A nitric acid oxidation furnace lower part ammonium nitrate on-line detection system and method

Abstract

This invention discloses an online detection system and method for ammonium nitrate in the lower part of a nitric acid oxidation furnace, belonging to the field of nitric acid production safety monitoring and process control technology. The system includes a multi-point sampling device, a sample gas pretreatment unit, an ammonium nitrate concentration detection unit, a data processing and control unit, and an alarm and linkage execution unit. Through multi-point distributed sampling and heat tracing, it is adaptable to high-temperature, high-pressure, and highly corrosive operating conditions. After condensation and gas-liquid separation, the sample gas undergoes dual-channel cross-validation detection using ultraviolet absorption spectroscopy and ion-selective electrode method, significantly improving accuracy. The data processing module incorporates a three-dimensional early warning model combining absolute concentration value, rate of change, and acceleration of change. When exceedances occur, it automatically links with the DCS system to adjust process parameters. This invention achieves online real-time detection and precise leak location of ammonium nitrate in the lower part of the oxidation furnace for the first time, forming a fully automatic closed-loop control of detection-early warning-linkage, effectively eliminating safety hazards.

Description

Technical Field

[0001] This invention belongs to the field of nitric acid production safety monitoring and process control technology, specifically an online detection system and method for ammonium nitrate in the lower part of a nitric acid oxidation furnace. Background Technology

[0002] Nitric acid is one of the core raw materials in the basic chemical industry, and the mainstream industrial production process is the ammonia oxidation process. In the production process, gaseous ammonia and air react in an ammonia oxidation furnace under the catalysis of a platinum-rhodium catalyst at a high temperature of 860℃ to produce nitric oxide. The reaction formula is: 4NH3 + 5O2 → 4NO + 6H2O. This step is the core process of the entire nitric acid plant.

[0003] However, in actual operation, oxidizers have long suffered from a common safety hazard in the industry—internal leakage. Some gaseous ammonia leaks directly from gaps into the lower part of the oxidizer or the waste heat boiler area without undergoing catalytic combustion through the platinum mesh. When the leaked ammonia comes into contact with nitrogen oxides in the process gas, it reacts to form substances such as ammonium nitrate and nitrosamines. Ammonium nitrate is a highly explosive chemical with an extremely high risk of explosion in a high-temperature, confined environment. If the deposition exceeds the standard, it can easily lead to a safety accident. Therefore, the ammonium salt content in the lower part of the oxidizer must be strictly monitored.

[0004] Currently, there are still many shortcomings in the industry's detection of ammonium nitrate in the lower part of oxidation furnaces, and the actual application effect is not ideal: First, there is a lack of mature online real-time detection methods. Currently, enterprises mainly rely on manual sampling and offline testing. Manual sampling is not only cumbersome and results in delayed data, but also poses safety risks. Most existing online analysis equipment is only used for the detection of exhaust gas or finished acid, and there is no specific online detection solution for ammonium nitrate in the lower part of the oxidation furnace.

[0005] Secondly, the accuracy of traditional detection methods is insufficient. Current methods for determining trace amounts of ammonium salts in nitrogen oxide gases mostly employ Nessler's reagent colorimetric method or formaldehyde nitrogen determination method, which suffer from low detection sensitivity, large fluctuations in results, and generally low values.

[0006] Third, the low frequency of testing makes it difficult to provide early warnings. Due to limitations in manual testing, it is difficult to detect abnormal increases in ammonium nitrate concentrations in a timely manner. Often, by the time test results show that the levels exceed the standards, safety hazards have already formed.

[0007] Fourth, conventional online detection equipment cannot be adapted to on-site working conditions. Commercially available online concentration meters cannot be directly used in the high-temperature, highly corrosive process gas environment of 200–500℃ and 0.5MPa at the bottom of the oxidation furnace.

[0008] Fifth, there is a disconnect between detection and process control. Existing solutions cannot link detection data with the operating parameters of the oxidation furnace, thus failing to achieve automatic control.

[0009] Based on the above situation, developing a detection system that can detect the concentration of ammonium nitrate in the lower part of the oxidation furnace online in real time, and can also link with the process control system to realize early warning and automatic control, has high practical application value for ensuring the safe and stable operation of the nitric acid plant. Summary of the Invention

[0010] To overcome the above-mentioned defects in the prior art, the present invention provides an online detection system and method for ammonium nitrate in the lower part of a nitric acid oxidation furnace.

