Spray-columns operation

Dislribttlors Most spray columns operate with the drops being formed at the ends of jets from the dispersed phase inlet distributor. The orifices or nozzles for introducing the dispersed phase are usually not smaller than 0.13 cm (0.05 in) in diameter in order to avoid clogging, nor larger than 0.64 cm (0.25 in) in order to avoid formation of... 

As already mentioned, the viscosity of the dispersed phase affects the maximum obtainable transfer coefficients in spray-column operation lower viscosities allow higher coefficients at lower operating temperature level. For the hot-top spray column, a linear dependence of the transfer coefficients and the fluidity of the dispersed phase was found (T2). This phenomenon may also be associated with reduction in surface tension. A decrease in drop diameter and increase in transfer area per unit volume of column may then be expected to increase the volumetric transfer coefficients. 

Van den Akker (1978) carried out a Hnear stabflity analysis for a liquid-liquid spray column operated with a positive temperature gradient. The leading idea was that local differences in mixture density would give rise to a multiple circulation pattern in a way similar to the multicellular natural convection mode in a vertical slot heated from one side (Elder, 1965 Lee and Korpela, 1983). The only way to find in the Hquid—Hquid spray colurrm... 

Liquid Dispersion Spray columns are used with slurries or when the reaction product is a solid. The absorption of SO9 by a hme slurry is an example. In the treatment of phosphate rock with sulfuric acid, offgases contain HF and SiF4. In a spray column with water, solid particles of fluorosilic acid are formed but do not harm the spray operation. The coefficient /cl in spray columns is about the same as in packed columns, but the spray interfacial area is much lower. Considerable backmixing of the gas also takes place, which helps to make the spray volumetri-caUy inefficient. Deentrainment at the outlet usually is needed. 

Two methods of operating spray columns are shown in Figure 13.32. Either the light or heavy phase may be dispersed. In the former case (a) the light phase enters from a... 

Bypassing-Controlled Trayed or packed columns operate with countercurrent flow and can achieve many equilibrium stages in series by good distribution of gas and liquid, and careful control of details. Other devices such as sprays are vulnerable to bypassing and are limited to one equilibrium stage. 

Low pressures favor high vapor velocities and low liquid flow rates and, therefore, spray regime dispersions. Flooding in vacuum columns and in columns operating at a low liquid-to-vapor ratio is usually caused by the spray entrainment mechanism. 

Effect of pressure. In vacuum columns, vapor velocities are generally high and liquid flow rates are low, which coincides with an operating point in the spray regime. If the column operates at high liquid loads, it may operate in the froth regime. The emulsion regime is unlikely to occur in vacuum columns. 

The overpressure system is consists of a pump operating with a nominal pressure of 6 bars. The system allows an independent distribution on one of the four spraying columns. 

Deodorization. The neutralized/bleached oil is pumped into a deaerator operated under a pressure of 500 Pa to evacuate entrained air. From the deaerator, the oil passes through a shell and tube economizer and is heated to a temperature of 240°C by means of a thermal oil heater. The stripper and deodorizing column operates under a pressure of 600-1000 Pa volatile components such as low-molecular-weight fatty acids, ketones, aldehydes, and other odoriferous substances are stripped off by live steam. The rising vapors laden with volatile components pass through a cyclone scrubber where fresh fatty acid oil is sprayed on top of the vessel to recover outgoing fatty acids. 

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