Analytical device and corresponding method for determining a concentration of an analyte
By using pressure and flow rate sensors in a high-temperature digestion device to monitor the liquid sample feeding process, the problems of sample injection uncertainty and leakage detection are solved, enabling reliable monitoring and high-precision measurement of sample volume and supporting predictive maintenance of the system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ENDRESS HAUSER CONDUCTA GMBH CO KG
- Filing Date
- 2025-11-28
- Publication Date
- 2026-06-12
Smart Images
Figure CN122193137A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to an analytical apparatus and a corresponding method for determining the concentration of an analyte. Background Technology
[0002] For example, adding feed liquids to reaction vessels plays a crucial role in analytical techniques. In such applications, it is typically necessary to add analytes or reagents. The purpose of adding feed liquids is usually to introduce a specific volume of the substance into the reaction vessel.
[0003] For example, in wastewater analysis where analytes must be fed into a reaction vessel, an important application is determining the carbon and / or nitrogen content in the wastewater, such as total organic carbon (TOC) or total bound nitrogen (TNb). In known methods for determining these parameters, a small volume of liquid sample (e.g., several hundred microliters) is supplied to the reaction vessel of a high-temperature digestion apparatus. In the reaction vessel, formed by a high-temperature reactor, for example designed as a pyrolysis tube, the organic components are thermally decomposed into carbon dioxide (CO2), and the nitrogenous components are decomposed into nitrogen oxides (NOx). In this context, NOx refers to a mixture of nitrogen oxides with nitrogen in different oxidation states, but with NO as the predominant component. During the reaction in the high-temperature reactor, a gaseous mixture is generated, which, in addition to CO2 and NOx, contains vaporized water (H2O) and possible other pyrolysis and reaction products of the substances in the sample. The gaseous mixture is then passed sequentially through a cooler with a water separator, a gas filter, and an analysis unit, with the carrier gas flowing permanently through the reaction vessel, which is typically also supplied with the necessary reaction oxygen. The amount of CO2 or NOx produced is determined, for example, by infrared or chemiluminescence measurement, and the TOC or TNb content of the liquid sample is determined from this value.
[0004] The dominant temperature in the high-temperature digestion apparatus during operation is well above the boiling point of the added liquid sample. During the determination of total organic carbon (TOC) or total nitrogen (TNb), the temperature inside the reaction vessel is typically between approximately 650°C and 1300°C, depending on whether the sample digestion is supported by a catalyst. Upon contact with the walls of the reaction vessel or other surfaces present within the vessel, the sample reaches its boiling point or the reaction temperature required to react with the oxygen contained in the carrier gas within a very short time. Therefore, the sample added to the reaction vessel immediately enters the gas phase through evaporation and / or the formation of gaseous reaction products after being added.
[0005] The existing system has several drawbacks: it cannot be guaranteed that the sample has actually been injected into the oven. Furthermore, the volume of the injected sample is only theoretically known. Moreover, the overall state of the system is also unknown, such as whether contamination exists. Leaks in the system cannot be detected. Summary of the Invention
[0006] Therefore, the object of the present invention is to provide a method for operating an analytical device that overcomes the shortcomings of the methods described above. Specifically, a method for operating an analytical device is specified that ensures reliable monitoring of the dosage of liquid samples on the one hand, and reliable measurement modes with high accuracy on the other.
[0007] This objective is achieved by an analytical device for determining the concentration of analytes, particularly oxidizable components, in a liquid sample. The device includes a feeding mechanism, specifically a pump, for feeding the liquid sample into a high-temperature digestion apparatus for digesting the liquid sample and forming a gas mixture. The high-temperature digestion apparatus has a reaction vessel with a liquid inlet for the liquid sample and a gas supply line for supplying a carrier gas, and is connected to an analysis chamber via a gas outlet. During operation of the device, a flow of carrier gas is formed between the gas inlet and the analysis chamber. A pressure sensor is located in the direction of the gas flow. An analytical chamber is positioned upstream of the gas supply line, wherein a pressure sensor is coupled to a control unit for further processing the pressure signal output by the pressure sensor; wherein a first flow rate sensor is positioned upstream of the analytical chamber, specifically within the gas supply line for supplying carrier gas, in the direction of gas flow, wherein the first flow rate sensor is coupled to a control unit for further processing the flow rate signal output by the flow rate sensor; and wherein a second flow rate sensor is positioned downstream of the analytical chamber in the direction of gas flow, wherein the second flow rate sensor is coupled to a control unit for further processing the flow rate signal output by the flow rate sensor.