[0011] This invention is achieved using the following technical solution: An online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace includes: Multi-point sampling device; The sample gas pretreatment unit is connected to the multi-point sampling device and is used to cool, condense, and separate the high-temperature process gas sample to obtain condensate. An ammonium nitrate concentration detection unit is connected to the liquid phase outlet of the sample gas pretreatment unit and is used to perform dual-channel detection of the ammonium nitrate concentration in the condensate. The data processing and control unit is connected to the multi-point sampling device, the sample gas pretreatment unit and the ammonium nitrate concentration detection unit respectively, and is used for data acquisition, processing and early warning judgment; The alarm and linkage execution unit is connected to the data processing and control unit and is used to issue an alarm signal and output linkage control commands when an early warning is triggered.

[0012] Preferably, the multi-point sampling device includes multiple sampling probes arranged at different radial positions and heights at the bottom of the oxidation furnace for extracting process gas samples.

[0013] Preferably, the sampling probe of the multi-point sampling device is made of high-temperature and corrosion-resistant alloy material, and a ceramic or stainless steel filter element is installed at the front end; the outer wall of the sampling pipeline connected to the sampling probe is equipped with a heat tracing and insulation layer so that the temperature of the sample gas is higher than the dew point during transportation; the sampling probe is arranged in the lower conical section of the oxidizer, the bottom outlet pipe of the oxidizer, and the inlet position of the waste heat boiler downstream of the oxidizer.

[0014] Preferably, the sample gas pretreatment unit includes a switching valve group, a condenser, a gas-liquid separator, and a flow regulator connected in sequence; the switching valve group is used to select different sampling points for cyclic detection; the condenser is used to cool the high-temperature process gas sample to 20-60°C, so that the condensable components are condensed into liquid and then sent to the ammonium nitrate concentration detection unit to adapt to the high-temperature, high-pressure, and highly corrosive working conditions.

[0015] Preferably, the ammonium nitrate concentration detection unit adopts a dual-channel cross-validation scheme, which includes a flow cell, an ultraviolet / visible spectrophotometer and an ammonium ion selective electrode detection module (33).

[0016] Preferably, the inlet of the flow cell is connected to the liquid phase outlet of the gas-liquid separator to receive the condensate; the outlet of the flow cell is connected to the waste liquid discharge pipeline to discharge the condensate after detection; the flow cell is provided with a light-transmitting window, and the light source emitting end and the light signal receiving end of the ultraviolet / visible spectrophotometer are respectively arranged on both sides of the light-transmitting window to form a light path penetration connection; the detection probe of the ammonium ion selective electrode detection module is inserted into and immersed in the liquid phase space inside the flow cell.

[0017] Preferably, the connection relationship of the ammonium nitrate concentration detection unit includes: Fluid connection: The fluid inlet of the ammonium nitrate concentration detection unit is connected to the outlet pipeline of the condenser; Signal connection: The photoelectric signal output terminal of the ultraviolet / visible spectrophotometer and the electrical signal output terminal of the ammonium ion selective electrode detection module are both communicatively connected to the data acquisition terminal of the data processing and control unit, so as to synchronously and in real time transmit the detected nitrate concentration signal and ammonium ion concentration signal to the data processing and control unit.

[0018] Preferably, the data processing and control unit has a built-in ammonium nitrate concentration early warning module. The early warning model combines the absolute value of the ammonium nitrate concentration, the rate of change, and the acceleration of change to make a comprehensive judgment. When any one of them exceeds a preset threshold, a graded early warning signal is triggered.

[0019] Preferably, the alarm and linkage execution unit is communicatively connected to the device's DCS system. When the ammonium nitrate concentration exceeds the safety limit, it sends a control command to the DCS system to trigger linkage operations such as reducing the ammonia-air ratio, increasing the oxidation furnace temperature, activating platinum mesh differential pressure detection, or issuing a shutdown suggestion.

