Bashir, Fidal I; (2024) Techno-Economic Analysis of Methanol Synthesis from Steelworks Off-Gases. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Carbon Capture, Storage and Utilisation (CCUS) is central to meeting the global ambition of achieving Net-Zero Emissions (NZE) by mid-century; a goal underscored by the Paris Agreement to limit the average global temperature increase to less than 1.5 °C above pre-industrial levels. With over 140 countries committed to net-zero targets, covering 90% of current greenhouse gas emissions, it is essential to address the need for deep transformation across the global energy system. To decarbonize hard-to-abate industries like steel and cement, CCUS remains a very attractive option. Steel manufacturing predominantly depends on coal, both as a source of heat and primarily utilised as a reducing agent to obtain iron from iron ore and impart the required carbon content in steel. Over the last few decades, despite advancements and investments, the iron and steel industry has seen a rise in CO2 emissions, driven by the growing steel demand. While there has been a marginal decline in the direct CO2 intensity of crude steel production recently from 2 tonnes of CO2 per tonne of steel to about 1.41 tonne CO2 per tonne of steel, more rapid advancements are necessary to align with the objectives set in the NZE by 2050 Scenario [1]. The current decade is crucial for developing and commercializing innovative, near-zero-emission production methods, expected to contribute to 8% of primary production by 2030. Yet, amidst a global energy crisis, current low- and near-zero-emission efforts fall short of the NZE Scenario targets, with high-emission projects making up about two-thirds of all announced global projects, highlighting a significant gap in meeting NZE objectives. In addressing the steel industry's challenge of reducing CO2 emissions, CCUS and methanol production stand out as key mitigation strategies. CCUS captures CO2 emissions from steel production for storage or reuse, thus preventing its atmospheric release and promoting a circular carbon economy. Concurrently, methanol production transforms captured CO2 into methanol, a sustainable chemical feedstock and fuel, reducing the carbon footprint of the steel, chemical and transportation sectors and offering a renewable energy-based solution. The integration of CCUS and methanol production into steel plants signals a pragmatic step towards reducing industry emissions. This PhD thesis presents a comprehensive techno-economic analysis of methanol synthesis from 4 steelworks off-gases, framed within the urgent global climate change mitigation context and the drive towards CCUS strategies. The research explores the design and economic assessment of Pressure Swing Adsorption (PSA) systems for recovering CO2, CO, and H2 from steelworks off-gases. Using Aspen Adsorption for modelling, three distinct PSA units are designed and validated against literature experimental data for specific gas separations. The simulations produce 99.3% purity and 80% recovery for H2, 98% purity and 87% recovery for CO, and 96.9% purity and 75% recovery for CO2. The cost analysis demonstrates the economic viability of PSA, with separation/production costs of 2,768 £/t for H2, 52.78 £/t for CO, CO2 capture cost of 16.89 £/t and 54 £/t for CO2 avoided, placing it within range of 20-56 £/tCO2 which is the standard for power plants. The above findings establish the potential of PSA as a cost-effective alternative to traditional separation technologies in the steel industry context. Integrated process models for methanol synthesis using the Aspen Plus chemical process simulation tool, encompassing CO2 capture and storage, are analysed. Direct CO2 hydrogenation is examined along with alternative methods. In particular, three process configurations are simulated, each integrating a Heat Exchanger Network (HEN) for enhanced energy efficiency. For these configurations, the Levelized Cost of Methanol (LCOMeOH) ranges from 439 to 474 £/tMeOH, which is lower than the 2023 average selling price of 493 £/t. The Carbon Avoidance Costs (CAC) vary between 10.49 and 17.83 £/tCO2. The Levelized Cost of Hydrogen (LCOH) from Steam Methane Reforming (SMR) is 21.29 £/MWhth. These processes achieve CO2 intensity of 1.1 to 1.32 tCO2/tsteel, which is lower than the industry reference of 1.8 tCO2/tsteel. Various distillation configurations are explored, analysing their impact on energy efficiency and costs associated with methanol synthesis. An optimized split tower configuration achieves a levelized distillation cost of 7.28 £/tMeOH and a specific energy consumption of 2.62 MJ/kg methanol separated, this compares with 4 MJ/kg using conventional distillation methods. The techno-economic assessment reveals the potential economic feasibility of methanol production from steelworks off-gases under certain conditions, providing valuable information for CCUS initiatives.

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