 Let me take this opportunity to give a brief background of the organization. Spectra Dynamics has the head office in Vadodara and it has sales support office in Mumbai and Delhi. We provide consulting services mainly to process industry involving conceptual design, front-end engineering design, some part of detail engineering activities and we also provide advanced process solutions wherein we offer simulation-based services, advanced process control to operating plants and also the integrated engineering software solution. In short span of time of less than 3 years, we have been able to execute more than 40 projects to the industry leaders from different industry segments. You can reach www.SpectraDynamics.com for more details about Spectra Dynamics. So, the agenda that I have charted for this seminar is the distillation columns, very basics about distillation column, I am sure you have had quite deep sessions on the design and thermodynamic and simulation aspects of distillation column. The main emphasis of this presentation would be on column internals including trays, trays versus packed columns, random packing, structured packing and packed column internals as well. So, in the distillation column you know that the feed above feed this section is the rectification section and below that is the stripping section. There is a condenser for condensing the vapors to create a reflux which will be part of it will be reflux pack and the distillate product comes out from the top and there is a reboiler for generating the vapor. So, as to achieve vapor liquid traffic within the column. So, the main objective of the distillation column internals is to achieve the vapor liquid contact. In the design aspect the height of the column is determined by the difficulty in separation. Difficulty in separation would depend upon the desired purity of the products and what is the relative volatility between the different components of the solution from which the separation is to be achieved. Height also will get determined by the kind of the amount of energy that you will be putting in to achieve the distillation column and it will also depend on the efficiency of internals. So, if you design a distillation column wherein you have you are putting a very large heat input then you would have a height which would be reduced significantly because of higher vapor that will be getting generated. So, higher vapor liquid traffic. So, number of theoretical stages that would be required would get reduced. So, we will have to strike a balance between the we will have to optimize in such a way that the heat consumption is such as the operating cost and capital cost is balanced out. The diameter of the column is determined by the vapor liquid traffic that the column is going to column has to handle. So, the amount of liquid that is getting fed, the amount of stripping vapor and the reflux based on that the hydraulic calculation is required to be carried out to determine the diameter for a distillation column. The diameter of the column would also depend upon the operating pressure. Higher the operating pressure the vapor density will be lesser sorry vapor density will be higher and hence the column diameter would reduce. So, if you are operating a column under vacuum then because the vapor density is very less for the same amount of mass flow of vapor the volumetric flow will be much larger and hence the diameter of the column that is required will turn out to be much larger. The diameter will also depend upon the capacity of the internals that means, the capacity to handle the vapor liquid traffic of a particular internal would determine the diameter of the column. So, essentially I am going to talk about different column internals and its capability with respect to its efficiency and its capability with respect to its vapor liquid handling capability. So, for carrying out process calculation for achieving the diameter identifying the diameter and the height of the column there are various studies that is required to be done. Process calculations the simulation studies will arrive at based on that you will arrive at the number of theoretical stages that is required which would depending upon the efficiency of the internal it will translate into the height of the distillation column and based on these calculations you will also generate the vapor liquid traffic within the column based on which the diameter of the column would get determined. There are various simulation software packages to identify the number of theoretical stages that is required and the vapor liquid traffic to achieve desired separation for the required purities, for the required throughput and capacities ok. So, number of theoretical stages for trade column based on tray efficiencies will translate into number of trays. So, and for the packing based on packing HETP that is the height equivalent to theoretical plate it will translate into the height of the packed plate. I am sure all these these are basic concepts and you would be aware of these things I am just giving a very brief idea about this so that in my subsequent discussion I can refer to some of these aspects. The based on the vapor liquid traffic the hydraulic design calculations are carried out. There are various methodologies of hydraulic design calculation right from the generalized pressure drop correlation curve the and the proprietary softwares developed by different distillation column internals vendors. So, based on that the pressure drop across the internals is calculated and the operating point with respect to flooding capacities is also calculated. In the column internals there are various process requirements. So, the primary requirement is to achieve the desired efficiency and to achieve the desired to handle the desired capacities. These are two main fundamental primary requirement for any column internal. So, what the column internal what it does is it allows to achieve a vapor liquid contact which can be as intimate as possible to achieve good amount of interaction for transfer of transfer of one say light component to from one phase to another phase to in order to achieve the separation. The secondary requirements which are also equally important is the pressure drop consideration, the resistance to fouling and the resistance to corrosion. So, based on this primary requirement and the secondary requirement the selection of the column internals is determined. There are various types of column internals like trays, random packing, structured packing, the grids and the packed column internals. In a trade column in the this is a picture of a single pass cross flow tray. So, in which from the down comer of the tray above the liquid will enter onto the tray and it will flow across the tray and go to the next down comer to feed it to the tray below whereas, the vapor will flow from bottom of the tray to the next tray on the top. So, that is how it is called as a cross flow tray. So, here we have to understand one important thing that this is the desired flow path of vapor and liquid. The liquid has to flow across the tray and the vapor has to come from bottom and go to the tray above. Now, for example, if the liquid which is flowing across if there is not sufficient resistance from vapor and if this liquid through the holes of the tray if it instead of going to the down comer here if it falls down in the tray below then it is not getting sufficient residence time on the tray to achieve the vapor liquid contact. So, this will result in deterioration in the efficiency. Similarly, when the vapor which is going which is coming from bottom and going to the tray above if it carries some liquid of this tray onto the tray above then it is it results in axial back mixing which again deteriorates the concentration gradient which would result in deterioration in the