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Appendix C RESULTS OF AN EXPERIMENT TO DETERMINE WHETHER DUST SUSPENSIONS IN BUCKET ELEVATOR LEGS CAN BE KEPT BELOW THE LOWER EXPLOSIVE LIMIT BY PNEUMATIC MEANS* To determine whether the normal dust suspensions in a typical elevator leg could be reduced below the lower explosive limit, the following tests were made. The purpose of the test was; (a) to measure the effects of various volumes of air removal and (b) to compare the results obtained by taking aspiration from the boot-top, which creates turbulence in the boot and base of the up-leg, as opposed to taking aspiration from the sides of the up-leg, which provides a more laminar air sweep of the boot and is in accord with the natural aerodynamics of the leg. The indications obtained from these tests are significant. CONCLUSIONS** The test procedure was to insert probe header into the leg casing at locations indicated in Figure C-l. Two tests were run at each sample location for approximately one minute each, one with the probes up and one with the probes down. Refer to air flow schematic (Figure C-2) for sampling procedure, which illustrates the probes. The three graphs in Figure C-3 show the results from each sample location. The highest concentration of dust was found in the up-leg above the boot. When aspiration was moved from the top of the boot to the up-leg above the boot (dirtiest part of the leg), the dust concentration at all three sample points was lowered to below the lower explosive limit. This testing procedure may have some weakness and it may not be a totally true representation of the condition within the leg for two reasons. 1. The short duration of tests (approximately one minute) and the small amount of air sampled. 2. Variation in the collected data between probe up readings and probe down readings. * Courtesy of Russell Brackman, MAC Equipment, Inc., Sabetha, Kansas and Ken Buss, The Pillsbury Company, Minneapolis, Minnesota. ** This report and the conclusions herein are based on testing and techniques that are based on assumptions, therefore the accuracy is uncertain. Pillsbury and MAC Equipment, Inc., accept no responsibility in regard to any parties use of any information contained herein. Further, the conclusions drawn may not be applicable to other equipment or operating conditions. 103
104 LOCATION: Air Volume From Bucket Elevator Suction Location. A & B --- Duct Size A=l2" .785 Ft.' =14" 1.06 READINGS 9) t I VELOMETER 5) I l) I I I I > 2) 6) l0) i .^ 3) 7) ll) 4) 8) l2) i I Total = Avg. FPM Ft.2 x 3 J 7 FPM = CFM 2^i 1 / | fi --- PRELIMINARY DATA k'l iHllWIh i J . R,:.- Irot Flnl,itr ,- f i,.!. it., ic nnn nnu i â¢ Head Pulley Dia. 60_" And RPM 44_ Belt Speed 691 FPM And Width J>4"" Bucket Size _ * " - Spacing _lpl" _Centers Bucket Make Maxi Lift Casing Size _10"x.28" 4 _3QVMGL"._ Feed Side Of Leg Down ll" x 8' Double Row ' Product Handled jf2 Yellow Corn Product Moisture l2..2 to. .l3i / l Feed Point Air Temperature Relative Humidity Barometric Pressure 65 Sample Points On Elevator Casing I) Down Side Above Feed Point 2) Up Side Below Suction Point B& Above Feed Point 3) Up Side Above Suction Point B A) Suction Point On Top Of Leg Boot B) Suction Point On Up Side Of Leg Above Feed Point NOTE: Main body of leg Is slip form concrete construction. FIGURE C-l Preliminary data sheet for a bucket elevator test.
106 / \ 4 \ -o H H Minimum Eiplosive^^^^^^^^ \ * 1 a Suction Top Of Boot Limit! n Suction Up Side Of Leg W Suction Top Of O Bool And Up Side Of Leg 10 Dust Concentration In Grams Per Cubk Meter i0 1 \ 0 â¢ a) Sample Point #1 i 2 J < 5 Dust Contfol Aspiration in l.000 CFM b) Sample Point #2 \ \ I . Suction Top Of Boot ft \ H \ Suction Up \ Limits V Suction Top n Of Boot ind /â¢ v Up Side of Let Gram* Per Cubic Meter â¢ X â¢ 0 23456 Dint Conml Aspiration in l.000 CFM Dust Concentration in Grams Per Cubk Meter Suction Top 1Of Boot Suction Up Side Lej Suction Top Of Bool And Up Side Of Le1 I 2 i 4 3 6 Dust Control Aspirition in l.000 CFM c) Sample Point #3 FIGURE C-3 Dust concentrations at three sample points.
107 These tests indicate the following which correlates with previous tests conducted even though they may not represent the exact condition within the leg. A. The heaviest dust concentration area is on the up side of the leg above the feed point and below the suction point (B). B. With increased air suction, dust concentration is reduced. C. The most efficient use of the air suction is on the up side of the leg above the feed inlet. Suggestion; Further research and study is necessary to improve sampling technique and accuracy. TEST PROCEDURE TO DETERMINE DUST CONCENTRATION IN BUCKET ELEVATOR A. Determine air volume being drawn from bucket elevator a. Duct cross section in ft . b. Duct velocity in fpm using velometer (see Figure C-4). c. Identify suction location. B. Take air measurements to determine dust concentration a. Location of sampling point b. Gas-meter reading before and after test c. Weight of clean filter media. Weight of filter media after test. d. Conduct air sample test. e. Convert collected data to grams per meter3. C. Record the preliminary data (see test data form of Figure C-l) .
108 CHART I For accuracy of plus or minus 2%- as in laboratory applications, extreme care is required and the following precautions should be observed: l. Duct diameter 4" or greater. 2. Make an accurate traverse per sketch at right and average the readings. 3. Provide smooth, straight duct sections l0 diameters in length both upstream and downstream from the pi tot tube. 4. Provide an egg crate type straightener upstream from the pi tot tube. 5. Minimum number of points considered acceptable versus duct area. * l ft 2 = 8 points l -2 ft.5 - l2 points > 2 ft. * 20 points Now that we have the velocity stated in feet per minute and we have the cross sectional area of the duct stated in square feet we can multiply these two together and determine the cubic feet per minute or CFM, as we normally refer to ft. CFM = Area Ft.2 x Velocity ft/min. STATC PRESSURE READING VELOCITY READING IN FPM /-VELOCITY PRESSURE READING IN INCHES OP WATER TOTAL PRESSURE READING FIGURE C-4 Use of pitot tube and velometer.