Volume SH 1: Part
1 Equipment for Pumping Slurries and Pastes
This part
reviews the wide selection of both rotodynamic and positive
displacement pumps for solid/liquid mixtures such as
fine particle, high viscosity pastes, coarse particle
settling slurries and even unsaturated three phase cakes.
The appropriate choice depends on the application such
as in-plant transfer of slurry through 50 or 75 mm pipe
between different operations, the hoisting of ore or
coal from mines, the disposal of waste including tailings
or the long distance hydraulic conveying of solids over
several hundreds of kilometres. Each application will
have its own set of design variables, the main ones
being volume flowrate, transport system head (and hence
required pump discharge pressure), maximum particle
size and slurry abrasiveness.
While various
types of rotodynamic (including centrifugal) pump are
probably the most commonly specified, particularly for
in-plant and dredging applications, the advantages of
some positive displacement pumps are being increasingly
recognised, in particular their relative insensitivity
to change in system head. Rotodynamic pumps are essentially
low head, high flowrate prime movers whereas positive
displacement pumps give high head, low flowrate. This
review describes most of the commercially available
solids handling/slurry pumps and provides guidelines
on the selection of an appropriate pump for a particular
duty.
Scope of the Review
A survey of users of the Slurry Handling Knowledge Base
regarding future state-of-the-art reviews to be written
has shown that there is a strong need for collated information
on the design and selection of pumps and pumping systems
for slurries and pastes. This subject received almost
twice as many marks than any of the other ten titles
suggested in the circulated questionnaire. This review
will complement the review already written on the design
of pipeline for slurries and pastes.
The main aims of the current review are:
- to review in Section
2 the various types of pumps available for transferring
various classes of "wet solids" down a pipeline.
The "wet solids" may be variously classed
as settling slurries, non- settling highly viscous
pastes and unsaturated, compressible cakes.
- to give guidance in
Section 5 on how a slurry to be pumped should be evaluated
in terms of its flow properties, its abrasivity and
its stability both under gravity and during passage
through the pump.
- to indicate in Sections
6 and 7 how a knowledge of slurry properties combined
with operational requirements can be used to select
and size an appropriate pumping system.
In addition, in Section
3, typical problems with selecting and operating pumps
will be discussed, including pump priming, pump wear,
pump cavitation arising from excessive head losses on
the pump suction side, and particle attrition or degradation
problems during flow through the pump.
In Section 4, some features of designing a pumping system
such as the use of multiple pumps, either in parallel
or series, will be reviewed.
Sections 5, 6 and 7 include methods for evaluating the
relevant properties of the paste or slurry, how a knowledge
of these properties is used currently in pump selection
and how pumps are sized by combining information on
slurry properties and operational requirements.
Section 8 describes some case studies appearing in the
published literature where accounts have been made of
selection and sizing procedures used for pumps required
in a number of industries.
Finally Section 9 identifies where further research
and development effort is required to solve some of
the more commonly-met problems.
Types of Pumping
System
A very wide range of slurry pumps is available. Together
they cover a wide range of
- slurry variables: such
as particle size, solids concentration, non-Newtonian
flow property, solids abrasivity, solids friability;
and
- operating variables:
such as flowrate, discharge pressure, suction conditions
and type of installation and its location.
Each application must be
considered separately and none of the pumps available
is suitable for universal duty. Depending on the application
there may be a very wide choice of pump or the choice
may be very limited.
The term "slurry" used in these notes refers
to any mixture of suspended solids in a liquid phase.
Thus a slurry can be a few percent coarse solids in
water or a low or high concentration, fine particle
non-Newtonian mixture. It can be a paste such as drilling
mud, or strawberries suspended in a glucose syrup base.
Slurry pumps are used in a wide variety of operations
including
- transfer of "non-settling"
or settling slurry in pipes between different unit
operations within a processing plant, or between two
closely located plants;
- transport of solids
over long distances (10`s or 100`s km) from mine or
quarry to power station or processing plant;
- hoisting of mined material
up vertical shafts in mines;
- removal of rock cuttings
suspended in drilling muds during oil production;
- dredging operations
in harbours and estuaries;
- recovery of mineral
deposits on the ocean floor, perhaps in the future.
The rest of this volume
consists of:-
Chapter 2:
Types of pumps
Chapter 3: Typical problems in slurry
pumping
Chapter 4: Slurry pumping systems
Chapter 5: Slurry property assessment
Chapter 6: Pump selection
Chapter 7: Pump sizing
Chapter 8: Case studies for pump selection
and operation in various industries
Chapter 9: Some research and development
requirements for slurry pumps
Chapter 10: References
Chapter 11: Appendices : Manufactures,
distributors and agents Back
to Top
Volume SH 1: Part
2 Selection of Pumps for Slurries and Pastes
Part 2
gives a coherent logical methodology to selecting and
sizing a pump for a given slurry or paste. Guidance
on the design of pumping systems is given. The report
is based on Part 1 and a large amount of information
derived from pump users and suppliers.
The first
four sections deal with general considerations to be
taken into account when selecting and sizing pumping
systems. Section three gives a summary of pump operating
parameters. Section five provides the methodology for
ascertaining preliminary pump design requirements. Section
six consists of a series of pump selection charts and
section seven allows the user to size selected pump
types. The final sections give advice on discussions
with suppliers, testing and cost estimation.
The first
three appendices consist of a pump design sheet, summary
of roto-dynamic pump and system matching and slurry
rheology. Appendix D gives two example calculations
showing the use of this design guide. Appendix H is
a comprehensive buyers guide giving contact addresses
and brief noteform details of pump ranges.
This part
is the basis for SPA (Slurry Pump Adviser), software
to select a suitable slurry pump.
Volume SH 1: Part
3 Metering Pumps for Slurries and Pastes
Part 3
consists of a survey of commercially-available metering
pumps for slurries. Most positive displacement pumps
can be used for metering and dosing applications because
of their flat performance characteristics, i.e., flowrate
though the pump is relatively insensitive to differential
pressure across the pump compared with rotodynamic pumps.
However, the metering accuracy of positive displacement
pumps not specifically designed for metering applications
will be a function of the fluid properties and differential
pressure, and some pump manufacturers have these relationships
in graphical form which allows prediction of specific
flowrate.
Pumps designed
specifically for metering applications fall into two
main classes: packed seal piston or plunger pumps, or
diaphragm pumps (either one or two diaphragms) which
are actuated either mechanically or hydraulically. Special
design features, such as diaphragm and valve design,
are used to handle slurries. Both double diaphragms
and combinations of tubular and flat diaphragm are used
with high viscosity fluids including slurries and pastes.
