Study On Characteristics For Co-gasification Of Biomass And Coal In Fluidized Bed Based On CFD-DEM Method

Global consumption of fossil fuels continues to increase,promoting the large-scale development of alternative renewable energy sources.Compared with coal,biomass is more suitable for gasification because of its physical characteristics to obtain high calorific value of combustible gas.The biomass fuel rich in alkali metal and alkaline earth metal AAEM?Alkali and alkaline earth metals?can induce catalytic activity to promote the conversion of carbon in coal fuel.At this stage the fossil fuels will still be the main source of energy and emissions.The biomass and coal fuel for co-gasification can effectively improve fuel efficiency and reduce the pressure in the pollution of the environment.The fluidized bed gasification technology is one of the most commercialized clean combustion technologies in the world.This kind of gasifier is more suitable for gasification of relatively inferior biomass fuel and is more suitable for combined gasification process.This paper uses the method of numerical simulation study the fluidized bed gasification process.The CFD-DEM?Fluid Dynamics-Discrete Element?is used to study the biomass gasification including chemical reactions process,which usually used in the cold flow process as one of hot spots in recent years.The coupling model is established and its reliability is verified to make up for the deficiency of the CFD-DEM method in application fields.Different from the traditional two-fluid method,the advantage of this method is to track the particles discretized,and calculate the true motion and force of each particle.This method can provide high fidelity,high detailed gas solid motion information to study the influence between flow and reactions,which has laid the foundation for co-gasification of biomass and fossil fuels.The gasification process of biomass in fluidized bed is simulated by CFD-DEM method.I studied the movement rule of particles after entering the furnace and the influence of chemical reaction on the movement and calculated the output and distribution characteristics of gasification products.The influence of gasification temperature and steam fuel ratio on gasification process is summarized.The variation law of gasification product yield with this parameter is obtained.It is concluded that H₂,CO,CO₂ and CH₄have similar distribution trends during gasification.H₂ and CO are greatly affected by gasification temperature,while CO₂and CH₄ are not sensitive to temperature change.The influence of steam fuel ratio S/B on the yield of syngas components is very small.Based on CFD-DEM method of fluidized bed the co-gasification between biomass and coal in numerical simulation has been down.The AAEM catalysis in the biomass gasification reaction is verified.I set up six group contrast simulation experiment and study the rules of blend ratio on gas production,calculating the corresponding calorific value of syngas,carbon conversion rate,hydrogen conversion rate and cooling efficiency.For co-gasification process with steam,the hydrogen conversion rate and cold gas efficiency compared with separate gasification process are obviously enhanced.When the biomass accounted increase to 75%,the content of CO and CO₂ is the lowest while the content of H₂ and CH₄ is the highest,and the high calorific value of the syngas SGHV?synthetic gas heating value?,hydrogen and carbon conversion efficiency reach the maximum under this mixed fuel ratio.The cold gas efficiency affected by the mixed fuel ratio is not obvious and reaches its maximum when the biomass content is 50%.