Process water analyzer

Abstract

The invention relates to a process water analyzer (10) for automatically analyzing parameters of a water sample. Comprising a process liquid storage tank (70, 72) having a process liquid (70 ', 72') wherein a process liquid storage volume (V70, V72) in the storage tank (70, 72) defines a storage liquid level (I70, I72) at a storage liquid level height (h70, h72), a metering chamber (30) fluidly connected to the process liquid storage tank (70, 72) and fluidly positioned downstream of the process liquid storage tank (70, 72), and a positive displacement metering pump (20) fluidly connected to the process liquid storage tank (70, 72) and fluidly positioned downstream of the process liquid storage tank (70, 72). And a valve (30) fluidly connected to the top of the metering chamber (30), the metering pump (20) is used for sucking the process liquid (70 ', 72') into the metering chamber (30), an air cushion (27) is always vertically arranged between the metering pump (20) and a metering chamber liquid level (I) in the metering chamber (30), so that a liquid column (Ic70, Ic72) with an effective vertical liquid column length (c70, c72) is provided between the storage liquid level (I70, I72) and the metering chamber liquid level (I), and the air cushion (27) is used for sucking the process liquid (70 ', 72') into the metering chamber (30). The metering pump (20) directly sucks in a pressure-adapted gas volume (Vgas) of the air cushion (27) having an air cushion pressure (P) in order to pump a set process liquid volume (Vliquid) into the metering chamber (30), and wherein a process liquid dose control unit (200) is provided in order to control the process liquid volume (Vliquid) in the metering chamber (30). The process liquid dose control unit (200) provides a value of the pressure-adapted pumped gas volume (Vgas) as a function of the gas cushion pressure (P) affected by the effective vertical liquid column length (c70, c72).

Description

Technical Field

[0001] The present invention relates to a process water analyzer for automatically analyzing parameters of a water sample. Background Art

[0002] Process water analyzers determine a parameter of the water quasi-continuously. This parameter can be an analyte, such as the concentration of a substance, for example ammonium or phosphate, or a more complex parameter, such as total organic carbon (TOC). Process water analyzers include one or more process liquid storage tanks with the process liquid required to provide the complete measurement process. Typical process liquids are reagents for providing a reaction with the analyte, such as a color reaction, or other process liquids, such as cleaning liquids or standard solution liquids.

[0003] The process liquid is stored in a process liquid storage tank filled with the process liquid. The process liquid storage volume in the storage tank defines a storage liquid level at a storage liquid level height.

[0004] A metering chamber is provided which is fluidly connected to the process liquid storage tank and is arranged fluidly downstream of the process liquid storage tank and upstream of a measuring chamber of the analyzer unit in which a final quantitative measurement of the parameter is provided, for example by photometric means.

[0005] In order to meter the process liquid accurately, process water analyzers are usually provided with a very precise positive displacement metering pump, which allows firstly a set process liquid volume to be sucked from a process liquid storage tank into a separate metering chamber and then to be pushed from the metering chamber to the analyzer unit, for example to a photometer.

[0006] An air cushion is always arranged vertically between the metering pump and the process liquid level in the metering chamber to avoid any direct contact between the process liquid and the metering pump. This measure avoids any contamination of the metering pump by any process liquid, thereby ensuring a longer service life of the metering pump.

[0007] Between the storage liquid level of the process liquid and the metering chamber liquid level of the same process liquid there is always a hydrostatically relevant liquid column with an effective vertical liquid column length. The higher the effective vertical liquid column length, the more the gas cushion expands during the metering pumping process step due to the weight of the liquid column suspended directly below the gas cushion. The vertical liquid column length depends on the storage liquid level of the process liquid in the storage tank.

[0008] In order to detect the storage liquid level directly, all process liquid storage tanks require multiple filling level sensors, which is expensive. Therefore, preferably no filling level sensor is provided for any storage tank. As a result, the length of the vertical liquid column between the metering chamber liquid level and the storage liquid level cannot be accurately known, and thus the expansion effect of the vertical liquid column on the air cushion between the metering chamber liquid level and the metering pump cannot be known. As a result, it is impossible to pump a precisely set process liquid volume into the metering chamber. The resulting inaccuracy of the pumped process liquid volume is in the range of several percentage points, which makes it necessary to always pump the worst-case process liquid volume, so that in most cases the process liquid is consumed more than necessary. If the analyzer unit of the process water analyzer is a photometer, a systematic overdosing of the process liquid volume can lead to systematic photometric faults caused by the inherent color of the process liquid. Summary of the invention

[0009] It is an object of the present invention to provide a process water analyzer having improved accuracy for pumping a set volume of process liquid from a process liquid storage tank to a metering chamber.

