PASTE SUPPLEMENT 2019
Developments in tailings pipeline transportation
This paper* from Robert Cooke and Joshua Stowe from
Paterson & Cooke reviews recent developments in the
design and implementation of tailings pipeline
transportation systems. The discussion focuses on
pipeline operation with a stationary bed, pipeline
operation in laminar flow, bed height detection
instrumentation and leak detection systems
he conventional slurry pipeline design
approach is to select a pipeline diameter
which ensures the pipeline operates in
turbulent flow without a deposit for all expected
operating conditions. Recent improvements in
the understanding of slurry pipeline flows allow
for the design of pipelines operating with a
deposit on the pipe invert. Designing for the
formation of a deposit at low flow rates allows
the system to operate at moderate velocities for
high flow rates, optimising system energy
requirements and maximising pipeline wear life.
Tailings pipelines are increasingly operated at
higher solids concentrations where there is a
greater likelihood the pipeline will operate in
laminar flow due to the higher tailings rheology.
Historically, slurry pipelines have been operated
in turbulent flow but we now know that laminar
flow pipeline operation is possible as there are
several operational laminar flow tailings
pipelines. While our understanding of laminar
flow slurry pipelines is not complete, recent
research provides guidance on how to approach
the design of these pipelines.
New sensor technology has led to the
development of an instrument that provides
reliable indication of bed deposit height within
a pipeline. This technology is particularly
helpful in operating pipelines with a deposit and
has application in better understanding the
operation of laminar flow pipelines.
Failure of tailings pipelines can result in
consequent damage to surrounding structures
and unacceptable spillage into the environment.
Modern pipeline leak detection technology
allows operators to better manage this risk by
ensuring safe and reliable operation of tailings
pipelines.
T
Introduction
While there has been continual improvement in
the models for predicating deposition velocity
and pipeline friction losses, the fundamental
design philosophy for tailings pipelines has
remained the same over the previous three or
four decades. The approach has been to design
tailings pipelines to operate in turbulent flow
without a deposit on the pipe invert. Recent
improvements in the understanding of slurry
P4 International Mining | APRIL 2019 Supplement
pipelines flows, has allowed for new
approaches to the design of tailings pipelines:
n In some cases, it is advantageous to design
tailings pipelines to operate with a settled
deposit under certain operating conditions.
n New research is providing insights on how to
design pipelines to operate in laminar flow.
This is particularly important for high
concentration tailings.
n New sensor technology is providing
additional insights into the flow behavior
within the pipeline allowing operators to
effectively control pipelines operating with a
deposit and/or in laminar flow.
n Modern leak detection technology ensures
safer and more reliable operation of tailings
pipelines.
This paper provides an overview of the each
of the above advances in the design and
operation of tailings pipelines.
Operating tailings pipelines with a
deposit
Tailings pipelines, and slurry pipelines in
general, are typically designed to operate
without a deposit on the pipeline invert – ie the
minimum operating velocity exceeds the
turbulent deposition velocity. This approach has
been adopted due to concerns regarding
potential blockage of a pipeline operating with a
deposit. Figure 1 shows a typical design duty
envelope for a tailings delivery system as a
function of solids throughput and solids
concentration by mass.
If the pipeline is
designed to operate
without a deposit at
the lowest duty flow
rate (4,480 m 3 /h), the
operating velocity at
the highest duty flow
rate (6,590 m 3 /h) will
be about 1.5 times the
deposition velocity.
Considering that the
pipeline wear and
energy requirements
are roughly
proportional to the square of operating velocity,
this results in an operationally inefficient
system when the pipeline is operated close the
maximum design flow rate – which is where
most systems tend to operate after the post-
startup debottlenecking optimisations.
An alternate design approach is to ensure the
pipeline operates without a deposit for the
nominal flow rate and accept that a deposit will
form when operating at lower flow rates. This
results in the selection of a larger diameter
pipeline, but there are significant benefits in
terms of reduced pumping and energy
requirements and lower pipeline wear. Table 1
shows that the energy requirements are
reduced by about 35% compared with the
conventionally designed tailings pipeline. The
design of pipelines to deliberately operate with
a deposit requires that several measures are
considered to mitigate the risk of possible
pipeline blockage:
n The designer needs to be able to accurately
model the behaviour of tailings pipeline
operating with a deposit.
n Steep slopes (>15%) should be avoided when
selecting the pipeline route. In cases where
steep slopes are unavoidable, smaller
diameter pipe should be considered in these
sections to avoid the formation of a deposit.
n The design should limit the amount of
material deposited onto the pipe invert. In
establishing this limit, we suggest the
designer consider the flow conditions if there
is a process change which results in rapid
remobilisation (re-suspension) of the
deposited material.
n Reliable operation requires that the system
has good flow rate control (ie accurate flow
rate measurement and variable speed pump
drives).
n Ideally the pipeline should be equipped with
instrumentation to detect the height of
deposited material on the pipe invert. This is
Figure 1: Tailings pipeline operating envelope