【作者】 徐斌；

【导师】 查晓雄；

【作者基本信息】 哈尔滨工业大学 ， 结构工程， 2014， 硕士

【摘要】 近年来国内外土木工程领域研究表明,二氧化碳气体作为一种新型建筑材料添加剂,可用来改造水泥基建筑材料如混凝土、水泥瓦、水泥再生砖的材料性能。利用二氧化碳作为添加剂,不仅使改造后的建材性能优良,而且能大大减少温室气体的排放。直接从大气中捕获二氧化碳十分困难,实验室生产的二氧化碳只会加重对环境的污染,因此如何高效捕捉排放源中二氧化碳将直接影响这种新型材料在土木工程中的广泛应用。煤炭能源消耗是二氧化碳最大集中排放源,将燃煤烟气中产生的大量废气二氧化碳进行捕集回收,对水泥基材料进行碳化改造,不仅可以提高建筑材料的性能,而且能有效控制大气中二氧化碳的排放、减缓温室效应,可谓一举两得。本文对燃煤烟气中二氧化碳捕集过程进行相应研究,并利用计算流体动力学对碳捕集过程进行模拟分析,为二氧化碳在建筑行业的广泛应用奠定基础。目前可利用的二氧化碳捕获技术主要包括:燃烧前捕获技术、富氧燃烧捕获技术及燃烧后捕获技术。燃烧后脱碳技术当前最可行的方法,工业中常利用化学溶剂吸收法进行燃烧后碳捕集。本文利用计算流体动力学对碳捕集吸收塔装置中氨水吸收二氧化碳过程进行模拟。采用化学溶剂吸收法,以吸收塔内填料层为单元模型,分别模拟了填料单元内气相单相流、气液两相流动过程以及带化学反应的气液两相吸收过程。由气相单相流动可得到与吸收反应相关的压降信息,有助于对填料设备的几何构造进行优化。由气液两相流动可模拟得到液体从液膜到溪流、液滴的流动状态。将模拟结果与相关文献实验结果对比,验证了模型模拟方法的正确性,也为后续研究氨水吸收二氧化碳的气液吸收过程奠定了基础。由组分输运模型、通用有限速率模型和化学反应动力学建立了带化学反应的气液吸收模型,并通过填料表面生成碳酸氢铵浓度计算得到二氧化碳的吸收率。在该模型基础上,考虑气液质量传递过程,编写UDF程序,建立了考虑气液质量传递的化学反应模型,并将两种模型模拟结果进行了分析对比。在此基础上,改变氨水吸收二氧化碳过程的操作条件如:气液体入口流量、二氧化碳入口浓度、氨水入口浓度、压强等,分析了吸收塔填料层内碳捕集过程的影响因素,模拟结果与相关文献实验结果一致。更多还原

【Abstract】 In recent years, research has shown that in the field of civil engineering, carbon dioxide becomes a new pattern additive material to reform cement-based materials performance such as concrete, cement tile and cement brick. Combination building material has excellent performance, and usage of carbon dioxide can significantly reduce greenhouse gas emission. Carbon dioxide in atmosphere is difficult to obtain, laboratory pr oduction will increase the carbon dioxide distribution to pollute the environment. However, how to capture carbon dioxide effectively from emission sources will directly affect the usage of new combination building materials in civil engineering. The fossil fuel consumption is the main stationary source of the carbon dioxide emission. We can capture carbon dioxide from coal-fired flue gas to reform cement-based building materials performance. It also effectively control emission o f carbon dioxide in the atmosphere and mitigate greenhouse effect. The present study does some research on carbon dioxide capture from coal-fired flue gas and uses CFD to simulate the carbon capture process. T his research lays the foundation for the widely use of carbon dioxide in c onstruction industry.Three different approaches exist to mitigate carbon dioxide emissions: pre-combustion, oxy-fuel technology and post-combustion carbon capture. The most commercially viable approach to be fitted in fossil fuel power plants is the post-combustion capture which absorbs carbon dioxide from the flue gas using chemical reaction technology.The present study uses CFD to deal with numerical modeling and simulation of carbon dioxide capture from flue gases by aqueous ammonia as an absorbent. This method belongs to chemical reaction absorption. A representative elementary unit is created to study the absorption process. The simulations include single-phase gas flow, gas-liquid multiphase flow and gas-liquid absorption process within chemical reaction. We can get pressure drop data from single-phase gas flow simulations, which can aid the optimization of future structured packing designs. From gas-liquid multiphase flow simulations, we can find liquid phase flow distribution on wall surface, from film flow, rivulet flow to droplet. T his is helpful to gas-liquid simulations with chemical reaction and results are found to be consistent with the reported experiment study. Gas-liquid absorption process within chemical reaction is a complex process. Combine species transport model, general finite-rate model with chemical reaction kinetics, we establish the chemical reaction model and get CO2 absorption rate from mole fraction of production NH4HCO3. On the basis of previous model, we consider the mass transfer from gas phase to liquid phase in carbon dioxide capture. Programs are compiled to simulate mass transfer process. At last, a preliminary analysis is made for these two model results. On the basis of previous simulations, various operating conditions including liquid inlet flow, gas inlet flow, CO2 inlet mass fraction, ammonia concentration and pressure on CO2 capture process are examined. T he modeling results are found to be consistent with the reported experiment on CO2 absorption rate at different operating parameters.更多还原