- 3 hours ago
In this video you will understand
1. How to design a horizontal three phase separator
2. Residence time for various process vessel
3. Liquid separation from continuous vapor phase
4. Vapor separation from continuous liquid phase
5. Guideline for level in separator
1. How to design a horizontal three phase separator
2. Residence time for various process vessel
3. Liquid separation from continuous vapor phase
4. Vapor separation from continuous liquid phase
5. Guideline for level in separator
Category
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LearningTranscript
00:00what is calculating the diameter for the continuous vapor phase velocity will be
00:04lower down rate so time required for even in kg per hour hydrocarbon formula is
00:12gd for the d required to go up and liquid separation horizontal vessel and use in
00:18this equation for the d square welcome to the channel today we are going to understand the
00:25basics of three phase separator and that how to design a three phase separator we are performing
00:29one example and while solving this example we are understanding the step by step for the designing
00:35this three-phase separator so let's start so design standard used for the two-phase three-phase
00:43separator design api api 12g basically used and api 421 used for the water and uh west water system
00:51system and api 12g used for the oil and gas two-phase three-phase separator basically api 2g
00:58annexure c talks about the design calculation of the separator to use the api 12g we should
01:05understand first the basics because 12g directly ask us to assume the diameter and gives us the k
01:12factor for that particular diameter so in this session we are seeing how to get the diameter
01:18directly we will go in the basics we will see the what are the three laws and that three laws
01:23is how to use it here the second is gpsa guideline gas processing supply association it is a detailed
01:29guidelines available we are taking some material from this gpsa also there are saddle dp guidelines
01:36and uvp guidelines so we all this for basically these three majorly we used in today's section
01:43session and we will try to find it out how to get the diameter directly not assuming the diameter and
01:49then finding the k factor we are we are design we are understanding the basics to get the diameter
01:56directly so steps to design the three-phase separator three-phase horizontal separator why we
02:04consider three-phase separator because three-phase separator will cover both two-phase as well
02:10so first step is calculate the diameter to satisfy the residence time so because sometimes the separator is
02:17also used for a buffer vessel or a vessel which will give the reflux so we have to maintain some
02:25residence time for that reflux and for that that diameter has to satisfy so for this i have made
02:33a separate video and that link is already there so it is a very simple to calculate the diameter for
02:39the
02:39residence time the next second step is to calculate the diameter for the vapor phase separation from the
02:46liquid phase so in this step we have to we will see how the vapor getting separated from the continuous
02:53liquid phase
02:54and then third step is calculate the diameter from for separating a liquid phase from the vapor phase so
03:01in this case continuous phase is vapor phase and the dispersed phase is the liquid phase then third is
03:08calculating the diameter for the separating a heavy phase from the lighter continuous phase so for this
03:15three we have to find out the diameters and then if we need a coalescer coalescing blanket then for
03:25this also i have made a separate shot for this and we will see in this session itself how the
03:30coalescing
03:31blanket and what it used and for this also we need to calculate the diameter if it is required so
03:38we will
03:38take take take that also in this so we will not miss anything then step six is the mr pad
03:45requirement and
03:46its design that has to be done but first this five steps will tell you the diameters or give you
03:53the
03:53diameters and the largest diameter you have to consider for your design out of this five then six
04:01as i said seventh is the you have to consider the governing largest diameter from the top of the
04:06first five steps then find out the l based on the l by d ratio
04:13and then inlet distributor connecting piping and the levels how inlet distributor because inlet distributor is
04:21also very important in the separator it gives the momentum transfer the largest transfer due to the
04:29momentum transfer so whether we have to use half pipe whether we have to use a special scoop and
04:34tetor or a half cut pipe or any other type of inlet distributor what is the basis for that that
04:42we will
04:42see in the step nine so to understand the design we will start with the problem itself and we will
04:50design our three-page separator by solving this problem
04:54for for each steps from step one to step nine so design a three-page separator for the following data
