Types of mist eliminator

Generally, one of two main types of mist eliminator is used for removal of SOs and acid mist (6). The Brink "HV" type, or equivalent is used to remove particles of three microns and larger in size, while for removal of finer particles, the Brink "HE" type, or equal, is used. 

If mist eliminators are used, they must be carefully designed, specified, and supported. Plugging of mist eliminator pads is not an uncommon problem. Occasionally, a dislodged part of a mist eliminator pad is sucked into the compressor rotor or becomes lodged in downstream piping (232, 239). These potential problems should be discussed with the manufacturer. The beneficial effects and the various types of mist eliminators available are extensively described elsewhere (101, 165, 270, 431 33). 

C empirically evaluated constant, which depends on the type of mist eliminator (C = 0.036 m/s for stills without separation aids, [2.6], C = 0.107 m/s for demisters in regular process operation in columns and stills [2.7])... 

Demisters are specified to remove essentially 100% of particles above 3 p,m in diameter. Removal of smaller particles depends on the type of element chosen, but in the service under discussion, it usually is specified as 99% or better. The tight construction required leads to greater pressure losses than in other types of mist eliminator. A compensating advantage is that performance improves on turndown. 

Mist eliminator is used to remove the liquid droplets in vapor flow. There are three types of mist eliminator -wire mesh, vane, and fiber bed. Each has its own plication. 

Table 7.2 Types of mist eliminators for industrial gases... 

The most common type of mist eliminator is the wire mesh, and it is made with knitted wire. This type of mist eliminator has high surface area and void volume. A mesh is made with wire having a diameter in the range of 0.1 to 0.28 mm and a typical void fraction of 0.95 to 0.99. Due to very low wire thickness, the material of construction requires careful consideration. Stainless steel wire is the most popular mesh material. 

More recentiy, sulfuric acid mists have been satisfactorily controlled by passing gas streams through equipment containing beds or mats of small-diameter glass or Teflon fibers. Such units are called mist eliminators (see Airpollution control methods). Use of this type of equipment has been a significant factor in making the double absorption process economical and in reducing stack emissions of acid mist to tolerably low levels. 

In drying towers of sulfur-burning plants, mesh pads or inertial impaction-type mist eliminators are usually adequate. High efficiency mist eliminators are usually used in drying towers of spent acid or metallurgical plants. 

TABLE 14-21 Operating Characteristics of Various Types of Fiber Mist Eliminators as Used on Sulfuric Acid Plants ... 

Figure 4-19. Capture efficiency vs particle size for four types of DEMISTER knitted mesh mist eliminators. By permission, Otto H. York Co., Inc.

Figure 4-27B. Fiber-pack mist eliminator pack separators. By permission, Koch Engineering Co., Inc. Note that other manufacturers have basically the same concept however, the identification of types are peculiar to each.

This type of technology is a part of the group of air pollution controls collectively referred to as wet scrubbers. Fiber-bed scrubbers are also known as wetted-filter scrubbers and mist eliminators. The technology is based on the removal of air pollutants by inertial and diffusional interception. 

Flo. 9—These popular mist eliminator designs are wire mesh pods, vane eliminators and arch plates. Wire mesh is least expensive, but velocity sensitive Vane eliminators impose laminar flow and directional changes on gas stream. Arch plates, consisting of cylinders of corrugated piste, function much like vane-type eliminators. 

If a wet method for collection is selected, such as a wet electrostatic precipitator, fiber-type self-draining mist eliminator, or wet scrubber, ammonia can be regenerated from the salt solution by reaction with a readily available metal oxide such as lime or zinc oxide with formation of a stable sulfur product for disposal. These metal oxides, however, as well as their reaction products, are insoluble and could cause deposition on heat transfer surfaces and/or clogging in the regenerating equipment. Therefore, as indicated in Figure 2, to ensure continuity and reliability of the process, a soluble metal oxide was utilized (in the form of sodium hydroxide solution) to regenerate the ammonia in the experimental work described. This procedure also allows more eflFective utilization of the metal oxide the soluble oxide (NaOH) can be regenerated in batch equipment outside the continuous portion of the process by reaction with either the aforestated insoluble reactants, lime, or zinc oxide. Better control is aflForded in a batch reactor with more eflBcient use of reactants. However, in full-scale equipment undersirable deposition of reactant and product may be controllable so that batch operation may not be necessary. 

Lactobacillus bacteria can destroy gut pathogens in farm animals for faster growth.259 This offers an alternative to the use of antibiotics. A mixture of 29 types of live bacteria is being marketed for the elimination of Salmonella from chickens.260 These are sprayed as a mist over newly hatched chicks. A brief burst of 290°F steam kills Salmonella on chickens.261 This is an alternative to irradiation or treatment with bactericides. 

The power required to move flue gas through the scrubber, from the absorber inlet to the mist eliminator outlet, was calculated from pressure drop and gas flow-rate data reported in the literature for a range of superficial velocities, liquid/gas ratios, and internal scrubber packings. A fan of the wet induced-draft type was assumed for each case, operating on saturated flue gas at 125°F. The gas-side power input was added to the power delivered through the slurry recirculation pumps which was calculated from the volumetric flow rates and the minimum discharge pressures required for the given scrubbers. The total power input for SO2 absorption was thus determined as ... 

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