AU2016228931B2

AU2016228931B2 - Online sampling device

Info

Publication number: AU2016228931B2
Application number: AU2016228931A
Authority: AU
Inventors: Simon MCCASKIE
Original assignee: Alcoa of Australia Ltd
Current assignee: Alcoa of Australia Ltd
Priority date: 2015-03-06
Filing date: 2016-03-04
Publication date: 2020-07-09
Anticipated expiration: 2036-03-04
Also published as: CN107615038B; CN107615038A; WO2016141403A1; BR112017018483A2; BR112017018483B1; AU2016228931A1; AU2020250295A1

Abstract

An online sampling device comprising: a sampler; an analyser; a delay member; and ancillary equipment, wherein the delay member is downstream from the analyser and is adapted to inhibit exposure of a sample to the ancillary equipment and the ancillary equipment employs a sample removal fluid to remove sample from the device.

Description

"Online Sampling Device"

FIELD OF THE INVENTION

[0001] The present invention relates to an online sampling device. More particularly, the present invention is intended for the online sampling and analysis of a process stream, such as a process stream from the Bayer Process.

BACKGROUND ART

[0002] In many industrial applications, online sampling methods are employed to monitor the properties of a process stream in real-time. Online sampling devices typically comprise an analyser and ancillary equipment, wherein the analyser conducts chemical analysis on a sample and the ancillary equipment, being downstream from the analyser, supports the operation of the online sampling device. Various types of analysers are used for the online sampling of process stream and these include pH meters, conductivity meters and turbidity meters. The ancillary equipment may include valves, sensors and siphons.

[0003] The Bayer process involves the digestion of bauxite ore in a caustic solution usually at high temperatures and elevated pressure. The caustic solution dissolves the major aluminum bearing compounds (aluminium trihydroxide and aluminium oxy- hydroxides), forming a slurry containing the dissolved compounds in Bayer liquor and insoluble impurities. The slurry is cooled and the insoluble impurities separated. The remaining dissolved compounds are passed to a precipitation stage, wherein aluminium is recovered from the Bayer liquor by precipitation of an alumina bearing phase usually aluminium trihydroxide (AI(OH)₃). The precipitate is calcined to recover alumina as a product.

[0004] In the Bayer process, online sampling methods are employed in order to control the process streams to the desired specifications. Furthermore, periodic online analysis of the process stream at various locations within the operation can be used to control the process so as to maximise the yield of alumina or other products.

[0005] A problem encountered when using online sampling devices lies in the risk of exposure of ancillary equipment to the sample being measured. Such exposure may affect the internal working components of the equipment to the extent that they can increase the operating and/or maintenance costs, adversely affect the on-line availability or cause failure of the equipment. For example, the on-line analysis of liquor in a Bayer process operation may be complicated because of the high alkalinity, ionic strength, alumina supersaturation, temperature and total solids content that occur in certain Bayer process streams. As such, the exposure of ancillary equipment, such as tubing, pressure sensors and valves, to the Bayer process stream is undesirable given that interaction with these streams can prevent the equipment from working efficiently.

[0006] The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. This discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0007] Each document, reference, patent application or patent cited in this text is expressly incorporated herein in their entirety by reference, which means that it should be read and considered by the reader as part of this text. That the document, reference, patent application or patent cited in this text is not repeated in this text is merely for reasons of conciseness.

[0008] Throughout the specification and claims, unless the context requires otherwise, the word "comprise" or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

DISCLOSURE OF THE INVENTION

[0009] In accordance with the present invention there is provided an online sampling device comprising: a sampler; an analyser; a delay member; and ancillary equipment, wherein the delay member is downstream from the analyser and is adapted to inhibit exposure of a sample to the ancillary equipment and the ancillary equipment employs a sample removal fluid to remove sample from the device.

[0010] The solutions where the device of the invention may be employed are often highly corrosive and saturated solutions. These types of solutions often demonstrate a propensity to auto precipitate. It will be appreciated that such solutions could precipitate inside the device of the invention. For example, precipitation could occur in the sampler, the analyser or the delay member. Preferably, the velocity of the sample removal fluid in the device is sufficient to remove any particles that may have precipitated in the device.

