Storage capacity assessment of liquid fuels production by solar gasification in a packed bed reactor using a dynamic process model

The first multi-day performance analysis of the feasibility of integrating a packed bed, indirectly irradiated solar gasification reactor with a downstream FT liquids production facility is reported. Two fuel-loading scenarios were assessed. In one, the residual unconverted fuel at the end of a day is reused, while in the second, the residual fuel is discarded. To estimate a full year time-series of operation, a simplified statistical model was developed from short-period simulations of the 1-D heat transfer, devolatilisation and gasification chemistry model of a 150 kWth packed bed reactor (based on the authors' earlier work). The short time-series cover a variety of solar conditions to represent seasonal, diurnal and cloud-induced solar transience. Also assessed was the influence of increasing the solar flux incident at the emitter plate of the packed bed reactor on syngas production. The combination of the annual time-series and daily model of syngas production was found to represent reasonably the seasonal transience in syngas production. It was then used to estimate the minimum syngas storage volume required to maintain a stable flow-rate and composition of syngas to a FT reactor over a full year of operation. This found that, for an assumed heliostat field collection area of 1000 m2, at least 64 days of storage is required, under both the Residual Fuel Re-Use and Discard scenarios. This figure was not sensitive to the two solar sites assessed, Farmington, New Mexico or Tonopah Airport, Nevada. Increasing the heliostat field collection area from 1000 to 1500 m2, led to an increase in the calculated daily rate of syngas throughput that could be maintained over a full year by 74%, to 5.9 kmol/day. Importantly, a larger heliostat field collection area was calculated to reduce the required storage capacity to approximately halve 35 days, which in absolute terms corresponds to 3.0 tons of syngas. Nevertheless, a requirement for this capacity of storage suggests that the use of the packed bed solar gasification reactor for FT liquids production is unlikely to be viable without substantial changes to the design and operation of the reactor and/or downstream processing plant.