WO2006007631A1

WO2006007631A1 - On-line/in-field bayer process liquor analysis

Info

Publication number: WO2006007631A1
Application number: PCT/AU2005/001029
Authority: WO
Inventors: Vincent Robert Dooley
Original assignee: Alcoa of Australia Ltd
Current assignee: Alcoa of Australia Ltd
Priority date: 2004-07-16
Filing date: 2005-07-14
Publication date: 2006-01-26
Anticipated expiration: 2007-01-16
Also published as: BRPI0512445B1; CA2572319A1; RU2007105832A; BRPI0512445A; RU2393457C2; EP1774281A1

Abstract

A liquor analyser apparatus and method intended for use in real-time or near real-time in-field/on-line analysis of Bayer process liquors to determine the total alumina, total caustic, and total alkali concentrations, and if required, the total concentration of impurities, in the liquor is disclosed. The apparatus and method obviates the need for laboratory analysis, aside of any calibration analysis for initial set-up. The apparatus provides concentrations of alumina, total caustic and total alkali by relying on accurate determination of liquor temperature, density, sound velocity, conductivity and maximum conductivity of the liquor under isothermal dilution. The apparatus is formed around a vessels (11), (13), and (15) with sensors to measure these parameters. The vessels (11), (13), and (15) are fluidly connected in series, with vessel (15) draining to a reservoir (17). A pump (19) is provided to recirculate fluid from the reservoir (17) to the vessels (11), (13), (15) in a closed circuit manner. The vessels (11), (13), (15) and reservoir (17) are contained within a water jacket chamber (21) which is maintained at a suitable constant temperature. The apparatus has a sample inlet (23) and a water inlet (25), and a drain (27). An overflow (29) from the reservoir (17) connects to the drain to discharge fluid during dilution analysis of the fluid. Sample flows are controlled by automatic operation of valves MV1, MV2, MV3, and MV4. Water flow control is controlled via solenoid valves SV1, SV2, SV3, and SV4. Operation is automated by a PLC.

Description

"On-Line/ln-Field Bayer Process Liquor Analysis"

Field of the Invention

This invention relates to on-line analysis of multi-component fluids, and in particular on-line analysis of multi-component fluids containing impurities. In particular this invention relates to an apparatus and method for rapidly performing these determinations on-line and/or in-field, without having to convey batch samples to a laboratory for analysis. In one embodiment this invention provides for determination of concentrations of alumina, total caustic and total alkali in a Bayer process liquor stream.

Background Art

Control of Bayer liquor composition is crucial to obtaining stable control of the Bayer process to maximise alumina yield and overall performance of the process. The components of a Bayer liquor include sodium hydroxide, sodium aluminate and alumina, sodium carbonate, and a range of impurities. In general the impurities maintain constant ratios to one another and can be treated in terms of physiochemical properties as a single impurity. The precision of existing on-line analysers is limited by the inability to resolve the effects produced by the carbonate and impurities.

Devices developed in the past to analyse Bayer liquors in particular, have utilised some of the parameters comprising density, refractive index, sound velocity, conductivity, maximum conductivity and viscosity in varying combinations to determine liquor composition.

Conductivity is measured to determine the alumina/total caustic soda ratio. The maximum conductivity value observed during isothermal dilution is used to determine the alumina / total caustic soda ratio.

Density is measured to determine total alkali (total OH^" and CO₃ ^2') concentration. A refractometer can be used to measure density in some slurry applications. Refractive index and sound velocity are generally considered as alternatives to density measurement.

Sound velocity can be measured and used to determine concentration as total caustic soda or total alkali. Conductivity and density measurements in combination have been used to estimate values of alumina and total caustic soda and sometimes total alkali. A refractometer can be substituted for the density meter. All of these methods require temperature measurement for compensation. Current methods are also typically used with laboratory feedback into the equations to attempt to account for carbonate and impurity changes.