05:01so we have this data we have the flow rates we have vapor flow rate of in given in kg
05:07per hour
05:07hydrocarbon flow rate and water flow rate this is a mixture of three so and we have got the density
05:13and
05:13the viscosity if you remember the formula of terminal velocity or the all the three laws we need only these
05:20three
05:20things so we'll solve this problem as well as we'll understand the basics for each steps whenever it
05:28comes like residence time and levels how to maintain all one by one will understand as well as we'll solve
05:34this problem so as per our problem basically this is our our separator which is a overhead from some of
05:43the column and maybe some water is getting injected in between and then it get cooled and then it comes
05:49to
05:49the separator so now here we have to separate the three three-page so vapor will go out
05:54the liquid hydrocarbon maybe it can go for reflux as well and the
05:59heavier liquid can come out or it can go for the sour water or anything
06:05so as in my earlier lecture in the basics of three-page separators we understood the terminal velocity
06:13which we have to find it out for the all the three cases and when we are separating vapor phase
06:19from
06:20the continuous liquid phase then we use the stroke expression which we already derived in our earlier
06:26session you can simply watch it also when we separating a liquid phase from a continuous vapor phase
06:42hydrocarbon or light liquid phase then we will use the intermediate law stroke's newton's law will not
06:49be used because it is used for the heavier particles and also the higher Reynolds number
06:57before starting the design we should know what are the factors affecting its design so there are three
07:02main factors which affects the three-phase separator or separator design first is the vapor capacity
07:07vapor capacity determines the cross-sectional area which is your continue vapor continuous phase we will
07:14define by this and then when we want to separate a liquid from the gases continuous phase then that's why
07:22vapor capacity is important liquid capacity this will be used for the two purpose one is for the getting
07:27the residence time if you have any requirement of store and that and then degassing
07:36relieving the getting the vapor out from the continuous liquid phase or a separating the heavy
07:41liquid phase from the continuous liquid phase lighter continuous liquid phase then operability issue
07:48this includes the deal the unsteady flow of liquids or slug this will be used for the step one
07:54for the residence time now along with the above factor we should know few of the following parameters
08:00also required that is pressure temperature flow rates which we got in our problem statement physical
08:05properties also we should know that is density viscosity we got it degree of separation how much degree of
08:11separation is required because this will define the requirement of coalescer and the mist eliminator so
08:18mist free liquid is there or not so based on this you can define that whether you need a
08:22coalescer or a mist eliminator so these factors are important before start the design
08:31first step is calculating the diameter based on the residence time so in our earlier lecture i
08:38already informed that the vessel sizing is the first step in designing the separators
08:45and to design on the residence time first we have to consider the liquid level which is at the center
08:51of the center up to the center of the vessel to avoid any fluctuations and absorbing the surge
09:00so then we have to select the lyd ratio so this is the vessel and we are considering the level
09:04up to
09:05the center line and then we find out the residence time so in this lecture when how to design a
09:11vessel in
09:12this we discuss about the residence times required for a buffer vessel for a pump suction vessel or any
09:19intermediate vessels between the two units and we now discuss about the residence times required
09:25for the separator so now we'll see what what is the guidelines for the residence time for the separator
09:31specifically residence time guideline basically residence times affecting your cost and sizing of the
09:41vessel so that's why residence time shall be optimized you should use the optimized residence time so this
09:46is based on the gpsa guideline or a guideline and some uop guidelines this is a typical retention time
09:53for gas liquid separator so if you have a natural gas condensate separation you should use 2 to 4 minute
09:59if it is a fractionator feed tank you should use 10 to 15 minutes reflux accumulator 5 to 10 minutes
10:06fractionator column some 2 minutes amine flash drum 5 to 10 minutes refrigeration surge
10:10time 5 minutes refrigeration economizer 3 minute heat medium oil surge tank anything like that then you
10:17should use 5 to 10 minutes so this is the minimum requirement you can go little bit higher or it
10:23has
10:23to be depend on which guidelines you are following also residence time is depending on the difficulty of
