Dust extraction

The objective of the design/analysis process is to ensure (as far as possible) that the correct quantity of air flows through each hood. As different air quantities, hood types/sizes and/or duct lengths usually are involved, this is not always a simple task. The correct air flows may be achieved by performing  

even if the rough duct design technique is selected, some form of balancing still should be performed so that the final duct sizes are close to optimal (in terms of pressure and velocity). 

The correct application of either sizing technique will result in a duct network that works well on air. It is equally important to ensure that each air flow is adequate to transfer all the particulates from the hood/enclosure to the collection and/or cleaning device. Unfortunately, many dust control systems have been designed and/or are being operated with little or no regard for what actually has to go through the hood-duct network. This can result in  

Case Study. Such a situation was found to occur in the duct network shown in Fig. 21 and installed to extract iron oxide dust at various points along a cold strip processing line. The stated problems were insufficient suction at the hoods, buildup of contaminant in the hoods and along the processing line (causing cleanup problems due to eventual mixing with hydraulic fluid, lubricant, water, etc.). Analysis of the system found the following  

The solution to the above problem is to re-size the entire network, in particular branches I-V and II-V, with the aim of ensuring a suitable minimum transport velocity along each section of duct. 

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BS 893, Methods of Testing Dust-Extraction Plant and the Emission of Solidsfrom Chimneys, British Standards, London, 1940. 

F. F. L. Morgan. Dust extraction systems for surface grinding wheels. U.S. Patent no, 2 819 571. W ashington, DC Patent Office, 1958. 

Transfer tower Bunker conveyor Dust extraction Coal feeder Coal mills... 

Are raw process and waste materials stored in a safe and appropriate manner for example, are bulk acids in tanks bunded with secondary containment, are flammable materials in a fire-protected, ventilated store, are powders and pellets in areas fitted with dust extraction segregation of noncompatible materials Provide details of existing storage arrangements, inducing plans and specifications. Identify risk areas. Identify the risk category. 

Establish whether any appreciable buildup will affect dust extraction efficiency... 

Vj-mm appears to increase with duct diameter, I). This trend has been recognized in many traditional pneumatic conveyors (Wypych and Reed, 1990 Zenz, 1964 Cabrejos andKlinzing, 1994), but also appears to be relevant for dust extraction (Cable, 1994 Miletich, 1994), which can be considered as a form of low-concentration pneumatic conveying (e.g., Vj= 10 m s 1 may be suitable for a particular contaminant in a duct size ofD = 100 mm but may cause deposition in D = 300 mm). Further evidence of this can be seen in the work of Zenz,... 

For dust extraction systems, the concentration of solids usually is quite low. For this reason, the methods employed to calculate pressure loss are based on air-only conditions. Comprehensive information is available (ASHRAE, 1985 ACGIH, 1992) to assist the designer in estimating the pressure loss caused by pipe branches, ducts, elbows, etc. 

BS893 1940 British Standard 893 (British Standards Institution, London). The method of testing dust extraction plant and the emission of solids from chimneys of electric power stations. 

Two approaches were evaluated for increasing the size of the lint samples. In one approach, we simply used six speclments of 3.33 g each to comprise a 20-g lint sample. In the other approach, we doubled the thickness and weight of the specimens and used three specimens of 6.67 g each. We found that the cotton-dust analyzer technique was sensitive to variations in the thickness and weight of the batt. Doubling the batt weight and thickness reduced by about 50% the amount of dust extracted from a 20-g lint sample. Therefore, we decided to use six specimens... 

Purification of dust extract yields a compound consistent with the structure compound accounts for a slow... 

PMN infiltration also occurs following exposure to some common microbial cotton contaminants (Enterobacter aerogenes (44), Klebsiella pneumoniae or Escherichia coll), but not others (. subtills) (45). Cotton dust extracts pretreated at 80 C and 100 C for 20 minutes cause successively higher leucocyte responses, indicating that the chemotactlc effect is not solely affected by viable bacteria (46). Thus, while the increase seen in PMNs may not, by itself, represent a pathological alteration, it could be of importance in the later development of pathological effects. 

Cotton dust activates complement vitro by both the classical (antibody dependent) and alternative (antibody independent) pathways (12,47,48). It is proposed that endotoxins may be the agents responsible for complement activation (49). Cotton dust extractions maximizing endotoxin content are 10 times more potent than other extracts in activating complement (12). Activation of complement via the alternative pathway has also been... 

In 1 ml of aqueous extract of cotton dust, there may be as much as 30 ug of endotoxin-like material moreover, most dust extracts contain endotoxin. Cotton extracts are pyrogenic in rabbits, but daily injections produce tolerance, an effect similar to that of purified endotoxins. Further, rabbits made tolerant to injections of cotton extracts are also tolerant to I.V. injections of purified abortus equi endotoxin. Conversely, rabbits made tolerant to endotoxins are also tolerant to cotton extracts (62). 

Histamine is released from whole rabbit blood by both cotton extracts and endotoxins, however, the ability of AECD to release histamine is greater than would be expected from endotoxin content alone. Antweiler (63), however, was unable to show in vivo histamine release by endotoxins obtained from cotton extracts in rabbits nor could he show an acute fall in blood pressure of cats after I.V. endotoxin injection, as occurred with subsequent injections of compound 48/80 or other dust extracts. He concludes that endotoxins are not responsible for any histamine releasing activity of cotton dust. 

