田间“限氧喷雾”制备生物炭技术与炭质表征

Biochars Made in the Field Using Coupled Oxygen-Limiting and Mist-Spraying Technique and Their Properties

生物炭具有改良土壤、固碳减排、吸附重金属和有机污染物等方面的有益作用,但其农业和环保应用面临着成本过高这一瓶颈问题.在田间直接将生物质转化为生物炭,可节省原材料收集与炭品运输等环节的费用,降低使用成本.可通过喷雾技术在田间限氧条件下实现生物炭的制备,其工艺如下:物料在槽内经逐层压实后,采用单向引燃、逐次喷雾的方式辅助竹柳和棉秆成炭;采用多位点引燃、逐层喷雾的方式辅助芦苇成炭.制炭期间,土槽中的侧壁开孔方管起通气和限氧作用以控制适燃,铁质密网起限氧、防尘和提供喷雾通道等作用以控制成炭.采用该技术制备的生物炭表现出了较好的同槽均质性和异槽同质性,成炭率达30%,制备得到的炭含有丰富的羧基(0.71~1.43mol/kg)、酚羟基(0.43~1.09mol/kg)官能团,且具有较大的比表面积(45.5~83.2m2/g).田间“限氧喷雾”技术为生物炭的制备提供了新的思路和技术选项,也为其农业和环保应用创造了条件.

Biochars have a range of functions from improving soil properties and remediating contaminated soils to reducing greenhouse gas emission from soil and increasing carbon content in soil. Their large-scale application,however,has been constrained by high costs of production and transportation. To solve this problem,a novel method has been developed for biochar production in the field with a coupled oxygen-limiting and mist-spraying technique. Agricultural and forest residues are placed in a soil trough and compacted layer by layer,a steel square tube with multiple holes is imbedded in the biomass,and an iron mesh is put on the top of it. The tube has the function of adjusting ventilation and oxygen supply to maintain flame temperature during biomass burning;and the mesh allows for the formation of a water film to limit oxygen supply. In field operations,cotton stalk or Salicaceae in the trough is ignited at one direction,whereas reed straw is ignited at multiple positions,for biomass carbonization,followed by water mist spraying layer by layer for a quick stop of carbonization. The biochars thus obtained have a yield of about30% and are relatively homogeneous. They have abundant carboxyl group (0.71-1.43 mol/kg) and phenolic hydroxyl group (0.43-1.09 mol/kg) and a specific surface area of 45.5-83.2 m2/g. Being able to produce good-quality biochars directly in the field at a low cost,this method makes feasible agricultural and environmental application of biochars.