Analysis of Operation Parameters in a Dual Fluidized Bed Biomass Gasifier Integrated with a Biomass Rotary Dryer: Development and Application of a System Model

Nargess Puadian,Jingge Li,Shusheng Pang

doi:10.3390/en7074342

Abstract

An integrated system model was developed in UniSim Design for a dual fluidized bed (DFB) biomass gasifier and a rotary biomass dryer using a combination of user-defined and built-in unit operations. A quasi-equilibrium model was used for modelling biomass steam gasification in the DFB gasifier. The biomass drying was simulated with consideration of mass and energy balances, heat transfer, and dryer’s configuration. After validation using experimental data, the developed system model was applied to investigate: (1) the effects of gasification temperature and steam to biomass (S/B) ratio on the gasification performance; (2) the effect of air supplied to the fast fluidized bed (FFB) reactor and feed biomass moisture content on the integrated system performance, energy and exergy efficiencies. It was found that gasification temperature and S/B ratio have positive effects on the gasification yields; a H2/CO ratio of 1.9 can be achieved at the gasification temperature of 850 °C with a S/B ratio of 1.2. Consumption of excessive fuel in the system at higher biomass feed moisture content can be compensated by the heat recovery such as steam generation while it has adverse impact on exergy efficiency of the system.

Highlights

Dual fluidized bed (DFB) steam gasification has been proven to be a promising technology for converting biomass into a hydrogen-rich syngas for liquid fuel synthesis or for production of pure hydrogen for fuel cell applications [1]
The developed dual fluidized bed (DFB) gasification model has been solved in UniSim and the simulation results of producer gas composition and its H2/CO ratio are compared with the corresponding experimental data reported in [32]
An integrated system model for dual fluidized bed (DFB) gasification and rotary dryer has been developed in UniSim simulation environment

Summary

Introduction

Dual fluidized bed (DFB) steam gasification has been proven to be a promising technology for converting biomass into a hydrogen-rich syngas for liquid fuel synthesis or for production of pure hydrogen for fuel cell applications [1]. A DFB gasification system reported in [1,2,3,4] consists of a bubbling fluidized bed (BFB) gasification reactor fluidized with steam as the gasification agent and a fast fluidized bed (FFB) combustion reactor fluidized with air for char combustion. In the DFB biomass gasification, the biomass is fed into the bed layer of BFB reactor where steam gasification occurs. Char generated from the gasification flows with circulating bed material to FFB reactor where it is combusted. The circulating bed material such as silica sand or olivine carries heat from the FFB reactor to the BFB reactor for endothermic gasification reactions. A controlled amount of excessive fuel may be added to provide sufficient heat to achieve target gasification temperature in the BFB reactor. The gasification process produces a hydrogen-rich producer gas with much higher calorific value of approximately 13 MJ/Nm3 compared with that from air gasification, which is approximately (FT) synthesis of transport fuels [4]

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