In favor of the endotoxin theory is the demonstration that endotoxins are active if administered by aerosol (62,64), as is the agent of byssinosis. In a rabbit model, inhalation of either endotoxin or cotton dust extract produces histological patterns consistent with chronic bronchitis (65). Also, in a variety of animal species, fever and dyspnea occur after short periods of inhalation of endotoxins, but when endotoxin solutions are Inhaled on two consecutive days, the second Inhalation is without effect. This suggests tolerance to endotoxins, and parallels the Monday syndrome, characteristic of byssinosis (62). 

Both histamine and 5-HT have been demonstrated in extracts 5-HT is responsible for some of the bronchoconstrictor activity of cotton dust extracts. Brom-lysergic acid, a specific 5-HT inhibitor, partially reduces activity, suggesting the presence of an "unknown contractor." This does not appear to be acetylcholine or bradykinin. Thus, although histamine, 5-HT, and the "unknown contractor" can cause immediate contractor responses, delayed onset contractions may still be due to secondary release of histamine (105). 

Histamine release from pig lung occurs in response to extracts from cotton pericarp, seed, leaf, root and bract (112). Extracts of sisal release histamine from both pig and human lung, but the reactivity is less than cotton dust extracts. The use of chopped lung for histamine assay is not always reliable, however, nor is it sufficiently sensitive. 

Cotton dust extracts have been shown to affect cyclic nucleotide levels (122). Guinea pig lungs, in response to AECD, show a decrease in cAMP levels with a concomitant increase in cGMP. Further, there is a high correlation (r = 0.95) between lung histamine levels and cAMP/cGMP ratios. Other workers (123) have shown stimulation of cAMP in human peripheral blood lymphocytes in response to AECD. 

Laboratory exposure to dust clouds and dust extract aerosols results in chest tightness, dyspnea and decreases in both expiratory flow and dynamic lung compliance (4). Bouhuys et al. showed that aerosols of cotton dust extract inhaled by man produced reversible small-airway obstruction within 10 minutes O) the same effects were noted in cardroom workers exposed to dust on Mondays, i.e. decreased maximum expiratory flow rates and increased airway resistance ( ). These changes are compatible with narrowing of small airways as the principal effect of acute dust exposure. 

Within 30 minutes of their administration, 6 -adrenergic drugs often reverse most of the functional deficit in Monday morning byssinotics. As there is no mucous secretion, airway smooth muscle contraction is considered the primary response. Exposure of man to histamine aerosols produces pulmonary function changes similar to those seen after exposure to dust extract. However, exposure to histamine aerosol invariably initiates constriction of smooth muscle more rapidly than exposure to cotton dust ( <15 minutes), and dissipates within minutes, while the acute effects of inhalation of cotton dust and dust extracts lasts for hours. The slowly developing and prolonged effects of dust and extracts suggest that mediators other than histamine are involved. 

Small airway constriction and recruitment of leukocytes on pulmonary surfaces are prominent, documented responses to the inhalation of cotton dust. Currently, one or both of these effects are generally ascribed to endotoxin (8-10), to antigen-antibody reactions (11), to lacinilene C-7 methyl ether (1, 13), to a low molecular weight ( 1000 daltons), neutral, highly water soluble substance that is stable in boiling water and found in cotton bracts (14), to chemotaxins present in cotton mill dust extracts (15, 16) or to histamine releasing substances (17). 

Our studies have shown that cotton dust extracts contain deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) (27). DNA is present in varying concentrations in cardroom cotton dust (28) and emanates from bacteria, fungi, protozoa and plant cells. DNA might be important in the pathogenesis of byssinosis, as minute amounts can cause complement conversion. 

In vitro studies indicate that cotton mill dust extracts do activate complement by the alternative pathway. Kutz et al. (36) proposed that endotoxin is not the only agent responsible for complement activation, as microgram rather than nanogram quantities of purified endotoxin are required to induce the degree of complement activation observed with crude cotton dust extract. Several investigators (36, 37) have thus proposed endotoxin... 

The platelet hist UIline release assay demonstrated that cotton mill dust extract, cotton bract extract, cotton leaf extract, dialyzed CMD extract, polyphenols, compound 48/80, rutin, trimethylamine HCl, quercetin, catechin, tannic acid, ellagic acid and sodium metasilicate all release histamine directly (48). Thus not only do tannin compounds induce histamine release, but they may also form higher molecular weight polymers and contain components that survive acid hydrolytic conditions (48). Tannins are widely distributed in the plant kingdom. 

Mohammed ( ) reported that acetone treatment of aqueous cotton dust extract caused the precipitation of several sugars and an aminopolysaccharide. The sugars were present in concentrations equal to those which exhibited contractile activity on guinea pig... 

Cotton dust and cotton bract extract contracted smooth muscle with forces equivalent to a 0.32jj0.05 jug/ml concentration of 5HT and 0.7+0.1 ug/ml concentration of 5-HT, respectively ( ). However, cotton bract extracts were blocked by methysergide, a 5-HT antagonist, while cotton dust extracts were not. Diphenhydramine, a histamine antagonist, failed to significantly affect either of the extracts ( ). 

Antweller ( ) in 1961 injected Salmonella abortus equl and E. coll endotoxins Intraperltoneally into rats and looked for mast cells in the mesentery and the histamine content of the abdominal fluid. Negative results were obtained with amounts of the endotoxins (up to 10 yg) thought to be similar to that in cotton dust although large doses of endotoxin were known to cause rapid histamine release in cats and dogs. He concluded that endotoxins did not produce histamine release or the biological effect of cotton dust extracts. 

Histamine Liberation. Histamine liberation is not caused by fungal extracts, fungal cultures. Bacillus cultures, or their extracts, but is caused by cotton dust extracts and by known endotoxins when a sensitive method is used. 

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