efficiency. This is same thing, but with a different picture. Now the down comer will have some liquid in order to ensure that the vapor from tray below does not enter the down comer because down comer is the place where the vapor liquid disengagement should take place. When the vapor is flowing from the tray below to tray above at that point of time there is some froth which is generated onto the tray and there is a tendency that some amount of clear liquid majority of clear liquid and some froth will go into the down comer. So, the job of the down comer is to provide sufficient residence time sufficient residence volume and time in order to allow the vapor and liquid disengagement in the down comer so that the vapor of the of this off say tray number 10 will not go to tray number 9 below but it will go to tray number 11 above and the clear liquid will go to the tray below. So, these are the components of the trade column. So, this is the down comer this is the active tray area wherein the actual contact between vapor and liquid takes place during which the mass transfer actually takes place and this is the outlet wire which gives which ensures that there is some amount of liquid pool onto the tray deck to achieve the contact between vapor and liquid and from the outlet wire it will go to the down comer to the down comer and from the down comer it will go to the next the tray below. Is it into the. Correct. See this liquid sealing is important so that vapor should not enter the down comer. So, in the typical situation the height of the exit wire is higher than the down comer clearance so that the the down comer clearance is always filled up with the liquid and vapor does not enter which is called as a static seal. I would come to the next stage where it is a dynamic seal wherein the exit wire height can be lesser than the down comer clearance I will talk about that when it comes to high high performance trace ok. So this is the straight down comer this is clearance under down comer that is down comer clearance this is the outlet wire this is a seal plate which is a flat seal plate and this length from the down comer panel to the exit wire is called as a flow path length during this or during this flow it that is the length of the liquid flow path and that is why it is called as a flow path length during which the actual vapor and liquid gets in contact with each other to achieve the mass transfer. This area this cross sectional area here is called as a bubbling area where the vapor gets contacted on to the liquid pool on the tray above. This area is the free area because after the vapor gets contact gets an intimate contact with the liquid there is a tendency of foam froth formation and the free area in this zone is basically it also again gives time to separate the vapor from liquid and vapor has to go up and liquid has to flow to the down comer. Any deterioration in this path say vapor is going to the down comer and to the next tray below or liquid go from the tray below is going to tray above is the actual back mixing which would lead to deterioration in the efficiency. This is this one is the inlet wire. So at times when the static seal is not available meaning that the down comer clearance is higher than the exit wire height that means there is no static seal available. So at that point of time we can have an inlet wire which is taller than the exit wire height then it will provide the sealing of the down comer to avoid the vapor flow through the down comer. So this is one case even in conventional trays you can have the inlet wire to avoid that situation. Now you might come with a thought that why the down comer clearance at first place why not we keep lesser to avoid the inlet wire itself. Now there are possibilities wherein the liquid load on the tray is very high and if you keep say 50 mm of the down comer under down comer clearance. Now you have a certain diameter and when the liquid is coming only through that rectangular box of 50 mm height and whatever that chord length is it will have certain velocity. Now as you go up on the liquid loading that velocity will increase higher the velocity whatever vapor is coming from below it will push that vapor towards the down comer. Now when vapor is going pushed towards the down comer then there is more froth which will be generate which will be there in the down comer and the down comer capacity will become inadequate. Down comer capacity with respect to vapor liquid disengagement will become inadequate because of higher liquid velocities under the down comer. So to reduce the liquid velocities under the down comer we need to increase the down comer clearance under down comer clearance. So you get more rectangular area so your liquid velocities flowing on entering velocity on the tray would reduce and in turn it will avoid the possibility of froth getting pushed into the more and more froth getting pushed into the down comer. So in such a situation when you are exceeding the limit or you are exceeding the exit wear height at that point of time the requirement of inlet wear will come. Now you can think that even the exit wear height we would increase to avoid the inlet wear but as we increase the exit wear height then the liquid pool on the tray deck will increase because you are increasing the exit wear height. When the liquid pool is increasing there is a higher resistance for vapor up flow which will translate into higher pressure drop. So these are few important considerations while deciding a type of the tray and while carrying out the hydraulic design for a tray column. You can see here that this one was the straight down comer whereas this is a slanted down comer this is a completely a sloped down comer. The sloped down comer trays are typically used wherein the liquid handling capacity is lesser and vapor handling capacity required is higher. So once we slope it here then the active area is increasing because the down comer cord the down comer width is reducing in the bottom. So you know you can see here that in this zone in this zone here the flow path length and bubbling area is only this much whereas since you have slanted the tray you can get more active area more bubbling area. So you can have now more vapor handling capacity ok. So these are few of the tray terminologies which we have already discussed about. This is the inlet panel this side this is the man-way panel. This man-way panel is essentially used during the installation of the tray. When the trays are installed it is installed from typically from bottom to top. So the installation person would install all the components of the tray except the man-way panel and then he will go and then tray above again install all the components of the tray except the man-way. So say if there are 20 trays when the trays are installed all the 20 man-way panels of each the panel of each tray man-way panel would not be installed and the inspector will inspect whether the trays has been installed correctly and then from bottom to top it will keep on boxing up the man-way panel and he will come out from the top manhole. So that is the function of the man-way panel. Now there are few things which are not appearing on slide. Now the tray would reside on something called as a tray support ring and it is clamped. The tray panels are clamped onto the tray support ring. Then this is the downcomer part and this portion is called as downcomer beam actually it is a downcomer panel but which gives a mechanical support to the tray and that is why it is called as a downcomer beam and this is also a bottom part of downcomer panel. So the downcomer is again clamped onto downcomer bolting bar. So there is a vertical tower attachment on which the downcomer panels are bolted. This is the exit where and on the tray deck we will have different kinds of active units either valve