Pneumatic Dust Control in Grain Elevators Guidelines for Design Operation and Maintenance (1982) / Chapter Skim
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Hoods, Transitions, and Ductwork
Hoods, Transitions, and Ductwork
Pages 11-28
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From page 11... ...
Volume flows and velocities also must differ elsewhere in a pneumatic system if it is to operate properly. For example, the volume flow in a main duct is the sum of the volume flows in the branch ducts leading into it.
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From page 12... ...
A method of calculating airflow or velocity near hoods of various types is given in "Industrial Ventilation"1. We have already seen that the minimum capture velocity for grain dust is 200 fpm.
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(from "Industrial Ventilation," 16th Edition, 1980)
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From page 14... ...
However, the proper distance and hood design will depend on a number of factors including belt speed, belt width, method of feeding the belt, idler spacing, and the physical room available. In many cases where there are a number of belt loaders loading onto a single belt in series, the installation of a continuous belt cover with suction being applied at several points along the belt is the best method of controlling the dust.
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15 < _l Qto S-l 0)
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m -H c ft 4J O S> 3 0 0i M •H .X rH 4J O rH C tfl id -H D 0 -H II 01 U a o u ^H x *
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18 I if 6 "0 9"0 13"0 f h " d T t T I /*
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FIGURE 3-6 Tube sizing chart. (Friction of air in straight ducts for volumes of 10 to 2000 cfm.)
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(Friction of air in straight ducts for volumes of 1000 to 100,000 cfm.)
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FIGURE 3-8 Improperly designed suction hoods.
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The sum of the pressure losses in the components of a system is the static pressure of the system. This static pressure, or suction, must be provided by the exhaust fan selected for the system.
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The metal must withstand normal corrosion and also erosion -- a high-velocity stream of grain dust can be extremely abrasive. Also, ductwork and other enclosures under suction must withstand pressure equivalent to the difference between the internal static pressure and atmospheric pressure.
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FIGURE 3-9 Principles of duct design. (from "Industrial Ventilation", 16th Edition, 1980)
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(from "Industrial Ventilation", 16th Edition, 1980)
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(from "Industrial Ventilation", 16th Edition, 1980)
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From page 27... ...
TABLE 3-2 Suggested Gauges for Ductwork Under 15"'Static Pressure3 Duct Diameter Gauge Under 8 inches 20 8-18 inches 18 18-30 inches 16 More than 30 inches 14-12 a See "Round, Industrial Dust Construction Standards," Sheet Metal and Air Conditioning Contractors, National Association, Inc., Vienna, VA., 1981, particularly where static pressure exceed 15".
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