Research On The Co-Pyrolysis Reclamation Of Coal And Municipal Solid Waste

In this paper, treatment and disposal technologies of municipal solid waste (municipal domestic waste and municipal sludge) were summarized. Then the present status of co-pyrolysis of coal and municipal solid waste was further discussed in detail, and these two materials were selected as raw materials for co-pyrolysis experiments. The main works were as follows:(1) Effects of material ratios of co-pyrolysis, pyrolysis temperature and other factors on the product distribution were studied with shenhua coal and municipal domestic waste as the starting materials. The modern analysis methods (GC/MS and GC, etc) were employed to determine the properties of pyrolytic carbon, tar and pyrolytic gas, which could be basic parameters for the co-pyrolysis reclamation process of coal and municipal domestic waste.(2)The sludge-coal based activated carbon was prepared from low-quality coal and municipal sludge by carbonization and activation technology. Then several parameters were investigated to obtain the optimum process conditions, including material ratios of co-pyrolysis, activation agent ratio, activation temperature, temperature holding time, etc. Besides, in order to reduce the production cost and the activation agent ratio, the effects of complex activator on carbonization and activation reaction were explored preliminary, and the surface topography of activated carbon was analyzed by SEM and BET surface area measurement.The results showed that:(1)There was an obvious thermogravimetic overlap area between shenhua coal and organic compositions of municipal domestic waste, which made the co-pyrolysis mutual effect possible. The main pyrolysis product of shenhua coal was pyrolysis carbon, calorific value of which was 29.30MJ/kg. The tar from shenhua coal contained 30.79% alkane and 41.13% arene with benzene and naphthalene amounting 23.00%. The pyrolysis gas contained 51.59% H2, while the content of CO2 was only 4.82%. The pyrolysis carbon of municipal domestic waste contained massive ash, whose calorific value was only 4.78MJ/kg. Beside of 25.70% alkene and 28.38% alkane, the tar from municipal domestic waste still contained plentiful oxycompounds like alcohols and esters, etc. The pyrolysis gas of municipal domestic waste contained 31.64% CO2, while H2 was only 7.32%. There was a certain synergy in the process of co-pyrolysis:with the increase of additive quantity of shenhua coal, the yield and calorific value of pyrolysis carbon increased, but the yield of pyrolysis tar and gas decreased. And the benzene and naphthalene increased by 3.20%～7.48%, the hydrocarbon increased by 10.14%～12.69%, and the oxycompounds decreased by 6.60%～14.64%. As a result, the calorific value of tar increased and presented a tendency of chain alkylating.There was a great effect of pyrolysis temperature on the distribution and properties of co-pyrolysis products:with the rising of temperature, the yield of pyrolysis carbon and the content of volatile decreased, but the content of ash and fixed carbon increased. The content of arene, alkene and alkane showed a trend from ascent to descent, and reached maximum at 850℃. The content of CO2, CH4 and CnHm decreased gradually while the content of CO and H2 increased gradually, which caused the calorific value of pyrolysis gas decreased.(2)After mixed directly and carbonized at 600℃, there was a mutual effect between municipal sludge and low-quality coal making the iodine adsorption value of carbon structures and the number of initial pores increased. Combining the single factor experiment with the determination of iodine adsorption value, the optimal conditions of carbonization and activation technology were determined (low-quality coal, municipal sludge and activator K2CO3 mixed in the proportions of 30:70:44 and reacted for 90min at 900℃), and under these conditions the iodine adsorption value of activated carbon could be up to 1064mg/g after pickling and drying. On the other hand, complex activator (K2CO3 and potassium A) showed notable effects on the performance of activated carbon. Under the precondition of stable iodine adsorption value of activated carbon, the adding of potassium A significantly reduced the adding amount of K2CO3. The result indicated that when low-quality coal, municipal sludge, K2CO3 and potassium A were mixed in the proportions of 30:70:22:4.4, the iodine adsorption value of activated carbon could reach 842mg/g, BET specific surface area was 669.95 m2/g, the pore volumes of mesoporous and micropore were 0.30ml/g and 0.19ml/g respectively, while the total was 0.62ml/g. The average pore size of activated carbon was 5.54nm, the structures of which were shown more parallel walls.