Condensate temperature control

As with condensers, temperature control is not effective, as the saturated vapour temperature is constant at constant pressure. Level control is often used for vaporisers the controller controlling the steam supply to the heating surface, with the liquid feed to the vaporiser on flow control, as shown in Figure 5.20 (see p. 232). An increase in the feed results in an automatic increase in steam to the vaporiser to vaporise the increased flow and maintain the level constant. 

Perfect control is assumed for the composition/ratio controller, level controllers, gas condenser temperature controller, and speed controller. 

As with condensers, temperature control is not effective, as the saturated vapor temperature is constant at constant pressure. Level control is often used for vaporizers, the controller controlling the steam supply to the heating surface, with the... 

Considering that for a product in a sublimation step at 100 pB a temperature variation of the condenser between —50°C and —80°C results in a vapor pressure difference of approximately 30%, this demonstrates how important condenser temperature control is in terms of validation. 

The temperature of this ice condenser used to be monitored but not eontrolled, which meant that the condenser temperature was the result of the thermal equilibrium between the heating system of the shelves and the refrigeration system s maximum available power. However, as already identified for the shelves, the expansion of the frigorific fluids makes condenser temperature control very dilficult in terms of uniformity. 

Finally, condenser temperature control can also be used for control of sublimation rate in the case of high mass transfer at the beginning of... 

The geometry of the chamber-condenser valve (Figure 14.10) must be chosen in such a way that there is a good water vapour distribution so that the ice can grow evenly over the condenser pipes installed in the condenser. Temperature control of the condenser pipes is effected over thermal expansion valves the cooling agent is injected directly into the condenser pipes (evaporator). 

As an alternative to Item 5, one may use a recirculating coolant system ( tempered coolant) with condensate temperature control of makeup coolant. This keeps the condenser dynamics constant and eliminates the problem of retuning the controller as the load changes (see Figure 3.9). 

Finally, it is increasingly common to provide no condensate temperature control, but to run with full cooling at all times. This saves a control valve. Further, the quality of cooling water is sometimes so poor that a minimum velocity must be maintained in the exchanger to minimize fouling. For accurate control of internal reflux, an internal reflux computer is required (discussed in Section 11.1). As pointed out by BoUes, however, it is necessary to limit subcooling in some columns to avoid foaming on the top tray. 

An additional problem with condensate temperature control, via cooling-water manipulation, relates to column safety. In an instance with which one of the authors is painfully familiar, an atmospheric column with such a control system was running at a very low feed rate. Condensate temperature became too low, so the controller closed the cooling-water valve located in the exit line from a vertical condenser. The water in the shell b an to boil, the valve could not pass the required volume of steam, the cooling-water pump stalled, and product vapor issued in great quantities fix>m the vent. Fortunately, an alert operator shut the column down before any damage occurred. 

As a consequence, unaided condensate temperature control is not recommended. There should be an override fix>m cooling-water exit temperature. Further, to minimize the hazard of winter freezeup, a limiter should be provided to prevent complete valve closure (see Chapter 9). 

The preferred arrangement for a vacuum or a pressure column with a large amount of inerts is shown in Figure 3.10. Here the inerts are pulled off or blown out through a vent line in which there is a throtde valve manipulated by the subcooled-condensate temperature controller. For a vacuum column, the low-pressure source is usually a steam jet. If the downstream pressure fluctuates too much, it may be necessary to use a cascade temperature-vent flow-control arrangement. 

High cooling water exit temperature override on condensate temperature control... 

The thermal expansivity of Ni—Fe alloys vary from ca 0 at ca 36 wt % Ni (Invar [12683-18-OJ) to ca 13 x 10 / C for Ni. Hence, a number of compositions, which are available commercially, match the thermal expansivities of glasses and ceramics for sealing electron tubes, lamps, and bushings. In addition, the thermal expansion characteristic is utilized ia temperature controls, thermostats, measuriag iastmments, and condensers. 

Condensing Organic Va.por, The eutectic mixture of diphenyl and diphenyl oxide is an excellent vapor medium for precise temperature control at temperatures higher than those practical using steam. This mixture can achieve 315°C while holding pressure at 304 kPa (3 atm) absolute. In contrast, steam would require 10.6 MPa (105 atm) pressure. 

An alternate means of reboiler control is to remove the control valve from the steam line and provide a condensate level controller for the chest cascaded from the tray temperature. The alternate method uses A tube surface for control, with the condensate covering more or less tube surface to vary the area exposed to condensing stream. Condensing area is many times more effective for heat transfer than area covered by relatively stagnant condensate. The reboiler must have extra surface to allow part of its surface to be derated for control purposes. 

Abnormal Heat Input From Reboiler - Reboilers are designed with a specified heat input. When they are new or recently cleaned, additional heat input above the normal design can occur. In the event of temperature control failure, vapor generation may exceed the process system s ability to condense or otherwise absorb the buildup of pressure, which may include noncondensibles due to overheating. 

Absorber oil then flows to a still where it is heated to a high enough temperature to drive the propanes, butanes, pentanes and other natural gas liquid components to the overhead. The still is similar to a crude oil stabilizer with reflux. The closer the bottom temperature approaches the boiling temperature of the lean oil the purer the lean oil which will be recirculated to the absorber. Temperature control on the condenser keeps lean oil from being lost with the overhead. 

Temperature Control (Manual) (Automatic). Instruments Controls (Weather Protected) (Explosion ProoO Level Controls - To Be Pressure Gauges To Be Condenser Cooling Water ... 

Temperature control Of the factors mentioned, temperature is probably the easiest to control this can be accomplished by means of a thermostat or by operating at the boiling point of the testing solution with an appropriate reflux condenser to maintain the solution at a constant concentration. Control to 1°C is not hard to accomplish. 

In the vacuum mixer, water evaporation is also used for the temperature control, since the evaporation rate can be influenced by the grade of the vacuum. The water vapor, however, does not escape from the mixer, but is condensed and returned into the mix, the composition of which is thus not changed. 

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