Experimental Research And Simulation Based On Aspen Plus Of Biomass Gasification In Fluidized Bed

Due to overexploitation and irrational utilization of conventional energy,countries are actively looking for substitute of the normal regulations energy to solve the energy crisis.Among all energy,biomass is the most promising renewable energy because of its huge production,storability and cleanness.In the thesis,both experimental research and simulation are combined together to study biomass gasification characteristics in a bubbling fluidized bed,in order to provide theoretical reference and technical support for utilization of biomass.The thesis selected straw as raw materials and air as gasifying agent,adding oxygen as secondary air to conduct experiments in a bubbling fluidized bed.Cold-state experiments were carried out to study the characteristics of feed rate,the resistance characteristics of air distribution plate and the critical fluidization velocity test to obtained the key basic parameters.Based on the thermal state experiments,the effects of gasification temperature,equivalence ratio(ER),ratio of secondary air,temperature of dilute phase and oxygen concentration of primary air on the gas component compositions,gas yields,gas heating value,gasification efficiency and carbon conversion efficiency were studied and the influence of secondary air ratio of tar precipitation was studied to investigate the properties of biomass air gasification in fluidized bed.Results show that higher gasification temperature is conducive to enhance the gasification performance,while the increasing ER weaken the combustible gas components,the gasification gas heating value reduced.Feeding secondary air results in higher temperature in dilute phase zone,leading to increase of combustible components.When increases secondary air ratio,the carbon conversion rate reaches the peak of 75.21%,the optimal secondary air ratio is about 15.24%.After the addition of secondary air,oxygenated compounds deoxidize progressively,part of monocyclic aromatic compound to PAHs,the content of N-containing heterocyclic compound decreases and aromatization of tar increase.When oxygen concentration increases from 21%to 45%,the gas heating value increases from 3.91MJ/kg to 5.03MJ/kg and the gasification efficiency increases from 29.60%to 33.59%,which shows higher oxygen concentration is conducive to higher quality gas and higher gasification efficiency.However,the gas yield is affected which leads to select appropriate oxygen concentration to ensure high gasification efficiency.A biomass gasification model was developed using Aspen Plus based on the Gibbs free energy minimization method.This model aims to predict and analyze the biomass gasification process using the blocks of the RGibbs reactor and the RYield reactor.The model was modified by the incomplete equilibrium of the RGibbs reactor to match the real processes that take place in a biomass gasifier.The model was verified and validated,and the effects of gasification pressure,moisture contents of raw material and types of materials on the gas component composition,gas yield,gasification efficiency and carbon conversion efficiency were studied on the basis of the Aspen Plus simulation.Pressurized conditions are conducive to the formation of CH4,which rapidly increase the calorific value of syngas as the gasification pressure increased from 0.1 Mpa to 6MPa.When the moisture contents of raw material increase,the growth rate of the CO2 content reaches 44.06%and the H2content,CO content,gas calorific value,gas yield and gasification efficiency decrease to some extent,which is not conducive to gasification.Gasification characteristics are greatly influenced by material characteristics.Gasification using materials with high carbon content and low ash content can be high-quality gasification.