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this video contents
1. THERMOSYPHON EFFECT
2. CLASSIFICATION THERMOSYPHON REBOILER
3. WHAT IS AN ONCE-THROUGH OR CIRCULATING REBOILER
4.HORIZONTAL / VERTICAL THERMOSYPHON REBOILER
5. HOW TO DESIGN A THERMOSYPHON REBOILER
6.DESIGN OF HORIZONTAL THERMOSYPHON REBOILER
7.VAPORIZATION RATE IN HORIZONTAL THERMOSIPHON REBOILER
1. THERMOSYPHON EFFECT
2. CLASSIFICATION THERMOSYPHON REBOILER
3. WHAT IS AN ONCE-THROUGH OR CIRCULATING REBOILER
4.HORIZONTAL / VERTICAL THERMOSYPHON REBOILER
5. HOW TO DESIGN A THERMOSYPHON REBOILER
6.DESIGN OF HORIZONTAL THERMOSYPHON REBOILER
7.VAPORIZATION RATE IN HORIZONTAL THERMOSIPHON REBOILER
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LearningTranscript
00:00hi friends welcome to our channel in today's topic we are going to understand what is thermosyphon
00:05reboiler and we are focusing more on the horizontal thermosyphon reboiler so we'll see what are the
00:11guidelines for thermosyphon reboiler what is the thermosyphon effect and so many things so let's
00:15start disclaimer for our channel and the content you shown in this videos key learnings from the
00:24today's session on the thermosyphon reboilers are we'll see the what is the thermosyphon effect
00:31what is the classification of thermosyphon reboiler what is the once through thermosyphon reboiler and
00:38circulating reboilers then horizontal and vertical thermosyphon reboilers then what are the design
00:47how to design a thermosyphon reboiler then how to design a horizontal thermosyphon reboiler
00:54then vaporization rate in the horizontal thermosyphon reboiler and htri interface
01:00for thermosyphon reboiler so thermosyphon effect basically everybody must have seen the
01:08solar heater so thermosyphon effect is the method of passive heat heat exchange based on the natural
01:16convection so natural convection happens in the solar heater where the fluid circulates without
01:22need of any mechanical pump so generally in the storage tank from the storage tank water
01:28cold water comes on the solar tubes it travels upward once it heated because of the density
01:36difference and comes into the same tank on the on the top of the that storage tank and the liquid
01:43come out from the little bit middle the hot liquid and the cold liquid enter at the bottom of that
01:49the same tank the driving in the driving entirely by the density gradient created by the temperature
02:00difference so because the low temperature the temperature of the cold liquid and temperature
02:05of the high hot liquid this gradient will move the liquid upwards without help of any pump
02:13so delta p drive whatever the delta p available for the drive it is based on the density difference
02:19of the cold fluid and the hot fluid into g and h head so this is basically a thermosyphon effect
02:29the classification of the thermosyphon reboiler so as you aware that the thermosyphon reboilers are mainly
02:35in conjunction with the fractionated in conjunction with the fractionated tower so the classification is
02:40done based on how the inlet comes from the fractionated tower so basically it classified into two
02:48once through and the recirculating thermosyphon reboiler so once through reboiler is from the column
02:56bottom first tray there is a collection pot and the whole liquid from the first tray or the tower comes
03:05in the
03:05collection collection box or a pot and then it whole liquid passes through the reboiler and comes
03:16inside the tower again the vapor will be go go to go out from the first tower first tray and
03:24liquid falls
03:24into the column sump and there will be a small wear on the the collection box which will fall the
03:33liquid in the
03:35sump so in this case the liquid sump levels normal high or low low is insignificant for the in the
03:44design of
03:45thermosyphon reboiler only the collection pot level is the governing for the thermal thermosyphon reboiler for
03:53the once through thermosyphon and recirculating thermosyphon reboiler it basically the the liquid from the
04:03tray one falls into the sump and sump is having a partition it may have a partition or it may
04:11not have
04:11a partition so if it is have a partition the liquid falls into this partition and then it flows through
04:18the
04:19reboiler and goes up the end liquid falls down again into the
04:25uh the partition area and the vapor flows away so that's why this uh liquid will comes the same liquid
