Evaluating Pressure Swing Adsorption as a CO2 separation technique in coal-fired power plants
Introduction
The atmospheric concentration of carbon dioxide (CO2) has increased by 40% since pre-industrial times, and recently passed the 400 ppm milestone. CO2 is regarded as the main responsible for the atmospheric greenhouse effect, which is producing the warming of the climate system. It is extremely likely that human influence has been the dominant cause of the observed warming (IPCC, 2013). One possible mitigation action for stabilizing the atmospheric CO2 concentration, while continuing exploiting fossil fuel resources, is Carbon dioxide Capture and Storage (CCS). CCS consists in separating CO2 from large anthropogenic point sources, such as thermal power plants, compressing it for transportation and permanently storing it in underground geological formation. There are different types of CO2 capture systems: post-combustion, pre-combustion and oxyfuel combustion (IPCC, 2005). Many different techniques have been proposed for capturing CO2. These includes: chemical or physical absorption, adsorption, reactive solids, membranes, cryogenic processes (Ebner and Ritter, 2009). To date, all commercial CO2 capture plants are based on absorption for separating CO2 (Herzog et al., 2009), as it is the most mature and well understood technology. However, its large scale deployment is hindered by the large power consumption, which negatively affects the energy efficiency of the plant. That, summed to other concerns related to the solvent toxicity and to the potentially high corrosion rate, makes advisable to investigate alternatives. In the current work, Pressure Swing Adsorption (PSA) process is analyzed as an option for post- and pre-combustion CO2 capture. PSA is a cyclic process. During the adsorption step, the CO2 present in the feed gas stream is fixed on the surface of the selected adsorbent. Following, the regeneration of the bed is carried out by a pressure swing operation. The potential advantage connected to this process is the absence of any thermal energy duty during the regeneration step. Adsorption processes have been successfully employed for CO2 removal from synthesis gas for hydrogen production (Cen and Yang, 1986, Ribeiro et al., 2008, Ribeiro et al., 2009, Yang and Lee, 1998, Yang et al., 1997). With regard to CCS applications, PSA process suitability has to be proven yet. A large number of studies have been done in order to assess PSA processes operating in the condition typical of post- (Agarwal et al., 2010, Choi et al., 2003, Chou and Chen, 2004, Ishibashi et al., 1996, Kikkinides et al., 1993, Ko et al., 2005, Liu et al., 2011a, Mehrotra et al., 2010, Na et al., 2001, Na et al., 2002, Nikolic et al., 2008, Plaza et al., 2010, Reynolds et al., 2006, Takamura et al., 2001, Tlili et al., 2009) and pre-combustion (Casas et al., 2013, Schell et al., 2013) applications. A significant lack was found in the analysis of more comprehensive systems (The Future of Coal, 2007), where the PSA process is integrated with the rest of the plant. Few works deal with the understanding of such complex arrangements. In post-combustion applications, only preliminary studies have been carried out, whose results can be considered partial (Panowski et al., 2010) and/or focusing on a particular side of the topic (e.g., economic considerations) (Ho et al., 2008). In pre-combustion applications, more thorough analyses have been performed. Liu and Green (2014) evaluated the applicability of PSA as CO2 removal technology in an Integrated Gasification Combined Cycle (IGCC). They simulated a warm PSA process based on a tailored adsorbent, able to perform at elevated temperature. The results achieved are in line with those of a Selexol absorption process. Other studies investigated the performance of Sorption Enhanced Water Gas Shift (SEWGS), an innovative CO2 capture process for pre-combustion applications, applied to both IGCC (Gazzani et al., 2013) and Natural Gas Combined Cycle (NGCC) (Manzolini et al., 2011). In either case the outcome appears to be extremely promising. The objective of this paper is to provide a full-plant analysis of coal-fired plants implementing CO2 capture by a cold PSA process, meaning that the process takes place at temperature levels suitable for many of the most common adsorbents. Coal was selected as fuel because of its higher emission index (higher CO2 emission per unit of energy released). Further, coal utilization is predicted to increase in the future, under any foreseeable scenario (The Future of Coal, 2007). Thus, CCS will become a critical tool in order to enable a sustainable exploitation of coal. Two plant configurations were considered, respectively to account for a post- and a pre-combustion scenario. Post-combustion CO2 capture is implemented by integrating a PSA process into an Advanced SuperCritical (ASC) pulverized coal plant. Pre-combustion CO2 capture is implemented by integrating a PSA process into an Integrated Gasification Combined Cycle (IGCC) plant. First, the layout of the thermal power plant, to be coupled with the CO2 capture unit, is defined and modeled. Following, the modeling of the PSA process is presented resulting in a dynamic computational model. The procedure for the choice of the optimal PSA process configuration is outlined. A full-plant analysis is then provided for both the scenarios. Simulations were also implemented for the reference case without CO2 capture and for the case with CO2 capture based on an absorption process. A plant-level comparison is carried out, returning the competitiveness of PSA process with regard to another technique of decarbonization (i.e., state-of-the-art absorption processes). The performance of the system is evaluated on three levels, namely CO2 separation performance, energy efficiency and footprint of the technology.
