Modelling of sorption enhanced chemical looping steam reforming (SE-CLSR) of methane in a packed bed reactor
Modelling of sorption enhanced chemical looping steam reforming (SE-CLSR) of methane in a packed bed reactor
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发表时间：
2016-07
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通讯作者：
S Z Abbas
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作者：
S Z Abbas
在吸附增强蒸汽甲烷重整 (SE-SMR) 工艺中，可生产浓度高达 98 体积的氢气 (H2)。 ％（干基），在装有重整催化剂和二氧化碳（CO2）吸附剂混合物的单个反应器中。这被定义为燃烧前捕获二氧化碳，产生的高纯度氢气可用作发电燃料、合成氨化肥或炼油厂中石脑油和其他重质瓦斯油的加氢处理。氢气生产和二氧化碳吸附剂再生之间需要循环操作，但吸附剂再生的能量需求很高。减少这种能源需求的一种建议方法是将 SE-SMR 与化学循环 (CL) 结合，通过金属材料与空气的高放热循环氧化，自然地将氮气 (N2) 从合成气中分离出来，金属材料在还原时充当重整催化剂（氧转移材料或“OTM”）。 SE-SMR 和 CL 的结合使该工艺更加节能，并且不需要 (i) 与传统蒸汽甲烷重整 (SMR) 工艺相比的高温（典型温度范围为 750-950°C），(ii) 重整器下游的水煤气变换 (WGS) 反应器，以及 (iii) 在重整器中使用天然气燃料进行外部加热。然而，作为循环操作的一部分，一个反应器运行产生的高纯度氢气是间歇性的，反应器交替以燃料反应器模式（FR）运行（使用燃料和蒸汽进料）或空气反应器模式（AR）（使用空气进料）。 CO2 的吸附使反应平衡转向更多的 H2 生产，并最终提高 H2 生产过程的效率。 H2 的生产、CH4 的转化和工艺的整体效率取决于许多操作参数。本文报道了入口温度、反应器压力、进料中的蒸汽与碳摩尔比(S/C)以及气体质量速度对甲烷过程的SE-SMR和吸附增强化学循环蒸汽重整(SE-CLSR)的影响。 SE-CLSR 过程模型的制定需要对填充床反应器进行建模。该数学模型涵盖了各种单独的模型（子模型）： SMR、SE-SMR、OTM 还原和还原型 OTM 的氧化。 gPROMS model Builder 4.1.0® 用于求解模型方程。在这项工作中，对超过 18 wt.% 的 SMR 过程进行了实验 IV 动力学研究和模型。 % NiO/α-Al2O3 催化剂适用于绝热固定床反应器，温度范围为 300-700°C，压力为 1 bar。通过将结果与作为本工作一部分获得的实验数据进行比较来验证该模型。模拟结果与实验结果非常吻合。平衡结果是使用化学平衡应用程序 (CEA) 软件生成的。对各种操作参数（温度、压力和 S/C）对 CH4 和水转化率 (%) 的影响进行了建模，并与平衡值进行比较。 SE-SMR的数学模型是根据工业操作温度和压力条件建立的。发现 873-973 K 是在高压（30 bar）条件下生产纯度超过 85% 的 H2 的最佳温度范围。所开发的 SE-SMR 模型根据文献数据进行了验证。 SE-CLSR过程的数学模型是在绝热条件下建立的。该模型是催化剂还原和还原催化剂氧化的组合。还原和氧化的各个模型是通过使用文献中可用的动力学数据开发的，然后用文献中提出的实验结果进行验证。已开发的 SE-SMR 过程模型与 OTM 还原模型相结合，以模拟燃料反应堆 (FR) 系统中发生的动态过程。该FR与空气反应器（AR）结合，组合模型运行10个周期。研究了在温度（873-1023 K）、压力（1-30 bar）、摩尔S/C（2-6）和气相质量通量（Gs = 2-7 kg m-2 s-1）的各种操作条件下该过程的灵敏度。在这项工作中，用于生产氢气的操作条件代表了现实的工业生产条件。灵敏度分析表明，所开发的 SE-CLSR 过程模型能够灵活地模拟各种温度、压力、S/C 和 Gs 的操作条件。
In the sorption enhanced steam methane reforming (SE-SMR) process, hydrogen (H2) can be produced in concentration up to 98 vol. % (dry basis) in a single reactor packed with a mixture of reforming catalyst and carbon dioxide (CO2) sorbent. This is defined as pre-combustion capturing of CO2 and the high purity H2 produced can be used as a fuel for electricity generation, synthesis of ammonia-derived fertilisers, or hydrotreating of naphtha and other heavy gas oil in petroleum refinery. A cyclic operation between the production of H2 and regeneration of CO2 sorbent is required, but the energy demand for the sorbent regeneration is high. A proposed method to decrease this energy demand is to couple SE-SMR with chemical looping (CL), which naturally separates the nitrogen (N2) from the syngas via the highly exothermic cyclic oxidation with air of a metallic material, which acts as the reforming catalyst when reduced (oxygen transfer material or ‘OTM’). The combination of SE-SMR and CL makes the process energy efficient and eliminates the need for (i) high temperature as compared to the conventional steam methane reforming (SMR) process (typical temperature range is 750- 950°C), (ii) the water gas shift (WGS) reactors downstream of the reformer, and (iii) external heating using the natural gas fuel in the reformer. However