10:29phase separation because a phase separation is more uh take time in i mean this time so it is more
10:36settling of two liquid phases required more residence time uh presence of suspended solids properties
10:43causing foaming anything that also required a more residence time last slide we saw the guidelines
10:51residence time guideline based on the service now here it is depending on the api gravity and as well
10:57as the temperature so if it is uh you have the above 35 api gravity uh hydrocarbon then you should
11:05require
11:05a retention time of three to five minutes and below it is required uh five to ten minutes
11:12for this temperature because it is at below api and uh and above then it is five to ten minutes
11:20and if it is
11:20below 80 fahrenheit then it is 10 to 20 minutes or if it is below 60 fahrenheit it is 20
11:26to 30 minutes
11:26similarly for this ethylene glycol and this you need a very high residence time
11:33if your cholesterol and your temperatures are within this 100 degree fahrenheit and 60 degree
11:38fahrenheit you need to follow this uh separator uh this recent retention time caustic propane you need this
11:4530 to 45 minutes and caustic and gasoline which will be used in merox or some places so there is
11:51a more
11:51residence time is required also as per api 12j if your oil gravity is less than 35 then you can
11:59go
11:59for one minute residence time if it is 20 to 35 it is 1 to 2 and 10 to 20
12:04it is 2 to 4. so other
12:07there are some other more guidelines depending on for the separators we'll see
12:14if you vapor liquid separation horizontal vessel with normal liquid level at center line then you
12:19can go for the five minute liquid level if you have a three phase like vapor liquid and liquid
12:25separation horizontal vessel and minimum liquid level at normal liquid level at center line then
12:31you should go for a 10 minutes so this is our case because we are we have the three phase
12:36separator
12:37and uh the level is at center line so we go for the 10 minutes of residence time
12:43so if it is a liquid search drum you can go for 2 to 4 minutes if it is a
12:49drop leg boot is also
12:50available then it is 5 to 10 minutes for the level control if your drop leg or boot manually operated
12:58or manually drained then it should be minimum 60 minutes it is designed for its volume should be
13:04such that it should be sustained for the 60 minutes feed search drum 15 to 30 minutes reflex drum 2
13:13to 5
13:13minutes and product receiver 5 to 20 minutes so these are the guidelines for residence time for the
13:22separators as well as some boot because boot is required when we have a three phase separator
13:28this is the boot basically where you will separate the liquid heavy liquid from the lighter continuous
13:35phase of liquid so i i hope all the guidelines are covered in this three slides
13:43from the residence time guideline we got our residence time as a 10 minute
13:48and then we have to calculate the holdup volume for the vessel so which is flow rate into time so
13:55this flow rate in meter cube so our problem we have got a flow rates of and this is a
13:59liquid flow rate
14:00so our liquid is hydrocarbon and the water so this flow rates in kg per hour so you have to
14:06convert it
14:06into meter cube per hour we have a density so it is easy so when you put this total flow
14:12rate here
14:13and multiplied by the residence time you will get the volume and the volume
14:18to get the volume of the vessel you have to divide it by f which is the center line
14:25as we maintaining the level at the center line so this half of so it is a 0.5 f
14:30will be the 0.5
14:31and then you have to solve it for the cylindrical
14:37vessel so cylindrical the area of the cylindrical vessel is pi d square by 4 into l
14:42and when you solve d for the d you will get this formula and when you solve for this value
14:49your d will
14:50be 1.73 meter so this is our first diameter based on the step 1 similarly we will calculate the
14:57diameter
14:57for the all four steps and then we will select the largest one so step 2 is calculating the diameter
15:05based
15:06on the separation of vapor phase from the continuous liquid phase so for this we have
15:12to calculate the terminal velocity for the rising bubbles from the continuous liquid phase the velocity
15:19the terminal velocity vdv will be calculated based on the strokes law if you remember in our earlier
15:26basics of separation lecture we already covered that the vapor separation from the continuous phase
15:32which is when we have to do we use the strokes law so based on the strokes law we can
15:39calculate the
15:40terminal velocity and the formula is gdv square by rho l minus rho v divided by 18 mu l which
15:52is the
15:53viscosity so if you see where dp is the particle diameter and these are the vapor density liquid density
16:00and your viscosity of liquid and terminal velocity and the acceleration due to gravity so to calculate
16:06this we should know that the vapor first the level in the vessel and because the particle or vapor
