CN107615038B

CN107615038B - Online sampling device

Info

Publication number: CN107615038B
Application number: CN201680013730.2A
Authority: CN
Inventors: S·麦克卡斯基
Original assignee: Alcoa of Australia Ltd
Current assignee: Alcoa of Australia Ltd
Priority date: 2015-03-06
Filing date: 2016-03-04
Publication date: 2021-01-29
Anticipated expiration: 2036-03-04
Also published as: BR112017018483B1; AU2016228931A1; WO2016141403A1; AU2016228931B2; AU2020250295A1; CN107615038A; BR112017018483A2

Abstract

An online sampling device, comprising: a sampler; an analyzer; a delay member; and an accessory device, wherein the delay member is located downstream of the analyzer and is adapted to prevent exposure of the sample to the accessory device, the accessory device employing the sample removal fluid to remove the sample from the apparatus.

Description

Online sampling device

Technical Field

The invention relates to an online sampling device. More particularly, the present invention is intended for use in the on-line sampling and analysis of process streams (e.g., process streams from the bayer process).

Background

In many industrial applications, on-line sampling methods are employed to monitor the properties of process streams in real time. An online sampling device typically includes an analyzer that chemically analyzes a sample and ancillary equipment located downstream from the analyzer that supports operation of the online sampling device. Various types of analyzers are used for on-line sampling of process streams, including pH meters, conductivity meters, and turbidity meters. The auxiliary equipment may include valves, sensors and siphons.

The bayer process involves decomposing bauxite in a caustic solution, usually under conditions of high temperature and pressure. The caustic solution dissolves the major aluminum support compounds (aluminum trihydroxide and carboxy alumina) to form a slurry containing insoluble impurities and containing compounds dissolved in the bayer liquor. The slurry is cooled and insoluble impurities are separated. The remaining dissolved compounds are passed to a precipitation stage where aluminum is recovered from the bayer liquor by precipitation of an alumina-bearing phase, typically aluminum trihydroxide (al (oh)₃). The precipitate is calcined to recover alumina as a product.

In the bayer process, an on-line sampling method is employed in order to control the process stream to a desired specification. Furthermore, periodic online analysis of process streams at various locations in operation can be used to control the process in order to maximize the yield of alumina or other products.

A problem encountered when using an online sampling device is the risk of exposing the ancillary equipment to the sample being measured. Such exposure may affect the internal working components of the equipment such that they can increase operating and/or maintenance costs, thereby adversely affecting the on-line availability of the equipment or causing the equipment to malfunction. For example, online analysis of solutions in bayer process operations is complicated by high alkalinity, high ionic strength, high alumina supersaturation, high temperatures, and high total solids content in certain bayer process streams. Accordingly, it is undesirable to expose auxiliary equipment (e.g., piping, pressure sensors, and valves) to the bayer process stream given that interaction with these streams may prevent the equipment from operating efficiently.

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

The entire contents of each document, reference, patent application, or patent cited herein are expressly incorporated by reference herein, to the extent that the reader should read and consider them as part of this document. The citation of said documents, references, patent applications or patents is not repeated herein for the sake of brevity only.

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 Invention

According to the present invention, there is provided an online sampling device, comprising:

a sampler;

an analyzer;

a delay member; and

the auxiliary equipment is a device used for assisting the equipment,

wherein the delay member is located downstream of the analyzer and is adapted to prevent exposure of the sample to an ancillary device that employs a sample removal fluid to remove the sample from the apparatus.

The solutions in which the device of the invention can be employed are generally highly corrosive and saturated solutions. These types of solutions often exhibit a tendency to auto-precipitate. It will be appreciated that such a solution may be deposited within the apparatus of the present invention. For example, precipitation may occur in the sampler, analyzer, or delay member. Preferably, the speed of the sample removal fluid in the device is sufficient to remove any particles that may settle in the device, wherein the auxiliary apparatus comprises a sample removal fluid inlet located downstream of the delay member.

