Temporary plugs

Benzoic acid is also used as a down-hole drilling mud additive where it functions as a temporary plugging agent in subterranean formations. Since this is a secondary oil recovery appHcation, this use is heavily dependent on the price of cmde oil. 

Examples of the components of the gelling composition are a water-soluble polymer such as polyacrylamide, an iron compound such as ferric acetyl-acetonate or ammonium ferric oxalate, and a ketone such as 2,4-pentanedione [1247]. The composition forms a temporary gel that is useful for the temporary plugging of a formation. The temporary gels that are formed will disappear after 6 months. 

Before any work inside the column commences, it is essential to take steps for preventing small parts such as nuts eind bolts from finding their way into downstream equipment, such as pumps, heat exchangers, and control valves. In one case (145), a column bottom pump frequently lost suction because a leftover piece of rope ladder reached its inlet and lodged there. Temporary plugs in the column base and some drawoffs can effectively prevent such incidents. It is important to positively ensure that these plugs are removed prior to startup. 

Remove all temporary startup or checkout branches, nipples, and plugs, and replace them with properly designed welded plugs. 

If a firewater line needs to be temporarily isolated and an isolation means is not available on the immediate portion of the system needing work, a unique solution is to use a liquid nitrogen low temperature coil line freezing apparatus. This mechanism causes an ice plug to form in the line, effectively sealing the line from leakage, during the period the temporary isolation is needed. 

The electrical demands of a darkroom are not great. One outlet with a four-plug adapter or a good power strip with multiple outlets is often sufficient for a closet or temporary darkroom. 

Just before a plant startup, the operations team wondered if the piping upstream of a flammable gas compressor may not have been cleaned sufficiently to prevent dirt from entering the precision machinery. Concerned employees had a temporary filter installed in the suction line. The operations team was correct there was a sufficient amount of foreign material in the upstream piping to plug up the filter. [8]... 

The final open-loop reactor issue we discuss is the problem of inverse response or wrong-way behavior as it is called in the reactor engineering literature. The inverse response refers to the temporary increase in the exit temperature in some packed, plug-flow reactors following a decrease in the feed temperature (Fig. 4.12). The wrong-way behavior stems from the difference in propagation speed between concentration... 

Decisions to stop a project are the most difficult decisions. Although perseverance and full support by everybody are essential for the success of any project, there is a point where "the plug must be pulled". A feeling of personal failure if the project fails, selective perception and reporting of information, major setbacks being considered as temporary problems and the hope to recoup at least part of the investment are strong forces which hinder a reasonable decision at the right time. Staw and Ross (1991) have discussed the personal interests of people involved in such situations in more detail. 

Does the change involve the use of one-time maintenance items such as chemical cleaning, hot tapping, jumpovers, freezing lines to temporarily plug, or the temporary repair of hazardous chemical leaks ... 

If an instrument or instrument system malfunctions, the operator tries to correct the problem. If an alarm, flow- or temperature-measuring instrument or shutdown system malfunctions, the operator s first response should be an attempt to restore it to service. It may be a plugged impulse line, inadvertent flow shut off to an analyzer, etc. If the Instrument System is a Class 1 or 2, immediately go to Step 2. If the alarm is a Class J. the Lead Operator (or Shift Foreman) should be consulted and follow established procedures and his knowledge of the unit and the specifics of the situation to determine the temporary steps required. At the minimum, a note in the maintenance logbook must be made to initiate repairs. Stop Here for Class 3 Alarms. 

Cyclosporine A (CsA, Restasis 0.05%) was approved in 2002 by the FDA as an ocular therapeutic for patients with keratoconjunctivitis sicca (dry eye). Until 2002 the therapy of choice for the treatment of dry eye was artificial tears and punctal plugs and the occasional use of pulse doses of topical steroids.Artificial tears and pimctal plugs brought some temporary relief to patients, but the underlying cause of dry eye, inflammation, was not affected. Steroids carried the threat of a multitude of side effects. With as many as 7.1 million people in the United States alone encountering dry eye symptoms, the development of a therapy that eliminates the inflammatory events associated with the disease has been a significant benefit. 

The two most common types of plugs currently in use are collagen and silicone (Table 14-3). The water-soluble collagen rods are temporary, dissolving 4 to 7 days after insertion. Silicone plugs are more permanent but can be removed when necessary. 

Customary controls in pelleting plants normally comprise feed and product characteristics, such as feed rate and steam or liquid addition as well as product temperature, moisture, and strength. As shown in Figure 321, permanent or temporary overfeeding or excessive slip between the roller(s), die, and material— all resulting in too much material in front of the press roller(s)—may lead to choking and, ultimately, plugging of the equipment. Therefore, measurement of the power consumption of the press motor is often monitored and interlocked with the result that, if a maximum is exceeded, the plant stops. 

The fibrinolytic system removes the fibrin of the hemostatic plug and thus is responsible for the temporary existence of the fibrin clot. The proteolytic action of plasmin on fibrin and fibrinogen is extensive and more like the digestive proteolysis catalyzed by trypsin and chy-motrypsin than the proteolysis involved in proteinase precursor activation. The fibrinolytic subsystem includes the reactions of plasminogen activation, plasmin inactivation, and fibrin digestion. As is common throughout the hemostatic system, irreversible activation reactions of the fibrinolytic system are opposed by irreversible proteinase inactivation. 

Final elements must provide the desired capacity with the required precision of flow throttling over the desired range, usually 10% to 95% of maximum flow. The valve characteristic should provide a linear closed-loop gain, except choose linear or quick-opening characteristics for valves that are normally closed but must open quickly. Select the valve failure position for safety. The valve body should satisfy such requirements as required flow at 0% stem position, plugging, pressure drop, or flashing. The nonideal final element behavior, such as friction and deadband, should be small, as required by each application. Control valves should have manual bypass and block valves to allow temporary valve maintenance when short process interruptions are not acceptable. However, the bypass should never compromise safety interlock systems. 

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