16:15bubbles has to rise up in this liquid so this height also we should know and the time required for
16:22this we have to calculate and based on that we we have to calculate the diameter of the this vessel
16:27so
16:28first we have to understand what how the levels are based in the separator so we will see that how
16:33the levels are set in the separators so liquid levels in horizontal separator so this is in horizontal
16:42separators what we have so the normal liquid levels is usually set at the center line which we done for
16:49the residence times calculation with a low vapor and high liquids
16:55resistance time we can set the normal liquid level just above the center line to keep the liquid
17:02residence time more so when you have a less leak less vapor flow in our uh today's problem we have
17:09a less vapor flow rate and high liquid liquid continuous phase so in that case this is for the continuous
17:16phase resistance time this is this is not for the bubble rise because if you keep the higher level then
17:22bubble rising the bubble takes long time so when you have a very high vapor and the low liquid rates
17:29then you can keep your liquid level below the normal liquid level which is shown in this green line
17:38because then you will you can manage your vapor velocity on the top you will get the more surface
17:44so your vapor continuous vapor phase velocity will be lower down so high and low liquid levels at the set
17:53at a distance of from the NLL generally it is 25 percent of your diameter which is comes around the
18:0120
18:01percent of your cross sectional area means if you keep the level above the your central line 25 percent
18:09then it will be the based on the cross sectional area it will be around 20 percent and generally the
18:15minimum level is kept as the 25 percent of your diameter
18:21okay it is correspond to d 0.25 of the d will be your uh minimum liquid level which is
18:29comes around
18:2920 percent of your cross sectional area when you see the cross sectional area of this vessel
18:33this comes around the 20 percent of your total cross sectional area of your vessel
18:40so this way we have to adjust the uh levels in the horizontal separators and this vessel
18:46these levels will use to find out the diameter for your in the step 2 we will see that calculation
18:56suppose x is the distance from the bottom of the vessel to the minimum level
19:01so as you know x is the distance from the minimum level and minimum level generally considers 25 percent
19:07so consider x is a fraction of d so because this is the d completely and this will be the
19:12fraction
19:12of d maybe it can be 0.25 of d x equal to 0.25 of the d then the
19:21t the bubble rising from the xd is
19:24suppose there is a bubble at the bottom here vapor bubble required to go up is required it has to
19:31travel the distance xd is t is equal to xd by vdv so vdv is your terminal velocity or velocity
19:42of a
19:42dispersed phase which will which we can calculate by the based on the particle size and the strokes law
19:51so then t is equal to xd by vd the time required for vapor phase to go up
20:00next step in calculation is the calculating the continuous phase velocity or horizontal horizontal
20:05velocity so horizontal velocity or continuous phase velocity is the of the liquid phase is
20:12is calculated as volumetric flow of the liquid divided by the its flow area so volumetric flow rate
20:19for this section and the cross sectional area for that area so suppose if z is the fraction of cross
20:26sectional area correspond to x so in earlier slide we saw that x is your liquid height where the bubble
20:33has to rise and if you see the cross sectional area for this suppose z is the cross sectional area
20:40so cross sectional area for this vessel will be like this which is also with the fraction of your total
20:47total cross sectional area that is you know the cross sectional area is calculated as pi r square or you
20:54can say
20:54pi by 4 d square and z is the fraction of it because we are not we are just taking
21:00at the liquid height
21:00we want a cross sectional area so your horizontal velocity is flow rate divided by your cross sectional
21:08area fraction of your cross sectional area so v vtl is equal to ql upon 0.785 into z into
21:16d so you know
21:16the total cross sectional area is pi by 4 pi by 4 comes is 0.785 so total cross sectional
21:23area is
21:24this and z the fraction of it it may be the 20 percent fraction or which can be a 0
21:31.2 percent
21:32so in this q is your liquid flow rate in meter cube per second and this 0.75 d square
21:38is your
21:38total cross sectional area which is defined by this and we required a fraction of it only so this
21:45in this way we can calculate the horizontal velocity or a continuous phase velocity
21:51velocity suppose y is the distance between inlet and outlet of the vessel
21:58so this is the inlet of the vessel and this is the outlet of the vessel
22:02so you know the your l by d is 3 it means this horizontal distance is 3 d
