An Engineer's Choice

  • Thursday, 5 May 2016

    Types of Agitators, Agitator's Design and Significance


    Hello readers.....!!
    Today i gonna give you a description that limits upto my knowledge, and most of you may find it useful, about the Industrial Agitators, Types of Agitators, their Power Numbers, Design Equations and their significance in production.

    Introducing or discovering the types of agitators in pharma field is certainly a revolution because different agitators will have different purposes and different advantages, but most commonly used agitators are Anchor, Propeller, Turbine, Paddle etc., and still these agitators are sub divided into types, for example Round Anchor and Anchor combined with Gate are two types of Anchor.

    So, for knowing the types of agitators and their significance you don't need any basic knowledge, but just an idea that

    "what is an agitator ?, And what it can do ??"  
    "What is the difference between Agitation and Mixing ??"
    Agitator : An agitator is something which is used to stir liquid or mixture of liquids.

    Also Read:


    How to Select a Condenser?
    What Does a TR exactly means? 
    How to Calculate the Energy of Steam?

    What it can do ?? : It can be used in various operations, in a pharma industry it can be used in multiple operations like reactions, work up's, drying, filtration, etc.,

    Difference between Agitation and Mixing :


     Agitation is the process of keeping a mixture that has been mixed in the proper mixed state required for the 'end' product.

    Mixing refers to the actual stirring of different liquids and/or materials to blend them together into an end product or mixture. Once this mixture is 'mixed' it may require agitation to keep the mixture in the proper 'mixed' state.

    So, Now i'll go into our topic,

    There are two types of Agitators commonly used,

     1. Mechanical Agitators, 2. Electronically Controlled Agitators, I'll demonstrate commonly used Mechanical Agitators.


    Recommended For You:


    How to Select Motor Capacity of an Agitator? 
    How to do Scale Up calculations? 
    How to Design an Industrial Column?


    Paddle Agitators: This is one of the most primary types of agitators with blades that reach up to the tank walls. Paddle agitators are used where an uniform laminar flow of liquids is desired.



    Anchor Agitators : This simple agitator consists of a shaft and an anchor type propeller and can be mounted centrally or at an angle. It is mainly used in reactors.



    Radial Propeller Agitators : Radial agitators consist of propellers that are similar to marine propellers. They consist of two to four blades that move in a screw like motion, propelling the material to be agitated parallel to the shaft.



    Propeller Agitators : A propeller agitator is shaped with blades tapering towards the shaft to minimize centrifugal force and produce maximum axial flow. Propeller agitators are popular for simple mixing jobs.



    Turbine Agitators : Yet another type of process agitator is the turbine agitator. Turbine agitators can create a turbulent movement of the fluids due to the combination of centrifugal and rotational motion.


    Helical Agitators : These agitators have blades with a twisted mechanism, just like the threads of a screw. The curves result in a vigorous motion of the fluids to be agitated. Helical agitators are most useful for mixing viscous liquids. 



    A simplified brief description has been tabulated below. 

    Agitator Type Applications Advantages Disadvantages
    Paddle
    * Mixing of Solids,

    * Slurry Mixing,

    * Used during Crystals
     forming phase during
    Super saturated Cooling
    * Heavy duty,

    * Apt for Slow operation,

    * Can have 2 or 4 blades
    * Power Consumption
    is very high,

    * Inefficient Mixing
    Turbine

    *Straight Blade
    *Pitched Blade
    *Curved Blade
    *Disk Blade
    * Liquids and Gas reactions,

    * Highly used during
    Reaction and Extraction
    Operations.
    * Generates high
     Radial Flow,

    * Highly used for
     dispersion operations
    * Not preferred for
    solvents with high
     viscosity[NMT 20 cP]
    Screw type * Have to use in addition
     to other agitators.

    * Mostly used in Food processing.
    * Uniform mixing
    of High viscous
    masses.
    * Not preferred for im-miscible solvents.
    Helical Blade

    *Ribbon Type
    *Helical Screw
    * Most Probably used in
    Paint industry.
    * Can handle Visco
    -elastic liquids efficiently
    * Low possibility for Radial mixing
    Anchor * Highly used in Pharma Industry for Several Operations * Increase possible heat
     transfer rate in reactors,
    from reactor heat transfer surface
     to Mass.
    * Required high
    Efficiency Gear
    box,
    * Required high Power.
    Gate * Highly used for blending Operations * Provides efficient
    Mixing and agitation control,
    * Can handle Psuedo
    -plastic liquids.
    * Not preferred
    when both liquids and gases combine
    involves 
    Propeller * Suitable for GLR's,
    ANFD's, can handle Corrosive materials with Glass lining.
    * Will increase the homogeneity,

    * Can be used in two different patterns for
    drying and pressing. 
    * Need to be operated
    at high speed to
    avoid solid settlings
    in reactors.

