Cylinder purging

When shutting down the heaters should be switched off and the cylinder purged clean. 

Prior to decommissioning, cylinder contents shall be verified and removed and the cylinder purged with an inert gas. The decommissioning process should destroy the cylinder, rendering it unusable. No liquid or solid residues should be present. All materials that may have been absorbed into, or deposited onto the walls of the cylinder should be removed prior to disposition of the cylinder if they present a health or environmental hazard. 

When using extremely hazardous gases, it is advised that a separate cylinder purge gas source be employed, not the same inert source as used elsewhere in the plant, since only one cylinder would be affected if process gas should accidentally backfill a cylinder. The most convenient designs have the process gas panels and their associated purge gas panel all in the same cabinet. 

Co., .- w,...ors should be stopped periodically to check for wear. The inspection may occur every few months. To accomplish this the compi sor must be stopped, blocked in, and purged if the gas is hazardous valve is removed from the cylinder and a feeler gauge inserted throi the valve opening. A measurement is taken between the lower side of piston and the cylinder wall. 

Polycarbonate melts adhere strongly to metals and if allowed to cool in an injection cylinder or extrusion barrel may, on shrinkage, pull pieces of metal away from the wall. It is therefore necessary to purge all equipment free of the resin, with a polymer such as polyethylene, after processing. 

Gas storage cabinets are designed to contain one to four gas cylinders. The cylinders are connected to a gas distribution system which is also contained in the cabinet. Very sophisticated systems are available from cabinet manufacturers. These may include automatic or semiautomatic change-over capabilities, fire sprinklers, purging systems, and gas detection systems which may include alarms and automatic shutoff. Point-of-use scrubbers may also be incorporated into the design, depending on the gas being used (see Fig. 10.43). 

About two-thirds of the N2 produced industrially is supplied as a gas, mainly in pipes but also in cylinders under pressure. The remaining one-third is supplied as liquid N2 since this is also a very convenient source of the dry gas. The main use is as an inert atmosphere in the iron and steel industry and in many other metallurgical and chemical processes where the presence of air would involve fire or explosion hazards or unacceptable oxidation of products. Thus, it is extensively used as a purge in petrochemical reactors and other chemical equipment, as an inert diluent for chemicals, and in the float glass process to prevent oxidation of the molten tin (p. 370). It is also used as a blanketing gas in the electronics industry, in the packaging of processed foods and pharmaceuticals, and to pressurize electric cables, telephone wires, and inflatable rubber tyres, etc. 

Figure 12-2Q. Cast or nodular iron cylinders for pressures to 1,500 psi. Note double distance-pieces (left, vented or purged, to prevent oil and process gas from leaking past the shaft and right-end fixed clearance pocket). (Used by permission Bui. 85084, 1992. Dresser-Rand Company.)...

When packings are purged with air or other gas, the manufacturer should specify the quantity passing into the cylinder and out to the air. Accessibility of packing, bearings, and valves should be identified on drawings for review at the time of bid evaluation. 

Code of Practice No. 14, Hoses for the transfer of LPG in bulk. Installation, inspection, testing and maintenance. Code of Practice No. 15, Valve for LPG cylinders. Part 1. Safety valves for LPG cylinders. Part 2. Outlet valves for butane cylinders - quick coupling types Code of Practice No. 17, Purging LPG vessels and systems... 

Modem designs fitted with non-retum valves through which the plasticised rubber compound passes into the injection cylinder portion are capable of giving precise shot volume. The non-retum valve is activated by the injection pressure. The injection ram/non-retum valve unit ensures complete purging of the injection chamber. 

Traditionally, inerts have been obtained from sources such as high-pressure gas cylinders or tube trailers or through evaporation of cryogenic liquids from bulk tanks. Other sources of inerts include (NFPA 69, Standard on Explosion Prevention Systems, National Fire Protection Association, 2002 FM Global, Loss Prevention Data Sheet 7-59, Inerting and Purging of Tanks, Process Vessels, and Equipment, 2000)... 

Fig. 1.10. Transfer of air-sensitive liquids from metal cylinders, (a) A three-way metal stopcock constructed for use with syringes may be modified by the addition of a threaded fitting so that it mates with a lecture bottle. The side inlet is used to purge the apparatus initially and to blow liquid out of the syringe needle at the completion of the transfer. The cylinder is put under a low pressure of inert gas before the transfer is begun, (b) Sometimes air-sensitive liquids are sold in siphon-type cylinders, and the liquid from such a cylinder can be dispensed as shown here. As with the previous example, inert gas is used to force the liquid out of the cylinder.

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