 is the definition is the technique in which fine solids are transformed into a fluid like state through contact by a fluid in the bracket you can put either gas or liquid okay. So the phenomena we will discuss through the diagrams I will draw these diagrams so that the picture will be easy for you to understand gas or liquid then we have this one we call it as packed bed height, okay able to see, okay. So this is HP height of the packed bed and yeah at very low gas or liquid velocities there is not sufficient energy in this phase fluid phase where it can move the particles but on the other hand what it does is it only tries to find out where is wherever there is a small interstices yeah through that it will move and comes out, okay nothing happens at that time the bed remains as a bed and of course depending on very low flow rates one can also measure the pressure drops that I will draw the graph later. So at a particular point this situation this is fixed bed we can write fixed bed then same thing gas or liquid when you have this is the height still you have the particles very close just see here just a little bit more height this is H M F height at minimum fluidization velocity, okay good so this is okay yeah. So as I told you when you slowly increase either gas or liquid nothing will happen at very low fluid low velocities only the gas or liquid try to percolate through the pores and then when you go on increase very small increments then the gas or liquid at one point of time the drag force exerted by this fluid either gas or liquid will exactly balances the weight of the solids in the bed, okay so drag, drag is a force weight in the gravitational field is also a force so when the both the forces are same drag force balanced by the weight or weight balanced by the drag force then you will have the particle movement a later a little bit yeah the particles move a little bit but still the bed is not expanding that much the particles try to readjust themselves, okay for a more easy I mean in a relaxed manner so then it will try to move in that restricted place a little bit you know like small vibrations small movement of the solids. So at minimum fluidization velocity if you look at the bed it is not exactly like you know vigorously solids moving but definitely solids will readjust themselves but capable of moving even at that time but not to a great distances and the distance between each particle is also not that much that is the reason why you have anyway this side and this side it cannot expand it has to only expand in this direction that is why I put this is packed bed it is slightly less because of the readjustments, okay just because of the readjustment a little bit more but all the time we will take HP also equal to HMF at minimum fluidization conditions, okay but here at this point of time if I want to test the characteristics of this bed if I put a let us say an iron ball, right yeah at this here after the weight is balanced by the drag force if I put that steel ball then that will simply sink just for comparison if you do the same thing here when the bed has not yet fluidized that means it is still in packet condition what will happen it will simply stay at the top so that means the density difference has come and yeah not only that in fact if you have the cork also cork will just simply float exactly like it is in water not only that you have if you have a small hole here then it flows like a fluid, okay so just at the time of minimum fluidization velocity at the point of minimum fluidization velocity try to have a hole here side wall, okay then it comes as a jet it is exactly like if you have water in a tank and then put a hole then it comes as a jet and also one more property if I slightly tilt this, okay instead of putting vertically if you slightly tilt like this so when you tilt this but still your surface will be horizontal whereas that is not possible here in the packet bed conditions so that means what is that we have done already we have spoiled it because I think it was very happy stable without moving so then we made it as a fluid where it can easily move, right all the fluid properties it acquired like density difference something can sink and also something can float and when you change the direction to any inclined position but still all fluids maintain horizontal surface, right so same thing is there and if you put a small hole then it will like it will come like a fluid all the properties what we normally see for fluids are seen for the solids in the presence of another fluid that is the reason why it is called fluidization, okay that means you are imparting fluid properties to the otherwise immobile solid particles, okay tremendous advantages, okay because of these the first fluidized bed was in Germany Winkler gasifier I do not know whether you have studied in chemical technology Winkler Winkler WI and KLER Winkler gasifier that is one of the first applications of fluidized bed then later applications came to your FCC, food cutter kiking so from then onwards unlimited uses of fluidized beds but in the beginning is first the gasifier I think that was 1921, 1922 I think that time I am not very sure exact so the advantage of this fluidized bed is that now you can if you want you can easily transport the solids from one place to the other place and particularly you know in chemical engineering all the operations are multiphase and