or sieve or bubble caps and this entire part is called as active panel. In the cross flow trays the single pass trays or multi-pass trays are there basically single pass meaning the liquid flows across the tray only once and then only one flow path is there for liquid flow whereas in the multi-pass tray the two pass tray as shown here the liquid comes from two side downcomers of the tray above and goes to the center downcomer again gets split into the two side downcomers. So this is the picture of a two pass tray you can have even four pass tray or even odd number three pass tray also has been designed. The consideration of multi-pass tray comes from the requirement of additional liquid handling capabilities and depending upon the column diameter. So liquid from tray above is going to this center downcomer and it is splitting on both sides and goes to the side downcomer again it will merge it will come together and go into the center downcomer. Now you can imagine that say if there is a column of depending upon vapor velocities and liquid velocities if you design a column with 4 meter diameter. Now in a similar column in say 1.5 meter diameter the liquid flow path length if you consider to the inlet panel and downcomer panel each of say 300 mm and 300 mm then you get a liquid flow path length of 900 mm. So 1500 minus 300 minus 300 so 900 is the flow path length. Now when liquid is travelling across the tray and vapor is getting vapor is contacting the liquid up to certain length when the liquid travels whatever mass transfer has to occur has occurred and then any additional travel is not going to really yield with respect to additional mass transfer because whatever depending upon the efficiency of the internal whatever mass transfer was to take place on that particular tray that has been achieved. So any additional length is not contributing to the mass transfer for the additional vapor liquid contact because whatever equilibrium was to be achieved has been achieved. Now that additional length is a vest. Now when you go for a 4 meter diameter column you can imagine if you have a single pass tray and say 400 mm of the downcomer width on both side. So we will have almost 3.2 meters of flow path length. So maybe after 1.5 meter or 2.2 meters there is no mass transfer that is taking place on the tray but it is just because of maybe higher vapor velocities for which the diameter is considered to be 4 meter. Now in such a case when you go for multi pass trays then you can have the liquid distributed in the 2 passes or 4 passes for that matter and the flow path length is just more than adequate with respect to the mass transfer efficiency requirement. So you are improving the tray efficiency also and you are reducing the column diameter to a certain extent when you switch from single pass to multi pass tray for a larger diameter column. So instead of 4 meter single pass tray probably you can achieve the same task within 3 meter multi pass tray. These are various downcomer types straight downcomer, slope downcomer with resist inlet area. I will come to some of these concepts in the next slides why this resist inlet area is provided then there is a step downcomer then when the liquid handling capacities are very less then it is a pipe downcomer. And there are circular downcomers swept back wear the seal pan and the draw off pan. Let me explain one concept of this swept back wear. In the hydraulic calculation there is an important term called height of liquid over wear per length of wear. This terminology or this parameter is useful in arriving at the downcomer pressure draw. So when you have a very high liquid velocities above the exit wear and you have no space to increase the downcomer width. See if you increase the downcomer width your chord length will increase. Downcomer width is say this portion this is the downcomer width. So if you increase this downcomer width to this extent then your chord length the wear length would increase. So by increasing wear length you are reducing this parameter that is height of the height of liquid over wear divided by wear length or it is actually eventually converted into gallons per meter of liquid flow divided by length of wear GPM per LWI which contributes into pressure draw calculation. So to achieve lesser number of GPM per length of wear you need to increase the chord length. So to increase the chord length you can increase the downcomer width. But if you increase the downcomer width the active area available for vapor of flow would reduce and again it will contribute to higher pressure draw. So these are the we have discussed these parameters like capacity efficiency turn down pressure draw and fouling resistance. Down is an important aspect while designing as well as selecting the type of internal. Because when we design a column we have to have flexibility in terms of the operating capacities as well as in terms of if the feed composition is changing for a certain distillation column depending upon the availability of say crude or type of crude then at that point of time the required reflux ratios to achieve same level of purification would differ. So if the reflux ratios are changing to achieve the same level of purification that means the column has to handle that different vapor liquid traffic at different operating conditions or feed conditions. So we have to design column internals to suit all those two three types of crude to achieve the same level of separation. For example even in certain cases where it is a in the upstream there is a reaction and downstream there is a separation and reaction is catalyst base. So when the catalyst activity is good at the start of the run you would have certain feed composition to the column when whereas when the catalyst activity is deteriorated that is called as end of run then the feed composition would be different. So the column internals will have to be designed not only for the feed composition which is at the start of run of the catalyst but also at up to the end of run of the catalyst. Pressure drop and fouling resistance there are certain services which are fouling. So based on the fouling characteristics different types of internals are chosen. I will come to the types of internals and I will talk about the ability of the fouling resistance for different types. Flooding and internment we have briefly talked about these are the two important parameters flooding, internment, pressure drop while calculating the while arriving at the design of the column internals. So flooding essentially occurs when the vapour and liquid flow rate exceeds the capacity of the column and that is why flooding is an important parameter while sizing the distillation column. So the symptoms is and basically the flooded tray would act as a restriction to the liquid flow down to the next tray and the symptoms are buildup of liquid and excessive pressure drop across that zone. So two types of flooding one is the downcomer flooding which is basically high flow and small tray spacing and jet flooding which is low flow but excessive liquid internment. The liquid internment it increases with higher whole vapour velocities and also it increases due to reduced tray spacing. So as you reduce the tray spacing the probability of internment would increase and as the vapour velocities go up or if you put to achieve lesser pressure drop you will have more active units more holes or more sieves sieve holes or walls to achieve lesser pressure drop but because of which you can also reduce with the help of that you can also reduce the vapour velocities to reduce the internment. If you reduce the number of holes then the vapour velocity will increase and it will lead higher pressure drop as well as it will lead to higher probability of liquid internment. The liquid internment will decrease with increased liquid wear