One example of an attempt at on-line liquor analysis was an apparatus developed in Hungary by Aluteru FKI. The Hungarian analyser measures Bayer liquor for total caustic, total alkalinity and total alumina. The instrument utilises a unique relationship between the liquor components and liquor density, conductivity and maximum conductivity during isothermal dilution. This instrument relies on low variability in liquor impurities for accuracy in readings. Thus a serious disadvantage of the Hungarian analyser is that variability in the concentration of liquor impurities away from that for which the analyser is calibrated will lead to inaccuracies in parameters measured by the analyser.

Throughout the specification, 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

Sound velocity and density have hitherto been considered to be directly related and not independent, and therefore not used in conjunction in hitherto known devices and methods. Because of this belief, it wouldn't be contemplated to measure both parameters of sound velocity and fluid density, in liquor analysis. Surprisingly, investigations into sound velocity conducted during the development of this invention have revealed that sound velocity has enough independence from liquor density to provide another useful variable. The inventor's laboratory work conducted to date shows sufficient differences between density and sound velocity characteristics to enable the two to be used together to provide additional data. Sound velocity is a function of density and bulk modulus (inverse of compressibility). This test work has shown that changes in total caustic soda and alumina have quite different effects on sound velocity and density. That is, the bulk modulus plays an important part in the sound velocity values.

The test work also shows that the dilution technique can be used to provide more data than the simple alumina / total caustic soda ratio inferred by the maximum conductivity. It can be used to provide multiple equations for all measurements because the contributions to each measured variable by the different components during dilution change in different ways.

In accordance with the invention there is provided a process liquor analyser having: means to measure conductivity; means to measure sound velocity; means to measure density;

said analyser having a sample inlet to receive liquor sample and a water inlet selectively fluidly connectable with said means to measure conductivity, said means to measure sound velocity, and said means to measure density, and

said means to measure conductivity, means to measure sound velocity and means to measure density being contained within one or more vessels;

said analyser operable to receive a process liquor sample from said sample inlet and deliver said process liquor sample to said one or more vessels to take measurements of conductivity, sound velocity and density respectively of said sample, - A - and operable to drain said liquor sample, flush said one or more vessels with water from said water inlet, and to drain water from said one or more vessels before a further said process liquor sample is received.

In the analysis of a Bayer process liquor, the concentration of alumina, total caustic, and total alkali (and optionally total impurities) can then be determined from the measurements taken. This can be determined by regression (for example linear analysis) to develop simultaneous equations to calculate the liquor components. Alternatively reference samples (controls) could be prepared, so that in-field samples or on-line measurements can be assessed against the controls. In an electronic device, the data pertaining to the controls could be incorporated in a look-up table in data storage memory (volatile or non-volatile, for example rom, ram, hard disk etc).

Thus, preferably said process liquor analyser is adapted for analysis of a Bayer process liquor, and includes processor means to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) from the measurements taken of conductivity, sound velocity and density.

Preferably said processor means is arranged to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) using simultaneous equations developed by regression of measurements taken of conductivity, sound velocity and density.

Preferably the regression is in the form of a linear analysis.

Alternatively said processor means is arranged to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) through comparison of measurements of conductivity, sound velocity and density with measurements of conductivity, sound velocity and density for reference samples acting as controls, the measurements for which are incorporated in a look-up table in memory or other data storage device. Preferably said analyser is operable to controllably receive water from said water inlet to dilute said process liquor sample within said one or more vessels, to allow said means to measure conductivity to measure conductivity as said sample is diluted, and optionally to measure maximum dilute liquor conductivity.

Preferably said analyser is adapted for analysis of a Bayer process liquor, and includes processor means to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) from the measurements taken of conductivity, sound velocity and density, and conductivity during dilution.

Preferably said processor means is arranged^" to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) using simultaneous equations developed by regression of measurements taken of conductivity, sound velocity and density, and conductivity during dilution.

Preferably the regression is in the form of a linear analysis.

Alternatively said processor means is arranged to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) through comparison of measurements of conductivity, sound velocity and density, and conductivity during dilution, with measurements of conductivity, sound velocity and density, and conductivity during dilution for reference samples acting as controls, the measurements for which are incorporated in a look-up table in memory or other data storage device.

