Spray drying is transformation of feed from a fluid state into dried particulate form by spraying the feed into a hot drying medium. It is a continuous particle-processing drying operation. The feed can be either a solution, suspension, dispersion, emulsion or slip. The dried product can be in the form of powders, granules, or agglomerates depending upon the physical and chemical properties of the feed, the dryer design and final powder properties desired.

Feed is finely atomized and is introduced in the drying chamber along with hot air. The mixture of atomized feed and hot air moves towards the air exhaust of drying chamber. The time taken by this mixture to travel upto air exhaust is called as residence time of drying. During this residence time, the feed droplets loose its moisture to the hot air and is converted into dry powder particles. Hot air absorbs this moisture, so its absolute humidity increases while its temperature is reduced. The feed droplets while loosing its moisture to hot air, remain at temperatures much below the hot air temperature and it is exposed to hot air for a very short time. Hence spray drying is essentially known as "Low Temperature Drying". The temperature of feed droplet is the wet bulb temperature at the prevailing relative humidity.

The dry powder falling on to the conical portion of drying chamber slides down to bottom of drying chamber with the assistance of vibrators/knockers and is collected in collection bag/bottle through the rotary valve located at the bottom of drying chamber.

The air leaving the drying chamber entrains some of the dry powder which is recovered in the cyclone separator and collected through rotary airlock. The air leaving the cyclone separator still has traces of dry powder, which is further recovered by scrubbing in wet scrubber or passing it through bag filter.

In wet scrubber the dry powder particle are wetted by water and the resultant mixture is separated in straight cyclone. The air coming out of the straight cyclone is dust free and absolutely clean, which is exhausted to atmosphere through induced draft fan. In the bag house the exhaust air is filtered in fabric filter bags. Dust laden bags are cleaned during normal running cycle by compressed air pulse jet or vibrators or shakers.

IDEALLY SUITED FOR:

Inlet Temperature of Air:

Higher the temperature of inlet air, faster is the moisture evaporation but the powder is subjected to higher temperature, which may distort the chemical/physical properties of heat sensitive product. For spray drying capacity, high inlet temperature reduce the size of the plant and initial cost.

Outlet Temperature of Air:

Outlet air temperature will govern the sizing of powder recovery equipments and tem powder conveying ducts and plenum, higher is the outlet air temperature bigger will be the size of powder recovery equipment and conveying ducts and plenums. Outlet air temperatures control final moisture content of powder.

Product Heat Sensitivity Temperature & Drying Properties:

Wet bulb temperature will decide the size of drying chamber; smaller is the difference between wet bulb and dry bulb temperature. Larger drying chamber is required.

Atomization is the heart of spray drying which is dependent on following factors:

Spray drying plants are tailor made to suit product to be dried and it properties desired. Therefore a wide range of drying chambers, air dispersers and atomizers are used in different configuration which are given here.

Air Disperser

Air enters the drying chamber through the air disperser. The function of the air disperser is to provide the proper mixing and control droplet/particle travel during drying and remove the vaporized moisture rapidly away from the atomization zone. The air disperser and atomizer together influence the droplet-size distribution of the spray and force of spray/air contact.

We design a variety of air dispersers for various types of drying chambers and various applications.

The superior design, manufacturing and quality control feature of various drying plant accessories and components are available on request.

For proper operation and monitoring of the plant working, we provide, at suitable locations, reliable instruments and gauges viz.

1. Manometers.
2. Temperature Indicator cum Controllers.
3. Pressure Gauges.
4. Pressure Switches.
5. Voltmeters, Ammeters.

We prepare P&I diagram for following and the manufacturing is done as per Quality Assurance Plan.

1. Air Circuit.
2. Feed Circuit.
3. For various components.

We manufacture the plant in such way that entire plant is pre-fabricated at factory and assembles like mechano at site. Thus site activity is kept to bare minimum.

Atomizing Nozzles

The atomization stage in spray dryer produces bulk liquid into spray of droplets having high surface to mass ratio. The atomizing nozzles are based on the principle of –

1. Pressure Jet Nozzle.
2. Two Fluid Nozzle.

Two fluid nozzles are available on INTERNAL MIXING & EXTERNAL MIXING TYPE.

We import atomizing nozzles from

1. DELAVAN DELTA INC. (USA).
2. SPRAYING SYSTEMS CO. (USA).

They are made from wear resistant materials, Tungsten Carbide & Chrome Carbide etc.

Rotary Atomizers

These works on the principle of mechanical energy. Feed is sprayed radially through a high speed (10000 rpm and higher) rotary wheel. These atomizers are precision machined assemblies. We take rigorous running trials of these atomizers for a continuous run of atleast 24 hours for the bearing temperatures, vibration free smooth running as per standard ISO 1940.

Feed Pump

Pump is required in feed system to supply feed at high pressure to the atomizer. Spray dyer with nozzle atomizer will require positive displacement pump. Three major types of positive displacement pumps in use are:

1. Piston/Plunger Pump:

These pumps are robust in construction and compact in mechanism. High discharge pressure is available. Capacity can be adjusted from zero to max. both when pump is stopped or running. Multiplexing facility allow coupling of several pumps, driven by one common motor. Flow of each pump can be independently set or stopped as required.

2. Progressive Cavity Pump:

These pumps work on a unique principle of a highly precision manufactured metallic single helical rotor turning inside a double internal helix resilient stator with a slightly concentric motion.

The rotor rotates in the stator, the cavity formed between the two progresses from suction to delivery side gently carrying the feed.

1. High suction capacity and can handle high percentage of air with fluid.
2. Head developed is independent of speed and capacity is proportional to speed.
3. Handles mixtures containing high percentage of solids.
4. Suction and delivery ends can be interchanged by merely changing direction of rotation without affecting efficiency.

Diaphragm Pump

Diaphragm pumps are compact, robust, light in construction. These are hermetically sealed pumps. The plunger packing works in a safe and pure hydraulic fluid. The rugged diaphragm separates the hydraulic fluid and the metered fluid. These pumps have fully automatic lubrication multiplexing choice using single prime mover is also possible.

Drying Chamber

The function of drying chamber is to provide residence time to air/particle for obtaining desired dried-product moisture levels without heat degradation and unwanted wall deposits.

Sizing:

The most efficient way of contracting spray load with drying air is dependent upon the product. The drying chamber and method of air introduction through the air disperser are dependent on

1. The required particle size.
2. The required dried particle form.
3. The temperature to which the dried particle can be subjected (Heat Sensitivity temperature of powder).

Drying chambers are fabricated from thin sheet stainless steels. We provide distortion free reinforcements to drying chambers. They are ground and finished from inside upto 300# finish level depending upon the application. For food grade application this surface finish is critical as it avoids possibilities of microbiological growth on drying chamber surfaces.