Liquid to liquid mixing in pipelines and tanks
Liquid Jet Eductors
Liquid Jet Eductors use the kinetic energy of a motive liquid to entrain another liquid, completely mix the two, and then discharge the mixture against a counter pressure and are used in large numbers throughout industry for pumping and mixing operations.
Applications are so numerous, it is impossible to note all of them. General uses include lifting, pumping, mixing,
and agitating of liquids as well as handling granular solids and slurries. Some of the typical applications can be seen
- Draining flooded cellars, Emptying tanks and sumps or bunds, 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, Causticizing of oils, Mixing drilling mud, Producing emulsions
- Pumping food products, Pumping sand and filter clay or activated carbon
- Tank mixing, and various Proportioning operations
Liquid jet eductors consist of three basic components, namely a converging nozzle, a diffuser (or venturi), and a body to hold these parts in their relative positions and to provide a suction (or mixing) chamber. In addition, they can be equipped with accessories such as regulating spindles, snap valves and floats to control operation. When designing eductors experience is all-important to correctly design the nozzle, diffuser, and body and their relative positions as they are all highly critical and vary according to the physical properties of the liquids being handled.
As an example of eductor performance in a typical use, a 1.5 Inch Jet Eductor discharging against a 1 BarG back pressure will empty a 2 Cubic Meter water tank in less than 1 hour using water at only 4 BarG as the sole source of motive power.
Liquid jet eductors are manufactured in a variety of types and sizes as well as materials, our standard Type 264 and 266 ranges from 0.5 Inch to 6 Inch in size where as the Type 242 unit can range from 0.5 Inch up to and beyond 24 Inch. Variables such as pressure, temperature, density, required entrainment rates, and operating conditions must all be considered before determining the correct type and size of eductor to best suit to your requirements.
Typical Eductor Applications
A few of the primary applications where eductors are used can be seen below, this list is by no means exhaustive as their uses are numerous.
Pumping & Lifting
Water jet eductors are often used to empty tanks or to pump out sumps, bunds and cellars. The motive line should be fitted with a regulating valve and a pressure gauge while the suction line should be fitted with an strainer or mesh to prevent large particles entering the unit and causing blockages. Care should also be taken to ensure the discharge lines are always sealed to prevent air leaking back towards the eductor. To accomplish this either fit a U-bend to the discharge line, or always keep the open end of the discharge pipe submerged as this will allow stable and rapid entrainment of the suction liquid.
Where possible it is recommended that the eductor be installed a short distance above the liquid to be entrained and that short suction lines be used, however eductors will operate equally well with long suction lines. Care should be taken with suction lifts greater than 4.5 meters as operating capacities are considerably reduced.
Pumping Additives in to Liquids
The eductor is being used to introduce an additive into boiler feed water. A percentage of the water flowing from the pump is bypassed into the eductor where it acts as the motive force to draw in and entrain the additive. This is the preferred method of introducing additives as it does not reduce pressure in the main line downstream of the pump, and also allows the eductor to be kept to a much more economical size.
Tank Mixing Eductors
Tank Mixing Eductors can be used to agitate liquids, dissolve powdered solids into a liquid, keep solids suspended in a solution, or to mix two or more liquids intimately within a tank or other vessel without the use of baffles or moving parts. Mixing Eductors can be used to in the place of mechanical agitators and have the added benefit of having no moving parts to wear, break or become dislodged within the tank.
Two types of Tank Mixing Eductor are available, the first type of eductor is more suited when it is desirable to start mixing from a shallow level or where uniform local agitation is required over large shallow tank area, where as the second eductor type is used where greater liquid depths are present. Installations can use any number and combination of sizes and styles of eductor and they can be mounted practically anywhere within the tank or vessel.
Tank Mixing Eductors function by the flow of pressurised or motive liquid passing through the nozzle. The motive liquid entrains suction liquid and the two are mixed intimately in the venturi. The mixture is then discharged into the tank. The motive liquid can either be taken directly from the tank by means of a circulating pump or it can be a new liquid. Typically, standard units are able to entrain roughly 3 cubic meters of suction fluid for each cubic meter of motive fluid, however special designs can be made to give any mixing ratio within the Eductors physical operating range.
Tank Mixing Eductors can also be used to fill the tank through the eductors motive nozzle. This has the added benefit of allowing the mixing/agitation to occur as soon as the level of liquid in the tank covers the suction port of the eductor.
Tank Mixing Eductors help to mix & agitate the liquid in three ways:
- Primiary mixing occurs within the eductor between the motive and suction fluids.
- Secondary mixing occurs as the suction fluid is drawn towards the eductor creating localised movement within the tank
- Tertiary mixing occurs due to the jet action of the discharge plume as this helps to induce turbulence and movement several meters away from the eductor discharge.
The mixing action of the eductor can quickly and efficiently create movement with the entire tank or vessel, and with correct positioning of the units, help to minimise dead spots with in the tank.