Horizontal baffles

Laminae of clay and clay drapes act as vertical or horizontal baffles or barriers to fluid flow and pressure communication. Dispersed days occupy pore space-which in a clean sand would be available for hydrocarbons. They may also obstruct pore throats, thus impeding fluid flow. Reservoir evaluation, is often complicated by the presence of clays. This is particularly true for the estimation of hydrocarbon saturation. 

Large sulfuric acid plants are based on spray burners, where the sulfur is pumped at 1030—1240 kPa (150—180 psig) through several nossles iato a refractory-lined combustion chamber. An improved nossle, resistant to plugging or fouling, has been iatroduced (256). The combustion chambers are typically horizontal baffle-fitted refractory-lined vessels. The largest plants ia fertiliser complexes bum up to 50 t/h of sulfur. 

Calvert found that reentrainment from the baffles was affected by the gas velocity, the liquid-to-gas ratio, and the orientation of the baffles. Horizontal gas flow past vertical baffles provided the best drainage and lowest reentrainment. Safe operating regions with vertical baffles are shown in Fig. 14-112. Horizontal baffles gave the poorest drainage... 

FIG. 15-45 Second ScLeiLel extractor witL horizontal baffles and no wire-mesh packing between stages. [Repiinted with peimission of Am. Inst. Chem. Eng. J.,2, 74 (1956)]. 

For heat transfer performance, horizontal baffles to isolate tube-side passes in horizontal bundles are preferred over vertical baffles that isolate groups of tubes in vertical columns. The expansion of capacity by adding more tube bundles or sections in parallel is easier, and the MTD is better with the horizontal pass plates. The fan drive may be by any of the available means, including ... 

An empty vessel may be employed, but horizontal baffles can be used to reduce turbulence and assist the coalescence through preferential wetting of the solid surface by the disperse phase. More elaborate methods to assist the coalescence include the use of mesh pads in the vessel or the use of an electric field to promote coalescence. Chemical additives can also be used to promote coalescence. 

These parts are used in fluidized beds for various purposes. For example, gas distributors and various types of baffles are installed to decrease the size of the bubbles. Moreover, draft tubes are used to enhance gas or solid circulation. Other devices such as horizontal baffles limit circulation and backmixing of solids and gas. Horizontal or vertical tubes are used for heat management. Devices used to control or improve fluidization behavior, to improve fluidization of cohesive particles or to achieve solids recovery are within the various internals met in fluidized bed reactors (Kelkar and Ng, 2002). Immersed tubes in small diameter beds may lead to slugging. Furthermore, attrition of particle breakage may change the size distribution and possibly change the fluidization behavior. 

In cylindrical vessels, the bulk rotation of the liquid is generally prevented by the installation of baffles, which are usually attached to the vessel wall by means of welded brackets (see Fig. la). When this is not possible, they are either attached to the cover (e.g., in enamel-coated vessels) or are made in the form of a basket with pressure-fitted rings, as shown in Fig. lb (e.g., glass vessels, wooden vats, etc.). Generally, fully effective baffling in a cylindrical vessel is achieved with four vertical baffles of width dT/10. However, in recent years novel approaches (e.g., horizontal baffles) have been investigated. The dead volume behind the baffles is reduced by using baffles of width dT/12 at a small clearance of dT/50 from the wall. 

In recent years attempts have been made to improve the gas-liquid mass transfer by changing the design of the mechanically agitated vessel. Mann et al. (1989) evaluated the use of horizontal baffles mounted near the gas-liquid surface. Horizontal baffles prevent vortex formation, generate less shear than standard baffles, increase gas holdup, and improve gas-liquid mass transfer. The latter two results are due to the rotational flow below the baffles, which causes gas bubbles to move upward in a spiral trajectory and induces surface aeration. For a 12-inch i.d. and 18-inch-tall stirred vessel, they showed kLat to be improved by a factor of 1.6 to 2.3 with 30 to 50% lower agitation power compared to the standard vessel. 

In large-size mechanically-agitated multistage contactors, the speed of the agitator is kept at a relatively low level and horizontal baffles are provided. Here, RTD in the gas and liquid phases may show different behavior compared to a small-scale unit. 

Particle size distribution Weight mean diameter 50 < dp < 70 jum + 80 jum, 5-20 wt. % -40 /tm, 10-30 wt.% Improved fluidity Good fluidization Decreased catalyst loss and attrition Se vere erosion if particles are coarse Difficulty in recovering particles <10 /am Installation of internals Multistage fluid bed with horizontal baffles... 

The uniformity and contact efficiency of a fluid bed can be improved by immersion of a surface within the bed (G15,15, V12). Ikeda has defined a generalized equivalent diameter, considering that the commercial reactors have not only vertical internals but also horizontal baffles. Figure 24 indi-... 

Several investigations have been made on the flow characteristics in multistaged fluid beds. Nishinaka et al. (N6, N8, N9) have measured the average bubble holdup, the lateral distribution of bubble holdup, and the longitudinal dispersion of solid particles in four- and eight-stage fluid beds installed with various horizontal baffles. As shown in Fig. 25 the average bubble holdup (except for beds baffled with tube plates) is correlated by the equation of Nishinaka et al., (N8) ... 

The only result of such an apparatus is to set the entire solution to rotating with the paddles. Fairly heavy particles will settle out from the solution very readily and after a very short time the entire system will come to equilibrium, the solution and solids and paddles all revolving at approximately the same speed and the agitation ceases, becoming only that due to retardation on sides and bottom of tank. The natural improvement is to place along the sides of the tank and between the paddles some stationary horizontal baffles. 

Although two tube passes improves hi, one of the passes will be co-current. A 2-4 exchanger improves both and Hq, and in addition, the flow is more nearly countercurrent. We could also partition the shell side with a horizontal baffle in addition to the vertical baffles, producing two shell passes. 

BAFFLE TOWERS. These extraction towers contain sets of horizontal baffle plates. Heavy liquid flows over the top of each baffle and cascades to the one beneath light liquid flows under each baffle and sprays upward from the edge through the heavy phase. The most common arrangements are disk-and-doughnut baffles and segmental, or side-to-side, baffles. In both types the spacing between baffles is 1(K) to 150 mm (4 to 6 in.). 

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