음식물류 폐기물, 가축 분뇨, 하수 슬러지 등 유기성 폐기물로부터 생산되는 바이오가스는 온실가스 저감이 가능한 대체 에너지원이다. 바이오가스를 연료로 사용할 경우 탄소중립으로 간주되며, 연소 후 이산화탄소를 포집하면 탄소역배출(carbon negative emission)이 가능하다. 본 연구에서는 바이오가스의 정제 및 고질화, 가스엔진 및 가스터빈을 이용한 전기 생산, 매체순환연소(Chemical Looping Combustion, CLC)를 통한 전기 및 스팀 생산을 포함한 경제성 분석을 수행하였다. 탄소중립 시나리오로는 정제 및 고질화된 바이오가스를 바이오메탄으로 판매하는 경우(Case 1)와 이를 연료로 전기를 생산(가스엔진 또는 가스터빈)하는 경우(Case 2)로 구성하였다. 탄소 역배출 시나리오는 가스엔진 또는 가스터빈으로 전기를 생산한 후 이산화탄소를 포집하는 경우(Case 3), 정제된 바이오가스를 CLC 연료로 사용하는 경우(Case 4), 바이오메탄을 CLC 연료로 사용해 전기 또는 스팀을 생산, 판매하는 경우(Case 5)로 구성하였다. 분석에는 투자비, 운영비, 원료비를 포함하였으며, 제품은 바이오메탄(800원/Nm3), 전기(204.2원/kWh), 스팀(60,000원/톤), 탄소 배출권(12원/kgCO2), 액화 CO2(25원/kgCO2)로 가정하였다. 모든 규모(3, 15, 30 MWth)에서 바이오메탄 직접 판매가 가장 수익성이 높았으며, CLC를 활용한 탄소 역배출은 15 MWth 이상에서 경제성이 확보되었다. CLC가 바이오메탄 직접 판매보다 더 높은 수익을 내기 위해서는, 스팀 가격이 70,000~76,000원/톤 또는 탄소배출권 가격이 80~120원/kgCO2 수준까지 상승해야 함을 민감도 분석을 통해 확인하였다.

Biogas, produced from organic waste such as food waste, livestock manure, and sewage sludge, can serve

as an alternative energy source that reduces greenhouse gas emissions. Using biogas as a fuel is considered carbonneutral

and capturing carbon dioxide (CO2) after combustion enables carbon negative emission. This study conducted an

economic analysis of biogas utilization, covering purification and upgrading, electricity generation using gas engines,

gas turbines, and chemical looping combustion (CLC), as well as steam production via CLC. The carbon-neutral scenarios

included the sale of upgraded biogas as biomethane (Case 1) and electricity generation using biomethane in gas engines

or gas turbines (Case 2). Carbon negative emission scenarios were defined as electricity generation using gas engines or

turbines with CO2 capture (Case 3), the use of purified biogas in CLC (Case 4), and the use of biomethane in CLC to produce

and sell electricity or steam (Case 5). The analysis included investment, operating, and feedstock costs. Evaluated products

were biomethane (800 KRW/Nm³), electricity (204.2 KRW/kWh), steam (60,000 KRW/ton), carbon credit (12 KRW/

kgCO2), and liquefied CO2 (25 KRW/kgCO2). Direct biomethane sales showed the highest profit at all scales (3, 15, 30

MWth). Carbon negative emission scenario using CLC became viable at 15 MWth or larger, with the best result from

biomethane-fueled CLC producing and selling steam. For CLC to outperform biomethane sales, steam must reach

70,000~76,000 KRW/ton or carbon credit 80-120 KRW/kgCO2.

Biogas, Carbon negative emission, Chemical looping combustion, Economic analysis, Sensitivity analysis

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