Vent Sizing for Pressure Vessels / Equipments

Hello Everyone...........!!

Today here i gonna explain you about vent sizing of pressure vessels and process equipments based on the way of usage. Simply take the case of a Batch reactor, what will happen if there is no vent or pressure relief valve during a reaction........??

The result may vary with the size of the reactor, Simply the presence of a Relief valve will relief the over pressure that was developed inside and protects the reactor, Usually the reactor will be having a pressure resistance which is known as Design pressure, if the reactor is felt with more than the design pressure, then there may be a chance for explosion, and i said there may be a chance of explosion because after manufacturing of reactor there will be some recommended tests that were to be done like pressure test, spark test[if its a GLR], etc. While performing a pressure test, the vendor will cross the limit of design pressure and gives a specification called Test Pressure, which means the pressure upto which the test was carried out.  

So, now i'll tell you when there is a need for Vent/Relief valve:

Vapour / Gas removal rate < = Vapour / Gas generation rate,

If the above condition is satisfied, then there requires a Relief valve / Vent for the system.

The major factors that will decide the Vent size were:

• Maximum Vapour/Gas Generation rate,
• Type of fluid inside the container, whether its a gas or liquid.

In case of Maximum generation rate, If we need to vent out Vapour / Gas that was generated, then simply calculate the size from below equation:

V = A x S = 0.785 x D x D x S,

here, V = Volumetric flowrate in Cu.m / hr,

D is Diameter of Vent,

A is Cross sectional area of the vent neck,

S is the velocity with which the vapour / gas will escape, 

And coming to second case, if the Container / Vessel is containing any gas, then there wont be any problem because if its a solvent then there is a chance that solvent may be transform to vapours and create some vapour pressure, but as it is a Gas then whatever the pressure that is accumulated, that will be kept off like that. 

One more important term, named as WCM [ Worst Credible Maloperation ], Which means the highest pressure developed due to the maloperation responsible for the generation of vapour / Gas.

The calculation should obey the criteria, i.e., pressure that was developed during the WCM should safely pass through the vent provided, or the Relief valve should respond to the WCM pressure with a minimal response time 

The approach to Relief sizing depends on 2 cases:

• Fire case,
• Reaction case 

For a fire,

Vapour generation rate = Heat from fire / Latent heat of vaporization 

For a chemical reaction,

Vapour generation rate = Reaction rate x Reaction Enthalpy / Latent heat of vaporization.

So after getting the vapour generation rate, you can go with above mentioned equation, V = A x S,

if there is any problem while calculation, then better go with a direct equation which was developed & Proposed by Leung's Long form eqn.

A = [ m x q ] / G [ { (VxT/m)+(dP/dT)}^0.5  +  {Cp x dT}^0.5  ] ^2

m - Initial mass in vessel (Kg),

q - Heat evolution rate per unit mass in vessel(Watt/Kg),

G - Vent flow capacity per unit area at set pressure(Kg/Sq.m),

V - Vessel volume(Cu.m),

T - Vessel temperature(K),

dP/dT - Rate of change of vapour pressure with temperature,
Cp - Specific heat ( J/Kg.K),
dT - difference of temperature between Maximum allowable pressure & Set pressure ( °K),

As per the Equilibrium rate model, the Value of G [ vent flow capacity] can be calculated as below,

G = (dP/dT) x SQRT(T/Cp) = hfg / [ Vfg x SQRT( Cp x T) ]

That's it..........!!

Now, here i'll demonstrate the above mentioned formula with a calculation.

Consider a 10 KL reactor, having MOC SS316 with a design pressure of 3.2 Bar, and maximum allowable pressure as 4.2 Bar, i.e., 30% excess to design pressure

			Average
Pressure Bar	3.2	4.16
Bubble point temperature °C	110	120.5	115.3
Heat release rate ( watt/Kg)	1150	1660	1405
Liquid density ( Kg/Cu.m)	847	835	841
Vapor density (Kg/Cu.m)	3.75	4.62	4.19
Latent heat (KJ/Kg)	674.9	663.0	668.95
Liquid specific heat (KJ/Kg.K)	1.96	1.96	1.96
dP/dT	8300	9500
Vfg (Cu.m/Kg)	0.2655	0.2153	0.2404

Using equation developed from Equilibrium rate model,

At 3.2 Bar pressure, G = 0.5 x (dP/dT) x SQRT(T/C) = 0.5 * 8300 * SQRT( 383/1960)

= 2385 Kg/Sq.m S.

At 4.16 Bar Pressure, G = 0.5 * 9500 * SQRT(393.15/1960) = 2128.73 Kg/Sq.m S

The average value of 2385 & 2128.73 for G gives  2256.5 Kg/Sq.m S.

