Carbon capture from reheating furnaces in the Swedish steel industry : evaluation of techno-economic feasibility

Detta är en Uppsats för yrkesexamina på avancerad nivå från Luleå tekniska universitet/Energivetenskap

Sammanfattning: The reduction of greenhouse gas emissions is important to keep climate change under control. One of the largest CO2 emitters of the Swedish industries is the steel industry. This is, among others, due to the need of heat treatments and reheating processes depending on high temperatures and fossil fuels. The business organisation Jernkontoret and their department for energy and furnace technique is working towards reducing the emissions for these processes and one area of research is the carboncapture and storage (CCS) techniques. This report aims to give an overview of existing and emerging CCS techniques applicable for the reheating and heat treating furnaces, along with evaluating one post-combustion carbon capture technique for different cases provided by some involved companies. The carbon capture technique investigated in this project can be divided into three main sections; Oxyfuel combustion, pre-combustion and post-combustion capture. Oxyfuel relies on the usage of pure oxygen instead of air for the combustion of the fuel, this gives a high CO2 concentration in the flue gas (80-98%). Concentrations below 95% require further purification before compression and transportation to storage. Using pre-combustion capture the CO2 is removed before the combustion, this can be done by reformingthe used fossil fuel to a syngas (a gas with a high H2 and CO concentrations). The CO2 is formed by passing the syngas through a water-gas shift, which also increases the H2 concentration further. The CO2 can then be removed relying on reversible chemical reactions or the affinity between the CO2 and an absorbent. The post-combustion carbon capture also relies on reversible chemical reactions or affinity to an absorption medium, usually an amine solvent. The bond is then broken in the desorption unit, creating a pure CO2 stream and a reusable absorbent. The case studies were done only for a post-combustion capture process with a MEA-water solvent (20%) as the absorption medium. The simulation program Aspen Plus was used both for the technicaland economical values, executed by the PhD student Nan Wang at LTU. The values were interpolated/extrapolated nonlinear for each given case. Six different cases were given by four companies, four conventional furnaces and two oxyfuel furnaces. Evaluations for the oxyfuel furnaces were excluded, due to big differences between the model and case values and since the technique evaluated is not implementedat oxyfuel plants. The evaluations done for the conventional furnace cases gave a total cost of between 86 - 126 $/tonne captured CO2. This has to be viewed as a high cost investment even without having a full economic evaluation regarding cost for transportation and storage included.

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