海岸带环境过程实验室知识库

(1) 中国科学院烟台海岸带研究所中国科学院海岸带环境过程与生态修复重点实验室

Biochar has been reported for its beneficial effects on soil carbon sequestration, soil fertility improvement, and the immobilization of metal and organic contaminants in soils. Its large-scale agricultural and environmental application, however, is constrained by its high production cost in association with expensive equipment and operations and its high transportation cost of moving agricultural and forest residues to biochar production plant and delivering biochar to the end users. Exploring a technology for directed conversion from agricultural and forest residues to biochar in the field for local applications can significantly reduce the production and transportation costs of biochar, thus helping its applications. By mimicking the nature, where only agricultural and forest residues, water and fire were required for biomass carbonization and charcoal formation, a method for biochar production in the field was proposed and described in details. Briefly, this involved an aerobic process of biomass carbonization in a brick-constructed trough, and the formation of biochar by a fire-water coupled method. The carbonization process had the dual features: combustion on the surface of biomass and oxygen-limiting pyrolysis inside of the biomass. Three operational processes of aerobic carbonization and its termination were used to suit the production of biochars from different types of residues: 1) Large Salicaceae branches were ignited at one direction of the trough for aerobic carbonization, followed by a water-mist spray for immediate termination of the carbonization; 2) Medium-size cotton stalk was ignited at one direction for carbonization and then sprayed by a water column to crosscut formed biochar; 3) Small hollow reed straw was ignited at multiple directions, then water mist was sprayed layer by layer on biomass. The dislocated holes on side walls of brick trough performed as ignition points, channels for water mist and air ventilation channels. The biochars produced in the field by the proposed technology were characterized in this study. The biochars were relatively homogeneous, and the conversion rates from biomass to biochar were about 30%. Carbon content of biochar was 43.49%-60.30%, and nitrogen content was 0.52%-0.86%. The biochar also contained the abundant surface functional groups, with a carboxyl group content of 0.98-1.09 mol/kg and a phenolic hydroxyl group content of 0.53-0.59 mol/kg, and the specific surface area of the biochars varied between 16.0 and 262.2 m~2/g, which underpins their use as adsorbents for cations, such as ammonium ions and some heavy metals and other extraneous ions and molecules. The flue gas generated from the burning of the Salicaceae, cotton stalk, and reed straw in the carbonization process was treated by a multiple-step process to reduce particulate matter concentrations. PM 2.5 in the treated flue gas was reduced to 56, 66 and 68 mug/m~3 for Salicaceae, cotton stalk, and reed straw, respectively, and the corresponding PM 10 was reduced to 100, 114 and 128 mug/m~3, which meet the national emission standard. The biochar preparation technology provided herein is simple to operate, low in cost, and highly efficient. Based on labor, fuel, and water inputs, the productivity was 1 t/d per person, and the cost was 162.5 yuan/t by farmers. This technology for producing low-cost biochar would make its agricultural and environmental applications feasible.

生物炭具备固碳减排、提升地力、修复污染土壤等功效,但其推广应用面临着成本过高的难题。为降低其生产(设备与场地的运维费用)和使用成本(原料与炭品的运输费用),该文研发田间制炭技术,将生物质就地转化为生物炭。通过水-火联动技术,可在田间曝氧环境下制备得到生物炭。研究表明,原材料特性决定着成炭的操作工艺;其中,竹柳采用单向引燃、槽面喷水控温、通孔喷雾成炭的方式进行,棉秆采用单向引燃与控温、喷水横切炭体、喷雾成炭的方式进行,芦苇采用多位点引燃、槽面和通孔同时控温、逐层分区喷雾成炭的方式进行。采用该技术制备的生物炭表现出了较好的均质性,成炭率在30%左右;同时保存了较多的营养元素,如碳质量分数介于43.49%~60.30%、氮质量分数介于0.52%~0.86%;具有丰富的表面官能团,如羧基含量介于0.98~1.09 mol/kg、酚羟基含量介于0.53~0.59 mol/kg;具有较大的比表面积,介于16.0~262.2 m~2/g。竹柳、棉秆和芦苇在成炭过程中产生的烟气经尾气处理系统处理后(PM 2.5(56、66、68 mug/m~3)、PM 10(100、114、128 mug/m~3))均达到排放标准。该文提供的田间制炭技术操作简单、成本低且效率高。实践表明,农民在自家田里可制炭达1 t/(d·人),成本仅需162.5元/t。该文研究结果可为生物炭的推广应用提供参考。