Energy, exergy and thermoeconomic analyses for a power-to-green methanol production plant

Abstract

The feasibility of integrating a CCU (Carbon Capture and Utilization) plant into a green methanol production system was studied through detailed energy, exergy, and thermoeconomic analyses from process, economic, and environmental perspectives. In this system, wood chips are combusted with oxygen generated by an electrolyzer in a circulating fluidized bed boiler. Carbon dioxide, a primary component of flue gas, reacts with hydrogen produced by the electrolyzer to synthesize green methanol. The chemical formula for wood chip combustion was modeled and used in this study. Our thermodynamic modeling allows us to calculate the oxy-fuel combustion, carbon capture, and water electrolysis processes to obtain the amounts of carbon dioxide and hydrogen required to produce methanol. When the unit costs of wood chips and electricity are $0.15/kg and $0.120/kWh, respectively, and the system’s initial investment cost is $117.9 million, the production cost of green methanol is calculated to be $1.393/kg. Additionally, the unit costs of hydrogen and oxygen produced by the electrolyzer were $4.75/kg and $0.30/kg, respectively. However, if the unit cost of electricity is reduced by 50 %, the production cost of green methanol decreases to $0.90/kg, which is close to the market price. If the carbon dioxide produced is sold as carbon credits at $0.50/kg, the unit price of methanol drops to $0.89/kg. Using wind, solar, or nuclear energy to electrolyze water, the carbon emissions of this methanol plant are estimated to be around 0.11–0.45 kgCO₂/kgMeOH.