The iron and steel industry represents the largest energy consuming manufacturing sector in the world with average emissions being around 2 tonnes of CO2 per tonne of steel. The enormous CO2 footprint of steel mills, which accounts for 5 – 7 % of anthropogenic CO2 emission, must be substantially reduced.
A unique feature of the current steel making processes is the presence of energy containing residual gases; Coke Oven Gas (COG), Blast Furnace Gas (BFG) and Basic Oxygen Furnace Gas (BOFG). COG is the most energy rich of these streams containing ~65 vol% H2 while the BOFG has significant CO content (>50 vol%). BFG represents the greatest volumetric flow, and is hence the focus of particular attention but has low energy content, consisting of ~60 vol% N2 and ~20 vol% CO2. These gases are often used as a fuel within the plant to produce power or combined heat and power. Otherwise, CO is converted to CO2 by combustion at the mouth of the furnaces, and through flaring after gas cleaning in furnaces.
In an effort to reduce the environmental footprint, there is great interest in using these gases to produce value added products or implementing strategies to extract the thermal value from them while producing a CO2 product stream suitable for further utilisation or geological storage. In an effort to reduce the environmental foot print, there is great interest in using these by-product steel gases to produce high value chemicals instead of heat and power which would result in the emission of more CO2.
Methanol is a particularly attractive candidate for CO2 utilisation given its suitability as an alternative automotive fuel. Methanol is also a precursor for the production of other useful chemicals such as formaldehyde and acetic acid which can be processed to produce resins and polymers, representing a route for the permanent sequestration of the captured CO2. Methanol production therefore presents one of the few opportunities for CO2 utilisation where there is sufficient market demand given the diverse range of its applications.
The UK CCSRC Scientific Council Collaboration fund was awarded to Dr Richard Porter and Prof Haroun Mahgerefteh at University College London and Prof Meihong Wang at University of Sheffield to conduct a preliminary economic feasibility study for methanol production from steelworks off-gas (BOFG and COG) and biomass through the use of process simulation. By closing the mass balance for the process and integrating with engineering cost models to estimate the capital and operating costs, the study found that integrating methanol production in steel plants can be economically attractive. The investigators future work addresses techno-economic simulation for assessing the cost of methanol production while utilising BFG, and will also experimentally investigate the effect of feed gas ratio and stream impurities relevant to residual steel gases on the methanol synthesis process using selected catalysts.