load and increased fractional perforated area and also surface tension would play a significant role in the liquid internment. Lesser the surface tension the probability of internment is higher. This is typically these are various considerations while carrying out the hydraulic design for any kind of trade column based on the liquid flow and gas flow rates and as shown here this is the best operating point at the centre. So if you have very less liquid low and very high gas flow rate then it will lead to internment. If you have very high liquid flow rate and very less gas flow rate then it will lead to downcomer choke flood. If you have very high liquid rate and very less gas flow rate then it will lead to weeping. Weeping is another phenomenon wherein when liquid is flowing across the tray the liquid has to go to the downcomer to go to the next tray below but if the liquid weeps through the valve or holes before it goes to the downcomer that is called as weeping when it leaks through the holes. So that would result in channeling which would result in reduction in the mass transfer efficiencies. And dumping is nothing but when the liquid is falling from when the reflux is falling from top it instead of having any horizontal component of velocity directly dumps through the hole to the tray below again through the hole to the tray below. And bed expansion priming is very high velocities of gas and which will lead to internment and bed expansion. So all these things are to be avoided and this is the best suited operating point so as to have margins with respect to turn down flexibility as well ok. We all know the various types of conventional trays sieve tray, bubble cap tray and a floating wall tray. This is just a picture with respect to how a bubble cap tray would look like and this is during the shop the testing of with respect to dimension test. This is the mock assembly to check whether the dimensions are appropriate so that when it goes to the site it would enter the column properly ok. Sieve trays these are easy to manufacture and very inexpensive because you can realize there is a single unit operation with respect to manufacture of tray. It is just the punching of the plate to find to make a sieve tray there are no any additional mechanical operation. It is it has good efficiency at design conditions only. The turn down flexibility is very poor the moment vapor liquid traffic is changing you do not have any means to have a better turn down flexibility in case of a sieve tray. It is it is good in fouling applications because there are no obstruction so no possible reduced possibility of getting sedimentation or choking. Corrosion problem is lesser even though sometimes holes may get damaged because of high velocities and some kind of erosion related corrosion. In case of bubble cap tray though many of the bubble cap trays have been replaced with sieve tray or wall tray. But there are still certain applications where bubble cap trays are required to be used for its very good tray efficiency because when vapor escapes from the bubble cap tray it rises through the riser takes the u turn and from the bubble cap it enters into the liquid and after having contact with liquid only it will get escape to the tray above. So it ensures the very good contact between vapor and liquid and during which it exerts higher pressure drop. This is one concept that I would like to highlight here that in case of bubble cap tray the contact between vapor and liquid is very good because of which the efficiencies of the bubble cap tray is good. But the pressure drop is high because of the two u turns that the vapor has to take from the tray below to tray above. Now the mechanism of ensuring the vapor liquid contact with the elpa bubble cap tray is such that it has to take this two u turns. But actually in the vapor liquid contract in the contact these two u turns are not contributing it is a wasteful pressure drop it is not a useful pressure drop when it actually contacts the liquid at that point of time whatever pressure drop is occurring that is a useful pressure drop which is contributing into mass transfer whereas this two u turns is not really contributing into the useful pressure drop for the tray. So I would use this example or this concept to highlight that higher pressure drop means higher efficiency as long as that pressure drop is contributing into mass transfer. But if the higher pressure drop out of like in bubble cap tray very large part of it is not contributing into the mass transfer then it is unnecessarily spending more energy. So on this concept lot of development subsequently took place that there has to be a contact which is useful to achieve mass transfer. So whatever that pressure drop is occurring it has to be a useful pressure drop and not a wasteful pressure drop. Here also the bubble caps would obstruct the liquid flow when the liquid is flowing across the tray. Typically certain absorbers wherein the liquid used for as an absorbent is say DM water which is an expensive feed or any other kind of solvents which are expensive but absorption as required to be done then in such applications sometimes quite often the bubble cap trays are used because in such case the liquid flow required is very less and vapor load handle is high at the same time efficiency required is much larger. In wall trays there are essentially two types moving wall and fixed wall. The moving wall tray will as shown here in the picture will have a tray deck and a moving wall which will move up and down depending upon the vapor flow from below whereas in the fixed wall tray the walls will be punched out of the deck itself. So that is the fixed wall tray. Moving walls the walls moves up and down as per vapor load movement is restricted by wall legs. So the maximum lift will depend upon the leg length of the wall and this is one type of wall which is a leg wall then there is a caged wall wherein there is a cage and a disc. So depending upon the vapor load the disc will move up and down because of this functionality it offers larger turn down flexibility as compared to a sieve tray or a bubble cap tray. So when the vapor load is very high the walls will be 100% open 100% of the walls will be 100% open that will be the maximum capacity that can be achieved by a wall tray a moving wall tray. Whereas say if you are operating a column at 50% capacity then 50% of the walls will be closed and 50% will be open. If there are two different types of walls within the wall tray light walls and heavy walls. The adjacent rows light wall, heavy wall, light wall, heavy wall these kind of rows can be arranged on the tray deck. So when the vapor loads are less all light walls will be open and heavy walls will be closed. So the vapor distribution across the tray across the cross section of the column also will remain same because you are keeping one line of light one line of heavy. So at low vapor loads heavy walls will be sitting on to the tray deck and only light walls will be open and vapor will be going through the light walls. Pitch wood remains same is changing effective pitch is changing in the turn down condition but typically the pitch wood reduce light as well as the light wall will be fully open even the heavy wall will be fully open at the highest flow condition both the walls will be fully open true that is true but the mechanical design is such that it will take care of it and the escape area across the walls would remain same because the leg length is same. So the pressure drop across the walls would remain same and the pitch part of it when we design the column at that point of time the pitch is determined based on the highest flow condition and so as to ensure that proper mixing also is taking place and proper vapor liquid contract is taking place. But in the low flow condition actual number