WO2012035483A2

WO2012035483A2 - Monitoring of slurry flow conditions in a pipeline

Info

Publication number: WO2012035483A2
Application number: PCT/IB2011/053978
Authority: WO
Inventors: Hartmut Johannes Ilgner; João Manuel Rodrigues Vilela FELIX
Original assignee: Csir; Stoner (Proprietary) Limited; Paterson & Cooke Consulting Engineers (Proprietary) Limited
Priority date: 2010-09-15
Filing date: 2011-09-12
Publication date: 2012-03-22
Also published as: WO2012035483A3

Abstract

The invention concerns a method for monitoring slurry flow conditions in a non-vertical pipeline having a pipeline wall. The method comprises the steps of mounting a heater and a heat sensor externally on the wall, activating the heater to generate heat and deriving an indication of slurry flow conditions prevailing at the invert of the pipeline from the power supplied to the heater and/or from the thermal response of the heat sensor. The heater and heat sensor are mounted at the invert of the pipeline and in proximity to one another with the heater and heat sensor in thermal communication with the interior of the pipeline through the wall. In the preferred embodiment variable power is supplied to the heater such that a predetermined temperature differential is maintained between a reference temperature and a temperature sensed at the invert by the heat sensor. The required indication of slurry flow conditions prevailing at the invert is then obtained by monitoring the level of power supplied to the heater. The invention also concerns an apparatus for monitoring slurry flow conditions in a pipeline.

Description

"MONITORING OF SLURRY FLOW CONDITIONS IN A PIPELINE"

BACKGROUND TO THE INVENTION

THIS invention relates to the monitoring of slurry flow conditions in a pipeline.

In this specification the term "slurry" is used for convenience to refer to solid/liquid mixtures, including aqueous mixtures, in thickened or unthickened form, including, but not limited to, tailings, pastes, sludges (which may include biologically active solid ingredients) as well as industrial wastes from nuclear power or other operations, and oil sands.

In one application, the invention may be used to monitor slurry flow conditions in a pipeline provided to convey the slurry from a mineral processing plant to a slurry disposal dam or other site. By way of example, in the mining and mineral extraction industry, thickened slurry or tailings is pumped through pipelines from mineral extraction plants to tailings dams.

It is well established that the most economical operating condition for a given slurry is just above the critical deposition velocity. This critical velocity varies from case to case and is dependent on a number of different factors including concentration or density of the slurry, composition of the slurry, particle size distribution in the slurry, and so on. At velocities below the deposition velocity, solid particles in the slurry tend to settle in the pipeline to form either a sliding or stationary bed at the invert of the pipe section, which could in turn lead to pipeline blockage. It is also recognized that operating costs will be increased if the slurry is pumped through the pipeline at a velocity substantially in excess of the critical deposition velocity, because more power will be consumed and there will be greater frictional losses and pipeline wear. Similarly if the concentration or density of the slurry is reduced by increasing the water content in order to decrease the critical deposition velocity, there may be an undesirable wastage of water and/or a costly requirement to pump water back from the disposal site.

If the slurry contains larger particles, they will tend to settle out first and this may lead to undesired, unstable operating conditions. Therefore despite the abovementioned disadvantages and increased operating costs associated with higher pumping velocities, slurry pumping systems are generally designed to operate at a safety margin above the critical deposition velocity to ensure operational stability and avoid pipeline blockages.

In reality, the slurry ultrafines content in the particle size distribution, the maximum particle size and the mineral composition may vary considerably during operation of a slurry pumping system. It would be beneficial if the settling of particles during pipeline flow could be detected by means of instrumentation. In an optimal system the flow velocity should be controlled continuously to be at an appropriately low value while the concentration of the slurry is maintained at an appropriately high value.

Numerous attempts have been made with limited success in the past to achieve on-line optimisation of slurry pumping systems. Examples of such previous attempts, and the associated disadvantages, have been described in some detail in "Innovative Flow Control Philosophy, Based on Novel in- situ Measurements to Reduce Energy Consumption for Tailings Pipelines" by llgner HJ (proc. 16^th Int. Conf. On Hydrotransport, BHR Group, Santiago, Chile).

