Liquid wet vessel

The general guidelines outlined in API RP 521 [2] should be followed for the design of protechon against fire. Both liquid- and gas-filled vessels are to be analyzed for protection against fire. For liquid wet vessels, the required... 

The heat input into a liquid wet vessel depends upon the wetted area of the vessel. The following guidelines are used to estimate the wetted surface area ... 

Heat input to a vessel containing only gas is different from a liquid wet vessel, and the following procedure is normally used to design pressure protection of a gas-filled vessel ... 

Vertical Drums - The wetted vessel surface within 7.5 m of grade, based on normal high liquid level, is used. If the entire vessel is 7.5 m or more above grade, then only the surface of the bottom head need be included. 

The safety relief valve will protect the liquid-wetted areas of the storage vessel. The metal temperature will not significantly exceed the liquid temperature, which will be absorbing the latent heat of vaporization. However, above the liquid line no such cooling will take place. The metal temperature at the top of the vessel could therefore exceed safe limits. 

Liquid-full vessels (such as treaters) operate liquid full. Therefore, the wetted surface would be the total vessel surface within the height limitation. 

MENISCUS. The curved siirlaee or a liquid, particularly noticeable in vessels ol tubes of small diameter and due in the surface tension of the liquid. If the liquid wets the containing vessel, the meniscus is concave otherwise it is convex. The meniscus of mercury in glass is convex. 

In the method of the Jailing meniscus a liquid-wetted tapering tube is placed vertically in a reservoir, as in fig. 1.26. Inside the tube liquid is held by the capillary pressure. The tube is now moved upwards - or the liquid in the vessel downwards - to increase the hydrostatic pressure head, and this is continued until the liquid in the capillary collapses. From the hydrostatic head the Laplace pressure is obtained and from that the surface tension. The method is very simple and may be considered as the counterpart of the maximum bubble pressure technique there are also similarities to the situation sketched in fig. 1.8a. The idea is rather old... 

Liquid in liquid-fdled vessels exposed to direct or radiated heat from a fire will vaporize. The heat required to accomplish this will limit the shell temperature of the tank to only a slight rise. The amount of liquid vaporized depends on the rate of heat input from the fire and the relieving temperature. This can be determined by calculating the heat input to the wetted surface of the vessel and dividing this by the latent heat of vaporization. 

It is possible to calculate the capillary rise of a liquid with density p into a capillary tube (i.e., with inner diameter less than 1 mm for water) which is immersed in a large vessel of the liquid wherein the surface is sensibly flat, that is, if the inner radius is small and the pressure difference large. Suppose that the liquid wets the tube wall and forms a meniscus that is concave upwards (see Figure 20.5). The pressure immediately below the meniscus can be calculated balancing the pressure across the meniscus ... 

Carbon disulfide [75-15-0] is a clear colorless liquid that boils at 46°C, and should ideally be free of hydrogen sulfide and carbonyl sulfide. The reaction with alkaU cellulose is carried out either in a few large cylindrical vessels known as wet chums, or in many smaller hexagonal vessels known as dry chums. In the fully continuous viscose process, a Continuous Belt Xanthator, first developed by Du Pont, is used (15). 

Since static discharges frequently occur at the liquid interface as liquid drains from the wetted wall, a vapor ignition hazard may also exist [ 157,159]. These discharges may be either brush types or PBDs (2-6.2 and 2-6.5). In 1997 it was concluded that Manufacturers have so far not paid attention to requests by the operators of enamel apparatus for a coating which is completely or partially capable of dissipation [159]. However, this situation is believed to be changing and it might now be possible to specify special static dissipative coatings for the vessel and stirrer. 

Packed Towers (also known as wet-scrubbers) A packed tower is a vessel that is filled with some suitable packing material. The liquid is introduced at the top of the tower and flows down through the packing to the bottom, and in so doing, exposes a large surface area to contact with the gas. The gas may be introduced at either end of the tower since the gas and liquid flows may be either co-current or counter-current. The counter-current operation is most commonly used. 

Note that the wetted surface A used to calculate heat absoiption for a practical fire situation is normally taken to be the total wetted surface within 7.5 m of grade. "Grade" usually refers to ground level, but any other level at which a major fire could be sustained, such as a platform, should also be considered. In the case of vessels containing a variable level of liquid, the average level is considered. Specific inteipretations of A to be used for various vessels are as... 

The surface area of a vessel exposed to fire which is effective in generating vapor is that area wetted by its internal liquid contents. The liquid contents under variable level conditions should ordinarily be taken at the average inventory, for example See note below. 

J. Knockout drums (vessels) usually operate with only a small amount of liquid. Therefore, the wetted surface would be in proportion, but to maximum design liquid level. 

Note This author s suggested determination of A, values may be more conservative and not conform exactly to Code [33a.33c] recommendations. The Code [33a, Part 1, Sect D, Par. D.4] reads, to determine vapor generation, only that portion of the vessel that is wetted by its internal liquid and is equal to or less than 25 feet above the source of flame needs to be recognized. ... 

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