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Figure 5.32 Results of design spec.

The last item of interest is to compare the energy and capital costs of this heat-integrated two-column system with those of a single column making exactly the same separation. This single column is the same as the low-pressure column in terms of operating pressure, but its energy consumption, column diameter, and heat exchanger areas will be larger.

The comparison of the two alternative designs is given in Table 5.3. The energy consumption is reduced from 35.58 MW in a single column to 21.81 MW in the high-pressure column of the heat-integrated design. This cuts energy cost from $2,640,000 per year to $1,610,000 per year. The same energy value is used in both cases. However, higher-pressure steam is needed in the heat-integrated design because the base temperature is 428 K compared to 367 K in the single column. Using a 34.8 K temperature difference

TABLE 5.3 Comparison of Single and Heat-Integrated Columns

Single Low-Pressure High-Pressure

TABLE 5.3 Comparison of Single and Heat-Integrated Columns

Single Low-Pressure High-Pressure

Stages

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