    * Need to be
    operated at low speeds in drying operations.

    Diameter of Agitator: Usually the diameter of agitator depends on the Diameter of the vessel,

    It is generally 1/3rd the diameter of the tank for Marine Propeller, Axial flow turbine, Turbo Propeller, Disc Blade turbine, Flat Blade turbine, Backward Blade turbine.

    It is generally 4/5th of the diameter of the tank for Paddle, Anchor, Gate.

    Type of Agitators and their functions:

    Marine Propeller is generally an item produced by casting process in a foundry and it has 3 or 4 blades. Cast agitators have two basic advantages, uniformity of material and hard surface. These have tapering blades, and angle of blade varies from root to tip. This produces maximum axial flow. The diameter of Marine Propeller impeller is 15% to 30% of diameter of tank. These have tip speeds between 300 to 500 meters per minute.

    Axial Flow Turbine, Turbo Propeller and Flat Blade Turbine have blades ranging from 3 to 6. These have tip speeds between 200 to 300 meters per minute. The diameter of impeller is 25% to 60% of tank diameter. For Axial Flow Turbine and Turbo Propeller, the angle of blade varies from 30 degrees (for less viscous liquids) to 60 degrees (for more viscous liquids). Standard angle is 45 degrees. Power requirement increases with higher pitch angle. For Flat Blade Turbine, the length of blade is 25% of diameter, and disk diameter is 60% to 70% of the diameter of impeller.

    Paddle, Anchor, or Gate have only 2 blades. These extend close to the tank wall and have tip speeds between 80 to 150 meters per minute. These push and rotate the liquid in a laminar flow. There is no axial or radial mixing. The width of blade is 1/8th or 1/10th of the agitator diameter.

    Number of Agitators:

    There can be many number of agitators connected to a shaft, and it can be calculated as 

    Number of agitators = (Maximum liquid height x specific gravity) / Diameter of tank.
    Gap between two Agitators = Liquid height / (Number of impellers - 0.5). 
    Basic Design Equations for a Vertical Vessel and Agitator:

    Vessel Volume = (pi x vessel dia x vessel dia x vessel length) / 4.0
    Agitator Shaft length = vessel length + (vessel dia x 0.25)
    For Rectangular Tanks,
    Tank Volume = Vessel Length x Vessel Breadth x Vessel Height

    Agitator Shaft length = Vessel Height

     Based on geometry of vessel, many factors for impeller can be decided.

    Agitator Speed Power Number Pumping Factor Impeller Diameter
    Marine Propeller
    100 - 300 RPM
    * 0.3 for 3 bladed impeller,
    * 0.33 for 4 bladed impeller
    * 0.33 for 3 bladed,
    * 0.34 for 4 bladed.
    1/3rd of tank
    dia
    Axial Flow Turbine 100 - 300 RPM * 1.35 for 3 bladed,
    * 1.4 for 4 bladed,
    * 1.45 for 5 bladed,
    * 1.6 for 6 bladed.
    * 0.6 for 3 bladed,
    * 0.69 for 4 bladed,
    * 0.78 for 5 bladed,
    * 0.87 for 6 bladed.
    1/3rd of tank
     dia
    Turbo Propeller 100 - 300 RPM * 1.35 for 3 bladed,
    * 1.4 for 4 bladed,
    * 1.45 for 5 bladed,
    * 1.6 for 6 bladed.
    * 0.6 for 3 bladed,
    * 0.69 for 4 bladed,
    * 0.78 for 5 bladed,
    * 0.87 for 6 bladed.
    1/3rd of tank
    dia
    Disc Blade Turbine 100 - 300 RPM 5.0  0.7 - 0.8 1/3rd of tank
     dia
    Flat Blade Turbine 100 - 300 RPM 5.0 0.7 - 0.85 1/3rd of tank
     dia
    Backward Blade Turbine 100 - 300 RPM 5.0 0.65 - 0.85 1/3rd of tank
     dia
    Paddle 50 RPM 5.0 0.03 80% of tank
     dia
    Anchor 50 RPM 5.0 0.07 80% of tank
     dia
    Gate 50 RPM 5.0 1.0 80% of tank
     dia


    That's it.........!! Cheers..... if you understand, 

    Excel Sheet has been simulated for design of Agitator and you can download it here,



    Any Queries feel free to ask,

    Comments are most appreciated.!


    Note: Some of the Data Interpreted here is not of my own, but from a generous Genius "Satish Lele"


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    How to calculate Distillation Time cycle ?
    How to select a Vaccum pump ?
    How to Calculate Volume occupied by Torispherical Dish ?
      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

    15 comments:

    1. which utility is suitable for condensing acetone vapours under vacuum and under atmposphere in condensor...chilled water 8 deg. centigrade or brine -10 degree centigrade..

