Research On Reaction Characteristics Of Pulverized Coal Upgrading,Partial Pyrolysis And Gasification

Energy provides an important basis for human survival and development.With the rapid development of world economy,energy consumption is increasing,which also causes various environmental problems.Clean and efficient use of energy and low-carbon sustainable development are the future energy trendency.Coal is the main energy resource in China.It is usually used by direct combustion,which is inefficient and causes pollution problems.Therefore,application of clean coal development and utilization,converting coal to alcohol and ether fuel,natural gas,oil,ethylene glycol and other alternative petroleum products is of great significance to the healthy and sustainable development of China's national economy.Based on this,this study has carried out a series of research work.Firstly,the form characteristics of moisture,drying and reabsorption mechanism of lignite,microwave upgrading and removed water analysis,and low-temperature pyrolysis upgrading were investigated.Studies show that the moisture in lignite can be divided into free water,chemically bond water,transition bond water and physically bond water.When the temperature increases and the particle size decreases,the total drying time decreases.Microwave heating can effectively remove moisture from lignite and improve coal rank.The cation concentrations in the removed water are all below1ppm,the anion concentrations are all below 10ppm,and the concentrations of heavy metal cations are all below 0.03ppm.After activated carbon,ultrafiltration membrane and alkali neutralization treatment,the removed water can be recycled.Pyrolysis at low temperature changes functional groups in the coal,increases the aromatic carbon and ring condensation degree,and effectively improves the coal rank.With the pyrolysis temperature increasing,the char yield gradually decreases while the gas and tar yields increase to 20.5%and 7.6%,respectively.Next,the pyrolysis characteristics from moderate to high temperature were explored by using fixed-bed tube furnace and drop tube furnace.The pyrolysis products were analyzed by GC,FTIR,BET and GC-MS.In the fixed-bed,pyrolysis gas production increases with the temperature.The pyrolysis gas production of Shenhua coal ranges from 618 to 749 ml/g while that of Baiyinhua coal rangesfrom 418 to 510 ml/g.As for the gas composition,H₂ content increases,CO content slightly increases while those of CH₄ and CO₂,and C₂-C₄ hydrocarbon decrease.With the increase of pyrolysis temperature,the net calorific value of pyrolysis gas decreases,but its total calorific value increases.In the DTF,the contents of H₂ and CO increases with the increased pyrolysis temperature while the CH₄ content decreases.Pyrolysis can effectively remove the coal moisture and increase the fixed carbon content,thus to increase the coal rank.With the increase of pyrolysis temperature,the char and tar yields decrease gradually while the pyrolysis gas yield increases.Then,the characteristics of resultant char gasification,combustion and pollutant emission was explored and relevant models for dynamic analysis were established.Char reactivity is affected by the chemical reaction rate and the gasification agent diffusion.Reaction rate is related to the gasification temperature and the char chemical structure while the agent diffusion is related to the pore structure.The increase of gasification temperature accelerates gasification reaction,shortens gasification time and enhances gasification reactivity.Gasification atmosphere greatly influences gasification reaction.With the increase of partial pressure of CO_2,the gasification reaction rate rises.The mixed model makes up for the homogeneous reaction model and the shrinkage core model.The bituminous coal and char have high rank,their structures are stable and their gasification activation energies are high.Pyrolysis can effectively remove water and increase coal rank,resulting in the whole combustion curves moving towards higher temperature zone.NO_x and SO₂ emissions in the combustion are both lower than 30 mg/MJ-char.Finally,co-pyrolysis and co-gasification of pulverized coal and biomass were examined.The gasification products were controlled by the alkaline materials and efficienct Ni/ZrO₂ catalyst and the whole life cycle analysis was carried out.When coal and biomass are pyrolyzed together,the quality and yield of pyrolysis gas are much higher.Alkaline gasification of coal yields more H₂and less CH₄ than alkaline gasification of brown algae.The combination of hydroxide and Ni catalyst promotes the coal dehydrogenation and gas reforming,thus generating 51.12 mmol H₂/g coal with a high purity of 99.01%.Through the whole life cycle analysis,the energy outputs by direct combustion and alkaline catalytic gasification are 781 kJ/mol-cellulose and 1060 kJ/mol-cellulose,respectively.The CO₂ generated by biomass combustion is 60 times more than that of alkaline gasification.Alkaline gasification reaction can produce higher energy with suppressed CO₂ formation.It has a great potential in the Bioenergy with CO₂ capture and storage?BECCS?.