Search

A technical assessment of pneumatic conveying of solids at various operating temperatures for a high temperature solar particle receiver is reported. The power consumption of the conveying system was determined from a calculation of the pressure drop in the conveying pipes. The enthalpy loss of the transported particles was estimated from an energy balance and the heat losses through the wall. The power consumption of the pneumatic conveying system was found to decrease significantly with an increase in conveying temperature and to be less for a dense phase conveying system that for a skip hoist conveyor, where the solid input temperature is higher than 150 °C. The equivalent threshold temperature is 400 °C for a dilute phase conveying system. Nevertheless, including the enthalpy loss of the particles caused by the increases in both mechanical energy and gas enthalpy, the dense phase conveying is more energy efficient than skip hoist if the solid input temperature is higher than 450 °C while the dilute phase conveying always consumes more energy than skip hoist, under the studied conditions.

A heat transfer model was applied to simulate heat exchange in a direct contact counter current moving bed (CCMB) heat exchanger associated with a dry slag granulation process developed by CSIRO. Cold air is used to recover heat from hot solid slag granules in the heat exchanger. Experimental data was used to calibrate the heat transfer model. The model was then used to predict the solid and gas temperature distributions along the height of the bed, the heat loss, and the operating and design conditions for scale-up of the CCMB to semi-industrial and industrial operations. Two scenarios were examined using the model to determine conditions for i) minimising the solid outlet temperature and ii) maximising the gas outlet temperature. The model can also be used to determine the nominal bed height to ensure that the designed gas outlet temperature is achieved. The modelling results suggest that a relatively small bed height (below 0.5 m) will be sufficient for heat exchange. The model also suggests that a solid to gas mass flow rate ratio of 0.8 should be used to minimise the solid outlet temperature, while a ratio of 1.0 should be used to maximise the gas outlet temperature. Therefore an appropriate operating window for a CCMB heat exchanger for recovering heat from hot slag was found with a solid to gas mass flow rate ratio between 0.8 and 1.

This paper investigates the use of the multiphase particle in cell method (MP-PIC) in modelling the gas–solid flow in a laboratory-scale isothermal internally circulating fluidized bed (ICFB), and compares results with experimental observations previously published by Hadley et al. (“Experimental quantification of the solids flux in an internally circulating fluidised bed”, Fluidization XIII, 2010, pp. 885–892). Glass ballotini (140 μm mean diameter) were fluidized with room temperature air, and fluidisation velocities in both the central reaction chamber and two heat exchange chambers were varied to provide nine different chamber velocity ratio conditions for investigation. The model reliably predicted the overall bed dynamics of both gas and solid flow. Predicted solid recirculation rates were generally within one standard deviation of the mean experimental values, although under-prediction tended to occur at lower fluidisation rates. It was concluded that the MP-PIC method was a reliable tool for modelling bubbling fluidized bed behaviour of non-cohesive particles.

Since bubbling fluidized-bed scaling laws were first developed, there has been some debate about their correct application and the relative importance of the various scaling parameters, in particular, the solid-to-gas density ratio. In this paper, we highlight the differences in the existing literature and present the results from experimental fluidized-bed systems where the solid-to-gas density ratio has been changed by varying degrees. From our results, we conclude that there is some flexibility for altering the solid-to-gas density ratio when scaling bubbling beds of Geldart group B materials up to particle Reynolds numbers of at least 12, but further work is needed to clarify the range of particle Reynolds numbers over which the density ratio requirement can be relaxed. In contrast, when scaling group A materials, we find that the density ratio is an important parameter even if the particle Reynolds number is small.

Reactor models are idealized human constructs that attempt to capture the essence of the behaviour of the flow, mixing and contacting of reacting species and phases in order to be able to predict reactor conversions, yields and dynamic responses. Accurate modeling also requires an adequate representation of the chemical kinetics, while other factors such as heat transfer and thermodynamics may also play significant roles. Models are more complex for multi-phase reactors than for single-phase reactors as they must take into account the mixing behaviour within each individual phase, as well as the exchange of reactants and products between the phases. Each of these aspects is directly influenced by the flow patterns throughout the entire reactor.