04:35can be circulated again and again from this through the thermosyphon reboiler that's that's why it's called
04:41as a recirculating and if there is a no partition plate between the um in the sump then your high
04:52level low level and normal level liquid levels are important all three levels here when you design
04:58your general approach should be designed the normal level you should design considering the normal level
05:05thermosyphon design but it has to be investigated for both low liquid and high liquid the impact on the
05:11thermosyphon design
05:16thermosyphon reboiler further classified into horizontal and vertical type of
05:22thermosyphon reboiler so in horizontal it is once through so which will from the tray the liquid comes
05:29to the exchanger and comes out of the exchanger and the vapor two-phase comes down of the tray
05:38similarly horizontally circulating is the liquid comes from the sump it goes to the exchanger and it
05:46vapor goes inside the tower again similarly for the vertical once through it comes from the tray from the
05:54top first tray and it takes the it goes through the vertically through the heat exchanger and
06:02vapor forms similarly for the recirculating into the
06:08vertical so actually in vertical unit mostly from the vertical thermosyphon reboiler is often
06:17determined the height of the first distillation tower tray this height will be defined by this height of your
06:25vertical heat exchanger
06:29basically thermosyphon reboiler boiling side it is a shell side when it's a horizontal thermosyphon
06:36the liquid boils on the shell side and for vertical it boils on the tube side it is used for
06:43the
06:44viscosity if the more the viscosity more than 0.5 cp centipoise then you should go for the horizontal
06:51thermosyphon reboiler if it is less than 0.5 then it can be used in vertical space requirement very high
06:58space requirement for the horizontal one however the vertical can be placed in the lower space
07:07the maintenance but the maintenance of horizontal action is easier because bundle can be pulled from the
07:14ground and it is difficult because removal of head in vertical is difficult
07:21typically horizontal use when the large duties are there or low
07:26low head is required and it is used for the standard duty or the low duty low
07:31heat duties vertical will be used or if you want to use a vertical with a multiple
07:37shells then it will be like a column with the multiple shells can be used one column will have
07:45two reboilers on both the side or the three reboilers
07:50around the tower if because there is a limitations for the vertical thermosyphon reboiler
07:55the total height length and the weight and it is easy to maintenance to make it easy to maintenance
08:04guidelines for the thermosyphon reboiler design there are few key points for the thermosyphon
08:11reboiler needs to understand and keep in mind while designing the thermosyphon reboiler
08:16so thermosyphon reboiler is distinct between from the other reboilers
08:21because of the pipe for connecting to this exchanger with the tower so as we understand it is connected
08:28with the tower and there is a by some piper so it is defined difference between this is the difference
08:33between the thermosyphon reboiler and the other reboilers cattle type reboiler can be can be designed
08:40thermally independently and then piper can be designed separately like if any other reboiler
08:45uh you can design the thermosyphon reboiler uh you can design the thermosyphon separately in htri and
08:49pipe work can be designed hydraulics can be designed separately in other software or
08:55by um excel excel calculation but for the thermosyphon reboiler the connecting pipe work
09:03and the thermal design of this exchanger it's a single hydraulic system and should be designed together
09:09only this is the most important line you you just you cannot design a thermosyphon reboiler without
09:16its interconnecting piping it has to be designed together otherwise your design will not be
09:26good design before starting the design work these units you should essentially get the copies of tower
09:34drawing it which shows the piping connection and liquid levels in the tower and the orientations of
09:40the nozzles that that are with these are the very important points uh before you start your design
09:47on the thermal on the thermosyphon reboiler generally h and g type exchanger are used for the thermosyphon