[001 1] It will be appreciated that the sample removal fluid contacts at least a portion of the ancillary equipment and as such, should not have highly corrosive properties. The sample removal fluid may be any solution capable of removing sample without causing undue damage to the ancillary equipment. In one form of the invention, the sample removal fluid is an aqueous solution. Preferably, the sample removal fluid is water. It will be appreciated that industrial processes may not have water available. In such circumstances, the cleanest water available should be sourced. For example, in the context of the Bayer Process, condensate water would be appropriate.

[0012] The online sampling device may further comprise means to clean the analyser. In the context of the present specification, the term clean the analyser may include removal of at least a portion of material that has precipitated on or in, or otherwise fouled the analyser. Said analyser cleaning means may be provided in the form of a cleaning fluid inlet. Preferably, the cleaning fluid inlet is located near the analyser. Depending on the nature of the precipitate, the cleaning fluid may be an acidic solution or an alkaline solution. Preferably, the cleaning fluid is a strong acid or a strong base.

[0013] In a specific form of the invention, where the sample is a Bayer liquor, the cleaning solution is preferably a strong acid such as phosphoric acid or sulfuric acid.

[0014] The delay member may be provided in the form of a tube.

[0015] The term tube would be understood to include a pipe, hose or any other suitable elongate member.

[0016] The delay member may be straight, bent, stacked or coiled. [0017] Preferably, the delay member is coiled.

[0018] It will be appreciated that the length to diameter ratio of the delay member will vary depending on the properties of the sample to be analysed. For example, sample properties such as viscosity, temperature, density, pressure and total solids content can influence the flow of the sample through the delay member. Hence, the length to diameter ratio of the delay member will differ in each application, but may be readily ascertained by a person of ordinary skill in the art having reference to the parameters of the present invention.

[0019] Preferably, the delay member has a length between 5 to 15 metres.

[0020] Preferably, the delay member has a diameter between 5 to 25 millimetres.

[0021] Preferably, the delay member has a length to diameter ratio of between 500 and 2000.

[0022] Advantageously, the high length to diameter ratio reduces the likelihood of exposure of the ancillary equipment to a sample.

[0023] Advantageously, the delay member has a fixed volume. Advantageously, the fixed volume calibration of the delay member as discussed above.

[0024] It will be appreciated that the composition of the delay member will be influenced by the properties of the sample. The delay member is preferably made of a material suitable for handling samples that may damage the ancillary equipment such as samples with high acidity, alkalinity, ionic strength, temperature, propensity to scale and total solids content, for example. Chemically resistant polymers such as fluoropolymers may be appropriate for many applications. Particular examples include fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) and perfluoroalkoxy alkanes (PFA). Alternatively, the delay member may be made of a material such as such as Nylon®, polyethylene, and metals, such as stainless steel.

[0025] Preferably, the delay member is made of perfluoroalkoxy alkanes (PFA).

[0026] In one form of the invention, the delay member is internally coated to reduce scale formation. Such coating may be particularly advantageous when sampling fluids with a propensity to precipitate such as Bayer liquors. In one form of the invention, the coating is electroless nickel. [0027] In one form of the invention, the sampler is provided in the form of a sample tube for delivery of the sample from a process stream to the analyser.

[0028] It will be appreciated that the composition of the sample tube will be influenced by the properties of the sample. The sample tube is preferably made of a material suitable for handling samples having a high acidity, alkalinity, ionic strength, temperature, propensity to scale and total solids content, for example. Chemically resistant polymers such as fluoropolymers may be appropriate for many applications. Particular examples include fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) and perfluoroalkoxy alkanes (PFA). Alternatively, the sample tube may be made of a material such as such as Nylon®, polyethylene, and metals, such as stainless steel.

[0029] In one form of the invention, the sample tube is internally coated to reduce scale formation.

[0030] Preferably, the online sampling device further comprises an outlet member in fluid communication with the delay member and the analyser.

[0031] Preferably, the outlet member is in the form of an outlet tube.

