Charts that provide flow factors for conical and wedge-shaped hoppers are given in Jenike [1]; Examples are shown in Figures 9a and 9b. Stress profile in bulk solids silos. A characteristic form to describe the parts of the silo is shown in Figure 3.2. Figure 7. Episode 38 : Bin and Hopper Design < 1960s storage bins were designed by guessing Then in 1960s A.W. Copyright American Institute of Chemical Engineers. By understanding the fundamental principles and conducting proper flow properties tests, a chemical engineer can design reliable systems for storing and handling bulk solids. Suboptimal design of either piece of equipment or of both of them can adversely affect processing. The other point of intersection of this circle and the horizontal axis is the unconfined yield strength (fC). This behavior eliminates the formation of stagnant regions in the vessel, and affords a first-in, first-out flow sequence, which provides a more uniform velocity profile during operation. f5.2 Solid flow pattern As solid flow from a bin, the boundaries between flowing and non-flowing regions define the flow pattern. Any combination of and that falls within the limiting mass flow region of the chart will provide mass flow. Would you like to reuse content from CEP Magazine? Next, conduct the shear step: Reduce the vertical compacting and shear the sample until it fails. This lesson demonstrated how to calculate hopper drag load by approximating parabolic shapes with rectangular prisms, then calculating their weight and applying a cutting factor. Cone Bottom Silo Size Calculator Answer a few simple questions, and our silo sizing calculator will give you an estimate of the silo size you need for your materials. Figure 7 : equations will allow to estimate the flow but in no case to have an The abscisse is giving you a minimal This is especially true for hoppers with slotted outlets, where feeders should be designed to draw uniformly along the entire cross-section of the outlet in order for mass flow to occur. particles), Table 3 : of the discharge rate. The hopper throat dimension: If material particles are random-sized, (T)should be at least twice the diameter of the largest particle of material. Dilute phase pneumatic conveying design and calculation The physical properties and direct shear test data of the ten food powders served. FIGURE 6. By contrast, in funnel flow, an active flow channel forms above the outlet, but stagnant material remains (called ratholes) at the periphery of the vessel. but the type of powder feeder at the base of the silo will have also 2 types of equations are usually found in the literature : the Bulk solids and powder flow properties testing, silo and hopper design, discharge and conveyor technology . Test results are used to calculate the size of the hopper section outlet and the recommended hopper angle. angle of 23 degrees. Shear properties -Materials that are soft and spongy do not tend to flow well from hoppers.Particles tend to pack into each other causing bridging and promoting poor flow on the feeder. Adding a hopper with an opening 38 wide and 60 long results in a hopper drag load of 6,769 lbs, as follows. Its easy to request permission to reuse content. equipments The powder This lesson presents arching theory, how to calculate hopper drag load, how to design hopper pressure relief, and how to calculate the power required to overcome hopper feeder drag. The discharge rate can then be 100 times less corresponding to the estimated maximum time powder can stay in the vibration will be very limitated and will have few effect on 4. hopper for example). In funnel flow (Figure 6b), a channel of flowing solids forms above the outlet and stagnant material remains at the periphery. (expressed in terms of throughput, cycle time or number of batches / : critical outlet diameter to avoid ratholing [2], Figure 6 : The angle of wall friction () is the angle that is formed between the horizontal axis and a line drawn from the origin to a point on the wall yield locus. Abascus for G parameter calculation. A 3-deg margin of safety (with respect to the mass-flow hopper angle given in Figure 4) is recommended. It is usually desirable to have a mass Ft. 301 Crawford Pkwy, Clayton, NC 27520. compared to large particles). For random-sized material, the inside width of the opening (between skirts) should be a minimum of 2.5 times the diameter of the largest particle. Modify one hopper opening of 38 x 60 to four hopper openings, each at 19 wide x 30 long. The critical stress crit is determined from the intersection of the Flow Function and flow factor. Parsons, KS 67357 Phone: +1 620-423-3010 Fax: +1 620-423-3999 Figure 5. Take 3 degrees margin and select 20 degrees for This is shown in Figure 12. the wall friction angle as a function of the hopper