09:56reboiler and horizontal thermosyphon reboiler are less likely to foul than the cattle
10:03reboiler because the presence of the circulation liquid because in thermosyphon reboiler will have
10:09a circulation of the liquid however in cattle type reboiler it's a it's it's a stagnancy or you can
10:16see liquid overflows through from the wear so it it will have a mostly there is no velocity in the
10:23moving velocity on the in the cattle type reboiler so we'll see how to design a thermosyphon horizontal
10:30thermosyphon reboiler design of thermosyphon reboiler uh horizontal thermosyphon remains same as
10:37as a shell and tube heat exchanger uh regarding the uh in uh means the tubes and the baffles and
10:45that
10:45that remains the same as the shell and tube exchanger only difference is the tower uh drawing
10:51and interconnecting piping for this tower to the exchanger and and return back to the uh tower so this is
10:58the
10:58main important uh in the design aspect of this thermosyphon reboiler so suppose this is this is your
11:04fractionated tower and uh this lower based on the low level the difference between the low level and the
11:11bottom of the shell is called the static head
11:15the tan line to the grade it is uh h1 which is the height elevation of the your tower mostly
11:23generally
11:23seven meter to seven meter to eight meter it remains and then for the horizontal uh thermosyphon reboiler
11:30h2 can be uh the height from the grid to the bottom of the your shell and this can be
11:39minimized if you
11:41this height should be minimized in case when you have a uh total head means you want to maximize the
11:49static head then this height has to be minimized and then also the orientation of this uh column
11:59or the nozzles to be checked because then the feed is going from uh six o'clock direction and the
12:05return
12:06is coming at the three o'clock so you have you need an extra band uh in your uh inlet
12:13lines or in uh generally
12:14it should be taken in the inlet line instead of the return line
12:20and h2 this h2 can be calculated or as we said it can be minimized to get the maximum head
12:27then it
12:28can be calculated by the shell thickness nozzle projection piping plunges bend radius and piping
12:33plunge radius and the clearance so if you minimize this then this height will be get minimized similarly
12:38vertical head is the return nozzle elevation minus your h2 this height and the shell id similarly static
12:49head which is our the main uh driving force it will be the low low level elevation minus h2
12:57minus lowest tube height of the lowest tube so that will be your static head
13:05current so when when what are the static head you are getting is it's equal to your losses from the
13:13inlet line and outlet line including your exchanger dp then exactly balance then all pressure drops
13:21around the system so then it will be a very stable system when when this happens it will be a
13:25very
13:25stable system but however all the time you cannot uh uh make the exchanger horizontal exchanger
13:36very close to the ground because when you make it very close to the ground then your outlet line
13:42elevation will be very high suppose if this entry of your elevation or the tower nozzle is around 20 to
13:5130
13:51meter and if you keep your exchanger uh at the very close to the ground then this line design will
13:59be very
14:00high and the pressure drop also can be high so that has to be checked uh the optimum height of
14:07uh in such
14:07cases uh if the nozzle uh nozzle height is at 20 to 30 meter then this horizontal thermocyple reboiler will
14:15be
14:15placed on the uh placed on the structures very near to the again to the nozzle so because otherwise it
14:24will
14:24be have a very uh two phase line will have very high uh pressure loss and the vibrations issue so
14:30you cannot
14:31keep this height of uh very high height for this uh outlet line guideline for the thermocyple reboiler
14:42so driving force should be uh greater than or equal to the friction losses for the thermocyple reboiler
14:49suppose this is an once through uh reboiler then the losses uh coming in the inlet pipe
14:56exchanger and the riser should be lower than your driving force so what is the driving force
15:03uh it's uh it's a uh delta p or the or the differential pressure uh 1 by 44 into rho
15:11into
15:13rho means density of the inlet liquid into height of the column height of that inlet uh pipe then rho
