Method for determining a sample stream concentration value of an analyte in a sample stream

Description

[0001] The present invention relates to a method for continuously determining a sample stream concentration value of an analyte in a sample stream containing an analyte in a solvent.

[0002] Particularly when the analyte is at a concentration close to the saturation concentration, it can precipitate from the solvent and deposit on the surfaces of measuring devices, thus impairing the concentration measurement. This is the case, for example, with highly concentrated brines, such as saline solutions, for which density measurement with vibronic sensors is generally suitable for determining the concentration. However, if saline is deposited on the sensor surfaces, the density measurement and thus the concentration determination are distorted.

[0003] It is therefore the object of the present invention to remedy this situation.

[0004] The object is achieved according to the invention by the method according to patent claim 1.

[0005] The method according to the invention serves for, in particular continuously, determining a sample stream concentration value of an analyte in a sample stream comprising the analyte and a solvent, the method comprising the following steps: Preparing a measurement stream by diluting the sample stream with a solvent stream; determining a measurement stream concentration value of the analyte in the measurement stream; and determining the sample stream concentration value of the analyte in the sample stream, depending on the measurement stream concentration value and a dilution ratio of sample stream and measurement stream.

[0006] In one embodiment of the invention, determining the measurement current concentration value comprises detecting a measured variable that depends on the concentration of the measurement current in the analyte. In one embodiment of this embodiment of the invention, the measured variable comprises the density of the measurement current.

[0007] In a further development of the invention, the dilution ratio is determined on the basis of a mass flow rate measurement value of the solvent stream and a mass flow rate measurement value of the measuring stream.

[0008] In a further development of the invention, the dilution ratio is regulated to a constant value.

[0009] In a further development of the invention, the dilution ratio is controlled by controlling the mass flow rate measured value of the solvent stream to a constant ratio to the mass flow rate measured value of the measuring stream, wherein the ratio is not more than 1 / 2, for example not more than 1 / 4, and in particular not more than 1 / 5.

[0010] In a further development of the invention, the analyte comprises a salt, in particular NaCl.

[0011] In a further development of the invention, the solvent comprises an aqueous medium, in particular water.

[0012] In a further development of the invention, a density measurement value for the density of the measuring current is determined by means of a vibronic sensor based on at least one oscillation frequency of the vibronic sensor.

[0013] In a further development of the invention, the measuring current is discarded after detecting the measured variable and determining the mass flow rate measured value of the measuring current.

[0014] In a further development of the invention, the sample stream is taken from a process media stream whose mass flow rate is not less than one hundred times, in particular not less than one thousand times, the mass flow rate of the sample stream, wherein the sample stream concentration value is output as the process media concentration value.

[0015] In the invention, the sample stream has a concentration of the analyte which is not more than 4% of the saturation concentration and in particular not more than 2% of the saturation concentration below a saturation concentration of the analyte in the solvent.

[0016] In the invention, the measuring current has a concentration of the analyte which is not less than 8% of the saturation concentration and in particular not less than 12% of the saturation concentration below a saturation concentration of the analyte in the solvent.

[0017] A device for determining a sample stream concentration value of an analyte in a sample stream comprising the analyte and a solvent, in particular according to the method according to the invention, wherein the device is not part of the invention according to the claims, comprises: A first Coriolis mass flowmeter configured to control a solvent flow as a function of the sample flow to dilute the sample flow to a measurement flow; a second Coriolis mass flowmeter configured to determine a mass flow measurement value of the measurement flow; a density meter configured to determine a density measurement value of the measurement flow; and a computing and operating unit configured to calculate the concentration of the analyte in the sample flow.

[0018] The device comprises a mass flow controller for controlling the solvent flow, wherein the mass flow controller is configured to control the solvent flow to a setpoint value which depends on the mass flow measured value of the measuring flow, wherein the first Coriolis mass flow meter is configured to provide the mass flow controller with an actual value of the solvent flow.

[0019] The invention will now be explained in more detail with reference to an embodiment shown in the drawings.

[0020] It shows: Fig. 1 : A schematic representation of an embodiment of a device according to the invention for carrying out the method according to the invention; Fig. 2 : A flowchart of an embodiment of the method according to the invention; and Fig. 3 : Measurement data on the measurement value stability of the method according to the invention.