Preferably said reservoir includes an overflow to drain excess fluid as said process liquor sample is diluted.

In further alternative arrangements, the parameters of sound velocity and density may also be measured as said process liquor sample is diluted, said parameter(s) measured being factored into the determination of the concentration of alumina, total caustic, and total alkali (and optionally total impurities). Preferably said analyser is operable to flush said sample inlet with water from said water inlet and drain water from said sample inlet before a further said process liquor sample is received. In this manner the previous sample can be flushed before the next sample is taken.

Preferably said analyser is operable to flush said one or more vessels with liquor from said sample inlet and drain said one or more vessels before receiving a said process liquor sample for measurement. In this manner, the water used to flush the previous sample can be purged so that it does not dilute the sample to be measured.

Preferably said means to measure conductivity, means to measure sound velocity, and means to measure density are contained within separate vessels fluidly connected in series.

Preferably said means to measure conductivity, means to measure sound velocity, and means to measure density are connected in a circuit with a reservoir and a pump to recirculate said process liquor sample as measurements are taken.

Preferably the means for measuring density is selected from a density meter and a refractometer. Density meters suitable for the apparatus include those that work on the Coriolis principle (eg those manufactured by Micromotion), those that work on the vibrating loop principle (eg those manufactured by Anton Paar), and those that work on the vibrating time principle (eg those manufactured by Solartron). The most suitable refractometers are those that measure total internal reflection. Other types are not as suitable for taking measurements in Bayer process liquors, but may be appropriate in other applications.

Preferably said means to measure conductivity utilises the toroidal conductivity measurement method. This method is most suitable for Bayer process liquors. Contacting type conductivity measurement devices are not as suitable for Bayer process liquors, but may be suitable in other applications. Suitable toroidal types may include units manufactured by Rosemont, Foxboro, and Yokogawa. Preferably said analyser includes means to measure temperature associated with said circuit.

Preferably said means to measure temperature is associated with one or more of said one or more vessels.

Preferably said means to measure temperature is contained within a said vessel with said means to measure conductivity.

Alternatively said means to measure temperature is contained within all three vessels.

Preferably at least part of said circuit is associated with means to exercise stabilising control over temperature of said process liquor sample.

Preferably said means to exercise stabilising control over temperature includes a water jacket which may be heated or cooled as required. A water jacket has the advantage of possessing thermal momentum. Control over temperature to counter effects of sample temperature change my be exerted by known means such as Peltier effect devices, or known refrigerative devices operable in reverse cycle, or simple heaters. These may be in direct contact with the vessel(s) to control the sample temperature, or in fluid contact with the water jacket surrounding the vessel(s).

Also in accordance with the invention there is provided a method of performing an on-line/in-field analysis of a Bayer process liquor in a process stream, said method including steps of taking measurements of conductivity, sound velocity and density respectively of liquor directly in said process stream, and from said measurements, determining concentration of alumina, total caustic, total alkali, and optionally total impurities.

Further in accordance with the invention there is provided a method of performing an on-line/in-field analysis of a Bayer process liquor from a process stream, said method including steps of taking measurements of conductivity, sound velocity and density respectively of a sample taken from said process stream, and from said measurements, determining concentration of alumina, total caustic, total alkali, and optionally, total impurities.

Preferably regression is used to develop the equations necessary to calculate the liquor components. Measurements of density, conductivity, sound velocity and temperature are taken on a number of fluids of varying composition to obtain valid regressions. The regressions provide a set of equations of the form:

TC = Ai + A₂p + A₃K + A₄V₅

TA = B₁ + B₂p + B₃K + B₄V₅

Al = C₁ + C₂p + C₃κ + C₄V₃

Where

TC = total caustic

TA = total alkali

AI = alumina

p = density

K = conductivity

V_s = sound velocity

Temperature correction may be applied to the individual measurements in the form:

Pcorrected ⁼ PmeasuredU ^"*^" (^reference ""^" t_measured)J Alternatively, temperature correction may be applied using the Arrhenius Law method, where operation over a wide temperature range is required.

