Mixing Educator Basic Principle Engineering Essay

Mixing Educator Basic Principle Engineering Essay An educator is a device which mixes two liquids of different flow rates giving a solution of desired flow rate. Educators are made using a venturi design. It enables small pumps to circulate large volumes of tank solution. When pumping is used for solution agitation, the use of an educator will circulate four to five gallons of solution in the tank for every one gallon you pump. Fig 1.1: Mixing educator Basic principle It operates on the principle of flow dynamics pressurized fluid is accelerated through the nozzle to become a high velocity stream that entrains the tank content and intimately mixes with them. The combined stream exists the educator at a high velocity creating a flow field capable of causing additional agitation and mixing the tank contents. Tanks have used pumps without educators for solution mixing for years. Now with the usage of educators, the efficiency has been increased. Educators reduce the energy consumption of the pumps motors and will allow a smaller and less expensive pump to be used to perform the same job. Tank educators motive fluid may come from two sources. The tank liquid may be recirculated through the educator via and external pump or a secondary fluid maybe introduced into the tank. Secondary fluid can be liquid or a gas. Fig 1.2: Functioning of the Educator Usage Tank mixing educators are widely used in many applications to effectively and efficiently mix tank solutions. They offer many benefits over other approaches and are available in many different types of styles, sizes and materials. Tank Mixing Educators are used to agitate liquid, dissolve powdered solids in liquid, and to mix two or more liquids intimately within a tank or other vessel without the use of baffles or moving parts inside the tank. They are used to drain flooded cellars, empty tanks and sumps or bunds. Also used for pumping and mixing operations in oil treating systems. De-watering sand and coal barges, Introducing anti-knock fluids and colouring matter into gasoline. Continuous blending, Acidifying ,production of emulsions, Caustic zing of oils, Mixing drilling mud It can also be used to pump food products, sand and filter clay or activated carbon. Tank mixing. Educators are currently installed in the following types of re-circulating process tanks: Plating tanks Cleaning tanks Phosphate tanks E-coat paint tanks Sludge tanks Paint booths Anodizing tanks Cooling towers Fertilizer tanks Pulp tanks Decorative fountains Salt water aquariums Reef tanks Features As there are no moving parts in the educator, it minimizes the maintenance expenses. Optimum flow field enables more activity within the tank than competitive units without changing pumps. Compact design and ease of mounting prevents the educator from interfering with other tank equipment. The educator can be installed in a wide variety of open vessels or closed tanks.   It eliminates stratification and promotes a homogenous tank with relation to pH, temperature, solids or gas dispersion, and distribution of chemicals. As the educator can generate a directed flow field within the fluid being mixed including viscous fluids, slurries, and suspension ,it produces a unique agitation not available with other types of mixers. Liquids of different specific gravity can be mixed easily. It is excellent for scrubbing application. In-tank mounting eliminates the need for costly, complex mounting structures above tanks. Benefits Ensures homogeneous fluid mix throughout the tank. More thorough mixing results in solution uniformity such as temperature, pH level, solids/gas dispersion and chemical distribution which helps in ensuring product and process quality. Eliminates sludge build-up and reduces the tank cleaning time. Enables the usage of small pumps to circulate large volumes of tank solution. Smaller pumps are less costly to purchase- Units are small in relation to the work they do and cost is correspondingly low. Smaller pumps are less expensive to operate. Simplifies operation and maintenance as there are no moving parts it eliminates the need for compressed or blower air and the resulting oil contamination and/or ventilation problems. Self-Priming Educators are self-priming. They operate equally well in continuous or intermittent service. No Moving Parts Educators have a very simple design and are reliable. There are no moving parts to wear or break in a basic educator. Even when equipped with accessories such as regulating spindles, snap valves, float mechanisms only a little maintenance is required. Corrosion