In the context of materials recycling, updraft gasifiers are promising small and middle-scale reactors to obtain building blocks and/or energy from waste plastic and biomasses. To this aim, these kinds of materials can also be mixed and reduced into pellets, while the needed heat enters the process with a heated carrier gas. In order to preliminarily design a gasifier to check its feasibility with an available feedstock, currently available models are inadequate. Thermodynamic ones are useless for the purposes of sizing, while too detailed rate-based models (e.g. based on fluid-dynamic modelling) are too substrate specific, need detailed input data and are extremely time consuming. A dynamic model of a fixed-bed reactor for biomass gasification is presented here. The gasifier is loaded continuously from the top with solid pellets and fed with counter-current air flow. The model considers: i) a one-step gasification kinetics, yielding a product spectrum which matches experimental data from the literature; ii) dynamic gas and solid energy balances and iii) steady-state energy balance for the furnace. The model has been applied to describe a tubular furnace (Ø 40 cm) which gasifies 500–1000 kg day−1 of mixed wastes using air heated up to 1200 °C: on the basis of the produced chemicals, the energy consumption was estimated as ca. 2 MJ per kg of solid feedstock. This simplified approach proved robust in describing the overall yields and start-up dynamics, showing higher reliability than equilibrium models in addressing the temperature profiles, at the cost of a simplified reaction kinetic and pellet description with respect to more complex simulation models. The model validation was done by comparison between the calculations results and available pilot-plant data. An overall good fit of the data can be concluded. The solid-gas heat transfer and the bed packing are the main computational criticalities to achieve a reliable process description.

中文翻译：

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上升气流固定床反应器中混合塑料-生物质颗粒的气化：简化的动态模型


在材料回收的背景下，上升气流气化炉是有前途的中小型反应器，可以从废塑料和生物质中获取建筑材料和/或能量。为此，这些类型的材料也可以混合并切成颗粒，同时所需的热量通过加热的载气进入该过程。为了初步设计气化炉以检查其使用可用原料的可行性，目前可用的模型是不够的。热力学模型对于尺寸确定来说是无用的，而过于详细的基于速率的模型（例如基于流体动力学建模）则过于特定于基材，需要详细的输入数据并且极其耗时。这里提出了生物质气化固定床反应器的动态模型。气化炉从顶部连续装载固体颗粒并供给逆流空气流。该模型考虑： i) 一步气化动力学，产生与文献中的实验数据相匹配的产物谱； ii) 动态气体和固体能量平衡以及 iii) 熔炉的稳态能量平衡。该模型已应用于描述管式炉（Ø 40 cm），该炉使用加热至 1200 °C 的空气气化 500–1000 kg day−1 的混合废物：根据产生的化学品，能源消耗估计为约每公斤固体原料 2 MJ。这种简化的方法在描述总体产率和启动动态方面被证明是稳健的，在解决温度分布方面表现出比平衡模型更高的可靠性，但代价是相对于更复杂的模拟模型简化了反应动力学和颗粒描述。通过比较计算结果和可用的中试工厂数据来完成模型验证。 可以得出数据总体拟合良好的结论。固气传热和床填料是实现可靠的过程描述的主要计算关键。