More recently WO 2006/111832 has described a slurry flow control system in which a thermal sensor is mounted in the pipeline. A sensing face of the sensor is arranged flush at the pipe invert and exposed to the slurry. The sensor is calibrated to provide signals related to the velocity of the slurry at the invert and the slurry flow regime is then controlled on the basis of the signals output by the sensor. Difficulties have however been encountered in protecting the sensing face against slurry- induced abrasive wear which detrimentally affects the efficacy of the sensor.

SUMMARY OF THE INVENTION

According to the invention there is provided a method for monitoring slurry flow conditions in a non-vertical pipeline having a pipeline wall, the method comprising mounting a heater and a heat sensor externally on the wall, at the invert of the pipeline and in proximity to one another with the heater and heat sensor in thermal communication with the interior of the pipeline through the wall, activating the heater to generate heat and deriving an indication of slurry flow conditions prevailing at the invert of the pipeline from the power supplied to the heater and/or from the thermal response of the sensor.

The fact that the heater and heat sensor communicate thermally with the interior of the pipeline, i.e. with slurry inside the pipeline, through the wall of the pipe, means that these components are not in physical contact with the slurry and so are not exposed to abrasive wear caused by the slurry.

In one embodiment, variable power is supplied to the heater such that a predetermined temperature differential is maintained between a reference temperature and a temperature sensed at the invert by the heat sensor, and the required indication is obtained by monitoring the level of power supplied to the heater. The reference temperature may for example be sensed by a further externally mounted heat sensor spaced from the abovementioned heat sensor. In another embodiment, constant power is supplied to the heater and the required indication is obtained from temperature variations at the invert as sensed by the heat sensor.

The heater and heat sensor can be located in a heat sink on the wall at the invert. The heat sink may be defined by a recess in a thickened region of the wall. Alternatively the heat sink may be defined by an enclosure fixed to the wall. The enclosure may comprise an enclosed housing accommodating preassembled transducer components including heating and sensing components. The housing may be of heat-transmitting material and may be fixed externally to the pipeline wall in a manner permitting thermal communication between the transducer components and the interior of the pipeline through the pipeline wall. The housing may for example be fixed to the pipeline wall by means of thermally conductive adhesive.

The heat sensor may be located upstream of the heater in the heat sink. Alternatively the heater and heat sensor may be arranged in an overlying relationship.

The method summarised above may be used in a slurry flow control system in which one or more parameters of a pumping system operated to pump slurry through the pipeline may be adjusted to optimise the flow of the slurry and, for instance, avoid the creation of stationary bed conditions at the invert of the pipeline.

The method of the invention may also include the steps of mounting a further heater and heat sensor externally on the wall at at least one position around the circumference of the pipeline away from the invert and performing similar heating and temperature sensing activities at each of the other positions in order to derive indications of slurry flow conditions prevailing at each of the other positions. Further according to the invention there is provided apparatus for monitoring slurry flow conditions in a pipeline having a wall, the apparatus comprising a heater and a heat sensor, means for mounting the heater and heat sensor externally and in proximity to one another on the wall, at least at the invert of the pipeline, such that the heater and heat sensor are in thermal communication with the interior of the pipeline through the wall, means for powering the heater to generate heat and means for deriving an indication of slurry flow conditions prevailing at the invert of the pipeline from the power supplied to the heater and/or from the thermal response of the heat sensor.

Still further according to the invention there is provided a slurry flow control apparatus for controlling slurry flow in a pipeline wherein the slurry is pumped through the pipeline by a pumping system, the apparatus comprising a monitoring apparatus as summarised above and means for adjusting one or more operating parameters of the pumping system in order to avoid the creation of stationary or sliding bed conditions at the invert of the pipeline.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying diagrammatic drawings in which:

Figures 1(a) and 1(b) show a first embodiment of the invention in respective transverse and longitudinal cross- sectional views;

Figures 2(a) and 2(b) show a second embodiment of the invention in respective transverse and longitudinal cross- sectional views; Figures 3(a) to 3(c) show a third embodiment of the invention in a transverse cross-sectional view, a longitudinal cross-sectional view and a bottom view respectively;

Figure 4 illustrates a method according to the invention; and

Figures 5(a) and 5(b) illustrate a fourth embodiment of the invention.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Figures 1 (a) and 1 (b) show a non-vertical pipeline 10 having a wall 12. A region 14 of the wall 12 has an increased thickness compared to the rest of the wall. A recess 16 is formed externally in the thickened region 14 at the invert of the pipeline, i.e. at the lowest point thereof. The depth of the recess is such that the remaining wall thickness at the base of the recess, i.e. in the wall region designated 18, is typically the same as that in the remainder of the pipeline, so the pressure rating of the pipeline is not reduced in any way by the presence of the recess. Mounted in the recess 16 is an electrical heater 20 and a heat sensor 22 on which the heater is located.

