A novel solar hybridized dual fluidized bed (DFB) gasification process for Fischer−Tropsch liquid (FTL) fuels production is proposed and investigated here for the case with lignite as the fuel, although it is also applicable to biomass. The concept offers sensible thermal storage of bed material, the use of inert particles in the solar receiver to avoid the need for sealing, and a process that delivers a constant production rate and quality of syngas despite solar variability. This solar hybridized coal-toliquids (SCTL) process is simulated using a pseudodynamic model that assumes steady state operation at each time step for a one-year, hourly integrated solar insolation time series. The annual energetic and environmental performance of this SCTL process is investigated as a function of the solar multiple (i.e., the heliostat field area relative to that required to meet the demand of the DFB gasifier at the point of peak solar thermal output), bed material storage capacity, the assumed char conversion in the bubbling fluidized bed gasifier (BFBG), and the solar resource. This revealed that solar energy can be stored in the bed material to increase both the solar share and output while decreasing the CO 2 emissions, with a commensurate increase in the heliostat field area. For a solar multiple of 3 and bed material storage capacity of 16 h, the annual solar share is 21.8% and the annually averaged utilization factor of the heliostat field is 40.8%, assuming that the char conversion in the BFBG is 100%. However, the solar share is also found to be strongly dependent on the char conversion in the BFBG, so that the solar share decreases to zero as the conversion is decreased to 57%. The sensitivity of the SCTL performance to the quality of the solar resource is also reported.

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The time-dependent layer-formation process of the agglomerates for three common agricultural residues in Australia with different ash-forming elements, together with quartz sand as the bed material, were investigated in a lab-scale, fixed-bed reactor under combustion (5% v/v O 2 ) and steam-gasification (50% v/v steam) atmospheres at 900 °C. The impact of the atmosphere on the ash−bed material interaction was studied from the elemental composition and the morphology of the agglomerates, which were characterized with scanning electron microscopy in combination with energy-dispersive X-ray spectroscopy. The ash−bed material interaction mechanisms for the three feedstock were identified as part of the alkali metals react to form ash particles, which, for wheat straw and cotton stalks, consist of Na, Mg, Si, P, K, and Ca and, for grape marc, is composed mostly of KCaPO 4 ; the remaining alkali metals react with either Si from the quartz sand (for grape marc and cotton stalk) or reactive Si from the fuel (for wheat straw) to form a low-melting-point alkali silicate coating layer; Ca dissolves or diffuses into the coating layer (for wheat straw and cotton stalk); and the ash particles formed in the first step then deposit on, and progressively embed in, the coating layer. The elemental composition of the coating layer is relatively independent of both the reaction time and the gas atmosphere. The coating layer increases in thickness with an increase in the reaction time. The addition of steam results in the production of more liquid alkali silicates, which augment the agglomeration. Any residual S may form sulfate particles with K, Ca, or Na in a combustion atmosphere, while in a steam-gasification atmosphere, the S is released to the gas phase so that more alkali metal may remain to form the low-melting-point alkali silicate.

The interactions between quartz sand and wood, which was doped with either K or Na salts, were investigated in a lab-scale, fixed-bed reactor under either a steam gasification or a combustion atmosphere at 900 °C. For the cases of the potassium/sodium phosphate salts, the interaction was found to be melting induced, while for the cases of the other salts, it was found to be coating induced. Large agglomerates were found to have already been formed during the early stages of steam gasification for the wood samples doped with potassium/sodium carbonate and acetate. However, the agglomerates obtained under the combustion atmosphere were found to be insignificant for the wood samples doped with potassium/sodium chloride. Both the reaction atmosphere and the types of salts were found to affect the formation of potassium/sodium silicates in the agglomerates and the interactions between the quartz sand with gaseous K or Na significantly.

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