15:212 and
15:22h2 so height of the density of the mixed phase and the uh height of the riser so rho is
15:31the density in
15:31liquid liquid uh lb per feet cube h is in feet and 1 by 4 1 by 44 is the
15:38conversion factor for lb feet square
15:40into the lb uh inch square or a psi and as i said the p2 is the sorry rho 2
15:46is the uh mix vapor phase
15:49which is the liquid and vapor the density of the liquid and vapor has to be taken and we'll see
15:54how
15:54that is calculated then friction losses uh are the delta p which is includes the downcomer delta p
16:02friction losses then the exchanger delta p and the riser delta p so reboiler downcomer and riser
16:09so general guideline is that the reboiler delta p should be around 0.25 to 0.5 psi it should
16:17not be more
16:18than that and the losses in the riser and the downcomer should not exceed 0.1 to 1 psi per
16:26100 square 100
16:27feet this is the basic guideline and to maintain this delta and the ps um delta in the exchanger
16:35the general guideline for shell id and the tube length is if your shell id is around 12 to 17
16:41inches
16:43then you should have length of 8 feet and if it is 19 to 29 inches then it should be
16:5012 feet and if it
16:51is 30 um 31 inches then the your tube length can be around 16 so uh this is the basic
16:58guideline for
16:59this thermo cyclone horizontal reboiler so as you see the the driving force is should be greater than
17:07your friction your exchanger drop your friction uh at the outlet and the acceleration
17:11acceleration means because the two phase forms here in the riser then the volume of the vapor increases
17:19with the uh increases so because of that there is a acceleration loss comes in the riser pipe
17:29if your driving force is significantly higher than the losses you may need a restriction or if is to
17:36prevent the excess use so if it is very high then you need to have put some restriction
17:41in the inlet section either a wall or a restricted orifice and if it is a lower then you will
17:47be a
17:47chugging flow or there will be no circulation through the this reboiler but higher if it is a very high
17:54uh inlet driving force or the delta p then your vapor will be uh vapor rate generation vapor rate will
18:02be lower we'll see in the next slides so when we want to find out the uh minimum downcom or
18:11nozzle
18:11elevation this elevation for the horizontal reboiler then just for the calculation purpose we are introducing
18:19the safety factor 2 means we are increasing the uh instead of one one by 44 uh 144 it is
18:271 by 288
18:30so then the h1 which is the height from the same formula the earlier formula we seen in the our
18:36earlier slide should be greater than or equal to 288 into delta p delta p is your driving force
18:42minus delta h into rho 2 which is the density of mixed phase by rho 1 by rho 2 where
18:53the delta h is h1
18:54minus h2 and there is a recommended guideline for delta h it's three feet so generally this difference
19:04should be uh between h1 and h2 should be three feet if you take this three feet into
19:10this formula then you will find that h1 the height of your uh downcomer or nozzle height will be at
19:18least
19:19this formula and the density of the fluid in riser that rho 2 you can calculate
19:26for the mixed phases by this weight fraction or mass flow fractions
19:33we are seeing for the recirculating type of thermosyphon reboiler
19:37where the inlet is from the bottom the downcomer is uh inlet is not from the top of the or
19:44the first
19:44from the first tray it is from the bottom in that case uh h2 will be your h2 will be
19:52the riser
19:52height basically will be your h1 plus h3 so h1 is your minimum liquid level uh to the top of
20:00or top of
20:01the shell and h3 is your riser height from the low level so in that case you can find the
20:10h1 uh with
20:13the two added into delta p delta p is again the all the losses plus p2 by h p2 rho
20:202 h3 by rho 1 minus
20:23rho 2 similarly to get this rho 2 which is the mixed phase density uh you can follow this delta
20:33p is
20:33equal to rho mix into uh g by h so to find this delta p and your uh rho mix
20:41you can find there are
20:42multiple formulas given in some of the books which can be like that because of this two phase flow it
20:48can be like rho 1 into rho 1 into rho to the power 0.5 rho 1 minus rho 2
20:55to the ln of this so similar