[0020] A method for online detection of ammonium nitrate in the lower part of a nitric acid oxidation furnace includes the following steps: Step 1: Multi-point gas sampling The multi-point sampling device is started and operated, utilizing its structure arranged at different radial positions and heights in the lower part of the oxidizer to continuously extract process gas samples from the lower region of the oxidizer. This step obtains raw gas samples reflecting the distribution of ammonium nitrate in different spatial locations in the lower part of the oxidizer, providing a material basis for subsequent continuous detection.

[0021] Step 2: Sample Pretreatment The extracted raw process gas sample is transported to the sample gas pretreatment unit. This unit adjusts and pretreats the physical state of the high-temperature, high-pressure raw gas sample (such as cooling, phase transformation and separation), removes interfering factors that are not suitable for direct detection, extracts the test medium that meets the detection conditions, and outputs it stably.

[0022] Step 3: Ammonium nitrate concentration detection The pretreated test medium enters the ammonium nitrate concentration detection unit. This unit performs online analysis of the ammonium nitrate component in the test medium, measures its concentration in real time, and converts the measured concentration information into a data signal for continuous output, thereby achieving online and real-time detection of ammonium nitrate concentration at the physical level.

[0023] Step 4: Data Processing and Control Analysis The data processing and control unit receives concentration data signals from the ammonium nitrate concentration detection unit in real time. This unit converts, stores, and logically analyzes the received data, assesses the current ammonium nitrate concentration levels and their changes at various radial and height points, and generates corresponding control logic and command signals based on the analysis results.

[0024] Step 5: Alarm and Linkage Execution The alarm and linkage execution unit receives command signals from the data processing and control unit. When data analysis results indicate that the ammonium nitrate concentration is abnormal or reaches the preset trigger condition, the unit immediately executes an alarm action to alert the operator and simultaneously outputs a linkage control signal to drive relevant external process equipment to make adjustments, thereby completing a closed-loop response from monitoring to control.

[0025] The technical solution provided by this invention has the following advantages compared with the prior art: (1) For the first time, online real-time detection of ammonium nitrate in the lower part of the oxidation furnace was realized: the problem of adapting to working conditions under high temperature, high pressure and strong corrosion environment was solved, and the traditional manual sampling and offline analysis method was replaced.

[0026] (2) The detection timeliness is significantly improved, and potential safety hazards can be identified in advance: continuous detection at the minute or even second level can be achieved, and anomalies can be captured when the ammonium nitrate concentration is at a low level (such as 2-3 ppm) and just shows an upward trend.

[0027] (3) Multi-point distributed sampling can accurately locate the internal leakage area: By comparing the concentration differences at each point, the specific area of ​​internal leakage can be determined, which greatly shortens the troubleshooting time.

[0028] (4) Dual-channel cross-validation, high detection accuracy and strong anti-interference ability: the ultraviolet method and the electrode method corroborate each other, eliminate interference from other nitrogen-containing substances, and solve the problem of unstable results of traditional methods.

[0029] (5) Realize fully automatic closed-loop control of detection-early warning-linkage: directly link the DCS system to automatically adjust process parameters and eliminate delays caused by manual handling.

[0030] (6) The early warning model is more scientific and the hierarchical alarm is more reasonable: the three-dimensional comprehensive judgment supports yellow, orange and red hierarchical alarms, which effectively reduces false alarms and missed alarms.

[0031] (7) Strong adaptability and low implementation cost: It can be directly modified on the existing equipment without large-scale modification of the oxidation furnace body, and has good prospects for promotion. Attached Figure Description

[0032] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the overall structure of the online detection system for ammonium nitrate at the bottom of the nitric acid oxidation furnace according to the present invention.

[0035] In the diagram: 1-Multi-point sampling device, 11-Sampling probe, 12-Sampling pipeline, 21-Switching valve group, 22-Condenser, 23-Gas-liquid separator, 24-Flow regulator, 3-Ammonium nitrate concentration detection unit, 31-Flow cell, 32-UV / Vis spectrophotometer, 33-Ammonium ion selective electrode detection module, 4-Data processing and control unit, 5-Alarm and linkage execution unit, 6-DCS system. Detailed Implementation

[0036] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0037] In this description, it should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. It should also be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "joint" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0038] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0039] The specific embodiments of the present invention will be described in detail below.