Alternatively, models describing the density, conductivity etc may be developed from the test work (or known models may be used) and tuned to the liquor of interest yielding a set of equations where:

Commercially available models may be used or empirical models can be developed from the test work. Where the range of variability is small, a simple linear empirical model of the following form may be used:

p = D₁ + D₂TC + D₃TA + D₄AI

K = E₁ + E₂TC + E₃TA + E₄AI

V_s = F₁ + F₂TC + F₃TA + F₄AI

Temperature correction may be applied to the measurements or can be included in the equations.

Having developed an appropriate model for the given fluid, any appropriate mathematical method may be used to solve the simultaneous equations for the unknown values of the liquor components.

Preferably said method includes taking measurements of conductivity during dilution of said sample. Preferably the temperature at which measurements are taken is maintained within a predetermined range. The actual temperature selected should be one which is practical to operate at. Some density measurement devices require temperature stability, however where a density measurement device is chosen that is not temperature sensitive, temperature control is not so critical, as sound velocity and conductivity measurement can be readily temperature corrected.

Preferably said method includes stabilising the temperature of said sample within a narrow range of ± 2⁰C.

Preferably said method includes stabilising the temperature of said sample within a narrow range of ± 1⁰C.

Preferably said method includes stabilising the temperature of said sample within a narrow range of ± 0.5⁰C.

The Liquor Analyser of the invention utilises four unique relationships which exist between each of the Bayer liquor component concentrations and the solution density, characteristic sound velocity, conductivity and maximum conductivity during isothermal dilution. With these four relationships, the individual concentrations of the four components of the Bayer liquor can be determined, the four components being total caustic, total alkalinity, total alumina and impurities.

There are two possible methods of analysis that may be performed according to the invention. Both involve measuring conductivity, density (and/or refractive index) and sound velocity, with the second method also including in addition, measuring conductivity, density (or refractive index) and sound velocity during isothermal dilution.

The measurement of conductivity, density (and/or refractive index) and sound velocity can be applied as a continuous on-line system not requiring sampling or physical processing. It has the advantage of being relatively simple to measure and provides improved precision over existing continuous on-line methods. The measurement of these parameters during isothermal dilution requires physical processing and may require sampling or a bypass stream.

The inclusion of refractive index measurement with density measurement generally provides little extra benefit except to assist with diagnostics and confirmation of results. However, it is theoretically possible to apply these methods to solutions containing some solids and use the density and refractive index measurements to resolve the solids content and also to correct the other measurements for the effects of the solids. Refractive index measurements can be made in ways that are not affected by the presence of suspended solids.

The method of the invention gathers sufficient parameters to derive an adequate number of equations to mathematically resolve the number of unknowns.

The invention provides an apparatus and a method capable of giving the concentrations of alumina, total caustic and total alkali from a Bayer plant process stream on line and continuously without the need of laboratory analysis to update the calculation formulae. Sensors measure liquor temperature, density, conductivity, sound velocity passage through the liquor and additionally conductivity of variably diluted liquor and feed output signals to a computer or similar calculation device wherein they are used to solve a set of equations and output the liquor component parameters.

Brief Description of the Drawings

A preferred embodiment of the invention will now be described with reference to the attached schematic which is a diagram of the a process liquor analyser according to the invention.

Best Mode(s) for Carrying Out the Invention

The liquor analyser apparatus and method of the embodiment is intended for use in real-time or near real-time in-field/on-line analysis of Bayer process liquors to determine the total alumina, total caustic, and total alkali concentrations in the liquor. The embodiment obviates the need to have the analysis performed in a laboratory (aside of any calibration analysis). In addition, the total concentration of impurities can also be determined.

The apparatus provides concentrations of alumina, total caustic and total alkali by relying on accurate determination of liquor temperature, density, sound velocity, conductivity and maximum conductivity of the liquor under isothermal dilution. Automation of the apparatus is achieved using a programmable logic controller.