the H2 generation of a high purity from one reactor operation is intermittent, as part of a cyclic operation, with the reactor alternately operating in Fuel Reactor mode (FR), with fuel and steam feed or Air Reactor mode (AR), with air feed. Adsorption of CO2 shifts the equilibrium of reaction towards more H2 production and ultimately increases the efficiency of the process towards H2 production. Production of H2, CH4 conversion and overall efficiency of the process depend upon many operating parameters. The effects of inlet temperature, reactor pressure, molar steam to carbon ratio (S/C) in the feed, and gas mass velocity on the SE-SMR and the sorption enhanced chemical looping steam reforming (SE-CLSR) of methane processes is reported in this thesis. The formulation of the SE-CLSR process model requires the modelling of packed bed reactors. This mathematical modelling covers various individual models (sub-models) for; SMR, SE-SMR, OTM reduction and oxidation of reduced OTM. The gPROMS model builder 4.1.0® is used to solve the model equations. In this work, an experimental IV kinetics study and model of SMR process over 18 wt. % NiO/α-Al2O3 catalyst are presented for an adiabatic fixed bed reactor in the temperature range of 300-700°C at 1 bar pressure. The model is validated by comparing the results with the experimental data obtained as part of this work. The simulation results are in excellent agreement with the experimental results. The equilibrium results are generated using Chemical Equilibrium with Applications (CEA) software. The effect of various operating parameters (temperature, pressure and S/C) on the CH4 and water conversion (%) is modelled and compared with the equilibrium values. The mathematical model of SE-SMR was developed based on the industrial operating conditions of temperature and pressure. The 873-973 K was found to be the optimum range of temperature, under the high pressure (30 bar) conditions, for the production of H2 of purity exceeding 85%. The developed model of SE-SMR was validated against the literature data. The mathematical model of SE-CLSR process was developed under adiabatic conditions. This model is the combination of reduction of catalyst followed by oxidation of the reduced catalyst. The individual models of reduction and oxidation are developed by using kinetic data available in the literature and later on validated with experimental results proposed in the literature. The already developed model of SE-SMR process is combined with the OTM reduction model to mimic the dynamic process occurring in the fuel reactor (FR) system. This FR is combined with air reactor (AR) and the combined model is run for 10 cycles. The sensitivity of the process is studied under the various operating conditions of temperature (873-1023 K), pressure (1-30 bar), molar S/C (2-6) and mass flux of the gas phase (Gs = 2-7 kg m-2 s-1). In this work, the operating conditions used for the production of H2 represent realistic industrial production conditions. The sensitivity analysis demonstrates that the developed model of SE-CLSR process has the flexibility to simulate a wide range of operating conditions of temperature, pressure, S/C and Gs.