Now, we need to calculate the venting area from  Leung's Long form eqn.

dP/dT = ( 4.16 - 3.2 ) x 10^5 / ( 120.5 - 110 ) = 9143 N/Sq.m K



A =  [ 1500 * 1405 ] / 2256.5 [ { 10 * 288.5 * 9143/1500 }^0.5 +{1960 * 10.5 }^0.5] ^2

    =  0.0122 Sq.m

D = SQRT(0.0122/0.785) = 0.125 m = 5" (inch)


I think, now you got an exact idea of solving the data for getting the venting area for Pressure vessel,

Any queries please feel free to ping me...........................!!

Comments are Most appreciated....!!



About The Author

---

Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
Follow Me on Twitter AjaySpectator & Computer Innovations

Vacuum Steam Technology

Hello guyzz.... first of all happy Weekend to all.......!!

Today i gonna explain you a emerging technology, which is simply a revolution in industries and which is very hard to believe by all, i.e., Vacuum Steam.

Now, i'll explain you its features briefly, it is simply  a low temperature steam produces at a high pressure and later the pressure will be reduced with an equipment like inlet control valve or a pressure reducing system which can reduce the produced pressure very rapidly like a vacuum pump. 

May be its very difficult to believe the above and i'll tell you that we can produce this with the help of steam from boiler, and even we can automate it with just two interlock systems.


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The higher the pressure, the higher the temperature of saturated steam. At regular atmospheric pressure, saturated steam is roughly 100°C. Saturated steam generated from boilers, however, is generally much higher in temperature because it is generated at higher pressures. This steam (positive pressure steam) is therefore frequently used in industry for heating processes requiring temperatures above 100°C.

Alternatively, producing saturated steam for heating processes below 100°C is also possible. Such steam is often referred to as vacuum steam because it requires pressures below regular atmospheric pressure. Vacuum steam is generally generated at higher pressures after which pressure is reduced by using equipment such as an inlet control valve. A vacuum pump is also usually used to help achieve lower pressures at start-up and enable the smooth release of condensate.

Use of vacuum steam requires careful temperature and pressure reading. To determine steam temperature, referring to a steam table such as the one above is recommended. For example, through this steam table, we can see that if a process requires saturated steam at temperatures of 60°C or 90°C, saturated steam pressures should be set to 19.946kPa and 70.182kPa, respectively.

Also Read:

Outlines for Preparation of Design Qualification Document 

Outlines for Preparation of Operational Qualification Document

How to Generate the Vacuum Steam.....??

All you need is a pressure reducing control system and a vacuum regulator with a HMI(Human Machine Interface), 

Purpose of Pressure Reducing control system:

When the steam enters the chamber containing water, then the water will gets heated up and then a secondary steam will start generating, then the pressure of the secondary steam will be similar to that of the external steam and we have to produce steam of temperature 83 deg C, 

so as per steam tables the pressure corresponding to 83 deg C temperature will be 410 mmHg abs, so the external steam should be turned off when ever the produced secondary steam pressure reaches 410 mmHg, so to control the inlet pressure of the external steam, a pressure reducing control system is used.

Purpose of Vacuum regulator:

Usually vacuum regulator works on the principle of Air to close Diaphragm system, whenever the generated secondary steam pressure exceeds 410 mmHg, immediately the vacuum regulator will starts it work and opens,

 then by the suction pressure of the vacuum the generated secondary pressure will be reduced to 410 mmHg, So to reduce the produced secondary steam pressure, a vacuum regulator is used.

Purposed of HMI(Human Machine Interface):

The use of HMI is very simple, it will co-ordinate with both the valves at a time and make them work alternatively with a set point, the set point will be set by the operator based on saturated steam tables data.

You can use the follow link to generate the Steam temperature by giving the steam pressure as input.   Click Here

Advantages of Vacuum Steam over Regular Steam and Hot Water:

1) Vacuum steam can be generated at required Low temperatures, which will hold the energy equivalent to the regular Steam and much higher than the energy of Hot water,

2) The time cycles of operations like distillation, drying, heating can be reduced without affecting the quality of the manufactured product,

3) The Efficiency of the Vacuum steam is much higher than that of the Regular steam and Hot water as Vacuum steam will support RAMP Heating, which is recommended for pharma operations.


That's it......!!! This is all about Vacuum Steam, hope everyone who read this should have understand,

 if you want to add up something about Vacuum steam just mail me,

Comments are most appreciated.....!!


Related Topics:

[How To] Calculate rate of Distillation in a Batch Reactor ? 

Outlines for Preparation of URS document

Do you know how pressure varies with altitude ??

[How To] Scale-up for an Agitation process ??