      ReplyDelete
      Replies
      1. Hey Mr.Anonymous, if you are having two condensers, then go with chilled water for primary and chilled brine for secondary,
        and if you are able to maintain the vapour temperature above 15 deg C under vacuum, then go with -10 degC Brine or 5 degC chilled water, if the temperature below 15 degC then use chilled brine at -20 degC, and in case of the vacuum distillation, remember to have a equalisation line from secondary condenser to collection receiver,

        if the distillation is an atmospheric one, directly go with RT water at below 30 degC,

        Delete
      2. Can you explain theoretically and calculate and tell how to select utility as per the above post.pls. give ur mail id so that i can share the sketch..

        Delete
      3. using a better utility for condenser will enhance the rate of distillation, for a chilled brine at -10 deg C, the temperature difference can be considered as 7-8 deg C, and for a utility like chilled water having a inlet temperature of 8 deg C, the temp difference will be around 3-4 degC, because the reaction mass temperature will be around 15-20 degC under vacuum, so mostly the vapours will reach equillibrium with utility outlet, and in the process of condensing the vapour will exchange only latent heat, whereas in case of -10 degC brine, there will be exchange of sensible heat also, and if you want to calculate it theoretically then read the post in this link, then you will get a clear idea,

        http://pharmacalc.blogspot.com/2016/09/how-to-calculate-rate-of-distillation.html

        try to do a reverse calculation basing upon the fixed rate of distillation and find the LMTD of both cases, which uses brine at -10degC and chilled water at 8degC, then you will come to know the difference.

        Delete
    2. Hello sir,
      I am chemical engineering student I am doing my final year project on extraction of oil from slurry in oil refineries.can you suggest us some ideas

      ReplyDelete
    3. so i think, it is something like Lube oils refining, right??

      Thats a good one, and i too tried that during my project but finally got diverted, Give your best good luck,

      and regarding extraction any possible help i'll do, mail me @ pharmacalc823@gmail.com

      ReplyDelete
    4. Please tell me how to do piping? How to design pipeline Header and Tappings from it?

      ReplyDelete
      Replies
      1. A x V = A1 x V1 + A2 x V2 + A3 x V3 +......................
        But, V = V1 = V2 = V3 = .............. [this is as per thumb],

        A = A1 + A2 + A3 +................

        D^2 = D1 ^2 + D2 ^2 + D3 ^2 + ..............

        that's it,

        the number of tappings given should satisfy the above derived eqn.


        Regards,
        PHARMA ENGINEERING

        Delete
    5. what is the major difference between impeller,propellerand agitator

      ReplyDelete
      Replies
      1. Mostly there wont be anything like a Propeller, may be i've mentioned above that's just for understanding purpose, because Propeller is what you see in a table fan, and the agitator that was usually called as propeller in pharma industry is strictly called as Retreat curve agitator,

        Coming to your question, Impeller is nothing but an agitator, and for example if an retreat curve is having two agitators then it is said to have 2 impellers.
        That's it.

        Delete
    6. How can we calculate power for propeller & anchor used in glass lined reactor....

      ReplyDelete
      Replies
      1. Let it be a 10KL GLR, and the dia be 2.5m, and RPM is 110, by thumb dia of propeller will be 1/3rd of reactor dia,
        For Propeller,

        D = 2.5/3 = 0.83m, N = 110 rpm, rho = 1000 Cu.m / Kg, Np = 1.5

        P = 1.5 x 1000 x ( ( 110/60 ) ^ 3 ) x ( 0.83 ^ 5 ) = 3641 Watts = 3.64 KW,

        For Anchor.

        D = 2.5 x 0.8 = 2m, N = 48 rpm, Np = 5,

        P = 5 x 1000 x ( (48/60) ^ 3 ) x ( 2 ^ 5 ) = 81920 Watts = 81.9 KW.

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

        Delete
    7. Hi,
      Great site, and great work.
      We are a 30 year old manufacturing firm specializing in chemical and pharmaceutical reactors. We are currently looking for professionals who can independently design agitators for the process and mechanical aspect. If you know any such individuals, please ask them to reach out to me at anuj@thermotechengg.com.

      Cheers
      Anuj

      ReplyDelete
    8. how can we design spray ball ..how to select number of holes and flow from holes in spray ball?

      ReplyDelete
      Replies
      1. Hello, as like previously mentioned, A*V = ( A1 * V1 ) + ( A2 * V2 ) + ( A3 * V3 )+................,
        V = V1 = V2 = V3 = ............,
        So, A = A1 + A2 + A3 + ........,
        (D^2) = (D1 ^2) + (D2 ^2) + (D3 ^2) + ........,
        D is line size, D1, D2, D3,....... are nozzle sizes, for how many nozzles the equation satisfied, those many nozzles you need to consider for a spray ball.

        Regards,
        PHARMA ENGINEERING

        Delete

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