[0010] This object is achieved with a process water analysis device having the features of main claim 1 .

[0011] The process water analyzer for automatically analyzing parameters of a water sample according to the present invention comprises at least one process liquid storage tank having a process liquid, such as a colorimetric reagent, a cleaning liquid, a flushing liquid and / or one or more standard solution liquids. The process liquid storage volume defines a storage liquid level at a storage liquid level height, which is the vertical distance between the bottom of the storage tank and the level of the process liquid surface in the storage tank. The process liquid storage tank is preferably a disposable tank.

[0012] The process water analyzer is provided with a metering chamber which is fluidly connected to a process liquid storage tank and is fluidly positioned downstream of the process liquid storage tank. The metering chamber is preferably positioned vertically higher than the process liquid storage tank. The metering chamber is a separate chamber which is used to accurately quantify the volume of the liquid sample and the process liquid before pumping a defined volume of liquid to the analysis unit.

[0013] The process water analyzer is provided with a positive displacement metering pump, which is fluidically connected to the top of the metering chamber for sucking a defined set process liquid volume from a corresponding process liquid storage tank into the metering chamber via a liquid line, which has an inlet opening in the bottom area of ​​the process liquid storage tank and a liquid line outlet opening at the bottom of the metering chamber. An air cushion is always arranged vertically between the metering pump and the process liquid level in the metering chamber to avoid direct contact between the metering pump and the process liquid. This measure avoids any contamination of the metering pump by any process liquid, thereby ensuring a long service life of the metering pump.

[0014] If the process liquid storage tank is arranged vertically below the metering chamber, a liquid column with an effective vertical liquid column length is suspended vertically below the air cushion, thereby expanding the total volume of the air cushion, so that the static gas pressure in the closed air cushion is correspondingly reduced. The effective vertical liquid column length is the vertical distance between the metering chamber liquid level in the metering chamber and the storage liquid level in the storage tank. The storage liquid level has a total storage liquid level height above the bottom wall of the storage tank.

[0015] The process water analyser is provided with a process liquid dosing control unit which provides the value of a pressure-adapted pumped gas volume which depends on the gas cushion pressure which is influenced by the effective vertical liquid column length, the specific gravity of the process liquid and the liquid level surface area of ​​the process liquid in the metering chamber. According to the invention, the metering pump directly draws in the pressure-adapted pumped gas volume with the gas cushion pressure of the gas cushion and thereby indirectly pumps a precisely set process liquid volume into the metering chamber. This compensates for the gas volume expansion effect of the changing vertical liquid column, so that the accuracy of the process liquid volume pumped into the metering chamber no longer depends on the effective vertical liquid column length.

[0016] As a result, it is no longer necessary to pump generally offset volumes of process liquid, with a corresponding reduction in process liquid consumption. In photometric applications, systematic faults caused by the inherent color of the process liquid are no longer given.

[0017] According to a preferred embodiment of the invention, the process water analyser is provided with a gas pressure sensor, which is fluidically connected to the metering pump inlet / outlet opening for directly detecting and sensing the gas pressure of the gas cushion above the liquid surface of the metering chamber. Preferably, the gas pressure sensor is fluidically arranged in the top region of the metering chamber or between the metering chamber and the metering pump. Since the gas pressure of the gas cushion is directly determined by the gas pressure sensor, the resulting total volume of the gas cushion, which is substantially proportional to the gas pressure, can be directly calculated, so that ultimately the value of the pressure-adapted pumped gas volume can be calculated.

[0018] Preferably, the process liquid dosage control unit also determines the actual storage liquid level based on the gas cushion pressure provided by the gas pressure sensor.

[0019] According to an alternative embodiment of the present invention, a storage liquid level register is provided for providing the actual storage liquid level. The process liquid dosing control unit provides a pressure-adapted pumped gas volume based on the effective vertical liquid column length, which is dependent on the actual storage liquid level provided by the storage liquid level register. Generally, although the storage liquid level register can operate in different ways, it is preferred to record and accumulate the metering pump activity used to pump the process liquid, thereby calculating the storage liquid level of the process liquid in the storage tank. Since the actual storage liquid level can be known from the storage liquid level register, the effective vertical liquid column length is also known, so the value of the pressure-adapted pumped gas volume can be calculated.