About The Author

---

Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
Follow Me on Twitter AjaySpectator & Computer Innovations

Equipment Mapping

Hello Readers....!! Happy to be back here....!!!
Two days ago i got a query asking me to give some guidelines for Equipment mapping, and this seems to be a very interesting topic where everyone will have their own view which is convincing for themselves, and as i got this query to my mail i gonna present you here with my own view.

Before getting into the topic all should have a little idea about Equipment Mapping and what does it means exactly......???

Also Read:

[How to] Avoid Packing failures in Pharma 

[How to] Troubleshoot a pump  

What is Equipment Mapping ??

Equipment Mapping is the process/procedure to select and dedicate a particular material/equipment for performing a specific process on it by an qualified operator as per the predefined instructions.






When is it required ??

Equipment Mapping is necessary while going to achieve some target yield or to validate a process during a scale up, tech transfer, site transfer of a existing product or while performing a trial for a product that is newly manufactured.

What are the Equipments that are eligible for Mapping ??

The equipment which were mentioned in a particular Process flow/Piping & instrumentation Diagram, which are recommended while going for manufacturing of a product like Reactors, Receivers, Storage tanks, Filters, Filtration Equipments, Process Pumps, Vacuum Pumps, Dryers etc.

Now, i think you got a basic idea of Equipment Mapping, so now Lets go deep into the topic,

How to Map a Reactor ?

Generally reactors were classified into different types based on MOC[Material of Construction], like SSR, GLR, Halar lined reactors, PPR etc.
Based on the pH of the Reaction mass we can prefer the reactor, if the pH is 7 or above 7, we can go with SSR, or if the pH is below 7 we have to go with GLR or Halar lined reactors, as they were corrosion resistant.

And you need to know how to prefer a reactor capacity ?

If the reactor is used for carrying out reaction then the occupancy of the reactor should be in range of 30% to 60%,

If a reactor is used for Work ups like extractions/washings then the occupancy should be in range of 40%-75%, if there is 75% occupancy during extractions then the agitator should be a turbine or propeller, if there is minimal occupancy then the agitator should be Anchor.

For distillations/Product layer concentrations the preferred range of occupancy is 40-60%, as distillation is a Heat transfer operation the efficiency of Heat transfer will be high if there is Maximum occupancy but if the occupancy is more there may be chance of product carrying out into vapour line due to high vacuum. The most preferred agitator for distillation operation is Anchor.

You might like reading:

[How to] Evaluate the selection of ANFD technically ? 

What to know from a RC1e study ?  

How to Select Filters for filtration ?

Filters were of many types, the mostly pharma involved filters were Micron filter, candy filter, Leaf filter, Sparkler Filter, Nutsche Filter, Pressure Nutsche filter etc.

The above mentioned filters can be classified into two types based on their usage, 

1) Multi time filtration,
2) Single time filtration.

Multi time filtration: The term Multi time seems to be an rare term, but for delivering its purpose through its name i've mentioned multi time filtration and don't get confused over that, The main purpose of the multi time filtration equipment's were to separate the large size particles from the slurries or solutions, these filters efficiency depends upon the filter medium like filter cloth, and the filters that fell under the Multi time filtration were Leaf filter, Sparkler filter. The Main reason for considering those two in this category is they were widely used for filtering the carbon slurries / charcoal slurries with re-circulation, during re-circulation the particles were left over the filter cloth in leaf filter and over the cellulose bed in sparkler filter, and the small size particles will also be retained over these filter medium upon continuous re-circulation, as the bed thickness increases over the medium the pore size decreases.






Single time filtration: Single time filtration name itself denotes the filters from this category will be used only once in a whole filtration, it means every time a Multi time filtration filters will be accompanied by a single time filtration but it is used only once as a final effect, Micron filters, candy filters will come under this category as they will have low filtration area and finest pore size, they can resist even very fine size particles but can resist high volumes of particles over them.

How to Map Receivers ?

Usually receivers will be used for storage of solvents, product layers, impurity layers and some times during distillations to hold the distillate. 

Receivers used for storage should be mapped based on occupancy, and receivers can have a maximum of 90% occupancy, if the occupancy is more, then the vapors generated due to saturation will be low as there wont be much space left in the receivers and this is simply called breathing losses of solvent, 

Receivers used in distillation should have small capacities in order to increase the distillation effectiveness, this statement doesnt mean selecting a 10 L / 100 L receiver while distilling 2 KL or 3 KL, it means just to consider an optimized occupancy receiver which will enhance the rate of distillation, but not the one which will stay as a reason for low distillation rate.

And the Transfer lines of the receivers should be of small length to avoid accumulation of solvent in the receiver and also the flow of solvent from the receiver to the destination should be mostly of gravity but not by pumping, and the lines in between the receivers and destination shouldn't have any negative slopes, which will retain the solvent as holdup volume.