[0021] The Fig 1 The device 100 shown comprises a pipeline 100 in which a mass flow 2 of a process medium, for example a brine, flows. The process medium contains an analyte in a solvent, in the example, table salt in water, wherein the concentration (X 3 ) of the analyte is to be determined. For process control, a high concentration is desired, ideally the saturation concentration, which is to be verified by a measurement. However, the analyte can precipitate and thereby falsify the measurement and, in extreme cases, clog the measuring arrangement. To determine the concentration, a sample stream 3, which is, for example, less than 0.1% of the mass flow of the process medium, is branched off according to the invention and diluted in a constant ratio by supplying a solvent stream 7 from a reservoir 6 in order to prepare a measuring stream 7 whose analyte concentration is significantly below the saturation concentration.

[0022] In the simplest case, the reservoir can comprise a water pipe, whereby the static pressure of the solvent stream 4 should be higher than that of the sample stream 3.

[0023] In order to achieve a constant dilution ratio, a mass flow rate measured value (ṁ 7 ) of the measuring stream 7 is determined using a Coriolis mass flow meter 8. The mass flow rate measured value (ṁ 7 ) is preferably fed to a mass flow controller 5b with an adjustable throttle, which further receives an actual value of the solvent stream 7 from an upstream Coriolis mass flow meter 5a and is configured to adjust a mass flow rate measured value (ṁ 4 ) of the solvent stream 4 to a constant proportion R of the mass flow rate measured value (ṁ 7 ) of the measuring stream by means of the throttle, i.e.: m ˙ 4 = m ˙ 7 ⋅ R = m ˙ 3 + m ˙ 4 ⋅ R

[0024] This gives the ratio of the mass flow rate (ṁ 3 ) of the sample mass flow 3 and the mass flow rate (ṁ 4 ) of the solvent flow 4: m ˙ 3 = m ˙ 4 1 − R R

[0025] The concentration of the analyte X 3 in the sample stream 3 can therefore be determined from the concentration X 7 of the analyte in the measuring stream 7 according to: x 3 = x 7 ⋅ m ˙ 4 1 − R R + m ˙ 4 m ˙ 4 1 − R R = x 7 ⋅ 1 1 − R

[0026] To determine the concentration, a density measurement value of the measuring stream 7 is determined either with the Coriolis mass flowmeter 8 or a subsequently arranged, vibronic micromechanical density meter 9, and a temperature measurement value of the measuring stream 7 is recorded, with the temperature sensor being integrated into the density meter 9. The measuring stream concentration value X 7 is calculated as a function of the density measurement value and the temperature measurement value. After the density measurement value ρ of the measuring stream 7 has been recorded, the measuring stream is discarded. The calculation of the measuring stream concentration value X 7 or the sample stream concentration value X 3 can be performed by an integrated computing unit of the density meter 9 or by a separate computing unit 10, if present, to which the required measured values ​​for density and temperature are fed.

[0027] It is not mandatory to maintain a constant dilution ratio R. However, it is necessary that the dilution ratio be precisely known. For this purpose, it is sufficient to have the first Coriolis mass flowmeter 5a for measuring the solvent flow and the second Coriolis mass flowmeter 8 for measuring the measuring flow 7. An uncontrolled dilution ratio R of the correct magnitude can be specified using a constant or adjustable throttle in the solvent flow.

[0028] In particular, the use of a micromechanical density meter and Coriolis mass flowmeters with nominal diameters of 1 mm and less enables continuous concentration determination with minimal sample volumes, making discarding the sample stream easily justifiable. Thus, the required measurement accuracies for mass flow rates at DN1 can be easily achieved with flow rates of 0.6 kg / h to 6 kg / h. At DN0.4, flow rates of 0.06 kg / h to 0.6 kg / h are sufficient.

[0029] In this example, the device for determining the concentration of a brine is operated with R = 20%. Thus, the concentration of table salt in the sample stream is: x 3 , NaCl = x 7 , NaCl ⋅ 1.25

[0030] The concentration of the analyte in the measuring stream is four-fifths of the concentration in the sample stream, and is thus sufficiently far from the saturation concentration to reliably prevent precipitation of the analyte (here table salt).