The embodiment of Figures 1a and b includes a second recess 24, also formed in the thickened region 14 of the wall 12. The recess 24 is spaced from the recess 16 and is located at a high point in the pipeline cross- section. The depth of the recess 24 is the same as that of the recess 16. A reference heat sensor 26 is located in the recess 24 as shown.

In operation slurry, for example tailings generated in a mining environment by mineral processing operations, is pumped or is otherwise caused to flow, for example under gravity, through the pipeline 10.

The thickened region 14 effectively forms a heat sink around the recess 16 at the invert of the pipeline. This heat sink concentrates heat generated by the heater 20 into the proximity of the recess. At least some of the heat IB2011/053978

7

generated by the heater is taken up and removed by slurry flowing past. Accordingly the instantaneous heat level or temperature sensed by the heat sensor 22 at any given moment in time is dependent on the prevailing slurry conditions, for example the slurry density or concentration, slurry composition and flow velocity.

It will be noted that the heating and sensing operations are carried out without either the heater or the heat sensor being exposed to the slurry so there can be no slurry-induced abrasive damage to either of these components. In each case the components are separated from the slurry by the wall thickness 18. Similarly the reference heat sensor 26 is out of contact with the slurry and is separated from the slurr by the wall thickness 30.

Figure 4 illustrates how the components described above can be used in a method according to one embodiment of the invention.

In this embodiment, the heater 20 is supplied with sufficient power to enable it to maintain at all times a predetermined differential, for example +10°C, between a temperature sensed by the sensor 22 and a reference temperature sensed by the sensor 26.

In this example, if the instantaneous reference temperature sensed by the sensor 26 is 20°C, the power supply to the heater 20 should be at a level for the sensor 22 to sense a temperature of 30°C at the invert.

The numeral 32 indicates a power supply unit capable of supplying variable power to the heater 20. The unit 32 is controlled by a PID (proportional integral derivative) controller 34. Signals output by the sensors 22 and 26 are fed to the PID controller which controls the supply of power from the unit 32 to the heater 20 such that the heater generates sufficient heat for the sensor 22 to sense an instantaneous temperature of 30°C.

As slurry conditions, for example slurry velocity, composition, density or concentration, vary with time, the power supply to the heater 20 is varied continuously by the PID controller in order to maintain, the required 10^DC temperature differential. The varying supply of electrical power to the heater which is necessary to maintain the predetermined temperature differential is therefore related to the rate at which heat is removed by the slurry flow in the vicinity of the heater 20 and sensor 22, and is indicative of the instantaneous slurry conditions prevailing at the invert of the pipeline at each point in time. By monitoring the power supplied to the heater it is accordingly possible to monitor the prevailing slurry conditions.

Based on the indications of instantaneous slurry conditions which are derived it is then possible to vary relevant parameters, for example slurry velocity, concentration and so on in order to maintain optimal operating parameters.

In general the described apparatus may be used to ensure that the slurry velocity is maintained at a level slightly above the critical deposition velocity.

In a simple arrangement, however, the apparatus may be used simply to detect the onset of undesirable stationary or sliding bed conditions at the invert which could in time lead to a pipeline blockage.

For example if it is found that there is a certain reduced heating power requirement to maintain the predetermined temperature differential this could be taken as indicative that slurry flow at the invert has slowed down and that the onset of the undesirable stationary or sliding bed condition is imminent or has occurred. When such a condition is detected, the slurry may for example be pumped at a higher velocity or it may be diluted further with water to avoid possible pipeline blockage. Variation of the pumping velocity and/or dilution can be carried out automatically in response to the sensed conditions.

The numeral 40 in Figure 1 (a) generally indicates an arrangement of recess, heater and heat sensor similar to that provided at the invert of the pipe. The arrangement 40 will typically be monitored in exactly the same way as the arrangement at the invert in order to provide indications of the slurry conditions at a position above the invert.