[0008] Because the temperature of the reaction vessel is above the boiling point of the added liquid, the liquid immediately transforms into a gaseous phase upon entering the reaction vessel through evaporation and / or by forming gaseous reaction products. In particular, upon contact with surfaces within the reaction vessel (e.g., the inner wall of the reaction vessel, the surface of inserts disposed within the reaction vessel, or the catalyst bed), heat is rapidly transferred to the sample, especially immediately, for example within less than 0.3 seconds, and particularly within less than 0.1 seconds, causing the sample to immediately transform into a gaseous phase upon contact with the surface. Inserts containing bulk material may be provided within the reaction vessel, the surfaces of which can undergo rapid heat transfer to the impacting sample. The transformation of the sample into a gaseous phase results in a brief increase in pressure within the reaction vessel, hereinafter referred to as a pressure surge or pressure pulse.
[0009] The pressure signal is recorded using pressure sensors positioned within the gas flow. These pressure sensors, also known as pressure sensors, can, in principle, be positioned anywhere along the gas flow path. A preferred location is outside the reaction vessel because of the lower temperatures present inside. Pressure changes within the reaction vessel caused by flow resistance during the gas flow can also be detected by pressure sensors positioned outside the reaction vessel, specifically within the supply line that introduces the gas into the reaction vessel.
[0010] This system enables early identification of maintenance needs (predictive maintenance) through pressure and flow rate measurements. Differential flow rate measurement allows for early leak detection. The system ensures that samples are injected into the oven. However, by measuring the maximum pressure over time and integrating the pressure, it is possible to assess whether the required amount has entered the oven.
[0011] In one embodiment, the analytical apparatus includes a data processing unit that controls all functions of the analytical apparatus, and in particular controls or executes the methods described above for determining the concentration of analytes in liquid samples. The central data processing unit specifically controls the feeding device for adding liquid samples and evaluates signals from the detection devices arranged in the analytical chamber. Specifically, the central data processing unit calculates and outputs the analytical results. However, it can also be designed as a stand-alone data processing unit.
[0012] Between the gas outlet of the reaction vessel and the analysis chamber, a filter unit for removing solid particles from the gas flow and a condensation unit for condensing water from the gas flow can be arranged in the flow path of the gas flow.
[0013] This analyzer uses changes in pressure and flow rate behavior for condition identification and proactive maintenance (often referred to as "predictive maintenance"). Leaks can be identified early using differential flow rate measurements. The system identifies whether a sample has been injected into the oven and whether the required amount has been reached. It also enables early detection of catalyst bed overload due to non-flammable residues in the sample.
[0014] One embodiment provides a method for continuously introducing carrier gas.
[0015] One embodiment provides feeding samples into the oven in batches, specifically every 5 to 10 minutes.
[0016] This objective is further achieved by a method for determining the TOC content in a liquid sample using the aforementioned analytical equipment.
[0017] One embodiment provides that leakage is inferred by the difference between determined flow rates.
[0018] One embodiment provides a method for determining whether any sample has arrived at the oven based on pressure measurements.
[0019] One embodiment provides for determining and controlling the sample quantity based on the pressure measurement, wherein incorrect feeding, particularly insufficient sample quantity, is detected.
[0020] To determine the amount of sample added to the reaction vessel, it can be compared with a reference pressure value and a pressure change associated with the current pressure signal. The current pressure signal can be identified from the pressure signal sequence, and the pressure change can be compared with a predetermined threshold. Based on the comparison results, it can be determined whether the pressure change corresponds to the pressure fluctuation caused by adding the sample to the reaction vessel.
