(284c) Techno-Economic Analysis of Solid Sorbent Direct Air Capture (DAC) in Temperature-Vacuum Swing Adsorption (TVSA) Cycles Using Detailed Process Modelling and Optimization

Carbon-dioxide removal (CDR) techniques, such as direct air capture (DAC) provide viable pathways to achieve net-zero CO₂ emissions by 2050 [1]. There has been intense debate on the cost of DAC with values ranging from 40-1000 USD/tonne of CO₂ captured being reported [2-4]. Reliable cost estimates accounting for the various components and contingencies are needed for large-scale implementation of DAC. In light of this, a detailed costing tool is developed and presented in this work. A variety of solid sorbents have been reported in the literature and we chose a few representatives for this study [5, 6]. These representative sorbents are arranged into a packed bed air contactor, and operated following the widely studied 4-step temperature-vacuum swing adsorption (TVSA) cycle [2, 7]. The key focus of this work is to use experimentally measured CO₂/H₂O equilibria and kinetics that are representative of process conditions. The process performance, i.e., CO₂ purity, recovery, specific energy, and CO₂ productivity, are evaluated using the 1-D in-house detailed process model [8].

The costing tool considers capital expenditures (CAPEX), operational expenditures (OPEX), and sorbent expenditures (SORBEX). The costing tool's basis was capturing 4000 tonnes of CO₂/year. The CAPEX includes the collector device, fans, and vacuum pumps. The total direct costs of these components were estimated and regressed using representative costing curves [10]. Contingencies are estimated in accordance with the NETL baseline reports [11]. The variable OPEX accounts for the hot water utility costs based on the specific energy requirement of the process. For the SORBEX, initial purchase and replacement costs were considered, with sorbents being replaced every 2 years [12]. The costing tool was then integrated with the detailed process model. To perform a techno-economic analysis, two different studies were done. First, the cost of DAC was estimated for the operating conditions that offered minimum specific energy and maximum productivity to establish the cost trends. Second, considering the operational parameters as variables, process optimization was performed to minimize the cost of DAC with a constraint on CO₂ purity. Sensitivity studies on the sorbent cost and CO2 uptake kinetics were also performed to elucidate the key features needed for next-generation DAC sorbents.

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