Simulation Of Coal Gasification Process In The Fluidized Bed-Entrained Flow Integrated Coal Gasifier

The coal gasification technology is widely used in power generation, chemical production, and fuel gas industry due to its low cost, high efficiency, and good for environment. Gasifier is the core component in the coal gasification technology. At present, gasifier mainly include fixed-bed, fluidized bed and entrained flow. Because of the low operation temperature in fixed-bed gasifier, raw gas contains a lot of phenols. In addition, fixed-bed gasifier need using high quality lump coal as the material. The two above restrict it's utility; Entrained flow gasifier operates under high temperature, high pressure and uses fine coal as feedstock, which lead to increase carbon conversion and effective gas components, therefore it has been getting quickly expansion. But for coal with high ash and high ash fusion temperature, using entrained flow gasifier usually need to lower ash fusion temperature of high fusibility coal by adding fusion agents, which increases cost of using inferior coal. The operating temperature (<1373.15 K) of fluidized bed is moderate, with dry feeding and dry cinder-discharging, and a wide variety of feedstocks, which make it more suitable for utilization of inferior coal in China. Because of the limitation of operating temperature in Ash Agglomerating Fluidized Bed, carbon content in fly ash is up to 70%, which makes carbon conversion in Ash Agglomerating Fluidized Bed not high enough. To solve this problem, Institute of Coal Chemistry, Chinese Academy of Sciences(ICC, CAS) develops a novel integrated coal gasification process. The new gasifier combines fluidized bed and entrained flow gasification into one unit. Within the process, the fly ash is used as feedstocks, using the high temperature(1473.15 K-1673.15 K) of entrained flow gasifier to gasify the residual carbon in fly ash, which realizes maximum utilization of elements and obtains the rational use of energy. Furthermore theoretically speaking, char and raw gas in the dense phase of fluidized bed can cool the high-temperature product gas and fine ash from entrained flow gasifier, avoiding the ash fusion phenomenon at high temperature. The sensible heat can be completely used, and heat carried by high-temperature gas and fine ash from entrained flow gasifier are used in coal gasification. Hydrodynamics in the integrated gasifier is very complex, the roal of the integrated zone in the new gasifier is not understanded clearly. At present, the integrated coal gasifier is at initial experimental stage, movement patterns of materials, the mutual influence of fluidized bed and entrained flow, temperature and material distribution in the gasifier is still not clear. All the problems bring about the great difficulty for the reactor engineering scale-up and operating parameter optimization. This paper is based on experimental results made by ICC, CAS on a 300mm (i. d.) integrated gasifier. Firstly, a reactor network model of integrated gasifier is established by CHEMKIN4.0 software on the bases of mass balance, energy balance and chemical equilibrium as well as hydrodynamics of the integrated gasifier; Secondly, the difference of the main parameters after integrating entrained flow are obtained by using the reactor network model, and the corresponding changeable rules are presented; The next, effect of heat transfer by ash on the dense phase of fluidized bed and effect of gasification reaction kinetics of fly ash on coal gas components are studied; Finally, the influence of fly ash on the system performance is studied.Based on the established reactor network model and the corresponding calculation and analysis, the following conclusions can be acquired:1. We established a reactor network model of integrated gasifier, divided the gasifier into different zone on the basis of hydrodynamics in the different regions. This method overcomes the disadvantage of studying the gasifier as a unite, and can effectively reflect the regional patterns in the gasifier at different times.2. The high-temperature gas and fine ash from the entrained flow gasifier that carry sensible heat encounter the dense phase of the fluidized bed. Heat transfer makes the temperature rise in the integrated area and the outlet coal gas; Compared with the fluidized bed gasifier, carbon conversion rise from 84.9% to 92.2%, which proves that the integrated gasifier is beneficial to improving the carbon conversion; CO content increases, CO2 content reduces, and other gases content change little after integrating the entrained flow gasifier.3. The temperature change in the dense phase of the fluidized bed is not sensitive to the heat transfer of the fine ash from the entrained flow, cooling the fine ash (or slag) with char can be achieved while avoiding the risk of ash slagging in the dense phase of the fluidized bed; The effect of heat transfer of fine ash on carbon conversion in the dense phase can be ignored; The effect of heat transfer of fine ash on gas component in the dense phase is also little; Carbon conversion of fly ash achieves 64.1%, realizing the low reactivity fly ash regasification; The rate constants of fly ash gradually decrease along the entrained flow axis.4. The addition of fly ash causes the temperature, carbon conversion and effective gas components drop a little, but the residue carbon from Ash Agglomerating Fluidized Bed is effectively utilized, which enhances the total carbon conversion. The integration concept is rational.