angle. Values of the allowable hopper angle (measured from vertical) are on the x -axis, and values of the wall friction angle are on the y -axis. hopper geometry, The typical discharging aids are described in the following table, Table 4 : on It is important to note that, for fine Additionally, skirts must run parallel to trough sides and must be reinforced to resist bulging outward against the trough. Reduced potential for material buildup at inlet, Reduced potential for spillage at back and sides. The Rulmeca Corporation Conveyor Drive Power Calculation Program Design Imperial 7.30 may be used to add hopper drag load to a standard loading condition. We can approximate two active volumes with two rectangular prisms in which L = L T. To conservatively simplify the calculation, ignore T. Therefore, each prisms volume may be calculated as follows, The active weight of 2 prisms may be calculated as follows, Total active weight = 2 prisms x volume of each prisms x material bulk density, Hopper drag load = 0.5 x total active weight. In a bin, the powder is submitted to pressure, due to the fact that For this, the scenarios of discharging aids to the silo will be necessary. Similarly, wall-friction test results allow engineers to determine hopper geometries that are required to promote mass flow. The kinematic angle of internal friction () and effective angle of internal friction () can also be determined, as shown in Figure 7. FIGURE 8. Typical, the calculations include dimensional analysis for critical bin opening dimensions, bridging, arching, ratholing, consolidated bin opening pressures, vertical pressures and horizontal pressures in the silo. Rulmeca Corporation Conveyor Drive Power Calculation Program Design Imperial 7.30. is divided in different areas that represent different flow factor. To determine the permeability of a bulk solid, run a gas through a bed of powder contained in a cylinder. He served on the executive board of AIChEs Particle Technology Forum and is a past chair of the Boston AIChE section. there is a height of powder in the bin, the powder on top pushing on Define the hopper geometry based on the chosen flow pattern enter the length, width of rectangular bases and height between the bases in the To measure the friction between a bulk solid and a vessels wall material, place a sample of the bulk solid inside a retaining ring on a flat coupon of the wall material. Continue to ignore T and calculate the volume of each prism, as before. The AIChE online library includes articles, journals, books, blog posts, and more on a variety of topics. Use this video in conjunction with our growing library of tutorials on how to design and maintain bulk handling belt conveyors. In addition, a 1-inch minimum clearance at the sidesand a 1.5-inch clearance on the bottom and the rear wall of the pan of the feeder must be maintained in both loaded and unloaded conditions. Measuring degree of mixing At the point where the two lines intersect, the arch stress and the cohesive strength of the bulk solid are the same, and equal to the critical stress. atmosphere. The maximum flowrate of a fine powder can be several orders-of- magnitude lower than that of coarser materials, due to an adverse gas-pressure gradient that forms. If you are author or own the copyright of this book, please report to us by using this DMCA report form. additional equipments to promote the flow of material. Shear cell testers are used to measure cohesive strength, internal friction, and compressibility. Figure 1. As defined above the design of the feeder needs to be The following formula can be used for assessing the discharge rate of coarse powders : Equation 1 : Hopper discharge rate for coarse solids With : m s = hopper discharge rate in kg/s B = outlet diameter of the hopper in m bo = powder bulk density at outlet conditions in kg/m3 ' = mass flow hopper angle in deg 2.2 Fine powder discharge rate equilibrate pressures : i.e. To find the kinematic angle of internal friction, draw one line tangent to the smaller Mohrs circle and another that is horizontal at its intersection with the yield locus; the angle between them is the kinematic angle of internal friction. The test is performed using an instrument (shown in Figure 2) that involves placing a sample of powder inside a retaining ring on a flat coupon of wall material. During this step, the vertical compacting load is replaced with a smaller load, and the sample is again sheared until it fails. It is calculated from an powder and the discharge of hoppers. possibility exists to actually install a pipe in between the NOT to be used with This is accomplished by first testing the material to measure wall friction, and then calculating the minimum hopper angle that will allow mass flow. It is generally advantageous in the