System for regenerative thermally reversed adsorption

Abstract

A system for the adsorption of a substance from a warm fluid containing the same. An initially relatively cool bed of adsorbent is fed with a relatively warm fluid containing an adsorbate. A sharp thermal wave is generated as the warm fluid enters the cool bed. A high pulse in concentration of the adsorbate develops ahead of the thermal front if the bed properties are appropriate. The concentration of adsorbate immediately ahead of the wave is related to adsorbate concentration in the inlet stream, the shape of the adsorption isotherms, the effective heat capacities and the original and final bed temperatures, bed design, thermal conductivities and dispersivities. There is a sharp drop in concentration at the forward edge of the concentration pulse. This pulse in adsorbate concentration is harvested by aspirating fluid from the bed at the time the pulse arrives at the end of the bed. For some purposes a total cycle of discharge and recharge of the bed is desirable. Following the discharge of the high concentration pulse from the bed, the bed is seen to be filled with fluid at the inlet concentration and temperature in approximate equilibrium with the solid. When the flow of fluid, free of the removed adsorbate, is passed through the bed at the cool temperature, a concentration wave will precede the thermal wave toward the original bed inlet. All the fluid that leaves the bed before the concentration wave reaches the inlet is desirably recycled. Provisions for the mass flow imbalance are proposed. The general requirements for this recycling process are described. The system is useful, for example, for concentrating urea in an artificial kidney, for concentrating NO in engines and power plants for oxidation to NO.sub.2 and subsequent capture, for concentrating SO.sub.2 in exhaust gases of systems using sulfur-bearing fuels, for concentrating organic impurities for removal from water, for concentrating alcohol, and the like.