[0021] In doing so, a baseline pressure value can be formed by calculating the average of at least two pressure signals preceding the current pressure signal in a pressure signal sequence, specifically by calculating a moving average. For example, the baseline pressure value at the start of the method can be set as the dominant pressure in the reaction vessel before sample feeding begins. During liquid feeding, continuous pressure signals are recorded, and a moving average is calculated taking into account the most recent pressure signal in the sequence to adjust the baseline pressure value.
[0022] Since the baseline pressure value corresponds to the dominant "background pressure" in the reaction vessel, it represents the "zero line" or "baseline" of the pressure curve.
[0023] One embodiment provides for determining a reference pressure value based on pressure measurements, particularly by averaging over a certain period of time, and inferring a fault, such as contamination, in the analytical device based on changes in the reference pressure value.
[0024] One embodiment provides inferences about possible maintenance based on pressure curves and flow rate measurement curves. Attached Figure Description
[0025] Please refer to the attached diagram for a more detailed explanation.
[0026] Figure 1 The analytical device for which protection is sought is illustrated schematically.
[0027] Figure 2 The path of the carrier gas is schematically shown.
[0028] Figure 3 The CO2 signal at the top and the measured pressure at the bottom are shown.
[0029] Figure 4a The image shows the CO2 signal at the top and the measured flow rate at the second flow rate sensor at the bottom.
[0030] Figure 4b The image shows the CO2 signal at the top and the measured flow rates at the first and second flow rate sensors at the bottom.
[0031] Figure 5 The flow rate measured by two flow rate sensors is shown.
[0032] Figure 6 The pressure curves during the saltification process in the oven are shown.
[0033] In the accompanying drawings, the same features are marked with the same reference numerals. Detailed Implementation
[0034] In such Figure 1 In the analytical apparatus 1 shown for determining, for example, TOC or TNb content in a liquid sample (e.g., a wastewater sample), the sample is supplied from a feeding device 2 (shown only schematically) via an injection nozzle 3 to a reaction vessel 5, which is designed as, for example, a pyrolysis tube. Simultaneously, an oxygen-containing carrier gas is supplied to the reaction vessel 5 via another supply line 7. To avoid inaccurate determinations, the carrier gas must have chemical purity, i.e., it must be free of at least CO2 or other carbonaceous compounds.
[0035] Figure 2 The path of the carrier gas in this respect is shown. Before the carrier gas is recorded in terms of pressure (see below, pressure sensor 39), it passes through filter 45, first flow rate sensor 41, and most importantly, CO2 removal unit 47. The carrier gas is pumped into the analytical apparatus 1 by pump 49. Alternatively, compressed gases (e.g., nitrogen, artificial air, oxygen, or compressed air) may also be used; in the following, a pump is assumed to be used. Subsequently, the carrier gas and the sample to be analyzed then enter a high-temperature digestion apparatus, which has an oven (reaction vessel 5, see below), analytical chamber 35, and second flow rate sensor 43.
[0036] exist Figure 1In the example shown, reaction vessel 5 includes an insert 9 containing a catalyst 11 for supporting the reaction of the liquid sample with an oxygen-containing carrier gas. To support the reaction of the liquid sample with the carrier gas, a correspondingly high internal temperature can also be set for reaction vessel 5. The temperature of reaction vessel 5 can be regulated by means of a heating device 13 surrounding reaction vessel 5. The reaction zone is located in the region of insert 9, where the temperature dominates between 650°C and 1300°C during operation. Optionally, bulk material (not shown) can also be contained within the reaction zone, for example, it can be retained by a channeled bottom screen of insert 9. When the interior surface of a given reaction vessel comes into contact with, for example, the surface of catalyst 11 or bulk material, the liquid sample to be analyzed heats up to its boiling point or reaction temperature within a very short time, i.e., a fraction of a second, particularly less than 0.4 seconds, and transforms into the gas phase. When the liquid sample is injected into a high-temperature oven, the sample evaporates abruptly (volume expansion), creating a pressure surge, which can also be measured as an increase in volume / mass flow rate.
[0037] The method is performed in a permanent measurement mode, also known as a continuous measurement mode. In this mode, carrier gas is continuously supplied.