Similar arrangements can be provided at various positions spaced around the pipe circumference. If for example the indications derived from the monitoring activities at the invert are indicative of the formation of a stationary bed condition, the further indications derived from monitoring activities at higher elevations could be used to ascertain the depth of the stationary bed, and this information could also be useful in optimising the pumping parameters. Such further arrangement(s), located away from the invert, could also be used simply to provide an indication of whether slurry is flowing or not flowing in the pipeline.

It is envisaged that an existing slurry pipeline could be retrofitted with apparatus such as that seen in Figure 1 by installing in the pipeline a short pipe section with a thickened wall region 14 formed with the necessary recess(es).

Figures 2(a) and 2(b) show another embodiment in which the recess 16 is again formed in a thickened region 14 of the wall 12 of the pipeline 10. In this case, the heater 20 is mounted at an upstream end of the recess 16 and heat sensors 22.1 and 22.2 are mounted in the recess at different distances from the heater.

In this case, an indication of the slurry flow conditions at the invert can be obtained by monitoring the heating power requirement to maintain a predetermined differential between temperatures sensed by the respective sensors 22.1 and 22.2. In this regard it will be understood that the sensor 22.1 will sense a temperature higher than that sensed by the sensor 22.2 because it is closer to the heater 20.

Figures 3(a) to 3(c) illustrate yet another embodiment in which the wall 12 of the pipeline is not thickened at all. Instead the heat sink is provided by thermally bonding a heat sink structure 50 to the existing pipe wall and mounting heating and sensing components 20 and 22 in the structure 50. As in the previous embodiments, the heat sink serves to concentrate the applied heat in the zone where the sensor 22 senses temperature. A power supply apparatus is provided to control the supply of heating power to the heater 20 in order to maintain the heat level or temperature sensed by the sensor 22 at a constant level. Alternatively, this configuration could be used in a system such as that illustrated in Figure 4, with the heating power being varied to ensure that there is a predetermined differential between the temperature sensed by the sensor 22 and that sensed by a reference sensor. In either case, the heating power will be indicative of the instantaneous slurry flow conditions.

In practice, arrangements such as those described above can be provided at various positions along the length of a pipeline, further facilitating optimisation of the slurry flow regime taking into consideration the prevailing conditions at different positions along the pipeline.

In the examples described above, indications of the slurry flow conditions at the invert of the pipeline are obtained by monitoring the heating power requirement to maintain a predetermined temperature or a predetermined temperature differential between spaced apart locations. In other embodiments of the invention, it would be possible to supply the heater with constant power and to monitor instantaneous temperature variations attributable to varying slurry flow conditions. For example, in an arrangement such as that in Figures 2(a) and 2(b), the onset of a stationary bed condition would be evidenced by a diminishing differential between the temperatures sensed by the sensors 22.1 and 22.2. In an arrangement such as that in Figures 1 (a) and 1 (b), the onset of such a condition would be evidenced by a build-up of heat in the vicinity of the heater since this would indicate that such heat is not being removed by flowing slurry.

Figures 5(a) and 5(b) illustrate another embodiment of the invention which has similarities to the embodiment illustrated in Figures 3(a) to 3(c). In this case the open heat sink structure 50 is replaced by an enclosed housing 60 in which a heater and one or more sensors are permanently mounted such that the housing and components therein form a unitary, preassembled transducer, with the housing itself serves as a heat sink for the heating and sensing components.

In a case where the pipeline is made of steel, the housing could for example be of aluminium. In order to ensure proper thermal communication between the heating and sensing components in the housing 60, the housing is bonded to the external surface of the pipeline by means of a suitable, thermally conductive adhesive 62.

As in previous embodiments, a reference heating and sensing operation, or merely a sensing operation, can be carried out a higher level in the pipeline by means of a second transducer including an enclosed housing 64, bonded in thermally conductive manner to the wall of the pipeline by means of a thermally conductive adhesive 66.

The difference in outputs from the transducer components in the housings 60 and 64 can be used to determine if settlement has occurred, i.e. if stationary or sliding bed conditions are imminent or have taken place.

At full flow in the pipeline, both transducers will sense the removal of heat by the slurry flowing in the pipeline. Any difference between their respective outputs is stored as a reference value. As soon as slurry settlement commences, the levels of heat removal at the invert and higher up in the pipeline will differ, and the difference between the transducer inputs will vary. An alarm may be triggered if this difference varies from the reference value by more than a predetermined amount. In response to the alarm, the slurry flow velocity may be increased and/or the slurry dilution may be varied in order to avoid or eliminate the settlement condition. The velocity and/or dilution variations may be carried out automatically.

