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The selective recycling of carbon dioxide (CO2) upstream of post-combustion capture processes can greatly reduce both the size of equipment and capital costs by process intensification. For combined cycle gas turbine (CCGT) power plants, flue gas flow rates can be lowered by two thirds and CO2 concentration greatly increased from 4% to 14% v/v. Selective recycling of carbon dioxide (CO2) can be achieved in CCGT plants with a low pressure drop, regenerative rotary CO2 transfer device using physical adsorption. A newly developed kinetic model of this CO2 transfer device shows that, for an activated carbon material with suitable equilibrium properties, a mass requirement of circa 600 tonnes is necessary for a new build CCGT plant of 800 MW with 90% capture. This is 3.7 times higher than the mass previously reported, by means of an equilibrium model, for the best performing commercially available activated carbon material. A rigorous design shows that the mass of 600 tonnes of activated carbon can be distributed on a honeycomb structure on two CO2 transfer wheels of 30m diameter and 2.2m height, rotating at 1rpm, with a preferential direction of leakages towards the flue gas side. The design then provides the basis for an optimisation study of CO2 recovery rate and adsorbent mass by examining first kinetic properties of the CO2 adsorbent to inform material development and research; second, rotational speed; and, last, the partitioning of the wheel. Further, the selective recycling of CO2 is examined as a retrofit option for CCGTs with solvent based post-combustion capture. The aim is to explore the possibility to increase overall capture level beyond the initial design of 90% capture using an integrated model consisting of a gas turbine combined cycle, a rotary CO2 transfer device and a post-combustion capture unit and compression train. The operation of the absorber column at reduced gas velocity is, however, shown to be detrimental to retrofitting selective CO2 recycling to existing CCGT plants with solvent-based capture. Finally, a comparison between a new build CCGT with PCC and fully integrated regenerative selective CO2 transfer wheel to a new build CCGT with PCC without SEGR is performed. The results show a possible reduction in absorber total packing volume of 42% and a marginal increase of net power output of 0.3% relative to a new build CCGT with PCC without SEGR.

With an increased urgency for global action towards climate change mitigation, this research was undertaken with the aim of evaluating post-combustion CO2 capture as an emission abatement strategy for gas-fired power plants. A dynamic rate-based model of a capture plant with MEA solvent was built, with imposed chemical equilibrium, and validated at pilot scale under transient conditions. The model predicted plant behaviour under multiple process inputs and disturbances. The validated model was next used to analyse the process and it was found that CO2 absorption is mass transfer limited. The model was then improved by explicitly adding reactions rate in the model continuity, the first such dynamic model to be reported for the capture process. The model is again validated and is observed to provide better predictions than the previous model. Next, high fidelity models of a gas-fired power plant, a scaled-up capture plant and a compression train were built and integrated for 90% CO2 capture. Steam for solvent regeneration is extracted from the power plant IP/LP crossover pipe. Net efficiency drops from 59% to 49%, with increased cooling water demand. A 40% exhaust gas recirculation resulted in a recovery of 1% efficiency, proving that enhanced mass transfer in the capture plant reduces solvent regeneration energy demands. Economic analysis reveals that overnight cost increases by 58% with CO2 capture, and cost of electricity by 30%. While this discourages deployment of capture technology, natural gas prices remain the largest driver for cost of electricity. Other integration approaches – using a dedicated boiler and steam extraction from the LP steam drum – were explored for operational flexibility, and their net efficiencies were found to be 40 and 45% respectively. Supplementary firing of exhaust gas may be a viable option for retrofit, as it is shown to minimise integrated plant output losses at a net efficiency of 43.5%. Areas identified for further study are solvent substitution, integrated plant part load operation, flexible control and use of rotating packed beds for CO2 capture.

Natural gas has become the UK’s foremost primary energy source, providing some 39% of our energy needs. The National Transmission System (NTS) has developed from its humble beginnings when natural gas was first discovered in the North Sea in the 1960s to become a complex interconnected network delivering up to 550 million cubic meters of gas daily. Gas has also become an increasingly important energy source for power generation, currently generating 35% of our electricity. This presents major challenges for the planning and operation of both the electricity and gas networks as their interdependence grows into the future. With the government’s goal of drastically reducing emissions from power generation by 2020, Combined Cycle Gas Turbine units, and therefore the NTS, will have to offer a new degree of flexibility to quickly respond to the intermittency of the growing penetration of wind generation on the electricity transmission system. Coupling this with the decline in the UK natural gas resources resulting in the NTS becoming reliant on imports to meet demand, it is becoming increasingly difficult to decouple the security of the gas supply from the security of the electricity supply in the UK. This study presents the modelling challenge of assessing this growing interaction and provides a robust methodology for completing a security analysis using detailed network models of the UK gas and electricity transmission systems. A thorough investigation of the intraday operation of the two systems in 2020 is presented given the growth of wind generation in the UK. The results are analysed and the implications for combined modelling and assessment are discussed as we enter a new era for UK energy security.