No abstract

An analysis of system operation and performance has been undertaken, for the first time, of a solar-hybrid coal-toliquids polygeneration facility incorporating solar resource variability. The energetic and environmental performance of a coal-toliquids process that is integrated with a solar hybridized, oxygen blown, atmospheric pressure gasifier (CTL sol ) is compared with that of a reference, nonsolar, autothermal, pressurized gasification integrated, CTL ref configuration. To allow the plant to respond to solar resource transience, pressurized storage of upgraded syngas and oxygen is incorporated into the proposed CTL sol system. The CTL sol process is simulated using a dynamic model that assumes pseudosteady state operation at each time-step, for a 12month, hourly averaged solar insolation time-series. Both the CTL sol and CTL ref systems were modeled using AspenPlus and Aspen HYSYS (v 7.1) software. The analysis of the CTL sol system's performance showed an annually averaged improvement of 21% to the total energetic output and a reduction of 30% in the mine-to-tank greenhouse gas emissions relative to the CTL ref system assuming equilibrium gasification conditions of 1400 °C and 1 bar-a. The integration of a pressurized syngas storage facility was shown to enable the CTL sol system to allow the variation in throughput of each unit of process equipment to be maintained within normal operational ranges despite the fluctuations in the transient solar input to the solar-hybrid coal gasification process.

The release of volatile inorganic elements during thermal conversion of algal biomass may cause operational problems in industrial reactors such as fouling, deposition, corrosion, and bed agglomeration. The release of Cl, S, P, K, and Na during the thermal conversion of algal biomass has been experimentally investigated in this paper. A freshwater macroalga (Oedogonium sp.), a freshwater polyculture of microalgae, and a marine microalga (Tetraselmis sp.) were used as feedstocks to assess the influence of different species and culturing environments on the release of the inorganic elements. Char and ash samples were prepared in a laboratory-scale fixed-bed reactor under isothermal conditions ranging from 500 to 1100 °C, under pyrolysis, combustion, and gasification atmospheres. The release of the inorganic elements was quantified by mass balances based on elemental analyses of the char and ash residues. Differences in the release of Cl, S, K, and Na were significant between the marine alga and the freshwater algae but were only minor between the freshwater microalgae and the freshwater macroalga. In the freshwater algae, the majority of the total Cl was released at low temperatures, below 500 °C. The majority of the fuel-S was also released at low temperatures. The remaining S was released with increasing temperature during combustion and gasification but was partially retained in the char during pyrolysis. Retentions of K and Na in the char and ash residues were both relatively high. Only 20−35% of the total K and 35−50% of the total Na in the freshwater algae had been released by 1100 °C. In the marine alga, only around 20% of the total Cl was released below 500 °C with the majority being released above 850 °C. The fraction of S released at low temperatures was also lower when compared to the freshwater algae. Potassium and Na were more or less completely released from the marine alga by 1100 °C under pyrolysis and combustion conditions and by 1000 °C under gasification conditions. The release behavior of P was similar for all of the tested algae. Phosphorus release commenced around 850 °C under pyrolysis, combustion, and gasification atmospheres, and by 1100 °C, 40−70% of the total P had been released from the algae. Select ash residues were analyzed using X-ray diffraction and scanning electron microscopy, coupled with energydispersive spectroscopy, in order to gain insights into the release mechanisms. A two-step mechanism has been proposed for S release. The alkali metals and Cl were released proportionally from the marine alga but disproportionately from the freshwater algae. It is expected that K, Na, and Cl were released from the marine alga primarily by sublimation of alkali chlorides. Different mechanisms were responsible for the release of these elements from the freshwater algae. It has been suggested that Cl is dissociated from the alkali metals and then released as HCl vapor, and that K may be released by volatilization of melted Kphosphates. Sodium appeared to be released by similar mechanisms to K...

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.