Spray operations

Commonly, the most important feature of a nozzle is the size of droplet it produces. Since the heat or mass transfer that a given dispersion can produce is often proportional to (1/D ) , fine drops are usually favored. On the other extreme, drops that are too fine will not settle, and a concern is the amount of liquid that will be entrained from a given spray operation. For example, if sprays are used to contact atmospheric air flowing at 1.5 m/s, drops smaller than 350 [Lm [terminal velocity = 1.5 m/s (4.92 ft/s)] will be entrained. Even for the relative coarse spray of the hoUow-cone nozzle shown in Fig. 14-88, 7.5 percent of the total hquid mass will be entrained. 

Liquid Dispersion Spray columns are used with slurries or when the reaction product is a solid. The absorption of SO9 by a hme slurry is an example. In the treatment of phosphate rock with sulfuric acid, offgases contain HF and SiF4. In a spray column with water, solid particles of fluorosilic acid are formed but do not harm the spray operation. The coefficient /cl in spray columns is about the same as in packed columns, but the spray interfacial area is much lower. Considerable backmixing of the gas also takes place, which helps to make the spray volumetri-caUy inefficient. Deentrainment at the outlet usually is needed. 

Open-fronted extraetion booths for spraying operations, or adhesive applieation operations. 

After drying, the anodized parts are primed with the adhesive primer. Time between anodize and priming is limited to prevent contamination of the active oxide layer. The primer is air-dried for a time to allow the solvents to evaporate and then baked at elevated temperature to cure. Many adhesive primers have very tight thickness requirements, for instance 0.00015" to 0.001", and require skilled spray operators to apply. A primer layer that is too thick can result in low peel strength while a layer that is too thin might not be continuous and could result in insufficient wetting of the surface by the adhesive during cure. 

The metal spraying operation using zinc or aluminium as a protective coating is usually followed by a painting scheme. The choice of sprayed metal and paint scheme depends on the service conditions , but normally this type of system is used on prestige buildings or structures, where longevity is of prime importance and maintenance requirements need to be kept to a minimum. 

In Charlotte, N. C., all residual sprays are regulated, in that they may be used only after establishments have closed for the day. All food must be protected during the spraying operation. 

Another pathway by which targeted pollutants enter the wastewater stream is through the disposal of spent batch process solutions into the sewer system. Spent solutions consist of aqueous wastes and may contain accumulated solids as well. Spent solutions are typically bled at a controlled rate into the wastewater stream. Other sources of pollutants in wastewater streams include cleanup of spills and washdown of fugitive aerosols from spray operations. 

MAFF/Joint Medical Panel of the Scientific Subcommittee on Pesticides of the Ministry of Agriculture, Fisheries, and Food and the Toxicology Committee of the British Agrochemical Association (1986/1992) Estimation of Exposure and Absorption of Pesticides by Spraying Operators, MAFF, Pesticides Registration Department, Harpenden Laboratory, Harpenden, Herts, England. 

Spray/cascade units are available in which the hot salt is sprayed over the surface of the product. This type of system can lose a lot of heat during the spraying operation. 

Often pesticide wastes, which require special disposal facilities, are in a dilute form and result from rinsates from containers, spray tanks, and equipment wash water. These may originate from the small applicator or large commercial operator. Such wastes should be sprayed on an area for which they are approved or placed in a safe disposal facility. Occasionally, fairly large volumes of recommended concentration dilute mixtures resulting from livestock dipping operations, overestimating the amount needed for a spray operation, etc., must be discarded. 

Shallow soil samples were taken with a soil probe on March 2A, 1980, the two-inch diameter cores being divided Into 0-3, 3-7, and 7-10 Inch horizons. The top layer comprised of turf and roots was discarded as It would be contaminated by pesticides from tree spraying operations. The top layer was likewise discarded when deep soil samples were collected on August 7, 1980. 

Chemicals processed. Waste pesticide solutions were collected after spray operations during late May, June, and July of 1983, and consisted primarily of three compounds 2,4-D [(2,4-dichloro-phenoxy)acetic acid], atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)- -triazine) and paraquat (1,1 -dimethyl-4,4 -bipyridinium dichloride). Our efforts were primarily directed at these pesticides, which are shown in Table I together with their formulations and concentrations. 

Contact of the material with the skin may cause dermatitis. Dermal absorption and ingestion of aerosol droplets trapped in the nose appear to be the primary routes of entry in spraying operations. 

In a study of 30 workers engaged in spraying paraquat over a 12-week period, approximately 50% of them had minor irritation of the eyes or nose one worker had an episode of epistaxis. Of 296 spray operators with skin exposure described as gross and prolonged, 55 had damaged fingernails. The most... 

Hearn CED, Keir W Nail damage in spray operators exposed to paraquat. BrJ Ind Med 28 399-403, 1971... 

Spray guns (of glass or plastic), operated by compressed air or a rubber bulb-type hand blower (e.g. Fig. 2.135) are available from, for example, Bibby Science, or Shandon. This spraying operation must of course be carried out with considerable care and it is advisable to place the plate at the bottom of a large rect-... 

D levels were measured in urine samples collected prior to, during, and after actual spray operations from workers involved in ground and aerial applications of amine and ester formulations of... 

EPA Study. The first published report of studies on 2,it,5-T applicators was by Shafik et al. of EPA in 1971 (] ) They analyzed urine samples collected from people occupationally exposed to 2,lt-D and 2,it,5-T, and reported higher exposure in spray operators than in those who had less direct contact with the herbicides. 

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