Heat PFTR reactors

For shdl and tube heat exchange Numerous related topics including evaporation Section 4.1, distillation. Section 4.2, crystallization Section 4.6, freeze concentration Section 4.3, melt crystallization. Section 4.4, PFTR reactors Sections 6.5-6.12. Approach temperature 5 to 8°C use 0.4 THTU/pass design so that the total pressure drop on the liquid side is about 70 kPa. Allow 4 velocity heads pressure drop for each pass in a multipass system. Put inside the tubes the more corrosive, higher pressure, dirtier, hotter and more viscous fluids. Recommended liquid velocities 1 to 1.5 m/s with maximum velocity increasing as more exotic alloys used. Use triangular pitch for all fixed tube sheet and for steam condensing on the shell side. Try U = 0.5 kW/m °C for water/liquid U = 0.3 kW/m °C for hydrocarbon/hydrocarbon U = 0.03 kW/m °C for gas/ liquid and 0.03 kW/m °C for gas/gas. 

Note, however, that the significance of heat removal or addition (Q positive or negative) is quite different with the batch reactor, requiring a heat removal that varies in time, the CSTR requiring a constant heat removal rate, and the PFTR requiring a heat removal rate that varies with position z in the reactor. These are sketched in Figure 5-3. 

Note that the batch reactor requires programming Q(t), and the PFTR requires either a very high U A, [to remain at T (z)] or programming QU). The CSTR operates with a fixed Q because T is uniform throughout the reactor for given conditions, and for steady-state operation Q is independent of time. Therefore, the CSTR is usually much simpler to design for stable heat removal. This is another attractive feature of the CSTR It is much easier to... 

We stiU must use a PFTR in many chemical processes, and we must then determine how to program the cooling or heating to attain a temperature profile in the reactor close to that desired. The subject of this chapter is the proper temperature management to attain desired operation of a PFTR. In the next chapter the nonisothermal CSTR will be considered specifically. 

Find Q t) or Q(z) necessary to maintain a 5 liter batch reactor or PFTR isothermal reactor at 300 K for the reaction A B, r = kC/ in aqueous solution with k = 2.0min , Cao = 2 mole/liter, A Hk = -30 kcal/lliole. What is the average rate of heat removal for 95% conversion ... 

Flow pattern Next one decides whether a batch or continuous reactor is suitable and, if flow, whether a mixed of unmixed reactor is preferred. Initially one may do calculations for PFTR and CSTR to bracket all flow patterns. This is the subject of Chapters 3 and 4. The choice of catalyst and heat removal method will be very important in deciding the best flow pattern. 

Design a PFTR solids reactor in which heat from the walls requires a finite time to heat the solid particles to the reaction temperature and compare its operation with the isothermal situation. 

Flow systems in use may be classified as heated laminar tubes, or plug flow tube reactors, (PFTR) and burners, or heated turbulent flow reactors and well-stirred reactors, or continuous stirred-tank reactors, (CSTR). 

Phases liquid, gas-liquid bio solids. Liquid use for residence time >4 h for systems where PFTR conditions are desired. Heat of reaction highly exothermic reaction rate, slow. Capacity 0.2 to 100 kg/s. Gas-liquid bio solids variety of reactor configurations to remove soluble BODj from waste-water aerated lagoon. Pure-oxygen backmix-activated sludge, CSTR in series 85 to 95% removal, compact unit for use where space is limited. 

The equality in reactor behaviour of the stationary PFTR and unsteady BR, which was explained in Section 4.1.5, allows the direct formulation of the heat balance for the cooled BR. If the length of the PFTR is substituted by the characteristic reaction time for the batch process, and if the Stanton munber formulation is based on its general definition regarding the overall heat removal mechanism, the unsteady heat balance of the cooled BR is obtained. 

More complex is the plug-flow tubular reactor (PFR or PFTR), in which the composition of the fluid, flowing as a plug, gradually changes down the length of the reactor, with no composition or temperature gradients in the radial direction. Furthermore, mass- and heat-transfer... 

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