It will be appreciated that the sample removing fluid contacts at least a portion of the ancillary device and therefore the sample removing fluid should not have high corrosive properties. The sample removal fluid may be any solution capable of removing the sample without unduly damaging the ancillary equipment. In one form of the invention, the sample removal fluid is an aqueous solution. Preferably, the sample removing fluid is water. It will be appreciated that industrial processes may not have water available. In this case, the cleanest water available should be purchased. For example, in the context of the bayer process, condensed water is suitable.

The online sampling device may also include a means to clean the analyzer. In the context of the present specification, the term cleaning the analyzer may include removing at least a portion of material that has precipitated on or in the analyzer or otherwise contaminated the analyzer. The analyser cleaning device may be provided in the form of a cleaning fluid inlet. Preferably, the cleaning fluid inlet is located in the vicinity of the analyser. Depending on the nature of the precipitation, the cleaning fluid may be an acidic solution or a basic solution. Preferably, the cleaning fluid is a strong acid or a strong base.

In a particular form of the invention, wherein the sample is a bayer liquor, the cleaning solution is preferably a strong acid, for example, phosphoric acid or sulphuric acid.

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

The term tube will be understood to include a pipe, a hose or any other suitable elongate member.

The delay member may be straight, curved, stacked or coiled.

Preferably, the delay member is coiled.

It will be appreciated that the ratio of the length to the diameter of the delay member will vary depending on the characteristics of the sample to be analysed. For example, sample characteristics such as viscosity, temperature, density, pressure, or total solids content can affect the flow of the sample through the delay member. Thus, the length to diameter ratio of the delay member will vary from application to application, but will be readily determined by one of ordinary skill in the art with reference to the parameters of the present invention.

Preferably, the length of the delay member is between 5 and 15 metres.

Preferably, the diameter of the delay member is between 5 mm and 25 mm.

Preferably, the length to diameter ratio of the delay member is between 500 and 2000.

Advantageously, the large length to diameter ratio reduces the likelihood of exposure of ancillary equipment to the sample.

Advantageously, the delay member has a fixed volume. Advantageously, the fixed volume of the delay member as described above is corrected.

It will be appreciated that the characteristics of the sample will affect the composition of the delay member. The delay member is preferably made of a material suitable for handling samples that may damage ancillary equipment, for example, samples with high acidity, high alkalinity, high ionic strength, high temperature, high fouling propensity, and high total solids content. Chemically resistant polymers (e.g., fluoropolymers) may be suitable for many applications. Specific examples include Fluorinated Ethylene Propylene (FEP), Polytetrafluoroethylene (PTFE), and Perfluoroalkoxyalkane (PFA). Alternatively, the delay member may be formed of, for example

Polyethylene and metal (e.g., stainless steel).

Preferably, the delay member is made of Perfluoroalkoxyalkane (PFA).

In one form of the invention, the delay member has a coating on the inside to reduce scale formation. Such coatings are particularly advantageous when sampling fluids that have a tendency to precipitate (e.g., bayer liquor). In one form of the invention, the coating is electroless nickel.

In one form of the invention, the sampler is provided in the form of a sample tube for transporting the sample from the process stream to the analyser.

It will be appreciated that the characteristics of the sample will affect the composition of the sample tube. The sample tube is preferably made of a material suitable for handling samples having, for example, high acidity, high alkalinity, high ionic strength, high temperature, high fouling tendency, and high total solids content. Chemically resistant polymers such as polytetrafluoroethylene may be suitable for many applications. Specific examples include Fluorinated Ethylene Propylene (FEP), Polytetrafluoroethylene (PTFE), and Perfluoroalkoxyalkane (PFA). Alternatively, the sample tube may be made of, for example

Polyethylene and metal (e.g., stainless steel).

In one form of the invention, the interior of the sample tube has a coating to reduce scale formation.

Preferably, the in-line sampling device further comprises an outlet member in fluid communication with the delay member and the analyzer.

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

It will be appreciated that the characteristics of the sample will affect the composition of the outlet tube. The outlet tube is preferably made of a material suitable for handling samples having, for example, high acidity, high alkalinity, high ionic strength, high temperature, high fouling tendency, and high total solids content. Chemically resistant polymers such as polytetrafluoroethylene are suitable for many applications. Is specified inExamples include Fluorinated Ethylene Propylene (FEP), Polytetrafluoroethylene (PTFE), and Perfluoroalkoxyalkane (PFA). Alternatively, the outlet tube may be formed of, for example

Polyethylene and metal (e.g., stainless steel).

