Mixing of liquids, solids and high viscosity materials


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A Practical Course on Industrial Mixing Technology & Equipment.

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Mixing of liquids, solids and high viscosity materials

  1. 1. Mixing of Liquids, Solids and High Viscosity Materials A Practical Course on Industrial Mixing Technology & Equipment 22-23 February, 2013 Mumbai CII Naoroji Godrej Centre of Excellence
  2. 2. Introduction • Jayesh R. Tekchandaney • Director Technical – Unique Mixers • Founder of Mixing Expert • Author – “Process Plant Equipment Operation, Reliability and Control” Chapter 12 – “Mixers” John Wiley Publication
  3. 3. Objectives • Share knowledge and experience on Industrial Mixing • Discuss best practices in mixing • R&D, Process Engineers, Project Engineers, Plant Managers, Chemical Engineering Professionals and Students • Industries – Chemical, Food, Pharmaceutical, Ceramics • Creating better products at lower costs through improvements in mixing system performance “No matter how good you are, You can always get better. And that’s the exciting part” - Tiger Woods
  4. 4. Contents • Fundamentals of liquid mixing, solid mixing and high viscosity mixing • Mixing theory and concepts • Mixing equipment selection, design and operation • Advances in mixing technology • Mechanical components of mixing equipment • Solve any mixing problem framework
  5. 5. Course Map
  6. 6. Mixing • Process of thoroughly combining different materials to produce a homogenous mix • Mixing is a critical process • Quality of the final product, attributes are depend on the mixing performance
  7. 7. Poor Mixing • Non homogenous product lacking consistency in chemical composition, color, flavor, reactivity • Failed batches • Loss of high value product • Cost of poor mixing estimated as US$ 100 million per year
  8. 8. Reasons for Poor Mixing • Lack of understanding of material characteristics • Inadequate, inaccurate definition of mixing objectives • Incorrect selection of mixer • Wrong scale-up techniques • Limited knowledge on mixing equipment design, parameters
  9. 9. Polymer Company • Product purity – 90%, US$ 45,000/ton • Required purity – 95%, US$ 50,000/ton • Change in agitator operating parameters – 92 to 93 % • Change in agitator design – 95 % • Production capacity ~ 55,000 tons/yr • Profitability !!! • “Mixing Expert”
  10. 10. Challenges • Ever increasing customer expectation • Need for higher product purity, higher product value • Scale-up from laboratory to production • Need to lower production costs • Equipment operation and maintenance issues • Lower lead times
  11. 11. Challenges • Increase in costs of machines, materials, power and people • Intense competition • Operational Safety • Environmental Issues • Statutory obligations • Similar challenges, different environment
  12. 12. Challenges 20-20 ◊ Development of New Products ◊ Frequent Product Change Overs ◊ Minimum time from new product conception to implementation ◊ Little time for lab trials - pilot scale - production ◊ Multi-purpose equipment – Coating, granulation, heat transfer, drying ◊ Mixer is no longer a generic production tool. It is a critical and decisive business tool.
  13. 13. Explosive Company • Manufacture of explosive materials • Production size unit – 8 liters only • Equipment specifications detailed • Factory visit • The empty room • The real mixer
  14. 14. Explosive Company • Process engineers, plant personnel, engineering and maintenance team • Collaborative customization – Equipment specifications precisely defined • QAP • HAZOP • Trouble free mixer operation
  15. 15. Explosive Company
  16. 16. Module 1 – Mixing Concepts Fluid Mixing Mixing of Solids
  17. 17. All raw materials charged together or in a predefined sequence Mixed until homogeneity Output is measured in kg/batch Batch Mixing
  18. 18. Batch Mixing Batch mixing is preferred for applications where: • Production quantities are small • Strict control of mix composition is required • Many formulations are produced on the same production line • Ingredient properties change over time and compensation must be on a batch-by-batch basis • It is required to identify a batch for further follow up, example - pharmaceutical formulations, food products.
  19. 19. Continuous Mixing Material flows steadily from an upstream process into the mixer Material is mixed as it moves from the charging point to the discharge point The time that material is retained in the mixer is known as the retention time Weighing, loading, mixing and discharge steps occur continuously and simultaneously Output is measured in kg/hr
  20. 20. Continuous Mixing Continuous mixing is preferred for applications where:  Large quantities of a single product are to be mixed  In a continuous process line requiring high production rate  Strict batch integrity is not critical  Smoothing out batch product variations is required
  21. 21. Selection of Mixing Equipment Material Characteristics Process Set-Up Mixer Operating Parameters Mixing Accuracy Mixer Cleanability Equipment Costs
  22. 22. Design of Mixing Equipment Process Design Mixer Characteristics Mechanical Design
  23. 23. Scale-Up of Mixing Equipment Geometric Similarity Kinematic Similarity Dynamic Similarity
  24. 24. Module 2 – Fluid Mixing Fluid mixing includes mixing of liquid with liquid, gas with liquid, or solids with liquid. Mixing - Mixing refers to any operation used to change a non-uniform system into a uniform one (i.e. the random distribution into and through one another, of two or more initially separated phases). Mixing therefore requires a definition of degree and/or purpose to clearly define the desired state of the system [Ludwig, 1995].   Agitation - Agitation implies forcing a fluid by mechanical means to generate flow. Agitation does not necessarily imply any significant amount of actual intimate and homogeneous distribution of the fluid [Ludwig, 1995]. Fluid Mixing Processes - Mechanical Agitation - Jet Mixing - Gas Sparging - In-line Mixing
  25. 25. Fluid Mixing Applications Blending of miscible liquids Blending of immiscible liquids Liquid gas mixing Liquid solid mixing Fluid motion
  26. 26. Blending of Miscible Liquids  Blending of two or more homogeneous liquids  Liquid blending operation may be purely physical in nature or may involve chemical reaction  Low to medium viscosity liquid mixing involves macro-scale and micro-scale mixing concepts  Liquid blending can be achieved using top entering agitators, side entering mixers or jet mixers  Blending of miscible, mutually soluble liquids with viscosities upto 10,000 centipoise is carried out using axial and radial impellers  Viscous liquids are blended using close clearance impellers
  27. 27. Blending of Immiscible Liquids  Blending of mutually insoluble, immiscible liquids may be required to produce stable or unstable emulsions.  Stable emulsions - Shampoos, polishes and other specialty chemicals.  Liquid extractions employ an unstable emulsion to boost the rate of mass transfer and reaction - applications in petroleum, chemical, food and pharmaceutical industries.
  28. 28. Blending of Immiscible Liquids  Turbine impellers are used for the purpose of creating large enhancements in interfacial area; thereby increasing the rate of mass transfer and reaction.  Low shear hydrofoil design impellers can be used for coarse dispersions.  Axial and radial flow impellers are effective for fine emulsions.  High-shear impellers are required for preparing stable emulsions
  29. 29. Liquid-Gas Mixing  Type 1- Involves physical distribution and dispersion of the gas in the liquid. Application of this type is limited only if foam or froth is desired.  Type 2 - Involves mass transfer process such as absorption, stripping, chlorination, oxidation all of which require transfer of gas into liquid.  Radial flow impellers are preferred over axial flow impellers. Disk turbine impellers are most suited  Fermentation equipment - High solidity ratio hydrofoil impellers - produce large flows in biological operations to ensure adequate distribution of oxygen.  Special type of gas mixing systems are used for hazardous, expensive and critical applications like hydrogen which necessitate the need for recycling the gas of the vapor space above the liquid in to the vessel.