[0032] It will be appreciated that the composition of the outlet tube will be influenced by the properties of the sample. The outlet tube is preferably made of a material suitable for handling samples having a high acidity, alkalinity, ionic strength, temperature, propensity to scale and total solids content, for example. Chemically resistant polymers such as fluoropolymers may be appropriate for many applications. Particular examples include fluorinated ethylene propylene (FEP), polytetrafluoroethylene (PTFE) and perfluoroalkoxy alkanes (PFA). Alternatively, the outlet tube may be made of a material such as such as Nylon®, polyethylene, and metals, such as stainless steel.

[0033] In one form of the invention, the outlet member is internally coated to reduce scale formation.

[0034] The analyser may be a pH meter, conductivity meter, turbidity meter, spectrometer, spectrophotomer, fluorometer, sound velocity meter, density meter or any other meter or instrument known in the art for measuring the properties of a sample.

[0035] In one form of the invention the sample is a Bayer process liquor. [0036] The term Bayer process liquor will be understood to include any fluid that has run through at least a portion of a Bayer process, including, but not limited to, spent liquor, green liquor, digestion liquor, precipitation liquor, process lake water, washer overflow liquor and underflow slurries.

[0037] In accordance with the present invention there is provided a method for taking a sample from a process stream, the method comprising the steps of: withdrawing a sample from a process stream such that the sample enters the sampler, the analyser and the delay member; ceasing flow of the sample in the online sampling device; flushing the online sampling device with a fluid, thereby returning the sample into the process stream. BRIEF DESCRIPTION OF DRAWINGS

[0038] The present invention will now be described, by way of example only, with reference to the following figures in which:

Figure 1 is a schematic diagram of an online sampling device, in accordance with a first embodiment of the present invention; and

Figure 2 is a schematic diagram of an online sampling device, in accordance with a second embodiment of the present invention.

DESCRIPTION OF EMBODIMENTS

[0039] Figure 1 shows a schematic diagram of an online sampling device 10 in accordance with the first embodiment of the present invention, comprising: a sampler 12 an analyser 14; a delay member 16; and ancillary equipment 18, wherein the delay member 16 is downstream from the analyser 14 and is adapted to inhibit exposure of a sample to the ancillary equipment 18.

[0040] The sampler, which is in the form of a sample tube 12, is immersed in a Bayer process stream 20. The sample tube 12 is 2 metres in length and made of perfluoroalkoxy alkanes (PFA). The analyser 14 is provided in the form of a turbidity meter.

[0041] In Figure 1 , the Bayer process stream 20 is contained in a process vessel 22. The sample may be removed from the Bayer process stream 20 either by differential pressure between the process vessel and the on-line sampling device or via a pump.

[0042] The online sampling device 10 further comprises an outlet member in the form of an outlet tube 24 which is in fluid communication with the analyser 14 and the delay member 16. The outlet tube 24 comprises a bubble trap 26 that can act to remove bubbles in the online sampling device 10. Specifically, bubbles that may be entrained in the sample, which have been partially drawn into the delay member 16, typically rise out of the sample and present a stream of bubbles through the analyser 14. This may result in the malfunction of the analyser 14 and, as such, the bubble trap 26 acts to remove this stream of bubbles. It will be appreciated that the bubble trap may not be required if the delay member 16 is above the analyser 14.

[0043] The delay member 16, which is in the form of a PFA tube 16, is coiled. The delay member 16 has a length to diameter ratio of 1000:1 . The length of the delay member 16 is 10 metres long and the diameter is 10 millimetres.

[0044] The ancillary equipment 18, which is located downstream from the analyser 14, acts to support the operation of the online sampling device 10. As shown in Figure 1 , the ancillary equipment 18 comprises a fluid inlet 28, an isolation valve 30, a filter 32, a non-return valve 34, a restrictor 36, an idle purge valve 38, a blast valve 40, a pressure sensor 42, a drain valve 44, a drain restrictor 46 and a discharge outlet 48.

[0045] The fluid inlet 28 provides an opening for the flow of fluid to the online sampling device 10. The fluid may be fresh or recycled water, dilute Bayer process liquor, a descaling solution, a caustic solution, an acid or any other fluid appropriate for cleaning the online sampling device. The isolation valve 30, which is located upstream from the fluid inlet 28, controls the supply of the fluid to the online sampling device 10. The filter 32, located upstream from the isolation valve 30, minimises any larger unwanted objects present in the fluid from flowing to the delay member 16, the analyser 14 and into the Bayer process stream 20. The non-return valve 34, which is located upstream from the isolation valve 30 relative to the fluid flow, directs th flow of fluid contained in the online sampling device (that may be contaminated with the Bayer process stream) away from the isolation valve 30.

