Ash-induced Agglomeration of bubbling fluidized beds during gasification of biofuels with low melting ashes

低熔点灰渣引起的床层颗粒团聚是特别富碱生物燃料在沸腾床系统中热转化的关键问题。气化炉内结焦的形成机理尚不清楚，尤其是在存在残炭颗粒的情况下，结焦温度变化的潜在影响。因此，该项目的主要目标是识别热气化过程中的结焦机理，并澄清影响装置和燃料/灰参数以及高焦含量的因素。为了实现这一目标，我们提出了实验和数值相结合的方法：在实验方面，对实验室规模的沸腾气化炉中的时间分辨压力波动的分析将允许在早期阶段检测到灰分引起的沸腾床流体动力学的变化。我们将在不同的原料、装置参数和残炭含量下进行实验。此外，数值格子-玻尔兹曼模拟将预测单个床料颗粒被液体熔膜和焦炭颗粒覆盖的团聚的形成。在单颗粒尺度上对颗粒碰撞的模拟将提供关于温度和灰分性质的团聚趋势。最终，将建立一个大尺度的、接近实际的模型，并将其与实验结果进行比较，以审查结块准则，并制定合理和验证的热流化床气化结块机理。

Ash-induced agglomeration of bed particles due to low melting ashes is the key problem of the thermal conversion of particularly alkali-rich biofuels in fluidized bed systems. The mechanism of the formation of agglomeration in gasifiers is still not clear in detail, especially the underlying effect of altered agglomeration temperature in presence of residual char particles.The main objective of the proposed project is, therefore, the identification of agglomeration mechanism during thermal gasification and the clarification of influential plant and fuel/ash parameters plus high char contents. To achieve this goal, we propose a combination of experimental and numeric approaches:On the experimental side, the analysis of time-resolved pressure fluctuations in lab-scale fluidized bed gasifiers shall allow the detection of ash-induced changes of the fluidized beds fluid dynamics at an early stage. We will perform experiments with different feedstock, plant parameters and residual char content.In addition, numerical Lattice-Boltzmann simulations will predict the formation of agglomerates of individual bed material particles covered with liquid melt films and coke particles. The simulation of particle collisions on single particle scales will provide the agglomeration tendency with respect to the temperature and ash properties. Eventually, a large-scale, close to reality model will be developed and compared to experimental findings in order to review the agglomeration criteria and formulate a plausible and verified agglomeration mechanism for thermal fluidized-bed gasification.