[0038] The sample liquid is fed in batches, where a specific volume, typically 100 µl to 1500 µl, of the sample liquid is digested in a reaction vessel. This amount is rapidly added to the oven in the form of a sample jet. The amount of analyte oxidation products contained in the carrier gas stream leaving the reaction vessel depends accordingly on both the volume of sample liquid fed and the concentration of the analyte in the sample liquid.
[0039] The entire flow path of the carrier gas is sealed from the external environment, preventing any gas from escaping from the analytical apparatus 1. The gas flow exits the analytical apparatus 1 through the gas outlet (not shown) of the analytical chamber 35. Alternatively, the carrier gas can be supplied back to the analytical apparatus 1 via the gas supply line 7 in a cyclic manner. The component downstream of the reaction vessel 5 in the analytical apparatus 1 provides flow resistance to the gas. Thus, pressure changes inside the reaction vessel 5 can also be detected in the gas supply line 7, i.e., pressure changes inside the reaction vessel 5 caused, for example, by pressure changes in the gas supply line 7 related to the change in sample volume to the gas phase. A pressure sensor 39 arranged in the gas supply line records the dominant pressure in the gas supply line 7 and converts it into, for example, a proportional electrical signal related to that pressure, also known as a pressure signal. From a series of such pressure signals, pressure changes in the reaction vessel 5 can be inferred. The pressure sensor 39 is connected to the input of the data processing unit 37 on the output side for transmitting the pressure signal. Since the entire flow path of the carrier gas is sealed from the external environment, the pressure sensor 39, used to record the dominant pressure within the reaction vessel 5, can in principle be placed anywhere along the flow path, such as in the area of the gas outlet 19 or within the filter unit 21. However, a location within the gas supply line 7 is particularly advantageous and requires greater precision, as the temperature there remains low, for example, within the range of room temperature.
[0040] The sample volume can be determined and controlled by measuring the pressure. In particular, this allows for the detection of incorrect feeding, such as insufficient sample volume. Correspondingly, a response can be made, and if necessary, an additional amount of sample can be added.
[0041] The analytical apparatus 1 also includes a first flow rate sensor 41 and a second flow rate sensor 43. The first flow rate sensor 41 is located immediately adjacent to the pressure sensor 39, i.e., at the gas supply line 7, i.e., at the inlet. The second flow rate sensor 43 is located downstream of the carrier gas flow rate analysis chamber 35, i.e., at the outlet.
[0042] In the top illustration, Figure 3 The CO2 signal (discovered in the analysis chamber 35 and by the data processing unit 37) is shown, as is the measured pressure at the bottom. Figure 4a The CO2 signal is shown at the top, and the flow rate measured at the second flow rate sensor 41 is shown at the bottom. Figure 4b The CO2 signal is shown at the top, and the flow rates measured at the first flow rate sensor 41 and the second and third flow rate sensors 43 are shown at the bottom.
[0043] exist Figure 3The graph shows that different amounts of CO2 (reference numerals 36a-e) resulted in different pressures (reference numerals 40a-e). The horizontal axis of the graph depicts time in seconds, and the vertical axis depicts pressure in arbitrary units (au). The curve of the measured values shows that a relatively constant pressure dominated in the reaction vessel during the time period between 0 and approximately 40 seconds. Subsequently, a sample was added to the reaction vessel. This event caused a sharp increase in the pressure values measured later, ranging from 60 au to 120 au. Eventually, the pressure decreased again.
[0044] The pressure signal sequence from pressure sensor 39 is evaluated by means of a data processing unit coupled to pressure sensor 39. The sensor signal, converted by pressure sensor 39 and possibly amplified by an amplifier (not shown), is transmitted to data processing unit 37 and may be digitized. Data processing unit 37 includes, for example, an averaging unit that forms a time average for at least some pressure signals in the sequence preceding the currently recorded pressure signal, for example, a moving average for all pressure signals recorded within a predetermined time window. Similarly, instead of a time window, a certain number of pressure signals in the sequence preceding the current pressure signal can be specified. Forming a moving average for at least a portion of the pressure signals in the sequence preceding the current pressure signal is equivalent to a digital low-pass filter. Correspondingly, other equivalent filtering functions can also be used. The time average obtained in this way forms a reference pressure value, which corresponds to the dominant reference pressure in reaction vessel 5. The time curve of the reference pressure value forms a "zero line" or "baseline" for the dominant pressure in reaction vessel 5. Pressure pulses generated due to the conversion of the sample volume to the gas phase cause the pressure to increase above this reference line.