The apparatus is formed around a vessel 11 containing means to measure density, a vessel 13 containing means to measure sound velocity, and a vessel 15 containing means to measure conductivity. The vessels 11 , 13, and 15 are fluidly connected in series, with vessel 15 draining to a reservoir 17. A pump 19 is provided to recirculate fluid from the reservoir 17 to the vessels 11 , 13, 15 in a closed circuit manner, when all valves are closed, as will be described later. The vessels 11 , 13, 15 and reservoir 17 are contained within a water jacket chamber 21 which is maintained at a suitable constant temperature. The temperature can be any suitable temperature close to that of the sample, for example. In Bayer process liquors the water temperature can be maintained at a temperature between 50° and 60 ⁰C. Water jacket chamber 21 temperature control is via electronic temperature controller and an electric heater.

The apparatus has a sample inlet 23 and a water inlet 25, and a drain 27. An overflow 29 from the reservoir 17 connects to the drain to discharge fluid during dilution analysis of the fluid. Sample flows are controlled by automatic operation of motorised ball valves MV1 , MV2, MV3, and MV4. Water flow control is controlled via solenoid valves SV1 , SV2, SV3, and SV4. The system has caustic wash capability if an external supply of suitable wash is available. Alternative cleaning/descaling methods may be utilised if desired.

As will be described in more detail, under control of processor means in the form of a programmable logic controller, the apparatus automatically removes a sample of the liquor from the process stream and passes the sample into the vessels 11 , 13, and 15 and reservoir 17. It should be noted that in alternative embodiments the processor means may be a microprocessor, or may be incorporated in computer software run on a stand-alone or networked computer.

The programmable logic controller records the magnitude of each of the four measured variables of temperature, density, sound velocity, and conductivity, once sample temperature stability at within ± 2 ⁰C is attained. Maximum conductivity under isothermal dilution is determined immediately after. Algorithms to determine concentrations of alumina, total caustic, total alkali and impurities are performed in the controller.

The on-line liquor analyser operation will now be described. The programmable logic controller is programmed to sample the process liquor stream at predetermined intervals. The interval times are adjustable from the main controller.

The programmable logic controller is programmed to operate the analyser by the following sequential operations. Once the programmable logic controller reaches the end of an interval, at which time a sample is required, motorised valves MV1 and MV2 are opened, draining flush water from the sample chambers. This water has been present in the chambers since the last operation.

Filling of the vessels with sample liquor commences with motorised valve MV2 being closed and motorised valve MV4 opened, allowing sample liquor to flow into and fill the sample chambers. Motorised valves MV1 and MV4 are then closed. The circulation pump 19 is started and circulates the sample through the vessels 11 , 13, and 15 and reservoir 17, scavenging any remaining water into the sample. The circulation pump 19 is stopped, motorised valves MV1 and MV2 are opened, allowing the sample in the vessels 11 , 13, and 15 and reservoir 17 to be drained. This sequence of filling, circulating and draining is repeated to remove any remaining water from the flushing stage which would otherwise dilute the sample.

Measurement of a sample of process liquor commences with motorised valve MV2 being closed and motorised valve MV4 opened, allowing a sample of process liquor to flow into and fill the vessels 11 , 13, and 15 and reservoir 17. Motorised valves MV1 and MV4 are then closed. The circulation pump 19 is started and circulates the sample through the vessels 11 , 13, and 15 and reservoir 17. Valves MV3, MV4 and SV3 are opened for several seconds to purge samples from the sample inlet 23 and fill it with water . The sample is allowed to cool until the temperature is within ± 2 ⁰C of the selected constant temperature and the rate of temperature change is less than 0.2 ⁰C per minute. At this point the controller records measurements of temperature, conductivity, sound velocity and density.

Water is then slowly added to the sample, by intermittent operation of solenoid valves SV1 , SV2 and SV3 to determine liquor conductivity during dilution and maximum dilute liquor conductivity. As the sample is diluted, the conductivity increases until it peaks and then begins to decline. This peak measurement is recorded by the controller and used in algorithms with the other data to determine concentration of alumina, total caustic, total alkali and impurities in the sample liquor.