20:58this you can use any one this is only for given for the guidelines but all these formulas are available
21:04in the books so while designing the thermosyphon reboiler we uh we are seeing the losses to calculate
21:12the fraction friction losses inlet and outlet but there are uh minor guidelines are there or you can
21:18say minor things to be noted which are like the losses starts from the contraction losses so if you
21:25know there will be a nozzle to this tower it may be the size we don't know in the pipe
21:30size uh it will
21:31be can be different so that contraction losses has to be considered then losses in the inlet pipe due to
21:37friction and discontinued uh discontinuities including some bends and this this has to be considered
21:43because if you see there is a t and maybe there is some bend if the uh the direction or
21:51the orientation
21:51of this exchanger is different then nozzle losses at the inlet of this exchanger to be considered
22:00then friction losses through the bundle and the static losses through the bundle this is this will be
22:07should be taken care in the losses then losses in the outlet pipe framework again if it is a two
22:13inlet and then it's coming uh the friction losses into this pipe and the static head losses in vertical
22:20pipe this is the static head losses will be there if the two because of the two phase and then
22:26expansion
22:26losses if there is any expansion because of the temperature rise so this type of losses has to be
22:32considered uh for the uh total uh in the total calculation
22:40vaporization rate is the one of the most important point part in the thermocypherly boiler
22:45how much should be the vaporization so vaporization rate depends on the mass of
22:51vapor divided by it will be calculated as mass of vapor plus the mass of liquid into the
22:56100 it is calculated like that and generally in the horizontal thermocypherly boiler the vaporization
23:03rate varies between the 5 percent to 40 percent it is more than the uh vertical generally more than the
23:10vertical thermocypherly boiler horizontal will give you the more vapor rate also it can be also correlated
23:19with the recirculation rate because the recirculation uh is defined the ratio of the mass of the liquid
23:26and the to the mass of the vapor so if you see your recirculation ratio if you considering recirculation
23:34ratio of 5.5 then your vaporization will be the 67 percent so one third will be the uh vaporization
23:43rate
23:44if you have your recirculation ratio of 1 then the 50 percent will be the vaporization so 50 percent is
23:51the vaporization mass vaporization and 50 percent your liquid so that's why your recirculation ratio
23:57comes as 1. if it is 3 then uh recirculation ratio is 3 means 3 times liquid pass uh then
24:06it's uh your
24:07uh 25 percent will be the vapor formation similarly when it's a 5 it will be the 17 uh percent
24:15of the
24:15vapor formation and when the 5 percent of vapor formation is required then this recirculation
24:21will happen the circulation ratio will happen to the 20 times the high uh rate of vapor will lead to
24:29the
24:29heat transfer surface drying out if you have a very high uh vapor flow rate and this will in this
24:36will
24:37lead to increase the tube wall temperature and it may tube may fail because because of increasing in your
24:43tube wall temperature however uh the dry out of heat transfer surface will takes place
24:51at lower heat flux uh inside the tubes then outside the tubes but uh outside the tube in horizontal
24:58thermal thermal secondary boiler the boiling happening at outside of the tube so uh this
25:07the higher heat flux or lower heat flux uh will not uh act more on the thermal uh horizontal
25:15thermal secondary boiler but it will be more significant on the vertical thermal secondary boiler
25:21therefore higher vaporization rate is possible in horizontal uh unit than the vertical unit
25:28so this is the reason because your heat flux lower heat flux
25:34is not drying out your on the outside of the tubes
25:39so this so that's why the vaporization rate is more in the horizontal which is around 5 to 40 percent
25:45but
25:45it is in the vertical it is around 33 percent max or 30 percent is the max will not go
25:52beyond the 30
25:53percent or 33 percent of the vaporization rate in vertical thank you very much and follow our channel
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