The time-varying radiation applied in the temperature-sensitive reaction system stabilized with heat storage technology

Abstract

Solar thermal plants could boost the application of methane production from microalgae. In this paper, a unique combination of solar thermal plants and microalgae bioreactor is studied. Because the microalgae pyrolysis is temperature-sensitive, and the solar radiation is time-varying, a thermocline heat storage tank is applied to stabilize the system. The impact of unsteady solar environments is important, because it is related to the versatility and flexibility of the small-scale solar systems. A theoretical model of the system, which consists of six sub-models: solar radiation, solar collector, heat storage tank, heat exchanger, pyrolysis reactor, and fermentation reactor, is developed to assess the yearly performance. In particular, the solar radiation conditions in Nanjing, China are considered. The research results show that the solar thermal bioreactor with a heat storage tank work with a steady temperature of 517 K under time-varying solar radiation. With a heat storage discharge power at 225 kW, the bioreactor produces methane at a rate around 1.4 L/s, consuming about 370 kg/day of dry microalgae. With heat storage and proper control, the variation of pyrolysis temperature is limited to 50 k, which ensures steady bioreaction. Interrupted by a short pause of solar radiation, the system has good robustness. Overall, the research results presented in this work prove the feasibility of the proposed novel system and provide a reference for the design of a solar thermal plant for clean methane production in the future.