you should have better contact between these two phases now we have either solid or liquid or liquid liquid you know two immiscible liquids or gas liquid you know you will have all combinations of the phases in chemical engineering so our idea is how to have the best contact between these two phases so that kind of excellent contact will come here if I have a solid phase and then either gas or liquid I am trying to use okay excellent contact and theoretically speaking if I look at the particle in an ideal fluidized bed each particle is simply suspended by the fluid so that is why like our fluid mechanics we always draw on beautiful circle as a particle around that you will show very nice stream lines okay so what is happening when I show the stream lines whether it is heat transfer process whether it is mass transfer process then beautifully each particle is uniformly either taking if it is mass transfer adsorbing or if it is coming out from the leaching and all that so beautifully comes out heat transfer also same thing heat is uniformly transported and on the other hand if you look at the packed bed of the same height what happens packed bed is resting one above the other all the particles right so that means always some contact area will go for the solids that contact area is not available in the packed bed conditions okay talking about the same particle size right and normally we use the particles very very small particles in a fluidized bed to take care of our surface area per unit volume advantage that means when you are going for smaller and smaller size you know surface area per unit volume equation is 6 by dp diameter of the particle surface area per unit volume so when you are decreasing particle size surface area will be tremendously increasing okay so if you are going for 1mm then 0.1mm 0.01mm 0.01mm is 100 microns right 10 microns 10 microns so then go to 1 micron then you will have tremendous surface area and we can use that kind of surface area also for the solids so that we will get very high transport processes right good so that is the one now till here we are almost in ideal conditions this is fluidized but beyond that if you increase what will happen beyond that if I increase let us first save only I have liquid okay the behavior from here the behavior if I use liquid as the fluidizing medium or if I use gas as fluidizing medium the behavior changes that is why first we are taking liquid so if I take liquid and then go for example at this point I can also say that I have emf the velocity corresponding to this minimum fluidization condition is emf so beyond this if I go and let us say I am using 2.5 times or 3 times emf right so then if I use that then beautifully this expands in the presence of liquid why I am telling beautifully is the inter particle distance between the yeah the inter particle distance in the bed is almost uniform when you have liquid and that is why we call this one as smooth fluidization or particulate fluidization particulate fluidization right it is very nice to see one can easily predict also the length of the bed how it is expanding and we can just imagine here beyond minimum fluidization velocity the drag force of course is just balancing so beyond that you are increasing velocity so drag force will be definitely more so when it is more what is happening how it is transformed the drag force is transformed in the form of expanding the bed okay but if you take the pressure drop I will come to the pressure drop later at this point onwards you have the same pressure drop for the solids weight is not changing right I mean weight is same weight is not changing so keeping the weights same and when you increase the drag force okay by changing the liquid by changing the liquid velocity or gas velocity so the pressure drop is not going to change only thing is in the bed you will have different conditions coming right so like that in the particulate fluidization condition the pressure drop will not change but the bed can be very smoothly varying now the same situation if I show for gas it is not so smooth so you will have here a bed these are the bubbles so you will have small bubbles forming here growing like this even though we take spherical bubbles they are not like that yeah this is the bubble gas bubbles will form and these bubbles are not seen in the liquid solid fluidization okay and the reason for the bubbles I think we do not know yet exactly but we know how they form because whenever I have a perforated plate and with a small perforation and the solids are just resting on that the gas has to move through that so when it is moving it will try to push the solids slightly away from the from its way so when it is pushing so then there will be a wall like thing just above the that area so that wall this wall is nothing but solids only solids only just forming like this so when it is just pushing it up then they form that wall and the wall cannot break because just after that also you have lot of solids so it is not breaking so the entire bed almost in the small void there it will try to push it up and beyond here at the top because there are no further solids there then it has to break and when it is breaking then all the solids till then it is just moving like this okay yeah just moving and then when the bubble breaks there all the solids now cannot be supported by anything there is nothing to be supported so they