Condensers cooling-water throttling

Figure 6-32 illustrates ejector systems with large condensable loads which can be at least partially handled in the precondenser. Controls are used to maintain constant suction pressure at varying loads (air bleed), or to reduce the required cooling water at low process loads or low water temperatures [2]. The cooler W ater must not be throttled below the minimum (usually 30%-50% of maximum) for proper contact in the condenser. It may be controlled by tailwater temperature, or by the absolute pressure. 

The oldest, most direct method of pressure control is throttling on the cooling-water supply. This scheme is shown in Fig. 13.5. Closing the water valve to the tube side of the condenser increases the condenser outlet temperature. This makes the reflux drum hotter. The hotter liquid in the reflux drum creates a higher vapor pressure. The higher pressure in the reflux drum increases the pressure in the tower. The tower pressure is the pressure in the reflux drum, plus the pressure drop through the condenser. 

Focus attention on exchanger duties which are calculated from small temperature differences (e.g., a condenser duty calculated from the inlet and outlet temperatures and cooling water flow, where the temperatures are less than 10°F apart). Often, the flow can be throttled to increase the temperatm-e difference if this is impractical, high-accuracy temperature indicators may be required. 

Controlling reflux drum temperature by throttling cooling water to condenser caused boiling of cooling water when control valve cloeed. This resulted in atmospheric product release. 

Pay attention to low-rate operation of control systems throttling cooling water to condensers. 

Throttling cooling water flow to water-cooled condensers is generally not recommended because of fouling and silting which frequently occur at reduced water velocities. Consequently, water-cooled condensers should be provided with tempered-water systems as described in Chapter 13. Tempered-water systems result in better control, reduced maintenance, and reduced pumping costs. 

While the 20 ft/sec may be maintained in the summer, more efficient condensation in the winter may reduce vapor flow. This can cause the riser velocity to drop below the minimum to prevent phase separation. Throttling the cooling water will stabilize the tower pressure, but may result in salting up the exchanger with water-hardness deposits. 

As mentioned in Chapter 3, some plants like to control condensate temperature by throttling cooling water as shown in Figure 3.2. This seldom works well. 

Apparatus. The generator employed is shown in fig. 10. There are six important points. (1) The column. <4 is designed so that throttling is avoided it is at least 2 ft. long and surmounted by a reflux doublesurface water-condenser B. (2) A Perkin triangle (air-cooled), inserted between the down-condenser and the traps, enables any phosphorus oxychloride which distils to be removed. (3) It is convenient to have three traps, viz. C, ice and salt D, acetone and carbon dioxide E, liquid air. (4) The intermittent addition of the solid antimony trifluoride presents a problem. The mechanical solid feed... 

The reactor was charged with coal (50 g dry basis) and solvent (600 ml) and heated (7°C min- ). When the temperature reached 300°C, solvent (1 1 h 1) was pumped via a dip tube, which acts as a preheater, into the bottom of the reactor and through the coal bed. A 15 micron filter was placed in the exit line. The pressure was controlled by adjusting throttling valves and the gaseous phase was condensed by a water-cooled condenser. 

A way to achieve cooling and supersaturation of mixtures is adiabatic expansion of a gas due to a throttle effect. In the realm of gas and gas-condensate fields, low-temperature separation (LTS) schemes are used, which include a combination of technological processes directed towards cooling of the production from wells to the requisite temperatures to facilitate separation. The LTS scheme is applied after the gas has been purged of most of the mass of liquid phase in the entrance separator, practically without changes of pressure and temperature. LTS is subsequently applied to condense water vapor and heavy hydrocarbons (HC). LTS entails the following processes. 

These types of chillers are corrrmonly used in gas or kerosene operated refrigerators. The difference is that here solar-heated water would be used to provide heat irrput in the generator (see Fig. 19). In the system shown the refrigerant is expelled from the rich solution and the weakened solution is returned to the absorber. The refrigerant vapor dissipates some of its heat to the environmerrt (may be water cooled) and condenses. This Uqttid errters the evaporator through a throttle valve (or a high-resistance thin pipe), where, in the low-pressure chamber, it evaporates and takes on some heat from its environment (e g., from a water jacket), thus it produces chilled water. The vapor then returns to the absorber and is absorbed by the ab-... 

In the Heatric process, the warm wet pressurised gas from the inlet separator is pre-cooled in the PCHE and then throttled in a Joule-Thomson (JT) valve to a lower pressure. The drop in pressure produces a cooling effect and both hydrocarbon liquids and water condense out of the gas. The two-phase stream passes to a separator where the liquids are removed. The cold dry gas from the separator is returned to the exchanger to chill the incoming warm, wet gas (Figure 9.3). Refrigeration... 

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