# Pharma Engineering

For Engineer By Engineer

• ## Thursday, 24 March 2016

Today i wanna Demonstrate HOW TO SELECT VACUUM PUMP CAPACITY for a operation in pharma operations, especially pharma because the use of vacuum can make tremendous change in field of Pharma, one right selection of Vacuum pump can reduce huge efforts in specific operations like crystallisation, drying, saturation, Separations etc.
So the its the main target of a process engineer or project engineer to provide with the right vacuum pump to manufacturing team for achieving high yields in small span of time, but before going to discuss about vacuum pump selection, i want all to know about the vacuum some more briefly,

What is Vacuum? Vacuum is simply a pressure below atmosphere. To create vacuum in a system, a pump is required to remove mass (gas/vapor) from the system. The more mass is removed, lower is the pressure that exists inside the system. Various vacuum levels are defined depending upon the ultimate vacuum as:

Range                                Absolute pressure range ‰
Coarse Vacuum                          10 – 760 Torr ‰
Medium Vacuum                        0.001 – 10 Torr ‰
Fine Vacuum                              10^-3 – 10 ^-7 Torr ‰
Ultra High Vacuum                     < 10^-7

Pumping speed: It is the volumetric rate of exhausting, generally expressed in Lts/min., m3 /hr or cfm. It is the rate at which the inlet of the pump actually removes the gas / vapor load. It should not be confused with Displacement of the pump. Displacement of a pump is the geometric volume swept by the pump per unit time at rated operating speed. For most of the pumps, pumping speed is close to displacement value at no load conditions (FAD-Free air delivery) and changes with inlet pressure, reaching to zero where the pressure attained is said be pumps ultimate pressure.

The below data gives an approximate idea of how booster combination can yield lower pressures while maintaining high pumping speeds.
Vacuum Pump              Pressure Range   Pressure Range with Booster

Single Stage Ejector             150 Torr                  15 – 30 Torr

Water Ejector                         100 Torr                  10 – 20 Torr
Water Ring Pump                  40 – 60 Torr             5 – 10 Torr
Liquid Ring Pump                 20 – 30 Torr             2 – 5 Torr
Piston Pumps                          20 – 30 Torr             2 – 5 Torr
Rotary Piston Pumps             0.1 Torr                     0.01 Torr
Rotary Vane Oil Pump          0.01 – 0.001 Torr       0.001 – 0.0001 Torr.
Vacuum Booster being a very versatile vacuum machine is used in a wide range of processes, some of them being;
Coarse vacuum applications
• Vacuum Drying Application.                                • Tray dryer
• Rotary vacuum dryers                                           • Flash Drying
• Vacuum Distillation processes.                             • Solvent recovery.
• Vacuum Filtration                                                  • Replacement of Steam Ejectors.
• Enhancing the performance of Water Ring Pumps /Water ejectors
• Vacuum Flash cooling / Evaporative Cooling        • Vacuum Crystallization
Medium Vacuum applications
• Efficient backup for Diffusion Pump Systems.     • Thin Film Deposition /Coating
• Short path/ Molecular distillation.                         • Solvent Recovery.
• Vacuum Heat Treatment and Degassing / Vacuum Furnaces
• Freeze Drying                                                        • Vacuum Impregnation
• De-humidification                                                 • De-gassing

And Now i think you gained some brief knowledge regarding vacuum, and now i'll get into point directly of selecting a pump capacity,

For an installed system air leakage load can be estimated by “Drop Test / Pressure rise test” method. Based on the fact that air leaks into the system at a constant rate as long as the pressures in the system is below 400 Torr because of critical flow conditions, the above test is effectively used to determine the leak rate of assembled system.
The system is evacuated to pressures between 10-100 Torr and isolated. The pressure is allowed to rise, but not exceeding about 300 Torr and the time lapsed is noted.