In one form of the invention, the interior of the outlet member is coated with a coating to reduce scale formation.

The analyzer may be a pH meter, conductivity meter, turbidimeter, spectrometer, spectrophotometer, fluorometer, sound velocity meter, densitometer, or any other measuring instrument or instrument known in the art for measuring a characteristic of a sample.

In one form of the invention, the sample is a bayer process solution.

The term bayer process liquor will be understood to include any fluid that runs through at least a portion of the bayer process, including, but not limited to, waste liquor, green liquor, decomposed liquor, precipitated liquor, process lake water, scrubber overflow liquor, and underflow slurry.

According to the present invention there is provided a method of extracting a sample from a process stream, the method comprising the steps of:

extracting a sample from the process stream such that the sample enters the sampler, the analyzer and the delay member;

stopping the flow of the sample in the in-line sampling device;

the in-line sampling device is flushed with a fluid,

thereby returning the sample to the process stream.

Drawings

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

FIG. 1 is a schematic view of an in-line sampling device according to a first embodiment of the present invention; and

fig. 2 is a schematic view of an on-line sampling device according to a second embodiment of the present invention.

Detailed Description

Fig. 1 shows a schematic view of an online sampling device 10 according to a first embodiment of the present invention, comprising:

a sampler 12;

an analyzer 14;

a delay member 16; and

the auxiliary devices 18 are arranged in such a way that,

wherein the delay member 16 is located downstream of the analyzer 14 and is adapted to prevent exposure of the sample to the ancillary device 18.

A sampler in the form of a sample tube 12 is immersed in the bayer process stream 20. The sample tube 12 is 2 meters in length and is made of Perfluoroalkoxyalkane (PFA). The analyzer 14 is provided in the form of a turbidimeter.

In fig. 1, a bayer process stream 20 is contained in a process vessel 22. The sample may be removed from the bayer process stream 20 by a pressure differential between the process vessel and an in-line sampling apparatus or via a pump.

The in-line sampling device 10 further includes an outlet member in the form of an outlet tube 24 that is in fluid communication with the analyzer 14 and the delay member 16. The outlet tube 24 includes a bubble trap 26 that can be used to remove bubbles in the in-line sampling device 10. In particular, bubbles that may be entrained in the sample that have been partially drawn into the delay member 16 generally rise away from the sample and appear as a stream of bubbles through the analyzer 14. This may lead to failure of the analyzer 14 and therefore the bubble trap 26 is used to remove the stream of bubbles. It will be appreciated that if the delay member 16 is located above the analyser 14, then a bubble trap is not required.

The delay member 16 in the form of a PFA tube 16 is coiled. The length to diameter ratio of the delay member 16 is 1000: 1. The length of the delay member 16 is 10 meters and the diameter is 10 millimeters.

Auxiliary equipment 18, located downstream of the analyzer 14, is used to support the operation of the online sampling device 10. As shown in fig. 1, the auxiliary equipment 18 includes a fluid inlet 28, an isolation valve 30, a filter 32, a check valve 34, a flow restrictor 36, an idle purge valve 38, a shock valve 40, a pressure sensor 42, a bleed valve 44, a bleed flow restrictor 46, and a drain outlet 48.

The fluid inlet 28 provides an opening for fluid flow to the in-line sampling device 10. The fluid may be fresh or recycled water, dilute bayer process solutions, de-scaling solutions, caustic solutions, acids, or any other fluid suitable for cleaning an in-line sampling device. An isolation valve 30 upstream of the fluid inlet 28 controls the supply of fluid to the in-line sampling device 10. A filter 32 located upstream of the isolation valve 30 minimizes any larger unwanted objects present in the fluid to prevent them from flowing to the delay member 16, the analyzer 14, and into the bayer process stream 20. The check valve 34 directs the flow of fluid contained in the in-line sampling device (which may be contaminated by the bayer process stream) away from the isolation valve 30, the check valve 34 being located upstream of the isolation valve 30 with respect to the fluid flow.