[0046] The restrictor 36, which is located upstream from the non-return valve 34, controls the flow of fluid so that it has a low flow. The idle purge valve 38 controls the supply of the low flow of fluid to the delay member 16, the analyser 14 and into the Bayer process stream 20. The blast valve 40, which Is also located upstream from the non-return vaive 34, controls and supplies a high flow of fluid to the delay member 16, the analyser 14 and into the Bayer process stream 20.

[0047] The pressure sensor 42 monitors the pressure in the online sampling device 10, such that the presence of either a low or high pressure can be detected to reduce the risk of damaging the online sampling device 10. For example, the build-up of material in any of the sample tube 12, outlet tube 24 or delay member 16 would result in a change in pressure that the can be detected by the pressure sensor.

[0048] The drain vaive 44 allows fluid in the online-sampling device to be drained via the discharge outlet 48 and the drain restrictor 46, being located upstream from the drain valve 44 controls the flow of fluid that Is being drained to a low flow.

[0049] In Figure 2 there is shown an online sampling device 50 in accordance with a second embodiment of the present invention, the online sampling device 50 being in man respects similar to the online sampling device 10, like numerals denoting like parts. The ancillary equipment 18 of the online sampling device 50 comprises a siphon system 52. The siphon system 52 is employed in circumstances where the Bayer process is not under pressure, so that the sample can be removed from the Bayer proces stream 53.

[0050] The siphon system 52 comprises a siphon valve 54, a siphon leg 56 and a siphon bubble trap 58. The siphon Ieg 56 has a sufficient height 80 to establish a siphon to remove the sample from the Bayer process stream 20. The siphon valve 54 acts to control the flow of fluid down the siphon leg 56 and, as such, controls the sample acquisition (see below). The siphon bubble trap 58, which is located downstream from the siphon leg 58, minimises the rise of any bubbles to the head of fluid, which would otherwise replace the fluid. As such, the siphon bubble trap 58 ensures that the head of fluid is substantially held.

[0051] The online sampling device further comprises cleaning means 62 adapted to periodically clean the analyser 14. The cleaning means 62 comprises a reservoir 64 of sulfuric acid, a filter 66, a pump 68 and a non-return valve 70.

[0052] The online sampling devices 10, 50 are operable in four states, an idle state, a sample state, a purge state and a cleaning state.

[0053] When a sample is not required, the online sampling device 10, 50 operates in the idle state. In this state, a flow of fluid is supplied to the online sampling device 10, 50 via fluid inlet 28 by opening the isolation valve 30 and the idle purge valve 38, while the blast valve 40 and drain valve 44 remain closed. The restrictor 36, which is located ahead of the idle purge valve 38, controls the flow of fluid so that it has a low flow. The fluid flows through the delay member 16, the analyser 14 and ultimately the sample tube 12. A low flow of fluid enters the process stream 20. This low flow of fluid prevents the ingress of sample into the online sampling device 10, 50. It will be appreciated that the low flow of fluid is in a quantity that does not affect the operation of the online sampling device 10, 50 or the Bayer Process. For example, fluid flow of about 20 L per hour would have no impact on a total flow of several hundred kilolitres per hour or more as may be found in Bayer Process streams. It will be further appreciated that the low flow of fluid may have a high reserve pressure so as to guarantee the supply of fluid into the Bayer process stream 20. The online sampling device 10, 50, when idle, is therefore primed with fluid.

[0054] In the sample state, when a sample is required, the idle purge valve 38 is closed and the drain valve 44 is opened causing sample to enter the sample tube 12. If the siphon system 52 is employed, then the siphon valve 54 is opened to allow sample to enter the sample tube 12. The time taken for the sample to reach the approximate midpoint of the delay member 16 can be calibrated prior to use, such that an automated timer or control system (not shown) can be used to position the sample front at the approximate midpoint of the delay member 16. As discussed above, the high length to diameter ratio and the fixed volume facilitate the calibration of the delay member. Where the sample is a dark Bayer liquor, it is may be possible to see the sample inside the delay member 16, provided that the delay member 16 is sufficiently transparent. When the sample front reaches the approximate midpoint of the delay member 16, the drain valve 44 is closed to prevent further movement of the sample 12. if the siphon system 52 is employed, then the siphon valve 54 is closed to prevent further movement of the sampie 12. A measurement is then taken by the analyser 14.

