Crude unit valves

A common troublespot in refinery crude units is the desalter relief valve, which often relieves into the crude column. Lifting of this relief valve has caused pressure surges. Guidelines 4 and 5 are important with regard to the location of this valve (296). It is best to have this relief valve discharge elsewhere. 

The operating superintendent of a medium-sized crude unit obliterated all of the above difficulties. He tore out the valve trapout tray and drawoff pan. A new, all-welded pan was installed. Several large chimneys allowed for vapor passage. The pan was seal-welded to the tray ring and the problem was corrected. (Note, in large-diameter towers, a seal weld can fail due to thermal expansion.)... 

Summarize the degree of fractionation between products. A table or curves comparing current operations with past or design valves is instructive. Figure 27-2 shows how to present such data for a crude unit. 

Fractionation problems same as crude unit Water pockets upset trays Check steam under relief valves... 

Clean steam condensate is the best source of wash make-up water. Condensate collected from fractionator reflux drums is sometimes acceptable. River, lake, or well water with high total dissolved solids (TDS) is bad. These solids can precipitate out on the mix valve and cause excessive pressure drop. In one refinery, using untreated river water in a crude-unit desalter for a few months reduced desalting efficiency from 90% to 65% salt removal. 

Both the failure of the isolation valves to hold and the difficulty in draining the system were due to solid build up in the circuit. In the previous two-year period, the refinery had changed its crude feedstock resulting in operating difficulties on the unit desalter. Carryover of salts led to accelerated corrosion in the crude column and associated piping circuits. 

Especially on sulphur recovery units and heavy crude oil service, there could be excessive seat leakage of 316 SST trims caused by sulphide corrosion/pitting. In this case retrofit the valve with, for instance, an Inconel 718 nozzle and disc insert (with high nickel content). In any case, make sure that a proper material selection for the service is used. 

II) Turbine (12) Rectification column (pressure section) (13), (16), (19) combined condenser-evaporator unit (14) Rectification column (low-pressure section) (15) Crude argon column (17) Pure argon column (18) Reboiler (20) Ar- process pump (21) Internal compression pump (22) Throttle valve. 

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