and Erosion Resistant Because they can be made of practically any workable material, or coated with corrosion-resistant materials, educators can be made highly resistant to the actions of the liquids handled or the environment in which located. Educators can be used in hazardous locations where electrically operated alternates would require explosion proofing at considerable cost .Hence they are very safe. Automatically Controlled Units can be adapted for automatic control by means of a pressure liquid regulating spindle or a snap-valve and float arrangement. Easy to Install Connections can be made to suit your piping requirements. Little space is required to accommodate units and they are normally so light in weight they can be supported by the piping to which they are attached. CHAPTER 2 TYPES OF EDUCATORS Water jet educators The Water Jet Educator is a type of ejector which utilizes the kinetic energy of a pressurized liquid to entrain another liquid, mix the two, and discharge the mixture against a counter pressure. These types of ejectors are used throughout industry for pumping, mixing and various other operations. During the operation, the pressure liquid enters the educator through the pressure nozzle producing a high velocity jet. This jet action creates a vacuum in the line which causes the suction liquid to flow up into the body of the educator where it is entrained by the pressure liquid. Both liquids are discharged against back pressure after being thoroughly mixed in the throat of the educator .The body with no pockets permits the pressure liquid to move straight through the educator and reduces the possibility of solids in the suction material collecting and clogging. In the suction chamber the pressure drop held to a minimum. Advantages: Low initial cost. Self-priming Easy to install Little or no maintenance required No moving parts No electrical connections required Fig 2.1: Water Jet Educators Automatic educators Automatic Water Jet Educators are used to pump out sumps where liquid accumulates slowly but must be evacuated when it has reached a predetermined level.As the liquid in the sump (basin, tank, cellar, bilge, etc.) is accumulated, it raises the ball float until the upward action of the float opens the snap-acting valve, admitting motive fluid into the pressure connection of the educator. The jet action of the motive fluid creates a vacuum in the educator and entrains the suction fluid, discharging both the fluids then. The sump level drops to a point where the snap acting valve shuts off ,as the suction fluid is pumped out. Pumping action does not take place until the sump again fills to the operating level. Advantages: Automatic operation. No electrical connection required. Only 2 moving parts- snap-acting valve and ball float. The full assembly is so compact it can be installed in tanks as small as 13 1/2 diameter. Condensate and mixing educator Fig 2.3: Condensate Educator These educators are designed to mix two liquids in various proportions in operations where the pressure liquid is the greater proportion of the mixture. In operation, the pressure liquid issues from the nozzle at high velocity and entrains the suction liquid. The high turbulence in the throat of the educator mixes the two liquids, blending and emulsifying thoroughly and completely. Colloidal suspensions are produced.. The pressure drop between the pressure liquid and the discharge should be at least 10 psi for adequate mixing, and the difference between the discharge pressure and the suction pressure should not exceed 75% of the difference between the operating pressure and the suction pressure. Applications: Removal of condensate Mixing gasoline Diluting acids and alkali Blending and proportionating chemical solutions Tank mixing educator It is done by mechanical agitation. They are used to agitate liquid, dissolve powdered solids in liquid, and to mix two or more liquids intimately within a tank without using baffles or moving parts inside the tank. Normally, the tank is filled by means of the educators. Mixing occurs as soon as the level of liquid in the tank covers the suction of the educator. In addition to the mixing obtained between the fluids in the educator, the jet action of the discharge from the educator serves to agitate the tank thus preventing stratification. Hopper equipped educator Hopper-Type Educators are made for handling slurries or dry solids in granular form and are used for ejecting sludges from tank bottoms, for pumping sand from filter beds and for washing and conveying granular materials. Typical materials handled include: