16 replies to this topic

[mephis96]

Hi all, anyone experience in using kettle reboiler in factory? Or anyone experience in design kettle reboiler.

 

Currently my company using kettle reboiler. The problem is my bottom product still got some of top product (Overhead product still having at bottom product). My finding that my hot fluid (heat oil) enter at bottom tube and out at top tube.

 

Anyone know is it the problem which hot fluid should enter at top tube and out at bottom tube. Already issue about it but my senior said that is not the problems.From my readings, hot fluid always enter at top tube and go out at bottom tube. Thank you very much. Much appreciate if can send link or attachment for refferences.

[Bobby Strain]

You need to look at much more than this. Chasing this will not help you resolve your problem.

 

Bobby

[breizh]

Hi,

Booby is right , much more efforts on your side are required .

Is it a new problem ? 

You should review all the process parameters before and after the problem. Spend time on your DCS to review them over the time .

You may have issue with equipment , trays or packing collapsing , HX fouling ,Etc.

 

Good luck and let us know your findings

Breizh 

[latexman]

Kettle reboilers boil liquid isothermally, so LMTD of countercurrent flow is identical to LMTD of cocurrent flow. Therefore, hot fluid in top and out bottom or in bottom and out top has the same heat transfer.

You need to focus on areas that will actually affect “The problem is my bottom product still got some of top product”.

[mephis96]

Thank you bobby and latexman for you advice and info.

 

Thank you also briezh. Yup its still new. My feed component was 2, which is component X and Y.

Details about componen X and Y as below;

 

X=0.9%

X= boiling point 170c

 

Y=0.1%

Y=boiling point 202C

 

both liquid low vicsousity.

 

But as you said, i will go further in DCS, equipment and packing. Because our HQ use different reboiler which is Shell and Tube heat exchanger. But ours use kettle reboiler. HQ can cut almost 99.999% but ours only can cut up to 99.99% only. For parameter we follow HQ also in fact we try to use temp higher still cannot cut that top product totally. Anything or findings i will update here. Thank you guys for your respond and good advice.

[breizh]

Hi,

To be clear what are the impurities you want to remove , here we are talking ppm ?

What HQ stands for ?

Are you operating under vacuum ? if yes what type of equipment do you use ?  

What about the condenser , which fluid to you use to cool down the vapors? 

To me you should focus on process parameters .

Good luck

Breizh 

[latexman]

What other parameters are different from headquarters (HQ?)?  Feedstock, process, column internals, number of theoretical stages, feed point, condenser, etc.?

[mephis96]

Actuall our product is NMP (N-methylpyrollidone). We want to remove impurities called which GDS. Our feed into tower got GDS purity 1800ppm. But at our bottom product got GDS purity 30ppm.

 

HQ means our headquarter factory.

 

Equipment for tower used was packed collumn and operate under vacuum -1barg.

Top condensor used water to condensate vapor product

Kettle reboiler used Hot oil as hot fluid

 

What different from HQ was at HQ they use shell and tube heat exchanger but ours use kettle reboiler. 

[breizh]

Hi,

 

Based on my experience with the separation of products with high boiling points , pay attention to the vacuum system , a slight change on pressure could affect the separation . 

Other area of concern could be the packing , make sure they are the same ( site vs HQ) , same supplier . In other words I've seen BX packing from a reputable company performing much better than a local company .

 

About packing you need to make sure the installation is correctly done , no possibility of by pass , same for the distributors .

 

About kettle reboiler , you need to ensure that the bundle is covered with liquid with a weir in good condition , pay also attention to the heat transfer , both sides  (tubes outside coked and hot oil degradation inside ) 

 

You mentioned  water used as cooling medium , what is the temperature at the outlet of the condenser and what is the nature of the phase ( liquid or vapor or 2 phases) , this could  affect the vacuum with carry over of materials.

 

Note : my experience with cooling of high boiling points products ( > 200 C) was the use of Hot oil .