industry to design a mass 2. particularly used to finalize the discharge. Bulk solids and powder flow properties testing, silo and hopper design, discharge and conveyor technology . equation : Equation 2 Uniform flow is achieved with the ratio of the hopper throat (T) and the hopper gate height (H) is 0.6. Three flow patterns can occur in a bin: mass flow, funnel flow, and expanded flow. optimization, 4. ASTM D-6773, Standard Shear Test Method for Bulk Solids Using the Schulze Ring Shear Tester, ASTM International, 2008. Schulze, D., Powders and Bulk Solids Behavior, Characterization, Storage, and Flow, Springer, New York, 2007. The discharge will be more complete and Sales: sales@tankconnection.com. -------------- of your process, Airlock Simply click here to connect instantly to licensing services, where you can choose from a list of options regarding how you would like to reuse the desired content and complete the transaction. The development of the hopper design spreadsheet add-in for conical and wedge types of hopper by Oko et al [1] guides the engineers through the established methodologies to use measured powder . In the photograph, you can see a typical hopper from the side and from the top. Prior to Jenikes work, bins and hoppers were typically designed primarily from an architectural or fabrication standpoint (for instance, hopper walls were sloped 30 deg from vertical to reduce the waste of wall materials, or 45 deg to minimize headroom requirements and simplify design calculations). for a hopper discharging to a mixer, to be able to release air in the mixer to avoid overpressure. The flow function is the relationship between the major stress and the unconfined yield strength. From these characteristics, a critical discharge diameter can be filled with bulk solids has a very different profile compared to Explore areas of advancement below. Then draw a second semicircle tangent to the yield locus through the origin. | Privacy Policy An envelope of the Mohrs semicircles forms the effective yield locus (Figure 4). This should prevent blockage at the throat opening. except for sand where it is 2.9. He developed testing methods, equipment, and design techniques and conducted experiments to confirm and refine his groundbreaking analysis [1]. In mass flow (Figure 6a), the entire bed of solids is in motion when material is discharged from the outlet. Corrosion monitoring is a crucial part of maintaining the operational integrity of a refinery. Further use of this site will be considered consent. As stated earlier, if T/H is outside the range of 0.5 to 1.0, the material flow pattern is disturbed. After a number of values have been recorded, the wall yield locus is identified by plotting shear stress against normal stress (Figure 3). The larger-valued intersection of the semicircle with the horizontal axis is the major principal stress (1). Do you critical diameters and help to position discharging aids in the This Aluminium and Some bulk materials gain cohesive strength and adhere to wall surfaces when they are stored at rest, so if a bin is not expected to operate continuously, time tests are conducted to measure the cohesive strength and static friction between the wall surface and the bulk solid after storage at rest (3). Mass flow (a) ensures a more-uniform discharge of bulk solids than funnel flow (b) or expanded flow (c). Feeders are positioned after a hopper to control the discharge, with materials who can be transformed during their storage (sugar Discharging powder is often overlooked, And measurement of necessary particles properties. Join now. The above diagram gives flow factors for conical hoppers, = 50 degright FIGURE 9b. Figure 5 : It must be noted that different losses. The curve drawn tangent to the larger Mohrs circles is the effective yield locus. deformed [4]. dose the solid if necessary, or reach another unit operation while and lessons learned, Carson, Jenike and Johanson, [4] Feeder Design for Solids discharge is done for dosing purposes, is often overlooked. the powder high enough to break arches and make the product flow To calculate the drag load in this example, calculate the four volumes, determine the active weight of the four prisms, determine the total cutting force by multiplying the total active weight by 0.5. hoppers will be preferred, because of the easiness of cleaning. Mixing speed The diameter of the outlet of a conical funnel-flow hopper should not be less than the critical rathole dimension. The next step in the data analysis is to determine the major principal stress (1), i.e., the maximum normal stress exerted on the bulk solid during the test, and the unconfined yield strength (fC), i.e., the cohesive strength of the bulk solid. You have completed However, it may be necessary to have ASTM D-6128, Standard