In-leakage

The pump-down time 0 for evacuating a vessel in the absence of air in-leakage is given approximately by... 

The amount of inerts which has to be removed by a pumping system after the pump-down stage depends on the in-leakage of air at the various fittings, connections, and so on. Air leakage is often correlated with system volume and pressure, but this approach introduces uncer-... 

Three examples of ordinaiy gas seals are shown in Fig. 12-61. On direct rotary dryers, few gas seals are intended to be completely gastight, but by careful control of the internal pressure, generally Between 0.25 and 2.5 mm of water below atmosphere, dusting to the outside is prevented and in-leakage of outside air is minimized. 

NOTE TLe fan on tLis dryer Landles about 5.2 mVs at outlet conditions. Tbe outlet-air temperature includes cold air in-leakage, and tbe true temperature drop caused hy evaporation must tberefore be estimated from a beat balance. 

A rolling mill drive motor failed in service. Investigation revealed the motor was short circuited by water in-leakage. This forced a prolonged shutdown, as the motor could not be replaced on site. High humidity was initially assumed to be the problem. Upon close inspection of the motor air coolers, however, it was determined that water leaked from headboxes into the air plenum spaces. Severe corrosion at tube rolls was observed (Fig. 2.9). 

Tubes were almost plugged with deposits (Fig. 4.30A and B). The deposits contained almost 40% sulfur by weight. Hydrocarbon in-leakage had occurred through small cracks that originated on internal surfaces beneath deposits. 

Isolate and identify possible sources of in-leakage, such as perforated heat exchangers or makeup water contamination. 

Close examinations revealed that metal loss was confined to in. (13 mm) of the internal surface at the inlet end (Fig. 11.25). Note the two perforations near the bottom of the photograph. Generally, the metal loss was confined to the region within the tube sheet, but occasioneJly perforations occurred just beyond the tube sheet, resulting in leakage of cooling water. 

It should be noted that for values of s/c greater than 15, the reduction in leakage attained by using a staggered labyrinth is very small. The reduc... 

Glove boxes have been described in Section 10.2.3.6 as systems with only exhaust air. There are glove boxes with both supply and exhaust air openings inside the closed volume (see Section 10.4.6.4) that look and function like the boxes described earlier. The use of supply air directly to the closed volume means that the control of the flow rates must be very accurate. Otherwise the box may be at a higher pressure than the surrounding areas, resulting in leakage of contaminants. 

Secure locking nuts Operation omitted (08) Locking nuts left unsecured None Failure to secure locking nuts could result in leakage during transportation... 

Air in leakage, depending on the quantity, can create an explosive mixture in some process reaction systems therefore, the system should be tested for air leaks and kept as tight as practical. 

Pounds/hr air -I- non-condensables -I- process released air + process released non-condensables)/Hr = Air in leakage, Ib/hr (6-7)... 

The hot well is the sump where the barometric leg is sealed. It must be designed to give adequate cross-section below the seal leg and for upward and horizontal flow over a seal dam or weir. At sea level the hot well must be a minimum of 34.0 ft below the base of the barometric condenser. For safety to avoid air in-leakage, a value of 35-36 ft is used. For an altitude corresponding to a 26-in. Hg. barometer, the theoretical seal height is 29.5 ft actual practice still uses about 34 ft. 

Buffering media supplied directly from customer s source. Filter or pressure regulator may be required. In cases where inlet pressure is below atmosphere and in-leakage of ambient is undesirable, buffering media may be process gas from compressor discharge. 

Applications where positive sealing is necessary. No in-leakage of ambient air and no out-leakage of process gas. Specially suited for higher pressure applications. 

Process gas may be used as buffering media, if clean and dry, to avoid in-leakage of ambient for exhauster duty. 

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