Control condenser

Condensation. Control or reduction of volatile gases and vapors by condensation is most feasible for organic compounds (49,55). 

It was learned very early that the angular aperture of the substage condenser controls specimen contrast. Decreasing that aperture, usually with a continuously adjustable iris diaphram, greatly increases contrast. It was not, however, appreciated fully until Ernst Abbe s classic contributions (7,8) in the period ca 1880—1889 that decreasing the aperture to increase contrast also decreases the resolving power of the microscope. 

In the flow schematic (Fig. 22-80), the condenser controls the vapor pressure of the permeating component. The vacuum pump, as shown, pumps both hqiiid and vapor phases from the condenser. Its major duty is the removal of noncondensibles. Early work in pervaporation focused on organic-organic separations. Many have been demonstrated few if any have oeen commerciaHzed. Still, there are prospects for some difficult organic separations. 

Figure 1. Condensate controller maintains a positive pressure differential across all the tubes.

One means of overcoming this problem is to install a condensate controller, which maintains a positive pressure differential across all the tubes (Fig. I). A condensate controller provides a specialized purge line, which assures a positive flow through the coil at all times. 

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A good condensate control program, using the correct mix of different distribution ratio (DR) neutralizing amines, will minimize corrosion and limit iron transport. A standard control method is often... 

Figure 3.10. Condensers, (a) Condenser on temperature control of the PF condensate. Throttling of the flow of the HTM may make it too hot. (b) Condenser on pressure control of the HTM flow. Throttling of the flow of the HTM may make it too hot. (c) Flow rate of condensate controlled by pressure of PF vapor. If the pressure rises, the condensate flow rate increases and the amount of unflooded surface increases, thereby increasing the rate of condensation and lowering the pressure to the correct value, (d) Condenser with vapor bypass to the accumulator drum. The condenser and drum become partially flooded with subcooled condensate. When the pressure falls, the vapor valve opens, and the vapor flows directly to the drum and heats up the liquid there. The resulting increase in vapor pressure forces some of the liquid back into the condenser so that the rate of condensation is decreased and the pressure consequently is restored to the preset value. With sufficient subcooling, a difference of 10-15 ft in levels of drum and condenser is sufficient for good control by this method.

Minimum pressure operation can be achieved by adjusting the set point of the pressure controller so as to keep the condenser fully loaded at all times. This can be done by using valve position control (VPC), which keeps the condenser control valve in a nearly fully open position ([a] in Figure 2.87) or by refrigerant level control ([b] in Figure 2.87). The column pressure can also be minimized on the basis of condensate temperature ([c] in Figure 2.87). 

Step 8. Several control valves now remain unassigned. Steam flow to the trim heater controls reactor inlet temperature. Cooling water flow to the trim cooler is used to control the exit process temperature and provide the required condensation in the reactor effluent stream. Liquid recirculation in the absorber is flow-controlled to achieve product recovery, while the cooling water flow to the absorber cooler controls the recirculating liquid temperature. Acetic acid flow to the top of the absorber is flow-controlled to meet recovery specifications on the overhead gas stream. Cooling water flow to the cooler on this acetic acid feed to the absorber is regulated to control the stream temperature. Cooling water flow in the column condenser controls decanter temperature. 

Since the evaporation rate varies between stages, the feed rate needs to be adjusted to allow sufficient concentration to achieve the target yield. One method to accomplish this is to set the feed rate directly proportional to the solvent removal rate, which is determined by monitoring the condensate flow rate from the subsequent effect. The gain on the condensate controller output will determine the concentration of the mother liquor, leaving the crystallizer and control product yield. Product purity is likewise controlled if the saturation limits of other components in the feed are being approached. 

When the condenser contains excess heat transfer area, the fraction of condenser area that is flooded can be manipulated to vary the rate of condensation. This principle is used in "flooded condenser control schemes (Sec. 17.2.2). 

Flooded reflux drums. These are used as part of flooded condenser control schemes (Sec. 17.2.2). A flooded drum is only suitable when substantial fluctuations in product rate can be tolerated (e.g., product goes to storage). A flooded drum provides no surge for controlling and smoothing out product fluctuations, but it maintains surge for the reflux pump and reflux circuit. 

Reboiler and condenser controls regulate the energy inflow and outflow in a distillation column. These controls must adequately respond to column changes, minimize transmission of distimhances into the column, and be energy efficient. Failure to achieve the first two functions will lead to column instabilities failme to achieve the third wastes energy. 

Column pressure control is frequently integrated with the condenser control system. This control is often regarded as the most important control in the column. It has been the author s experience that a column will not achieve stable operation imless steady pressure can be maintained. 

As previously described (Chap. 16), column pressure control is usually integrated with the condensation system. Pressure and condensation controls therefore need to be considered simultaneously. An ex-... 

Some general guidelines for pressure and condensation control (77) are... 

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