Most commonly, linear regression is used to develop the equations necessary to calculate the liquor components. Measurements of density, conductivity, sound velocity and temperature are taken on a number of fluids of varying composition to obtain valid regressions. The regressions provide a set of equations of the form:

TC = A₁ + A₂p + A₃K + A₄V₅ + A₅κ_maχ

TA = Bi + B₂p + B₃K + B₄V₅ + B₅κ_max

Al = Ci + C₂p + C₃K + C₄V₅ + C5K_maχ

Imp = H₁ + H₂p + H₃K + H₄V₈ + H₅κ_max

Where

TC = total caustic TA = total alkali

Al = alumina

p = density

K = conductivity

V_s = sound velocity

Kmax = maximum conductivity during isothermal dilution

Imp = impurities

and A_x, B_x, C_x, and H_x are constants.

pcorrected ⁼ PmeasuredU ^"*^" preference "~ tmeasured).

Alternatively, models describing the density, conductivity etc may be developed from the test work or known models may be used and tuned to the liquor of interest yielding a set of equations where:

p = /Vv(TC, TA, Al, Imp, t)

κ = /n/(TC, TA, Al, Imp, t)

V₈ = /Vv(TC, TA, Al₁ Imp, t)

^Km₃X = ZVv(TC TA₁ AI, Imp, t)

Where t = temperature Commercially available models may be used or empirical models can be developed from the test work. Where the range of variability is small, a simple linear empirical model of the following form may be used:

p = D₁ + D₂TC + D₃TA + D₄AI + D₅lmp

K = Ei + E₂TC + E₃TA + E₄AI + E₅I mp

V_s = F₁ + F₂TC + F₃TA + F₄AI + F₅I mp

Km_ax = G₁ + G₂TC + G₃TA + G₄AI + G₅lmp

where D_x, E_x, F_x, and G_x are constants.

In most cases, the last equation reduces to κ_max = J₁ + J₂.^AI/_Tc where J_x are constants.

Prior to flushing, the pump 19 is stopped. The flushing of the liquor analyser apparatus then commences with motorised valves MV1 and MV2 being opened and the sample draining from the vessels 11 , 13, and 15 and reservoir 17. Motorised valve MV2 is closed and motorised valve MV3 and solenoid valve SV3 are both opened, allowing flush water to fill the vessels 11 , 13, and 15 and reservoir 17. Motorised valve MV1 is then closed, solenoid valve SV3 is closed and circulation pump 19 is started to provide flushing water turbulence to wash the probes and vessels 11 , 13, and 15 and reservoir 17. Washing of the vessels 11, 13, and 15 and reservoir 17 continues for 2 minutes (in practice, any time sufficient to clean them), pump 19 is stopped, motorised valves MV1 and MV2 opened allowing the vessels 11 , 13, and 15 to drain.

The above described flushing washing and draining procedure is repeated sufficiently to adequately flush the equipment, after which the vessels 11 , 13, and 15 and reservoir 17 are filled with water, motorised valves MV1 , MV3 and MV2 are closed.

In addition to this the programmable logic controller, at operator selectable intervals, for example 20 minute intervals, briefly opens motorised valves MV3, MV4 and solenoid valve SV3 to flush the sample tapping point

While the programmable logic controller operates by solving simultaneous equations to derive concentrations of alumina, total caustic, total alkali, and total impurities, in an alternative embodiment it may be possible to utilise a look-up table established from measured data of samples of known composition. Generally the procedure will involve developing physiochemical property models. Normally it is best to develop the physiochemical property models by laboratory work using laboratory precision instruments. However, in some cases this can be done in the field with the field instruments. In each case it is necessary to get sufficient measurements across a variety of liquor compositions to adequately describe in mathematical terms the relationships between the component values and the measured physiochemical properties. This is more easily done in the laboratory where experimental design can be applied and liquors can be modified to suit the design. In the field it is usually necessary to wait until sufficient variability has occurred in the liquor of interest. The model may be empirical or theoretical as long as it adequately describes the process over the normal operating range. In some cases the physiochemical property models may already be known in which case it is only necessary to test sufficiently to verify or tune the model for the application.

