Numerical and experimental study of tensile stresses of biomass combustion ash with temperature variation

• The effect of temperature on tensile stresses has been investigated by DEM simulation.
• The cohesive force was modelled using the combined CFM–BPM model.
• Empirical equations were proposed to link the parameters of model with temperatures.
• Tensile strength first increased from room temperature to 500 °C and then decreased.
• There are three regimes of phase transition in biomass ash with temperature variation.

The consequent lack of basic understanding of the cohesiveness of ash particles at high temperature is a major hindrance to advancing biomass combustion technology. This paper presents an investigation of the effect of temperature on tensile strength by a combined experimental and numerical method. Experimentally, tensile strength and fracture distance of palm residues combusted at 820 °C were measured as a function of temperature (25–800 °C). The results showed that the tensile strength is strongly dependent on temperature and the liquid bridge between particles may transform into partially solid bonds with increasing temperature. In numerical simulation by means of discrete element method (DEM), the cohesive force between particles was modelled using the so called Bonded Particle Model (BPM) and Capillary Force Model (CFM). The parameters of BMP and CFM models at different temperatures were determined by an empirical equation. Comparison with the existing test results showed that the model can reasonably describe the behaviour of biomass combustion ash under various temperatures. It was therefore confirmed that the proposed cohesive force model can be used in the DEM-based simulation of biomass ash deposition in the combustion devices, leading to better understand the phenomena of shedding and erosion in the future.

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