Whole process simulation of MSW gasification and melting system based on Aspen Plus
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摘要:
城市固体废物（MSW）气化熔融工艺能够减少二噁英的生成和熔融固化重金属，是一种清洁高效的固体废物处理方式。已有研究多针对MSW的热解特性以及污染物的生成与排放，而对气化熔融工艺系统模块之间的影响和各反应器间物质流、能量流的联动变化过程研究不足。利用Aspen Plus模拟平台，基于吉布斯自由能最小化原理，对MSW气化熔融工艺进行了全流程模拟研究，分析了垃圾干燥温度、垃圾含水率、气化温度、气化介质以及灰熔点对工艺流程节点参数、物质流和能量流的影响，并提出了优化的工艺流程和运行参数。结果表明：在垃圾热解模拟时，垃圾含水率为9%，通过烟气循环能达到能量自给；在相同条件下，以水蒸气作为气化介质的气化效率最高，且在气化温度为850 ℃，水蒸气当量比为50%时，达到最佳工艺效果；当气化后产生的焦炭在熔融炉内燃烧刚满足灰熔点温度时，灰熔点的升高使气化剂比例、气化气有效气体摩尔流量和碳转化率不断降低。不同工况下的物质流、能量流的变化对实际工程具有指导意义。
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关键词:
- 城市固体废物（MSW） /
- 气化熔融 /
- 全流程模拟 /
- 节点参数 /
- 熔融炉
Abstract:The gasification and melting process of municipal solid waste (MSW) can reduce the formation of dioxins and melt heavy metals, which is a clean and efficient solid waste treatment method. At present, most of the research is on the pyrolysis characteristics of MSW and the generation and emission of pollutants, while the research on the influence between the modules of the gasification and melting process system and the linkage change process of material flow and energy flow between each reactor is insufficient. The whole process simulation of MSW gasification and melting process was carried out by using Aspen Plus simulation platform based on Gibbs free energy minimization principle. The effects of waste drying temperature, waste moisture content, gasification temperature, gasification medium and ash melting point on the process node parameters, material flow and energy flow were analyzed, and the optimized process flow and operation parameters were proposed. The results showed that when the moisture content of garbage was 9%, the simulation of garbage pyrolysis could achieve energy self-sufficiency through flue gas circulation. Under the same conditions, different gasification agent media had the highest gasification efficiency using water vapor as the gasification medium, and the optimal process was achieved at a gasification temperature of 850 ℃ and a water vapor equivalence ratio of 50%. When the char produced after gasification was burned in the melting furnace to meet the ash melting point temperature, the increase of ash melting point made the proportion of gasification agent, the effective gas molar flow of gasification gas and the carbon conversion rate decreased continuously. The changes of material flow and energy flow under different working conditions has guiding significance for practical engineering.
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图 1 MSW气化熔融处理系统示意
Figure 1. Schematic diagram of MSW gasification and melting treatment system
图 3 垃圾含水率与干燥温度对流程的影响
Figure 3. Influence of waste moisture content and drying temperature on the process
表 1 Aspen Plus中部分常用单元
Table 1. Some commonly used units in Aspen Plus
单元模块 模块名称 用途 适用条件 Flash2 分流器 把入口物流分成多个规定的出口物流 用于水蒸气与固体分离 SSplit 分流器 把每个入口子物流分成多个规定的出口物流 分流器，流体固体分离器 Mixer 股流混合器 把多个股流混合成一个股流 股流混合器 RStoic 化学计量反应器 具有规定反应程度和转化率的化学计量反应器模型 用于模拟单一或多个反应的反应器 RYield 收率反应器 具有规定收率的反应器模型 只考虑质量平衡而不考虑元素平衡的反应器 RGibbs 吉布斯自由能最小的平衡反应器 通过吉布斯自由能最小化实现化学和相平衡 化学平衡和相平衡同时发生的反应器 
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表 2 MSW的工业分析和元素分析
Table 2. Industrial analysis and elemental analysis of MSW
% 工业分析 元素分析 Mar Vd ASHd FCd Cd Hd Od Nd Sd Cld 50.78 58.10 30.52 11.38 40.56 4.69 21.15 0.98 1.74 0.36 注：M为水分，V为挥发分，ASH为灰分，FC为固定碳；下标ar为收到基，d为干燥基。
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表 3 主要的还原反应和氧化反应
Table 3. Major reduction and oxidation reactions
序号 化学反应 反应热（ΔH）/（MJ/kmol） 反应类型 R1 C+CO2→2CO 172 还原反应 R2 C+H2O→CO+H2 131 R3 CO+H2O→CO2+H2 −41 R4 CH4+H2O→CO+3H2 206 R5 CO+3H2→CH4+H2O −227 R6 C+2H2→CH4 −75 R7 C+1/2O2→ CO −111 氧化反应 R8 CO+1/2O2→CO2 −283 R9 C+O2→CO2 −394 R10 H2+1/2O2→H2O −242
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表 4 热解气化模拟结果与试验数据对比
Table 4. Comparison of pyrolysis and gasification simulation results and experimental data
气化气组分 各组分所占气化气体积分数/% 相对误差/% 模拟数据 试验数据[24] H2 43.16 41.36 4.35 CO 23.52 23.34 0.77 CO2 13.86 14.77 6.16 CH4 17.73 18.66 4.98 C2H4 1.24 1.34 7.46 C2H6 0.49 0.53 7.54
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表 5 气化介质工况
Table 5. Working conditions of gasification media
% 工况 气化介质占比 水蒸气 CO2 烟气 1 100 0 0 2 0 100 0 3 60 40 0 4 60 0 40
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表 6 不同气化剂对气化气特性的影响
Table 6. Effect of different gasification agents on gasification gas characteristics
工况 气化剂种类 气化气组分占比/% 热值/
(MJ/m3)H2O H2 CO CO2 CH4 1 水蒸气 1.62 55.85 40.60 1.11 0.82 11.46 2 CO2 1.83 46.32 48.76 2.63 0.69 11.41 3 水蒸气和CO2 1.66 52.47 43.60 1.55 0.72 11.43 4 水蒸气和烟气 1.81 54.62 40.49 2.38 0.70 11.26
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