* The Leak Rate “QL” is calculated as,

QL = PxVs/ t
where QL leak tare in Torr Ltrs/sec
P pressure rise in Torr
VS system volume in Litres
t is elapsed time in seconds

* For the known leak rate, the capacity of vacuum pumping system can be evaluated by the expression,
Savg = 3.6xQL / P
Where Savg = Average pump speed in m3/hr
QL = Leak rate Torr ltr/sec
P = System Pressure in Torr

[ You might get a doubt that, how the formula for pump capacity is derived, but there is nothing but just a unit conversion by incorporating the required end vacuum(i.e., ultimate pressure).

Let's get into units now, air leakage rate holds units of Torr. Lt/Sec.
Ultimate pressure holds units of Torr.

So, (Torr. Lt/Sec) / Torr = Lt/Sec, which can be derived by dividing Air leakage rate with Ultimate pressure.

by doing so, we'll get in Lt/Sec, now simply convert it into m3/hr,
for that we need to multiply with 3600/1000 = 3.6,

Now i think you got an idea, how i used that 3.6 in the main formula.]

* As a thumb rule for pressures in the range of 10-100 Torr pipeline “D” may be selected as
D = 2.4 (Q)^0.5

where D= diameter of pipe in mm

Q= Pumping speed in M3/hr .

Case Study was requested by Mr. Srikanth,
Pl find below case:

Let's suppose, i need to select a vacuum pump for a 10 KL distillation system, where i need to attain 750 mmHg of vacuum atleast.

So, lets start the show,

I've taken a vacuum leak test for the system,
applied vacuum, attained 756 mmHg of vacuum.

Hold the vacuum for 10 mins, so my evacuation time is 10 mins,
Observed vacuum leak is 30 torr. Let's suppose the air load is 3 Kg/hr at that particular area.

Now using above formulas,
Air leakage rate = 500 Torr.Lt/Sec,

Pump capacity required = 180 Cu.m / hr,

Considering safety i'll prefer 30% excess, i.e., 234 Cu.m / hr ~ 250 Cu.m /hr.

Line size from pump to system required is 1.27" ~ 2".

That's it

That's it Cheers, comments are appreciated,

Many of the readers found this somewhat difficult to calculate, and for them i've simulated these in an excel sheet, and download this excel sheet below.

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.

1. When do we select oil vaccum pump .. Steam circulation pump .water circulation pump ?

2. Mostly that depends upon the case, if we need a vacuum of range 400torr-600torr that to while operating a system like steam under vacuum, we will go for water circulation pump and basically the vacuum attained from the water circulation pump depends upon the water temperature in the sump,

and when ever we need some thing like coarse vacuum we will go for steam ejectors,

and coming to oil vacuum pumps, there are two types, 1) oil ring pump- in this kind vacuum will be created through oil circulation and 2) oil lubricated rotary vane vacuum pump- in this kind just rotary vanes were used to create vacuum and oil is used to reduce wear-tear purpose, and when we need oil ring during drying and distillations(product layer concentrations, not solvent recoveries), and this oil ring pumps if the trap coolant is not efficient the vacuum attained will be low.......!!
So based on the case we will go for vacuum pump.

1. what is the effect of temperature on vacuum?

3. Hello sir,

I am working for a vacuum pump company practically I am dealing with lots of chemical application still I am having some doubts about pump selection for distillation and drying under vacuum.I want to stay connected with you to get clarified .Please help me by providing some mail contact.my mail id is tamilmech086@gmail.com.
Thanks

1. pharmacalc823@gmail.com

4. Is it possible to creat vacuum more than 760 mmHg vacuum??

1. Not possible Pratim.

Regards,
Ajay K

2. Because of not possible of vacuum 760mm/hg

3. Dear Mustafa,

The vacuum that can be generated depends upon the area and its altitude, Pl read the post :
https://pharmacalc.blogspot.com/2016/05/pressure-and-its-altitude-dependence.html

The amount of pressure available = The amount of vacuum can be generated.

