Steam cycle options for capture-ready power plants, retrofits and flexible operation with post-combustion CO2 capture

The energy penalty for post‐combustion carbon dioxide capture from fossil‐fired power plants can be greatly reduced ‐ independently of the intrinsic heat of regeneration of the solvent used ‐ by effective thermodynamic integration with the power cycle. Yet expected changes in electricity generation mix and the current immaturity of post‐combustion capture technology are likely to make effective thermodynamic integration throughout the operating life of such plants a challenging objective to achieve because of a requirement for extensive part‐load operation and also for matching to future technology improvements. Most previous published studies have, however, focused on base‐load operation of the power cycle and the carbon dioxide capture plant and with the assumption of a fixed technology. For carbon dioxide capture‐ready plants the characteristics of the capture plant are also not known when the plant is designed. The plant must operate initially without capture at a similar efficiency to ‘standard’ plants to be competitive. Capture‐ready plants then also need to be able to be retrofitted with unknown improved solvents and to be capable of integration with a range of future solvents. This study shows that future upgradability for post‐combustion capture systems can be facilitated by appropriate steam turbine and steam cycle designs. In addition fossil‐fired power plants with postcombustion capture may need to be able to operate throughout their load range with the capture unit by‐passed, or with intermediate solvent storage to avoid the additional emissions occurring when the absorption column is by‐passed. Steam cycles with flexible steam turbines can be adequately designed to accommodate for part‐load operation with these novel operating conditions and with rapid ramp rates. Several approaches for effective capture‐ready pulverised coal and natural gas plants are also described. These achieve identical performance before retrofit to a conventional plant with the same steam conditions, but have the potential to perform well after capture retrofit with a wide range of solvents, at the expense of only a small efficiency penalty compared to hypothetical plants built with perfect foreknowledge of the solvent energy requirements. For existing plants that were not made capture‐ready, and provided sufficient space is available and other physical limits are not too constraining, ways to achieve effective thermodynamic integration are also discussed

Addressing Technology Uncertainties in Power Plants with Post-Combustion Capture

AbstractRisks associated with technology, market and regulatory uncertainties for First-Of-A-Kind fossil power generation with CCS can be mitigated through innovative engineering approaches that will allow solvent developments occurring during the early stage of the deployment of post-combustion CO2 capture to be subsequently incorporated into the next generation of CCS plants. Power plants capable of improving their economic performance will benefit financially from being able to upgrade their solvent technology. One of the most important requirements for upgradeability is for the base power plant to be able to operate with any level of steam extraction and also with any level of electricity output up to the maximum rating without capture. This requirement will also confer operational flexibility and so is likely to be implemented in practice on new plants or on any integrated CCS retrofit project

Maintaining the Power Output of An Existing Coal Plant with the Addition of CO 2 Capture: Retrofits Options With Gas Turbine Combined Cycle Plants

AbstractIt is likely that a significant number of existing pulverised coal-fired power plants will be retrofitted with post-combustion capture as part of a global rollout of carbon capture and storage. Previous studies have demonstrated that the energy penalty for post-combustion carbon dioxide (CO2) capture can be greatly minimised by effective integration of the capture system with the power cycle. Nevertheless, the power output of the site is, in most cases, reduced and the volume of electricity sales would drop. For other plants, the existing steam cycle may not be able to be integrated effectively for steam extraction, or space and access around/to the steam cycle may be impossible. As an alternative to steam extraction, it is possible to retrofit existing coal plants with a gas turbine combined cycle plant (CCGT) to maintain, or even increase, the site power output. The gas turbine can be integrated to the existing coal plant in various ways to supply all the heat, or a fraction of the heat, and the power required for the capture systems. An important consideration is whether carbon emissions from both, the combined cycle and the retrofitted coal plant are captured, or from the latter only.This paper examines these different options for carbon capture retrofits to existing coal plant and presents a novel configuration with the sequential combustion of gas turbine flue gas in the existing coal boiler while capturing carbon emissions from the combustion of coal and natural gas

On the retrofitting and repowering of coal power plants with post-combustion carbon capture: An advanced integration option with a gas turbine windbox

Retrofitting a significant fraction of existing coal-fired power plants is likely to be an important part of a global rollout of carbon capture and storage. For plants suited for a retrofit, the energy penalty for post-combustion carbon capture can be minimised by effective integration of the capture system with the power cycle. Previous work on effective integration options has typically been focused on either steam extraction from the power cycle with a reduction of the site power output, or the supply of heat and electricity to the capture system via the combustion of natural gas, with little consideration for the associated carbon emissions. This article proposes an advanced integration concept between the gas turbine, the existing coal plant and post-combustion capture processes with capture of carbon emissions from both fuels. The exhaust gas of the gas turbine enters the existing coal boiler via the windbox for sequential combustion to allow capture in a single dedicated capture plant, with a lower flow rate and a higher CO2 concentration of the resulting flue gas. With effective integration of the heat recovery steam generator with the boiler, the existing steam cycle and the carbon capture process, the reference subcritical unit used in this study can be repowered with an electricity output penalty of 295 kWh/tCO2 – 5% lower than a conventional steam extraction retrofit of the same unit – and marginal thermal efficiency of natural gas combustion of 50% LHV – 5% point higher than in a configuration where the gas turbine has a dedicated capture unit

Vacuum Assisted Acidification: A Novel, Robust and Accurate Technique for the Measurement of CO 2 Loading in Solvents and its Application in Post Combustion Capture

AbstractA method for measuring the CO2 loading of post combustion capture solvents has been developed which first separates CO2 from the solvent by acidification of the solvent under vacuum conditions, then traps the CO2 via deposition, and finally quantifies the CO2 by pressure measurement in a calibrated volume. A preliminary comparative assessment shows that the measurement accuracy and precision of the method compares favorably to other methods currently used at post combustion capture research facilities and that there is potential for continuing development of the method for use in industrial field applications

Financing new power plants ‘CCS Ready’ in China–A case study of Shenzhen city

AbstractWe evaluate the benefits of a ‘CCS Ready Hub’ approach, a regional ‘CCS Ready’ strategy, which not only includes a number of new coal-fired power plants but also integrates other existing stationary CO2 emissions sources, potential storage sites and potential transportation opportunities into an overarching simulation model. A dynamic top-down simulation model was built based on economic decision criteria and option pricing theory. The model inputs and assumptions build on spatial sampling and analysis using a geographic information system (GIS) approach, engineering assessment of local projects and outputs of a CCS retrofitting investment evaluation through cost cash flow modelling. A case study of Shenzhen city in the Pearl River Delta area in Guangdong in southern China is presented, based on engineering and cost assessment studies and stakeholder consultations and building on existing geological surveys and infrastructure plans. The simulation results show that financing ‘CCS Ready’ at regional planning level rather than only at the design stage of the individual plant (or project) is preferred since it reduces the overall cost of building integrated CCS systems. On the other hand, we found the value of considering existing stationary CO2 emissions sources in CCS ready design. Therefore, we recommended that making new plants CCS ready or planning a CCS ready hub should consider existing large emissions sources when possible