Study On Refuse Derived Fuel Product From Waste And Energy Utilization

With the rapid growth in municipal solid waste(MSW)generation and the leading energy and environmental issues,the emphasis on MSW end-of-pipe treatment can no longer meet the needs of sustainable development.Under the background of launching the ecological civilization construction,environmentally-friendly treatment of reduce,reuse and safety has received first choice of the third-generation MSW treatment technology.Source pre-treatment and quality upgrade and thermal treatment under controlled atmosphere are important approaches for energy utilization and harmless disposal of MSW in order to overcome the lack of basic and application researches for development of traditional thermal conversion technology in our country,but thermal conversion characteristics and pollutants migration and transfer mechanism of high heating value waste under controlled atmosphere are still unclear after classification.In view of the facts,the present study based on source separation and controlled atmosphere investigates different units including source pre-treatment and quality upgrade module,thermal conversion module,emission control module,and preparation of RDF(Refuse Derived Fuel).In terms of source pre-treatment and quality upgrade,changes of characteristics before and after separating are investigated in preparation of RDF.Effects of RDF which are prepared by traditional technology and source pre-treatment on environment are evaluated by using LCA(Life Cycle Assessment),classified technology is designed to separate MSW into dried waste and waterish waste;high heating value waste is separated from dried waste by mechanical separation technology,which could make moisture content decrease from 54%to 18%,and the content of electronic waste is nearly zero;chlorine content decreases 35.8%-43.7%.Results of LCA reveal that the source separation method can reduce the environmental load value by over 40%compared with traditional method.In terms of thermal conversion under controlled atmosphere,firstly,tube furnace experiments combined with Aspen plus:application to investigate pyrolysis characteristics of RDF which are affected by the factors including final pyrolysis temperature,material ratio,catalysts,additives,and heating rate.Results show that the rising pyrolysis temperature increases the yield of liquid and gas phase products and decreases the yield of semi-coke,which could promote H2 and CO yield;pyrolysis ratio decreases with biomass proportion of material reducing.In comparison to adding waste lime in RDF,adding sewage sludge could decrease the yields of liquid products and semi-coke and increase the yield of pyrolysis gas.The present study also investigates preparation of fuel oil from RDF fast pyrolysis at medium temperature,which reveals oil yield and phenolics content increase(up to 15.9%and 44.0%respectively)with sawdust proportion of RDF increasing but heat value of oil decreases(from 27.7 MJ/kg to 24.6MJ/kg);oil yield reaches 7.0%after adding CaO,and the heat value of pyrolysis oil is 27.3MJ/kg after adding MnO2;the heat value could increase from 26.3MJ/kg to 22.4MJ/kg with content of cloth increasing in pyrolysis.Secondly,gasification characteristics under poor oxygen atmosphere are investigated in a fluidized bed.The content of CO2 increases with rising equivalence ratio,and contents of H2,CO and CH4 and low heating value decrease.The optimum operating conditions are determined as follows:the equivalence ratio is 0.4;pyrolysis temperature is 700?.Adding NaCl could promote secondary cracking of tar during gasification and enhance the yield and quality of gas noticeably;the content of H2 and ratio of H2/CO are increased in the temperature range of 800-900?.This paper mainly studies effects of many factors on emission control of RDF incineration.Firstly,the effects of operating parameters such as material ratio,incineration temperature,oxygen content at furnace outlet and emission of normal pollutant,HCl and dioxins with an addition of CaO are investigated by a fluidized bed.Results reveal that gas concentrations of RDF incineration are lower than national standard after classification,and the model of fluidized bed incineration is built according to Gibbs free energy.The amount of CO decreases and that of SO2 increases respectively with the plastics content of RDF increasing;the content of NO rises to the turning point,then flats.CO emission decreases with rising bed temperature,and SO2 emission increases slowly;with oxygen increasing,CO emission reduces,and SO2 and NO emission shows an inverse trend.HCl is formed mainly in the low-temperature area;the emission concentration of HCl increases with the increase in its plastic proportion for RDF,and that of HCl and dioxins decrease with the increase in addition quantity of CaO and oxygen content at furnace outlet;the RDF of 45%plastics emits the highest concentration of total dioxin toxicity.The increasing temperature of the bed decreases the toxic concentration of the dioxin;when the temperature is 850?,the total production of dioxin from the RDF reaches 0.1469 ng I-TEQ Nm-3.In terms of RDF preparation,the system whose disposal throughput is 3t/d are designed based on concept "source pre-treatment and quality upgrade-separation-crushing-forming".Separation efficiency,product feature and energy consumption analysis of the system are evaluated in the present study,and the products are added to fuel of power plants for application test.The screening efficiency of trammel and rolling rubber tube is 88.02%and 89.72%,respectively;the maximum screening efficiency of pneumatic separation is 93.26%;the efficiency of the whole system is higher than 85%.The unit consumption is 164.64 kWh/t;the length and grain diameter of RDF product is about 12-25mm and 8-12mm,respectively.Incineration gases of RDF and coal co-combustion in power plant meet the standard discharge.