Q & A > Question Details
We have a 50,000 bbl/d capacity crude unit designed for Iranian light crude oil. The main crude column needs to be replaced due to ageing. We would like to take this opportunity to revamp to unit capacity as well to about 70,000 bbl/d. Based on a previous study carried out, the unit capacity can be increased up to 70,000 bbl/d by installing a pre-flash drum before the charge heater. However, now we have to replace the main column. In another study carried out, it has been identified that the some modifications are required to be done to the charge heater such as re-tubing with different metallurgy and changing the passes from 1 to 2 etc. if the unit capacity is increased up to 70,000 bbl/d (without a pre flash drum).
I would like to know whether installation of straight 70,000 bbl/d capacity column or installation of same capacity 50,000 bbl/d along with a new flash drum (to avoid charge heater modifications) is more economical.
18/03/2017 A: Ganesh Maturu, Self, maturu.ganesh@gmail.com
As per theory, it gives advantage and margin in heater with preflash drum option. However following points to be considered before considering preflash drum.
1.If there is a preflash drum, we need high heater outlet temperature to maintain same overflash at the crude column flash zone. Remember heater duty may be lower but required outlet temperature will be higher. Reason for requirement of high outlet temperature is that lighter partial pressure increases at heater outlet as all the lighter material removed in preflash drum. To maintain required flashing, we need to increase heater outlet temperature. So first check what is the increase in heater outlet temperature.
2. Increasing heater outlet temperature increases coking tendency in heater and its operation.
3. Check that sufficient velocity is maintained in heater as vapor phase is reduced in heater in preflash option.
4. Heat transfer coeffient in heater tubes reduces as the velocity is reduced in heater tubes.
5. Coking issues increases in heater because of all the above reasons mentioned. Need to consider preflash option case by case basis. There is no straight and direct answer.
20/01/2017 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
I agree completely with Mr. Vetters. I am wondering, however, why the upgraded tube metallurgy would be needed in one case and not the other, assuming the same crude.
20/01/2017 A: Satyalal Chakravorty, Sr Consultant, satya1354@yahoo.co.in
Scheme with pre-flash column is the best and economic option and implemented in many refineries. Merits are: 1) main column can be changed with same capacity , 2) reduction in furnace duty resulting in savings due to energy conservation, 3) reduction in vapour traffic /less overhead load in main column allowing to push more T’put. But strategy would be to have both pre-flash column & higher capacity main-column with appropriate metallurgy ( also for furnace) to process opportunity crudes & enabling capacity augmentation & flexibility . Check the foundation & side strippers' capability and also the flare load for which it is essential to carry out HIPPs.
19/01/2017 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
There are too many unknowns which can have a significant impact on the right answer for anyone to be able to answer your question without some sort of engineering study. There are multiple different preflash options that vary significantly as far as cost and benefits. The plot area available and where equipment will go are all major factors. How you treat the project options as far as capital vs. maintenance can also be important. If a new 70,000 bpd column can go back in on the same foundation as the existing tower, that will reduce cost significantly compared to needing to put the tower on a new foundation. The different options may have different turnaround durations needed to complete the project, so downtime economics are important. Replacing heater tubes may be more expensive, but going to a different metallurgy may reduce corrosion and give you flexibility to process lower cost, higher margin crudes. Cost is an important factor to consider but not the only one. This sampling of issues, which is far from complete, illustrates why an engineering study is needed to reach a good decision.