Factors in Reactor Design for Carbon Dioxide Capture with Solid, Regenerable Sorbents

摘要

Fossil-fuel burning power plants, which produce a substantial amount of electric power within the United States, are point sources that can emit significant quantities of carbon dioxide (CO_2). In a carbon sequestration scenario, the CO_2 must first be captured from the point source, or flue gas, and then be permanently stored. Since the capture/separation step dominates the cost of sequestration, various capture/separation technologies are being investigated, and regenerable, solid sorbents are the basis for one promising technique for capturing CO_2 from flue gas. The solid sorbent must be able to absorb the CO_2 in the first step and then be regenerated by releasing the CO_2 in the second step. Due to the low operating pressure of a conventional pulverized coal-fired combustor and its subsequent low partial pressure of CO_2, it is envisioned that temperature swing absorption is applicable to the sorbent capture technology. Various CO_2 capture sorbents are being examined in this research area, for example physical adsorbents as well as chemical absorbents. However, with respect to process development, various reactor configurations are presently being considered. The reactor designs range from stationary beds of sorbent to those systems where the sorbent is transported between the absorber and regenerator. Emphasis is placed on design implications of employing a regenerable solid sorbent system. Key sorbent parameters required for the sorbents have been identified, including the heat of adsorption, heat capacity of the solid, delta CO_2 loading between the absorption and regeneration steps, and any role co-sorption of competitive gases, such as moisture, may play. Other sorbent properties, such as the effect of acid gases within the flue gas or the attrition of the sorbent, must be considered in the reactor design. These factors all impact the reactor design for a particular type of sorbent. For a generic sorbent, reactor designs have been formulated, including a stationary, isothermal reactor, a fluidized bed, and a moving bed. Through calculations, benefits and disadvantages of the designs have been outlined. The implication of the sorbent properties (and thus desired experimental information) on sorbent reactor design are described, and recommendations for operation of these types of capture systems are discussed.