SYSTEM AND METHOD FOR MAXIMISING SOLIDS CONCENTRATION OF

SLURRY PUMPED THROUGH A PIPELINE FIELD OF THE INVENTION

The present invention relates to systems for transporting slurry through pipelines.

BACKGROUND TO THE INVENTION

Fine particle mineral slurries are commonly transported by pipeline in the mineral and coal industries. Normally it is preferred to pump at as high a solids concentration as possible to minimise water usage. For typical fine particle slurries the maximum concentration is generally limited by the onset of laminar flow which is related to the rheology (viscosity) of the slurry. Turbulent flow is required to be maintained in the pipeline to prevent coarser particles settling and causing unstable operation and increasing pump pressure over time.

It is common to control slurry concentration by using a nuclear density meter to measure slurry density and to set the density set point as high as possible within the pumping capability of the system. Control based on density measurement is satisfactory when the rheology of the slurry does not vary for any particular concentration. However, there are many cases where, because of differing ore types, the rheology of the slurry can vary considerably even though the slurry density remains constant. In these cases the density set point must be set sufficiently low to accommodate the highest rheology ore type, meaning that unnecessary water is added to the lower rheology slurries.

It is an object of the present invention to provide a system which optimises the solids concentration of slurry flow through a pipeline with reduced water wastage.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided a method for controlling slurry flowing through a pipeline, the method including the steps of: providing dense slurry into a sump; adding water into the sump to dilute the dense slurry; pumping the diluted slurry from the sump to a main pipeline; providing a section of testing pipeline in-line with the main pipeline;

measuring parameters relating to a turbulence parameter Y of the diluted slurry flowing through the test pipeline; determining a current turbulence parameter Y and comparing the current turbulence parameter Y with a predetermined maximum threshold value; wherein, if the current turbulence parameter Y is greater than the predetermined maximum threshold value, increasing the volume of water being added to the sump until the current turbulence parameter falls to a predetermined minimum value; otherwise, if the current turbulence parameter Y is less than the predetermined maximum threshold value, decreasing the volume of water being added to the sump.

Preferably, the section of testing pipeline has a larger internal cross- section than the main pipeline.

In exemplary embodiments, the measured parameters include: the differential pressure along the length of the section of testing pipeline; the density of slurry entering the section of testing pipeline; and the volumetric flow rate of slurry entering the section of testing pipeline.

In preferred embodiments, the steps of increasing or decreasing the volume of water being added to the sump includes adjusting a flow valve in the water feed pipe. This adjustment may be conducted in periodic increments. Preferably, the rate of diluted slurry being pumped from the sump is adjustable to maintain the slurry level in the sump below a selected level. Ideally, this adjustment is responsive to the output of a level detector in the sump.

According to a further aspect of the present invention there is provided a system for controlling slurry flowing through a pipeline, the system including: a sump, into which dense slurry and diluting water are added; one or more pumps for pumping diluted slurry from the sump to a main pipeline; a section of testing pipeline provided in-line with the main pipeline; a plurality of detectors for measuring parameters relating to a turbulence parameter Y of the diluted slurry flowing through the test pipeline; a controller arranged to receive the outputs from the detectors, the controller being programmed to determine a current turbulence parameter Y and

compare the current turbulence parameter Y with a predetermined maximum threshold value; wherein, if the current turbulence parameter Y is greater than the predetermined maximum threshold value, the controller causes an increase in the volume of water being added to the sump until the current turbulence parameter falls to a predetermined minimum value; otherwise, if the current turbulence parameter Y is less than the predetermined maximum threshold value, the controller causes a decrease in the volume of water being added to the sump.

The present invention advantageously provides a slurry pipeline system which controls water usage to keep the same to a minimum and maximise the solids concentration of slurry delivered by the pipeline. BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the present invention will now be described with reference to the accompanying drawing, in which: Fig. 1 illustrates a schematic diagram of the components of a slurry pipeline system. DESCRIPTION OF PREFERRED EMBODIMENT

As basis for the present invention, there is practical use made of a so- called turbulence parameter Y. The parameter Y is given by the equation:

Pressure Drop across a Measurement Length

SG ^a x Q "

where SG is specific gravity/density of the slurry and is related to the solids concentration of the slurry

Q is volumetric flow rate of slurry.

The exponents a and b will vary slightly between applications but typically a = 1.3 and b = 2.

It has been found that, under required homogeneous turbulent flow conditions for slurry flowing through a particular pipeline system, the turbulence

parameter Y is essentially constant over a normal range of flow rates, slurry densities and slurry rheology. It should be appreciated that this constant parameter can vary between different pipeline systems, hence a new pipeline system needs to undergo testing and analysis to determine its own normal turbulence parameter. Under undesirable conditions, such as when there is a transition from turbulent flow to laminar flow or when the flow rate falls below a deposition velocity (whereby coarse particles begin to settle), there is a marked increase in the turbulence parameter Y.