How to Succeed in Mapping of Filtration Equipments ?

Mapping of filtration equipment's always remains as a  difficult task for an engineer, as even if the pore size of the filtration medium is of enough size, but the filtration wont happen due to the nature of the slurry, it may be of different reasons like pH, low temperatures etc., if the pH of the reaction mass is high then the mass will be sticky so the filtration rate will be low if a filtration equipment like ANFD is selected, and with the same filter cloth that is used in ANFD, if used for a centrifuge then the filtration may happen comfortably, so the Filtration equipment must be tested with our traditional method of Trail and Error without any hesitation, and some of the mass won't create that much headache as mostly they will be compatible with equipments like ANFD and Filter Press.

if a reaction mass is compatible with ANFD then mostly it will have compatibility with centrifuge also, but being an engineer centrifuges should be avoided as they are of high hazard, and also the solvent loss during handling will be more.

Also while mapping of the filtration equipment's like ANFD & PNF's, there should be some basic considerations. Out of which the major one is cake height.

You might like reading:

[How to] Select a condenser for a reactor? 

[How to] Select a Batch Size ?  

I'll show you how to select an ANFD / PNF.

The cake height in these filters should be 20% of the total height. If its ANFD the cake height shouldn't be higher than the stoke height.

Lets suppose the expected wet output will be 30 Kgs, so for this case we need to map an filtration equipment, and lets consider that the filtration is fast.

So we can go further with ANFD or PNF. Now we need the capacity of the filter.
Let the BD of the material is 0.3 Kg/L. 
So the volume occupied by the wet cake will be 30/0.3 = 90 L.

We are having two PNF's and we need to select one outta those, 
1st filter capacity is 0.25 Sq.m(0.8 m height), 2nd filter capacity is 0.5 Sq.m(1.0 m height).

Considering the 1st filter, the cake height would be 0.09/(0.25) = 0.36 m
The height percentage would be ( 0.36 / 0.8 ) x 100 = 45 %.

Considering the 2nd filter, the cake height would be 0.09/(0.5) = 0.18 m
The height percentage would be ( 0.18 / 1.0 ) x 100 = 18 %.

So, as in the 2nd filter case the height percentage is below 20%, we can comfortably proceed with it.






The reason behind the 20% is that the remaining empty space will attribute to the adequate press dry with nitrogen pressure. Hence the expulsion of the ML's / filtrate would be good enough.


Here, Stoke means the length of the agitator shaft.

How to Map Drying Equipment's ?

Drying Equipments are the most critical one in pharma Industry, as the yield mostly depends on them on the final stage of manufacturing, mostly filtration equipments will be accompanied with drying setup also, and some times drying will be a part of product concentration equipments as like ATFD[Agitated Thin Film Dryer], APD[Agitated Pan Dryer] etc, and these drying equipments will be two types,

1. Direct Contact Dryers,
2. Indirect Contact Dryers,

If a material is hygroscopic then Indirect contact dryers should be preferred, as if we go with a direct contact dryers, the material may transform it self into liquid,

There are many types of dryers available in market like Vacuum tray dryers, Rotary cone vacuum dryers, agitated thin film dryers, Agitated nutsche filter dryer, Air tray dryers, Agitated pan dryers, Fluidized bed dryer etc.

Mostly if the material is having tendency to loose the solvent or water content from its lattice and wherever agitation is required, then its better to go with dryers like ANFD, APD. 

And if the batch manufacturing process is off small scale and the solvent to be removed is having high volatileness, then its better to go with Vacuum tray dryers/tray dryers.






If the Crystal lattice is having a high tendency to hold water content/solvent content, then the material should be taken for size reduction with a miller and after reduction it should be taken into a dryer like FBD, where direct heating takes place.

And finally coming to dryers like ATFD[Continous dryer], APD, these are far critical equipments than other dryers, they can be used from product layer concentration to final stage drying.

Finally, what ever may be the capacity of the dryer, it should have a maximum occupancy of 60-70%, as if there is high occupancy than the mentioned then the vacuum that needs to perform its job would be uncomfortable, i mean the vacuum contact area with material will become low, and the efficiency of drying will become less.

That's it......!! This is upto my knowledge and hope you will understood this simply,

 If anything to be added from your knowledge, comment here or mail me, 

Comments were appreciated........!!!



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[How to] Calculate time-cycle required for heating/cooling ?  

[How to] Calculate vapour column diameter ?  

[How to] Calculate time-cycle required for distillation ?   

 About The Author

---

Hi! I am Ajay Kumar Kalva, Currently serving as the CEO of this site, a tech geek by passion, and a chemical process engineer by profession, i'm interested in writing articles regarding technology, hacking and pharma technology.
Follow Me on Twitter AjaySpectator & Computer Innovations