Techno-Ecological Evaluation of Methanol and Acetic Acid Production from Steel Mill Off-Gases

This paper presents a techno-ecological comparison of two prospective synthesis routes to produce methanol and,
subsequently, acetic acid from steel mill off-gases. Different scenarios for future developments in the energy sector are considered. The main objective is to provide a forward-looking perspective on the techno-ecological possibilities of carbon capture and utilization systems for the steel industry. The proposed scenarios compare the direct conversion of carbon oxides in the blast furnace gas with a process plant system consisting of a pre-conversion, purification, separation, and a reaction unit. The resulting methanol product can be used in a downstream unit together with the carbon monoxide separated from the basic oxygen furnace gas to produce acetic acid. The investigated processes and sub-processes are parameterized using process simulation, where heuristic rules are applied, and fundamental sensitivity analyses are performed to determine optimal operating points. To satisfy the hydrogen demand for the methanol reaction, an additional hydrogen production unit with water electrolysis using grid electricity is required. This creates a sector coupling system between the steel plant, the chemical industry and the energy sector. The methanol production scenarios are evaluated using several key performance indicators specifically designed to target the technological, energy and environmental aspects of the entire synthesis routes. The performance indicators are developed and calculated based on the energy demand and integration potential of the process, the energy demand for hydrogen production, the conversion and recirculation potential of hydrogen, and the projected emission factors for heat and power from the German grid mix.The results indicate that emissions from the future German grid mix for hydrogen production and the conversion potential of carbon oxides in the methanol reactor are critical factors in determining the technological and environmental viability of the overall carbon capture and utilization system. The evaluated synthesis routes show great potential for carbon capture and utilization to reduce the carbon dioxide emissions from the steel industry, especially when coupled with hydrogen produced from renewable and low-carbon energy sources.