  30. 30. Liquid-Solid Mixing  Wide range of industrial applications like catalyst polymer systems, paper pulp industry, washing of solids, crystallization processes  Type 1- Suspension of solids into the liquid, a physical process  Type 2 - Dissolving of solids in the liquid phase, a mass transfer process  Axial Flow Impellers with high pumping efficiencies are best suited for majority of solid suspensions.
  31. 31. Fluid Motion  Some applications require a combination of liquid- solid-gas mixing  Physical processes such as heat transfer may be required  Description of mixing is provided in terms of the fluid motion produced by the impeller  Defining the magnitude of the required fluid motion, the system description can be provided for the desired process objective
  32. 32. Power Consumption in Agitated Vessels Impeller Type Impeller Diameter Speed of Rotation Fluid Density Fluid Viscosity Vessel Design, Attachments
  33. 33. Dimensionless Numbers • Reynolds Number • Froude Number • Power Number ρ- Density of the fluid in Kg/m3 n – Rotational speed in revolution / sec Da – Impeller diameter in meters µ – Fluid viscosity, Pa-s g – Acceleration due to gravity, 9.8m/s2
  34. 34. Flow Regimes  Laminar Flow - Reynolds number < 10  Turbulent Flow - > 103 to 105  Flow is considered transitional between these two regimes  Impeller power numbers are compared in the turbulent regime, which for common use is taken as Re > 105  In laminar flow, the liquid moves with the impeller. At a distance away from the impeller, the fluid remains stagnant. In such cases, the Froude number accounts for the force of gravity which determines the fluid motion.
  35. 35. The power number Np depends on the impeller geometry and the location of the impeller in the vessel. In the laminar regime, Power number is inversely proportional to the Reynolds Number. The power depends largely on the fluid viscosity. In the transitional regime, the power number changes slightly. In the turbulent regime, the power number is constant and independent of the fluid viscosity. Power Number Plot of the Power number versus the impeller Reynolds number for different types of impellers, vessel geometrics.
  36. 36. Power Consumption in Agitated Vessels . Using the power number equation, the power consumed by an impeller for specified system geometry can be determined. The connected motor power should be higher since it has to account for the electrical and mechanical losses of the agitator drive system.
  37. 37. Flow Number  The flow number (pumping number) is defined as NQ = QP / nDa 3 QP – effective pumping capacity m3 /s  For most impellers operating in the turbulent regime, the flow number varies in the range of 0.4 – 0.8  The pumping number is used to define the pumping rate of an impeller.
  38. 38. Flow Characteristics  Depends on the vessel size and geometry, the internal attachments like baffles, and the fluid properties.  The velocity of the fluid has three components – • Radial velocity component - Acts perpendicular to the agitator shaft • Axial velocity component - Acts parallel to the shaft • Tangential or rotational component - Acts in a tangential direction to a circular path around the shaft. Tangential flow is detrimental – creates vortex.
  39. 39. Impeller Flow Patterns
  40. 40. Shear  Relative motion of the liquid layers within the mixing vessel results in shearing forces that are related to flow velocities.  The fluid shear stress is the multiplication of fluid shear rate and fluid viscosity  These forces, represented by shear stress carry out the mixing process  Pumping capacity is important in establishing shear rate due to the flow of the fluid from the impeller.  Understanding the location and magnitude of shear generated by an impeller in an agitated vessel has significant implications for design.  Most axial flow impellers are low-shear and have high pumping efficiencies.  Radial flow impellers provide high shear but are low pumping.
  41. 41. Liquid Agitation Equipment  Top Entering Mixers  Side Entering Mixers  Portable Mixers  Jet Mixers  Motionless Mixers
  42. 42. Equipment Top Entering Mixers
  43. 43. Vessel  Vertical cylindrical vessel with a liquid height which is equal to the tank diameter  The vessel top and bottom may be provided with flat or dished ends  Dished bottom heads can be 2:1 ellipsoidal, torispherical, hemispherical or conical  Nozzles - Agitator mounting, feeding, measurement instruments, manhole, material discharge  Design for the operating temperature and pressure conditions.  The thickness of the vessel shell and dished ends should be calculated using the relevant pressure vessel design codes.
  44. 44. Baffles are installed on agitator vessels to produce a flow pattern conducive to good mixing and to prevent vortex formation. In standard agitation equipment configurations, 4 vertical baffles are provided each of which has a width of 1/10th or 1/12th of the tank diameter. Baffles are generally offset from the vessel wall by a distance equal to1/3rd to 1/6th width of the baffle. Baffles increase the power consumption of the mixer but in turn improve the process performance. Baffles
  45. 45. Draft tube is a cylindrical duct slightly larger than the impeller diameter and is positioned around the impeller. Used with axial impellers to direct the suction and discharge flows. The impeller draft tube system acts as a low efficiency axial flow pump. The top to bottom circulation flow is of significance for flow controlled process, suspension of solids and for dispersion of gases. They are particularly useful in tall vessels having high ratio of height to diameter. . Draft Tubes
  46. 46. Heat transfer surfaces are provided for applications which require heating or cooling of process. Heat transfer for an agitated vessel is dependent on the following: • Overall heat transfer coefficient • Surface area for heat transfer • Temperature difference between the heat transfer fluid and the process fluid. The heat transfer co-efficiencies can be estimated using established corrections The turbulence created by the action of the impeller improves the heat transfer coefficient.   Heat Transfer Surfaces
  47. 47. Impellers • Based on the liquid viscosity, impellers can be classified as turbines for low viscosity fluids and close clearance impellers for high viscosity fluids. • Depending on the flow patterns developed by the mixing impellers, they are classified as axial flow impellers and radial flow impellers. • Impeller designs may also be classified based on the amount of shear that they produce. Axial flow impellers • Marine propellers • Pitched bade turbines • Hydrofoil impellers Radial flow impellers • Rushton turbine • Smith Impeller • Open blade turbine • Coil or spring impellers   Low clearance impellers • High shear impellers
  48. 48. Axial Flow Impellers The impeller blade makes an angle of less than 90° with the plane of impeller rotation. The locus of the flow occurs along with axis of the impeller, parallel to the impeller shaft. Axial flow impellers are used for blending, solid suspensions, solid incorporation or draw down, gas inducement and heat transfer applications. Commonly used axial flow impellers for transitional and turbulent flow applications include, marine propellers, pitched blade turbines and hydrofoil impellers.   Fluid flow pattern of axial flow marine propeller.  Impeller is mounted at the centre of a baffled vessel
  49. 49. Marine Propellers Speed range – 400 to 1800 rpm Top Entering – Diameter < 450 mm Side Entering – Diameter 250 mm to 850 mm In a theoretical environment, one full revolution would move the liquid longitudinally a fixed distance depending upon the of inclination of propeller blades. The ratio of this distance to the diameter of the propeller is known as the pitch of the propeller. Propellers are available with 1.0 pitch ratio; these are often referred to as square pitch. Variations include four bladed propellers, propellers with saw tooth edges for tearing action, perforated blades for shredding and breaking of lumps. Marine propellers are also used on side entering mixers. They are mounted with the impeller shaft inclined at an angle with respect to the vessel centerline, for improving process results. Three blade marine propeller
  50. 50. Pitched Blade Turbine Impeller Diameter - 450 mm to 3000 mm Hub with even number of blades are mounted at an angle of 10° to 90° with respect to the horizontal The most commonly used impeller of this type is the four bladed 45° pitched blade turbine Mixed flow impeller as fluid discharge has both axial and radial components Generally down-pumping Up-pumping in applications such as gas dispersions and floating solids mixing Used in flow control applications 45° pitched blade turbine impeller
