Utilities in distillation operation include: heating and cooling media along with power, high pressure air, and vacuum. For this distillation column, and most industrial distillation columns, process steam is used as a heating medium for both the reboiler and the heat exchanger for the feed. The steam pressure is regulated manually through a regulator to about 1.1 bar as shown on the gauge, which gives a steam temperature of about 101 °C. The steam flow rate to the reboiler is controlled by a flow controller, and the flow rate is measured by a steam flow meter. All these values allow the calculation of reboiler duty from the steam side. Domestic water is used as a cooling medium for the condenser and the two secondary heat exchangers for the top and bottom product streams. The cooling water flow rate to the condenser is controlled by a flow controller, and the inlet and outlet temperatures are monitored by two temperature sensors. Again, these measured values allow the determination of the condenser duty from the utility side. Note that the cooling water valve needs to be fully open during the column start-up, while a much smaller flow rate is used during the column operation. As a rule of thumb, the temperature difference between inlet and outlet should be more than 25 °C.
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