Abstract
The ability to operate flexibly is critical for the future implementation of carbon capture and storage (CCS) in thermal power plants. A dynamic test campaign examines the response of a CO2 absorption/desorption pilot-scale plant to realistic changes in flue gas flow rates and steam supply, representative of the operation of a Natural gas combined cycle (NGCC) plant fitted with post-combustion capture. Five scenarios, demonstrating the operational flexibility that is likely to be encountered in an energy market with significant penetration from intermittent renewables, are presented, with 30% monoethanolamine (MEA) as the absorbing solvent. It complements a wider effort on dynamic modelling of these systems where a lack of dynamic plant data has been reported.The campaign focuses on analysing critical plant parameters of the response of the pilot plant to a gas turbine shutdown, a gas turbine startup and three enhanced operational flexibility scenarios, including two for power output maximisation and one for frequency response with a rapid increase of steam supply to the reboiler. The campaign also demonstrates the use of continuous in situ solvent lean loading measurement with the use of a novel online continuous liquid sensor.It confirms that no significant barriers to flexible operation of amine post-combustion capture are found, although there remains scope for the improvement of plant response. Solvent inventory and circulation times are found to have a significant effect on capture rate during certain dynamic operations. A large solvent inventory increases total circulation times, which can result in additional time being required for the plant to return to steady state following a perturbation. The plant is forced to operate with a non-optimal capture rate while the solvent loading at the absorber inlet stabilises is identified as a potential impact.Use of interim solvent storage and continuous online measurement of solvent CO2 loading, combined with comprehensive knowledge of liquid circulation times and potential mixing effects, are suggested as methods for improving plant response to dynamic operation, thereby increasing CCS plant flexibility.
Highlights
In any energy generation portfolio with considerable input from renewable sources such as wind and solar, natural gas or coal-fired thermal power stations will be required to meet variable demand during periods when these intermittent sources are not generating electricity (Pöyry, 2009)
An alternative strategy would be to accept a lower CO2 capture rate while maintaining more representative values of liquid to gas flow ratio (L/G) ratio, lean loading and rich loading, but due to equipment limitations caused by the turndown ratio of the liquid pump and steam inlet valve, further reductions in flow rate would result in considerable flow instability, especially during dynamic scenarios which require additional turndown
Lean loading Rich loading Desorber inlet temp (C) Desorber outlet temp (C) Reboiler outlet solvent temp CO2 capture rate (%) Gas flowrate shutdown (t=20min) the target liquid/gas flow ratio is established at t = 5 min and the absorber temperature profile increases in magnitude (Fig. 9a), the capture rate begins to drop due to the lean solvent loading becoming gradually higher than at baseload operation, resulting in a lower driving force for the absorption of CO2 (Fig. 8c)
Summary
In any energy generation portfolio with considerable input from renewable sources such as wind and solar, natural gas or coal-fired thermal power stations will be required to meet variable demand during periods when these intermittent sources are not generating electricity (Pöyry, 2009). Pilot-scale test campaigns on realistic dynamic operating scenarios are necessary to obtain more data for model validation and provide a more complete understanding of how CCS plants respond to variations in generation plant output. This knowledge allows researchers to devise operating strategies and develop hardware and software capabilities to increase flexibility, allowing PCC to cope with rapidly-changing generation plant output. In this test campaign the response of a CO2 absorption/ desorption pilot-scale plant to five dynamic operating scenarios is examined. Full dynamic data obtained from these scenarios are supplied as an attachment to the electronic version of this paper
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