  51. 51. Hydrofoil Impellers High efficiency impellers designed to maximize fluid flow and minimize shear rate. 3 or 4 tapering twisted blades, cambered and sometimes provided with rounded leading edges. The blade angle at the tip is lower than that at the hub. Resultant flow is streamlined. Vertices around the impeller are lower. Lower power number than PBT. The solidity ratio is the ratio of the total blade area to a circle circumscribing the impeller. Low solidity ratio - Liquid blending and solid suspensions. Higher solidity ratio - Axial flow patterns as the viscosity increases. In gas-liquid dispersions wide blades provide an effective area of preventing bypass of gas through the impeller hub. Myths about Hydrofoil Impellers Hydrofoil Impeller Hydrofoil impeller with different solidity ratios
  52. 52. Radial Flow Impellers The impeller blade is parallel to the axis of the impeller. Radial flow impeller discharges flow along the impeller radius Radial flow impellers are used for single and multi-phase mixing applications. Effective for gas-liquid and liquid-liquid dispersions. Commonly used radial flow impellers include, the Rushton turbine, bar turbine, open blade turbine. Radial flow pattern produced by flat blade turbine
  53. 53. Rushton Turbine, Smith Impeller The Rushton turbine is a disk type (six blade turbine) radial flow impeller. The diameter of the disk ranges from 66 to 75 percent of the internal vessel diameter. Impeller design is best suited for gas liquid contacting because of the circular disk. Gas is introduced through a sparger below the impeller; the disk directs the gas along a path of maximum liquid contact and prevents the gas from taking the direct vertical route along the mixer shaft Variant of the Rushton turbine is the Smith impeller in which the impeller blades are semi - circular or parabolic, instead of flat. For gas dispersion, the impeller shape allows for much higher power levels to be obtained in the process as compared to the Rushton turbine. . Six blade Rushton turbine impeller Smith impeller
  54. 54. Open Blade Turbine, Coil Impeller In open blade turbine, the blades are directly mounted on the hub. The number of blades may be two, four, six or eight. Two-blade paddle is generally used for solid suspension or blending applications requiring high flow and low shear. Paddles are normally operated at low speeds Coil impellers were developed for applications where solids frequently settle at the bottom of the vessel Spring design ensures that the impeller has adequate mechanical rigidity, strength to overcome the resistance offered by stiff solids during mixing operation Flat blade turbine impeller Coil impeller
  55. 55. Low Clearance Impellers The anchor impeller and the helical impeller are the two commonly used close clearance impellers. The diameter of the close clearance impellers is typically 90 – 95 percent of the inside diameter of the vessel. The shear near the vessel wall reduces the build up of stagnant material and promotes treat transfer. The anchor impeller is a radial flow impeller Helical impeller provides axial discharge of material by producing strong top to bottom motion Anchor blades may be used in combination with other types of impellers Anchor impeller Helical impeller
  56. 56. High Shear Impellers Used for application such as grinding, dispersing pigments and making emulsions High shear impellers are operated at high speeds and are generally used for addition of the second phase Saw tooth impeller generates heavy turbulence in the area around the impeller. Star shaped impeller having tapered blades provides intermediate shear levels. Start shape impeller is used in polymerization reactor. High shear impellers may be used in combination with other types of impellers such as anchor. Saw tooth impeller Helical impeller
  57. 57. Impeller Selection • Application • Process function • Material properties • Viscosity • Equipment SizeImpeller selection (Source: Penny, W.R., "Guide to  trouble free mixers", Chem. Eng.,Vol.77, No.12,  1970, p.171)
  58. 58. Vessel and Impeller Design
  59. 59. Side Entering Mixers Side entering mixers are mounted at an angle of 7-10 degree to the tank centre line. Power levels for side entering mixers are low to the order of 0.01 KW/m3 Usually operate at an output speed of 400 rpm Low installation cost, easy to install The mixing efficiency of side entering mixers is low as compared to the top entering mixers Side entering mixers do not require baffles, but correct positioning of the impeller is absolutely necessary Used for very large tanks used in storing petroleum, crude oil and gasoline and in vessels which are used for long term storage.
  60. 60. Portable Mixers Small size mixers easy to mount on vessels or drums that may not require agitation at all times The propeller impeller with small diameter and high speed results in low torque is best suited Mounted using a clamp from the rim of the tank, with an adjustment that allows the mixer shaft to be set at an angle of 10-15 degree from the vertical Can be swiveled to locate the mixer shaft off centre Baffles are not required with portable mixers.
  61. 61. Jet Mixers Mechanical energy required for mixing of fluids is imparted through high velocity jets Jet mixers are driven by external pumps located outside the tank The liquid jet entrains and mixes the surrounding fluid using the mechanical energy supplied from the pump. Single or multiple jets may be provided depending on the application, size of the vessel. Jet Mixers are used in large storage tanks to maintain homogeneity of the liquid stored.
  62. 62. Motionless Mixers Motionless or static mixers use stationary elements of various profiles, geometries that are placed inside pipes or conduits. The material to be mixed is pumped through this pipe where mixing occurs through successive diversions and recombination of the process fluid. For ‘n’ elements, there are 2n division and recombination. For a mixer with 20 elements, the number of combinations would be over 1 million. Applications – Liquid blending, mixing gases, dispersion of gases into liquids, Chemical reaction, dispersion of dyes and for mixing solids in viscous liquids, heat transfer.
  63. 63. Module 3 Solid Blending  Chemical process industries involve solid mixing of chemicals, ceramics, fertilizers, powdered detergents.  In pharmaceutical industry small amounts of a powdered active ingredient are precisely blended with excipients such as sugar, starch, cellulose, lactose or lubricants.  Most powdered food products like soft-drink premixes, food flavors and instant foods are produced from custom mixed batches.  Worldwide production annually accounts for over a trillion kilograms of granular and powdered products that must be uniformly blended to meet quality and performance goals
  64. 64. Material Properties Affecting Blending • Angle of Repose • Flowability • Bulk Density • Particle Size, Distribution • Particle Shape • Cohesiveness • Adhesiveness • Agglomeration • Friability • Abrasiveness • Explosiveness • Material Composition • Surface Characteristics • Moisture Content of Solids • Density, Viscosity, Surface Tension of Liquids Added • Temperature Limitations of Ingredients
  65. 65. Material Properties Affecting Blending    Angle of Repose - The angle of repose of a bulk material is the angle formed between the horizontal and sloping surface of a piled material, which has been allowed to form naturally without any conditioning.    Flowability - Flowability is the ease with which a bulk material flows under the influence of gravity only. The “Coefficient of Friction” of a powder is the tangent of the angle of repose and is the measure for its flowability. Flowability of bulk solids depends upon factors such as particle size and size distribution, particle shape, bulk density, cohesiveness, all of which affect blending.
  66. 66. Material Properties Affecting Blending    Bulk Density  - Bulk density is defined as the mass of a material that occupies a specific volume. It includes not only particle mass but also the air entrained in the void spaces between the particles. It is generally measured in kg/m3 or lb/ft3.  Particle Size, Distribution - Particle size and size distribution in powders have a considerable impact on the flow properties of powders. As a result, the dynamics of blending is affected by the size of particles and their distribution in the bulk solids. Particle size is generally quantified in microns or as mesh size.   Particle Shape - Particle shape affects inter-particle powder friction and thereby the flow, blending properties of the powder.