borax, charcoal, diatomaceous earth, lime, mash, fly ash, rosin, rock and granulated salt, sand, dry sawdust, light soda ash, dry sodium nitrate, powdered sulphur, wheat and many others. Fig 2.5: Hopper Equipped Educator Advantages: no moving parts easy design (made from machine able or cast able materials) no maintenance required Water jet sand educator Water Jet Sand and Mud Educators are used in pumping out wells, pits, tanks, or sumps where there is an accumulation of sand, mud, or other material not easily handled by the standard educator. Heavy sludge residue can be handled easily from refining operations. They have an open suction and are designed to be submerged in the material being handled. The pressure liquid, passing through the nozzle, produces a high velocity jet which entrains the sludge or mud. Discharge then takes place through a vertical pipe or hose. Annular Multi-Nozzle Water Jet Educator Annular Multi-Nozzle Water Jet Educators are designed to handle solids and semi-solids. Water is introduced though the nozzles on the periphery. The pressure water creates a vacuum which draws in and entrains the material being handled. Fig 2.7: Multi -nozzle Water Jet Educator. Advantages: Highest efficiency Low discharge High air handling capacities. Plastic tank educators There are 2 types: PPL (Glass Reinforced Polypropylene) and PVDF (KYNAR ®). Educator circulation ratio of supply to discharge is1:5 Polypropylene (PPL) It is a polymer prepared catalytically from propylene which differs from HDPE by having an isotactic replacement of a hydrogen atom by a methyl group on alternate carbon atoms in the main chain. Although largely unreactive chemically the presence of the methyl groups makes Polypropylene slightly more susceptible to attack by strong oxidizing agents than HDPE. Quick Facts: Maximum Temperature: 275 °F 135 °C Minimum Temperature: 32 °F 0 °C Melting Point: 338 °F 170 °C   Tensile Strength: 4,500 psi   Hardness: R95   UV Resistance:  Poor   Translucent ,Rigid Specific Gravity: 0.90 Advantages: High temperature resistance Excellent resistance to dilute and concentrated acids, alcohols ,mineral oils . Good resistance to aldehydes, esters, aliphatic hydrocarbons. Limited resistance to aromatic and halogenated hydrocarbons. KYNAR (PVDF): Is a high molecular weight thermoplastic polymer with excellent chemical inertness. Quick Facts: Melting point : 352 ° F Heat deflection at 66 psi (ASTM D 648) : 300 ° F Heat deflection at 264 psi (ASTM D 648) : 235 ° F Maximum serving temperature for short term : 340 ° F Maximum serving temperature for long term : 285 ° F Thermal conductivity (ASTM C 177) : 1.32 Btu-inch/hr-ft~2-  ° F Specific heat : 0.23 Btu/lb-  ° F Coefficient of linear thermal expansion (ASTM D 696) : 7.110~5 Applicable temperature range for thermal expansion : 50-300 ° F Advantages: Highly resistant to oxidizing agents and halogens. Completely resistant to aliphatic aromatics, alcohols, acids and chlorinated solvents. Resistant to most acids and bases. Mechanically strong Thermally stable Resistant to low temperatures Self-extinguishing Non-toxic High dielectric strength Stable to ultraviolet and extreme conditions. CHAPTER 3 CUSTOM TANK EDUCATOR MANIFOLD DESIGN Manifold designs can be customized for various applications. Shown below is a type of design used by various industries for a number of applications. The main advantage of such a design is that it is highly efficient. Fig 31: Manifold Design CHAPTER 4 TYPES OF COATING 4.1 Fusion Bonded Coating A single coating offers excellent abrasion resistance that it can withstand the punishment of sand blasting.5-3 mils thick coating can be applied. Fig 4.1 Machine able Excellent Abrasion Resistance 300 ° F Continuous Service Impact Resistant Withstands Saltwater Environment Self-Lubrication Electrical Insulation 4.2 Edathon Coating This coating is applied by electrostatic powder spray or fluidized powder bed. Its strength, radiation resistance, wear resistance and creep resistance are greater than those of other fluoropolymers such as PTFF,FEP or PEA. Excellent Corrosion Resistance Excellent Abrasion Resistance 300 ° F Continuous Service Good Non-Stick Characteristics Excellent Dielectric Insulation Resistance to radiation High chemical and temperature resistant Fig: 4.2 Edathon Coating Edathon Coated Tank Nozzle CHAPTER 5 DESIGHNING OF AN EDUCATOR 5.1 Materials of Construction Carbon steel 316 SS Bronze PVC PPL PVDF Titanium Teflon Fiberglass 5.2 Design and Dimensions As it is one of the most cost-efficient and effective ways for manufacturers to get the best performance from their re-circulating