How to Design and Implement Chutes in Bulk Solids Handling Systems

Chute Design Essentials

How to Design and Implement Chutes in Bulk Solids Handling Systems

Chutes are in use in almost every bulk solids handling plant. Although everybody knows them, they are mostly overlooked, except for those cases where they cause extra-attention and -work due to malfunctioning. This article attempts to give the reader some simple rules to apply to chute design.
(ed. WoMaMarcel - 20/4/2016)
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The transfer of material onto the belt is illustrated in Fig. 22.

The following formulae have been developed as a means of estimating belt wear at a transfer point:

                              (36)

where:

ρ  = bulk density
vey = vertical component of the exit velocity


Fig. 22: Feed onto the belt.

The abrasive wear parameter Wa:

                              (37)

where:

μb = friction coefficient between the bulk solid and the conveyor belt
Vb = belt speed

The wear will be distributed over the acceleration length La. The wear parameter may then be expressed as

                              (38)

where:

                             (39)

where:

θe = chute slope angle with respect to vertical at exit.

Kb is a non-dimensional wear parameter. In Fig. 23 it is plotted for a range of vb/ve  values.


Fig. 23: Non-dimensional wear parameter versus slope angle.

As shown, the wear is quite severe at low chute angles but reduces significantly as the angle θe increases. For the chute to be self-cleaning, the slope angle of the chute at exit must be greater than the angle of repose of the bulk solids on the chute surface. It is recommended that

                              (40)

8. Conclusion

This collection of rules and formulae has been presented as a reminder to the industry that chute design requires a lot more attention that it is currently given. While sophisticated computer software is an essential tool in modern materials handling, the basic design of particu- late flow is equally essential where the software is not available. The application of the equations and principles pres­ented should provide the designer and plant engineer with the means to apply these principles in a practical manner and with sufficient accuracy to confidently predict the performance of the chutes.

Acknowledgement

This is article is based on a presentation of the authors during Belton 18, 5./6. August 2015 in Johannesburg, South Africa.

References

[1]    Sabrina, W.E., R.P. Stahura, and R. Todd-Swinderman: Chute   Problem Checklist.  Bionic Research Institute. Chute Design Conference. (1992)
[2]    Roberts, A.W.: Chute Design Considerations for Feeding and Transfer.    Beltcon 11 Conference. 2001. Johannesburg. IMHC. (2001).
[3]    Stuart-Dick, David, and Anthony T. Royal: Streamlined Design of Chutes to Handle Bulk Solids. Bionic Research Institute. Chute Design Conference. (1991).
[4]    MHEA Mechanical Handling Engineers Association: Recommended Practice for Troughed Belt Conveyors.
[5]    Shortt, G. et al.: Diploma Course in the Design and Operation of Belt Conveyors. Johannesburg: Conveyor Manufacturers Association of South Africa.
[6]    Pitcher, D.M.: Loading, Discharging and Cleaning of Belt Conveyors.  Beltcon 1 Conference. 1981. Johannesburg. IMCH. (1981).
[7]    Rozentals, J.: Rational Design of Conveyor Chutes. Beltcon 2 Conference, 1983. Johannesburg. IMCH. (1983).
[8]    Roberts, A., and C. Wheeler, et al: Design Course on Belt Conveying of Bulk Solids. TUNRA. Australia and CMM and Wits University, Johannesburg.
[9]    Electronic Course: Flow of Solids in Bins, Hoppers, Feeders and Chutes. Jenike & Johannsen (eds). AIChE.

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