PROCESSCONSULTINGSERVICES, INC.

Process Notes

Failure to design the vacuum unit as an integrated system will invariably result in unsatisfactory yield and poor product quality (high vanadium, nickel, microcarbon, or asphaltenes), and ultimately, an unscheduled shutdown. To avoid these revamp problems the charge pump, fired heater, transfer line, column internals and ejector system must all be evaluated and designed as a unified whole so that critical variables – heater outlet temperature, coil steam injection rate, flash zone temperature and pressure – may be properly balanced. A thorough understanding of requisite theory is necessary and computer modeling is useful but theory and simulations are not enough. Process flow sheet models must be calibrated using actual field data, and appropriate allowances made for less-than-ideal equipment performance. One cannot rely alone on manufacturers’ specification sheets because only rarely will they reflect actual field-tested perfor-mance. Only by exercising such caution can under-utilized equip-ment be exploited and investment

For a detailed discussion of how vacuum

unit equipment design influences

temperatures and pressures ask for

Technical Paper 168.

Charge pump-through-ejector: Single System

A single integrated vacuum system

3400 Bissonnet Suite 130Houston, Texas 77005USA

Ph: [1] (713) 665-7046Fx: [1] (713) 665-7246info@revamps.comwww.revamps.com

The critical link: heater-ejector system

in new equipment minimized. An experienced revamp engineer will then be able to optimize critical temperatures and pressures to ensure satisfactory yields, product quality and length of run.

FiredHeater

Transfer Line

Ejector

Hot Well

LVGO

HVGO

ShortResidue

Steam

ChargePump

Peak Film Temperature

ExcessiveCracking

Line

Oil

Res

iden

ce T

ime

Today many refiners have set 4-5 year run length and higher HVGO TBP cutpoints as goals. Increasing heater outlet temperature to achieve these goals requires all equipment to work together to keep cracked gas low,

for if an ejector system is incapable

of handling higher cracked gas

production from a 10-15ºF increase

in heater outlet temperature, column

flash zone pressure will increase

and gas oil yield can actually be

reduced. Hence, not only must the

ejector system be sized properly

but the heater must be well designed

to minimize both cracked gas and

coke make – and the two must be

balanced. Contrary to conventional

wisdom this means designing

upstream: from the ejector system

back to the heater (and all the way

back to the charge pump to ensure

total unit performance.) For the

designer to accomplish this, base-

line and revamp process models

must reflect existing equipment

design including all shortcomings.

This entails making a thorough test

run. Following these guidelines

can effect a significant increase in

revenue – the bottom line goal of

every revamp.

Ejector system performance curves and

real-world problems are covered in

Technical Papers 114 and 160, while

vacuum unit fired heater fundamentals

and common causes of heater coking

are discussed in Technical Papers

148 and 170.

ENQUIRY NO 212www.ptqenquiry.com

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