Technical and Economic Conditions for Efficient Implementation of CO2 Capture - process design and operational strategies for power generation and process industries

Doktorsavhandling, 2017

This thesis investigates the operational parameters of fossil-based power generation and industrial processes in future energy systems that have stringent constraints on CO2 emissions, and, consequently, large shares of renewable energy. CO2 capture and storage, which is the focus of this work, is required for power and industrial processes that emit CO2. This work investigates the heat requirement and the costs for implementation of CO2 absorption in power and process industries, and the potential for thermal power with or without CO2 capture to balance an electricity system with a large share of variable generation. The work uses modeling of: absorption-based CO2 capture processes and coal-based power generation, under both steady-state and transient conditions; and the electricity system, which includes generation technologies with CO2 capture. It is shown that the specific heat requirement for CO2 separation can differ by up to 1,000 kJ/kg of CO2 captured between different processes industries, due to differences in the flue gas CO2 concentrations. Furthermore, the volume of the CO2 source is crucial in terms of the cost of CCS. Specific investment costs of 10–20 €/tCO2 are estimated for large sources, such as steel mills, cement plants, and recovery boilers in pulp mills, as compared to >35 €/tCO2 for small refinery stacks and lime kilns in pulp mills. Energy costs are, however, typically >20 €/t and represent the largest fraction of the total capture cost for large sources. This underlines the importance of a cost-effective heat supply, which can in some cases come from the excess heat in industrial processes. For an established system, the transport cost is modest. However, during ramp-up, the investments required for transport are of the same magnitude as those for the CO2 capture plant. On an energy systems level, the imposition of strict targets on CO2 emissions has greater adverse effects on investments in flexible coal-based generation than enforcing strict targets on generation from renewables. Improving the cycling properties (minimum load levels and start-up times) of coal plants benefits the electricity system by ensuring higher capacity factors for wind and solar power, and increases the competitiveness of coal versus NGCC plants, by providing a similar level of operating flexibility at a lower cost. With the existence of strict CO2 targets, CO2 capture becomes a prerequisite for coal-based power generation. The load-following capability of coal-fired power plants is not significantly affected by the implementation of a CO2 absorption process. In contrast, frequent cycling and operation with a decreased CO2 capture rate are limited by the system due to increased emissions.