simply fall when they are falling they come to the bed that is how you have good mixing in gas solid fluidized beds because of this bubble formation and the bubbles are not there at minimum fluidization velocity that is why at this point whatever gas you have all the gas is used only to support the solids but here when I have that you know 2.5 times or 3 times as I told you the gas velocity then that extra gas beyond what we use for minimum fluidization velocity extra gas beyond minimum fluidization velocity that goes in the form of gas so that is why many researchers accepted that if I am sending u as the velocity and the velocity at minimum fluidization is umf so u minus umf multiplied by cross sectional area is the volume of gas that is in the bubbles correct no u is the actual gas let us say 10 liters okay I mean velocity wise and now I directly can tell volumetric flow rate wise and I need only 2 liters per hour or 2 liters per minute as the gas required for minimum fluidization velocity so that extra 8 liters per minute is the gas that is going in the form of bubbles okay it is not exact measurement but I think these very difficult contacting pattern for gas solid right so that is why it is not exact many people say that no no no some other gas is going this way that way still fighting is going on but still majority of the gas goes only in the form of bubbles and the our imagination is that there is no other way to go to to go for the bubbles okay I mean for the gas to go so that is why either it has to support the solids and go otherwise it has to go as bubbles right so that is the reason why you have here a kind of uh aggregative fluidization where it is not uniform because why it is not uniform where the bubbles form where the bubbles break you cannot say in fact when you have this situation you can do that experiment in your house also take a water you know put in a some vessel and then bubble it just look from the top can you find out at what point bubble come and then what point bubble breaks you cannot same thing happening so that is why some people say that this is also boiling solids we do not see the bubble we see only the wall you know the empty space in the solid the empty space in the solid is seen as bubble okay and people have photographed I will also show you that photograph later okay some photographs have been taken and I think people thought that you know there are definitely bubbles okay it is that is why many people still have lots of doubt if gas liquid one can see that is what normal things those are all low hanging fruits what we say okay when you are able to imagine when you are able to see very clearly okay so then the description of that understanding of that is much easier but something beyond our mind if you are not able to see and then you have to imagine okay so that is why a measurement is required where you because you are not able to see that of course you can see that when you have a glass column but I think you know that voids and all that definitely can be seen but to be still perfect and measure it and then find out what kind of bubbles we are getting why they are coming under what conditions like for example that they also depends on your velocity that also depends on particle size okay particle density all kinds of things will come how the bubbles are forming right good so that is why this is not no more smooth fluidization this is called aggregative fluidization aggregative so essentially what we have to remember here is that till minimum fluidization velocity whether you have gas or liquid doesn't matter because both are going to behave same way same way and then beyond that when you are using liquid fluidization liquid solid where liquid solid applications also after biochemical engineering there are many for example wastewater is one of the applications you know liquid solid systems in fluidization in using fluidization beds okay of course leaching you know one method of extracting the ores is leaching so if you want to take from copper from copper ore you take copper ore and then fluidize with sulphuric acid for example you will get copper sulphate and again copper sulphate you take it to electrochemical cells and then sulphur so for separately cu separately you can deposit right yeah cu so then you get one of the purest form that is how zinc and copper and all kinds of things they do but that is the leaching operation where fluidized bed can be used why fluidized bed is very good there is that you can have small particles number one in packed bed you cannot have that kind of particles and number two surface area is more so then the rate of leaching will be very high and on the other hand every particle will be uniformly fluidized particularly when you have liquid system then on the whole each and every particle is uniformly leached out you know that can be used for leaching each and every particle so like that there are many examples which we can give and liquid liquid solid and there is not many exciting things in liquid solid because everything we know what is going to happen there correct no because there are no bubbles whereas here many many exciting things because first of all I do not know how to measure the bubble perfectly and the people who have measured the bubbles are only two dimensional bubbles what they measured three dimensional bubbles they could not measure they only estimate by some technique