Heat-integrated wall reactor

T. loannides and X. E. Verykios, Development of a novel heat-integrated wall reactor for the partial oxidation of methane to synthesis gas, Catal. Today, 1998, 46, 71-81. 

The heat-integrated wall reactor (HIWR) was first presented by loannides and Verykios. It consists of two tubular reactors, one centered inside the other. The walls of the inner tube are covered with catalyst and gas travels from the end of the inner combustion chamber to the outer reforming chamber, in a counter-current manner. Heat produced in the inner tube will be transported through the wall and provide heat to the reforming reaction. Experimental studies using a RI1/AI2O3 catalyst showed an increased conversion (e.g. 87% vs 56%) and smoother temperature... 

The Si is deposited by automated CVD with HF heating in a horizontal cold wall reactor chamber under atmospheric pressure for easy implementation in industry. For lower gas consumption and to stimulate the chemical reactions the coating process can be at low pressure, where the chemical reactivity is usually higher. Up-scaling from a laboratory scale or bench scale unit to industrial application is based on a totally computer-controUed laboratory process. Total automation eases transferability and integration with other industrial processes. 

Heat can be removed from or added to a reactor through heat exchange across the walls. For an integral reactor we write the rate of heat removal from the reactor Q as... 

The first study of CVD tungsten for application to integrated circuits was done by Shaw and Amick,18 working with the hexafluoride. They carried out their depositions in an atmospheric-pressure horizontal cold-wall tube reactor (see Figure 17, Chapter 1), where the susceptor that held the wafers was inductively heated. 

Continuously operated, fixed bed reactors are frequently used for kinetic measurements. Here the reactor is usually a cylindrical tube filled with catalyst particles. Feed of a known composition passes though the catalyst bed at a measured, constant flow rate. The temperature of the reactor wall is usually kept constant to facilitate an isothermal reactor operation. The main advantage of this reactor type is the wealth of experience with their operation and description. If heat and mass transfer resistances cannot be eliminated, they can usually be evaluated more accurately for packed bed reactors than for other reactor types. The reactor may be operated either at very low conversions as a differential reactor or at higher conversions as an integral reactor. 

Theologos and Markatos (1992) used the PHOENICS program to model the flow and heat transfer in fluidized catalytic cracking (FCC) riser-type reactors. They did not account for collisional particle-particle and particle-wall interactions and therefore it seems unlikely that this type of simulation will produce the correct flow structure in the riser reactor. Nevertheless it is one of the first attempts to integrate multiphase hydrodynamics and heat transfer. 

The influence of heat losses through the reactor wall have been studied [5,23]. Radial temperature gradients inside the monolith material can often be neglected, because the operation is usually adiabatic. This means that modeling of one single channel is adequate. Any nonuniform flow distribution may be incorporated into a reactor model by integration of the single channel performance over the whole cross section of the reactor. 

Mathematical models of cross-flow air-dryers and regenerators differ from those of the cross-flow reactors, since one must consider the fact that the sides of the channel walls are partly made of a reactive solid substance that is capable of exchanging a species with the process streams. These mass and heat balances result in nonlinear Volterra-type integral equations, which have been studied by Roy and Gidaspow [37,70]. 

Heat is lost from the surface by conduction through the susceptor and mount, by forced convection of gas over the substrate, and by radiation to the reactor walls, provided the temperature of the substrate is sufficiently high. Endothermic chemical reactions also result in heat loss from the film. The substrate temperature is monitored with a thermocouple or an optical pyrometer and controlled using a traditional proportional-integral-derivative (PID) controller and power source. 

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