Section snippets
Modeling of the power plant
The model of the power plant was developed by Thermoflow Inc. products: STEAM PRO, GT PRO and THERMOFLEX. The focus is on coal-fired power plants, since combustion of coal produces high specific emission of CO2 per unit of electricity generated. Accordingly, two thermal power plant layouts were selected to represent the most common systems for coal-based power generation. These systems are an Advanced SuperCritical (ASC) pulverized coal plant and an Integrated Gasification Combined Cycle (IGCC)
Adsorption bed model
The mathematical model for the dynamic simulation of an adsorption bed relies on material, energy and momentum balances. The adsorbents are considered to have a bi-disperse structure (i.e., a population of macro and micropores). Three material balances would be theoretically necessary, one for the bulk gas phase, one for the macropores and one for the micropores. In order to reduce the computational time requested to solve the set of equations, a simplification was introduced. This
Definition of the performance parameters
The CO2 separation performance is primarily evaluated in terms of CO2 recovery and purity . In the pre-combustion scenario it is also useful to define the H2 recovery , giving that H2 is fuelling the downstream gas turbine cycle. The CO2 recovery may be misleading when large energy penalties result from the CO2 separation process. For this reason, an additional parameter was introduced, namely the CO2 capture efficiency . The CO2 capture efficiency is the real measure to
Conclusions
In the current work, the suitability of PSA process for CO2 capture in coal-fired power plants has been assessed. The effectiveness of PSA is evaluated on three different levels: CO2 separation performance, energy efficiency and footprint of the technology. A post- and a pre-combustion scenario have been considered.
In the post-combustion scenario a PSA process is integrated with an Advanced SuperCritical (ASC) pulverized coal plant. The outputs of the full-plant analysis were compared to those
Acknowledgement
The authors gratefully acknowledge the financial support provided through the “EnPe – NORAD's Programme within the energy and petroleum sector”.
References (60)
An examination of how exposure to humid air can result in changes in the adsorption properties of activated carbons
Carbon
(1988)A parametric study of a PSA process for pre-combustion CO2 capture
Sep. Purif. Technol.
(2013)- et al.
Carbon dioxide recovery by vacuum swing adsorption
Sep. Purif. Technol.
(2004) - et al.
Infrared spectroscopic studies of the adsorption of carbon dioxide and the coadsorption of carbon dioxide and water on CaY- and NiY-zeolites
J. Colloid Interface Sci.
(1976) - et al.
CO2 capture in integrated gasification combined cycle with SEWGS – Part A: Thermodynamic performances
Fuel
(2013) - et al.
An experimental adsorbent screening study for CO2 removal from N2
Microporous Mesoporous Mater.
(2004) Technology for removing carbon dioxide from power plant flue gas by the physical adsorption method
Energy Convers. Manag.
(1996)Dual mode roll-up effect in multicomponent non-isothermal adsorption processes with multilayered bed packing
Chem. Eng. Sci.
(2011)Multi-bed vacuum pressure swing adsorption for carbon dioxide capture from flue gas
Sep. Purif. Technol.
(2011)Integration of SEWGS for carbon capture in natural gas combined cycle. Part A: Thermodynamic performances
Int. J. Greenh. Gas Control
(2011)
Power generation with CO2 capture: technology for CO2 purification
Int. J. Greenh. Gas Control
Post-combustion CO2 capture with a commercial activated carbon: comparison of different regeneration strategies
Chem. Eng. J.
Optimization of CO2 compression and purification units (CO2CPU) for CCS power plants
Fuel
A parametric study of layered bed PSA for hydrogen purification
Chem. Eng. Sci.
Linear driving force approximation in cyclic adsorption processes: simple results from system dynamics based on frequency response analysis
Chem. Eng. Process.: Process Intensif.
Evaluation of dual-bed pressure swing adsorption for CO2 recovery from boiler exhaust gas
Sep. Purif. Technol.
Carbon dioxide capture and recovery by means of TSA and/or VSA
Int. J. Greenh Gas Control
Comparative studies of CO2 and CH4 sorption on activated carbon in presence of water
Colloids Surf. A: Physicochem. Eng. Asp.
Diffusion of CO2 in 4A and 5A zeolite crystals
J. Colloid Interface Sci.
A superstructure-based optimal synthesis of PSA cycles for post-combustion CO2 capture
AIChE J.
Bilinear driving force approximation in the modeling of a simulated moving bed using bidisperse adsorbents
Ind. Eng. Chem. Res.
The effect of water on the adsorption of CO2 and C3H8 on type X zeolites
Ind. Eng. Chem. Res.
Bulk gas separation by pressure swing adsorption
Ind. Eng. Chem. Fundam.
Optimal operation of the pressure swing adsorption (PSA) process for CO2 recovery
Korean J. Chem. Eng.
Comparison of activated carbon and zeolite 13X for CO2 recovery from flue gas by pressure swing adsorption
Ind. Eng. Chem. Res.
Enabling advanced pre-combustion capture techniques and plants. European best practice guidelines for assessment of CO2 capture technologies
State-of-the-art adsorption and membrane separation processes for carbon dioxide production from carbon dioxide emitting industries
Sep. Sci. Technol.
Chemical Reactor Analysis and Design
New method for prediction of binary gas-phase discussion coefficients
Ind. Eng. Chem.
Dual pressure swing adsorption units for gas separation and purification
Ind. Eng. Chem. Res.
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