Prediction model of thermal conductivity of coal-water slurry based on coal particle-bonded water composite phase

Abstract

Coal-water slurry gasification is one of advanced coal gasification technologies. The improvement on the efficiency of coal-water slurry gasification is helpful to promote the clean and efficient utilization of coal. Coal-water slurry preheating technology is considered as one of the key technologies to improve the energy utilization efficiency of coal gasification. At present, the variation pattern and intrinsic mechanism of thermal conductivity of complex liquid-solid suspensions are still not fully understood. The thermal conductivity is an important basic parameter of the medium flow heat transfer, characterizing its thermal conductivity in the steady-state thermal conductivity process. The transient hot wire method is used to measure the thermal conductivity of the same concentration coal-water slurry at different temperatures. The experimental results show that the higher the temperature, the higher the thermal conductivity. The thermal conductivity of coal-water slurry is determined at different mass concentrations with a room temperature. The experimental results show that it can be divided into two stages: the mass concentration increases from 51% to 58% in a drop zone, and the thermal conductivity decreases rapidly, its value decreases from 0.401 W/(m·K) to 0.358 W/(m·K); and the mass concentration continues to increase from 58% to 67% in a constant zone, and the thermal conductivity basically remains at 0.358 W/(m·K). Based on the experimental results, the parallel prediction model of thermal conductivity of coal-water slurry with coal particle-bonded water composite is proposed by considering the parallel model, Maxwell model, generalized self-consistent model and other composite models. The water in coal-water slurry contains free water and bound water, and the bound water will form a coal particle-bound water composite phase with coal particles, and the coal-water slurry is regarded as a two-phase composite composed of the composite phase and the free water phase. In the drop zone, with the increase of coal particle concentration, the free water phase decreases, the composite phase remains basically unchanged, and the thermal conductivity of coal-water slurry decreases rapidly. In the constant zone, the amount of bound water in the composite phase decreases with further increase in coal particle concentration, but the thermal conductivity of the composite phase remains basically stable. The model prediction results agree well with the experimental data.

Keywords

• water-coal slurry
• concentration
• thermal conductivity
• coal-water composite model
• bound water