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HOW CAN WE CALCULATE THE EXACT REQUIRED LENGTH OF VAPOUR LIQUID SEPARATOR

USING L/D RATIO METHOD
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USING RESIDENCE TIME TECHNIQUE
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Topic: Using L/D Ratio to derive Height of Vapour Liquid Seperator  (Read 14264 times)

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michal

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Using L/D Ratio to derive Height of Vapour Liquid Seperator
« on: June 10, 2006, 03:37:04 AM »
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« Last Edit: June 12, 2006, 06:02:01 AM by geodome »

mbeychok

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Re: vapour liquid separator
« Reply #1 on: June 10, 2006, 11:51:35 AM »
Read my posting of "Design of vapor-liquid separator" on May 29, 2006, 05:09:34 PM which recommends using an L/D of 3 to 4 and then also checking to make sure that the separator contains sufficient liquid hold-up volume. It isn't a matter of "either L/D or liquid hold-up", but rather a balancing of both factors.
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Donaldson Tan

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Re: vapour liquid separator
« Reply #2 on: June 10, 2006, 03:24:55 PM »
This is the thread mbeychok is referring: http://www.chemicalforums.com/indexphp?topic=8913.0

Anyway, the general rule of thumb is it depends on what set of data you have.

There is no point trying to do by method 1 when your given data is suitable for method 2.
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

Ahmed

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Using L/d = 3-4
« Reply #3 on: June 12, 2006, 01:05:34 AM »
In a V/L seperator design we use lenght-to-diameter ratio of 3 to 4.What if i use the ratio of 2?
There are two conditions to design wheter to use residence time of 3sec. or to use L/D = 4.Which one is a good practice?

mbeychok

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Re: Using L/d = 3-4
« Reply #4 on: June 12, 2006, 01:58:13 AM »
Ahmed:

Have you read the thread in this forum at http://www.chemicalforums.com/index.php?topic=8913.0 that describes how to size a vapor-liquid separator?

The suggested L/D ratio is just a rule-of-thumb and you may use other ratios if you wish.  Why is it a rule of thumb?  Because many years ago it was determined to be the most economical ratio for balancing the cost of small-to-moderate size pressure vessels against the design strength of such vessels. But like all rules-of-thumb, it is not necessarily the best choice in all cases.

In fact, after you have calculated the maximum velocity of the up-flowing vapor and thus determined the minimum diameter of the upper section of the flash drum ... you can use a larger diameter for the bottom half of the vessel in order to provide more liquid hold-up volume if you need it.  In other words, you can use a swaged vessel (different diameters for the upper and lower sections) as long as you are aware that a swaged vessel is more expensive. Using a swaged vessel means you have a smaller overall length-to-diameter ... with the upper section diameter being that required by the calculated maximum vapor velocity and the lower section having a larger diameter to give you more liquid hold-up volume.

« Last Edit: June 12, 2006, 06:03:22 AM by geodome »
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