Chemical and Petroleum Engineering, Vol. 36, Nos. 9–10, 2000

A SAFETY VALVE FOR CRYOGENIC MEDIA

V. M. Krasil’shchikov

UDC 621.646.4:621.6.036

There is a problem over a safety valve for a cryogenic medium in that it is difficult to provide slide sealing, as icing occurs on the sealing surfaces (slide and saddle), on account of the flow of the cryogenic medium (liquefied gas) through the saddle (hole). The pressure beyond the valve falls sharply and there is rapid expansion of the working medium, which transfers from one state of aggregation to another: from liquid to solid in the form of an ice on the sealing surfaces of the slide and as a snowy mass in the output cavity. To eliminate this icing, one needs a certain counterpressure beyond the valve, which involves an additional energy source and expense. Also, the carrying capacity is reduced and it is sometimes necessary to use two valves instead of one. In the [1] design, the icing problem is resolved by installing a washer in the exit cavity whose diameter is such as to give rise to a counterpressure there (up to the washer) when the valve operates, but it reduces the carrying capacity and does not eliminate partial icing on the sealing surfaces. This also affects the closure time (the time to recover the required sealing) and causes erosion in the sealing surfaces, with the result of premature failure. The advantages of the proposed design [2] developed at the Central Special Designs Office are that it excludes icing on the slide and provides the required carrying capacity without an additional source of energy to produce the counterpressure beyond the valve. The new design (Fig. 1) contains the body 1, seating 3, and slide 9. The sleeve 4 is concentric with the seating and slide and has holes 6 on the side surface. There are the annular gaps 2 between the sleeve, slide, and seating. The sleeve has an unpierced section 5 opposite the sealing surfaces of the seating and slide, while the holes 6 are placed symmetrically on opposite sides of the unperforated part, which has a conical rim on the inside, while concentrically with the sleeve there is the annular screen 8 having annular gap 7 from the sleeve.

Fig. 1. Safety valve for cryogenic media.

Reduktor Scientific Center. Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, No. 9, p. 45, September, 2000. 560

0009-2355/00/0910-0560$25.00 ©2000 Plenum Publishing Corporation

When the pressure at the inlet rises to the complete opening pressure pco, the slide lifts off the seating, and the medium emerges from the seating and strikes the conical rim on the unperforated part of the sleeve, where it is divided into two flows, which pass through the annular gap 2 between the seating and the slide and through the holes 6. The total working area of the holes 6 on either side of the unperforated part exceeds the area of the annular gap 2, so the pressure drop and correspondingly the temperature drop occur in the holes 6 far from the surface of the seating and slide, i.e., the probability of icing on the sealing surfaces is reduced. This design is intended to protect pipeline systems and vessels handling low-temperature (low-boiling) media such as liquefied gases to prevent excessive pressures without counterpressure or with slight counterpressure up to 0.1 pw at the instant of operation. The new design can be used in any cryogenic system with liquefied gases such as aircraft equipment, filling railroad tankers with liquid gases, in various systems operated in the Far North or Antarctica, and in the gas, ammonia, and refrigeration industries, such as in turbines of cooling type.

REFERENCES 1. 2.

Author’s Certificate 1373951, IPC F16k17/04, A Safety Valve. Author’s Certificate 1686242, IPC F16k17/06, A Safety Valve.

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