Vacuum startup

Test run steps can frequently be incorporated into process startup procedures. Two examples would be pulling a vacuum on vessels and verifying it holds, or distilling a solvent and checking for the presence of water to verify the mechanical integrity of the heating and cooling equipment. 

J. E. Troyan s series of articles on plant startup has a cause/effect table on instrumentation in Part II. This article also has troubleshooting hints for distillation, vacuum systems, heat transfer, and filtration. Here is the table on instrumentation. 

Generally this type of unit serves to compress gases from vacuum up to atmospheric pressure. Often after initial startup, the unit must pump-down the system (such as a closed process system of vessels) by gradually bringing down the... 

Troyan13 tells how to spot certain symptoms during the startup phase so that problems may be averted. Some examples follow. Noisy equipment or a higher-than-normal temperature may mean poor lubrication. This could be due to plugging because of dirt that accumulated during construction. Vibration may mean that the equipment should be anchored better. Excessive pressures or unexpected vacuums may be due to spray painting that clogged ventilators. In one case, a tank was filled with water and then spray-painted. When the tank was emptied, a vacuum was formed that collapsed it. 

Completion of the full process will take 3 to 4 days depending on the dehydration protocol chosen. Vacuum drying (Support Protocol 1) will take a full day. Extraction, isolation, and startup of prepurification will take another day. It is advisable to crystallize overnight and to filter, wash, and dry the crystals the next day. If a second crystallization step is desirable add another day. 

When the plant is located in built-up areas, there might also be an atmospheric condenser that receives the steam, which is vented during the startup to decrease the noise level at the plant. The auxiliary circuits of the steam turbine are the lube oil, control fluid, and vacuum system for the condenser. 

ER E discussions with Texaco and with Shell on bottoms processing are summarized herein. Texaco has indicated that its partial oxidation process could be applied to coal liquefaction bottoms on a commercial scale and that operation of their 12 T/D pilot plant with coal liquefaction bottoms representative of a projected commercial feedstock would be adequate to set the design basis for a commercial facility. Texaco indicated that three to four years after successful operation of the 12 T/D unit a commercial facility could be ready for startup. In initial discussions, Shell has indicated that development of the Shell/ Koppers partial oxidation process for coal liquefaction bottoms would involve operations of both their 6 T/D pilot plant and their 150 T/D demonstration unit. It was estimated that the 150 T/D facility might become available in the late 1980/early 1981 time frame for possible operation on vacuum bottoms. 

Unfortunately the temporary filter was placed between the compressor and a low suction pressure trip. The compressor suction pressure was reduced to a vacuum and air intruded into the system. The air reacted within the system. A decomposition occurred further downstream and a major fire caused many months delay in the startup of this unit. 

For a period of time just after startup, the piping upstream of this compressor operated under a vacuum. This upstream piping was equipped with a set of double block and bleed valves to a scrubber that circulated diluted caustic soda. During this unusual startup configuration, moisture was sucked into the system and the wet chlorine completely dissolved the stainless steel ball within the 3-inch (7.6 cm) quarter-turn valves. 

The stainless valves were improper, but if they leaked slightly during normal operation dry chlorine would enter the scrubber and harmlessly be neutralized. FFowever, during this startup with the piping under a vacuum, moisture from a slight leak managed to combine with the dry chlorine and create an aggressive corrosive fluid. 

Limit the Amount of Moisture Near the Top of Your Cold Trap. A common error when first starting up a vacuum system is pouring liquid nitrogen too high into a Dewar. People often overfill Dewars in the early startup process... 

This operation requires the personal skill of the startup person. That person is required to integrate/interrelate extruder and down-stream equipment. Extruder screw speeds and haul-off rates may then be increased. Downstream equipment is adjusted to meet their maximum operating performance, such as having the vacuum tank water operate with its proper level and vacuum applied. The extruder can be fine-tuned to obtain the final required setting for meeting the desired output rate and product size. 

Time during which the end lempemure has Lobe kept Startup condenser cooling and vacuum pump Stun of evacuaiion... 

Apricot was used as a model for studies of fruit puree clarification. Various puree concentrations were treated for 30 min at 50° C with 0.4 cc/L, each, of commercial cellulase and pectinase enzyme and clarified by filtration through a 0.45(im pore size ceramic microfilter. Sparkling clear apricot juice was produced at flux rates from 90-190 L/m2h. Above 13° starting Brix. juice flux showed little increase with increasing starting Brix. Dissolved solids flux increased substantially with increasing starting Brix. Permeate remained clear and retained most of its flavor and aroma when concentrated by vacuum evaporation to 58° Brix. There appears to be some retention of enzymes by the filter. Retained enzymes were successfully utilized in a 4 h trial in which untreated puree was continuously added to retentate. in amounts equal to permeate removed, after startup on enzyme-treated puree. 

Once inert gas purging and leak testing are completed (in either a pressure or a vacuum tower), the column is usually depressxired to a small positive pressime (5 to 10 psig) until the plant is ready to proceed with the startup. 

Once steaming is completed, the column should be opened to let air or inert gas in on shutdown, or placed under gas pressure (inert gas such as nitrogen or fuel gas, or process gas) at startup. The alternative of leaving small steam purges to keep the column pressure up at the conclusion of steaming is often unsatisfactory and resulted in creation of vacuum in some instances (3). Unless the column is fully open to the atmosphere, so that no vacuum can be created, a pressure of at least 5 to 10 psig should be kept in it (3). 

When a light mixture (e.g., top product, off-spec top product, or a feed stream void of the heavy components) is used for startup, an excessive bottom temperature is unlikely to occur. In this case, feed can be introduced and the reboiler started before vacuum is fully drawn. This practice is often used when startup time is critical. 

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