[0020] Preferably, the metering chamber and / or any liquid storage tank is not provided with any continuous liquid level sensor which could determine the actual level of liquid in the metering chamber or the liquid storage tank.

[0021] Preferably, the metering pump is a piston pump. Piston pumps pump fluid very accurately and with high consistency.

[0022] Preferably, the metering pump is provided with an electric stepper motor.An electric stepper motor in the context of the present invention is every motor which allows precise control and registration of the number of rotation steps of the motor rotor.

[0023] Preferably, the gas pressure sensor is a differential gas pressure sensor, which measures the difference in gas pressure relative to the atmospheric pressure of the immediate process water analyzer environment. The differential gas pressure sensor compensates for the effects caused by any deviation of the actual ambient atmospheric pressure from a standard pressure (e.g. 1013 mbar). Thus, the use of a differential gas pressure sensor makes it superfluous to accurately determine the actual atmospheric pressure of the water analyzer environment.

[0024] Preferably, a total atmospheric pressure sensor may be provided to determine the total atmospheric pressure as a reference. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] An embodiment of the present invention is explained with reference to the drawings.

[0026] The figure schematically shows a process water analyzer according to the invention having a process liquid dosage control unit which uses a gas pressure sensor to provide a value for a pressure-adapted pumped gas volume in order to accurately pump a set process liquid volume into a metering chamber. DETAILED DESCRIPTION

[0027] Figure 1 A process water analyzer 10 for automatically analyzing a parameter of a water sample from a wastewater plant tank 80 filled with wastewater 80' is schematically shown. The analyzer 10 is provided with a photometer 50, which photometrically analyzes and determines the concentration of a parameter of the water sample pumped from the wastewater tank 80 to a photometer measurement chamber 52 of the photometer 50 by a sample pump 82. The photometer measurement chamber 52 is provided with a photometric unit 54, which includes a photometric light source 541 and a photometric receiver 542. Generally, the measurement chamber may be part of another type of analyzer measurement unit.

[0028] In the drawings, the vertical direction is y, and the horizontal plane is defined by x and z.

[0029] Process water analyzer 10 further includes: two process liquid storage tanks 70, 72 with process liquid 70', 72'; metering chamber 30, which is fluidly connected to process liquid storage tanks 70, 72 via vertical supply lines 73, 73', respectively; and positive displacement metering pump 20. However, six or even more different process liquid storage tanks may be provided.

[0030] In the present embodiment, the process liquids 70', 72' are a reagent liquid and a cleaning liquid. The reagent liquid may be a reagent for colorimetric determination of, for example, phosphate. The actual process liquid storage volumes V70 and V72 in the respective storage tanks 70, 72 result in storage liquid levels I70, I72 having storage liquid level heights h70, h72 above the bottom wall surface 74 of the respective storage tanks 70, 72. A typical total liquid volume of a new and fully filled process liquid storage tank is, for example, 2.0 liters.

[0031] The metering chamber 30 with a typical volume of 3.6 ml is vertically located above the process liquid storage tanks 70, 72 and is fluidically connected to the process liquid storage tanks 70, 72 via two process liquid inlet openings 37, 38 at the horizontal bottom wall 31 of the metering chamber housing 32. The process liquid inlet openings 37, 38 define the vertical top ends of the supply lines 73, 73', respectively. The vertically downward ends of the supply lines 73, 73' are arranged close to the bottom wall surface 74 of the corresponding storage tank 70, 72. A switchable supply line valve 41, 42 is arranged on the route of each supply line 73, 73'.

[0032] An exhaust opening 33 is provided at the top wall of the metering chamber 30, which allows the interior of the metering chamber to be exhausted with atmospheric pressure PA when a switchable exhaust valve 34 is open. A pump line opening 35 is provided at the top wall of the metering chamber 30. The interior of the metering chamber 30 is fluidically connected to the metering pump 20 via the pump line opening 35 and the pump line 35'. A differential gas pressure sensor 60 is provided at the pump line 35'. The metering chamber 30 is provided with an optical single-point liquid level sensor 58, which detects whether liquid is present at the vertical level of the liquid level sensor 58.

[0033] The metering chamber 30 is further provided with an analyzer liquid outlet opening 36, which fluidically connects the metering chamber interior with the photometer measuring chamber 52 via a connecting line 43' and a switchable photometer line valve 43. After providing a photometric measurement, the liquid of the photometer measuring chamber 52 is drained into a waste container.