A flow restrictor 36, located upstream of the check valve 34, controls the flow of the fluid so that the fluid has a low flow rate. The idle purge valve 38 controls the supply of low flow of fluid to the delay element 16, the analyser 14 and into the bayer process stream 20. An impact valve 40, also located upstream of the check valve 34, controls and supplies a high flow of fluid to the delay member 16, the analyzer 14 and into the bayer process stream 20.

The pressure sensor 42 monitors the pressure in the online sampling device 10 so that the presence of low or high pressure can be detected in order to reduce the risk of damaging the online sampling device 10. For example, a buildup of material in any of the sample tube 12, the outlet tube 24, or the delay member 16 will cause a pressure change that can be detected by the pressure sensor.

The bleed valve 44 allows fluid in the in-line sampling device to be bled off via a bleed outlet 48, and a bleed restrictor 46 upstream of the bleed valve 44 controls the flow of the fluid being bled off to a low flow.

In FIG. 2, an in-line sampling device 50 according to a second embodiment of the present invention is shown, the in-line sampling device 50 being similar in many respects to the in-line sampling device 10, like reference numerals referring to like parts. The auxiliary equipment 18 of the in-line sampling device 50 includes a siphon system 52. Siphon system 52 is employed in this case: wherein the bayer process is not under pressure, enabling removal of a sample from the bayer process stream 53.

The siphon system 52 includes a siphon valve 54, a siphon leg 56, and a siphon bubble trap 58. The siphon leg 56 has a sufficient height 60 to establish a siphon to remove a sample from the bayer process stream 20. The siphon valve 54 is used to control the fluid flow down the siphon leg 56 and as such control the sample collection (see below). A siphon bubble trap 58 located downstream of the siphon leg 56 minimizes any bubble rising toward the head of the fluid that would otherwise displace the fluid. As such, the siphon bubble trap 58 ensures that the fluid head is substantially maintained.

The online sampling device also includes a cleaning device 62 adapted to periodically clean the analyzer 14. The cleaning device 62 includes a sulfuric acid container 64, a filter 66, a pump 68, and a check valve 70.

The

online sampling device

10, 50 is capable of operating in four states: idle state, sampling state, purge state, and cleaning state.

When no sample is required, the

online sampling device

10, 50 is operated in an idle state. In this state, fluid flow is supplied to the

online sampling device

10, 50 via the fluid inlet 28 by opening the isolation valve 30 and the idle purge valve 38, while the shock valve 40 and the purge valve 44 remain closed. A restrictor 36 located in front of the idle purge valve 38 controls the fluid flow so that it has a low flow rate. The fluid flows through the delay member 16, the analyzer 14 and finally through the sample tube 12. A low flow of fluid enters process stream 20. This low flow of fluid prevents the sample from entering the in-

line sampling device

10, 50. It will be appreciated that the amount of low flow fluid does not affect the operation of the in-

line sampling apparatus

10, 50 or the bayer process. For example, a fluid flow rate of about 20 liters per hour (L) does not affect the total flow rate of hundreds of kiloliters per hour or more as may be found in a bayer process stream. It will also be appreciated that low flows of fluid may have a high reserve pressure in order to ensure the supply of fluid into the bayer process stream 20. The

online sampling device

10, 50 is therefore filled with fluid at idle.

In the sampling state, when a sample is needed, the idle purge valve 38 is closed and the vent valve 44 is opened, causing the sample to enter the sample tube 12. If a siphon system 52 is employed, a siphon valve 54 is opened to allow the sample to enter the sample tube 12. The time taken for the sample to reach about the midpoint of the delay member 16 may be corrected prior to use so that an automated timer or control system (not shown) can be used to position the sample front at about the midpoint of the delay member 16. As described above, a large length to diameter ratio and a fixed volume help correct the delay member. In the case where the sample is a dark bayer solution, the sample inside the delay member 16 can be seen, provided that the delay member 16 is sufficiently transparent. When the sample front reaches about the midpoint of the delay member 16, the bleed valve 44 is closed to prevent further movement of the sample 12. If a siphon system 52 is employed, the siphon valve 54 is closed to prevent further movement of the sample 12. The measurements are then taken by the analyzer 14.