[0031] In summary, with reference to Fig. 2 The essential steps of the method according to the invention are as follows: The method (200) for determining a sample stream concentration value (X 3 ) of an analyte in a sample stream comprising the analyte and a solvent begins with the preparation (210) of a measurement stream by diluting the sample stream with a solvent stream. This ensures that the concentration of the analyte in the measurement stream is significantly below the saturation concentration of the analyte, and precipitation of the analyte cannot falsify the measurement. The next step involves determining (220) a measurement stream concentration value (X 7 ) of the analyte in the measurement stream, which here is essentially done on the basis of a density measurement.Finally, the determination (230) of the sample stream concentration value (X 3 ) of the analyte in the sample stream is carried out by calculation as a function of the measuring stream concentration value (X 7 ) and the dilution ratio (R) between the sample stream (3) and the measuring stream (7).

[0032] Fig. 3 shows data from concentration measurements on an undiluted sample stream with approximately 26.1 mass% salt up to t = 420 h, based on density measurements on a brine with a constant saturation concentration. Here, a steady increase in concentration is apparently measured, as salt settles on the oscillator and thus causes a mass increase, which distorts the measurement. From 420 hours onwards, however, a dilution with R = 22% occurred. The measured data show the salt concentration in the sample stream at a constant 20.4 mass%. The conversion according to x 3 = x 7 ⋅ 1 1 − R results in a concentration of 26.15 mass% for the undiluted sample stream. This represents a significant improvement over the state of the art in terms of measurement accuracy and stability.

Claims

1. Method (200) for determining a sample stream concentration value (X3) of an analyte in a sample stream (3) comprising the analyte and a solvent, the method comprising the steps of: preparing (210) a measuring stream (7) by diluting the sample stream (3) with a solvent stream (4); determining (220) a measuring stream centration value (X7) of the analyte in the measuring stream (7); and determining (230) the sample stream concentration value (X3) of the analyte in the sample stream as a function of the measuring stream concentration value (X7) and a dilution ratio (R) of sample stream (3) and measuring stream (7), wherein the sample stream (3) has a concentration of the analyte which is not more than 4% of the saturation concentration and in particular not more than 2% of the saturation concentration below a saturation concentration of the analyte in the solvent, and wherein the measuring current (7) has a concentration of the analyte which falls below a saturation concentration of the analyte in the solvent by not less than 8% of the saturation concentration and in particular not less than 12% of the saturation concentration.

2. Method according to claim 1, wherein determining (220) the measuring stream concentration value (X7) comprises sensing a measure that depends on the concentration of the measuring stream in the analyte.

3. Method according to claim 2, wherein the measure comprises the density of the measuring stream (7).

4. Method according to one of the preceding claims, wherein the dilution ratio (R) is determined on the basis of a measured mass flow rate (4) of the solvent stream (4) and a measured mass flow rate (7) of the measuring stream (7).

5. Method according to one of the preceding claims, wherein the dilution ratio (R) is controlled to a constant value.

6. Method according to claim 5, wherein the dilution ratio is controlled by controlling the mass flow rate measurement value (4) of the solvent stream (4) to be in a constant ratio to the mass flow rate measurement value (7) of the measuring stream (7), wherein the ratio is no longer 1 / 2, for example no longer than 1 / 4, and in particular no longer than 1 / 5.

7. Method according to one of the preceding claims, wherein the analyte comprises a salt, in particular NaCl.

8. Method according to one of the preceding claims, wherein the solvent comprises an aqueous medium, in particular water.

9. Method according to claim 3, wherein a measured density value for the density of the measuring stream (7) is determined by means of a vibronic based on at least one vibration frequency of the vibronic sensor (9).

10. Method according to one of the claims 2 and 4 and, if applicable, dependent preceding claims, wherein the measuring stream (7) is discarded after detecting the measured variable and determining the mass flow rate measured value (7) of the measuring stream.

11. Method according to one of the preceding claims, wherein the sample flow (7) is taken from a process media flow (2) whose mass flow rate is not less than one hundred times, in particular not less than one thousand times, a mass flow rate of the sample flow (3), wherein the sample flow concentration value is output as a process media concentration value (X3).