Condenser vacuum control

Optimization and vacuum control strategies (a) minimizing (floating) pressure by maximizing coolant valve opening, (b) floating pressure control of partial condenser with vapor distillate, (c) floating pressure control when the distillate is both vapor and liquid. 

The pyrolysis unit consisted of an insulated 316 stainless steel preheater tube (1.3 cm i.d. X 50 cm length) which extended 1 in. into a 316 stainless steel fixed bed tubular reactor (2.5 cm i.d. x 46 cm length), which was heated by a cylindrical block heater. Two type J (iron-constantan) thermocouple probes were used to both monitor the internal catalyst bed temperature and maintain a consistent reactor wall temperature in combination with a temperature controller, A syringe pump, condenser, vacuum adapter, receiving flask, nitrogen cylinder, and gas collection system were connected as shown in Fig uTe 2. The reactor midsection was packed with 40 g of activated alumina, which was held in place by a circular stainless steel screen. The preheater and reactor were operated at 180-190 and 450 C, respectively. The entire process remained at normal atmospheric pressure throughout the mn. 

Operational Characteristics Feed enicis at higher saturation temperature than is maintained in the crystallizer body. Ciystallizer temperature, product recoveiy, and sluny density are regulated by vacuum control. Heat of ciystallization and the sensible hest of the feed are removed by evaporation and condensation of solvent. The condensate may either be removed or a portion or all returned. 

All these items, plus the extra size of condensers, the vacuum pump and vacuum controls, add to the capital cost of a plant and the complexity of its operation. 

Anticipated operational occurrences are off-normal events, usually plant transients, which can be coped with by the plant protection systems and normal plant systems but which could have the potential to damage the reactor if some additional malfunction should happen. Their typical frequency of occurrence may be more than 10 year Some of the anticipated occurrences (PIEs - postulated initiating events) are due to the increase of reactor heat removal (as might occur for an inadvertent opening of a steam relief valve, malfunctions in control systems, etc.). Some are due to the decrease of reactor heat removal (such as for feed-water pumps tripping, loss of condenser vacuum and control systems malfunctions). Some are due to a decrease in reactor coolant system flow rate, as in the case of a trip of one or more coolant pumps. Some are connected with reactivity and power distribution anomalies, such as for an inadvertent control rod withdrawal or unwanted boron dilution due to a malfunction of the volume control system for a PWR. Events entailing the increase or decrease of the reactor coolant inventory may also happen, due to malfunctions of the volume control system or small leaks. Finally, releases of radioactive substances from components may occur. 

A6. A distillation column is operating under a vacuum The column has 18 stages with the feed at stage 9, a partial reboiler, and a partial condenser. The pressure drop per stage is 1.0 mm Hg. The pressure of the condenser is controlled at 100 mm Hg. The pressure of the reboiler is a. higher than 100 mm Hg, b. 100 mm Hg, c. lower than 100 mm Hg. 

FIGURE S.11 2 Sdiemes for control of column pressure (a) pressure control for an atmospheric column (vent bleed to atmosphere) (b) split range valves in a block and bleed anangement (vent Weed to vacuum) . (c) hot vapor bypass pressure control and (flooded condenser pressure control. 

E. Provide sufficient steam volume to avoid lifting the primary safety valves as a result of a loss of condenser vacuum (LOCV) event (normal control systems are operational). 

Increase in reactor heat removal inadvertent opening of steam relief valves secondary pressure control malfunctions leading to an increase in steam flow rate feedwater system malfunctions leading to an increase in the heat removal rate. —Decrease in reactor heat removal feedwater pump trips reduction in the steam flow rate for various reasons (control malfunctions, main steam valve closure, turbine trip, loss of external load, loss of power, loss of condenser vacuum). 

Reactor pressure increase Several events may cause this e.g., inadvertent closure of one turbine control valve, pressure regulator downscale failure, generator load rejection, turbine trip MSIV closure, loss of condenser vacuum, loss of nonemergency AC power to station auxiliaries, loss of feedwater etc. All these have been analysed. Features are included in the instrumentation and control systems or redundancies to maintain reactor pressure through a combination of component automatic responses or operator actions, depending on the identified cause. 

International practice considers the analysis of ATWS for a variety of initiating events such as loss of feedwater, loss of load, turbine trip, loss of condenser vacuum, loss of off-site power, closure of main steamline isolation valves, uncontrolled boron dilution, inadvertent control rod withdrawal, etc. ATWS analyses are performed in general by using best-estimate tools to determine the preventive (e.g. a diverse scram system) or mitigative measures (e.g. initiation of turbine trip and emergency feedwater supply) which need to be implemented for strengthening plants defence in depth. 

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. 

---