Precipitator types removal

Chemical Neutralization. Spray-type air washers are used extensively for removal or neutrali2ation of noxious components from large volumes of air, particularly exhaust air streams. Appropriate reagents are sprayed into the washer to purify the air by neutrali2ation, eg, sodium hydroxide solution is used if the air contains acidic gases. The solution must be continuously reconcentrated and any precipitated salts removed. The contact efficiency of such washers is high, and the simple constmction provides easy maintenance and constant efficiency (see AiRPOLLUTlON CONTROL METHODS). 

B. -Ethyl-fi-methylglutaric acid. A mixture of 280 g. (1.36 moles) of K,a -dicyano- -ethyl- -methylglutarimide (Note 5) and 1.35 1. of 65% (by weight) sulfuric acid is heated under reflux in a 5-1. round-bottomed flask for 8-10 hours (Note 6). The mixture is allowed to cool, and the precipitate is removed by filtration on a sintered glass (or other suitable type) filter. The crude -ethyl-/3-methylglutaric acid is recrystalhzed from water (Note 7). The yield of product is 174-191 g. (73-80%), m.p. 78-80°. 

Iron and aluminum precipitate out when treated with ammonia and are removed by filtration. Other metals, such as copper, zinc, lead and arsenic are precipitated and removed as sulfides upon passing hydrogen sufide through the solution. Colloidal particles of metaUic sulfides and sulfur are removed by treatment with iron(ll) sulfide. The purified solution of manganese(ll) sulfate is then electrolyzed in an electrolytic cell using lead anode and HasteUoy or Type 316 stainless steel cathode, both of which are resistant to acid. Manganese is deposited on the cathode as a thin film. 

The classic example of a radiometric titration concerns the titration of some unknown material with a radioactive reagent to give a radioactive precipitate. In this case, the activity of the supernatant or the precipitate can be followed as a function of titrant volume, as shown in Figure 4.10. In this type of titrations, the tracer must have a long half-life and must emit high-energy 3 or y rays so as to minimize self-absorption corrections (assuming, as is common practice, that the supernatant or precipitate is removed from the system and counted in an external sample counter after the addition of each volume of titrant). 

This system can be applied to purification of air at underground parking places, offices, homes and other areas. For example, Daikir Industry Co. developed an air purifier using thin honeycomb type Ti02 photocatalysts irradiated by small UV lamps. The purifier consists of the photocatalvst and an electric precipitator tor removing both aii pollutants of formaldehyde, odorous species, etc., and particulate matter. 

Wet removal processes are further controlled by precipitation types and rates. Dry deposition processes on surfaces are affected by atmospheric transport rates that mix fresh pollutant into the surface boundary layers and by the physical properties of particles. For the Eastern U.S., the approximate annual deposition rates of sulfate can be compared as follows (Table III), considering that deposition flux is the product of a concentration and a velocity of deposition (Vd) (20) ... 

Simple (RO)4Si compounds may readily be prepared by the reaction between a chlorosilane and an alcohol (or phenol) (Scheme 41). A problem in this type of reaction is that the HCl formed may canse unwanted side reactions. This may be minimized by blowing dry N2 gas throngh the reaction mixture or heating the reaction so that HCl is driven olf as it is formed, or a tertiary amine snch as pyridine may be added to the reaction, which forms an amine hydrochloride salt that precipitates to remove the HCl. Sihcon alkoxides may also be made by reaction of a sihcon halide and an aUcah metal alkoxide (Scheme 41). ... 

In practice, two types of plants are generally used for chemical precipitation hardness removal One type uses a sludge blanket contact mechanism to facilitate the precipitation reaction. The second type consists of a flash mix, a flocculation basin, and a sedimentation basin. The former is called a solids-contact clarifier. The latter arrangement of flash mix, flocculation, and sedimentation were discussed in previous chapters on unit operations. 

For acid production sinter gas is usually cleaned by drop out of dust in an open chamber or flue followed by hot electrostatic precipitators of the plate and wire type with two or three fields in series. This is followed by wet gas scrubbing and wet electrostatic precipitators to remove mist from the scrubbing operation. A mercury removal scrubber may be included, if mercury levels in the clean gas are high enough to give product acid above 1 ppm mercury. Mercury removal is not always necessary as it is with zinc concentrate roasting. 

The combination of lime and heat forms a flocculent-type precipitate with various components in the juice, which consist mostly of insoluble lime salts, coagulated protein, and entrapped colloidal and suspended matter. The precipitate is removed by sedimentation or settling in continuous closed-tray clarifiers (i.e., Rapi-Dorr, Graver, BMA, and Bach Poly-Cell). The juice leaving the clarifier is a clear brownish liquid. 

Problems of removal of mercury from aqueous effluents are more comphcated in plants that manufacture a variety of inorganic and organic mercury compounds it is generally best to separate the effluent streams of inorganic and organic mercurials. When phenyhnercuric acetate is precipitated from its solution in acetic acid by addition of water, the filtrate is collected and reused for the next precipitation. This type of recycling is necessary not only for economic reasons but also to minimise recovery operations. 

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