10 replies to this topic

[Robert74]

Reduced crude oil (RCR) of flow rate 35,000 BPSD is required to be processed in vacuum distillation tower.
- What is the estimated overhead vapor flow rate at top of tower?
- Is this flow required for selecting the suitable liquid Ring vacuum pump?
- vacuum pump will rise pressure a little more than atmospheric 100 KPa, what is the estimated power?
- Rising pressure from few kPa (around 5 kPa) to 100 kPa will produce much heat, is that heat will be absorbed by pump liquid? How much is that heat?

Thank you

[breizh]

Hi Robert ,

Let you consider the resource attached to support your work .

Hope this is helping you .

 

Breizh

[Robert74]

Dear Sir, Many thanks for your reply.

[shvet]

 - What is the estimated overhead vapor flow rate at top of tower?

 

Column overhead vapor flow (in kg/h) = air leaks + cracking gases + steam (from feed and bottom steaming both)

Vapor flow (in act. m3/h) = vapor flow (in kg/h) / vapor density (act. m3/kg)

Vapor density depends on composition, temperature and pressure (on top of column or in pump suction). Accurate hydraulic calculation is exhorted since pressure drop has a major impact on vapor density.

For air leaks see equation 7.59 and table 7.11 in Couper, Penney, Walas "Chemical Process Equipment Selection and Design" 2012.

For gases which are produced in charge heater you should do your own estimation. Crude oil residue cracking rate strongly depends on temperature and residence time in high temperature zone.

For steam flowrate you should see column material balance.

 

 

- Is this flow required for selecting the suitable liquid Ring vacuum pump?

 

Depends on your vacuum system.

Do you have a precondeser upstream your vacuum system? It can help you to reduce vapor flow by water condening and by this way total required vacuum system cost and consumption.

 

 

- Rising pressure from few kPa (around 5 kPa) to 100 kPa will produce much heat ... How much is that heat?

 

Ask a process engineer to simulate your column and vacuum hydraulic circuit. If you have not one you should be consulted by experienced engineering company.

 

P.S. For high capacity vacuum column I (and Lieberman too) would recommend diesel ejectors instead of liquid ring pump. For more information see para. 26.18 and 26.19 in Lieberman's Process Equipment Malfunction.

Edited by shvet, 30 October 2016 - 11:23 PM.

[Robert74]

Dear Mr. Shvet

I'm impressed about the diesel ejector which might reduce power or heat requirements of vacuum system considerably. Unfortunately, I could not reach your reference book. You are kindly requested to help me get some websites that describe this method.

Many Thanks

[shvet]

 I'm impressed about the diesel ejector which might reduce power or heat requirements of vacuum system considerably.

 

No no. Diesel ejector can or can't reduce power consumption. For this issue you should be consulted by an ejector manufacturer. This device is much more simplier and by this way more reliable as Lieberman says. I have the same experience as Lieberman. Diesel ejector is a device some kind of "switch on and forget" it means an operator has no way to misoperate or break it down.

Extraction from Lieberman

Extraction from Walas

 

There is a lot of liquid ejector manufacturers you should contact with one of them. Unfurtunatly I can't help.

Edited by shvet, 31 October 2016 - 11:28 PM.

[Robert74]

Dear Mr. Shvet,

Thank you very much.

[shvet]

For more information how to do first approximation of cracking gases see fig. 13-4 chapter 13 in Lieberman's Troubleshooting Process Operations 1991. There also you can find more useful information about vacuum columns and vacuum systems.

[Robert74]

Dear Mr. Shvet,

Well noted. Your replies are highly appreciated  .

[breizh]

Hi Robert ,

Litterature about ejectors , to support previous answers.

 

Good luck

Breizh

[Robert74]

Dear Mr. Breizh,

Many thanks for your overall documentation of Ejector. It was great help  .

Edited by Robert74, 09 November 2016 - 06:24 AM.