of wall requirement is reduced. So you can have larger pitch whereas in high flow condition you need to know you need to have more number of walls so pitch gets automatically reduced. So it balances between pressure drop and the vapor liquid contact. In case of fixed wall tray the tray walls are punched out of the tray deck and the opening remains fixed. So in case of fixed wall tray the operating turn down flexibility is reduced as compared to moving wall tray. So wall trays would offer better turn down situations more flexible when the feed rate is varying efficiency remains same even though the gas drops the gas rate drops and walls are more likely to plug or fall because it has the legs more obstruction so more tendency to fall in. The pressure drop across the tray would slightly reduce. So bottom pressure might change as long as if you are controlling the top pressure then the bottom pressure would change depending upon at a higher or lesser vapor load. Now but at the same time the pressure drop during low flow condition would be lesser and high flow condition will be higher. So the bottom pressure would change if you are maintaining the top operating pressure. Yeah now if you are having the turn down flexibility by means of a wall tray now imagine a situation wherein for 100 percent if you do not have a flexibility then okay. So now if you are using a wall tray in such situation then what will happen is the escape area the vapor escape area in term in case of higher flow rate is say X when you are reducing the throughput the vapor flow at that point of time the escape area will reduce and now for reduced escape area you have reduced vapor flow rate but pressure drop may not be same but slightly lesser but will not be lesser in proportionate say at 100 percent you had a pressure drop of across the column of 2 kg and now at 50 percent the pressure drop will not be 1 kg because you are reducing the escape area. So pressure drop if not 2 it may be 1.8 or 1.9. So pressure drop and this is the it is a good question let me explain this if you are changing the pressure drop then bottom pressure would change if bottom pressure is changing the bottom saturation temperature will change if that is changing then your bottom product purity would change and this is the concept of having better operating flexibility. So even at lower flow conditions we need to maintain similar pressure drop to achieve similar bottom temperature and that is the reason where this wall tray will be useful when at lower operating conditions you have lesser openings and hence similar pressure drop. So as to achieve the bottom column bottom pressure to achieve the temperature and purity. See typically depends upon the type of tray that has been used say for example wall tray yeah might have to rush little bit because it is 12.15 I have to cover random packing as well as structured packing. So but I do not please do not hesitate to ask me questions. Dwell flow trays basically it has the vapour and liquid flow path in the same there is no downcomer. Baffle trays are good for heat transfer application and it can handle very large amount of solid and coke. Disc and donor trays and ripple trays are few other example of the dwell flow trays. ERD trays are the trays which are used for collecting or partial draw or segregating between two different sections but these are not essential these are not mass transfer devices these are transition trays. ERD trays are extra resistant design trays for example in certain fertilizer complexes there are very high flow rate of gas at high pressure and the bottom most tray would see very large impact momentum. So the bottom two or five trays are designed with additional mechanical strengthening those trays are called ERD trays the process consideration remains same but the mechanical considerations differs drastically. So there the tray man-way panel strengthening, tray hardware truss ends and tie trusses are required to additionally strengthen the trays. So this is the tray development timeline so around 1930s or 25 the bubble cap tray was invented and started in commercial use around 1955 the sieve and wall trays were evolved and in late 19 and in 19 wall tray yes both of these were parallely evolved considering the fact that bubble cap are expensive to manufacture it offers very large amount of pressure drop and they industry people and scientists started realizing that there is lot of energy which is getting wasted lot of pressure drop which is not contributing into the mass transfer. So that is how these concepts of sieve tray and wall tray came into picture and then in 1990s the high performance trays came into picture. All this while the drivers for advancement were to increase in efficiency to achieve more intimate contact between evaporated liquid increase in capacity to maximize the useful pressure drop, optimize the revamp cost and time so that the cutting and welding required is minimum because companies had installed columns and they realized that instead of 120 tons per day now they need to manufacture 150 ton per day and they still have good demand and good margins. So revamp came into picture so how revamps can be done in faster time with less of cutting and welding the advances took place in those direction and to increase fouling resistance in order to increase the run length ok. Most of the things we have discussed on this slide with respect to contacting zone. So there is a contacting zone here, this is the contacting zone, this is the down flow zone and this part is the vapor disengagement zone. So capacity limitation is either by bubbling area or by the down comer capacity with respect to disengaging vapor and liquid. So high performance tray came into picture when the technologies were developed to increase the active area to enhance the efficiency of the active area by using mini walls and the using of push technology and also advanced down comer technology and inlet area enhancements. So what was done is in the sieve trays they had performed some experiments that if you have 14 percent open area with 13 mm dia sieve holes on a tray and for same 14 percent open area if they go for 25 mm hole area. So number of sieve holes would reduce for larger hole size but the escape area still is 14 percent. So they thought that probably the pressure drop would remain same but which was not the case with smaller holes with the same 14 percent open area the pressure drop was lesser. There are some equations which has subsequently derived this. So for the same escape area of 14 percent to 14 percent escape area that is escape area divided by active area the bubbling area. So that was 14 percent by keeping that same but by reducing the hole diameter and by adding the number of holes the pressure drop across the tray was reduced. So in turn the capacity handling has increased. So that was the aspect that is used in high performance trays. So you will find on the high performance trays the mini walls are used whether fixed or floating but a mini wall. So typical hole size is 39 mm for a wall for a wall tray. So these walls would have holes wall diameter of something like 28 or 29 mm because of which the number of walls they used is more with the same escape area they could get lesser pressure drop and in turn higher capacity. So in the market right now this coagulate has VG0 and MV1. VG0 is a fixed wall and MV1 is a moving wall or mini wall both of these are mini walls and solar has wall tray called MVG mini VG mini V grid wall. So with the help of this mini wall the active area the utilization of active area has been enhanced and with the help of advanced techniques for area using under the down comer. You can imagine that the vapour which is otherwise below this you cannot use this area because this is the inlet panel. So vapour is flowing through this cross