process tanks, it is easy to see why tank mixing educators are the design of choice for all major manufacturers. To obtain optimal mixing performance, it is important to understand these product differences and how to specify and install educators. Liquid mixing educators consists of a nozzle, a venture and a body to hold parts in their relative positions and to provide a suction chamber. Additional accessories such as regulating spindles, snap values and floats for controlled agitation can also be added to the design. Liquid jet educators are manufactured in a variety of types and sizes as well as materials .The standard type are: 264 type-0.5 inch to 6 inch 266 type-0.5 inch to 6 inch 242 type-0.5 inch to 24 inch Before determining the correct type and size of the educator certain variables such as pressure, temperature, density required ,entrainment rates and operating conditions must all be considered. Fig 5.2 Design Fig 5.3: Dimensions of an Educator Table 1: Types of educators Dimension A Dimension B Dimension C Dimension D Size Max Free Passage IN (mm) IN (mm) IPS (mm) IN (mm) 3/8 0.2656 5.00 (127) 2.50 (64) 3/8 MNPT (10) .50 (12) 3/4 0.4062 7.25 (184) 3.69 (94) 3/4 MNPT (20) .81 (20) 1-1/2 0.5625 10.88 (276) 5.50 (140) 1-1/2 FNPT (40) 1.12 (28) 2 0.8125 14.50 (368) 7.69 (195) 2 FNPT (50) 1.62 (41) 3 1.1875 22.00 (559) 11.75 (298) 3 FNPT (80) 2.50 (63) 4 consult 25.00 (635) 12.00 (305) 4 FNPT (100) 3.00 (76) 6 consult 35.00 (889) 25.00 (635) 6 FNPT (150) 4.50 (114) CHAPTER 6 WORKING As the motive liquid enters the tank contents into the suction openings ,a thorough mixing takes place within the unit before being discharged. Further mixing and agitation is provided by the discharge flow within the tank. The motive fluid is drawn from the tank. Requirements for Mixing: Minimum inlet pressure 10 PSIG Maximum inlet pressure 100 PSIG For efficient operation the inlet pressure should be within the range of 20 to 70 PSIG. As the solution is pumped through an educators orifice, a low pressure area is created that acts to pull solution from behind the bell shape of the educator and direct the solution out of the bell end.  Ã‚  For each gallon of solution that is pumped through the educator, five gallons of additional solution is circulated within the tank. Fig 6.1: Working CHAPTER 7 GUIDELINES FOR SPECIFYING MIXING EDUCATORS Step 1: Determine the needed turnover rate: How many times per hour does the tank solution need to circulate through the educators? The answer is application dependent and based on solution viscosity and the number of particulates. A general rule of thumb is 20 turnovers per hour. Some typical guidelines are given below: à ¢Ã¢â€š ¬Ã‚ ¢ Plating and rinsing tanks: 10 to 20 turnovers per hour although (some plating tanks may require more than 30 turnovers per hour). à ¢Ã¢â€š ¬Ã‚ ¢ Cleaning tanks: at least 10 turnovers per hour à ¢Ã¢â€š ¬Ã‚ ¢ Heavily soiled tanks: up to 20 turnovers per hour à ¢Ã¢â€š ¬Ã‚ ¢ Critical cleaning tanks: more than 20 turnovers per hour. Step 2: Calculate the needed flow rate: Multiply the turnover rate by the tank volume and then divide by 60. Example: Let, turnover rate/hr. =10; Tank volume=800 gallons Then 10 x 800=800 gph Now 8000 à · 60 =133.3 gpm Step 3: Determine the needed inlet flow rate: As educators mix at a 5:1 ratio, take the gallons (litters) per minute and divide by 5. Example: 133.3 à · 5 = 26.7 gpm Step 4: Determine the educator size required with the help of the performance table. Step 5: Determine how many educators you need: Multiple educators may be used to obtain the needed flow rate or to prevent stagnation which is a common problem in square and rectangular tanks. In general, using multiple educators in larger tanks will provide more effective mixing than one centrally located educator. Step6: Determine the educator placement: As little agitation occurs below the level of the educator, in order to obtain maximum liquid turnover, the educators should be positioned as close as possible to the bottom of the tank. If settling cannot be tolerated, install the educators 1 (.3 m) above the bottom of the tank. Educators should be placed so the flow field will reach the farthest and highest liquid level at the opposite side of the tank. Mounting adapters are available to direct flow as needed. The educators should be placed 12 (.3 m) apart for uniform and even agitation. CHAPTER 8 OBSERVATIONS AND CALCULATIONS Mathematical Model The educator designed here is made up of fiberglass and is based on the operating data for type 264. For the test the eductant used is water and the suction fluid used is blue