Regeneration of activated carbons used in waste‐water treatment by a moving‐bed regenerator

Abstract

A method was developed for calculating the distributions of weight loss and temperature of spent activated carbon in a moving-bed regenerator in which the solid flow was regarded as being plug flow. A kinetic model developed earlier, which was based on regeneration consisting of many first-order reactions each with different frequency factors and different activation energies, was successfully applied to a design method for the regenerator. The flow pattern of the solid particles and heat transfer characteristics in a small moving bed were clarified experimentally, and the information obtained was used to calculate the distributions of weight loss of the spent carbon and temperature in the moving-bed regenerator by means of the design method. The calculated results were in fairly good agreement with the experimental data obtained in a small moving-bed regenerator. The adsorption capacity of the regenerated carbon was comparable to or greater than that of the virgin carbon. Activated carbon has been used in many adsorption processes for removal of toxic substances, recovery of valuable substances, separation of mixtures, and so on. Recently, the use of activated carbon in advanced waste-water treatment has attracted attention. For this treatment to be economical, the spent activated carbon must be repeatedly regenerated and reused. KENJI HASHIMOTOThe granular activated carbon used in waste-water treatment can be regenerated thermally in a steam atmosphere. The regenerator used is usually a moving-bed reactor, which provides uniform regeneration and minimizes the loss due to abrasion. The spent carbon fed into the regenerator is heated from room temperature to almost l,OOO°C. During the heating process the spent carbon i s regenerated through such reactions as thermal desorption and pyrolysis of the adsorbates, and gasification of the carbonized adsorbates and the activated carbon itself. To design such a moving-bed regenerator, the kinetics of the thermal regeneration reactions and the heat transfer characteristics and flow pattern of the solid particles in the regenerator must be investigated. This paper aims to present a rational design method for a moving-bed regenerator in which solid particles descend in a plug flow, and to examine whether thermal regeneration in the moving bed effectively restores the adsorption capacity of the activated carbon. CONCLUSIONS AND SIGNIFICANCEA method was developed for calculating the distributions of temperature and weight loss of spent carbon in a moving-bed regenerator where the solid flow was assumed to be plug flow. The kinetics of thermal regeneration was represented by a distribution curve of the activation energy for pyrolysis and the rate constant for gasification obtained by measurement of thermogravimetric curves. The effective thermal conductivity and the wall heat transfer coefficient were measured for the same moving bed. The distributions of temperature and weight loss in the moving-bed regenerator were calculated by applying the method developed to the data obta...

Modeling of the simulated countercurrent moving-bed chromatographic reactor used for the oxidative coupling of methane

“…* Continuous iirteriititteitt iitovirtg bed (Hashimoto et al 1983a(Hashimoto et al -b, 1987Kishihara et al 1989;Storti et aI. 1988;Kubota et al 1989;Svedberg 1976;Maki et al 1987;Ruthven and Ching 1989) Discontinuous moving bed (McGary and Wankat 1983) True corzntercurrertf (Hashimoto et al 1983b(Hashimoto et al , 1985Ruthven 1983Ruthven , 1984Ruthven and Ching 1989;Ching et al 1991;Rhee et ai. 2971Rhee et ai.…”

Modeling of the simulated countercurrent moving-bed chromatographic reactor used for the oxidative coupling of methane

“…Non-coittiiiuoizs moving feed Semi-contiitztous movingfeed (Barker et al 1983;Hidajat et al 1986b) Coittinuous SCCS (Ernst and Hsu 1989;Storti et al 1989;Ruthven 1985, Ruthven 1984;Ruthven and Ching 1989;Hidajat et al 1986a) True counfercwrent (Storti et al 1989;Barker 1971) Differential models: * Continuous iirteriititteitt iitovirtg bed (Hashimoto et al 1983a(Hashimoto et al -b, 1987Kishihara et al 1989;Storti et aI. 1988;Kubota et al 1989;Svedberg 1976;Maki et al 1987;Ruthven and Ching 1989) Discontinuous moving bed (McGary and Wankat 1983) True corzntercurrertf (Hashimoto et al 1983b(Hashimoto et al , 1985Ruthven 1983Ruthven , 1984Ruthven and Ching 1989;Ching et al 1991;Rhee et ai. 2971Rhee et ai.…”

Removal of Some Common Textile Dyes from Aqueous Solution Using Fly Ash

“…The adsorption process perhaps provides an attractive alternative for the treatment of water contaminated with colorants, especially if the adsorbent is inexpensive and does not require any pretreatment step before its application. Although most commonly used adsorption agents in industry are activated carbon, , their high operating costs and regeneration of the spent carbon hamper their large-scale application . Other materials which include peat, chitin, silica, hardwood sawdust, , bagasse pitch, paddy straw, rice husk, slag, acid-treated spent bleaching earth, palm fruit bunch, barley straw, bone char, and natural zeolites have also been examined, but their level of success is not much greater.…”