Test Method for Shear Testing of Bulk Solids Using the Jenike Shear Cell, ASTM International, 2006. We use cookies to provide our services, analytics, and marketing. The limiting discharge rate from a mass-flow hopper for fine powders can be calculated using Equation (6): The magnitude of the pressure gradient depends on the bulk density and the permeability of the powder. Note: a minimum safety factor of 3 deg should be used. This video explains how to calculate hopper drag load on feeder conveyors and how to reduce that load through the installation of hopper pressure relief systems. it can reduce accumulation from 1 batch to another. At a critical solids-discharge rate, the solids-contact pressure drops to zero, and efforts to exceed this limiting discharge rate will result in erratic flow. However, Now lets review how to decrease hopper pressure even more. Otherwise, a small change in powder properties may cause the flow pattern inside the hopper to change from mass flow to funnel flow bringing its associated risk of flow problems. additional equipments to promote the flow of material. a good flow of product when discharging a hopper. Powder has a given ability to slide and fall when it is stored in a The active zone is defined by the length and width of the hopper opening, called L and W. We can conservatively approximate the active volume with a rectangular prism, rather than a parabolic shape. are used to determine outlet dimensions that prevent a cohesive arch or stable rathole from developing. that can seem easier. Otherwise, material may flow preferentially from the upside of the valve and affect the flow pattern inside the vessel. Notice that the required power drops from 23.2 HP to 12.2 HP. See Schulze [4] for a discussion of the challenges of accurately predicting the pressure gradient. Batch / naturally. Their common objective is the prediction of material behavior within a prescribed bin hopper system. Hopper shape, angle, and internal surface required for bin flow pattern Outlet size and shape engineered to avoid poor flow and ensure discharge rate Feeder selection and design to maintain reliable discharge from hopper outlet Unique design features for powder and bulk solids reliable handling, processing Experience Highlights 2. you hopper. Required power = 6,769 lbs x 100 fpm = 676,900 ft-lbs/min, Required power = (676,900 ft-lbs/min)/(33,000 ft-lbs/min per HP) = 20.5 HP. : Johanson equation (discharge rate through outlet for coarse When T/H is below 0.5 or above 1.0, material flow patterns become drastically distorted, significantly reducing feed rates. The flow rate on the hopper front wall should be slightly less than the flow rate on the back wall. : critical outlet diameter to avoid arching [2], With b the bulk density under a consolidation These shear cell tests are also used to find the effective angle of friction () and the kinematic angle of internal friction (). Figure 3 : For many materials, flow problems can be eliminated by ensuring that a mass flow pattern exists in the vessel. How enough, without getting over the maximum pressure authorized. This type is to be preferred to get close to a FIFO The knocker Hopper Recommendations 1. The rathole will then periodically fail as the base of the material falls above the screw. From a design point of view, it is important to be able to determine the loads acting on feeders in hopper/feeder combinations and the corresponding power requirements. If the width is smaller than the length, assume height = 3 x W. If the length is smaller than the width, assume height = 3 x L. We can now determine the active weight as follows. Calculate the outlet diameter, cone angle and position of Reduced material speed in the rear of the hopper allows for non-uniform flow and a reduction of bed depth.Reduced material depth means reduced feeder capacity. In food application, conical "lump" parameters are used. While feeder design will be covered in a future article, in order to choose the hopper design best suited to your application, consider the following material-related factors. There are no upcoming Events at this time. 5. of the hopper (which can lead to some overdesign compared to what is Peat, rock, flourno matter which material you process, your hoppers must move it to feeders at an optimal flow rate without damaging it. critical outlet diameter would be too large for being implemented), Access our Privacy Policy in the It is 1st The first step in the design process is to determine the fundamental properties needed to predict the flow behavior of bulk solids: cohesive strength, internal friction, compressibility, wall friction, and permeability. Connect with a Rulmeca Team Member now. compensation in both hoppers. moment the product stuck on the side is collapsing : indeed, the