Bed side heat transfer

Equation (19-64) is similar to generic PFR Eqs. (19-17) and (19-18). The overall heat-transfer coefficient U is based on the bed side heat-transfer area AR and includes three terms heat transfer on the bed side b, thermal conduction in the vessel wall w. and heat transfer on the coolant side c ... 

The two-dimensional model can be used to develop an equivalent one-dimensional model with a bed-side heat-transfer coefficient defined as [see, e.g., Froment, Chem. Eng. Sci. 7 29 (1962)]... 

Here, hi are the heat-transfer coefficients in the bed side and the coolant side, k , is the wall thermal conductivity, and A, are the heat-transfer areas. The coolant side heat-transfer coefficient can be obtained from general heat-transfer correlations in tubes (see any heat-transfer text and the relevant sections in this Handbook). For the process-side heat-transfer coefficient, there is a large body of literature with a variety of correlations. There is no clear advantage of one correlation over another, as these depend on the particle and fluid properties, temperature range, etc. e.g., see the correlation of Leva, Chem. Eng. 56 115 (1949) ... 

Effective thermal conductivity of catalyst bed Overall heat transfer coefficient of the reactor shell Overall heat transfer coefficient of the membrane tube Gas/wall convective heat transport coefficient on the catalyst side Gas/membrane convective heat transfer coefficient on the catalyst side... 

Figure 10-158A. Styles of Mueller Temp-Plate heat transfer plates. (1) Double-embossed surface, inflated both sides. Used in immersion applications, using both sides of the heat transfer plate. (2) Single-embossed surface, inflated one side, used for interior tank walls, conveyor beds. (3) Dimpled surface (one side), available MIG plugwelded or resistance spot welded. Used for interior tank walls, conveyor belts. (Used by permission Bui. TP-108-9, 1994. Paul Mueller Company.)...

The last term on the left-hand side of eq. (3.301) corresponds to the heat transfer to the external fixed-bed wall. The overall heat transfer resistance is the sum of the internal, external, and wall resistances. In an adiabatic operation, the overall heat transfer coefficient is zero so the corresponding term in the energy balance expression drops out, while in an isothermal operation this coefficient is infinite, so that 7 f 7 s 7W. 

Fixed-bed reactors resemble multitube heat exchangers, with the catalyst packed in vertical tubes held in a tubesheet at top and bottom. Reaction heat can be removed by generating steam on the shell side of the reactor or by some other heat-transfer fluid. However, temperature control is more difficult in a fixed-bed than in a fluulized-bed reactor because localized hot spots tend to develop in the tubes. 

Industrial steam reformers are usually fixed-bed reactors. Their performance is strongly affected by the heat transfer from the furnace to the catalyst tubes. We will model both top-fired and side-fired configurations. 

Absorption of hypochlorous acid into water, a liquid-side mass transfer-limited process, showed HTU values as low as 4 cm, with a strong dependence on liquid-flow rate. Heat of absorption removal was identified as a potential issue with absorption in rotating beds (9). 

The higher heat transfer coefficients experienced by Hickman led to the concept of placing a peripheral reboiler and core condenser on either side of a rotating packed bed (50). This concept would be useful for distillation applications that need reflux and boilup. The internal exchangers as part of the rotor would decrease the required heat transfer surface area but would involve additional design and fabrication complexity. 

VOC emissions from printing and chemical plants are oxidized in reverse flow reactors that couple reaction with regenerative heat transfer. The concept here is to maintain a catalyst zone in the center of a packed bed with inert heat-transfer packing on either side. 

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