It should be appreciated that the scope of the invention is not limited to the specific embodiment disclosed herein. The measurements may be taken in a number of vessels to suit the particular instruments or a single vessel containing all of the measuring instruments.

Methods not involving dilution can be applied to full stream conditions or simple side streams but can be done also by sampling systems. Methods involving dilution (as described in the embodiment) will generally require a sampling system and some processing of the sample to maintain a constant or relatively constant temperature. This can be performed with any conventional temperature control method such as a heat exchanger, heat tracing or water jacket. Methods involving dilution will most probably require the circulation pump to keep the fluid passing through the cells and to ensure a homogenous solution is achieved during dilution. A simple stirrer could be used if a single cell is used. Dilution can be achieved by a number of different means such as a dilution pump, solenoid valve or other valves. A pump may not be required in methods not involving dilution.

Dilution methods may involve adding heated water to determine conductivity during dilution and maximum conductivity during dilution. This technique may be applied when analysing spent liquor where scaling is not such an issue.

While the embodiment has been described in relation to Bayer process liquors, it may have application in analysis of multi-component fluids in other industries where the particular measurements are suitable. Specifically contemplated is analysis of liquors in the pulp and paper industry.

Claims

The Claims Defining the Invention are as Follows

1. A process liquor analyser having: means to measure conductivity; means to measure sound velocity; means to measure density;

said analyser operable to receive a process liquor sample from said sample inlet and deliver said process liquor sample to said one or more vessels to take measurements of conductivity, sound velocity and density respectively of said sample,

and operable to drain said liquor sample, flush said one or more vessels with water from said water inlet, and to drain water from said one or more vessels before a further said process liquor sample is received.

2. A process liquor analyser as claimed in claim 1 adapted for analysis of a Bayer process liquor, including processor means to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) from the measurements taken of conductivity, sound velocity and density.

3. A process liquor analyser as claimed in claim 2 wherein said processor means is arranged to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) using simultaneous equations developed by regression of measurements taken of conductivity, sound velocity and density.

4. A process liquor analyser as claimed in claim 2 wherein said processor means is arranged to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) through comparison of measurements of conductivity, sound velocity and density with measurements of conductivity, sound velocity and density for reference samples acting as controls, the measurements for which are incorporated in a look-up table in memory or other data storage device.

5. A process liquor analyser as claimed in claim 1 wherein said analyser is operable to controllably receive water from said water inlet to dilute said process liquor sample within said one or more vessels, to allow said means to measure conductivity to measure conductivity as said sample is diluted, and optionally to measure maximum dilute liquor conductivity.

6. A process liquor analyser as claimed in claim 5 adapted for analysis of a Bayer process liquor, including processor means to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) from the measurements taken of conductivity, sound velocity and density, and conductivity during dilution.

7. A process liquor analyser as claimed in claim 6 wherein said processor means is arranged to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) using simultaneous equations developed by regression of measurements taken of conductivity, sound velocity and density, and conductivity during dilution.

8. A process liquor analyser as claimed in claim 6 wherein said processor means is arranged to determine the concentration of alumina, total caustic, and total alkali (and optionally total impurities) through comparison of measurements of conductivity, sound velocity and density, and conductivity during dilution, with measurements of conductivity, sound velocity and density, and conductivity during dilution, for reference samples acting as controls, the measurements for which are incorporated in a look-up table in memory or other data storage device.

9. A process liquor analyser as claimed in any one of claims 5 to 8 wherein said reservoir includes an overflow to drain excess fluid as said process liquor sample is diluted.

10. A process liquor analyser as claimed in any one of claims 6 to 8 wherein a parameter selected from either or both of sound velocity and density is measured as said process liquor sample is diluted, said parameter(s) measured being factored into the determination of the concentration of alumina, total caustic, and total alkali (and optionally total impurities).

11. A process liquor analyser as claimed in any one of the preceding claims wherein said analyser is operable to flush said sample inlet with water from said water inlet and drain water from said sample inlet before a further said process liquor sample is received.

12. A process liquor analyser as claimed in any one of the preceding claims wherein said analyser is operable to flush said one or more vessels with liquor from said sample inlet and drain said one or more vessels before receiving a said process liquor sample for measurement.

