* Corresponding author. Tel.: 00-212-4-43-4649; fax: 00-212-4-43- 6769. E-mail address: belghit@ucam.ac.ma (A. Belghit) Chemical Engineering Science 55 (2000) 3967}3978 Heat and mass transfer in a high temperature packed moving bed subject to an external radiative source Abdelhamid Belghit*, Michel Daguenet, Agami Reddy De & partement de Physique, Faculte & des Sciences Semlalia, Bd. Prince Moulay Abdellah-BP: 2390-40 000-Marrakesh, Morocco Laboratoire de Thermodynamique et Energe & tique, Universite & de Perpignan, Avenue de Villeneuve, 66860 Perpignan Cedex, France Civil and Architectural Engineering, Drexel University, 32nd and Chestnut Streets, Philadelphia, PA 19104, USA Received 24 September 1998; received in revised form 28 July 1999; accepted 17 November 1999 Abstract A numerical model of a moving chemical bed reactor for gasifying coal using concentrated solar radiation is proposed. It permits the determination of the temperature pro"les for both the gas and the solid phases, the velocity and the pressure drop pro"les as a function of control parameters such as incident radiative #ux, gas #ow rate and particle size. The results of this model are in a satisfactory agreement with the experiment ones.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Moving bed; Heat-mass transfer; Solar radiation; Gasi"cation; Coal 1. Introduction Various technical approaches are used to convert coal to gaseous and liquid fuels. The energy necessary to drive endothermic coal gasi"cation reactions can be supplied by partial coal combustion (part of the coal is burned with oxygen to provide the energy for process-heat losses as well as that necessary to drive the endothermic gasi"- cation reaction), by preheating the reactant gas (carbon dioxide, steam), or by an external radiative source. These energy requirements can be met using concentrated solar energy (Aiman, Thorness & Gregg, 1981; Taylor, Berjoan & Coutures, 1983; Belghit, Royere, Berjoan & Daguenet, 1985; Belghit, 1986) or by high temperature nuclear reac- tors (HTR) (Juntgen & Van Heek, 1975; El Issami & Belghit, 1992). The gasi"cation of coal is a very important economical operation. It is performed at relatively high temperatures, between 7003C and 13003C. The produced gas, consisting primarily of CO and H  , can be used as a feedstock for many chemical processes. It can be converted to me- thane, methanol, gasoline, and polymer monomers, and it can serve as a source of H  for coal liquifaction, hydrogenation of oil shales, and ammonia production (Gregg, Taylor, Campbell, Taylor & Cotton, 1979). Such a system would have several advantages over a conventional oxygen-driven gasi"er (Gregg, Aiman, Otsuki & Thorness, 1978):  Pure oxygen, which is expensive, is not necessary.  Higher yields of gas per ton of coal are achieved because no fuel is burned to provide process heat, and the produced gas contains both the energy of the fuel and the added solar energy.  The solar energy is chemically stored in the form of a transportable fuel. A moving bed reactor, for gasifying coconut charcoal (which is nearly pure carbon: 1.5$0.5 wt% H with a low ash content of 1.2 wt%) with CO  was experimentally studied (Taylor et al., 1983; Belghit et al., 1985; Belghit, 1986). Experiments were carried out on a vertical solar furnace located at the Laboratory of CNRS in Odeillo, France. Fig. 1 shows a schematic diagram of the moving bed gasi"er. It has a window, an insulated central body containing the coconut charcoal bed, and a mechanism to feed this material into the focus at the top of the bed which is counter-current to the gas #ow. The #ange directly below the window was drilled in four places for CO  injection. The fuel was fed with a hand operated plunger. The tests were performed with incident solar intensities   between 300 and 1000 W, temperatures ¹  from 900 0009-2509/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 0 0 9 - 2 5 0 9 ( 9 9 ) 0 0 5 7 5 - 8