  67. 67. Material Properties Affecting Blending    Cohesiveness - Cohesiveness describes the tendency of a material to adhere to itself.  Adhesiveness - Adhesiveness is described as "external cohesiveness" which is the ability of material to adhere to other surfaces.  Agglomeration - Adherence of particles due to moisture, static charge or chemical or mechanical binding results in agglomeration.  Friability - Friability describes a bulk material where particles are easily crumbled or pulverized.  Abrasiveness - The abrasiveness of a material is determined by its hardness factor and the shape of its particles. The hardness of materials is quantified by Moh's hardness factor.  Explosiveness - In certain conditions, some bulk materials can form potentially explosive mixtures when combined with air.  Material Composition - Composition of unit particle is its quantitative and qualitative makeup. Individual units of pure substances have their unique molecular composition and arrangement that dictates their behavior and distinguishes them from other substances. The chemical composition is important because chemical reactivity shall be a major factor in choice of a particular substance for the application.  
  68. 68. Material Properties Affecting Blending    Surface Characteristics - Surface characterizes include surface area and electrostatic charge on the particle surface. Smaller particle have a larger surface area which lead to formation of weak polarizing electrical forces termed as “Van Der Walls” forces. When electrostatic charge is generated due to friction between two surfaces, the electric charge generated is referred to as “Triboelectric” charge.  Moisture of Liquid Content of Solids - Increased surface exposure of fine particles to the atmosphere may result in moisture adsorption, absorption. Materials that naturally contain bound moisture or tend to adsorb, absorb moisture are termed as hygroscopic.  Density, Viscosity, Surface Tension of Liquids Added - Some blending operations require addition of liquids into the solids for a specific purpose. In such cases, it is essential to know the properties of the liquids to be added during blending and its purpose.  Temperature Limitations of Ingredients - An unwanted rise in the temperature of materials during the blending operation beyond product limits can lead to product degradation, melting or even be a source for ignition. Effects of each property must be considered individually, their combined effect as a set of group of co-related variables must be accounted.
  69. 69. Structured and Random Blend Structures  In structured blends, the different blend components interact with one another by physical, chemical, molecular means or a combination of these resulting in agglomeration. The agglomerates formed thus comprise of a uniform blend of smaller particles.  Fine materials in particular have a tendency to adhere only to themselves, without adhering to the dissimilar components. e.g. carbon black, fumed silica. For blending of these materials, shear blending mechanisms are adopted.  When the different blending components do not adhere or bind to each other within the blender, the result is a random blend structure.  Dissimilar particles readily segregate under the influence of external forces like gravity, vibration and get collected in zones of similar particles. e.g. a blend of salt and pepper.  Completely random blends are rarely encountered in industrial applications.
  70. 70. Mechanisms of Solid Blending • Diffusion Blending • Convection Blending • Shear Blending These three mechanisms occur to varying extents depending on the type of mixers, blenders and the characteristics of the solids to be blended.
  71. 71. Mechanisms of Solid Blending Primary Mechanisms of Solid Blending ◊ Diffusion Blending ◊ Convection Blending ◊ Shear Blending
  72. 72. Diffusion Blending • Diffusion blending is characterized by small scale random motion of solid particles. • Blender movements increase the mobility of the individual particles and promote diffusive blending. • Diffusion blending occurs where the particles are distributed over a freshly developed interface. • In the absence of segregating effects, the diffusive blending will in time lead to a high degree of homogeneity. • Tumbler blenders like the double cone blenders, v- blenders function by diffusion mixing.
  73. 73. Convection Blending • Convection blending is characterized by large scale random motion of solid particles. • In convection blending, groups of particles are rapidly moved from one position to another due to the action of a mixing agitator or cascading of material within a tumbler blender. • The blending of solids in ribbon blenders, paddle blenders, plow mixers is mainly a result of convection mixing.
  74. 74. Shear Blending • Shear blending is the high intensity impact or splitting of the bed of material to disintegrate agglomerates or overcome cohesion. • Shear blending is very effective at producing small-scale uniformity generally on a localized basis. • Blenders with a high speed chopper blades, intensifiers are an examples of shear blending.
  75. 75. Segregation (De-mixing) • Occurs during blending, transport, storage or discharge. • Greater with free-flowing powders since they can separate easily (based on size, shape, and density) Overcome by • Minimizing physical differences • Increasing cohesiveness of formulation • Optimizing blending conditions
  76. 76. Segregation Mechanisms • Blending and segregation (de-mixing) are competing processes. • Segregation is defined as the separation of particles into distinct zones due to particle size, shape, density, resiliency, or other physical attributes like static charge. • Common particle segregation mechanisms include - Sifting segregation - Fluidization segregation(air entrainment) - Dusting segregation (particle entrainment)
  77. 77. Sifting Segregation • Sifting - smaller particles slipping between larger ones. – Particle size differences > 3:1 – Mean Particle size > 300 mμ – Free flowing pile formed through funnel – Major component is > 3 times minor one. • Sifting segregation occurs when fine particles concentrate in the center of a bin during filling, while more coarse particles roll to the pile’s periphery. • Smaller particles move through a matrix of larger ones. • During discharge, the fine particles shall flow out first followed by the coarse material.
  78. 78. Fluidization segregation • Fluidization segregation occurs when the finer, lighter particles (generally smaller than 100 microns) rise to the upper surface of a fluidized blend of powder, while the larger, heavier particles concentrate at the bottom of the bed. • The fluidizing air entrains the lower permeability fines and carries them to the top surface. • Fluidization segregation generally occurs when fine materials are pneumatically conveyed, when they are filled or discharged at high rates, if gas counter-flow occurs
  79. 79. Dusting segregation • Dusting segregation is commonly encountered with fine pharmaceutical and food powders being discharged from blenders into drums, tableting press hoppers and packaging equipment surge hoppers. • In dusting segregation the fine particles get concentrated near the container walls or at points furthest from the incoming stream of material.
  80. 80. Minimizing Segregation Segregation of materials can be minimized or eliminated using one of the following approaches • Changing the properties of the process material • Changing the process • Changing the equipment design
  81. 81. Design Practices for Minimizing segregation •Solid blending should be located as far downstream in the process as possible. •Post-blend handling of the material should be minimized. •Surge and storage bins should be designed for mass flow (no stagnant regions in hopper) •Velocity gradients within bins should be minimized •A mass-flow bin with a tall, narrow cylinder is preferred as compared to short, wide bin. Keeping the material level in the bin high is preferred. •Use venting to avoid air counter-flow (inducing fluidization segregation). •Minimize the generation of dust
  82. 82. Scale Up of Solid Mixers Maintaining constant tip speed (also known as peripheral speed) Tip speed = πD n D – Agitator diameter (m) n – Rotational speed of the mixer (revolutions per second) Maintaining the Froude number constant.  Froude Number (Fr) for solid mixing equipment can be defined as: • v – Tip speed of mixing (m/s) • R – mixer radius (m) • - angular velocity (rad/s)ω
  83. 83. Scale Up of Solid Mixers Pilot Scale Development • Evaluate and determine blending times • Start at 10 minutes, further samples based on observations • Sampling methods, sizes and locations are developed Qualify Production Blender • Verify blending time, speed of rotation, power drawn Production Blending Instruction • Blender speed and blending time to be specified • Consistency of operation and performance batch after batch
  84. 84. Solid Blending Equipment • Tumbler blenders Double Cone Blender, V- Blender, Octagonal • Convective blenders Ribbon Blender, Cone Screw Blender, Paddle Blender, Plow Mixer, Twin Shaft Paddle • Silo blenders Gravity Silo Blender, Mechanical Silo Blender • Pneumatic blenders
  85. 85. Tumbler Blenders Function mainly by diffusion mixing. Rely upon the action of gravity to cause the powder to cascade within the rotating vessel. Mixing homogeneity of upto 98 percent and higher can be achieved using tumbler blenders. Blending efficiency is affected by the volume of the material loaded into the blender and speed of the blender rotation Can be provided with high speed intensifier bars for disintegration of agglomerates. Preferred for precise blend compositions Best suited for free-flowing, non- segregating powders.