For reasons described previously, one or more further transducers could be included at other levels around the circumference of the pipeline and/or along the length of the pipeline. In each case, including those described earlier, the higher level sensors could be used to provide an indication of flow conditions, or conditions of no flow, at each of the higher levels.

It will be understood that the control technique just described could equally well be implemented in the earlier embodiments.

A major advantage of the embodiment of Figures 5(a) and 5(b) is the fact that it is a simple matter to retrofit one or more of the preassembled transducers to the pipeline wall at any desired location(s) along the length of the pipeline.

Claims

1.

A method for monitoring slurry flow conditions in a non-vertical pipeline having a pipeline wall, the method comprising the steps of mounting a heater and a heat sensor externally on the wall, at the invert of the pipeline and in proximity to one another with the heater and heat sensor in thermal communication with the interior of the pipeline through the wall, activating the heater to generate heat and deriving an indication of slurry flow conditions prevailing at the invert of the pipeline from the power supplied to the heater and/or from the thermal response of the heat sensor.

2.

A method according to claim 1 wherein variable power is supplied to the heater such that a predetermined temperature differential is maintained between a reference temperature and a temperature sensed at the invert by the heat sensor, and the required indication of slurry flow conditions prevailing at the invert is obtained by monitoring the level of power supplied to the heater.

3.

A method according to claim 2 wherein the reference temperature is sensed by a further externally mounted heat sensor spaced from the first- mentioned heat sensor at a position above the invert.

4.

A method according to claim 1 wherein constant power is supplied to the heater and the required indication of slurry flow conditions prevailing at the invert is obtained from temperature variations at the invert as sensed by the heat sensor.

5.

A method according to any one of the preceding claims wherein the heater and heat sensor are located in a heat sink on the wall at the invert.

6·

A method according to claim 5 wherein the heat sink is defined by a recess in a thickened region of the wall.

7.

A method according to claim 5 wherein the heat sink is provided by an enclosure fixed externally to the wall.

8.

A method according to claim 7 wherein the enclosure comprises an enclosed housing accommodating preassembled transducer components including heating and sensing components.

9.

A method according to either one of claims 7 or 8 wherein the housing is of heat transmitting material and is fixed externally to the pipeline wall in a manner permitting thermal communication between the transducer components and the interior of the pipeline through the pipeline wall.

10.

A method according to claim 9 wherein the housing is fixed to the pipeline wall by means of thermally conductive adhesive.

11.

A method according to any one of claims 5 to 10 wherein the heat sensor is located upstream of the heater in the heat sink.

12.

A method according to any one of claims 5 to 10 wherein the heater and heat sensor are arranged in an overlying relationship in the heat sink.

14.

A method according to any one of the preceding claims comprising the step of mounting a further heater and heat sensor externally on the wall of the pipeline at at least one position around the circumference of the pipeline spaced away from the invert and performing similar heating and temperature sensing activities at each of such other positions in order to derive indications of slurry flow conditions prevailing at each of such other positions.

15.

A slurry flow control method for controlling the flow of slurry pumped in a pipeline by a pumping system, the slurry flow control method comprising the steps of using a method according to any one of the preceding claims to monitor slurry flow conditions at least at an invert of the pipeline and adjusting one or more operating parameters of the pumping system in order to avoid the creation of stationary or sliding bed conditions at the invert of the pipeline.

16.

Apparatus for monitoring slurry flow conditions in a pipeline having a wall, the apparatus comprising a heater and a heat sensor, means for mounting the heater and heat sensor externally and in proximity to one another on the wall, at least at the invert of the pipeline, such that the heater and heat sensor are in thermal communication with the interior of the pipeline through the wall, means for powering the heater to generate heat and means for deriving an indication of slurry flow conditions prevailing at the invert of the pipeline from the power supplied to the heater and/or from the thermal response of the heat sensor.

17.

A slurry flow control apparatus for controlling slurry flow in a pipeline wherein the slurr is pumped through the pipeline by a pumping system, the apparatus comprising a monitoring apparatus according to claim 6 for monitoring slurry flow conditions at the invert of the pipeline and means for adjusting one or more operating parameters of the pumping system in order to avoid the creation of stationary or sliding bed conditions at the invert of the pipeline.