okay by sending light for example or by sending some not trace or not a number also this one radio activity you know some signals they send from this to that side nowadays I think people trying to use what is called TEM transmission electro yeah so that kind of sophisticated methods are now coming to measure okay and that to measure it is a three when you have a three dimensional column you will have some bubbles here backside also you have some bubbles this side also you have some bubble this side also you have some bubbles which side you measure whatever side you focus that is not uniformly reproduced all the time okay so that is why they take from various sides and then average the bubble size bubble size is one of the most difficult parameters which we have to estimate properly and that itself is the starting point for all our calculations so that is the reason why it is very difficult gas solid flutations okay good and because it is very difficult there are challenging things if it is very simple I think you know there is no problem at all because there is the phenomena is so complicated that is the reason why I told you that you have many exciting things in gas solid flutations okay then next one if you have let us say I have done the same thing here beyond this minimum flutation velocity in a small this kind of column okay very narrow column if you take narrow cross section then what you see is this bubbles occupy the entire cross section and then somewhere here they break because of instability okay yeah so these are the these remember you have when it is going up near the walls you will not have that much drag because velocity we take zero you know near the wall so the solids will be slipping near the wall somewhere it will go up and then because of some instability it will go to almost to the top okay if there is no disturbance but somewhere if you have disturbance means many many chaotic conditions that is why you know I do not know whether you heard of there is what is called a chaotic theory for each and everything there is chaos in this world in this universe not only world so that is why every maybe with very very small fluctuations are very very large fluctuation large fluctuation means we feel small fluctuation means we do not even notice them but everything can be analyzed in terms of only this kind of fluctuations right so chaotic theory that means system is not stable it is chaotic but people see that there is an order in the in the chaotic environment there is still an order now if you go to mount road and if you stand there for some time first time it looks very chaotic I do not know why people are going this side car is going this side I think bullock carts might be going that side and all that you observe that let us say one week you will find a pattern how how do you find a pattern the same 18 b bus will come all the time okay really 23 c will go there so if you are able to look patiently there you see some pattern coming may be there is some bench car that same bench car because that fellows office may be somewhere there nearer okay so always you know when you patiently observe that you will find a pattern so that is what you know order out of chaos I do not know whether there is a wonderful book which I could not complete in last 20 years I think I told you know James like is chaos that is a beautiful book to read the other book is that Ilya Ilya Prygogin heard of him Prygogin P-R-I-G-O-G-I-N-E he is a noble laureate in chemistry he wrote this book order out of chaos okay actually he wrote that in French and someone translated into English horrible translation because that is why I think nothing moves there there is no flow in that book oh my god how many years I have that book I am not able to still complete but there is wonderful information about thermodynamics about biological systems all order and how do you see sorry all chaos how do you see order out of that James click is beautiful book once you start like now you can read okay but the other book is very very difficult where tremendous amount of information is there excellent information so that is why here also because of those fluctuations somewhere because of instability the slugs will break and then all the particles will come down when they are coming down again you know some of the bubbles also may be broken and that is why some of the fluidization researchers thought that let me take because you see you see how human mind works because to break the problem into simpler problem so is it difficult is it easy to have thousand bubbles and then try to characterize thousand bubbles or one bubble and then try to characterize one book so that is why what they did was okay let me take the small diameter column okay let me create slugs and let me understand how the slug because there is only one slug any time correct no so that is why but most of the time what happens is when you have this kind of thing it is too much aggregative fluidization and this is a big void most of the time in the bed if you see there will be only 20 percent or 10 percent solids the rest is only gas gas bubbles you know one bubble that means one bubble here another bubble there another bubble there may be five six bubbles will occupy but that bubble is very slug you know very lengthy bubble and occupying the entire cross-section so it is not allowing to solids to have many solids so that is why they