Pneumatic Dust Control in Grain Elevators Guidelines for Design Operation and Maintenance (1982) / Chapter Skim
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Dust Control in Problem Areas
Dust Control in Problem Areas
Pages 49-72
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From page 49... ...
On the other hand, a properly designed pneumatic system can eliminate explosible concentrations of dust in enclosed spaces, as well as satisfy the environmental and occupational requirements. Ideally, the materials-handling system in an elevator should be designed from the start with proper dust control in mind.
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From page 50... ...
Tests have shown that a properly designed pneumatic system can avoid explosible concentrations of dust in a leg (see Appendix C)
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From page 51... ...
It has been commonly believed that a volume flow of about 750 cfm was sufficient to accommodate a typical 20,000 bph leg. We now know, however, that 750 cfm will not avoid explosible concentrations of airborne dust; such a volume flow in some cases may not even handle the air displaced by the entering grain.
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From page 52... ...
52 wrww \ WWCNWW ftnAMtMA ) T rfl Horizontal Cross ^ yy Ml ^ ' Section of Leg , 1 1 ,^D^ iMMWWW Boot - Feed FIGURE 6-1 Rule of thumb for calculating airflow in elevator leg.
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From page 53... ...
A dust-collection take-off at the top of the upper garner can create negative pressure in the bin, thus eliminating dust emissions. The pressures inside and outside the scale hopper must be equal during the weighing cycle to obtain accurate weight.
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From page 54... ...
54 I 5 c o a .s>«-£S§ Q m CD 4-l H ai *
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From page 55... ...
55 Floor Floor Scale Hopper Floor Lower Garner Aspiration (Chinese Hat) Canvas or Flexible Connection in Duct Gate NOTE: System must be airtight.
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From page 56... ...
The lower the speed of the grain entering a distributor, the easier it is to maintain negative pressure in the device and capture airborne dust. The closest feasible approach to choke-feeding should be used.
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From page 57... ...
57 Weigh Cycle: A, B, C Closed Scale Dump: B & C Open A Closed Scale Fill: A & B Open C Closed Aspiration Upper Garner Scale Hopper Lower Garner FIGURE 6-4 Scale -- Garner intervent system.
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From page 58... ...
58 Intervent Intervent FIGURE 6-5 Rotating or Mayo spout dust control.
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From page 59... ...
59 Grain Aspiration Tapered Fitting FIGURE 6-6 Enclosed distributor dust control system.
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From page 60... ...
Suction hoods below the tripper pulley usually plug with grain and should be avoided. There should also be a hood at the head pulley of the tripper belt.
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From page 61... ...
61 Top Hood Shown Plan View Only Spout Hood Style A Blast Gate Spout Hood Style B ELEVATION FIGURE 6-7 Zipper suction for tripper.
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From page 62... ...
However, this alternative may not be practical where grains cannot be comingled. TABLE 6-1 Air Volume for Traveling Trippers3 Belt Width Approximate Capacity Air Volume 24 inches 10,000 bph 3,500 cfm 30 inches 15,000 bph 3,800 cfm 42 inches 30,000 bph 5,500 cfm 48 inches 40,000 bph 6,000 cfm 60 inches 60,000 bph 6,800 cfm a The figures above assume belt speeds of 500 fpm or less.
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From page 63... ...
Whole grain that carries over the head pulley usually is released directly under the pulley. This grain is best handled by a mechanical pickup, such as a minature loop conveyor or screw conveyor.
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From page 64... ...
Truck and Rail Unloading Critical areas for controlling grain dust outside elevators are the receiving pits, where trucks and railroad cars are unloaded. Still, there are basic methods for solving the problem.
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From page 65... ...
Square feet of Area "D" x 33 cfm = cfm Total 1, 2, 3 cfm FIGURE 6-8 Suggestions for control of grain dust at truck dumps.
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From page 66... ...
Truck and Rail Loading There are several ways to control dust when loading trucks and railroad cars with free-pouring grain. The methods for open-top trucks, hopper cars, and boxcars are generally similar.
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From page 67... ...
This approach works well when loading trucks, but is less convenient with railroad cars. Marine Loading Controlling dust when loading vessels with free-pouring grain involves methods much like those used with trucks and railroad cars.
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From page 68... ...
68 Air Suction Air Conduit Must be Flex Hose or Swivel Joint Telescoping Grain Spout Outer Sleeve Must Be Telescoping or Collapsible Must Maintain 12" Clearance to Be Most Effective Dead Box FIGURE 6-9 Retractable spout deadbox for truck load-out.
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From page 70... ...
of Grain on Long Free-Falls GOOD DESIGN Easiest to Control Dust POOR DESIGN Most Difficult to Control Dust FIGURE 6-11 Load-out spout design,
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From page 71... ...
The latter approach is not effective during topping-off procedures. Other Loading Devices The deadbox principle described under Truck and Rail Loading (Figure 6-9)
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