  86. 86. Double Cone Blenders Consists of two conical sections separated by a central cylindrical section. The blender is mounted at the centre of the container between two trunions that allow the blender to tumble end over end.   Charging of material into the double cone blender is through one of the conical ends whereas the discharge is through the opposite end. The recommended fill-up volume is 50 to 60 percent of the total blender volume. Blending time is generally 10 to 15 minutes.
  87. 87. V Blender Two hollow cylindrical shells joined at an angle of 75 degrees to 90 degrees. Material continuously splits and recombines. Repetitive converging and diverging motion, combined with increased frictional contact between the material and the vessel’s long, straight sides result in gentle yet homogenous blending.   The recommended fill-up volume is 50 to 60 percent of the total blender volume. The blend time ranges from about 5 to 15 minutes.  
  88. 88. Advantages The following are distinct advantages of tumbler blenders: • Ease of product charging, operation and discharging of material. • The shape of the blender shell ensures complete discharge of product material. • Particle size reduction is minimized due to the absence of moving blades, agitators. •The absence of shaft projection, seals in the working area of the blender eliminate the possibility of product contamination. •Cleaning of tumbler blenders is easy. •Tumbler blenders require minimal maintenance
  89. 89. Disadvantages The disadvantages of the tumbler blender are as follows:   • Tumbler blenders need high head room for installation. • Segregation problems occur with mixtures having a wide particle size distribution or large differences in particle densities. • Highly cohesive materials cannot be handled in tumbler blenders since they tend to form a bridge over the blender outlet.
  90. 90. Convective Blenders •Blending occurs because of the random movement of particles through out the mixing vessel caused by the action of the mixing elements. •Depending on the rotational speed and the geometry of the mixing elements, solid particles are thrown randomly and the product is sheared or fluidized. •Combination of the mixing mechanisms results in effective and efficient mixing. •Can be designed for operation in both batch as well as continuous modes. •For materials that tend to form agglomerates during mixing, high speed choppers can be provided for disintegration of the agglomerates.
  91. 91. Convective Blenders • Horizontal ribbon blender • Vertical ribbon blender • Vertical cone screw blender • Paddle blender • Plow mixer • Twin shaft paddle mixer
  92. 92. Horizontal Ribbon, Paddle Blender •U-shaped horizontal trough containing a rotating double helical ribbon or paddle agitator. •Clearance of 3 - 6 mm is maintained •Charging material is through top nozzles. Discharge through bottom valve. •- Working capacity ranges from 40 – 70 % of total volumetric capacity. •Blending time - 15 to 20 minutes, •90 to 95 percent or better homogeneity. •Specific power - 5 to 12 kW/m3 •Ribbons are Best suited for free flowing and cohesive products. •Paddles are suitable for wet and heavy materials
  93. 93. Vertical Ribbon Blender Blender container is cylindrical, with a conical bottom Flexibility to operate at capacities from low volumes to 90 % volumetric capacity The material at the walls is lifted vertically upwards. After reaching the top, material travels down along centre of the blender. 100 percent material discharge Can handle friable products such as cereals, plastics Are more expensive than the horizontal blender configurations.
  94. 94. Vertical Cone Screw Blender Consists of a conical shape vessel with a screw agitator that rotates about its own axis while orbiting around the vessel’s periphery Drive system generally consists of two motors; one for rotation of the main drive, the other for the rotation of the screw Blender can operate efficiently with batch sizes from 10-100 % of total working capacity 100 percent material discharge Mixing time ~ 10 to 15 minutes
  95. 95. Plow Mixer Operate on the principle of a mechanically generated fluid bed with three dimensional movement of the product. Cylindrical drum containing plow shaped mixing elements mounted on a horizontal shaft May be fitted with high speed chopper units for applications which require break down of lumps or when the mixer is to be used for wet granulation Tulip shaped choppers and the X- mass tree chopper
  96. 96. Plow Mixer Working volume ranges from 30 percent to 70 percent of the total drum volume. Plow tip speed of more than 200 metres per minute to effect fluidizing action Mix ratios of as high as 1:20,000 Mixing time is 5 minutes with 95 to 98 percent homogeneity. Capable of handling viscosities of up to 600,000 centipoises. Specific power for the mixer drive generally ranges from 30 to 40 kW/m3
  97. 97. Twin Shaft Paddle Blender Paddles mounted on twin shafts in a ‘w’ shaped trough Normal filling level of material in the mixer is slightly above the shafts Overlapping motion and paddle design facilitates rapid fluidization and ensures excellent movement of particles Surplus space in the mixer trough to provide air around the particles so that they can move freely Twin shaft, counter-rotating paddles lift the particles in the centre of the mixer trough, in the fluidized zone, where mixing takes place in a weightless state.
  98. 98. Twin Shaft Paddle Blender Normal working volume is about 25 percent of the total volume of the trough Range of operation of the mixer is 40 to 140 percent of the rated capacity Peripheral speed ~100 metres per minute Mixing time can be as low as 1 minute. Mixing homogeneity of 98 – 99 percent. Choice of discharge valves including half bomb bay doors, spherical disc valves are available. High speed choppers can be provided Rotating twin shaft paddle mixers are the most recent development.
  99. 99. Selection of Solid Mixer
  100. 100. Silo Blenders • Several industrial applications where the methods of production, the properties of material or the nature of process may lead to variations in the quality of the solid powders as a function of time • Instances where material blended in small batches, are required to be homogenized to produce a single bulk lot • Homogenization of material is carried out in large silos, using either gravity blending techniques or using mechanical silo blenders
  101. 101. Gravity Silo Blender Convenient and economical method of blending large volumes of free flowing powders Use multi-tube construction on inserts to create velocity gradients within the silo Material is simultaneously drawn off by a system of tubes positioned at different heights and radial locations, brought together and mixed. Capacities ranging from 5m3 to 200 m3 Low energy, less than 1 kW-hr per ton of product being blended
  102. 102. Mechanical Silo Blender Provided with a screw housed in a cylindrical shell, isolating the bulk material in the silo from the material inside the shell Material from the bottom section of vessel is lifted by the screw and spread over the upper sections Principle of blending is based on the differential travel speeds of product particles in the conical section of the vessel, and the velocity of material in the screw region. Power required - 1.5 to 2 kW-hr per ton
  103. 103. Pneumatic Blender Air or gas is injected intermittently at high velocities at the bottom or the sides of the silos, to blend powder materials that exhibit expansion characteristics when aerated. The solid particles rise due to the drag force of the injected air. Increase in air velocity causes agitation in the bed, resulting in formation of bubbles, which cause blending to take place. The blending action can be optimized by adjusting the air pressure, pulse frequency, or on/off duration. Specific power input ranges from 1 to 2 kW-hr per ton of product. The largest pneumatic blenders are used in cement industry with blender capacities of upto 10,000 m3 .    