try to break it particularly Australians there are few who are trying to do that and this is called slugging bed yeah there are many things here you know this aggregative as I told you when you have more and more knowledge you also try to look more and more and more and more narrowly between velocities okay between aggregation and then if I go slightly more than that what we what we call as turbulent bed okay the difference between aggregative and turbulent is the bubbles are slowly trying to dissolve okay dissolve what dissolve to go for pneumatic pneumatic conveying that means when around terminal velocity the bubbles may disappear solids may try to go out okay so another concept is I think definitely would have heard of circulating fluidized beds circulating fluidized beds no not heard I told thousand times I say in the last semester also Anand Kumar looks as if it is a new word for him Latin or Greek you have not heard don't remember okay yeah so you allow the entrainment and then bring the solids again continuously and circulate them okay what is the advantage because now I don't have bubbles I can clearly find out what is going what is happening at least in the bed but what is the drawback drawback may be that the amount of solids in the bed may be small so normally it happens around 15% solids 20% solids whereas here I have 50% solids and also 60% solids okay 60% is more around 50% because normally packed bed will have what percentage of you know packed beds will have what percentage of solids normal packing spherical particles okay how can you have 80% I say in packed bed packed bed has also porosity which one is 60 you are talking voidage or solids I have asked solids voidage is 60% I know andra call it solid what do you say before that 40 to 50% why 40 to 50% it is a packed bed under what conditions it will be 40% under what condition it will be 50% Dhanitha, Prabhu will give a nice answer, Prabhu what 5% increase 65% solids why 65% told you know beautiful that is the reason I asked you at the end you are the final answer okay yeah always averaging things okay I think like Buddhas thing take the middle path if you take extreme path you have to unnecessarily work hard take the middle path happy no problem no one can push you that corner no one can push you this corner walk okay Buddhas fundamental thing it seems take the middle path always in your life don't be an extremist that is the idea okay yeah you tell me why 40 and why 50 65 is not correct 45 see in material sense they derive and then show it also if you have ideal spherical particles how much fraction you get size it will not depend if you have spherical particle shape is spherical I am telling you know spherical-spherical exactly there is around you know 0.32 or something you get structure if you take that is voidage I am talking voidage is around 32 and you have 60% solids okay in packed bed because they are not 100% serious spherical most of the time we can take around 40% voidage and 60% solids if I take 100 liters I will have 60 liters of solids and 40 liters of voidage okay so that is what yeah so that is why now the operations depend on on what regime you operate like for example next one is we have pneumatic conveying here again it is same either gas or liquid again you come back to the original to the same okay so when you go to the pneumatic conveying you have only few solids that is pneumatic regime so that means solids are we say pneumatic regime but I think you know hydraulic hydraulic regime also we will say where the transportation of solids are occurring because of water okay liquid so this is pneumatic again but does not matter whether you have liquid or solid you will have this so what are the basic conditions here basic conditions for fluidization first of all it should be vertical you should take a vertical column okay and then put a distributor plate put a distributor plate and then the distributor design also is one of the very very important crucial factors and then it slowly increase the velocities such that the entire bed is supported by the drag force of the fluid and beyond that if you increase then if you have a liquid system it nicely expands nicely expands means anywhere smooth fluidization and the inter particle distance is uniform throughout the bed etc and if you take the same condition that means 2.5 mm or 3 mm and then conduct the same thing with gas right so the gas will have aggregative fluidization where the gas goes in the form of bubbles so that creates aggregations and that also creates good mixing in fact you will not have that kind of good mixing here you will have here very good mixing for solids that is why Levenspiel says that you know thalic anhydride is the plant where chemical engineers design it seems any chief engineer designing thalic anhydride plant plant okay if you ask them to sit on the plant just before startup it seems he says that very few chief engineers would have left in the world because definitely something will happen and explode chief engineers will be converted into some other mass okay may be operate anything can happen so that is the reason so for that to control that kind of heat you know that is generated if you want to dissipate that heat this condition is the best condition okay this is what also what they do you know circulating fluidized bed before circulating fluidized bed there was fluidized bed combustors I do not