6 replies to this topic

[adeliry]

Dear,

we run a packed column under vacuum condition to separete "Ethyl benzene+toluene+benzene" as top product and "Styrene monomer" as other, because of styrene can polymerized in high temperature without any initiator, there for we use DNBP as polymerization inhibitor, pressure in column is 280 mmHG abs and temperature in column is 112 oc on top and 120 oc in bottom.

because DNBP is decomposed over 60 oc and decomposing rate is maximized around 122 oc, there for we think if we decrease the pressure then we can wok with lower temperatures, may be pressure decrease will not help us about separation and also increase the load of condenser but the condenser capacity is high enough that we can decrease the pressure.

I want know what is the other limitations to decrease the pressure in vacuum columns other than condenser and vacum pump capacity? is it caused to high vapor velocity and flooding or......?

if we can run column in 116-118oc in bottom it can save us DNBP ussage up to 50 percent.

[Zauberberg]

Hydraulic capacity of tower internals will likely be the first bottleneck, assuming that you're having the capability to pull higher vacuum. The tower will be operating closer to jet flooding limit, which might be exceeded if vapor superficial velocity becomes too high. Condenser capacity should not be an issue, since lower operating pressure in vacuum applications is (usually) followed by marginal decrease in overhead stream temperature.

Refer to Kolmetz's library of technical articles, and you will find a lot of useful references regarding aromatic(s) fractionation systems.

http://kolmetz.com/T...les-topics.html

[adeliry]

Hydraulic capacity of tower internals will likely be the first bottleneck, assuming that you're having the capability to pull higher vacuum. The tower will be operating closer to jet flooding limit, which might be exceeded if vapor superficial velocity becomes too high. Condenser capacity should not be an issue, since lower operating pressure in vacuum applications is (usually) followed by marginal decrease in overhead stream temperature.

Refer to Kolmetz's library of technical articles, and you will find a lot of useful references regarding aromatic(s) fractionation systems.

http://kolmetz.com/T...les-topics.html

thanks for your response, the website that you recommended have very ussefull information, thanks very much.

but it is not mentioned that what is margins to reduce pressure, when we reach to flooding borders?.

can you advise me more?

[Zauberberg]

Adeliry,

The best way (and the only recommended way) is to execute plant performance test, once when you prepare all the items for such event. It will undoubtedly tell you what are the limits of existing equipment, and up to what values you can push their performance. It's easy to do it, so just go ahead and start preparing performance test worksheets. By doing this, you will also discover and learn a lot of beautiful things.

Best regards,

[adeliry]

Adeliry,

The best way (and the only recommended way) is to execute plant performance test, once when you prepare all the items for such event. It will undoubtedly tell you what are the limits of existing equipment, and up to what values you can push their performance. It's easy to do it, so just go ahead and start preparing performance test worksheets. By doing this, you will also discover and learn a lot of beautiful things.

Best regards,

It is good idea,and we did it before ( we decrease the pressure from 320 mmHg to 280 mmHg), but we afraid of some unstable conditions that cause purity problem, but if you are agree i try to do it, you think we must be expect flooding? can it cause machanical damage on packings?....

[Qalander (Chem)]

Adeliry,

The best way (and the only recommended way) is to execute plant performance test, once when you prepare all the items for such event. It will undoubtedly tell you what are the limits of existing equipment, and up to what values you can push their performance. It's easy to do it, so just go ahead and start preparing performance test worksheets. By doing this, you will also discover and learn a lot of beautiful things.

Best regards,

It is good idea,and we did it before ( we decrease the pressure from 320 mmHg to 280 mmHg), but we afraid of some unstable conditions that cause purity problem, but if you are agree i try to do it, you think we must be expect flooding? can it cause machanical damage on packings?....

Dear adeliry May I just add slightly to what is explicitly indicated by my friend Zauberberg.

1.Performance test run(as suggested )should include prior calibration of whole system pressure /vaccume gauges against common master gauge)

2.Preferably there must be additional check points(if any ntapping available)to find out any minor changes in pressures across vertical height.

3.You should then be in aposition to obtain reading in various operating conditions

4.Data generated will also provide the internal packing's conditions of plugging or pressure drop(s)

5. In this way further decisions may be made to alter overall pressure or

6.the system needs some other actions for improvement(s)

Hope this helps
Regards
Qalander

[Zauberberg]

Hi Adeliry,

During the performance test, all changes of process parameters should be adjusted gradually in small increments; that way nothing abnormal should happen. It is recommended to - as suggested by Qalander - calibrate all the instruments prior to conducting test run, and to provide additional field measurements wherever possible (not to rely solely on DCS outputs). When you establish steady-stade operation under new process conditions, wait for few hours and then take the samples of tower bottom and overhead products - to confirm if performance is satisfactory or not. Since you are planning to operate closer to flooding limits, make sure that test run is performed under plant design conditions (= 100% throughput), since this will show you whether you can process the design feed rate under new conditions, or not.