Regards,
AJAY K

5. Thank you Sir...How drying time and filtration time can be scaled up???

1. Dear Pratim,

As per my theory, the time parameter will remain same during scaleup, but as per practical experience the time parameter will automatically vary from standard, so the drying time will remain same, but where as the filtration time will vary based on equipment selection, if Filter press is considered for filtration the rate of filtration will be high, if ANFD is considered the filtration rate will be somewhat low, because simultaneous permeation cant be done practically in ANFD, if centrifuge is considered the rate of filtration depends on the feeding rate, optimum feed rate gives better results.

Regards,
AJAY K

6. Can we put nitrogen pressure on GLR??

1. Usually the Design pressure of GLR will be around 2 Kg/cm2, so we can go upto 1.6 Kg/cm2.

Regards,
AJAY K

2. Dear sir,

3. Dear Narayana,

It depends upon the vendor, Usually Sachin Industries Ltd, De Dietrich process systems, Glascoat will also provide a design pressure of 6 Kg/cm2, in general i've mentioned about the safe range.

Regards,
AJAY K

7. Specially in which case pressure reduce valve is necessary??I mean in which it plays it's role?

1. For controlling steam pressures, we use PRV station with air to open type.

Regards,
AJAY K

8. Is Safety valve required for every type of batch reactors?How to select the specification of safety for different capacity reactor??(5.0 KL,20KL)

1. pl refer to this post Pratim,

http://pharmacalc.blogspot.com/2016/10/vent-sizing-for-pressure-vessels.html

Regards,
AJAY K

9. What is delta p

1. Dear Rudra,

dP is the pressure drop during leak test which is carried out by putting the system under hold.

Regards,
AJAY K

10. Hi, what may be typical evacuation time?

1. Dear ,

Evacuation time depends on the system volume, vacuum line size to system.

Regards,
AJAY K

11. Dear sir,
could you please explain the cfm of a vacuum pump with an example?

1. Dear Sir,

cfm is nothing but just units of flowrate, cubic feet / min.

Regards,
AJAY K

12. Dear sir,
What is system pressure P? Does it mean the required vacuum in the reactor?
which delta P pressure drop during leak test do we consider, is at the vacuum pump or at the reactor?

1. Dear Sri,

P means the ultimate pressure, what is required on the system under continuous application of vacuum
dP shall be considered for the system, not at pump.

Regards,
AJAY K

13. Not the abbreviation sir, need calculation with an example.
TIA

1. Dear Sir,

Post updated with a case study.

Regards,
AJAY K

14. dear ajay,

how u got the pump capacity req = 180m3/hr

1. Dear Ajay,

Use the above mentioned formula, Savg = 3.6 x Ql x P.

Regards,
AJAY K

2. Thanks for the great article.
But, I still cannot figure out how you come up with 180m3/hr in the example.

QL=500
P=750
How can Savg be 180m3? Thanks.

3. Dear Zeon,

Pump capacity = Air leakage rate x 3.6 / ultimate pressure = 3.6 x 500 / 10 = 180 m3/hr.

Ultimate pressure i've considered as 10 torr.

Best Regards,
AJAY K

15. Dear sir,

I think little mistake in flow rate cal. formula Savg.=3.6*QL/P.

Thanks & Regards.

http://www.everestblowers.com/wp-content/themes/everest-blowers/pdf/everest-bulletin.pdf

Regards,
AJAY K

16. Dear sir,

what is air load & where did you consider air load in equations?

1. Dear Krishna,

While considering the pump capacity we are adding the ultimate pressure, which is a consideration of air load, also the system we have considered is a confined space and while calculating air load, we have considered pressure drop,

Hope you got it, if any queries pl feel to comment / message me.

Best Regards,
AJAY K

17. Dear Ajay,

How the diameter D= 2.4 (Q)^0.5 has been arrived.

1. Hii Sasank,

Q is the pump capacity, and these equations were taken from everest dry screw pump catalogue.

Best Regards,
AJAY K

18. Dear Ajay,

can you share everest screw vacuum pupm calculation link

19. From where we get air load value ????
You have take 3 Kg/hr

1. Hii Nilesh,

Thats the worst possible stagnant air flow in a confined space.

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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.

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