[0040] Example 1: System Structure like Figure 1 As shown in this embodiment, an online detection system and method for ammonium nitrate in the lower part of a nitric acid oxidation furnace is provided. It mainly consists of five units and is integrated into a DCS system 6 for control. A multi-point sampling device 1 has six sampling probes 11 evenly arranged along the circumference of the cone section at the bottom of the oxidation furnace, four at the bottom outlet pipe, and two at the waste heat boiler inlet. The probes 11 are made of Hastelloy alloy and have sintered stainless steel filter elements at the front end. The sampling pipeline 12 is externally wrapped with electric heating tape as a heat tracing and insulation device 12 to maintain the pipeline temperature above 120°C and prevent water vapor condensation and ammonium nitrate crystallization blockage. In the sample gas pretreatment unit, the switching valve group 21 is set to switch a sampling point every 15 minutes for rotation. The condenser 22 uses a shell-and-tube heat exchanger to cool the sample gas to 40°C using circulating cooling water. The gas-liquid separator 23 collects the condensate and sends it to the detection unit; non-condensable gases are discharged after washing with alkaline solution. The flow regulator 24 stabilizes the sampling gas flow rate at 2L / min. In the ammonium nitrate concentration detection unit 3, condensate continuously flows through a quartz flow cell 31. An ultraviolet / visible spectrophotometer 32 emits 210nm wavelength ultraviolet light that penetrates the flow cell, and the nitrate concentration is calculated according to Beer's Law. Simultaneously, an ammonium ion selective electrode detection module 33 is immersed in the condensate to measure the ammonium ion concentration. The data processing and control unit 4 compares the two sets of data. If the deviation is within 5%, the average value is taken as the final ammonium nitrate concentration. If the deviation is too large, an instrument fault alarm is triggered, effectively eliminating interference from impurities such as nitrite.

[0041] Example 2: Online Detection and Linkage Control Method Based on the system of Embodiment 1, this embodiment provides an online detection method, the specific process of which is as follows: Step 1: The multi-point sampling device 1 continuously extracts process gas, and the heat tracing and insulation device 12 ensures that the sample gas does not condense.

[0042] Step 2: The sample gas enters the pretreatment unit, is cooled to 40°C, and the condensate is separated.

[0043] Step 3: The condensate enters the detection unit 3 to complete the dual-channel detection of nitrate and ammonium ions, and obtain the real-time ammonium nitrate concentration.

[0044] Step 4: The data processing and control unit 4 runs the three-dimensional early warning model. The yellow warning threshold is set as an absolute concentration > 2 ppm or a rate of change > 0.5 ppm / min; the orange warning threshold is an absolute concentration > 5 ppm or an abnormal acceleration; and the red alarm threshold is an absolute concentration > 10 ppm.

[0045] Step 5: When the system determines that it is an orange warning, the alarm and linkage execution unit 5 issues an audible and visual alarm and automatically sends an instruction to the DCS system 6: reduce the ammonia feed rate by 8% (reduce the ammonia-air ratio) and increase the operating temperature of the oxidation furnace by 15°C to promote the full oxidation of the leaked ammonia.

[0046] Step 6: If, within a certain period of time, the concentration detected by the two probes on the east side of the lower cone section of the oxidizer is significantly higher than that of the probe on the west side (concentration difference > 3 ppm), the data processing module will automatically generate an "internal leakage location report" to accurately indicate that there is a breakage or leakage in the platinum mesh or seal on the east side, guiding maintenance personnel to conduct targeted troubleshooting.

[0047] The above description is merely a specific embodiment of the present invention, enabling those skilled in the art to understand or implement the present invention. Although detailed descriptions have been provided with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments, and they should all be covered within the protection scope of the claims.

Claims

1. An online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace, characterized in that, include: Multi-point sampling device (1); The sample gas pretreatment unit is connected to the multi-point sampling device (1) and is used to cool, condense and separate the high-temperature process gas sample to obtain condensate. The ammonium nitrate concentration detection unit (3) is connected to the liquid phase outlet of the sample gas pretreatment unit and is used to perform dual-channel detection of the ammonium nitrate concentration in the condensate. The data processing and control unit (4) is connected to the multi-point sampling device (1), the sample gas pretreatment unit and the ammonium nitrate concentration detection unit (3) respectively, and is used for data acquisition, processing and early warning judgment; The alarm and linkage execution unit (5) is connected to the data processing and control unit (4) and is used to issue an alarm signal and output linkage control instructions when the early warning is triggered.

