Dynamic Modeling Of Entrained Flow Gasifiers

This paper developed a dynamic reduced order modeling approach for entrainedflow gasifiers. In the reduced order modeling approach, the space inside the gasifier isdivided into several zones according to the flow characteristics in the gasfiier, then thesezones are simulated by chemical reactors with different flow characteristics (plug flowor well-stirred flow), finally all the reactors are combined in to a reactor networkwhich can simulate the whole flow field inside the gasifier. The advantedge of thisapproach is that it not only can provide a similar gasifier internal temperaturedistribution as predicted by complex computational fluid dynamics (CFD) models,enhancing the accuracy of heat transfer calculation and slag flow simulation, but alsohas a computationally efficiency high enough to achieve real-time dynamic simulation.The reduced order model in the present paper consisted of three coupled parts: areactor network model used to simulate the gas-solid reacting flow in a gasifier, a slaglayer model describing the slag flow and phase transformation processes, and a wallheat transfer model. An oxygen-staged entrained flow gasifier was taken as an exampleto describe the modeling process of the gas-solid reacting flow inside the gasifier. Thefurnace space was divided according to detailed flow information offered by athree-dimentional CFD model, the residence time distribution function was utilized toquantitatively access the similarity between the real flow characteristics and thepredicted flow characteristics by various reactor network orgnizations. An optimalreactor network organization was chosen and mathematical models describing thegas-solid flow and reactions in each reactor were presensted.Slag flow and phase transformation processes have great impact on the operation ofentrained flow gasifiers. In this paper, we carried out a high temperature slag flowexperiment and slag flow numerical simulations. The experiment data was utilized tovalidate a CFD slag flow model using VOF approach. Then we utilized the detailedvelocity and temperature profiles provided by the CFD slag flow model toquantitatively evaluate the accuracy of different simplification methods for slag flowmodeling proposed by previous researchers, and proposed a new dynamic slag layermodeling approach with higher accuracy. In addition, this paper presented two kinds forwall heat transfer models for refractory wall and mebrane wall, respectively. Two kinds of industrial gasifier were simulated with the presented model, arefractory wall gasifier and a membrane wall gasifier. Available industraial data andliterature data were utilized to validate the model. Key variables that have the greatestimpacts on slag layer thickness were investigated by sensitivity analysis. Throughanalysis, we find a measurable parameter which can be used as the indicator of the solidslag thickness in membrane wall gasifiers. Then the gasifier model was applied to thesteady-state design of an oxygen-staged membrane wall gasifier. The influence ofseveral important design parameters on the operation economy and safty wereinvestigated, and optimization suggestions were proposed. Finally, the dynamicprocesses of the two kinds of industrial gaisfiers under different kinds of disturbancewere simulated. The differences of dynamic charcteristics between the two kinds ofgasifiers were investigated.