ink. Eductant pressure, suction head and discharge pressure were varied and the eductant and suction flows were measured. For example: The following table shows the values calculate when using a .48 educator, with 15 PSI pressure available. The flow rate through the nozzle will be 25 GPM-The total amount circulated will be 125 GPM. Table 2: Observations Size orifice and NPT connection Pressure (PSI) 8 10 15 20 25 30 35 40 Nozzle Flow (USGPM) .20 1/4 NPT 3.2 3.5 4.3 5.0 5.5 6.1 6.6 7.0 .30   Ã‚   3/8   6.2 7.5 9.2 10.7 11.9 13.1 14.1 15 .37 3/4 11.8 13.5 17 19 21 23 25 27 .48 1 18.7 21 25 29 33 36 39 42 .62 1 1/2 33 41 47 53 58 63 67 8.2 Graphical Analysis The graph for flow vs. pressure drop was calculated for different diameters is show below: Fig 8.2 : Graphical Analysis (Flow Vs Pressure Drop) 8.3 Performance Table Table 3:Performance and observation The values for the designed educator we measured and tabulated below: Size IPS Pressure Difference, PSI 10 20 30 40 50 60 70 80 90 100 120 140 Motive Flow (GPM) 7.1 10.0 12.3 14.2 15.8 17.4 18.7 20.1 21.3 22.4 24.6 26.5 3/8 MNPT Outlet Flow (GPM) 35 50 61 71 79 87 88 90 91 92 94 96 Max. Plume Length 4 8 12 16 22 29 36 43 50 58 72 86 Table 4:Performance Study The estimated values for the educators of various other sizes are tabulated below: 3/4 MNPT Motive Flow (GPM) 15.4 21.8 26.7 30.8 34.5 37.8 40.8 43.6 46.3 48.8 53.4 57.7 Outlet Flow (GPM) 77 109 134 154 172 189 192 195 197 200 204 209 Max. Plume Length (FT) 5 11 17 24 33 42 53 64 74 85 106 127 Motive Flow (GPM) 30.8 43.6 53.4 61.6 68.9 75.5 81.5 87.2 92.5 97.5 107 115 1-1/2 FNPT Outlet Flow (GPM) 154 218 267 306 345 378 384 389 395 400 409 417 Max. Plume Length (FT) 7.5 16 24 34 46 60 75 90 105 120 150 180 2 FNPT Motive Flow (GPM) 61.6 87.2 107 123 138 151 163 174 185 195 214 231 Outlet Flow (GPM) 308 436 534 616 689 755 767 778 789 799 818 835 Max. Plume Length (FT) 11 23 34 48 65 85 106 12 148 170 212 255 Motive Flow (GPM) 142 201 246 283 317 347 375 401 426 449 491 531 3 FNPT Outlet Flow (GPM) 708 1,003 1,228 1,417 1,585 1,737 1,764 1,790 1,815 1,836 1,880 1,920 Max. Plume Length (FT) 16 34 51 73 99 129 161 193 225 257 322 386 4 Flanged Motive Flow (GPM) 246 349 427 493 551 604 652 698 740 780 856 920 Outlet Flow (GPM) 1,232 1,744 2,136 2,448 2,760 3,024 3,072 3,112 3,160 3,200 3,272 3,336 Max. Plume Length (FT) 22 41 60 95 132 164 196 228 260 295 360 424 6 Flanged Motive Flow (GPM) 493 698 854 986 1,102 1,208 1,304 1,395 1,480 1,560 1,712 1,840 Outlet Flow (GPM) 2,464 3,488 4,272 4,896 5,520 6,048 6,144 6,224 6,320 6,400 6,544 6,672 8 Flanged Motive Flow (GPM) 986 1,395 1,709 1,971 2,205 2,416 2,608 2,790 2,960 3,120 3,424 3,680 Outlet Flow (GPM) (FT) 4,928 6,976 8,544 9,792 11,040 12,096 12,384 12,448 12,640 12,800 13,088 13,344 10 Flanged Motive Flow (GPM) 1,971 2,790 3,418 3,942 4,410 4,832 5,216 5,581 5,920 6,240 6,848 7,360 Outlet Flow (GPM) 9,856 13,952 17,088 19,584 22,080 24,192 24,576 24,896 25,344 25,600 26,176 26,688 CHAPTER 9 CONCLUSION This report consists of the basic principle, the design and a performance study of the mixing educator. Chapter 1 is basically an introduction to the topic and summarizes the principle, applications, features and advantages of the educator. Chapter 2 summarizes the different types of educators used in the industries today. Chapter 3 shows the different custom made designs. Chapter 4 shows the types of coatings used on the educators and its advantages. Chapter 5 summarizes the designing of the educator. Its consists of the educators of different dimensions and their construction. Chapter 7 summarizes the guidelines for specifying the educator. Chapter 8 consists the mathematical model and the performance study. Tanks have used pumps without educators for solution mixing for years .Now with the usage of educators ,the efficiency has been increased .Educators reduce the energy consumption of the pumps motors and will allow a smaller and less expensive pump to be used to perform the same job CHAPTER 10 REFRENCES Robert D. Blevins, Applied Fluid Dynamics Handbook, 1984. Crane Co., Flow of Fluids Through Valves, Fittings and Pipe, 1988 J. R. Lawson, Educator Testing for Waste Dilution, Dec. 28, 1981. Otis, R. H., Preliminary Design Study for an Enhanced Mixing Educator for Gas Turbine Exhaust Systems, Masters Thesis, Restricted Distribution, Naval Postgraduate School, March 1998. Stephen W. Dudar,Preliminary Design Study of an Enhanced Mixing Educator System for the LHA (R) Gas Turbine Exhaust  [Chapter 5]. Robert H. Perry, Cecil H. Chilton, Sidney D. Kirkpatrick, Chemical Engineers Handbook, Fourth Ehtion, 1963.