生物质微波制氢工艺温控仿真及工业设计优化

Simulation and optimization of temperature control and industrial design of hydrogen production of biomass via microwaves

  • 摘要: 利用微波对生物质进行热解制氢是一种高效、快速、环保的技术手段,由于木质素是自然界唯一可再生的芳香碳氢资源,因此以木质素为主的林木类生物质是一种很好的制氢原料。目前制约其工业化的因素主要来自微波热点效应,因此本文通过生物质在不同微波频率下的穿透深度,对反应器进行整体建模设计,并通过正交设计仿真、CFD及HYSYS模拟来分别获得均匀温度场的工况条件、最佳反应器高径比以及工业化装置最大产品量时的操作参数。结果表明,当微波功率密度为30 W·g–1, 物料颗粒半径为4 mm,物料堆积密度为800 kg·m–3,反应器高径比为2.0,水蒸气中段和末段通量分别为290和1230 m3·h–1时,可以获得最大量氢气产品且温度场均匀,此时温度场的变异系数为0.009,氢气的产量为922.98 m3·h–1,摩尔分数为0.4781,产率为82.49%。

     

    Abstract: Hydrogen production of biomass via microwaves is an efficient, rapid, and environmentally friendly chemical engineering technology. Lignin is the only renewable aromatic hydrocarbon resource in the nature, and thus, the lignin-based forest biomass, which has the advantages of low sulfur, is a good raw material for hydrogen production. However, the microwave hot spot effect restricts the industrial application of hydrogen production by microwave. In this study, the reactor was carried out based on the penetration depth of biomass under different microwave frequencies was designed by modeling. Orthogonal design simulation, CFD, and HYSYS were used to obtain the distribution of temperature field with different microwave power density, the radius of biomass particles, bulk density, and the coefficient of variation. Based on the results, the optimal microwave power density was 30 W·g–1, the optimal radius of biomass particles was 4 mm, and the optimal bulk density was 800 kg·m–3, at which a favorable uniform temperature field was achieved, and its coefficient of variation was only 0.009, less than the standard value of 0.01. Then, to reduce energy consumption and improve product economy, the Computational Fluid Dynamics (CFD) method was used to analyze the cloud image of hydrogen production with different height to diameter ratio of the reactor. It was found that when the height to diameter ratio of the reactor was 2.0, the hydrogen-flow could not only fully contact with the falling materials, but also achieve thermal energy circulation by using its own high temperature. Finally, the industrial process of hydrogen production of biomass via microwave was added into HYSYS, and the operating parameters of the maximum hydrogen yield of the 10000-ton industrial device were simulated and optimized. In the reforming reaction, by adding steam in the mid-piece and the end-piece, the production yield of hydrogen can be maximized and the temperature of the reactor can be maintained continuously after the heat energy of hydrogen was recovered. Under the conditions optimized, when the mid-piece and end-piece fluxes of steam were 290 and 1230 m3·h–1, respectively, a favorable hydrogen production of biomass was achieved. The output of hydrogen, the mole fraction and the yield of hydrogen production were 922.98 m3·h–1, 0.4781 and 82.49%, respectively. Moreover, the hydrogen product can reach the high standard of 6.592 g hydrogen/ 100 g biomass, which was far superior to the industry level.

     

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