[0045] Ideally, the baseline should be aligned with... Figure 3 The horizontal axis of the graph shown is essentially parallel. Solid particles may accumulate, possibly due to impurities in the sample gas stream, and these particles could clog filter unit 21 over time. Both of these situations lead to a gradual increase in the reference pressure within reaction vessel 5. Figure 6 This situation is illustrated by an arrow. Therefore, in order to monitor the analytical device 1, the reference pressure value can be monitored by means of the data processing unit 37. For example, if the reference pressure value exceeds a specified threshold, this may indicate that the liquid sample is being fed too quickly, or that a clogged filter unit needs to be replaced. In this case, an alarm may be issued, triggering the implementation of maintenance actions.
[0046] exist Figure 4a The diagram shows different amounts of CO2 (reference symbols 36a-e). Figure 4aAt the bottom, the measurement results of the second flow rate sensor 41 are shown. At time 0, the sample is injected into the oven 5. Due to the sudden evaporation of the aqueous sample, the flow rate increases sharply (regardless of the amount of sample injected—this is why the peak point is the same for all quantities shortly after time 0). On the other hand, for different CO2 concentrations, the low points of flow rate at the second sensor 43 (reference symbols 44a-e) arise from cooling. There is a greater water load in the air, which condenses again in the cooler. Here, the volume then contracts again, and there is a measurable low point (the water's aggregation state changes from gaseous to liquid, which increases the density of water and reduces its volume; therefore, there is no longer water vapor in the gas phase, which reduces the volumetric flow rate at the outlet).
[0047] Figure 4b A certain amount of CO2 is shown (reference symbol 36a). At the bottom, Figure 4b The flow rate measurements from two sensors, 41 and 43, are shown. The flow rates are labeled with reference symbols 42a and 44a.
[0048] Below insert 9, an additional chamber 17 is arranged within reaction vessel 5, where a lower temperature than that in the reaction zone predominates during operation. A gas outlet 19 is located at the lower end of reaction vessel 5 (typically vertically oriented during operation and opposite to injection nozzle 3), leading to the interior of filter unit 21, allowing the gas mixture generated in reaction vessel 5 to flow into filter unit 21 along with the carrier gas via channels, chamber 17, and gas outlet 19. Filter unit 21 is connected to condensation unit 25 via gas line 23. Condensation unit 25 is used to separate water from the gas stream and is therefore optionally equipped with a cooler to accelerate condensation from the gas stream. The condensate is removed from analytical device 1 via line 27.
[0049] An optional drying unit 31, an additional filter 33, and an analysis chamber 35 are arranged downstream of the condensation unit 25 in the direction of gas flow. In the analysis chamber 35, the content of reaction products of the analyte contained in the gas flow, such as CO2 and / or NOx, is determined. Typically, an infrared measuring device, such as an infrared detector, is used to determine the CO2 content. A chemiluminescence detector is typically used to determine the NOx content. The measurement signals recorded in the analysis chamber 35 are supplied to a data processing unit 37, which has a computer, such as a microcontroller or microprocessor. The data processing unit 37 determines the concentration of the analyte in the sample added to the reaction vessel 5 based on the measurement signals. Furthermore, the data processing unit 37 also controls the feeding device 2 for adding liquid to the reaction vessel 5.
[0050] The liquid sample, fed into the reaction vessel 5 via injection nozzle 3, transforms into a gaseous phase almost immediately upon entering the reaction zone, particularly through heat transfer upon contact with high-temperature surfaces. If the liquid sample is an aqueous solution containing oxidizable components (other than water), the water is converted into gaseous H2O, for example, through evaporation, while the oxidizable components, such as organic carbonaceous or nitrogen-containing compounds, react with the oxygen-containing carrier gas to form gaseous oxides, such as CO2 or NOx. This can be sensed by pressure pulses or fluctuations within the reaction vessel 5, which can be recorded by pressure sensor 39 arranged in the carrier gas supply line 7. This can also be recorded in the flow rate. Figure 3 The pressure fluctuations 40a-e shown correspond to Figure 4a The flow rate curves shown are reference symbols 44a-e. Therefore, when a certain amount of sample is injected, pressure fluctuations 40a and simultaneous flow rates 44a, etc., can be recorded.
