| The removal of CO2and tar in fuel gas produced by biomass thermal conversionhas aroused more attention due to their adverse effects on the subsequent fuel gasapplication. In this thesis, the technical route of biomass pyrolysis in-situ CO2absorption and tar removal with CaO has been proposed in order to get high-qualityfuel gas. Mechanisms of the key processes and the optimum operation parameterswere investigated with combination of experiments and simulating calculations,which will be the foundation of the large-scale application of this technology.A thermodynamic database of the compounds from biomass thermal conversionwas preliminary established which could supply the basic data for thermodynamiccalculations and analysis. Through the simulations of thermodynamic equilibrium, theeffects of temperature, pressure, mass ratio of CaO to sawdust (Ca/B) on the productsdistribution of the biomass pyrolysis in-situ CO2absorption were investigated. Itindicated that atmospheric pressure,700℃and Ca/B of0.65would be the suitableoperating conditions to produce the high quality fuel gas with good economicprospects. Effects of the temperature, heating rate, CO2partial pressure, componentsof gas and ash on the CO2capture capacity of CaO were studied in TGA. The resultsshowed that the high conversion of absorption was got in the temperature of700℃and CaO conversion rate decreased with the increasing number of cycles. Gascomponents (H2, CO, CH4and water vapor) and MgO addition had the beneficialeffects on the carbonation reaction, while K2CO3addition decreased the absorptionactivity. Catalytic cracking of toluene using CaO was carried out in a fixed bedstainless-steel reactor based on the thermodynamic calculations. It was found thattoluene conversion rose with the increasing temperature and it was about52%at thetemperature of700℃. Water vapor could promote catalytic cracking of toluene, butexcess steam decreased the lower heating value (LHV) of product gas.Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) system has beenapplied to evaluate the behavior of sawdust pyrolysis in-situ CO2absorption and tarremoval with CaO. The results indicated that LHV of the permanent gas products rosewith the increase of Ca/B and it was near16MJ/Nm3and slightly changed above0.65of Ca/B. Aldehydes and ketones had the largest yields in the condensable products at different Ca/B. With the increase of Ca/B, the yields of aldehydes and ketones slightlydecreased, while those of other three groups significantly decreased. Compared to thatwith no CaO addition, total tar content obtained at0.65of Ca/B was reduced by40%.The high carbon content of66.9wt.%makes char suitable to act as a solid fuel, whichcan supply the energy needed by sawdust pyrolysis.Based on the results of calculations and experiments, one system of a movingbed pyrolyzer coupled with a fluid bed combustor (MFS) has been developed toproduce high quality fuel gas. With the operating conditions of pyrolysis temperatureof700℃,0.65of Ca/B and atmospheric pressure, the experiments were carried out inMFS system. The average contents of H2and CH4were about40vol.%and26vol.%,while those of CO and CO2were about17vol.%and4vol.%, respectively. LHV ofthe produced fuel gas was above16MJ/Nm3and the content of tar was under50mg/Nm3. Cold gas efficiency of the system reached51.2%and energy self-sufficiencywas achieved with good insulation through the analysis of system energy. Therefore,with high efficiency and simple operation, this technology may be a promising routeto achieve high quality fuel gas for biomass utilization. |
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