2000 Hook-up Book

Flash Steam

Flash Vessel Configurations Flash vessels can be either horizontal or vertical. For flash steam recovery (pressurized receiver) the vertical style is preferred because of its ability to provide better separation of steam and water.

SYSTEM DESIGN

Figure 52: Flash Vessel Configurations

Horizontal Flash Vessel

Vertical Flash Vessel

Flash steam outlet or vent pipe

Flash Steam outlet or vent pipe

Condensate inlet

Diameter

Diameter

Length

Length = 2 x diameter or 24" minimum

Height = 3 x Diameter or 36" minimum

Condensate inlet

35% of height

Condensate outlet

For proper installation of flash vessels, controls and traps refer to Figures II-76, 77, 78, 79, 80, 81, 82, 83 (starting on page 120)

Condensate outlet

Case in Action: Sour Water Condenser-Reboiler Temperature Control

Solution A 3" x 2" PPF with 2-1/2" FTB 125 pump/trap combination was designed into the new project as was a VS 204 air vent. The installation was immediately successful. Benefits • With faster start-up, it came up to temperature faster than any other comparable unit, to date, at the refinery. This improves productivity. • The feed rate is higher than designed because the unit is able to operate efficiently at any degree of turndown. • Installation cost is several times less costly for the pump/trap combo than traditional level control system that would otherwise have been used. • Maintenance cost is lower, through elimination of elec tric/pneumatic controls and electric pumps used in a traditional level control system.

The sour water condenser-reboiler is an important element in a refinery sulfur unit. Though the configuration/design will vary with the specific process used, the purpose and priority remain the same. Process water contaminated with ammonia and hydrogen sulfide gas (H 2 S) is stripped of those compounds for reuse. The remaining stream of con taminants goes to waste treatment. The process depends on accurate temperature control of the steam heated con denser-reboiler. 40 psig steam is supplied through a modulating con trol valve. Condensate is lifted 15 feet from the outlet at the bottom of the vertical condenser-reboiler to the overhead condensate receiver tank, which is maintained at 20 psig. Process load fluctuations and resultant turndown on the modulating steam control valve would have created a STALL situation, unacceptable process temperature con trol and reduced throughput.

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