CSTRs with cooling coils

Figure 6-15 Sketches of a CSTR with cooling either through a jacket (left) or a cooling coil (right). A separate energy balance must be solved for the coolant temperature if the temperature of the cooling fluid Tq is not constant and equal to the coolant feed temperature Tio-...

CSTR with cooling by external jacket and/or cooling coil. 

A schematic drawing is shown in Fig. 14. Two "prepoly CSTR s in parallel, each with a 1400-kg. holduo, fed a total of 44 kg./hr. of syrup at 80 C and 33-35% conversion to a second-stage LFR. The CSTR s were cooled via jackets and internal cooling coils, and slowly agitated with gate-type agitators. 

Example 2.6. The CSTR system of Example 2.3 will be considered again, this time with a cooling coil inside the tank that can remove the exothermic heat of reaction 2 (Btu/lb. mol of A reacted or cal/g mol of A reacted). We use the normal convention that 2 is negative for an exothermic reaction and positive for an endothermic reaction. The rate of heat generation (energy per time) due to reaction is the rate of consumption of A times 2. 

The parameters a, b, and m depend on the type of agitator and the presence or absence of baffles. For example, the values of these parameters for a flat-blade agitator with baffles are a = 0.74, b =, and m = 0.14. A similar equation can be used for a CSTR with an internal cooling coil (see footnote 1). 

Figure 3.24 gives the response to a 20% increase in feed flowrate. Figure 3.25 gives a direct comparison of the coil-cooled CSTR and the jacket-cooled CSTR with a jacket thickness of 0.025 m. Even with this very small jacket holdup, the coil-cooled system has tighter temperature control. 

Instability typically arises from the interaction of two phenomena with different dependences on a reaction parameter In a nonisothermal reaction, the dependence on temperature is exponential for heat generation by the reaction, but linear for heat loss to the cooling coil or environment in a reaction with chain branching, the dependence on radical population is exponential for acceleration by branching, but quadratic for chain termination. A reaction is unstable if acceleration outruns retardation. This can cause an explosion or, in a CSTR, lead to multiple steady states. Feinberg s network theory can help to assess whether an isothermal reaction admits multiple steady states in a CSTR. 

Nonisothermal operation of a liquid-phase CSTR with reversible exothermic nth-order chemical kinetics is the focus of this chapter. The reactor is well insulated from the surroundings, except for heat exchange across the cooling coil. The reaction scheme is... 

The schematic diagram of the CSTR is shown in Fig. 2.6. The inlet stream consists of pure component A with molar concentration, A cooling coil is used to maintain the reaction mixture at the desired operating temperature by removing heat that is released in the exothermic reaction. Our initial CSTR model development is based on three assumptions ... 

You have recently been put in charge of a facility that manufactures R. The facility operates 7890 h/year. The reaction is carried out in a single, ideal CSTR with a volume of 1000 gal. The reactor operates at 550 °F. The feed is a stoichiometric mixture of A and B at 100 °E Heat is removed through a cooling coil in the reactor. The fractional conversion of A, jca, in the reactor effluent is 0.95. 

In most exothermic processes carried out in a stirred tank reactor the bulk of the heat of reaction is carried away by external cooling, either via the wall of the reactor, or by means of an internal or extenal heat exchanger. Internal heat exchangers are usually vertical tube bundles or coils (spirals), mounted coaxially with the impeller shaft. When external heat exchangers are used, the reactor contents are pumped through it and back into the reactor. We consider here the CSTR the semi-batch reactor is treated in section 8.4.4. The steady-state heat balance for a first order reactor in a cooled CSTR can be written as follows ... 

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