Flexibility of Low-CO2 Gas Power Plants: Integration of the CO2 Capture Unit with CCGT Operation

Abstract

CCGT power is well-positioned for flexible operation due to its favorable dynamic character and is likely to play a significant role in the future intermittent power generation mix, specifically with an increasing penetration of intermittent renewable power capacity. However, concerns exist around the impact of adding Carbon Capture & Storage on the flexibility of low-CO 2 fossil fuel power plants. This paper presents the results of a study on the dynamics of a carbon capture plant in order to address the impact on flexibility. This will enable the development of the learning curve to improve flexibility of future commercial scale CCGT-CCS plants.A dynamic model was set-up for a CCS retrofit on an existing typical commercial CCGT plant. Various load-following, shutdown and start-up scenarios were studied. It was concluded that flexibility of gas-fired power plants for mid-merit cycling or base-load operation does not have to be limited by the addition of post-combustion CO 2 capture. It was concluded that only startup scenarios may lead to additional CO 2 losses, which can be limited by appropriate design. Various options to enhance start-up response have been identified and require further study and development to explore their value. The dynamic modelling capability built for this study provides an excellent tool to do this. It is noted that, starting from early FOAK CCGT-CCS power plants, a learning curve will be required to further develop flexible operation. Reference is made to the learning curve that delivered the current flexibility of CCGT power plants, where the steam cycle follows load variations on the gas turbine.

Off-design point modelling of a 420 MW CCGT power plant integrated with an amine-based post-combustion CO2 capture and compression process

“…Thus, decarbonised CCGTs will be required to operate in a flexible load following manner -providing peaking capacity in addition to their current role as midmerit provider in the energy system. This has been noted in a number of previous contributions to this literature, such as that of Ceccarelli et al (Ceccarelli et al, 2014) wherein a study detailing the likely start-up/shut-down behaviour of a CCGT-CCS plant was presented. For this reason, models that describe the dynamic and off-design point of these systems will be of increasing value.…”

“…Thus, CCGT-CCS plants can be deployed in response to a relatively low CO 2 price (Nogueira et al, 2014and Johnsson, Odenberger & Göransson, 2014and Gerbelová et al, 2013. Whilst novel technologies, such as molten carbonate fuel cells and calcium looping processes (Cormos & Simon, 2013), have been proposed for decarbonising CCGT power plants (Campanari et al, 2014), the vast majority of current academic literature focuses on the utilisation of post-combustion amine scrubbing as the technology of choice for this purpose (Spence, Horan &Tucker, 2014 andCeccarelli et al, 2014). In this context, an aqueous 30 wt% solution of monoethanolamine (MEA) is still considered the benchmark solvent for the majority of academic studies (Boot-Handford et al, 2014).…”

Dynamic modeling and control of an intercooled absorber for post-combustion CO2 capture

“…Lawal et al [27], Ceccarelli et al [28], and Walters et al [22] have recommended maintaining a constant liquid to gas (L/G) ratio in the absorber, defined as the ratio of liquid mass flow entering the top of the column to gas mass flow entering the bottom of the column. This method maintains consistent operation of the absorber column, producing rich solvent at a nearly constant loading with varying flue gas flowrates.…”

Making gas‐CCS a commercial reality: The challenges of scaling up

“…Therefore, a major challenge in the design of PCC amine plants integrated with gas‐fired plants is that they should be flexible to follow the load changes in the power plant. The behavior of amine PCC plants and their economic and environmental impact during flexible operation is not well understood at the moment, although it has recently attracted a great deal of attention . Optimization of the capture plant during dynamic operation is a crucial element to reduce overall operational costs and ensure the stable and efficient performance of the capture plant at all times.…”