22:10based on the l by d ratio so what we considering because inlet and outlet nozzle will have some gaps
22:15so y is l by d minus 1 and then the time required for liquid to flow from this inlet
22:23point to the outlet
22:25is t which is yd by vtl you know that velocity for the continuous phase is ytl
22:35and so distance between this this inlet and outlet is yd basically
22:42it may be the 2d of your diameter that 2 into diameter that is the distance because l by d
22:48is
22:483 which is the tan to tan part so this will be the yd so yd by this is the
22:54distance and this is the
22:55velocity so you can get the time for that
23:02suppose the time required for a liquid bubble to go the distance xd
23:10is t which is similar to the time required for liquid to flow from inlet to outlet so this is
23:18inlet
23:18and this is outlet so time required for your liquid to come from inlet to outlet is also t
23:26if these both t's are same then you can say t is equal to xd by vdv vdv is your
23:34terminal velocity
23:35and yd by vtl which is your horizontal phase velocity so this velocity and this velocity
23:41with this fractions can be we can say are required the same time so then xd into vtl and which
23:51is yd into
23:52just cross multiplication so if you understood this concept then for when we separating the liquid from
23:59the vapor phase we are also saying that the vapor time required for vapor to fall down or liquid to
24:05fall down from the vapor phase and the discontinuous phase is same that way we can calculate easily
24:10then if this concept is understood in earlier slides and these slides then it is very easy to
24:17calculate the diameter as we know we have the continuous phase velocity as your flow rate by
24:24cross sectional area which is fraction of again this cross sectional area which is the
24:30zd which is the fraction of your total cross sectional area and vdv is your terminal velocity
24:37or you can say stroke's law so when you replace this vtl and vdv in the above equation here
24:45then you will get this equation which is xd into ql by the cross sectional area and the yd into
24:58your
24:59stroke's law or your terminal velocity so in this this d d will get cancelled and this d you can
25:04if you
25:05rearrange it you can get this d this is your diameter of your horizontal vessels so based on
25:14this you can calculate the d we will see in the next slide so this is the last step in
25:22calculating
25:22the diameter from for the vapor phase separating from the liquid continuous liquid phase so when we
25:31solve for the d and we have x is equal to 0.25 and z this we are taking from
25:37our earlier slide where we
25:39are say that the minimum liquid level is 25 percent of your diameter or which is the 25 per 20
25:46percent
25:47of your cross sectional area so z is your cross sectional area which is a 20 percent means 0.2
25:52and x is your minimum liquid level which is 0.25 so that's why we are taking x as a
25:580.25 and z as a 0.2
26:01and l by d we consider the 3 in our first slide itself so y is your l by d
26:08minus 1 so y will come as
26:102 now we when we replace this or when we put this values in this equation for the d square
26:19and we solve this and you have to consider uh because in this this particle size also you have
26:27to consider so you particle size we can consider as 175 micron if you remember in our uh basics of
26:33separation uh separators uh session we already mentioned that the vapor vapor from liquid separation
26:40we can consider the uh vapor um we can say uh size of the vapor bubble as 175 micron so
26:48we are
26:48considering the same that my micron size if it is given in your problem you can take that otherwise
26:54this is a conservative value and this is our um inputs so flow rates are given because you have to
27:00get
27:01this uh density difference density is also given you have to follow the proper units and then you can
27:08get the d as 0.526 meter this is your diameter for diameter required for vapor phase to separate from
27:19the continuous liquid phase hope you are understood this
27:26so we got the uh diameter for the to satisfy the residence time which is 1.8 meter
27:34i just rounded off it is 1.75 so it is uh i rounded it to 1.8 and for
27:40the step 2 we got 0.52 something
27:42so which can be rounded up to 2.6 meter and now for the other uh step 3 and 4
27:49will uh will take in the
27:51next session because this session getting longer but if you understand this for this session then this
27:57third and fourth will be very easy to understand so thank you for watching
28:07so thank you very much if you have any question you can write to us or comment on the comment
28:13box or
28:13you can also reach on to us at conceptengineering2025gmail.com link of the sessions uh all the
28:21sessions we completed till date is module 1 pressure relief valve module 2 heat exchangers and model 3
28:27separators are going on so links for all this um available in description box you can go through it
28:33so thank you
28:34so
28:34so
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