Microalgae-based coproduction of ammonia and power employing chemical looping process

Hydrogen (H-2) production and storage technologies are the main challenges in the realization of H-2 utilization in which the goal is to achieve high conversion efficiencies and a high storage density. In this study, microalgae gasification and ammonia (NH3) production are proposed to efficiently convert microalgae to NH3 for efficient H-2 storage. The integrated system comprises drying, gasification, syngas chemical looping (SCL), NH3 synthesis, and power generation. Microalgae are converted to syngas in the gasification module and then introduced into the SCL module to produce high-purity H-2 and a separated carbon dioxide (CO2) stream. SCL is also employed to produce a nitrogen (N-2)-rich stream, which can replace a conventional air separation unit (ASU) system. The three operating parameters that are evaluated in this study include the steam to biomass (S/B) ratio during gasification, reducer operating temperature during chemical looping, and recycle to feed streams ratio. An increase in the S/B ratio has a negative effect on the total energy efficiency because the efficiency decreases owing to the reduced production of H-2 in the oxidizer. To maximize the efficiency of NH3 production, a higher recycle ratio is favorable. The proposed integrated system can obtain high total energy efficiency of up to 64.3%, comprising 63.8% NH3 production efficiency and 0.05% power generation efficiency.
QC 20190709