Techno-Economic Analyses of the CaO/CaCO3 Post-Combustion CO2 Capture From NGCC Power Plants

Introduction

Carbon Capture and Storage (CCS) is an economically competitive technology for CO2 mitigations in the 450 Scenario (IEA, 2015). The power sector is expected to be responsible for around 60% of the cumulative investment in CCS to 2040. Among various CO2 capture technologies, post-combustion capture using amine-based solvents is the most mature technology and is currently being demonstrated at large scale at different sites according to the Global CCS Institute (2016). However, other post-combustion technologies such as membranes, low-temperature, adsorption and absorption using more advanced solvents (Figueroa et al., 2008), have also been being investigated to further reduce the cost of CO2 capture to an acceptable level. CaO/CaCO3 looping or calcium looping (CaL) has been regarded as a promising alternative that is expected to achieve lower capture cost (Hanak et al., 2015) and avoid the emissions of potentially toxic chemical residues (Berstad et al., 2012). Increasing studies have been performed on CaL at different levels including experiments on reaction kinetics and sorbent performance enhancement (Grasa et al., 2008; Fang et al., 2009; Rodríguez et al., 2010; Martínez et al., 2012), reactors (carbonator/calciner) modeling (Alonso et al., 2009; Romano, 2012; Ylätalo et al., 2012; Martínez et al., 2013), pilot facilities test (Arias et al., 2013; Kremer et al., 2013; Dieter et al., 2014) and process simulation and system energy performance evaluation (Yang et al., 2010; Martínez et al., 2011; Berstad et al., 2012; Berstad et al., 2014; Ylätalo et al., 2014). More details can be referred to the comprehensive reviews (Hanak et al., 2015; Martínez et al., 2016; Perejón et al., 2016).

Due to large CO2 emissions from coal-fired power plants, most of CaL studies have focused on coal based power generation. Only a few studies (Berstad et al., 2012; Berstad et al., 2014; Cormos, 2015) have been performed for natural gas combined cycles (NGCC) which have lower CO2 concentration in the exhaust (∼4 vol% according to (Anantharaman et al., 2011)). The carbonation reaction is operated around 600 °C (Hanak et al., 2015). This temperature is close to the exhaust flue gas temperature of gas turbines. From a thermodynamic point of view, the CaL system therewith appears to have a possibility for efficient integration into the NGCC. Simulation studies (Berstad et al., 2012) on the entire NGCC with CO2 capture found that a basic CaL process using natural limestone sorbent resulted in a larger energy penalty than CO2 capture with amine solvents such as MEA (monoethanolamine). However, a subsequent study (Berstad et al., 2014) concluded that there is a large efficiency improvement potential for the CaL process. For example, the energy penalty can be considerably reduced when hot flue gas recycling and a solid-solid heat exchange are used, and also when operating parameters (calcination temperature, make-up ratio, solids circulation rate, etc.) are improved. As a result, compared to the MEA CO2 capture process, the thermal efficiency penalty (lower heating value-LHV basis) is reduced by 0.5-3.6% points (depending on the sorbents used).

As calcium looping is at a low level of maturity, a rather limited number of techno-economic studies has been performed and most of them have been focused on coal-fired power plants. Ylätalo et al. (2014) presented a conceptual design of a Cal system for a 250 MWth coal fired power plant. The sizing of reactors was based on flue gas flow rates, particle size and other proper assumptions. On the basis of the Kunii-Levenspiel models for circulating fluidized beds (Kunii and Levenspiel, 2000), Romano (2012) proposed a carbonator model that can be used for preliminary sizing calculation of carbonators. This model includes the carbonation reaction kinetics and solid vertical distributions in the reactor. Only limited techno-economic studies on CaL-based CO2 capture from NGCC plants have been published. Cormos (2015) presented a comparative study on the entire NGCC power plant with CO2 capture using CaL adsorption and MDEA (methyl-diethanol-amine) absorption. Similar to the study by Berstad et al. (2012) the CaL process was found to have a larger energy penalty (3.4% points in overall thermal efficiency) than the MDEA process. However, due to lower capital cost, this study evaluated the CO2 avoided cost of the CaL process to be 34 €/t (only half of the cost for the MDEA process). Eran et al. (2016) evaluated techno-economic performance for NGCC with CaL CO2 capture. It is concluded that the energy penalty related to CO2 capture can be considerably reduced when one additional heat recovery steam generator is introduced before the capture plant. The CO2 avoided cost was reported to be 29.3 €/t. Meanwhile, Hu and Ahn (2017) estimated CO2 avoided cost of a CaL process from NGCC at 72 and 68 €/t for respectively a case without and with exhaust gas recirculation. In these studies, limited information on the cost methodology was presented and the costing of the major equipment cost such as carbonator and calciner was not included in detail. Michalski et al. (2019) evaluated the techno-economic performance of coal-fired power plants with CaL CO2 capture using a bottom-up approach. The costing data of the CaL system is based on empirical correlations. De Lena et al. (2019) presented a techno-economic study for a cement production process with CaL CO2 capture. Again, empirical correlations for the costing of CaL systems have been assumed and used in the cost analysis. These empirical correlations have been used in another techno-economic study of coal-fired power plants where the CaL system has been proposed to capture CO2 and SO2 simultaneously (Coppola and Scala, 2020).

Against this background, the purpose of the present paper is to investigate the sizes and costs of a NGCC with integrated Ca-looping capture, and evaluate if this technology can compete with the reference CO2 capture with MEA from a cost point of view. Investigations are done for two cases previously assessed: case 1A in reference (Berstad et al., 2012), which has an net electric efficiency of 45.6%, and case 3A in reference (Berstad et al., 2014), which has a net electric efficiency of 52.3%. Case 1A is selected for this study since it is the simplest of all cases, i.e. could have a potential for low investment cost. Case 3A is selected for the opposite reason: its complex process configuration is likely to yield a high investment cost, but this could potentially be offset by the significantly higher process efficiency. In comparison, the reference NGCC with MEA capture has a net electric efficiency of 49.5% (case 0B in both papers (Berstad et al., 2012; Berstad et al., 2014)). Detailed equipment sizing calculations are performed and used as the basis of the cost estimation for both the CaL cases and the reference MEA plant. Finally, sensitivity analyses are performed to understand the uncertainties of the results and the impact of material performances is also discussed.