辣椒秆与LDPE共热解特性及其炭化产物还田适宜性评价

Co-pyrolysis characteristics of chili stalk and LDPE and the suitability evaluation of carbonized products for returning to farmland

针对中国部分地区农作物秸秆与农膜处理难的问题,利用外加热热解工艺,开展了辣椒秸秆(CS,chili straw)与低密度聚乙烯(LDPE,low density polyethylene)的共热解试验,研究了不同掺混比和热解温度对共热解产物产率、特性及共热解炭还田指标的影响。结果表明,混合样品的分解主要有脱水、挥发分析出、聚合物降解和焦炭形成4个阶段。随着热解温度的升高,共热解炭的产率呈下降趋势,共热解气和共热解油的产率增加;共热解气的LHV(low heat value)处于8.6~14.5 MJ/m^(3)之间,共热解炭的LHV处于19.6~28.5 MJ/kg之间。此外,随着温度升高,共热解炭的挥发分逐渐减少,固定碳和灰分逐渐增加;共热解炭的比表面积处于0.4~2.2 m^(2)/g之间,与温度呈正相关,与掺混比呈负相关,共热解炭的pH值与温度呈正相关,整体处于10.1~12.5之间,掺混比对pH值的影响不明显;共热解炭的PAHs(polycyclic aromatic hydrocarbon)含量及TEQ(toxic equivalent quantity)毒性低于其他研究平均值,只有15%-500℃(LDPE质量分数为15%,在500℃热解)中PAHs总量超过EBC设定的优质级阈值(4 mg/kg)。高温条件下利于PAHs的分解,共热解炭用于还田应适当提高热解温度,为农村秸秆和农膜处理提供参考。

Plastic binding ropes are necessary to hang or mulch some crops(such as peppers,eggplant,and beans)in the planting process.A large amount of plastic doping has been resulted in the straw of such crops.Since plastic is difficult to degrade,the exhaust gas that generated by its incineration has posed a serious threat to the ecological environment.General treatments cannot effectively deal with such mixed wastes,particularly for the soil absorption,composting,and incineration power generation.Among them,pyrolysis is one of the most important techniques to convert the waste into renewable biofuels.This study aims to deal with the crop straw and agricultural film in some areas.Taking pepper straw and low-density polyethylene as raw materials,the poly generation of slow pyrolysis was used to explore the effects of pyrolysis temperature(400,500,600,and 700℃)and mixing ratio(0,5%,10%,and 15%)on co-pyrolysis products.The results showed that the decomposition of mixed samples mainly included three stages:dehydration,volatilization,polymer degradation,and coke formation.The pyrolysis temperature shared the an outstanding influence on the product yield.Specifically,the average yield of co-pyrolysis char decreased from 46% to 31.1%,respectively,as the temperature increased from 400℃ to 700℃,whereas,the yields of co-pyrolysis gas and oil increased from 16.9% to 24.8% and from 37.1%to 44.1%,respectively.The Low heat value(LHV)of co-pyrolysis gas and char were 8.6-14.5 MJ/m^(3) and 19.6-28.5 MJ/kg,respectively,under the experimental conditions.The volatiles of co-pyrolytic carbon gradually decreased with the increase of in pyrolysis temperature,whereas,the fixed carbon and ash increased gradually.When the temperature was 400℃,the volatiles of co-pyrolysis char increased gradually with the increase of mixing ratio,whereas,the ash gradually decreased,indicating no outstanding change of fixed carbon.However,there was no influence of the mixing ratio on each component during pyrolysis at higher temperatures.The components showed a fluctuating trend.The specific surface area of the co-pyrolytic char increased slightly with the increase of in temperature,but there was the a decrease with the increase of in mixing ratio.The pH value of co-pyrolytic carbon was depended mainly on the pyrolysis temperature.There was little effect of the mixing ratio on the pH value.The relatively high pH value of the co-pyrolytic char was achieved between 10.1 and 12.5.The PAHs content and TEQ toxicity of pyrolytic char were lower than before.Only the total PAHs at 15%-500℃ was exceeded the EBC threshold of high high-quality grade(4 mg/kg).The main PAHs compound of co-pyrolytic char was 3-ring PAHs,where the less PAHs were found with the a high molecular weight.The co-pyrolysis with CS at a higher temperature decreased the TEQ value of the co-pyrolytic char under the mixing ratio with the addition of LDPE.But However,there was no increase in the toxicity of the co-pyrolytic char.High The high temperature was conducive to the decomposition of PAHs,and increasing temperature can fully meet the requirements of co-pyrolysis char returning to the field.The findings can provide a strong reference for the treatment of rural straw and agricultural film.