  104. 104. Module 4 – Mixing of High Viscosity Materials and Pastes “ The viscosities of materials to be processed are constantly on the rise, as there is an urgent need to cut levels of volatile organic compounds in most parts of the process industry ” MATERIAL APPROXIMATE VISCOSITY (in centipoise) Water @ 70 F 1 to 5 Honey 10,000 Chocolate Syrup 10,000 to 25,000 Ketchup or French Mustard 50,000 to 70,000 Plastisol 50,000 (2 -  2.5 million cps  during mixing process) Tomato Paste or Peanut Butter 150,000 to 250,000 Silicone Sealant 6 to 7 million  Solid Propellant 10 to 15 million  Dental whitening gels, polyester compounds, epoxies,  transdermal drugs, dental composites, butyl sealants,  automotive sound absorbing compounds, color pigment  compounding pastes, and chewing gum formulations.
  105. 105. High Viscosity Mixing “ Mixing in viscous systems can be achieved only by mechanical action or by the forced shear or by elongation flow of the matrix ”
  106. 106. Mixing Mechanisms Dispersive mixing : Dispersive mixing is defined as the breakup of agglomerates or lumps to the desired ultimate grain size of the solid particulates or the domain size (drops) of other immiscible fluids.   Distributive mixing : Distributive mixing is defined as providing spatial uniformity of all the components and is determined by the history of deformation imparted to the material.   Convective mixing : Convective mixing in the laminar regime is effected by shear, kneading and stretching of material and results in reorientation of the dispersed elements.
  107. 107. Mixing Challenges Equipment Design, Scale-Up : Because of the viscosity and temperature changes that occur during the mixing process, it is difficult to model the system. Mixer drive systems should provide constant torque throughout the speed range, even at very low rotational speeds. Power Requirement : Mixing requires large amounts of mechanical energy for shearing, folding over, dividing and recombining. Heat Transfer : Heat transfer is generally poor in viscous materials. Mixers for high viscosity materials therefore need to be designed for promoting efficient heat transfer.
  108. 108. BATCH Dual Shaft Mixer Triple Shaft Mixer Planetary / HSD Hybrid Double Planetary Mixer Kneaders Kneader Extruder Intensive Mixer Banbury Mixer High Intensity Mixer Roll Mill Pan Muller Mixer CONTINUOUS Single Screw Extruder Twin Screw Extruder Pug Mill Viscous Mixing Equipment
  109. 109. Mixing element operates within all parts of the mixing vessel. Low clearances between the mixing element and the mixing container (1 to 2 mm). The mixing elements may comprise of intermeshing blades that prevent the material from cylindering along with the rotating mixing element. Most mixers are provided with close-clearance blades and / or scraper devices to move stagnant material away from heat-transfer surfaces. High connected power per unit volume. (upto 6 kW / kg of product) High viscosity mixers operate at low speeds, require high power and therefore need high torque. Discharge of materials after mixing may be difficult and may require special arrangements. As the forces generated during mixing process are high, mixers are rigid in construction. Mixer Design
  110. 110. Change Can Mixers •Like most liquid agitators are vertical configuration equipment with a vertical cylindrical vessel •Provided with an arrangement for lifting of the agitator head, mixing element out of the mixing vessel once the mixing is completed, thus enabling the movement of the mixing vessel •Some change can mixers have mixing vessels that can be lifted and lowered with the agitator head stationary. •Change can mixers may be provided with one or more mixing blades.
  111. 111. Change Can Mixers The removal of the mixing vessel provides the following advantages: •Weighing of material can be accurately done. •Cleaning of the mixing vessel is easier thereby resulting in less batch to batch contamination. •The packing glands, seals do not come in contact with the material, thereby eliminating product contamination. •Multiple cans can be used to enhance the productivity without any down time during material charging, discharge. •Because of the vertical configuration, these mixers can be operated at as low as 10 percent of their designed working capacity. •Discharge of highly viscous materials from the mixing vessel can be achieved by locating the vessel on a separate hydraulically operated automatic discharge system.  
  112. 112. Single Planetary Mixer Mixing element (commonly known as the beater) rotates in a planetary motion inside the mixer bowl The most commonly used beaters are the batter, wire whip and hook type. The discharge of material from the mixer bowl can be by hand scooping when the material is pasty and does not flow or through a bottom discharge valve when the material is flowable. The single planetary mixer is used for mixing of dry and wet powders, light pastes, gels and dough.
  113. 113. Double Planetary Mixer The double planetary mixer includes two blades that rotate on their own axes, while they orbit the mix vessel (also known as bowl) on a common axis. The mixer bowl may be jacketed for circulation of heating or cooling media. The mixer can be designed for operation under pressure or vacuum. Material is generally discharged by manual scooping of the material from the bowl. For extremely viscous materials, hydraulically operated automatic discharge systems are available that push the material out through the discharge valve.
  114. 114. Planetary Mixer, HSD •Specific power - 30 to 50 kW/m3 •Fill levels - 20 to 85 % of bowl volume •Viscosity Range -1 to 8 million cps •Can be equipped with additional mixer shafts that are provided with other types of mixing impellers. •A high shear impeller can be used to incorporate powdered material or create a stable emulsion resulting in the formation of viscous paste
  115. 115. Double Arm Kneader Mixer Two mixing blades placed in a ‘w’ shaped horizontal trough Commonly used blade types are the sigma blade, masticator blade, spiral blade, shredder and naben blade Rotation of the blades is either tangential to each other or the blades may overlap within the trough. Blades pass the container walls and each other at close clearances generally (1-2 mm) The mixer bowl may be jacketed for circulation of heating or cooling media.
  116. 116. Double Arm Kneader Mixer Viscosity range upto 10 million cps Viscous mass of material is pulled, sheared, compressed, kneaded and folded by the action of the blades against the walls of the mixer trough. Fill Up is 40 – 65 % of bowl volume Mixing homogeneity upto 99 percent Specific power - 45 to 75 kW/ m3 Discharge of the material from the mixer - By tilting of the mixer container - Bottom discharge valve - Through an extruder, screw
  117. 117. Kneader Extruder
  118. 118. Intermix ®, Banbury ®
  119. 119. High Intensity Mixer Combines a high shear zone with fluidized vortex for mixing of pastes and powders Mixing blades placed at the bottom of the vessel scoop the material upwards at very high rotation speeds High blade impact disintegrates product agglomerates thereby resulting in an intimate dispersion of powders and liquids Scale up based on constant peripheral speed of the blade which is about 40 m/s Specific power - 200 kW/m3
  120. 120. Roll Mill Pair of smooth metal rolls set in the same horizontal plane, mounted on a heavy structure Provided with an arrangement for adjusting the distance between the rolls and regulating the pressure To increase the shearing action, the rolls are usually operated at different speeds Two roll mills are used primarily for preparing color pastes for inks, paints, and coatings. Rubber products and pastes are compounded in batch roll mills as they provide extremely high localized shear. Continuous mills for mixing pastes contain three to five horizontal rolls.
  121. 121. Pan Muller Mixer Industrial equivalents of the traditional mortar and pestles. Consist of two broad wheels mounted on an axle located inside a circular pan Mixers are available in the following designs: - Pan is stationary and the mixer rotates -Pan is rotating and the axis of the wheels is held stationary -Both the pan and wheels are rotating. Wheels are offset Muller mixers are used for mixing of heavy solids and pastes which are not too pasty or sticky
  122. 122. Single Screw Extruder Single Screw Extruder Single screw extruders consist of stationary barrel which houses a rotating screw having close clearance with the internal wall of the barrel. The material to be mixed is continuously fed in the feed throat area using a feed hopper. The design of the screw is such that the root diameter of the screw increases gradually from the feed point to the point of discharge. External jacket may be provided for heating or cooling of the product material. A discharge dye is fitted at the outlet to extruder the material in the required form, shape, profile. The specific energy required for polymer mixing application ranges from 0.15 – 0.3 kW- hr /kg.