[0051] Figure 5 The flow rate measurements of two flow rate sensors 41 and 43 are shown. As previously mentioned, the first flow rate sensor 41 is located relatively "forward" in the flow path of the carrier gas, and the second flow rate sensor 43 is located relatively "backward". If the difference between the measurements is too large, a leak is necessarily present.
[0052] List of reference symbols
[0053] 1. Analytical equipment
[0054] 2 Feeding device
[0055] 3 Injection Nozzle
[0056] 5. Reaction Vessel / Oven
[0057] 7 Carrier gas supply pipelines
[0058] 9 inserts
[0059] 11 catalysts
[0060] 13 Heating Equipment
[0061] Room 17
[0062] 19 Gas Outlets
[0063] 21 filters
[0064] 23 Gas pipelines
[0065] 25 condensing units
[0066] 27 pipelines
[0067] 31 Drying Unit
[0068] 33 Filter
[0069] 35 Analytical Laboratory
[0070] 36a-e CO2 content
[0071] 37 Data Processing Unit
[0072] 39 Pressure Sensor
[0073] 40a-e pressure
[0074] 41 Flow rate sensor
[0075] Flow rate at 42a 41
[0076] 43 Flow rate sensor
[0077] Flow rate at 44a-e 43
[0078] 45 filter
[0079] 47CO2 Removal Unit
[0080] 49 pumps
Claims
1. An analytical apparatus (1) for determining the concentration of an analyte, particularly an oxidizable component, in a liquid sample. – The analytical apparatus includes a feeding device (2), particularly a pump, for feeding the liquid sample into a high-temperature digestion unit, which digests the liquid sample and forms a gas mixture, wherein… The high-temperature digestion apparatus has a reaction vessel (5), which has a liquid inlet (2) for the liquid sample and a gas supply line (3) for supplying carrier gas. It is connected to the analysis chamber (35) via the gas outlet (19); – wherein, during operation of the device, a flow of carrier gas is formed between the gas inlet (3) and the analysis chamber (35); – wherein, a pressure sensor (39) is arranged upstream of the analysis chamber (35) within the gas supply line (3) in the direction of the gas flow. The pressure sensor (39) is coupled to the control unit (37) for further processing the pressure signal output by the pressure sensor (39); –In particular, the first flow rate sensor (41) is arranged upstream of the analysis chamber (35) in the direction of the gas flow, specifically within the gas supply line (3) for supplying the carrier gas. The first flow rate sensor (41) is coupled to the control unit (37) for further processing the flow rate signal output by the flow rate sensor (41); – wherein, the second flow rate sensor (43) is arranged downstream of the analysis chamber (35) in the direction of the gas flow. The second flow rate sensor (43) is coupled to the control unit (37) for further processing the flow rate signal output by the flow rate sensor (43).
2. The analytical apparatus (1) according to claim 1. in, The carrier gas is continuously introduced.
3. The analytical apparatus (1) according to claim 1 or claim 2. in, The samples were added to the oven (5) in batches, particularly every 5 to 10 minutes.
4. A method for determining the TOC content in a liquid sample using the analytical apparatus (1) according to any one of the preceding claims.
5. The method according to the preceding claim, in, Leakage is inferred from the differences between known flow rates.
6. The method according to any one of the preceding claims, in, The presence or absence of any sample in the oven (5) is determined by pressure measurement.
7. The method according to any one of the preceding claims, The sample quantity is determined and controlled based on the pressure measurement, wherein, Incorrect feeding was detected, especially insufficient sample volume.
8. The method according to any one of the preceding claims, in, A reference pressure value is determined based on the pressure measurement, particularly by averaging over a certain period of time. Furthermore, based on the changes in the reference pressure value, it is inferred that there is a fault in the analytical device (1), such as contamination.
9. The method according to any one of the preceding claims, in, Inferences about possible maintenance are made based on pressure curves and flow rate measurement curves.