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

Abstract

Synthetic natural gas (SNG)Supercritical water gasification Sensitivity analysis Bioenergy Process economics a b s t r a c t 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 À1 was obtained forRP. An EROEI of 0.08 was calculated for tubular PBR with a productivity of 75.1 t ha À1 a À1 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 À1 a À1 was found to be 1.01in the base case scenario and an SNG production cost of 266 V GJ À1. 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 À1 were found for RP, whereas for FPA-PBR an EROEI of 2e3.7 and SNG production costs of 30e103 V GJ À1 were obtained.ª 2013 Elsevier Ltd. All rights reserved. IntroductionThe potential of microalgae as a renewable energy source, as a provider of renewable bulk and high value chemicals for the chemical and pharmaceutical industry, as a source of proteins for animal feedstock and fertilizer has made them the subject of considerable research effort in the past [1,2]. However, the economic viability and energy efficiency of biofuels made from microalgae are presently intensively discussed. The main obstacles to large scale introduction of biofuels from microalgae are the high investment costs and energy input required for microalgae cultivation and harvesting [3,4]. b i o m a s s a n d b i o e n e r g y x x x ( 2 0 1 3 ) 1 e9Please cite this article in press as: Brandenberger M, et al., Producing synthetic natural gas from microalgae via supercritical water gasification: A techno-economic sensitivity analysis, Biomass and Bioenergy (2013), http://dx

Processing of Biobased Resources

“…F. Vogel and his group prefer supercritical conditions, which have the advantage of good solubility of organic compounds and gases. To handle the salt deposition, a special gravity separator is used (Brandenberger et al 2013;Dreher et al 2013). In nearcritical catalyzed gasification, the stabilization of the catalyst is a special challenge.…”

Mi̇kroalg Beslemeli̇ Bi̇yogaz Kojenerasyon Si̇stemi̇ni̇n Ekonomi̇k Anali̇zi̇

“…There is an increasing trend related to produce biogas from microalgae in the literature [1-3, 7-10] some latest studies are summarized below. Brandenberger et al [7] performed technoeconomic analysis of synthetic natural gas production by microalgae supercritical catalytic gasification. In this study, the production of microalgae was carried out in the outdoor pool and tubular-flat panel airlift photobioreactors.…”

Microorganisms as Direct and Indirect Sources of Alternative Fuels

“…The SCWG process enables recovery of some nutrients from the microalgae biomass because the fluid shows low solubility for salts [45]. Cherad et al [46] gasified macroalgae Saccharina latissima in a batch reactor at 500°C and 36 MPa and studied the influence of biochemical content and ash on syngas composition.…”