  123. 123. Twin Screw Extruder Twin screw extruders comprise of two screws that are housed in figure-‘8’ shaped barrels connected to each other. The mixing and the shearing action takes place due to the interaction between the screw and the barrel, and also due to the interaction between the two screws. The most common type of twin screw extruders is the counter rotating intermeshing type. The screw shafts are fitted with slip-on kneading or conveying elements that provide a wide range of mixing effects combined with compression, expansion, shearing and elongation of material. At the point of discharge, a plate with a well defined opening size is provided to control the amount of pressure developed and the quantity of discharge. Twin Screw Extruder
  124. 124. Pug Mills Pug mills consist of single or twin shaft fitted with short heavy paddles rotating within an open trough or a closed cylinder.. Paddles may position tangentially or may overlap each other. Solids are continuously fed into the mixing chamber from one end and discharged from the opposite end. Liquids may be added depending on process requirements. The product may be discharged through the open ports, or may be extruded through nozzles in the desired shape and cross section. The extruded material can be cut into pellets, blocks of required size. Pug mills are used to blend and homogenize clays, mix liquids with solids to form thick, heavy slurries.
  125. 125. Module 5 – Mechanical Components in Mixing Equipment • Motor • Gear reducer • Couplings • Mixer seals • Bearings • Variable speed operation devices
  126. 126. Motors Electrical Motors • While specifying electrical motors the following essential information should be provided: • Single phase / three phase AC or DC motors • Supply voltage (volts) • Frequency (Hz) • Power (hp) • Speed in revolutions per minute (rpm) • Motor frame size • Insulation class; A,B,F,H. This establishes the maximum safe operating temperature • Temperature classification • Amperage (full load motor current) • Duty • Type classification • Explosion proof motor • Other parameters like motor efficiency and so on may also be defined. - Motors should preferably not to be loaded beyond 90 percent of their maximum rated current. - While deciding the motor horsepower, besides the power requirement for mixing, the drive transmission losses should be considered Pneumatic Motors Hydraulic Motors
  127. 127. Gear Reducer Provides speed reduction and increasing allowable torque. The speed reduction ratios may vary from as low as 5:1 to as high as 100:1. Selection of Speed Reducers •Details of the prime mover •Details of the Mixer •Details of gear box design •Shaft connection The selection of gear box involves: •Selection of gear box for mechanical capacity. •Determining the service horse power for the gear box. •Selection of gear box based on thermal rating •Selection based on overhung loads, axial thrust loads
  128. 128. Gear Reducer Helical gears are used in parallel shaft gear reducers. Spiral bevel gears are used when the input and output shaft of the gear reducers are required to be at right angles. Worm gears are the most economical speed reducers capable of providing large speed reduction with a single gear set. Planetary gears consist of internal gear with small pinion known as sun gear, surrounded by multiple planetary gears.
  129. 129. Couplings A coupling is a mechanical device used to connect the mixer shaft to the shaft of the drive system for the purpose of transmitting power. Rigid Coupling - Rigid couplings are used when precise shaft alignment is required. Rigid couplings can be of the following types:  Sleeve or muff coupling •Clamp of split-muff or compression coupling •Flange Coupling Flexible Coupling - Flexible couplings are designed to transmit torque while permitting some radial, axial, and angular misalignment. •Elastomer couplings - Bushed pin coupling, Tyre, Spider or jaw coupling •Resilient coupling •Disc coupling •Diaphragm coupling •Gear coupling •Roller chain and sprocket coupling •Fluid coupling (Selection of Fluid Coupling)
  130. 130. Bearings The type and the magnitude of axial and radial loads transmitted by the mixer shaft depend upon the configuration of the agitator, vertical or horizontal, the forces caused by mixing operation. Different types of bearings used in mixers Ball bearings - Used for radial loads and moderate thrust loads. Ball bearings are generally used for high speed drive shafts and portable mixers. Tapered roller bearings - They are used for heavy radial and thrust loads. Spherical roller bearings - Spherical roller bearings are popular in side entering mixers, horizontal mixers where fluctuating loads can occur. Excellent for heavy radial loads and moderate thrust. Self aligning. Pillow block bearings - Pillow block bearings are commonly used in side entering, horizontal mixers Mixer bearings should be selected for a L-10 life of at least 10,000 hours.
  131. 131. Shaft Seals Mixers are provided with seals that are used to ensure that the mixer vessel contents are not exposed to the surrounding environment. Seals may be required when the operating pressure within the mixer is different from the atmospheric pressure or when the material being mixed is toxic, inflammable or can vaporize. Most common shaft seals are as follows: Stuffing boxes : A stuffing box consists of a housing located around the mixer shaft and is filled with a compression packing material to minimize the leakage Mechanical seals: Mechanical seals are most advanced type of seals used in the mixers.. With proper installation, they can handle high pressure, ensure nearly leak free operation. Hydraulic seals: Hydraulic seals are generally used for vapor retention and are limited to very low pressure applications. Lip seals: A lip seal is manufactured using elastomer material and is positioned in the gap between the rotating mixer shaft and stationary seal housing. These seals are not suitable for pressure applications and exhibit high leakage rates even at low pressures.
  132. 132. Variable Speed Operation Devices • Least expensive mechanical means for achieving variable speed operation is through the use of v-belts and sheaves with variable pitch diameters. These are however rarely used in modern day. • Two speed electrical motors are available and can offer variable speed operation of mixers at two defined speeds. • Variable frequency drives as the most preferred electronic device for changing the speed of the mixers. The variable frequency drive provides stepless speed variation where in the speeds can be infinitely adjusted and varied within the specified electrical frequency limits. • Variable speed operation can also be achieved using hydraulic motors, pneumatic motors or hydraulic couplings.
  133. 133. Mixer Installation • Mixer installation, start-up and maintenance should be carried out by trained technical personnel as per the directives of the mixer manufacturer. • Some equipment would require civil foundation. Consult the mixer manufacturer for such requirements. • The equipment should be positioned at the desired location taking into consideration the utility requirements/ availability. • It should be ensured that adequate space is provided around the equipment for operation and maintenance. • The alignment / level of the mixer assembly should be checked • It is recommended that the moving / rotating parts should be checked with manual operation of the drive winch assembly. • Complete all the electrical connections between the mains and electrical control panel. • Ensure that the mixer is connected in proper electrical phase sequence. The mixer shaft should rotate in the direction as recommended by the equipment manufacturer. • Earthing connection should be provided to the mixer body and its electrical control panel by using suitable size / type of cable as per country norms.
  134. 134. Mixer Start Up Follow up check-list before mixer start-up: • Check oil level of the gear reducer. In most cases, the grade of Oil is ISO VG 220 mineral oil. For details refer manufacturer’s literature. • Connect and check the electrical supply to the electrical control panel for mixer operation.. • Check the tightness of the bolts of the gearbox, motor, and other important drive components for proper bolting torques. • Check that the mixing vessel is thoroughly cleaned and there are no foreign particles inside. This exercise should be done prior to “switching on” of the mixer motor. • Ensure that the mixer bottom valve is in closed position. • Ensure that the safety guards for all rotating components are in position. • Check the connections of utilities to the mixer. • Understand the use of operating push buttons and digital instruments provided on the control panel thoroughly including that of emergency stop. If possible, check the operation of each push button, instruments individually and collectively before actual use of mixer.
