Polyethylene is the type of waste plastic that accounts for the most significant proportion of municipal solid waste.Waste polyethylene can be valorized via pyrolysis and produce value-added oil,gas,and char.On the ot...Polyethylene is the type of waste plastic that accounts for the most significant proportion of municipal solid waste.Waste polyethylene can be valorized via pyrolysis and produce value-added oil,gas,and char.On the other hand,self-sustaining smoldering is an emerging technical means to deal with sand/soil contaminated by organic matter.The high-temperature heat generated by smoldering can be used as a heat source for pyrolyzing waste polyethylene.Therefore,this study investigates numerically the pyrolysis of waste polyethylene driven by self-sustaining smoldering.A novel 4-step lumped kinetic model is proposed for simulating the pyrolysis of waste polyethylene.The results indicate that the operating parameters can determine the pyrolysis product yields by regulating the pyrolysis temperature and the volatile residence time.Note that higher temperatures and longer residence times favor the generation of shorter-chain pyrolysis products because of the intensified volatiles’secondary cracking.It can be concluded that a high interface-wall heat transfer coefficient(400 W m^(-2)K^(-1)),a low PE content(0.20),a high char concentration(2.4%),and a moderate air velocity(0.040 m s^(-1))are beneficial to oil yield.To some extent,this study may broaden the boundaries for the application of self-sustained smoldering-driven pyrolysis.展开更多
Crop performance on degraded soil needs special management practices to overcome soil quality limitations. In a 2-year(from summer 2006 to winter 2007–2008) field trial on a moderately degraded Alfisol in Swabi Distr...Crop performance on degraded soil needs special management practices to overcome soil quality limitations. In a 2-year(from summer 2006 to winter 2007–2008) field trial on a moderately degraded Alfisol in Swabi District(34°7′12′′N, 72°28′20′′E), Pakistan,the effects of three cropping patterns, cereal-cereal(CC), cereal-legume(CL), and cereal-cereal and legume intercrop(CLI), were tested in main plots under four fertilization treatments in sub-plots, including no fertilization(control), farmers' practice(FP, 60:45 kg ha^(-1) N:P_2O_5), recommended dose(RD, 120:90:60 kg ha^(-1) N:P_2O_5:K_2O), and integrated nutrient management(INM, 20 t ha^(-1) farmyard manure integrated with 50% N, 100% P, and K of recommended dose), using a split-plot randomized complete block design. The performance of CL was superior than CC in plant height, leaf area index(LAI), cob length, grain yield, biological yield, and grain protein(8%, 26%, 8%, 5%, 10%, and 8% increases, respectively), while CLI confirmed significant improvement only in LAI(25%) over CC. Response to nutrient inputs from all sources was in the order of INM > RD > FP > control, and the maximum net economic return by INM(23% and 2.5 times higher than RD and FP, respectively) indicated severe deficiency of both macro-and micro-nutrients in the soil as well as degraded physical properties. Increases in soil organic matter, total N, total mineral N, available P and K, total porosity, and available water-holding capacity by 6%, 34%, 24%, 50%, 13%, 5%, and 7%, respectively, and decrease in soil bulk density by 4% after four crop seasons indicated optimistic changes in soil quality as a result of the combined effects of fertilization from organic and inorganic sources and legumes within crop rotation. This study suggests that keeping the soil covered under cereal-legume rotation crops all year round and treatment with INM(50% N from organic source and 50% from inorganic source) are the best management practice for sustained production on degraded Alfisols.展开更多
基金supported by the China National Key Research and Development Plan Project(Grant No.2018YFA0702300)the National Natural Science Foundation of China(Grant Nos.51950410590 and52227813)。
文摘Polyethylene is the type of waste plastic that accounts for the most significant proportion of municipal solid waste.Waste polyethylene can be valorized via pyrolysis and produce value-added oil,gas,and char.On the other hand,self-sustaining smoldering is an emerging technical means to deal with sand/soil contaminated by organic matter.The high-temperature heat generated by smoldering can be used as a heat source for pyrolyzing waste polyethylene.Therefore,this study investigates numerically the pyrolysis of waste polyethylene driven by self-sustaining smoldering.A novel 4-step lumped kinetic model is proposed for simulating the pyrolysis of waste polyethylene.The results indicate that the operating parameters can determine the pyrolysis product yields by regulating the pyrolysis temperature and the volatile residence time.Note that higher temperatures and longer residence times favor the generation of shorter-chain pyrolysis products because of the intensified volatiles’secondary cracking.It can be concluded that a high interface-wall heat transfer coefficient(400 W m^(-2)K^(-1)),a low PE content(0.20),a high char concentration(2.4%),and a moderate air velocity(0.040 m s^(-1))are beneficial to oil yield.To some extent,this study may broaden the boundaries for the application of self-sustained smoldering-driven pyrolysis.
文摘Crop performance on degraded soil needs special management practices to overcome soil quality limitations. In a 2-year(from summer 2006 to winter 2007–2008) field trial on a moderately degraded Alfisol in Swabi District(34°7′12′′N, 72°28′20′′E), Pakistan,the effects of three cropping patterns, cereal-cereal(CC), cereal-legume(CL), and cereal-cereal and legume intercrop(CLI), were tested in main plots under four fertilization treatments in sub-plots, including no fertilization(control), farmers' practice(FP, 60:45 kg ha^(-1) N:P_2O_5), recommended dose(RD, 120:90:60 kg ha^(-1) N:P_2O_5:K_2O), and integrated nutrient management(INM, 20 t ha^(-1) farmyard manure integrated with 50% N, 100% P, and K of recommended dose), using a split-plot randomized complete block design. The performance of CL was superior than CC in plant height, leaf area index(LAI), cob length, grain yield, biological yield, and grain protein(8%, 26%, 8%, 5%, 10%, and 8% increases, respectively), while CLI confirmed significant improvement only in LAI(25%) over CC. Response to nutrient inputs from all sources was in the order of INM > RD > FP > control, and the maximum net economic return by INM(23% and 2.5 times higher than RD and FP, respectively) indicated severe deficiency of both macro-and micro-nutrients in the soil as well as degraded physical properties. Increases in soil organic matter, total N, total mineral N, available P and K, total porosity, and available water-holding capacity by 6%, 34%, 24%, 50%, 13%, 5%, and 7%, respectively, and decrease in soil bulk density by 4% after four crop seasons indicated optimistic changes in soil quality as a result of the combined effects of fertilization from organic and inorganic sources and legumes within crop rotation. This study suggests that keeping the soil covered under cereal-legume rotation crops all year round and treatment with INM(50% N from organic source and 50% from inorganic source) are the best management practice for sustained production on degraded Alfisols.
