Vacuum systems process control

Figure 6-33 diagrams vacuum system arrangements for process systems. It is important to examine the plant economics for each system plus the performance reliability for maintaining the desired vacuum for process control. 

Milled calcined product and reductant aluminum powder are made into briquettes by certain mixture ratio under different briquetting pressure. Put the briquettes into tank, turn on the furnace and vacuum system. By controlling the temperature, time and excessive coefBcient of reductant, the relationship between reduction rate of LiA102 and reaction conditions was studied. When the reduction process finished, accounted the reduction rate of LiA102 according to formula (3). 

The vacuum extraction process involves using vapor extraction wells alone or in combination with air injection wells. Vacuum blowers are used to create the movement of air through the soil. The air flow strips the VOCs from the soil and carries them to the surface. Figure 18.14 shows the flow diagram for such a process. During extraction, water may also be extracted along with vapor. The mixture should be sent to a liquid-vapor separator. The separation process results in both liquid and vapor residuals that require further treatment. Carbon adsorption is used to treat the vapor and water streams, leaving clean water and air for release, and spent GAC for reuse or disposal. Air emissions from the system are typically controlled by adsorption of the volatiles onto activated carbon, by thermal destruction, or by condensation. 

In-plant management practices may often control the volume and quality of the treatment system influent. Volume reduction can be attained by process wastewater segregation from noncontact water, by recycling or reuse of noncontact water, and by the modification of plant processes. Control of spills, leakage, washdown, and storm runoff can also reduce the treatment system load. Modifications may include the use of vacuum pumps instead of steam ejectors, recycling caustic soda solution rather than discharging it to the treatment system, and incorporation of a more efficient solvent recovery system. 

In addition to the vacuum valves, which perform solely an isolation function (fully open - fully closed position), special valves are needed for special functions. Typical are variable leak valves, which cover the leakage range from 10" ° cm /s (NTP) up to 1.6 10 cm /s (NTP). These valves are usually motor driven and suitable for remote control and when they are connected to a pressure gauge, the process pressures can be set and maintained. Other special valves fulfill safety functions, such as rapid, automatic cut-off of diffusion pumps or vacuum systems in the event of a power failure. For example, SECUVAC valves belong to this group. In the event of a power failure, they cut off the vacuum system from the pumping system and vent the forevacuum system. The vacuum system is enabled only after a certain minimum pressure (about 200 mbar) has been attained once the power has been restored. 

In analogy to other modern analytical instruments, a computer-based data processing and evaluation system is inserted in all mass spectrometers constructed today. All processes, from sample introduction using an autosampler, e.g., in an ICP-MS, to optimization of experimental parameters in the ion source, ion extraction, separation of ion beams and their registration, the vacuum system and the whole measurement procedure are supported and controlled by a fast and powerful... 

Now that we have determined what processes the facility will be used for, we can finalize utility requirements. The following utilities are required for our solid-dose facility heating, ventilation, and air conditioning (HVAC), hot and cold water, steam, electrical service, compressed air, vacuum systems, dust collection, chillers, effluent stream, and purified water. For the more specialized processes or special material handling, we may need specialized gases and breathing air. Purified water is one of the more difficult utilities to maintain the quality of. From a source of potable water, a series of treatments must be performed to control microbiological quality. Typical treatment options include carbon filters, reverse osmosis, and UV radiation. 

As you can see, this process is aided or thwarted by vacuum system design. Temporary isolation of the various parts of any vacuum system may be impossible by bad design. Therefore, be forewarned If you are designing a vacuum system, provide a stopcock at every branch of the system to aid in leak detection (section isolation not only helps in leak detection, but creates a more robust vacuum system allowing greater control and protection). 

The mold may be split or one-piece. The finished part is removed either by splitting the mold or, in the case of a one-piece mold, by collapsing the part with a vacuum. This process can be very labor intense. However it is also automated requiring relatively no labor. Automatic systems fill molds with plastisol carried by conveyor belts through an oven as it is being slushed (the mold is put into a control motion pattern). The plastisol can gel repeatedly to a thickness of 0.06 in. (15.2 mm). The excess plastisol is poured out of the mold and automatically returned to the main tank for reprocessing. The molds proceed to another oven where curing is completed. 

In direct ion beam deposition processes, ion energy in the range of a few tens of eV to a few tens of keV is used for diamond like film deposition. Careful control of ion energy in high-vacuum systems employing mass filtering of carbon ions (as in MSIB) has been shown to produce crystalline diamond materials up to several micrometers in size. ... 

The Fitzpatrick Co. roller compactor (Fig. 20) features two feed screws in series one horizontal and the second vertical. This system is designed to transfer powder bulk into a set of cantilevered rolls positioned in the horizontal mode one is fixed, the other floats. Operator interface allows for on-line monitoring and controlling feed screw speeds, roll pressure, and roll gap. Features such as on-line help and diagnostic functions, maintenance, and calibration screens are displayed. All functions are interfaced and adjustable by PLC for process control and report generating. The machines have vacuum deaeration and roll cooling capabilities. The sizing unit is separate from the compactor and is either a rotor bar or a hammer mill. 

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