier is very important for improving the scientific understanding of the gasifier operating performance and facilitating the optimization of the gasifier to achieve higher gasifier efficiencies.According to the fluid flow characteristics and gasification mechanism,a one-dimensional steady-state segmented model of the BGL gasifier was established.In this model,the BGL gasifier was divided into the concurrent-flow and the countercurrent-flow zones.The model was formed by coupling mass and energy conservation equations.The coal pyrolysis models,kinetics models,and heat transfer models were included in these equations.An industrial BGL gasifier was simulated by the proposed model and the simulation results were compared with its operation data.It was shown that the simulation results agreed with the operation data.Furthermore,the effects of oxygen-to-coal ratio and steam-to-coal ratio on the performance of the gasifier were investigated.The results indicated that carbon conversion and steam decomposition were influenced by different oxygen-to-coal ratio.As oxygen-to-coal ratio increased,carbon conversion increased gradually but steam decomposition increased firstly and then decreased.When oxygen-to-coal ratio was 0.47 kg·kg-1,the maximum of steam decomposition was obtained.Higher steam-to-coal ratio was beneficial to the water-gas shift reaction.The reason was that this reaction was restricted by chemical equilibrium.When the gasification agent was sufficient,the consumption of steam can be ignored than the increase of steam in the feedstock.Therefore,the steam decomposition decreased gradually with the increase of steam-to-coal ratio.According to the simulation results,the optimal operating conditions of the BGL gasifier were obtained,that was,oxygen-to-coal ratio was 0.47-0.49 kg · kg-1 and steam-to-coal ratio was 0.32-0.40 kg·kg-1.The level of methane in the synthesis gas which produced by an industrial BGL gasifier using bituminous coal was high.And the synthesis gas cannot be directly used as feed gas for synthetic ammonia.The method of supplementary combustion(that was,adding a set of nozzles above the original nozzles of the BGL gasifier and introducing supplementary combustion agent)was used to lower the methane level.When the feed rate of supplementary combustion agent(oxygen and steam)was 25%of the first nozzles(original nozzles),the carbon conversion and the methane level conformed to the industrial requirements.The performance of the gasifier was influenced by steam distribution proportion between nozzles at different positions.High hydrogen-carbon ratio feed gas for synthetic ammonia was produced by increasing the steam distribution proportion at the first nozzles.