Drum design

Ellison has published an extremely important factor for steam drum design called the Drum-Level-Stability Factor. As manufacturers have learned how to increase boiler design ratings, the criteria for steam drum design have lagged. The three historical steam drum design criteria have been ... 

An alternate method not used too much at this time is the drum design. The drum construction is somewhat different from the disc, in that the rotor body is of cylindrical construction. By using the hollow drum, conical roots, of bolted construction, can be used for the rotor, again, allowing for stagger adjustments to fine tune the axial compressor to the application if the need arises. The setting is done to a gauge at the factory, as with the stators. 

The blowdown drum design temperature is set by the extremes of emergency operating temperature which can result from any of the streams tied into it. If materials are handled at temperatures below 15 C, or if they can autorefrigerate to below 15 C, a minimum design temperature must also be specified. 

The drum design pressure should be 345 kPa gage, unless the drum is connected directly to the flare (without a seal drum), in which case the design pressure of the blowdown drum should be 1030 kPa gage. 

A vacuum pump seal drum design which provides a liquid seal (hydraulic flame arrester) to mitigate flame propagation backward into the vacuum system. The seal liquid is an organic stream (mostly Cg aromatics) that comes from the vacuum pump discharge drum overflow. 

Compressor Suction and Discharge Drums Design Method—Acoustic Low Pass Filters... 

Many types of WT boiler are of a one-drum design, but where mud drums are fitted, these should also be inspected. As its name suggests, much of the mud, sludge, dislodged scale particles, and other general debris in the boiler ends up in the bottom or mud drum. This material should be removed and the drum inspected for underdeposit corrosion, wall thinning, erosion, and other problems. 

Liquid seal drums Emergency vent streams are usually passed through a liquid seal, commonly water, before going to the flare stack. The liquid seal drum is usually located downstream of the knockout drum, and some vendors designs include them in the base of the flare stack. A liquid seal drum is used to maintain a positive pressure in the vent header system and upstream system. It also reduces the possibility of flame flashbacks, caused when air is inadvertently introduced into the flare system and the flame front pulls down into the stack it also acts as a mechanical damper on any explosive shock wave in the flare stack. Figure 23-58 is a schematic of a typical flare stack liquid seal drum, designed per API RP 521 criteria. 

Horizontal drum design—an example The following example from API-521, p. 47 (1st ed.) will serve to illustrate the application of the equations that have been developed ... 

The design-base particle diameter to be separated in the vapor space should not exceed the pad-disengage-mt-nt droplet diameter. 1). To be on the safe side, a maximum droplet diameter should be limited to 400 pm. In horizontal drum design, the mesh pad should be regarded as a polisher for removing small droplets not separated in the vapor space—i.e., as a secondary mechanism in vapor-liquid separation... 

Effluents from both furnaces are combined and enter the soaker this is a large vertical drum designed to provide additional residence time for conversion under adiabatic conditions. Effluent at 500 psig and 915°F enters the bottom zone of the main fractionator. 

If there is a question of losing a product such as an amine chemical, say diethanolamine, in an amine gas absorber overhead KO vessel, use this recommended 150-pm liquid particle sizing in the gas phase. I have personally witnessed hundreds of thousands of dollars of annual amine chemical losses in numerous amine gas-treating plants due to poor overhead KO drum design. Spend a few more very well justified dollars at design time and realize a payout of only a few weeks for this added expense I have witnessed 1.5 lb amine loss per million scf gas processed in an amine absorber overhead KO drum. For a 150-mmscfd gas plant absorber, 355 days per year production, at 1.20 per pound amine chemical cost, this computes to a 95,750 yearly loss. This is not a new discovery, as many an amine absorber installed in the 1950s had several trays in the tower top section dedicated to a water-wash section. I am confident that equal losses can be computed for other chemicals or petroleum products in similar fractionation overheads. 

With a reflux-drum design temperatures set at 120 °F, the required pressure depends on the composition of the overhead and whether the distillate product is removed as a liquid or as a vapor. In the former case, the reflux drum would operate at the bubblepoint pressure at 120 °F. In the latter case, the reflux drum would operate at the dewpoint pressure at 120 °F. There is no difference in these pressures if the overhead is a single pure component. If the overhead is a mixture of chemical components, the bubblepoint pressure is larger than the dewpoint pressure. If the volatilities of the components are quite different, running with a total condenser (bubblepoint pressure) can require a much higher pressure than running with a partial condenser. This is true even if some of the distillate product is taken off as liquid and some is taken off as vapor. 

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