Fig. 1 illustrates a schematic representation of a slurry control system. High density slurry discharges from a slurry thickener 6 and is pumped via a thickener underflow pump 7 into a sump 8. Water is fed into the sump via a feedpipe to dilute the slurry in the sump 8. The volume of water flowing into the sump is controlled by a flow valve 12.

Main slurry pumps 9 pump the diluted slurry to a main transfer pipeline 11. Figure 1 shows two main slurry pumps in series. It will be appreciated that the number of pumps can vary depending on requirements for the actual pipeline system.

In-line with the main pipeline 11 there is provided a section of testing pipeline 1. The diluted slurry is caused to flow through the testing pipeline 1 to the main pipeline 11 from the main pumps 9.

A density meter 2, for example a nuclear density gauge, measures the specific gravity/density of slurry entering the testing pipeline 1. A flowmeter 3, for example a magnetic flowmeter, measures the volumetric flow rate of slurry entering the testing pipeline 1. A differential pressure meter 4 measures the differential pressure over the length of testing pipeline 1.

A controller 5 receives signals indicative of the measured outputs of the density meter 2, flowmeter 3 and differential pressure meter 4. Based on the received signals, the controller 5 is programmed to calculate a current turbulence parameter Y using the equation noted above.

The controller 5 compares the current turbulence parameter Y with a predetermined maximum threshold value. This maximum threshold value is selected upon the basis of the onset of undesirable flow conditions in the testing

pipeline 1. Practically, such thresholds would be determined by conducting tests and analysis of the particular pumping system after initial installation. As discussed before, undesirable conditions include the presence of laminar flow (in the case of fine particle slurries) and the deposition of a bed of slurry particles (in the case of coarse slurry particles) in the testing pipeline 1. Typically, the maximum threshold value is approximately 10% above a turbulence parameter indicative of a homogeneous turbulent flow condition in the testing pipeline 1.

Ideally, the testing pipeline 1 has a larger internal cross-sectional area than the main pipeline 11. Due to the larger cross-section, the flow velocity in the testing pipeline 1 is lower than the main pipeline 11. Hence, while a transition to laminar flow may be present in the testing pipeline 1 ; required turbulent flow will remain in the main pipeline 11. Similarly, in the case of coarse particle slurries, as flow velocity reduces, deposition will initially occur in the testing pipeline 1 before the main pipeline. In the case of deposition, a bed of particles will begin to form in the testing pipeline, thereby increasing the pressure gradient. In each case, the onset of undesirable conditions in the testing pipeline 1 results in an increase in the current turbulence parameter Y.

The controller 5, on the basis of the current turbulence parameter Y and the comparison with the predetermined maximum threshold value, sends a control signal to the flow valve 12 to adjust the volume of water being added to the sump 8.

An example of the system operation will now be described. The controller 5 slowly, but continuously, increases the slurry density, i.e. solids concentration, by decreasing the volume of water being added to the sump 8. The increase in slurry density may be, for example, 0.01 SG point every 5 minutes. Eventually the onset of laminar flow and/or particle deposition will occur in the testing pipeline 1 and the current turbulence parameter Y will start to rise. As discussed before, at this time, turbulent flow will still exist in the main pipeline 11. When the current turbulence parameter Y reaches the maximum threshold value, the controller 5 starts to decrease the slurry density at a set rate by increasing the volume of water being added to the sump 8. This decrease in slurry density is maintained until the current turbulence parameter Y drops back to a predetermined minimum or normal turbulence value. Once this condition is

achieved then, after a set period of time, the controller 5 again starts increasing the slurry density, thereby repeating the process.

It will be appreciated that the above process, in fact, attempts to reduce water usage thereby increasing slurry density and maximising the solids concentration of the slurry flowing through the main pipeline 11.

The system additionally includes a level detector 10 in the sump 8. The output of the level detector 10 is used in a separate control loop with the controller 5 and the main pumps 9 to control the pumping speed of the pumps 9 to maintain the sump level below a selected threshold. As such, the pump speed is varied to vary the diluted slurry flow rate to suit input flow into the sump 8.

The length of testing pipeline 1 will depend upon the internal cross-section employed. However, it may be typically around 20m to 100m. Conveniently, the testing pipeline 1 will form the initial portion of the pipeline system with the main pipeline 11 continuing on from the end of the testing pipeline 1. However, conceivably, the testing pipeline 1 could be provided further downstream of the pipeline system. While the testing pipeline 1 has been schematically illustrated as a straight section, it may be provided in different configurations. For example, it may be advantageous to provide the testing pipeline 1 in the form of a loop, thereby bringing the ends of the testing pipeline physically close together. This loop configuration would greater facilitate the arrangement of the differential pressure meter 4.

While the present invention has been described with respect to specific embodiments, it will be appreciated that various modifications and changes could be made.