Advantageously, the large length to diameter ratio enables the fill rate and sample acquisition rate to be accurately determined, thereby contributing to the ability of the delay member to prevent the solution from contacting ancillary equipment.

When the measurement is completed, the

online sampling device

10, 50 enters a purge state. The in-

line sampling device

10, 50 is flushed with fluid by opening the shock valve 40. This ensures that any sample in the

online sampling apparatus

10, 50 is forced back into the bayer process liquor stream and is replaced with fluid, and that the analyser 14 is cleaned. In addition, the flushing of fluid through the in-

line sampling device

10, 50 substantially cleans the delay member 16, the analyzer 14, the outlet tube 24, and the sample tube 12. The

online sampling device

10, 50 then returns to idle until additional samples need to be sampled and analyzed.

Depending on the sample conditions, there may be periodic needs to operate the device in a clean state. It will be appreciated that solutions such as bayer liquor have a tendency to auto-precipitate. This precipitate, also known as scale, can precipitate inside an analyzer such as a transparence meter, affecting the results.

Depending on the state of the analyzer, the cleaning state may occur after each sample is taken and measured or after a group of samples is taken and measured or when needed. In the cleaning state,

valves

38 and 40 are closed and valve 54 is preferably open. Sulfuric acid from vessel 64 is pumped into analyzer 14 to remove scale. The system allows acid soaking for approximately 10 minutes after which it returns to idle. However, it is also possible to continue directly to the sampling state.

It will be appreciated that when the pressure system is used with an online sampling device 10, the pressure system will include a bleed pin that is operated by a valve to allow the pressure in the bayer process to force fluid out of the valve.

It will also be appreciated that the bleed flow restrictor 46 in fig. 1 will be dimensioned to incorporate the delay member 16 such that the positioning of the sample during measurement is manageable and repeatable, the bleed flow restrictor being located upstream of the bleed valve 44 with respect to fluid flow. It will also be appreciated that a bleed flow restrictor may also be located upstream of the siphon valve 54 with respect to fluid flow, wherein the bleed flow restrictor will be sized to incorporate the delay member 16 such that positioning of the sample during measurement is manageable and repeatable.

The applicant has found that prior art on-line sampling devices not using the present invention can experience auxiliary equipment failure after 4 to 8 weeks of use. These prior art devices direct the sample through the auxiliary equipment 18, the auxiliary equipment 18 thereby being exposed to high temperatures, small solid particles and precipitated fouling. In these cases, the main failure modes are jamming of the valve and blocking of the pipe work. In contrast, the

online sampling devices

10, 30 of the present invention have been operating for at least 9 months without failure of the auxiliary equipment 18.

It will be understood by those skilled in the art 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 analyzer;

a delay member; and

the auxiliary equipment is a device used for assisting the equipment,

wherein the delay member is located downstream of the analyser and is adapted to prevent exposure of the sample to the ancillary device which removes the sample from the in-line sampling apparatus using a sample removal fluid, wherein the ancillary device comprises a sample removal fluid inlet located downstream of the delay member.

2. The online sampling device of claim 1, wherein the online sampling device comprises an analyzer cleaning device.

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

4. An in-line sampling device according to any of claims 1 to 3, wherein the delay member is provided in the form of a tube.

5. An online sampling device according to any of claims 1-3 wherein the length of the delay member is between 5 and 15 metres.

6. An in-line sampling device according to any of claims 1 to 3, wherein the diameter of the delay member is between 5 mm and 25 mm.

7. An in-line sampling device according to any of claims 1 to 3 wherein the delay member has a length to diameter ratio of between 500 and 2000.

8. An online sampling device according to any of claims 1-3 wherein the analyser is a pH meter, conductivity meter, turbidimeter, spectrometer, spectrophotometer, fluorometer, sound velocity meter, densitometer or any other measuring instrument or instrument known in the art for measuring properties of a sample.