Demonstration of Swing adsorption cluster concept (SARC) for CO2 capture

Abstract

Adsorption-based post-combustion CO2 capture is enjoying significant research attention due to its wide applicability within the power and industrial sectors and its ability to retrofit existing infrastructure. Important research focus areas include reduction in energy penalty, cost and environmental impact. This thesis is focused on the experimental demonstration of the Swing Adsorption Reactor Cluster (SARC) for CO2 capture. The SARC concept combines a temperature and vacuum swings for sorbent regeneration. A heat pump is used for transferring heat from the exothermic carbonation reaction to the endothermic regeneration reaction. Sorbent regeneration under vacuum allows for a small temperature difference between carbonation and regeneration, leading to a high heat pump efficiency, thereby minimizing the resulting energy penalty of CO2 capture. This key principle behind the SARC concept was experimentally demonstrated in a benchscale prototype and, subsequently, in a standalone multistage reactor with inbuilt heat transfer surfaces designed and constructed at the Norwegian University of Science and Technology (NTNU) in close collaboration with SINTEF Industry. The final research outcome of this thesis was achieved in four different campaigns as follows: • Proof of concept for hybrid mode of regeneration (VTSA): The experiments were carried out in a bench-scale reactor designed for demonstrating the working principle of the SARC hybrid regeneration mode. This study compares combined vacuum and temperature swing adsorption (VTSA) to pure temperature swing adsorption (TSA). The comparison study showed that 50 mbar vacuum (VTSA) can reduce the required temperature swing by 30-40 °C compared to the TSA. A complete SARC cycle comprising of carbonation, evacuation, regeneration and cooling steps was successfully demonstrated, and the concept performed largely as expected. The study was completed using polyethyleneimine supported (PEI) on silica sorbent supplied by the project partner KRICT (Korean research institute of chemical technology, South Korea). • Sorbent screening: The main objective of this study was to identify the best performing sorbent for the Swing Adsorption Reactor Cluster (SARC) concept. The screening results of four sorbents indicated two PEI sorbents to be good candidates for the SARC application: a PEI sorbent functionalized with 1,2-epoxybutane supported on silica (referred to as EBPEI in the rest of the document) and a PEI sorbent supported on mesoporous silica containing confined metal organic framework nanocrystals (referred to as PEI-MOF in the rest of the document). Though PEI-MOF working capacity was higher than EB-PEI sorbent, the large-scale reactor simulation suggested that it did not result in an efficiency advantage relative to EB-PEI, mainly due to the higher vacuum pump power consumption of PEIMOF. • Demonstration of the Novel Swing Adsorption Reactor Cluster (SARC) Concept in a multistage fluidized bed with heat transfer surfaces: A multistage fluidized bed labscale reactor with inbuilt heat exchangers was designed for the experimental demonstration of the novel SARC concept. The study showed 90% CO2 capture from an N2/CO2 mixture approximating a coal power plant flue gas fed at 200 Nl/min, representing a CO2 capture capacity up to 24 kg-CO2/day. The lab-scale reactor utilized a vacuum pump and a heating oil loop (emulating the heat pump) to demonstrate the SARC concept. Experiments revealed that 1) the polyethyleneimine sorbent employed imposes no kinetic limitations in CO2 adsorption and only minor non-idealities in regeneration, 2) a high heat transfer coefficient in the range of 307-489 W/m2 K is achieved on the heat transfer surfaces inside the reactor, and 3) perforated plate separators inserted along the height of the reactor can achieve the plug-flow characteristics required for high CO2 capture efficiency while maintaining good fluidization conditions to maximize heat transfer. Finally, a sensitivity analysis revealed the expected improvements in CO2 capture efficiency with increased pressure and temperature swings, and shorter carbonation times, demonstrating predictable behaviour of the SARC reactor. This study provides a sound basis for further scale-up of the SARC concept. • Reactor validation and techno-economic assessment of the SARC concept applied to a cement plant for CO2 capture: The experimental results from the multistage fluidized bed reactor were used to validate a SARC reactor model developed by SINTE. The previous assumptions made in the model for the pressure drop, the heat transfer coefficient and the number of CSTR were revised based on the lab scale experimental results. The reactor model reasonably predicted the experimentally observed CO2 capture. Subsequently, industrial scale reactor modelling (using the adjusted model assumptions) and process simulations were completed. Two process schemes for SARC integration to cement plant were evaluated and new techno-economic assessments based on revised assumptions were completed for 6 new cases (compared to previously published). By combining the high experimentally observed heat transfer coefficient and the proven effectiveness of simple perforated separators for minimizing axial mixing with a new heat integration layout and shorter reactors, the CO2 avoidance cost was reduced from a previously published value of 50.7 €/ton to 38.7 €/ ton of CO2. This makes SARC not only the simplest option for retrofitting existing cement plants but also the most economical CO2 capture solution for new plants.