Producing synthetic natural gas frommicroalgae via supercritical water gasification: A techno-economic sensitivity analysis

A techno-economic sensitivity analysis of the production of synthetic natural gas (SNG) via catalytic supercritical water gasification (SCWG) of microalgae produced in raceway ponds (RP), tubular-, or flat-panel-airlift photobioreactors (FPA-PBR) has been perfomed. The aim of combining microalgae production with SCWG is to close material flows with respect to water and nutrients, the so called SunCHem process. The sensitivity analysis is based on an annual production of 86,500 t of microalgae biomass yielding 1.14 PJ of methane per year. The sensitivity analysis showed that with an annual algae productivity of 38.5 t per hectare of RP an energy return on energy invested (EROEI) of 1.84 can be achieved for the self-sufficient base case scenario. An SNG production cost of 194 V GJ 1 was obtained for RP. An EROEI of 0.08 was calculated for tubular PBR with a productivity of 75.1 t ha 1 a 1 in the base case scenario and thus was found to be inappropriate for SNG production. EROEI for FPA-PBR with an assumed microalgae productivity of 79 t ha 1 a 1 was found to be 1.01 in the base case scenario and an SNG production cost of 266 V GJ . With significantly more optimistic assumptions concerning microalgae productivity, energy input and capital requirement with respect to microalgae cultivation, an EROEI of 3.6e5.8 and SNG production costs of 53e90 V GJ 1 were found for RP, whereas for FPA-PBR an EROEI of 2e3.7 and SNG production costs of 30e103 V GJ 1 were obtained. a 2013 Elsevier Ltd. All rights reserved.