Two-fluid nozzles

Two-fluid nozzles do not operate efficiently at high capacities and consequently are not used widely on plant-size spray diyers. Their chief advantage is that they operate at relatively low pressure, the hq-uid being 0 to 400 kPa/m" pressure, while the atomizing fluid is usually no more than 700 kPa/m" pressure. The atomizing fluid may be steam or air. Two-fluid nozzles nave been employed for the dispersion of thick pastes and filter cakes not previously capable of being handled in ordinaiy atomizers [Baran, Ind. Eng. Chem., 56(10), 34-36 (1964) andTurba, Brit. Chem. Eng., 9(7), 457-460 (1964)]. 

Pipeline Contactors The power dissipation per unit mass for pipeline flow is similar to that for two-fluid nozzles. 

Improve spray distrihiition. Improve atomization hy lowering hinder fluid viscosity. Increase wetted area of the bed per unit mass per unit time hy increasing the number of spray nozzles, lowering spray rate, increase air pressure or flow rate of two-fluid nozzles. 

A spray-dryer eonsists of a feed tank, a rotary or nozzle atomizer, an air heater, a drying ehamber, and a eyelone to separate the powder from the air. A rotary atomizer uses eentrifugal energy to form the droplet. Pressure-nozzle atomizers feed solution to a nozzle under pressure, whieh forms the droplet. Two-fluid nozzles feed solutions separately into a nozzle head, whieh produces high-speed atomizing air that breaks the solution into tiny droplets. Both the feed solution and the drying air are fed into the drying ehamber in a standard eoeurrent flow [27]. 

Gas atomizing nozzle (two-fluid nozzle) the two-fluid (binary) nozzle where the binder solution (first fluid) is atomized by compressed air (second fluid) is the most commonly used nozzle for the fluid-bed granulation (Fig. 9A and B). 

Figure 9 (A) Schematic of a nozzle showing different parts. Source Courtesy of Schlick, Germany. (B) Schematic of a two-fluid nozzle. Continued)...

The two-fluid nozzle in its simplified model is based on energy transmission as shown below ... 

Energy + Liquid > Two-fluid nozzle > Droplets + Heat. 

The agglomeration process is a dynamic process where a droplet is created by a two-fluid nozzle, and deposited on the randomly fluidized particle. The binder solvent evaporates, leaving behind the binder. Before all of the solvent is evaporated, other randomized particles form bonds on the wet site. This process is repeated numerous times to produce desired agglomerated product. There are number of process variables that control the agglomeration. Process variables most important to consider are listed as follows ... 

Figure 7 (b) Schematic of a two-fluid nozzle showing liquid and air pathways. 

The liquid injection is realized using a two-fluid nozzle (Co. Schlick, type 943, form 3, ring-shaped beam 20°-40°, dnozzie = 2.3 mm). A adjustable hose pump conveys the liquid from a store tank, and compressed air is used for the better spreading of the liquid. The investigations of Henneberg et al. [38, 39] in an industrial fluidized-bed plant showed that high nozzle injection rates may lead to low particle concentrations near the nozzle, and to overspray. 

Two Fluid Nozzles, the spray is created by contacting two fluids, namely the feed slurry and compressed air. The compressed air provides the atomization energy. The device has the advantage of being relatively simple, uses a simple feed pump and affords a wide particle size distribution. On the minus side however, the consumption of compressed air is relatively high (0.25 - 1.0 lb air/lb feed) and this nozzle is typically limited to small plants. Figure 3.7 illustrates such a device... 

The object of atomization is to produce a large number of small droplets from a liquid stream so that the droplets can be dried into particles. Atomization is accomplished usually by one of three t3q)es of devices (1) a high-pressure nozzle, (2) a two-fluid nozzle, or (3) Airspeed centrifugal discs. These atomizers are low in cost, produce broad... 

---