Vacuum systems shutting down

The KDF filter was first tested in prototype on a coal mine in northern Germany. It was installed in parallel with existing vacuum filters and it produced filter cakes consistendy lower in moisture content by 5 to 7% than the vacuum filters. Two production models have been installed and operated on a coal mine in Belgium. The filter is controlled by a specially developed computer system this consists of two computers, one monitoring the function of the filter and all of the detection devices installed, and the other controlling the filtration process. The system allows optimization of the performance, automatic start-up or shut-down, and can be integrated into the control system of the whole coal washing plant. 

The process operates at 1 kPa (10 mbars) and 450 kW of power. When the condenser temperature reaches 580°C, the power is reduced to 350 kW. Cooling water is appHed to the condenser, throughout distillation, by means of sprays. Normally distillation takes 10—12 hours and the end point is signified by an increase in furnace temperature and a decrease in vapor temperature to 500—520°C. At this point the power is turned off and the vacuum pump is shut down. Nitrogen is then bled into the system to prevent oxidation of 2inc. 

Heavy water [11105-15-0] 1 2 produced by a combination of electrolysis and catalytic exchange reactions. Some nuclear reactors (qv) require heavy water as a moderator of neutrons. Plants for the production of heavy water were built by the U.S. government during World War II. These plants, located at Trad, British Columbia, Morgantown, West Virginia, and Savaimah River, South Carolina, have been shut down except for a portion of the Savaimah River plant, which produces heavy water by a three-stage process (see Deuterium and tritium) an H2S/H2O exchange process produces 15% D2O a vacuum distillation increases the concentration to 90% D2O an electrolysis system produces 99.75% D2O (58). 

For example, in rotary vacuum dryers it is possible to prevent the formation of explosible dust-air mixtures by setting and monitoring a certain partial vacuum (negative pressure). This pressure value must be determined by experiment for each type of dust. With pressures of less than O.I bar, in general, hazardous effects of dust explosions need not be anticipated. If the vacuum system malfunctions, the partial vacuum must be released by inert gas and the instaUation shut down. 

In order to avoid having to shut down the whole vacuum system each time the cryostat is vented after an experiment, it is advisable to place a small slide or butterfly valve between the turbopump and the expander port. When the system is reevacuated, the turbopump must be stopped before opening the valve, otherwise the ambient pressure shock wave that results might deform the delicate rotor and... 

Suggestion 3 has limited practicality. It can only be effective after work on the vacuum line is complete and you wish to shut down the system. This plan will not help vacuum lines left unattended and/or whose liquid nitrogen has boiled off. Regardless, if frozen oxygen boils off faster than can be released by the vent, the results would be the same as if no vent were available. Thus, the potential for disaster is still present. 

When shutting down a vacuum system, close off your system from the trap section. That way, as trapped compounds warm up and go into a vapor state, they will not be able to drift into the rest of the vacuum line. You should also vent your pump to the atmosphere. Many pumps do not have adequate check valves near their oil reservoirs. If they are shut off with a vacuum on the vacuum side, the mechanical pump oil can be drawn up into the system. So, to shut down a vacuum system (see Fig. 7.34), it is recommended that you ... 

For the STM experiments described below, the pressure at which just half of the clusters reach the FTM was found and recorded. A previously unexposed substrate was then rotated into the position previously occupied by the FTM and exposed for a measured time to this cluster flux. This procedure eliminates codeposition of clusters and uncondensed atoms and slows the clusters to thermal speeds before depositing them on a substrate. After several samples are prepared, the MECS and the vacuum system are shut down and bled up to atmospheric pressure and the samples are removed for analysis. No attempt was made to prevent the supported clusters from adsorbing gas phase contaminants. 

Should an emergency occur requiring immediate shutdown and over-ride of normal sequenhal shutdown, an EMERGENCY STOP pushbutton is provided for this purpose. This device interrupts power to all components in the oxidation unit control circuit, shuts down all motors, and closes the vacuum line valve and the chlorine pressure-reducing valve (PRV). The EMERGENCY STOP pushbutton is also used as a reset device to restore the system to normal operating status after an alarm situation has occurred. 

The whole chlorine processing train can be upset if air enters the system through a vacuum break. If the pressure in the chlorine header is close to the point where the vacuum seal opens, the chlorine compressor should be shut down. This will prevent air from being drawn into the whole chlorine handling system. 

When conditions are stable, the vacuum source should be shut down, and all evaporator stages should be individually isolated. Any source of major leakage (e.g., an open valve) should be identified and the problem eliminated. Rebalancing of the system may in some cases be necessary. Finally, with the system considered tight, the pressures in the various stages should be recorded for some period of time before approving the system for operation. The criteria used for this test depend on system design and vendor instructions. 

Generic Safety Issue (GSI) A-09 in NUREG-0933 (Reference 1), addresses the issue of assuring that the reactor can attain safe shutdown after incurring an anticipated transient with a failure of the Reactor Trip System (RTS). An ATWS is an expected operational transient (such as a loss of feedwater, loss of condenser vacuum, or loss of offsite power to the reactor) which is accompanied by a failure of the RTS to shut down the reactor. 

Residual cylinder content should be confirmed and recovered, or disposed of. The method of disposal of residual content will depend on the product and applicable environmental regulations. An appropriate disposal system should be available. Venting should be directed outside the building, away from building air intakes. Residual gas or liquid in all medical cylinders must be vented. Each vented cylinder is evacuated to a minimum vacuum of approximately 25 inches (635 mm) of mercury (Hg). The vacuum valve and each cylinder valve are closed, and the pump is then shut down. 

The condenser had been steadily losing vacuum. It was necessary to maintain steam to the main turbine seals in order to operate the condenser at a vacuum. When main steam is not available, seal steam is provided by the oil-fired auxiliary boiler. The auxiliary boiler broke down, so that seal steam could not be maintained. It was, therefore, necessary to shut down the condensate system completely. 

All evaporation systems include a vacuum chamber with associated pumps, and evaporation sources and their controlling electronics. Most also include methods for monitoring the flux of atoms generated by the sources and doors that cover the substrate and/or the sources during stabilization of the evaporation conditions or to modulate the beams of atoms striking the substrate without having to shut down the sources. Typical evaporation systems are shown schematically in Figure 11.1. 

---