Volume BSH 4:
Part 1 Gravity Transfer of Bulk Solids in Chutes
This part considers
the gravity transfer of pastes, cakes and semi-dry bulk solids
down open or closed chutes. The gravity transfer of dry, cohesionless
bulk solids has been the subject of much theoretical modelling,
principally by Roberts et al in Australia and Savage in Canada.
Unfortunately most, if not all the results of this work cannot
be applied to the flow of cohesive and adhesive pastes or
cakes. Nevertheless some guidelines based largely on practical
experience are available for chute design for wet, bulk solids
and these are described.
Volume BSH 4: Part
2 Gravity Transfer of Bulk Solids in Chutes : Design Guide
This part covers
the design of chutes used in bulk handling operations. These
are called upon to perform a variety of operations. For instance,
accelerating chutes are employed to feed bulk materials from
slow-moving belt or apron feeders onto much faster moving
conveyor belts. Transfer chutes are employed to direct the
flow of bulk material from one conveyor belt to another, often
via a three-dimensional path. In the case of flood-loading
of bulk rail wagons where discharge rates of several thousand
tonnes per hour are required, it is common to use telescopic
flood loading chutes in association with mass-flow bins. Discharge
chutes are used as part of the discharge process of such handling
equipment as bucket elevators, screw conveyors and belt conveyors,
as well as discharges points from unit operations such as
various designs of filter and centrifuge. Standpipes are a
special form of vertical chute used in feeding operations
where the existence of a pressure gradient requires a head
of solids to be maintained.
Some operations
require the use of moving chutes, a typical application being
the flow of materials from the buckets of a bucket elevator
during the discharge process. In other applications, such
as in loading coal into bulk ships, complex, multi degree-of-freedom
chute configurations are used to distribute the load uniformly
within the holds of the ship.
While noting
the broad range of applications and the used of special chutes
as mentioned above, the scope of this Design Guide is constrained
to fixed chutes, such as those more commonly encountered in
bulk handling operations. The need for fast, accelerated flow
is emphasised in order that blockages be prevented. This requires
the determination of the most appropriate chute profiles to
achieve optimum flow within the limitations of space available.
The methods of analysis to achieve efficient and effective
profiles are described.
An important
aspect of chute design is the knowledge of the relevant bulk
solid flow properties. In particular, the interaction between
the bulk solids and chute lining surfaces needs to be thoroughly
understood if streamlined flow without blockages and spillage
is to be achieved and wear is to be minimised. The relevant
test procedures to measure the required parameters are included
in the Guide. These procedures include the inverted shear
test for the measurement of the variation of wall or boundary
friction with normal pressure as well as the determination
of cohesion and adhesion. The latter parameters provide an
indication of the potential for build-up to occur on a chute
surface. The tests also include the measurement of lining
surface wear which, in association with the computed wear
profiles based on the analytical models, allows the absolute
wear and life of the lining materials to be determined.
A section of
the Design Guide is devoted to practical design and operation
considerations. This includes the selection criteria for chute
lining materials and the necessary objectives for the achievement
of efficient operation without spillage. Case study examples
illustrate the application of the design procedures to practical
industrial applications.