 

Very basic things are to perform heat and mass balances and compare the 2 units ( HQ and Yours) , make sure your instruments are performing well and are calibrated . 

 

Good luck 

Breizh 

[mephis96]

Alright breizh. next will focus on vacuum and do check leaking if have. might be a problem in separation also if got some leaking point right. But during production, hardly to find leaking point under vacuum condition.

 

About packing tower will cross check with drawing with HQ. Kettle reboiler everything was checked. Tube side all covered with liquid and have weir and got overflow liquid. Only hot fluid enter from bottom to top. If i change hot fluid from top to bottom, is it my vapour temp will increase? Because as we can see kettle reboiler focus on vapourize liquid at top before it overflow to another weir side. 

 

Ours CWS (cooling water supply)  temp was 29C and CWR was 35C.

 

Actually this tower was new expansion. Still under commisioning and testing to get product. All instrument was new. But will follow your advice for checking design and vacuum system. Thank you breizh.

[Bobby Strain]

One usually first increases the reflux and reboil to get better separation. So, why have you not mentioned this? Do you have a process simulator?

 

Bobby

[breizh]

Hi,

Which chemical is GDS ?

What is the maximum temp in the boiler you can achieve and how far is it compared to HQ ?

By the way , is it a continuous process or a batch process  ?

A process description or drawing  will  help a lot . 

 

Breizh  

[mephis96]

Bobby

 

Reflux had been control and adjust but result still the same at bottom result. Cannot totally remove top product.

 

 

Breizh

 

GDS is actually new chemical and not yet register in SDS even we here dont know what GDS stand for. Actually we start  bottom temp at 135C and GDS value at bottom = 35-40ppm. Then we increase bottom temp up to 155C and GDS result at bottom slightly reduce 30-35ppm.

But our HQ bottom temp at 160C and their GDS at bottom 0-10ppm. our process is continous but currently we shutdown for a maintenance. Next production we will try increase bottom temp up to 160C and will see the result. My assumption if increase to 160C, result will the same. Cause as before we increase temp up to 20C still no big difference in GDS value at bottom. Any updtaes will update here. Im very happy that you still with me   . For process description and drawing is p&c.

[Pilesar]

From your description of a 'new chemical' perhaps there are other components in your tower feed that are not allowing the same results achieved elsewhere. Is the vapor-liquid equilibrium fully understood? It is also possible your tower has mechanical problems such as improperly installed packing or missing wall wipers which allow liquid to bypass distillation stages. A first-principles computer model of your system would be useful for troubleshooting if you can find someone who understands how distillation works to look at the data. The process engineer who designed the tower should be helping with the commissioning if you are having performance problems.

[Bobby Strain]

It makes no sense that the bottom temperature can change so much and the composition remains the same. It suggests that the pressure is increased, too. Otherwise the boiling temperature of a pure component cannot change.

 

Bobby

[latexman]

How robust is your GC and the method used?  You may want to compare your analytical method and results to those at HQs.

[breizh]

Hi,

I agree with Bobby and Latexman comments . 

You need to match # the temperature profile of HQ at the corresponding pressure . 

 

I still don't understand the temperature set point in the reboiler which is below the BP of the light component !

 

Note : To support your operation you should have curves showing BP of your products versus Pressure .

 

As stated above, lab is a big player in your performance tests .

Make sure the methods are well applied , with the right standards . I'm a bit worried about that . 

When I was working in Indonesia we got use to perform round robin tests with all the facilities around the world to validate our methods , calibration , standards , technical skills by doing blind tests . Same sample was shared with all of the facilities and results were compared afterwards .

 

Take advantage that your facility is shut down to review the big picture and compare all the process parameters .

Share with us the results of your investigation .

 

What is your role within your organization , you may need support from HQ , at least communication with the chemist or Chemical engineer who developed the process ? 

 

Good luck

Breizh