Packed reactor tubes, heat

Heat Transfer in Packed Reactor Tubes Suitable for Selective Oxidation... 

Extensive experimental determinations of overall heat transfer coefficients over packed reactor tubes suitable for selective oxidation are presented. The scope of the experiments covers the effects of tube diameter, coolant temperature, air mass velocity, packing size, shape and thermal conductivity. Various predictive models of heat transfer in packed beds are tested with the data. The best results (to within 10%) are obtained from a recently developed two-phase continuum model, incorporating combined conduction, convection and radiation, the latter being found to be significant under commercial operating conditions. 

Wellauer T, Cresswell D L, Newson E J., "Heat transfer in packed reactor tubes suitable for selective oxidation", ACS Symp. Series, 196, 527 (1982). 

Temperature programmed reduction (TPR) experiments. TPRs were performed for each material using a quartz reactor tube (4 mm i d ), in which a 100 mg sample was mounted on loosely packed quartz wool. Samples were predried overnight at 120 °C. The sample was heated at 5 °C /min up to 700 °C under 20 mL/min flow of a 2 1 mixture of H2 Ar. 

When we want to look at the connection between the flow behavior and the amount of heat that is transferred into the fixed bed, the 3D temperature field is not the ideal tool. We can look at a contour map of the heat flux through the wall of the reactor tube. Fig. 19 actually displays a contour map of the global wall heat transfer coefficient, h0, which is defined by qw — h0(Tw-T0) where T0 is a global reference temperature. So, for constant wall temperature, qw and h0 are proportional, and their contour maps are similar. The map in Fig. 19 shows the local heat transfer coefficient at the tube wall and displays a level of detail that would be hard to obtain from experiment. The features found in the map are the result of the flow features in the bed and the packing structure of the particles. 

The pyrolytic reforming reactor was a packed bed in a quartz tube reactor. Quartz was selected to reduce the effect of the reactor construction material on the hydrocarbon decomposition rate. ° The reactor was packed with 5.0 0.1 g of AC (Darco KB-B) or CB (BP2000) carbon-based catalyst. The reactor was heated electrically and operated at 850—950 °C, and the reactants had a residence time of 20—50 s, depending on the fuel. The reactor was tested with propane, natural gas, and gasoline as the fuels. Experiments showed that a flow of 80% hydrogen, with the remainder being methane, was produced for over 180 min of continuous operation.The carbon produced was fine particles that could be blown out... 

The gases left the reactor at the bottom and flew to a 4-way valve. The tubes after the reactor were heated with heating jackets (60-80°C). The products were either analysed on-line or collected in a condenser for off-line analysis (Varian 3400 gas chromatograph with a packed column, 10% OV-17 on chromosorb W detector TCD). 

The final tubular reactor system considered is one in which a single cooled reactor is used. Figure 5.19 shows the flowsheet. The cooled reactor, which is assumed to be simply a shell-and-tube heat exchanger, has catalyst packed inside the parallel tubes. Steam is generated on the shell side, serving as a coolant. The liquid level in the shell is controlled by bringing in BFW to keep the tubes covered. The steam-side temperature is constant at all axial locations in the reactor because the BFW is vaporized at a constant temperature. The temperature of the steam is assumed to be equal to the reactor inlet temperature, and the temperature of the BFW is assumed to be equal to the steam temperature. 

Steam reforming reactors have the supported nickel catalyst packed in tubes and the endothermic heat of reaction supplied from a... 

Although two reactors are shown in Figure 1, they were not used simultaneously. The reactor shown in the center was the fixed bed reactor which is of primary interest in this contribution. It consisted of a 12.7 mm diameter X 250 mm long steel tube packed with 40/50 mesh catalyst (0.3 mm average particle diameter). The reactor was heated by a nichrome wire coil and was well insulated. The coil spacing was adjusted and was packed in insulation with the intent of making the reactor crudely adiabatic. A variac controlled heater on the reactor inlet and a thermocouple sensor kept the feed to the reactor at the nominal reaction (or feed inlet) temperature of 400°C. The tube of the fixed-bed, reactor was fitted with 12 thermocouples to record the axial temperature profile in the bed (Figure 1). 

JM proprietary methanol synthesis catalyst is packed in the shell side of the reactor. Reaction heat is recovered and used to efficiently generate steam in the tube side. Reactor effluent gas is cooled to condense the crude methanol. The crude methanol is separated in a separator (10). The unreacted gas is circulated for further conversion. A purge is taken from the recycling gas used as fuels in the reformer (3). 

FIG. 23-2 Heat exchange In packed reactors, (a) Adiabatic downflow, (b) Adiabatic radial flow, low AP. (c) Built-in interbed exchanger, (d) Shell and tube, (e) Interbed cold-shot injection, j) External interbed exchanger, (g) Autothermal shell, outside influent/effluent heat exchanger. Qi) Multibed adiabatic reactors with interstage heaters, (i) Platinum catalyst, fixed bed reformer for 5,000 BPSD charge rate reactors 1 and 2 are 5,5 by 9.5 ft and reactor 3 is 6.5 by 12.0 ft temperatures 502 433, 502 => 471, 502 496°C, To convert ft to m, multiply by 0.3048 BPSD to mVh, multiply by 0.00662. 

The above discussion primarily applies to membrane reactors where heat needs to be supplied to or removed from the catalytic zone which consists of a packed bed of catalysts in the tube core or a catalytic membrane itself. Transfer of the heat of reactions can be easier when the catalytic zone lies outside the membrane tubes. This is the case when, for example, a packed bed of catalysts is placed on the shell side of a shcll-and-tubc type membrane reactor. In a fluidized-bcd membrane reactor [Adris et al., 1991 Aldris et al., 1994], the catalytic zone is in the emulsion phase (solids-containing) of the... 

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