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Double Pass Sieve Plate


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#1 Kevindave

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Posted 02 April 2016 - 03:23 PM

Dear All, 

 

I need to design double pass sieve trays for a vacuum system, so please does anyone know how to design this kind of tray? because all published data are for single pass, is there a great difference in the assumptions?

 

Thanks alot for your time.



#2 Bobby Strain

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Posted 02 April 2016 - 09:04 PM

You should start with the search feature for this site. Or Google.

 

Bobby



#3 Kevindave

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Posted 03 April 2016 - 07:00 AM

Done, but i didn't find equations to check like the single pass. I need to know if all the checks ,downcomer design and residence time are the same design steps as the single pass ? 



#4 breizh

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Posted 03 April 2016 - 07:51 AM

Hi ,

Let you try :

Applied process design for chemical ans petrochemical plants , volume 2 , Ernest.E. ludwig .

 

another one : Ludwig's applied process design for chemical and petrochemical plants , volume 2 , A Kayode.Coker .

 

You can check also  in Perry chemical engeneers' handbook .

 

Good luck

 

Breizh


Edited by breizh, 03 April 2016 - 08:11 AM.


#5 Bobby Strain

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Posted 03 April 2016 - 01:29 PM

Try this.  http://www.academia....llation_Columns

 

Bobby



#6 Kevindave

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Posted 03 April 2016 - 04:43 PM

Thanks alot Mr. Bobby and Mr. Breizh. 



#7 PingPong

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Posted 04 April 2016 - 03:30 AM

Is this about the EB/SM splitter with a 6 - 7 m diameter that you mentioned in this topic:

http://www.cheresour...llation-towers/

 

I would expect such column to be designed with structured packing, not sieve trays.

 

In any case, if a column diameter is 6 to 7 meters one should consider four pass trays (i/o two pass)

or better: multiple downcomer trays, such as the Shell designs supplied by Sulzer: http://www.sulzer.co...HiFi-Extraction



#8 Kevindave

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Posted 04 April 2016 - 05:51 AM

Dear PingPong, 

Yes it is about the EB/SM splitter that i mentioned in the previous topic.
Ok i understand, but for a graduation project I have to design the internals, and the only available in coulson vol. 6 are sieve trays and there is no four pass mentioned (equations available only for single pass) by the way im facing a big problem in pressure drop of this column because of the large number of trays around 100 actual, and using sieve plates. so please what do you recommend me to do ? 



#9 PingPong

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Posted 04 April 2016 - 07:54 AM

im facing a big problem in pressure drop of this column because of the large number of trays around 100 actual, and using sieve plates. so please what do you recommend me to do ?
That's exactly why nobody uses trays in such column, but uses structured packing.

I strongly suggest you do the same.



#10 Kevindave

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Posted 04 April 2016 - 04:41 PM

Thanks alot Mr. PingPong.



#11 Kevindave

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Posted 06 April 2016 - 03:36 PM

Dear all,

For the double pass sieve trays calculations, the liquid flow rate will be divided by 2 as it is splitted into 2 downcomers. So what about the vapor flow rate can I keep it as it is ? or should i divide it by 2 aswell ?



#12 Padmakar Katre

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Posted 13 April 2016 - 03:49 AM

Dear all,

For the double pass sieve trays calculations, the liquid flow rate will be divided by 2 as it is splitted into 2 downcomers. So what about the vapor flow rate can I keep it as it is ? or should i divide it by 2 aswell ?

Hi,

Understand the basics. The calculations or correlations really don't understand the number of passes but the absolute values. Let me explain it for you, the geomterical outputs such as downcomer top and bottom area, weir length, active area, net free area are the one which will be used for checking the hydraulic capacity.

In your case it's a two pass tray so calculation sequence will be,

1. Assume a diameter of column - estimate col cross section area (A - m2)

2. Assume downcomer widths for side and central downcomer and estimate chord length (outlet weir length) (WL), downcomer inlet area (Dci)

3. Estimate the active area (column area minus 2*downcomer area)

4. Net free area is column area minus one DNCR area

 

Once you get these geomtrical parameters, perform hydraulic calculations to check the vapor and liquid capacity

1. Downcomer choke flood - refer Henry Z Kister Distillation Design Book to get the correlations like Koch, Nutter which are based on downcomer residence time. Downcomer choke flood is nothing but the ratio of liquid inlet velocity to maximum allowable velocity. Liquid flowrate and downcomer area will give inlet liquid velocity and max allowable velocity with the correlation. Use appropriate system factor if applicable to derate the capacity.

2. Jet Flood - refer same handbook to estimate the jet flood by Fair's correlation or Kister-Haas correlation.

3. Downcomer Backup Flood - it's simple pressure balance i.e. liquid from top tray is flowing towrads higher pressure and hence it should build up inside downcomer to overcome tray delta P and other resistances

4. Tray delta P - it is mainly sum of dry drop, wet drop and vapor head plus minor loss to form the vapor bubble (surface tension)

 

Once you get the active area, choose the open area which is nothing but the hole area (e.g. 10 mm size total 300 sieve holes) and estimate the dry pressure drop by simple orifice equation. Wet pressure drop is weir height plus liquid crest. Liquid crest will be calculated with some correlations given in Kister book which is function of weir load - m3/h-m (liquid flow in m3/h divide by weir length in meter)

 

it's really simple. All the best.

3.



#13 Kevindave

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Posted 14 April 2016 - 06:07 AM

Thanks alot Mr. Padmakar. 






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