  135. 135. Mixer Start Up The mixer should be first started at “no load” condition. • Start the mixer and check the direction of rotation of agitator shaft. The shaft should rotate in the direction recommended by the equipment manufacturer. • Check the power / current drawn by the mixer motor when assembled to the mixer. This current should be only marginally higher when compared to the current drawn by the motor under no load conditions. It should however be much lower than the maximum rated current of the motor. • Incase of excessive power drawn; check the electrical / mechanical features. • If the power drawn is in the range specified, allow the motor to run for 2-3 minutes and minutely observe the working of the mixer drive components. • Incase of any abnormality of the functions, try to analyze and rectify the defect by following the instructions provided in the equipment manufacturer’s manual. If the same can not be solved, contact the manufacturer for guidance. • If all the functions operate satisfactorily, test – run the mixer motor for longer period; for half an hour followed with 1 to 2 hours idle run. • Check the operation of the other features, instruments provided on the mixer.
  136. 136. Mixer Start Up • Load limited quantity of the process material in the mixer and observe its functions in terms of mechanical and electrical operations. Do not use the mixer for any process material, or operating conditions other than that for which it has been designed by the equipment manufacturer. • If the “no load” functions of the mixer are within the permissible limits, increase the material charge quantity gradually, following the specified limits of 50 percent material charge, 75 percent material charge and 100 percent material charge (“full load”). When the material is loaded to it full capacity the maximum current drawn by the mixer motor should not exceed 90 percent of the maximum rated motor current. • Check the temperature of the geared reducer, bearing housings, stuffing box area and so on. These should be within the permissible limits as specified by the mixer manufacturer. Incase of any abnormality or excess heating observed, contact the manufacturer. • Continue monitoring the power supply, load drawn at different percentage of loadings of the product mass and maintain records to check and confirm the performance of the mixer on full load condition. If the results are satisfactory the second batch trial can be conducted. Monitor the performance continuously for first few trials and maintain the records before the mixer is handed over for regular production. • In the case of continuous mixers, the process of mixer start-up would require several other considerations. In such cases, the equipment manufacturer’s guidelines should be strictly adhered to.
  137. 137. Mixer Maintenance • A sound preventive maintenance program is necessary to ensure trouble free operation of the mixer, increase equipment life and minimize downtime. • Equipment records, maintenance drawings, repairs and maintenance history should be well documented and easily accessible to the operational team. • The requirement of critical equipment spares should be clearly identified and available. • A preventive maintenance schedule, electrical and mechanical maintenance program, detailed lubrication program should be defined and strictly adhered to. • Lubrication is of the most critical aspects of equipment maintenance. • It is recommended that the first fill of the oil in the gearbox to be replaced after about 10,000 working hours of running or after two years whichever earlier. • Lubrication, greasing of the bearings should be carried out at least once a week. • The total de-greasing, re-greasing of the bearings should to be carried out based on operational usage.
  138. 138. Mixer Specifications
  139. 139. Module 7 – Advances in Mixing Technology ◊ CFM – Computation fluid mixing ◊ DPIV – Digital particle image velocimetry ◊ LDA – Laser doppler anemometry ◊ LIF – Laser induced fluorescence ◊ Mixing simulation programs ◊ Advances in manufacturing technology ◊ Scientists, Engineers, Managers need to abreast with new technologies ◊ Need for development of expertise
  140. 140. Advances in Mixing Technology ◊ Using DPIV technology, it is possible to measure the fluid velocity field in the mixing vessel at all points almost instantaneously ◊ LDA is probably the best method of non- intrusively determining mean velocity and turbulence data to high level of accuracy. ◊ LIF is a measurement technique, which provides both qualitative and quantitative assessment of mixing.
  141. 141. Advances in Mixing Technology ◊ The effects of vessel geometry and internals such as baffles can be factored into the system design. ◊ Mixing problems, such as low-velocity areas, circulation zones, staging and anomalies in the fluid flow and other potential problems can be identified using mixing simulation programs such as VisiMix and quickly resolved, instead of adopting the conventional and time consuming trial and error process.
  142. 142. Mathematical Modeling
  143. 143. Mixing Simulation
  144. 144. Solve Any Mixing Problem Framework ◊ Precise definition of the mixing objectives ◊ Accurate description of the mixing problems ◊ Answer Questions What in the mixing process does not work to your satisfaction ? Is the problem repeatable in nature or occurs occasionally ? Does the problem occur only with some products or processes ? What are the characteristics and properties of the material ?
  145. 145. Solution Framework Is there a difference in the process, equipment, product quality in lab and plant ? What is the basis of equipment selection, design ? Were these communicated to the equipment manufacturer ? What are the mixer capabilities ? What functions are performed by the mixer ? Is there any other mixer which has been tried for the same application? Can the mixing conditions be changed ?
  146. 146. Solution Framework ◊ Answer the questions to form the basis of corrective action plan ◊ Detail implementation plan ◊ Step 1 - Change of material addition sequence, mixer operating speed, batch cycle time – quick & easy ◊ Step 2 – Change of equipment design, equipment, process. Revalidate process and equipment – expensive and time consuming ◊ Seek Mixing Expert advise
  147. 147. Summary & Review
  148. 148. Education, Consultation, Manufacturing ◊ Mixing process review ◊ Mixing equipment review ◊ Laboratory and pilot scale trials ◊ Scale-up ◊ Mixing Simulation ◊ Mixer troubleshooting ◊ Short courses, seminars ◊ Mixing equipment specification ◊ Purchasing assistance ◊ Proposal evaluation ◊ Mixer inspection ◊ Engineering services ◊ Ask the Mixing Expert
  149. 149. References • Holloway M., Nwaoha C., and Onyewueni (Editors), Tekchandaney J.R. (2012). “Mixers” Process Plant Equipment, John Wiley. • Oldshue, J. Y. (1983). Fluid Mixing Technology, McGraw-Hill, New York. • Perry, R. H., and D. Green (eds.) (1984). The Chemical Engineers’ Handbook, 6th ed., • Mcgraw-Hill, New York. • McCabe, W.L., and Smith, J.C., (1993), Unit Operations of Chemical Engineering, McGraw Hill, New York. • Ludwig E.E., (1995), Applied Process Design in Chemical and Petrochemical Plants Vol- I, Gulf Publishing Company • Walas, Stanley M., (1998), Chemical Process Equipment - Selection and Design, (Butterworth-Heinemann Series in Chemical Engineering). Boston, MA: Butterworth-Heinemann, a division of Reed Publishing (USA) Inc. • Paul, E. L., Atiemo-Obeng, V. A., and Kresta, S. M. (Editors), (2004), Handbook of Industrial  Mixing, Wiley. • Maynard, E., (2008), “Blender selection and avoidance of post-blender segregation”, Chemical Engineering, May 2008. - • Clement, S. and Prescott, J. (2005), "Blending, Segregation, and Sampling", Encapsulated and Powdered Foods, C. Onwulata, Ed. (Taylor & Francis Group, N.Y.), Food Sciences and Technology Series Vol. 146, 2005. (www.crcpress.com) • Jenike, A, (1994), "Storage and Flow of Solids", Rev. 1980. University of Utah, Salt Lake City, 16th Printing, July 1994.
  150. 150. Acknowledgments Equipment photos and videos • Unique Mixers & Furnaces Pvt. Ltd. www.uniquemixer.com • Unimix Equipment Pvt. Ltd. www.uni-mix.com
  151. 151. THANK YOU ◊ Visit us – www.mixing-expert.com ◊ Email – info@mixing-expert.com ◊ Phone – (+91)-(22)-2580 1214 “Whatever you vividly imagine, ardently desire, sincerely believe, and enthusiastically act up on must inevitably come to pass” Paul Meyer