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

由于低熔点灰引起的床颗粒的灰诱导附聚是流化床系统中特别是富碱生物燃料的热转化的关键问题。气化炉中结块形成的机制仍不清楚，特别是在残余炭颗粒存在下改变结块温度的潜在影响。因此，拟议项目的主要目标是，在热气化过程中识别结块机制，并澄清有影响力的工厂和燃料/灰参数以及高炭含量。为了实现这一目标，我们提出了实验和数值方法的结合：在实验方面，在实验室规模的流化床气化炉的时间分辨压力波动的分析应允许检测灰引起的变化的流化床流体动力学在早期阶段。我们将使用不同的原料、装置参数和残余炭含量进行实验。此外，数值格子-波尔兹曼模拟将预测覆盖有液体熔融膜和焦炭颗粒的单个床料颗粒聚集体的形成。在单颗粒尺度上模拟颗粒碰撞将提供相对于温度和灰分性质的团聚趋势。最终，一个大规模的，接近现实的模型将开发和实验结果进行比较，以审查团聚标准，并制定一个合理的和验证团聚机制的热流化床气化。

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.