[0055] Advantageously, the high length to diameter ratio enables the accurate determination of fill rates and rates of sample procurement, contributing to the ability of the delay member to inhibit contact of the solution with the ancillary equipment.

[0058] When the measurement is complete, the online sampling device 10, 50 enters th purge state. The online sampling device , 50 is flushed with fluid, by opening th blast valve 40. This ensures that any sampie in the online sampling device 10, 50 is forced back into the Bayer process stream and replaced with fiutd and that the analyser 14 is cleaned. Additionally, the flushing of fluid through the online sampling device 10, 50 substantially cleans the delay member 16, the analyser 14, the outlet tube 24 and the sample tube 12. The online sampling device 10, 50 is then returned to the idle state until another sample needs to be sampled and analysed.

[0057] Depending on th sample conditions, there may be periodic need to operate the device in the cleaning state, it will be appreciated that solutions such as Bayer liquors have a tendency to auto precipitate. Such precipitates, also known as scale, can deposit inside the analyser such as a clarity meter, affecting results.

[0058] The cleaning state may occur after each sample is taken and measured or after a set number of sampfes or as required, depending on the conditions of the analyser. In the cleaning state valves 38 and 40 are closed and valve 54 is preferably open. Sulfuric acid from th reservoir 64 is pumped into the analyser 14 to remove the scale. The system allows the acid to soak for about 10 minutes after which time it returns to the idle state. However, it may also proceed directly to the sample state,

[0059] It will be appreciated that when the pressure system is used for the online sampling device 10, the pressure system will comprise a drain leg which is operated b a valve so as to allow the pressure in th Bayer process to force fluid out the valve.

[0060] It will further be appreciated that the drain restrictor 46 in Figure 1 , which is located upstream from the drain valve 44 relative to the fluid flow, will be sized in conjunction with the delay member 16 so that the positioning of sample during measurement i manageable and repeatabie. It will be further appreciated that a drain restrictor may also be located upstream from the siphon valve 54 relative to the fluid flow, wherein the drain restrictor will be sized in conjunction with the delay member 16 so that the positioning of sample during measurement is manageable and repeatable.

[0061] The Applicant has found that prior art online sampling devices not utilising the present invention can experience ancillary equipment failure after 4 to 8 weeks of use. These prior art devices direct sample through the ancillary equipment 18 and thus that ancillary equipment 18 is exposed to high temperature, small solids particles and the effects of precipitated scale. In these circumstances, the main failure modes are seizing of valves and blockage of pipe work. In contrast, the online sampling device of the present invention 10, 30 has been operated for a period of at least 9 months without failure of the ancillary equipment 18.

[0062] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications.

Claims

1 . An online sampling device comprising: a sampler; an analyser; a delay member; and ancillary equipment, wherein the delay member is downstream from the analyser and is adapted to inhibit exposure of a sample to the ancillary equipment and the ancillary equipment employs a sample removal fluid to remove sample from the device.

2. An online sampling device according to claim 1 , wherein the device comprises analyser cleaning means.

3. An online sampling device according to claim 2, wherein the analyser cleaning means comprises a cleaning fluid inlet.

4. An online sampling device according to any one of the preceding claims, wherein the delay member is provided in the form of a tube.

5. An online sampling device according to any one of the preceding claims, wherein the delay member has a length between 5 to 15 metres.

6. An online sampling device according to any one of the preceding claims, wherein the delay member has a diameter between 5 to 25 millimetres.

7. An online sampling device according to any one of the preceding claims, wherein the delay member has a length to diameter ratio of between 500 and 2000.

8. An online sampling device according to any one of the preceding claims, wherein the analyser is a pH meter, conductivity meter, turbidity meter, spectrometer, spectrophotomer, fluorometer, sound velocity meter, density meter or any other meter or instrument known in the art for measuring the properties of a sample.