sectional area only. Now what was done is an inlet panel the resist seal inlet or inlet panel has been introduced below the down comer and the holes are provided below this panel and the escape holes on the length on this side. So now vapour can enter not only from this area but also from this area. The hole sizing has been dynamically adjusted in such a way that vapour can still pass. Another important concept that I need to explain here is in a in any kind of tray there will be a gradient of liquid flowing from entry to the down comer. Now because of the gradient at this zone the liquid pool is going to be higher whereas here the liquid pool is going to be lesser. So the resistance for vapour up flow is higher in this area because of the higher static whereas here it is lesser. So vapour will try to take the least resistance path. So even whatever vapour is coming from here it will try to enter from here. So which is undesirable vapour distribution. So now for liquid to flow the gradient is going to be there. We cannot avoid that because otherwise the liquid flow will not take place. Now for higher length of higher static head we need to balance the pressure drop in such a way that the vapour can pass through that also. So what has been done is there is two component of pressure drop. One is when the vapour passes through the tray deck there is some pressure drop which is called as a dry tray pressure drop and then the vapour passes through the pool of liquid that is a liquid wet pressure drop. So here at this zone the wet pressure drop is going to be higher. So by increasing the vapour cross sectional area the dry pressure drop is reduced. So now the total pressure drop in this region as well as in this region is more or less same and that is how vapour will escape from both the regions. So by avoiding by having higher vapour cross sectional area for vapour up flow we are achieving balancing of the pressure drop for entry and exit zone and because of which now vapour is entering from this zone as well. So in the conventional tray that entry part was taking lesser participation in vapour liquid contact because of the higher resistance for vapour flow. In the high performance tray technology even that part has been used while increasing the capacity. So that is how the area under the down comer has been used to achieve higher vapour of vapour cross sectional area and to achieve higher capacity. Another concept on the same aspect when from a conventional tray the liquid travels from the down comer to the next down comer which is feeding below there is a possibility of the stagnation stagnant zones occurring at the periphery of the column. So this area is not contributing into the mass transfer. So what was done is the down comer shape has been increased in such a fashion that the flow towards the periphery also is taking place without creating a stagnant zone. So this area is now utilized effectively here for additional mass transfer and this down comer you can see that the down comer residence time or volume is reduced here because of this down comer. You will think that the capacity of down comer with respect to liquid handling capacity is reduced or froth handling capacity is reduced but here the down comer shape is an umbrella type. So when the liquid and the froth falls onto the down comer it will fall on that umbrella part. I will give you a classical example when we when somebody pours a beer in a glass of water when he keeps it vertical then the froth formation is higher. When he kills the glass and pours the beer then the froth formation is less because it is seeing more surface and hence resulting in lesser froth because of the surface tension property. So here when the apparent type of down comer is there umbrella type of down comer so it has more surface area for froth to fall on and because of which because of the surface tension property the disengagement of vapor and liquid is better. So even though the down comer volume residence volume or down comer liquid holding capacity is reduced but the effectiveness of down comer has been increased by providing this umbrella type of down comer. So now you need lesser down comer size so naturally your active area is increased so naturally your column capacity would increase again without compromising on the vapor liquid contact or disengagement or the efficiency part of it. So this anyway the person is not supposed to go from the down comer he has to travel from the man-way panel so there would not be any problem. So this is basically a super fact rate technology which is developed by Cochlit and the features that I have talked about like optimum contact device greater liquid handling capability maximizing active area and the flow path length improve bubbling activity distribution. There are some mechanical advances also took place with respect to mechanical strengthening and engineering features in order to reduce the installation time in order to reduce the column modification for revamp jobs. There are various high performance trays available in the market from Cochlit it is bifrack, maxfrack, nye, superfrack, ultra fact trays. So this has vortex down comer tray, matter MVG tray, MVG plus trays and Norton had developed Norton is now with BOTOR by Cochlit so Provol and Triton trays are now Cochlit products. Some of the pictures I have just shown it from bifrack is fixed wall tray with in two directions to have better vapor liquid contact, nye tray, maxfrack trays various I will just rush through this. So depending upon which operating regime based on vapor and liquid traffic you are operating the you are going to have the column design based on that you can have selection of which type of tray you should be using. So superfrack tray covers a very large area of operating regime whereas if you have a specific operating range in a mixed regime then you can go for either nye or Triton trays or if merits of trade columns I think I will skip through this because I am sure you would be aware of. Basically again same process requirements with respect to capacity efficiency, the fouling, the corrosion and pressure drop based on these considerations different either tray column or pack columns are chosen. Various kinds of random packing, burl saddles, rashigring then interlocks metal tower packing which is very popularly used, pall ring, cascade millering, nutter ring. Here also the development took place with the same drivers with respect to improving efficiency, capacity, fouling resistance. So first generation random packings were rashigrings just as if the pipe pieces were cut and used as a packing for vapor liquid contact. Then second generation was pall ring the you can see that the pall ring was nothing but the same pipe is with slots to achieve better vapor liquid contact and wettability. When rashigring was used very 100% of the specific surface area outside and inside was not really used in the mass transfer but it was contributing on to pressure drop. So wasteful pressure drop was much more. So when the notches were provided inside and outside the surface area was getting used for vapor liquid contact and in turn not only it increase the contact but it also reduced the pressure drop because of better escape area. And the third generation is basically IMTP packings CMR packing wherein the packing height to diameter ratio was changed because of which the specific surface area that is meter square per meter cube of packing was significantly improved which offers better vapor liquid contact on to the surface area of the packings. So these are various names of random packing rashigring, lisigring, burl saddles in the first generation, second generation pall ring interlock saddles and third generation is IMTP, CMR, Nutter ring, Pleximax. You will get good amount of information on this on the book called pack column