Separator impingement

Impingement separators employ baffles to achieve the separation. The gas stream flows easily round the baffles, whereas the solid particles, due to their higher momentum, tend to continue in their line of flight, strike the baffles and are collected. A variety of baffle 

Type of equipment Minimum particle size w Minimum loading (mg/m3) Approx. efficiency (%) Typical gas velocity (m/s) Maximum capacity (m3/s) Gas pressure drop (mm H2O) Liquid rate (m3/103 m3 gas) Space required (relative) 

Type of Minimum particle Minimum Approx. Typical gas Maximum Gas pressure Liquid Space no 

Each change of direction is a stage of separation, and by employing a number of such flow reversals, manufacturers are able to supply vane separators with very good efficiency characteristics. These separators are available from a number of manufacturers. 

Vane impingement separators are generally purchased from the vendor on a performance basis. Sizes will vary somewhat from one manufacturer to another consequently, the exact size cannot be determined before selection of the manufacturer. The pressure drop across vane impingement separators is approximately 0.25 psi plus 1.5 velocity heads based on the nozzle velocity. The total pressure drop will usually be less than 0.5 psi. 

Liquid loading is limited to roughly 5 to 10% of gas mass flow. Pockets can plug with solids and are difficult to clean unless the vanes are removable. 

Centrifugal separators cannot be sized with the F factor approach used with other types of separators because the maximum allowable velocity is a weaker function of gas density than the square root dependence in the F factor correlation. Maximum velocities for centrifugal separators depend upon the design and are different for each of the several manufacturer units. Pressure drop varies from 1 to 10 velocity heads depending upon the manufacturer. Velocity head should be based on inlet (outlet) nozzle velocity. 

Centrifugal separators have lower separation efficiency than vane separators. They must be provided with a trap device for liquid collection, and have a limited liquid handling capacity. Line-type units can be operated with velocities as low as 30 ft/sec without significant loss In separation efficiency. 

---

Katz (R-16) also siwdied wave-plate impingement separators (Fig. 14-Il0b) made up of 90° formed arcs with an 11.1-mm (0.44-iu) radius auda 3.8-mm (0.15-iu) clearance between sheets. The pressure drop is a function of system geometiy. The pressure drop for Katz s system and collection efficiency for seven waves are shown in Fig. 14-111. Katz used the Souders-Brown expression to define a design velocity for the gas between the waves ... 

Entrainment separation is accomplished with inertial separators, which are usually cyclones or impingement separators of various forms. If properly designed, these devices can remove virtually all droplets of the sizes produced in scrubbers. However, reentrainment of liquid can take place in poorly designed or overloaded separators. 

As the descriptive name suggests, the impingement separator allows the particles to be removed to strike some type of surface. This action is better accomplished in pressure systems where pressure drop can be taken as a result of the turbulence which necessarily accompanies the removal action. 

There are basically three construction types for impingement separators ... 

There are many baffle type impingement separators. The efficiency of operation for entrainment is entirely a function of the contacting action inside the particular unit. There are no general performance equations which will predict performance for this type of unit therefore manufacturers performance data and recommendations should be used. A few of the many available units are shown in Figures 4-28 to 4-31. Many use the Chevron-style verdcal plates as shown in Figures 4-17A and 4-30. 

Figure 4-30. Impingement separator. Courtesy of Peerless Manufacturing Co.

Figure 4-30. Impingement separator. Courtesy of Peerless Manufacturing Co. Figure 4-31. Combination separator. Courtesy of National Tank Co.

Explosions emergency relief, 450 Explosions, vapor cloud, 520 Explosive limits, 485 External fires, see fires Factors of safety, llow, 56 Fiber bed/pads impingement separator, 254, 255... 

Impingement separators, 246, 257 Chevron style, 248, 255 Efficiencies, 246 Knitted wire mesh, 246 York-vane efficiencies, 248 Inertial centrifugal separators, 266, 268 Kinetic energy, pump system, 187 Lamella plate classifiers, 239 Line sizing work sheet, 107... 

Figure 10.42. Impingement separator (section showing gas flow)...

A second type of impingement separation device is a knitted wire mesh pad. The primary mechanism of separation in the knitted wire mesh is impingement. It also utilizes centrifugal and gravitational force in the collection of small liquid particles. 

H Drum separators are generally divided into two categories gravity settlers and impingement separators. 

The velocity constant" K varies from 0.30 to 0.45 ft/s for a wire-mesh surface in an impingement separator, and from 0.15 to 0.25 ft/s for a gravity settler. 

Coalescence makes the settling droplets in the impingement separator larger than in the gravity settler. Consequently, K values must be related to Ppg of the impingement separator. 

Although Correlation (12b) provides onh estimates, it shows that, most likely, a droplet size of 300 pm is the minimum that will settle though the liquid phase. This can be achieved in impingement separators. 

---