[0034] The positive displacement metering pump 20 is provided with an electric pump motor 22 which is an electric stepper motor and actuates a pump piston 24 to move linearly within a pump cylinder 26. The total displacement of the metering pump 20 is 5.0 ml and the number of motor steps to actuate the piston 24 from one cylinder end to the other totals 5000 steps.

[0035] A gas cushion 27 is provided which is fluidly positioned between the pump piston 24 of the metering pump 20 and the actual metering chamber liquid level l of the liquid in the metering chamber 30. The gas pressure sensor 60 is a differential pressure sensor which measures the pressure difference between the gas pressure P of the gas cushion 27 and the atmospheric pressure PA of the environment of the analyzer 10.

[0036] The process water analyzer 10 comprises a process liquid dosage control unit 200, which is provided with a storage liquid level register 210, which controls all pumping actions and motor steps of the metering pump 20. The process liquid dosage control unit 200 receives the pressure signal of the gas pressure sensor 60 and the liquid presence indication signal of the liquid level sensor 58. The process liquid dosage control unit 200 also controls the photometer 50, the sample pump 82 and all switchable valves 34, 41, 42, 43.

[0037] After applying two new and completely filled process liquid storage tanks 70, 72 to the water process water analyzer 10, an initial automatic reference measurement is provided, which is controlled by the process liquid dosage control unit 200 to verify whether the new process liquid storage tanks 70, 72 are completely filled with the correct process liquid. The initial reference measurement is controlled by the process liquid dosage control unit 200:

[0038] The first supply line valve 41 is opened, and the second supply line valve 42, the photometer line valve 43 and the exhaust valve 34 are closed. The metering pump 20 delivers the predetermined pre-filling volume V through the corresponding supply line 73. prime The first process liquid 70' is sucked into the metering chamber 30. The pre-filling volume V prime The value of is large enough to ensure that the upper liquid level of the pre-filling liquid is indeed located directly above the liquid outlet opening 36.

[0039] Then, the first supply line valve 41 is closed, the second supply line valve 42 remains closed and the photometer line valve 43 is opened, so that the process liquid in the metering chamber 30 is pumped to the photometer 50 through the liquid outlet opening 36 by the started metering pump 20. The liquid in the metering chamber 34 falls to the liquid column reference level I', and the liquid level is maintained at the liquid column reference level I'. The liquid column reference level I' is preferably located precisely in the horizontal plane defined by the liquid inlet openings 37, 38.

[0040] In the next reference process step, the photometer line valve 43 is closed, the exhaust valve 34 is briefly opened and then closed again, so that the ambient atmospheric pressure PA serves as the reference metering chamber pressure P defined in the metering chamber 30 .

[0041] Then, the first supply line valve 41 is opened, and the other three valves 34, 42, and 43 remain closed, so that the vertical liquid columns Ic70 and Ic72 between the liquid column reference level I' and the storage liquid level I70 expand the air cushion 27, so that the total gas pressure P of the air cushion 27 is lower than the ambient atmospheric pressure PA.

[0042] The specific gravity of the process liquid 70' is known and has been stored in the process liquid dosing control unit 200, so that the dosing control unit 200 can determine or calculate the total vertical liquid column length c70' based on the pressure P, determine the precise storage liquid level I70 based on the liquid column length c70', and finally determine the actual process liquid storage volume V70 of the new process liquid storage tank 70 based on the storage liquid level I70.

[0043] The same procedure is also applied to another new liquid storage tank 72 so that process liquid dosage control unit 200 determines the liquid column length c72' of second liquid storage tank 72 and the resulting liquid process liquid storage volume V72.

[0044] The storage liquid level register 210 records all pumping actions and pump motor steps of the metering pump 20 to suck one of the process liquids 70', 72' from the process liquid storage tanks 70, 72 through the metering chamber 30, and continuously accumulates the consumed volume of the process liquid 70', 72', so that the remaining actual process liquid storage volume V70, V72 can always be roughly calculated.

[0045] Furthermore, the process liquid dosage control unit 200 can provide plausibility measurements from time to time in order to verify and, if necessary, correct the calculated actual process liquid storage volumes V70, V72 and the corresponding vertical storage liquid levels I70, I72 stored in the storage liquid level register 210. In the plausibility measurement, the pressure P caused by the liquid column Ic70, Ic72 of one of the process liquids 70', 72' is measured by the pressure sensor 60 and the plausibility of this pressure P is checked together with the roughly calculated metering chamber liquid level I and the roughly calculated storage liquid level I70 stored in the storage liquid level register 210.

