Research On Lignite Upgrading Technology And It's Life Cycle Assessment

The characteristic of resources in China is "coal-rich,oil-poor and gas-poor".Coal accounts for about 64%of the primary energy consumption,and aout 13%of the total amount of national coal resource is occupied by lignite.In present,with the rapid development of China's economy and the increasing requirements for energy,the supply of domestic high-quality coal has become increasingly strained.Lignite is mainly used for power generation and chemical industry.The usage of technology,which makes lignite widely development and utilization,to resolve the issues such as high moisture content,easily weathered,easily spontaneous combustion,high transportation costs per unit of energy,has become the key to solve our problem of a shortage of high-quality coal resources.The key technology to popularize the utilization of lignite is lignite upgrading,which mainly includes lignite pyrolysis and lignite drying.Aiming at the lignite produced by Baorixile Surface Mine,the influence of operating parameters(such as pyrolysis temperature,residence time,and so on)on lignite pyrolysis production and the chemical structures of semicoke are studied experimentally.It is helpful for lignite to both accelerate volatilize and increase heat value with the increase of pyrolysis temperature and residence time.The decomposition degree is enhanced with the increase of pyrolysis ending temperature,so the ratio of O/C in semicoke is lower,which is demonstrated that the rank of coalification of lignite is increasing.The lignite pyrolysis kinetic is also researched from 400? to 400?,experimental results indicate that the Dolye model is suitable to describe lignte pyrolysis procedure,in which the pre-exponential factor(A)is 0.14?0.21min-1 and activation energy(E)is 8.78?10.01KJ/mol.A pilot system with scale of 100 million tons per year is proposed for lignite pyrolysis technology.A pilot-scale high-power microwave drying system to deal with 15 million tons lignite per year is established.The lignite drying kinetic and the effect of operating paramters on drying production are sdtudied based on the experimental platform.The lignite drying kinetic model is established based on Midilli-Kucuk model,which is MR=1.0254exp(-2.0553×t1.5687)+3.5356t.In addition,the influences of different combination of heating powders,transport speed and coal seam thickness on dryingproduct(moisture content,heat value,resorption,drop strength)are studied.The experimetal results illustrate that microwave drying technology can effectively promote the internal moisture precipitation outside,meanwhile,material surface may not be over-heated and surface hardening(crust)is avoided.Therefore,uniform heating of whole grains is achieved and the rate and quality of drying is greatly improved.The overall temperature stays in low level and no volatiles precipitate.The structure of coal quality and composition is not destroyed and the system remains in high security level.Spontaneous combustion is found for the drying production of special lignite.The drying lignite owns an optimum moisture content after resorption,moisture content is about 11.3%for the lignite with diameter 6cm,about 10.5%for lignite with diameter 1-3cm and about 9%for lignite with diameter less than 1cm.So,the reasonable lignite diameter can be choosen for speical moisture content.In order to estimate the influence of lignite pyrolysis technology and lignite microwave drying technology on environment and economic cost quantificationally,life cycle impact assessment(LCIA)is used to study a new power generation technology including both lignite drying and pyrolysis processes.The system boundary and detailed life cycle inventory are firstly determined.The quantitative research results show that the key impact factors are electricity,electricity recovery,transport,coal mining and direct emission.It is helpful to increase lignite heat value by drying technology which will comsume much electricity,but it is benefit to decrease the influence to environment.LCIA and life cycle costing(LCC)assessment are adopted to study the effect of seven power generation proposals on environment and economic costing quantificationally.The relatively complete life cycle inventory is established,the key points are found to save energy and reduce emmision.The comparison results among different lignite drying upgrading technologies indicate that optimized energy consumption,raw coal/lignite consumption are the key points to make environment and economic achieve a win-win situation.In this dissertation,the quantitative relationship among main micro-variables,macro-environment and economic impact of lignite life cycle in China is confirmed.The results can not only provide useful data and theoretical support of the lignite usage for decision-makers in all areas,but also provide scientific evidences for improving energy efficiency and reducing environmental pollution caused by lignite pyrolysis and power plants.