Fired vessels

Figure 17-6. Hydrocarbon pressure vessel or protected fired vessel in a nonenclosed, adequotely ventilated area. (Reprinfed wilh permission from API RP 500.)...

W. Y. Wong, Fires, Vessels, and the Pressure Relief Valve, Chemical Engineering (May 2000). 

Hong Kong Harbor, Oil Tanker, Fire Vessel collided with another and fire ensued 3 Fatalities... 

The effect of fire exposure is predictable for pressure vessels, such as, spheres, spheroids or horizontal vessels. If no fire protection is provided or is not adequate or inoperative, the vessel will probably fail catastrophically in a prolonged fire. Vessel failure typically results from excessive metal temperature weakening the tank wall above the liquid level of its contents. This weakening can occur within a few minutes if the initial liquid level is significantly belowthe maximum flame height and the flames impinge on the shell. 

While the ASME has two different sections, Section I for fired vessels and Section VIII for unfired vessels, the PED encompass all these conventional vessels (excluding nuclear applications). Therefore, according to PED, unlike with ASME, these above considerations on accumulation and multiple valves installation also apply to boilers and other fired vessels as well as for unfired vessels as long as the pressures are higher than 0.5 barg. 

Example of PED categories fora fired vessel at temperatures above 110°C... 

Wong, W.Y. Fires, vessels, and the pressure relief valve. Chem. Eng. 2000, 84-92. 

Relief systems are expensive and introduce considerable environmental problems. Sometimes it is possibly to dispense with relief valves and all that comes after them by using stronger vessels, strong enough to withstand the highest pressures that can be reached. For example, if the vessel can withstand the pump delivery pressure, then a relief valve for overpressurization by the pump may not be needed. However, there may still be a need for a small relief device to guard against overpressurization in the event of a fire. It may be possible to avoid the need for a relief valve on a distillation column... 

In case of a major disaster, one platform in a region will be equipped to act as a control centre from which rescue operations are co-ordinated. Evacuation routes will be provided, and where large complexes are clustered together, a standby vessel will be available in the region to supply emergency services such as fire fighting and rescue. 

Based on these considerations, the conformity assessment tables comprise 4 tables for vessels and 4 tables for piping. A further table relates to fired or otherwise heated equipment. Specific procedures are set out for the assessment of assemblies and of safety accessories. 

Carbon disulphide should never be used if any alternative solvent is available, as it has a dangerously low flash-point, and its vapours form exceedingly explosive mixtures with air. Ether as a solvent for recrystallisation is much safer than carbon disulphide, but again should be avoided whenever possible, partly on account of the danger of fires, and partly because the filtered solution tends to creep up the walls of the containing vessel and there deposit solid matter by complete evaporation instead of preferential crystallisation. 

If a liquid which is being heated in a beaker or a conical flask catches fire, it is frequently sufficient to turn off the gas (or other source of heating) below and then at once to stretch a clean duster tightly over the mouth of the vessel. The fire quickly dies out from lack of air, and the (probably valuable) solution is recovered unharmed. 

For temperatures up to 100°, a water bath or steam bath is generally employed. The simplest form is a beaker or an enamelled iron vessel mounted on a suitable stand water is placed in the vessel, which is heated by means of a flame. This arrangement may be used for non-inflammable liquids or for refluxing liquids of low boiling point. Since numerous liquids of low boiling point are highly inflammable, the presence of a naked flame will introduce considerable risk of fire. For such liquids a steam bath or an electrically-heated water bath, provided with a constant-level device, must be used. If the laboratory is equipped with a... 

A small fire (for example, hquid in a beaker or flask, or an oil bath) may usually be extinguished by covering the opening of the vessel with a clean damp cloth or duster the fire usually dies out from lack of air. For larger fires, dry sand may be employed. Buckets of dry sand should be distributed round the laboratory and should be strictly reserved for this purpose. Most fires on the laboratory bench can be smothered by... 

CeUular polymers are also used for pipe and vessel insulation. Spray and pour-in-place techniques of appHcation are particularly suitable, and polyurethane and epoxy foams are widely used. Ease of appHcation, fire properties, and low thermal conductivity have been responsible for the acceptance of ceUular mbber and ceUular poly(vinyl chloride) as insulation for smaller pipes. 

The newer open-ceU foams, based on polyimides (qv), polyben2imida2oles, polypyrones, polyureas, polyphenylquinoxalines, and phenoHc resins (qv), produce less smoke, are more fire resistant and can be used at higher temperatures. These materials are more expensive and used only for special appHcations including aircraft and marine vessels. Rigid poly(vinyl chloride) (PVC) foams are available in small quantities mainly for use in composite panels and piping appHcations (see Elame retardants Heat-RESISTANTPOLYA rs). 

Distillation. This is the point at which refining begins and was the first method by which petroleum was refined. Originally, distillation (qv) involved a batch operation in which the stiU was a cast-iron vessel mounted on brickwork over a fire and the volatile materials were passed through a pipe or gooseneck which led from the top of the stiU to a condenser. The latter was a coil of pipe, or a "worm" (hence the expression worm end products), immersed in a tank of miming water. 

The areas for the reactors and storage tanks should be separated by fire walls, and must be adequately ventilated. Storage tanks should be blanketed by inert gas. A slight positive pressure of inert gas should be maintained in the reactor or storage tanks during the discharging of the resin or resin solution to prevent air from being sucked into the vessel to form an explosive mixture with the solvent vapor. 

Methyl bromide is nonflammable over a wide range of concentrations in air at atmospheric pressure and offers practically no fire hazard. With an intense source of ignition, flame propagation within a narrow range from 13.5 to 14.5% by volume has been reported. The material has no flash point. Thermal decomposition in a glass vessel begins somewhat above 400°C. 

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