[0046] As described above, the storage liquid level register 210 always roughly knows the actual storage liquid level I70, I72. For the measuring action, the process liquid dosage control unit 200 causes the metering pump 22 to pump and aspirate the pressure-adapted gas volume V of the air cushion 27. gas , so that the set process liquid volume V liquid The process liquid is pumped from the respective process liquid storage tank 70 , 72 into the metering chamber 30 .

[0047] Before the pumping action begins, the process liquid dosage control unit 200 determines the actual effective vertical liquid column length c70, c72 based on the actual storage liquid level I70, I72, and calculates the pressure-adapted pumped gas volume V according to the expected gas cushion pressure P affected by the effective vertical liquid column length c70, c72, the surface area of ​​the liquid with the metering chamber liquid level, and the corresponding specific gravity of the process liquid 70', 72'. gas As a result, the gas volume expansion effect of the vertical liquid columns Ic70, Ic72 is compensated so that the set process liquid volume V pumped and sucked is liquid Not affected by the actual storage liquid levels I70, I72.

[0048] Pressure adaptation gas volume V gas The adjustment and calculation of can be simply based on the gas cushion pressure P which is continuously controlled by the gas pressure sensor 60. The process liquid dosage control unit 200 calculates the pressure adaptation gas volume V based on the gas cushion pressure P, the liquid surface area and specific gravity of the process liquid 70', 72' gas , to pump a set process liquid volume V liquid .

[0049] When the set process liquid volume V liquid After being accurately pumped into the metering chamber 30 to reach the set process liquid chamber level I, the process liquid dosage control unit 200 switches the valves 34, 41, 42, 43 accordingly and enables the metering pump 20 to have the set process liquid volume Vliquid The complete liquid volume is pushed from the metering chamber 32 to the photometric measuring chamber 52 of the photometer 50 .

Claims

1. A process water analyzer (10) for automatically analyzing parameters of a water sample, comprising: A process liquid storage tank (70, 72) having a process liquid (70', 72'), wherein a process liquid storage volume (V70, V72) in the storage tank (70, 72) defines a storage liquid level (I70, I72) at a storage liquid level height (h70, h72), a metering chamber (30) fluidly connected to the process liquid storage tank (70, 72) and fluidly positioned downstream of the process liquid storage tank (70, 72), and a positive displacement metering pump (20) fluidly connected to the top of the metering chamber (30) for drawing the process liquid (70', 72') into the metering chamber (30), An air cushion (27) is always vertically arranged between the metering pump (20) and the metering chamber liquid level (I) in the metering chamber (30), thereby providing a liquid column (Ic70, Ic72) having an effective vertical liquid column length (c70, c72) between the storage liquid level (I70, I72) and the metering chamber liquid level (I), The metering pump (20) directly sucks a pressure-adapted gas volume (V) having an air cushion pressure (P) of the air cushion (27). gas ), thereby setting the process liquid volume (V liquid ) is pumped into the metering chamber (30), and A process liquid dosage control unit (200) is provided, wherein the process liquid dosage control unit (200) provides the pressure-adapted pumped gas volume (V) according to the gas cushion pressure (P) affected by the liquid column (Ic70, Ic72) having the effective vertical liquid column length (c70, c72). gas ) value.

2. The process water analyzer (10) of claim 1, wherein: A gas pressure sensor (60) is provided for directly sensing the air cushion pressure (P).

3. The process water analyzer (10) of claim 2, wherein: The process liquid dosage control unit (200) determines an actual storage liquid level (I70, I72) based on the gas cushion pressure (P) provided by the gas pressure sensor (60).

4. The process water analyzer (10) as claimed in any one of the preceding claims, wherein: The liquid storage tanks (70, 72) are configured without a liquid level sensor.

5. The process water analyzer (10) according to any one of the preceding claims, wherein: The metering pump (20) is a piston pump.

6. The process water analyzer (10) as claimed in any one of the preceding claims, wherein: The metering pump (20) is provided with an electric stepping motor (22).

7. The process water analyzer (10) according to any one of the preceding claims, wherein: The gas pressure sensor (60) is a differential sensor for measuring the pressure difference between the gas pressure (P) and the atmospheric pressure (PA).

8. The process water analyzer (10) according to any one of the preceding claims, comprising a storage liquid level register (210) for providing an actual storage liquid level (I70, I72), wherein: The process liquid dosage control unit (200) provides a pressure-adapted pumped gas volume (V) according to the effective vertical liquid column length (c70, c72) gas ), the effective vertical liquid column length depends on the actual stored liquid level (I70, I72) provided by the stored liquid level register (210).

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