13. A process liquor analyser as claimed in any one of the preceding claims wherein said means to measure conductivity, means to measure sound velocity, and means to measure density are contained within separate vessels fluidly connected in series.

14. A process liquor analyser as claimed in claim 13 wherein said means to measure conductivity, means to measure sound velocity, and means to measure density are connected in a circuit with a reservoir and a pump to recirculate said process liquor sample as measurements are taken.

15. A process liquor analyser as claimed in any one of the preceding claims wherein the means for measuring density is selected from a density meter and a refracto meter.

16. A process liquor analyser as claimed in claim 15 wherein said density meter is selected from apparatus that operate on the Coriolis principle, the vibrating loop principle, or the vibrating time principle.

17. A process liquor analyser as claimed in claim 15 adapted for analysis of a Bayer process liquor, wherein said refractometer measures total internal reflection in the Bayer process liquor.

18. A process liquor analyser as claimed in any one of the preceding claims adapted for analysis of a Bayer process liquor wherein said means to measure conductivity utilises the toroidal conductivity measurement method.

19. A process liquor analyser as claimed in any one of claims 14 to 18 wherein said analyser includes means to measure temperature associated with said circuit.

20. A process liquor analyser as claimed in claim 19 wherein measurements from said means to measure temperature are factored into the determination of the concentration of alumina, total caustic, and total alkali (and optionally total impurities).

21. A process liquor analyser as claimed in claim 19 or 20 wherein said means to measure temperature is associated with one or more of said one or more vessels.

22. A process liquor analyser as claimed in claim 21 wherein said means to measure temperature is contained within a said vessel with said means to measure conductivity.

23. A process liquor analyser as claimed in claim 19 or 20 wherein said means to measure temperature is contained within all three vessels.

24. A process liquor analyser as claimed in any one of claims 15 to 23 wherein at least part of said circuit is associated with means to exercise stabilising control over temperature of said process liquor sample.

25. A process liquor analyser as claimed in claim 24 wherein said means to exercise stabilising control over temperature comprises water jacket(s) surrounding said vessel(s).

26. A method of performing an on-line/in-field analysis of a Bayer process liquor in a process stream, said method including steps of taking measurements of conductivity, sound velocity and density respectively of liquor directly in said process stream, and from said measurements, determining concentration of alumina, total caustic, total alkali, and optionally total impurities.

27. A method of performing an on-line/in-field analysis of a Bayer process liquor from a process stream, said method including steps of taking measurements of conductivity, sound velocity and density respectively of a sample taken from said process stream, and from said measurements, determining concentration of alumina, total caustic, total alkali, and optionally, total impurities.

28. A method as claimed in claim 26 or 27 wherein measurements of density, conductivity, and sound velocity, and optionally temperature are taken on a number of fluids of varying composition, and from said measurements regression is used to develop simultaneous equations to calculate the liquor components of concentration of alumina, total caustic, and total alkali, and optionally total impurities.

29. A method as claimed in claim 28 wherein measurement of temperature is taken and used to apply temperature correction to the measurements of density, conductivity, and sound velocity.

30. A method as claimed in any one of claims 27 to 29 including taking measurements of conductivity during dilution of said sample.

31. A method as claimed in any one of claims 27 to 29 including taking measurement of maximum conductivity during dilution of said sample.

32. A method as claimed in any one of claims 26 to 31 wherein the temperature of the liquor at which measurements are taken is maintained within a predetermined range.

33. A method as claimed in any one of claims 26 to 32 including stabilising the temperature of said sample within a narrow range of ± 2⁰C.

34. A method as claimed in any one of claims 26 to 32 including stabilising the temperature of said sample within a narrow range of ± 1⁰C.

35. A method as claimed in any one of claims 26 to 32 including stabilising the temperature of said sample within a narrow range of ± 0.5⁰C.

36. A liquor analyser substantially as herein described with reference to the drawings.

37. A method of analysing a process liquor substantially as herein described with reference to the description of the embodiment.