know whether you heard of them or not these are not you know myth they are reality where they are working in thermal power plants what they do is they take very big size fluidized beds fluidized coal continuously feed the coal I have told you here batch only but continuously also we can do that experiment nothing will change okay if you are maintaining the same bed and all that so coal particles will be continuously fed and burning combustion is taking place now you put inside heat exchangers cooling coils they are not actually cooling water water pipes water tubes so then water will get evaporated to steam that steam will come out you know after getting sufficient steam then that is attached to your steam turbine the turbine is attached to generator from there we will get AC and all that okay really so that is why fluidized beds you know when compared to other beds this is very easy because particularly what happened was when people started thinking about environmental pollution if you have SO2 S as the one of the constituents in the coal that will become SO2 SO2 will come from the chimneys that is dangerous okay that is even spoiling Taj Mahal okay sulphur falling on Taj Mahal because how sulphur is falling on Taj Mahal where is acid there Madura refined this Madura refined this refined this also will you know desulphurization there is one step so the sulphur has to be removed so if you are not able to contain that only inside the reactors or inside the process equipment when it comes out then this acid rain will fall and unfortunately Shajahan used calcium carbonate which is reactive material it is not enough if you have used a granite nothing will happen whatever you do okay granite also will slowly dissolve you know some other things so this CA calcium carbonate reacts with H2 SO4 forming calcium sulphate so after sometime you will have calcium sulphate Taj Mahal okay so even now if you go and layer by layer if you see probably already first one or two mm or three mm four mm would have gone okay so that is the problem so at that time what they thought was that the sulphur can be contained and also NYX is a problem all these things are problems now in pollution so with the temperature control you can control NYX you can control SO2 and all that and another beautiful advantage in fluidized bed that to remove sulphur dioxide is you know you do not allow that one to go to chimney what you do is when you are sending when you are sending coal continuously you also send along with coal calcium carbonate calcium carbonate Taj Mahal only you make powder you make powder Taj Mahal and then put it inside what will happen because at that temperature calcium carbonate going to calcium oxide is very very fast is the non catalytic reaction which you already discussed type C reaction CAO CAO will form that is instantaneous what do you call that calcination calcination step is instantaneous then that becomes CAO CAO is highly reactive and you have in the coal sulphur from sulphur will react with oxygen in this because combustion you have to send oxygen anyway so sulphur dioxide will form CAO plus SO2 plus half O2 will give you CASO4 CASO4 is now solid it is not going to Taj Mahal now it is only at the bottom you will collect and try to use CASO4 for something okay CASO4 is nothing but a gypsum no yeah so that depends on you know hydration and all that okay so anyway that can be used that is the reason why they were only trying to convert the problem gaseous pollution into solid pollution because if you are not able to use this calcium sulphate that is gypsum then that is waste again again you have to dump somewhere when you dump it again because calcium sulphate is a unstable compound calcium sulphate is stable and sometimes calcium sulphate also will be there in this conversion it is not 100% converted to calcium sulphate so that will leech out and then sulphur again will go into water and all that we are doing a wonderful job as chemical engineers polluting the entire world okay that is what is our great contribution other things are great there but these also one of the greatest contributors now yeah unless you prevent you know you have to prevent that is why only we have green chemical engineering green chemistry all that you have to do it okay yeah so that is why please show some interest in chemical engineering okay all of you I say all of you where is interest in chemical engineering as I if you have real interest in chemical engineering you cannot you know ask for only marks you will ask for a project sir I want to do this I want to do this I want to do this how many projects are there how many things are there are you asking anything you are not asking anything no now you have you play everything you take tennis bat where it is manufactured by nano carbons you know carbon tubes yeah and then you play very well and with carbon nano carbons also I think some dresses many things are made and you don't know who has made it and then you only play cricket tennis and then throw the tennis bat out very the pride for you I made it as chemical engineer you made it okay even use car very happily driving or running or you know all that but you never feel that it is running because of petrol which you manufactured very the pride for you there is no pride why there is no pride because you are not involved very simple my logic is very simple if you are involved you cannot