Inertial collectors

Inertial collectors. In inertial collectors, an object is placed in the path of the gas. An example is shown in Fig. 11.1. While the gas passes around the shutters, particles with sufficiently high inertia impinge on them and are removed from the stream. Only particles in excess of 50/um can reasonably be removed. Like gravity settlers, inertial collectors are widely used as prefilters. 

Figure 11.1 An inertial collector. (Reproduced with permission from Stenhouse, "Pollution Control, in Teja, Chemical Engineering and the Environment, Blackwell Scientific Publications, Oxford, UK, 1981.)...

The most common inertial collector is the cyclone, which is used in two basic forms, the tangential inlet and the axial inlet. Figure 29-6 shows the two types. 

Other types of inertial collectors which might be used for particulate separation from a carrying gas stream depend on the same theoretical principles developed for cyclones. Table 29-2 summarizes the effect of the common variables on inertial collector performance. 

Ettect of Independent Variables on Inertial Collector Efficiency... 

The second mechanism important in wet collectors is removal of the wetted particles on a collecting surface, followed by their eventual removal from the device. The collecting surface can be in the form of a bed or simply a wetted surface. One common combination follows the wetting section with an inertial collector which then separates the wetted particles from the carrying gas stream. 

Inertial collectors for mists and droplets are widely used. They include cyclone collectors, baffle systems, and skimmers in ductwork. Inertial devices can be used as primary collection systems, precleaners for other... 

Inertial collectors. Inertial collectors were also discussed in Chapter 8 and illustrated in Figure 8.4. The particles are given a downward momentum to assist tihe settling. Only particles in excess of 50 im can be reasonably... 

Particulate Scrubbers Wet collectors, or scrubbers, form a class of devices in which a liquid (usually water) is used to assist or accomplish the collection of dusts or mists. Such devices have been in use for well over 100 years, and innumerable designs have been or are offered commercially or constructed by users. Wet-film collectors logically form a separate subcategory of devices. They comprise inertial collectors in which a film of liquid flows over the interior surfaces, preventing reentrainment of dust particles and flushing away the deposited dust. Wetted-wall cyclones are an example [Stairmand, Tram. lmt. Chem. Eng., 29,356 (1951)]. Wet-film collectors have not been studied systematically but can probably be expected to perform much as do equivalent dry inertial collectors, except for the benefit of reduced reentrainment. 

A disadvantage of cyclones and inertial collectors is that dust particles are frequently swept back into the exiting air stream. Wet scrubbers were designed to overcome this disadvantage. 

Inertial collectors use centrifugal force to separate the particles from the flue gas stream. The inlet flue gas is forced to follow a circular or conical path at high velocity in a cyclone. The particles are forced to move against the walls by the centrifugal force and settle down into hoppers. These devices separate the particles in the size range of 1.0-100 pm with 50%-90% efficiency. 

A wide range of existing devices have been used to sample viable airborne micro-organisms. They fall into the following three broad classes inertial collectors, filters and precipitators (electrostatic and thermal). Precipitators are complicated and bulky devices, are not widely used as collectors and... 

The most commonly used inertial collector is the cyclone (Fig. 5.6). This consists of a cylindrical vessel into which the gas stream is introduced tangentially. The rotational motion of the gas stream causes movement of the particles to the outer wall where deposition and aggregation occur. The dust falls to the base of the cyclone and is removed into a hopper, whilst the cleaned gas stream is removed at the top. The main disadvantage of the cyclone, and of other inertial collectors, is the low efficiency at small particle sizes, and for this reason the cyclone is most commonly used to pre-clean an air stream which is subsequently polished using a more efficient dust arresting device. 

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