Mini-channel-structured Adsorption Reactor with In-situ Heat Exchanger for Rapid CO2 Adsorption and Regeneration
This project aims to develop an adsorption/heat exchange (AHX) reactor technology and address shortcomings associated with conventional reactor technologies for flue gas CO2 capture by adsorption. Capturing CO2 on a solid adsorbent is an attractive process to eliminate emission of volatile solvents and concentrate dilute CO2 on a compact solid bed. The AHX reactor provides the following performance attributes to reduce energy consumption and capital cost of the adsorption process: The mini-sized straight channels enable flue gas to contact with the adsorbent at high space velocity and low pressure drop. CO2 capture productivity increases with the space velocity, and air blower power consumption is decreased by lowering the pressure drop.The adsorbent powder or fine particle is fixed between a dense metal sheet and a thin gas-permeable sheet. Intrinsic adsorption properties can be effectively utilized, while the adsorbent attrition or crush issue is eliminated. The low-pressure drop channel and fixed adsorbent structure enables rapid regeneration by pulling vacuum, i.e., fast vacuum-pressure-swing-adsorption (VPSA) operation. Rapid heat transfer between the adsorbent layer and a thermal fluid by thermal conduction is obtained by using the thin dense metal sheet as an interface between the adsorbent and the thermal fluid. The rapid heat transfer enables quick adsorbent regeneration by fast heating and cooling, i.e., rapid thermal-swing adsorption (TSA) operation. The adsorbent regeneration turnaround time has a direct and significant impact on the size and cost of the adsorption equipment. The mini-sized straight heat exchange channels are made to minimize the pressure drop of the thermal fluid and liquid pump power consumption to circulate a large volume flow rate between the heating and cooling. The simple structure of the AHX reactor renders a low-cost additive manufacturing process using inexpensive raw materials for the capture process involving relatively low temperature (<200°C) and low pressures (<2 bar). In Phase I, a few tasks are completed to address the scientific and technical risks with this new reactor technology, including 1) adsorbent materials and process conditions screened on a laboratory AHX test cell to identify a viable adsorbent of both high working capacity and fast kinetics under practically-relevant conditions; 2) fabrication feasibility of the AHX module demonstrated by building and testing a module prototype of 0.80 m2 active adsorption/heat exchange area for adsorption of 100 NL/min gas rate; and 3) preliminary designs to implement the AHX reactor to large-scale commercial plants conceived and used for technoeconomic analysis. No commercial adsorbent materials were found that can provide selective CO2 adsorption in humid gas. A proprietary sorbent research sample was acquired and tested on the laboratory AHX test cell under various conditions. It is found that this sorbent material is highly selective toward adsorption of CO2 molecules over H2O and air and enables CO2 capture over a broad range of concentration from air (0.04 %) to flue gas (15%). Rapid TSA and VPSA operation are demonstrated by many cycles of testing. The sorbent can be regenerated by heating to above 90°C without using any steam. No apparent performance degradation was observed. The sorbent loaded in the AHX cell shows exceptionally good performance compared to the literature reports so far. Potential risks to manufacture a practical AHX reactor are assessed by building an AHX prototype. First, the AHX cassette is designed and fabricated by i) forming mini-straight heat exchange channels between two dense stainless-steel sheets and ii) encapsulating the adsorbent powder on an exterior surface of the dense metal sheet by use of MoleculeWorks 40µm-thin, porous nickel membrane sheet. Each AHX cassette contains two 19 cm x 19 cm active adsorption/heat exchange surfaces. A flat and uniform layer of the sorbent powder was packaged in the AHX cassette. No powder leakage occurred. 12 of the AHX cassettes were assembled into a working module with attachment of gas and liquid (thermal fluid) manifolds. The AHX module prototype of 0.80 m2 total working area is demonstrated for CO2 capture from humid CO2/air gas at low pressure drops. The gas pressure drop across the module is 60 Pa at a space velocity of 12,000 1/h, which corresponds to a feed rate of 90 NL/min. The CO2 capturing productivity obtained with the module prototype is comparable to or higher than the laboratory test cell. It appears promising to develop additive manufacturing processes for fabrication of the AHX modules at low costs. For scale-up to natural gas fired power plants, the AHX module may be installed either in a fixed vessel or in a mobile cart. In the mobile cart configuration, the module unit can be transported periodically between the adsorption and regeneration chambers that are operated under respective adsorption and regeneration process conditions. The adsorption and regeneration chambers are fixed structures. The process economics analysis indicates that the AHX module is a major cost factor, and thermal energy consumption for regeneration is a second major cost factor. At the assumed unit cost level, the AHX module cost can be further decreased by increasing CO2 capturing productivity and shortening regeneration time. Since no steam is used for regeneration of the present adsorption process, thermal energy cost can be further reduced if low grade waste heat is available to heat up the thermal fluid. The technology has potential for significant reduction to CO2 capture cost.
- Research Organization:
- Molecule Works Inc.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- SC0020790
- OSTI ID:
- 1856072
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- MWI20220322; MWI report20220322
- Country of Publication:
- United States
- Language:
- English
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