Process Integration and Techno-Economic Assessment of CO2 Capture Processes Based on Phase-Change Solvents

Examensarbete för masterexamen
Master Thesis
Edvardsson, Rasmus
Quint, Herman
Carbon Capture and Storage (CCS) has been suggested as a promising technology to combat climate change and eventually reach negative CO2 emissions. An existing carbon capture method is Post Combustion Carbon Capture (PCCC), which is a type of CCS where typically an aqueous solution of amines is used to absorb CO2 from the exhaust gases of an industrial plant. PCCC is currently under research in an EU funded project called ROLINCAP, which investigates new types of absorption technologies, in hope of decreasing the cost of carbon capture. One of these technologies is the so-called phase-change solvents, which can reach a multiple phase equilibrium in the presence of CO2, each phase with different content in terms of amine, CO2 and water. Because of this quality, phase-change solvents require less regeneration energy compared to 30 wt% Monoethanolamine (MEA), which is the conventional solvent for absorption-based PCCC. In this thesis, PCCC using the 35 wt% phase-change solvent N-methylcyclohexylamine (MCA) is compared with using the conventional solvent 30 wt% MEA. The capture processes are theoretically implemented on a 400 MW natural gas combined cycle power plant located in Thessaloniki, Greece. Process integration between the power plant and capture plant was performed to reduce the overall process system energy consumption. The most cost-effective heat exchanger network design among many was chosen for each solvent for further evaluation. Finally, a techno-economic assessment was performed on the proposed capture plant designs, to estimate the capital and operational cost for each solvent process. This was performed with two different cost estimation methods: one factorial method, the other used at the engineering consultant company COWI which is an actor in the ROLINCAP project. Results from this thesis show that MCA is the better choice of solvent. It demands about half the heat for solvent regeneration compared to MEA and this difference is reflected in the operational costs. The MCA plant also has smaller flows and equipment, which resulted in lower electricity cost for machinery but also lower capital costs. Altogether, this makes the cost of capturing one tonne of CO2 much lower for MCA than MEA: 18.7 e/tonne CO2 compared to 47.3 e/tonne CO2. Another conclusion is that the potential of heat recovery between the power plant and capture plant is low. The reason is mainly because this is a retrofitting project which limits the integration potential due to constraints. These results should be used with care. The thesis is based on models and information received from other actors. Because of a misunderstanding and modelling irregularity, the capture plant models exclude 19% of the exhaust gas flow and use a different gas composition. Because of this, the capture plant dimensions are not representative for the natural gas power plant in question. However, the composition and flows are still reasonable, and could represent partial capture. Also, the modelled MEA absorption process operates at a higher pressure than MCA. Because of this, the exhaust gas needed to be pressurised which resulted in higher electricity consumption, which increased the operational cost drastically. The higher operating pressure was most likely not required, and the capture cost for the MEA process is therefore higher than it could be.
Energi, Hållbar utveckling, Energiteknik, Energy, Sustainable Development, Energy Engineering
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