炭化-还原两步法资源化利用城市固废废塑料的技术基础

Increasing municipal solid waste(MSW) is one of the most serious problems that restrict the sustainable development of the modern cities. However, recycling of the waste plastics from MSW as new resources is the key to its clean dispose. Based on the concept of flow sheet integrity, quality match and synergy enhancement, a novel technical clue for the utilizaton of waste plastics in the MSW through the rotary hearth furnace reduction unit of steel enterprise has been proposed through the comprehensive integration of carbonization of waste plastics with coal and rotary hearth furnace carbon composite direct reduction technology. In order to uncover the fundamental problems in the preparation of mixed reducing agent and the reduction of composite pellet, the research on the carbonization of waste plastics with coal and the process characterization, the reduction behavior of mixed reducing agent/iron ore composite pellet and carbon consumption mechanism, and off gas formation behavior during reduction and properties of reduced pellets have been conducted in the project. The physical and chemical structure and gasification characteristics of the carbonized product from waste plastics and pulverized coal would be revealed. The reduction mechanism of iron oxide by the new mixed reducing agent would be made clear. The synergy law between iron oxide reduction and plastics fast consumption during pellet reduction would also be obtained. The final products should meet the requirements of the subsequent processing unit. The research results can provide theoretical basis for the development of efficient, clean and low cost technology for the utilization of thermoplastic waste plastics in MSW by the newly proposed carbonization-reduction two step method.

日益增长的生活垃圾是制约城市可持续发展的难题，其中废塑料的资源化利用则是清洁治理城市生活垃圾的关键。基于流程完整、品质匹配、协同强化的理念，综合“热塑性废塑料-煤粉混合炭化预处理技术”和“转底炉含碳球团直接还原技术”，本项目提出了利用钢铁企业转底炉直接还原工序协同处置城市固废中热塑性废塑料的技术思路。针对废塑料-煤粉混合还原剂制备和混合还原剂-铁矿复合球团还原过程的基础问题，重点开展废塑料-煤粉共炭化预处理及过程表征、混合还原剂-铁矿复合球团碳热还原和碳素消耗机制、复合球团还原过程气体生成及金属化球团性能结构等的基础研究，揭示废塑料-煤粉共炭化产物的物理化学结构及溶损特性，明晰新型混合还原剂对铁氧化物的碳热还原机制，获得铁氧化物还原与塑料快速消耗转化的协同规律，制得满足后续工艺要求的产品，为开发适用于城市生活垃圾中热塑性废塑料低成本清洁高效资源化利用的炭化-还原两步法新技术提供理论支撑。

日益增长的生活垃圾是制约城市可持续发展的难题，其中废塑料的资源化利用则是清洁治理城市生活垃圾的关键。本项目提出了利用钢铁企业转底炉直接还原工序协同处置城市生活垃圾中热塑性废塑料的技术思路。针对废塑料-固碳粉粒化混合还原剂的制备和混合还原剂-铁矿复合球团还原过程的基础问题，重点开展了废塑料-煤粉共炭化预处理及过程表征、混合还原剂-铁矿复合球团碳热还原和碳素消耗机制、复合球团还原过程气体生成及金属化球团性能结构等的基础研究。主要试验结果如下：PE薄膜塑料-固体碳质粉末混合物的适宜热处理温度为400℃，适宜的PE配比为20%。PE会降低固碳粉的石墨化度，同时提高热处理产物中双键物质的含量，从而提高了产物的反应性。PVC可以通过低温热处理实现独立粒化。随着温度的升高，PVC破碎性能快速提高，340℃以后，温度对破碎性能影响很小，且PVC在370℃脱氯率最大，因此，PVC最佳热处理粒化温度为370℃。混合还原剂会引起含碳球团还原过程膨胀，强度降低，提高还原温度、延长还原时间，可提高球团强度。为了实现最大限度的废塑料消耗，在保证金属化球团强度和较高金属化率的前提下，添加20％的塑料较为合理。无烟煤与混合还原剂两种球团的还原控速环节均为碳的气化反应，混合还原剂球团的活化能较小，为287.91kJ/mol。PVC含碳球团在低温下可有较高的反应速率，C/O为0.8时金属化率最大，之后随着C/O的增加，金属化率降低。PVC含碳球团还原过程脱氯率较低，为43%~50%。氧化铁会促进碳氢化合物分解，提高产物气中H2和CO的浓度，同时塑料分解的气态产物也会促进氧化铁的还原。通过上述研究，揭示了废塑料-固碳粉共热产物的物理化学结构及溶损特性，明晰了新型混合还原剂对铁氧化物的碳热还原机制，获得了铁氧化物还原与塑料快速消耗转化的协同规律，为开发适用于城市生活垃圾中热塑性废塑料低成本清洁高效资源化利用新技术提供了理论支撑，有助于钢铁工业的节能降碳和绿色低碳循环发展经济体系的建立。