Condenser duty

Latent heat of vaporization decreases i.e., reboiler and condenser duties become lower. 

The dominant heating and cooling duties associated with a distillation column are the reboiler and condenser duties. In general, however, there will be other duties associated with heating and cooling of feed and product streams. These sensible heat duties usually will be small in comparison with the latent heat changes in reboilers and condensers. 

Let us now consider a few examples for the use of this simple representation. A grand composite curve is shown in Fig. 14.2. The distillation column reboiler and condenser duties are shown separately and are matched against it. Neither of the distillation columns in Fig. 14.2 fits. The column in Fig. 14.2a is clearly across the pinch. The distillation column in Fig. 14.26 does not fit, despite the fact that both reboiler and condenser temperatures are above the pinch. Strictly speaking, it is not appropriately placed, and yet some energy can be saved. By contrast, the distillation shown in Fig. 14.3a fits. The reboiler duty can be supplied by the hot utility. The condenser duty must be integrated with the rest of the process. Another example is shown in Fig. 14.36. This distillation also fits. The reboiler duty must be supplied by integration with the process. Part of the condenser duty must be integrated, but the remainder of the condenser duty can be rejected to the cold utility. 

Application of these equations gives the results in Table 13-12. A set of T is calculated from the normahzed by bubble-point calculations. Corresponding values of are obtained from y = K x. Once newA. andT are available, new values of Vn are calculated from energy balances by using data from Maxwell (Data Book on Hydiocaihons, Van Nostrand, Princeton, N.J., 1950). First, an estimate of condenser duty is computed from an energy balance around the condenser. 

Example 4 Calculation of the BP Method Use the BP method with the SRK eqiiation-of-state for K values and enthalpy departures to compute stage temperatures, interstage vapor and hqiiid flow rates and compositions, and rehoiler and condenser duties for the light-hydrocarhon distdlation-coliimn specifications shown in Fig. 13-51 with feed at 260 psia. The specifications are selected to obtain three products, a vapor distillate rich in Cri and C3, a vapor side-stream rich in n-C4, and a bottoms rich in n-C and n-Cg. 

Figure 2. Condenser duty for single-stage propane refrigeration system.

Figure 10. Condenser duty for two-stage propylene refrigeration system.

Figure 18. Condenser duty for three-stage ethane refrigeration system.

The heat duty of amine reboilers varies with the system design. The higher the reboiler duty, the higher the overhead condenser duty, the higher the reflux ratio, and thus the lower the number of trays required. The lower the reboiler duty, the lower the reflux ratio will be and the more trays the tower must have. 

L/D = reflux ratio Pf = packing factor Qc = condenser duty, Btu/hr Or = reboiler duty, Btu/hr Vr = reboiler vapor rate, Ib/hr Vs = superficial vapor velocity, ft/sec Pi = liquid density, Ib/ft ... 

Determine the approximate horsepower and condenser duty for a single-stage propane refrigeration system (see flow diagram of Figure 11-43). 

The total horsepower and condenser duty are the sums for each stage of the system. Then,... 

Figure 11-36. Condenser duty for single-stage propylene refrigeration system. (Excerpted by special permission Mehra, Y. R. Chemical Engineering, Jan. 15, 1979. McGraw-Hill, Inc., New York. All rights reserved.)...

For those condensing duties where permissible pressure loss is less than 0.07kpf/cm there is no doubt but that the tubular unit is most efficient. Under such pressure-drop conditions only a portion of the length of a plate heat exchanger plate would be used and a substantial surface area would be wasted. However, when less restrictive pressure drops are available the plate heat exchanger becomes an excellent condenser, since very high heat transfer coefficients are obtained and the condensation can be carried out in a single pass across the plate. 

Example 6.2 A condenser manufacturer gives a heat rejection capacity factor at 26°C wet hulh temperature of 1.22. What is the condenser duty if the cooling capacity is 350 kW ... 

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