internals by Striegel particularly for random packings it is a very good book. As for advancement in case of pack columns or packings was again for maximizing efficiency lot of advances took place in an effort to maximize the surface area in an effort to spread this active the surface area uniformly and promote better vapor liquid distribution within the column and reduce the liquid hold up and to maximize the wetting. How much ever efficient packing that you put in if the packing surface is not been properly wet then it will not contribute into vapor liquid contact and it will not contribute into efficiency. For maximizing capacity the advances took place in an effort to maximize void space per unit volume minimize friction and ensure uniform resistance to vapor liquid. So again the main concept beyond on which the advances took place was to maximize the useful area and minimize the wasteful area. In case of structured packing the in 1940s PANA pack which was if you see the asbestos roof rooftops. So it was arrangement of asbestos that kind of corrugated rooftop to achieve the vapor liquid contact to have better separations but they realize the vapor escape area is much less the vapor liquid distribution across the column is not uniform and that is how the second generation of structured packing developed. That was a wire mesh packing wire mesh packing is a wire gauge kind of packing which offers very good vapor liquid distribution and it requires very less amount of liquid to wet because of the capital reaction when a drop falls on a wire it will automatically wet the entire surface of the wire. So that is how the wettability is very high in case of wire gauge kind of packing and in turn it offers very good efficiency but it was very expensive and also it was very prone to fouling due to solids. So that is how the thin metal sheet structured packing got evolved corrugated structured packing in 1970s. So drivers were cost sensitivity to solids and high capacity and retaining high efficiency. So for wire gauge BX packing this is jointly developed by Coglitch and Schulzer so it is called as BX packing. Corrugated sheet metal packing there at in the market you have Flexi pack, Gem pack or Mela pack as the trade names for various vendors. In the structured packing the recent advances I will talk about is with respect to structured packing in this if you can see here that the two structured packing layers when installed in the column are rotated 90 degree to each other to achieve uniform vapor liquid distribution within the column. So what happens is when the liquid from the layer above is flowing to the layer below it takes a turn it takes a 90 it takes a turn at the intersection of the packing. Now when the liquid and vapor is travelling on to the surface of structured packing it is contributing into mass transfer it is contributing into efficiency part of it. But at the transition between the two layers there is some accumulation is taking place due to change of direction of liquid and vapor which is creating larger pressure drop. Now this pressure drop is not contributing into the efficiency part of it. So efforts were made to identify to eliminate or reduce this pressure drop which is occurring at the transition of the two structured packing layers. So what was done was the bottom most part of the packing instead of keeping it slanted it was smoothened out either it was kept vertical or there is a gradual curve because of which the transition from the layer above to layer below was made gradual because of which the accumulation of liquid at the transition zone is reduced and in turn reduce the pressure drop which was actually a wasteful pressure drop. So you can see here that at the intersection the part is straightened out because of which the transition becomes smoother. Grids are used for very high vapor liquid services wherein the efficiency is not important but more of heat transfer kind direct contact cooling kind of applications or where there is very large amount of solids are to be handled and number of theoretical stages required are very less. Various types of grids C grid, EF 25, flexi grid, snap grid, mela grid by different column internal vendors. Let me quickly run through the pack column internals also. So for packing to perform the pack column internals are required to hold the packings we need support plate to support the packings to hold the packings from the on the top side we need bed limiters or hold down plates. Liquid collectors are required for collecting and redistributing and liquid distributors and the feed pipes. It is very important that how much ever efficient packing that we are using the internals are to be the pack column internals are to be appropriately designed to avoid premature flooding and to avoid excessive pressure drop across these pack column internals. In fact, most of the failures in a pack column is attributed to the liquid distributed design rather than the selection or type of packing. So chimney tray feed pipe are other few of the column internals which are required chimney trays as I discussed earlier that it is either for collecting or partial drop and feed pipe is feeding you can imagine that in a small column if you have a just single feed pipe entering the vapor from bottom or liquid from top whatever the distribution effort required is lesser because the diameter itself is small. But if the column diameter is pretty large something like say 4 meter and if you have say 40 inch pipe and just put it below the bottom most tray then it would consume some amount of vertical length of the column for vapor to effectively get distributed. So either you need to provide that length empty to achieve that vapor distribution or you need to have some device which will distribute it faster and reduce the length. The moment you reduce the column height you would have significant benefit with respect to overall cost. So that is how the vapor distributors or liquid distributors are important. In case of pack column also if you do not distribute the liquid at the first place properly in the feed pipe then 2 or 3 layers of packings would actually get utilized in effective distribution. So there is a compromise there with respect to its contribution with respect to heat mass transfer just pictures of it. In liquid distributors there are various types gravity distributors pressurized distributors flashing feed and the selection criteria depends on the liquid rate plugging or fouling tendencies turn down requirements and nature of feed flow. Again the design parameter for the liquid distributor is the design quality which is basically drip point density. So drip point density is defined with respect to how many number of drip points are there divided by the cross sectional area. Just imagine a situation where suppose IMTP 70 is the packing that you are using. So IMTP 70 being a large diameter packing now the liquid dripping density required will be lesser because if you go for say IMTP 15 each of the packing needs to see some liquid when the liquid is fed on to the packing. So you would like to have larger drip point density larger number of drip points per meter square. So if you do not provide that then some amount of packed bed will actually get utilized in distribution of uniform distribution rather than mass transfer efficiency. In gravity distributors there are pan distributor pan type that is which will have a pan and either just holes for the liquid to go down and annular area for vapor to go up and in case of there are pan distributors with riser pipes also for vapor of flow and then there are I will show some of the pictures of this distributors. So this one is the orifice type distributor where there is vaporizers and liquid orifices and this is a ladder type gravity distributor which is just a pipe distributor. In the