stopped staying that every time you see that oh petrol chemical engineer okay so anything like that cement building whenever I see building oh beautiful chemical engineer really even computers computer science people think that they are doing so many wonderful things they can only do provided you give the floppy disks for them yeah hardware yeah materials okay this CDs and all that manufactured by us but still you don't even know that you are not proud of it okay so that is why history is very important what earlier people have done what you are going to do so that is why that is why you are not involved I think happy okay whether it comes in the examination or not that is all that it is sole motto from joining date 1 to finally till you get in the sac building that you know yeah that degree certificate called in the convocation degree certificate that useless paper right that is that will be useless if you don't know anything in that field is really useless okay so but anyway these things I am repeating so many times but in your mind all these subroutines are going on thinking that this idiot is talking all the time same thing okay yeah this is matrix no so you are in your own matrix holding me that this fellow tells only this nothing else okay good yeah so this is pneumatic conveying and now the fluidization yeah beyond somewhere here you have it if I take that as ut terminal velocity your fluidization range is from here to here that is why as I have been telling you all the time you know you have the float not flow what is that flow regimes even here we have a flow regime beyond this no one can operate that as a fluidized bed and beyond this also no one can operate till here yeah so beyond this also beyond this also no one can use that one as a fluidized bed because it is not simply fluidizing so that is the range of fluidization but in between you have so many operations like you know this is normal conventional fluidized bed then you have slightly turbulent or aggregative fluidized bed then you have here in between I have not shown you circulating fluidized bed all that depends on how much solids you have in the bed right aggregative fluidization and turbulent fluidization and normal fluidization you will have 60% solids 50% solids 40% solids till aggregative and also turbulent beyond turbulent the the particle starts coming out so at that time it you will have around 20% if you are able to operate around 20% then you have circulating fluidized bed beyond that if you go to only 3% solids 3% pneumatic conveying normally we get that so then you will have pneumatic conveying and beyond that no operation is feasible so all these things are there okay good I know none of you will write all these things because why what yeah I don't know you don't write yes sir correct because you think that the simply waste of paper waste of pen okay why should I write because it may come or may not come in the examination till then is my duty after my duty is over that's all who wants this throw the particles and books and then go and join some variance what a great great generation we have I say no respect for what we do what we are supposed to do not what we do what we are supposed to do okay all of you I am not only talking about that okay they may throw this that book 10 kilometers away you may throw 1 kilometer away that's all the difference okay that's all that's why it hurts us you know most of the time because when we are excited and then telling you sit there like a statue probably status statues would have reacted okay real statue if you take and put there and then talk 40 hours probably it will have some kind of movement there but here you have movement become finally statues okay good yeah so now if you want to understand this fluidized beds we need some parameters yeah I think anyway before that I think we will have the advantages and disadvantages what are the advantages in using the fluidized beds okay good control of solids that is one and then excellent heat and mass transfer transport processes inside that okay so heat and mass transfer rates are very high in the bed that is one smooth and control flow of solids and number 3 is isothermal conditions which prevent hot spots isothermal conditions which prevents hot spots due to vigorous mixing of solids vigorous mixing of solids what are the disadvantages because I think you know whatever you do definitely there will be some particle-particle collision some powder will always generate right so due to attrition that there is a disadvantage that is called attrition due to attrition of solids because we are talking about this one as a reactor so the catalyst may go out of the due to attrition of solids so the weight of catalyst may decrease in the bed that will come which pressure drop is more okay then what is in other other disadvantage attrition is one where you lose solids right yeah yeah on rock any other why why pressure drop is in factory bed what is happening in fact factory bed gives you more more pressure drop than fluidized bed so that is why pressure drop is not a problem because if you are using the same velocity is okay like 2.5 minimum putation velocity like that the pressure drop in the packed bed will be much more than fluidized bed pressure drop is not the disadvantage so there anything else range of velocity is U M F and U T beyond that you cannot go particle diamet yeah but that is not disadvantage