Figure 3. Effects on overall energy demand for CO2 capture (kWh/tonneCO2 normalized, where base case is 403.1 kWh/tonneCO2) and other relevant process conditions while varying (a) separator feed pressure, (b) separator operating temperature (blue: net heat removal process requirements), (c) separator vacuum pressure, and (d) liquefaction pressure (blue: minimum temperature of liquefaction column). All variations are with respect to the base case listed in Table 1.
Two significant physical phenomena must be considered when considering operating a PSA system for this process, the heat of adsorption and the pressure drop. Structured sorbent contactors can help address the challenges associated with these phenomena. Structured contactors can reduce pressure drop greatly32,60 and also fully manage or at least limit thermal effects in the bed.31-33,61 Using a fiber morphology, similar to those used in membranes, but with the polymer skeleton filled with sorbent particles, we can accomplish the same sorts of very low pressure drops experienced in hollow fiber membranes.32,60 To manage the heat of adsorption, which can be significant in high productivity beds with high operating capacities, the fiber sorbent bed can also incorporate microencapsulated phase change materials (μPCM).31 While fiber sorbent contactors have not yet been used industrially, their manufacturing process mimics that of both textile fibers and fiber membranes, so it is reasonable to expect their transition to application in adsorptive separations is feasible if they bring significant advantages.
The cost of fiber sorbent contactors containing phase change materials has not previously been considered in detail. Fiber beds were estimated to be made up of a multitude of individual fibers (diameter 650 µm, length 1 m). The weight ratio of phase change material to sorbent was taken at 1.25:1.The cost of the fibers was broken down into three parts, the price of the sorbent (base case economics take this value as $30/kg), the price of μPCM ($10/kg, based on an estimate from an industrial manufacturer), and the cost of the manufacture of the fibers and fixing them in flow modules ($20/m2 fiber external surface area). The manufacturing cost was estimated from the price of industrial hollow fiber membranes, which are also produced using dry-jet wet-quench techniques. Figure 4 shows the estimated breakdown in the cost of manufacturing the PSA unit containing fibers with phase change materials for our baseline case as a function of sorbent price. Across all considered sorbent costs, the price of manufacturing the fibers and potting them in modules dominates. Even in cases where the sorbent price is high ($100/kg), the device manufacturing costs rather than the material costs still make up the majority of the total cost. The effects of fiber diameter, the relative loading of phase change materials and sorbent loading on the overall cost of the separator is discussed in greater detail in S2.2 of the Supporting Information.