NH4OH Looping with Membrane Absorber and Distributed Stripper for Enhanced Algae Growth

Project Objectives: 1) A practical, reliable and cost-effective integrated CO2 capture and utilization technology will be developed, designed, constructed and tested for algae production using a NH3 solution as both capture reagent and algal nutrient via a membrane absorber and chemical additives to minimize NH3 emission in the CO2 depleted flue gas. This membrane absorber will be coupled with distributed strippers near a cluster bioreactor powered by solar energy for solvent regeneration and just-in-time CO2 and NH3 delivery to an algae bioreactor for productivity enhancement. 2) Distributed solvent regenerators will be designed, integrated and evaluated with a modular bioreactor. 3) A membrane CO2 absorber will be designed, integrated into an existing 0.1 MWth CO2 capture process and researched. 4) A TEA, TGA and LCA will be conducted and a TMP will be prepared and submitted. Overview of Proposed Integrated Capture and Utilization Technology: The proposed technology reduces costs related to CO2 capture (capital and operating) by 50% by eliminating both the flue gas- pretreatment step for cooling/SO2 removal and the steam extraction for solvent regeneration. It will also boost algae production by 50% by supplying CO2 and NH3 in the appropriate ratio for algae growth, compared to a state-of-the-art (SOA) intermittent, decoupled feeding system. There are three unique aspects of the proposed NH3-based looping technology to capture and fix CO2 from carbon-based fuel derived flue gas. First, a thermally- and oxidatively-stable, dual-function reagent, NH3, will act as both the absorbent for CO2 capture and as a nutrient for algae growth. Second, a downward flow gas-liquid indirect contact membrane absorber will prevent ammonia slip with assistance of <1 wt% chelating compound while capturing CO2 from the flue gas. Condensate from the saturated flue gas will continually wash the gas side of the membrane, while 20-50 ppm SO2 contained in the flue gas will react with and capture any NH3 that does slip from the liquid side to the gas side, forming salt species that dissolve in the condensate and thereby preventing gaseous emissions. The resulting ammonium sulfite and sulfate salts are fed to the algae as a minor nutrient. Third, rich solvent distributed regenerators installed near to algae bioreactor modules will provide local distribution of CO2 and NH3 at the appropriate ratio for algae growth. Regeneration will be powered by solar-thermal energy, eliminating the stream extraction of conventional aqueous CO2 capture technologies. Simultaneous, just-in-time supply of CO2 and NH3 in the appropriate ratio to the bioreactor will boost production markedly. Relevance and Outcomes/Impacts: The main public benefit of successful development of the proposed technology is continued utilization of low-cost fossil fuels, including coal, for the production of reliable electricity while affordably managing environmental concerns. There will be three major outcomes of this project: 1) significantly reduced complexity and cost associated with algae biofixation for utility CO2 sources; 2) building public confidence in CO2 capture and utilization technology that could be self-financing and sustainable; and 3) extending the proposed capture and fixation process to a broader spectrum of problems associated with CO2 emissions such as methanol plants.