orifice distributor usually is preferred for small diameter towers and the drip tubes are provided for fouling services. If you do not provide the drip tubes and the service is fouling then it will plug the holes and the moment any of the holes are plugged the uniformity of distribution will get affected adversely. So if you have the drip tubes the whatever fouling takes place that will sediment on to the deck of the distributor and it will not actually plug the drip tube drip will continue to drip the point drip the liquid at the packing below. Then there is V-notched and channeled trough type of distributor. This is a trough distributor this is a very advanced distributor wherein you will you are seeing here a feed pipe then there is a inner parting box then there is a parting box and then there are lateral troughs and there are diffusers as well. So in large diameter column the complexity of design of distributor also becomes very important or very crucial. So from the feed pipe to the drip point it is distributed the liquid is distributed in such a way that at turn down as well as turn up condition the liquid drop which falls on to the surface of packing will remain will fall at the same point to ensure the desired efficiency. Just imagine that if there is say this lateral trough and now at high flow condition the liquid level in the trough will be higher. So in this case when the liquid low is high at that point of time the static head is more and the on the surface of packing this liquid will drip here whereas when the liquid level is less then same from the same hole liquid will drip here. So now your distribution of liquid is changing. So this is not this is not desirable situation. So what is done is tube is provided here with the help of this tube even though whatever may be the flow the liquid will fall on to the tube and then drip down at the same point on the packing and the two levels are provided to ensure turn up and turn down condition. In turn up condition from both these holes liquid will drip on to the drip tube and it will fall on the same point on the packing and in the turn down condition only may be from bottom hole it will go and any fouling or anything that is taking place can get accumulated in this area. So these are this is all this development took place to have better turn down flexibility better resistance to fouling and ensuring uniform vapor liquid distribution and avoiding higher pressure drop at the same time achieving higher vapor capacities in the liquid distributed technology as well. And there is spray nozzle header distributors typically these are used wherein mass transfer as well as heat transfer has to be achieved typically from air water kind of systems where these kind of spray header nozzles are also used. Pipe orifice headers flash feed distributors are basically used when a two phase feed is to be fed to the column. So you can imagine that when the feeding pipe is carrying vapor as well as liquid and if you do not provide two different paths for it then along with vapor if liquid also is going then the momentum the impact on the tray above or packed bed above will be much larger which will lead to deterioration or fouling of trays. So in such case the slots are provided for vapor up flow and holes are provided for liquid down flow and even above the slots there are hoods that are provided. So whatever vapor goes up which will carry some liquid with the help of those sieved or slotted hoods the liquid will be sent back in the downward direction and vapor will be kept in the direction above. There are different types baffle type or gallery type of liquid distributors. So let me summarize by saying that for all these column internals be it a tray or a random packing or a structured packing or packed column internals the primary requirement is efficiency and capacity and the secondary requirement is to ensure the pressure drop resistance to fouling and resistance to corrosion. You can imagine that the structured packing will be a thin metal sheet which will be say 0.1 mm or 0.2 mm whereas trays will have a thickness of 2 mm or 3 mm. So if the service is very highly corrosive either you will have to go for an exotic metal while going in for structured packing but if that is going to be too expensive then higher thickness trays would be a better choice. So these kind of various considerations are there while selecting and designing the column internals. Typically minimum is 2 mm and maximum can be 3 or 3.5 mm that is it, yes 3.5 mm. You will see more panels, no the tray panels there will be multiple tray panels and multiple number of beams to give that strength, same beam supports would be given. See the tray, so all these panels, these are all tray panels, yeah so these are tray panels. Now in case of larger diameter instead of 3 you might have 50 panels. So now the panel size and the thickness would be such that the 3 mm or 3.5 mm will be adequate. So for these panels there will be beams which will be running below, say on this joint below this there will be a beam which is running which will give that additional strength. Now in certain cases like 12 mm columns there are girders between the two trays that are provided which will give support for the tray above and tray below for this mechanical strength. So tray number 1 will not have any support, tray number 2 and 3 there will be a girder which will support tray 1 and tray 2 likewise. So every alternate location there will be girders which will take care of tray below and tray above. Yes, yes all these are bolted panels so it can be independently open, not welded. There will be tray support ring TSR on which it will be clamped, welded trays had been used in the past. Very old techno in the initial days welded trays but then operation maintenance inspection becomes a problem. So these are all bolted trays, clamped trays. So the gap there is a tray support ring ok. The tray support ring is a horizontal portion on which the tray deck will sit and it works as a seal, I will show you that. Now you cannot have exact diameter outside diameter of packing cannot be exactly inside diameter of the column because there will not be a tolerance for installation absolutely. So typically the structured packing has something like 5 to 6 mm gap on each side yes. Now your question is right then in such situation channeling will take place, liquid will tend to flow to the periphery and then through the wall it will go down. So what is done is there is a wiper band, it is called as a wall wiper which is which serves two purpose. This is a very thin metal sheet which is used to tie if it is a small column diameter say 400 or 600 mm it will be a single brick, single layer of a structured packing. So you do not really require to tie it from the periphery. But imagine 800 say 4 meter or 2 meter diameter column in which structured packing is to be kept. You cannot have a single brick from installation point of field. So you will have multiple bricks which will be arranged in column and it has to be tied. So when it has to be tied this wiper band is used of course this wiper band is used for packing and it is just a metal whatever it is. This the upper part there will be in the packing element there will be upper part and lower part. So it is flexible material it is opened out when the packing is installed wiper band is it is a collar it is a collar kind of thing. So the collar is opened out. So when the collar is opened out it actually touches the wall. So whatever liquid is falling from the wall it will fall on to the collar and it will go inside. In fact this collar if you see from close angles it will have notches on this side which allow the liquid to go into the packing. When it goes into the structured packing automatically it will get spreading properly. It is a wall wiper back to the.