no that is only possible operational okay that is not a disadvantage because no one would like to have atoms to be fluidized sometimes it will help also to get smooth fluidization they take slightly coarse particle add fine particles so then it seems you will get better fluidization so this always counterintuitive and you get kick when you have counterintuitive things automatically what you imagine in your mind and what is happening is same there is no kick you know why because of solid if you are taking that one as a catalytic reactor catalyst is the the dissolved particle right where is the purity coming because reaction occurs in the particle inside the particle or outside the particle on the catalyst and then anyway product will diffuse out and then comes out what you are talking about the particles coming with the gas those we have we are masters of that what do you use cyclones not one ten also can use depending on particle size that is coming so you can use one first cycle cyclone second cyclone third cyclone four five cyclones also people use and beyond that also if you are not able to take from the cyclones then what is that use filters block electrostatic precipitators ESP plants very common okay so all those things are there all those things are there unfortunately you are not putting your mind to assimilate your knowledge I think definitive process would have told you in particle technology and all that deactivation disadvantage what you are trying to tell actually when you have a deactivating catalyst today is excellent it is very good you can take out the particles like water okay and then feed continuously always you know you can maintain some amount of fresh catalyst inside the bed it is not fresh actually mixed and fresh yeah regenerate you can use like if you are using like FCC okay take out all the solids take the regenerator and then send it back there is another one because this okay so this fluidizer bed is it equivalent to CSTR or plug flow reactor solids are in perfect mixing condition is it disadvantage or advantage for reaction that is one of the disadvantages why because concentration gradient is not much so what do you do what do you do to overcome that what do you do if you want to go towards plug flow you are using only mixing flows that is all so people use 2 or 3 fluidizer beds okay you know how beautifully they use that they use like this this is one down comeer another down comeer another down comeer if you are using only 3 this flow comes out so this is gas these are solids coming out solid solid gas gas this is just CSTR 1 CSTR 2 or mixed flow reactor 1 MFR 1 MFR 2 MFR 3 it is just one above the other you need not put one above the other you can also put parallely one here next one next one allows of gravity because it is like a fluid so it comes from one bed to the other bed if you are maintaining certain gravity you know certain level so automatically it comes so that is why if you want to you know you have to write there non-uniform residence times you know when you have mixed flow you have non-uniform residence times for the solid phase okay that is the disadvantage why it is disadvantage because if I take coal combustion for example right solids are in the perfect mixing condition because of mixing some particles will come out very quickly and practically the combustion in that in that particle is almost and there may be another particle which is overburnt and then only ash is left on the other hand if you take exactly our plug flow reactor each and every particle would exactly burn depending on the time which you have given may be 10 minutes or may be 10 seconds whatever so that is why you get uniform combustion there but here also you will get uniform combustion but at low level okay at low level because you have at any time coal must be large amount you have to put to compare with the to compare with the ideal plug flow reactor correct no that is why in fact for a given conversion why CSTR will be bigger and plug flow reactor will be smaller is the residence time distribution problem one easy example which you can remember is coal combustion okay so certain amount I am burning in a plug flow reactor but if I want to get the same conversion in mixed flow I have to necessarily use larger bed because the total amount of solid some converted some unconverted all that must compensate the ideal plug flow reactor where all solids are uniformly but so that is why you will have bigger size for mixed flow and smaller size for plug flow for a given conversion okay so that is why yeah so this is one of the disadvantages and there is another disadvantage you know attrition we told okay that is one that is with respect to particles but with respect to walls of the reactor you have attrition okay erosion I do not say attrition erosion of the walls and after sometime wall may disappear shrinking core model yeah wall thickness keep on decreasing because of like shrinking core and finally disappearing wall will disappear because always you know the solids are moving at very high velocity it will erode erosion takes place so slightly you may lose some of the material of the wall and thickness will be smaller if it is high pressure and all that it may burst out sometime that is another disadvantage okay so I think this is fine and next class tomorrow morning first over we will now try to find out what are the parameters you should