Energy Transfer by Use of Trim Heat Exchangers

Consider the system shown in Fig. 7-4 in which a trim heat exchanger is used to cool the stream B2 to the temperature T0 before it is returned to the reboiled absorber. This example was formulated and solved as Example 4-11. Specification of LM, D2, Wl9 and W2 fixes Vv Thus, in the capital 0 method there are four g functions as shown in Chap. 4. 

In the application of the IN Newton-Raphson method, Vt is required as specified and the temperature T0 of B2 entering column 1 or the trim heat exchanger duty Qc is taken as the new independent variable. In this case the 2N -f 1 variables x and the functions f are as follows 

The remaining functions /i,/2, consist of the enthalpy balance functions see Chap. 4. 

The proposed calculational procedure consists of first making one trial calculation on the reboiled absorber by use of the [2N + 1] formulation of the Newton-Raphson method and then one trial on the distillation column by use of the 0 method. Then the capital 0 method is applied to the system in order to place it in agreement with the specified values of the terminal flow rates Wly W2, and D2. 

After a solution to the problem has been found, the duty QCi of the trim heat exchanger is found by means of an energy balance enclosing it. 

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