2. The online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace according to claim 1, characterized in that, The multi-point sampling device (1) includes multiple sampling probes (11) arranged at different radial positions and heights at the bottom of the oxidation furnace for extracting process gas samples.

3. The online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace according to claim 2, characterized in that, The sampling probe (11) of the multi-point sampling device (1) is equipped with a ceramic or stainless steel filter element at the front end; the outer wall of the sampling pipeline (12) connected to the sampling probe (11) is equipped with a heat tracing and insulation layer so that the temperature of the sample gas is higher than the dew point during the transportation process; the sampling probe (11) is arranged in the lower cone section of the oxidizer, the bottom outlet pipe of the oxidizer, and the inlet position of the waste heat boiler downstream of the oxidizer.

4. The online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace according to claim 1, characterized in that, The sample gas pretreatment unit includes a switching valve group (21), a condenser (22), a gas-liquid separator (23), and a flow regulator (24) connected in sequence. The switching valve group (21) is used to select different sampling points for cyclic detection. The condenser (22) is used to cool the high-temperature process gas sample to 20-60°C, so that the condensable components are condensed into liquid and sent to the ammonium nitrate concentration detection unit (3) to adapt to the working conditions of high temperature, high pressure and strong corrosion.

5. The online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace according to claim 1, characterized in that, The ammonium nitrate concentration detection unit (3) includes a flow cell (31), an ultraviolet / visible spectrophotometer (32), and an ammonium ion selective electrode detection module (33).

6. The online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace according to claim 5, characterized in that, The inlet of the flow cell (31) is connected to the liquid phase outlet of the gas-liquid separator (23) to receive the condensate; the outlet of the flow cell (31) is connected to the waste liquid discharge pipeline to discharge the condensate after detection; the flow cell (31) is provided with a light-transmitting window, and the light source emitting end and the light signal receiving end of the ultraviolet / visible spectrophotometer (32) are respectively set on both sides of the light-transmitting window to form a light path penetration connection; the detection probe of the ammonium ion selective electrode detection module (33) is inserted into and immersed in the liquid phase space inside the flow cell (31).

7. The online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace according to claim 5, characterized in that, The connection relationships of the ammonium nitrate concentration detection unit (3) include: Fluid connection: The fluid inlet of the ammonium nitrate concentration detection unit (3) is connected to the outlet pipe of the condenser (22); Signal connection: The photoelectric signal output of the ultraviolet / visible spectrophotometer (32) and the electrical signal output of the ammonium ion selective electrode detection module (33) are both connected to the data acquisition terminal of the data processing and control unit (4) for synchronously transmitting the detected nitrate concentration signal and ammonium ion concentration signal to the data processing and control unit (4) in real time.

8. The online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace according to claim 1, characterized in that, The data processing and control unit (4) has a built-in ammonium nitrate concentration early warning module. The early warning model combines the absolute value of ammonium nitrate concentration, the rate of change and the acceleration of change to make a comprehensive judgment. When any one of them exceeds the preset threshold, a graded early warning signal is triggered.

9. The online detection system for ammonium nitrate in the lower part of a nitric acid oxidation furnace according to claim 1, characterized in that, The alarm and linkage execution unit (5) is connected to the DCS system (6) of the device. When the ammonium nitrate concentration exceeds the safety limit, it sends a control command to the DCS system (6) to trigger linkage operations such as reducing the ammonia-air ratio, increasing the temperature of the oxidation furnace, starting the platinum mesh differential pressure detection, or issuing a shutdown suggestion.

10. A method for online detection of ammonium nitrate in the lower part of a nitric acid oxidation furnace, characterized in that, Includes the following steps: Step 1: Multi-point gas sampling The multi-point sampling device (1) is started and operated. It uses its structure, which is arranged at different radial positions and heights in the lower part of the oxidation furnace, to continuously extract process gas samples from the lower region of the oxidation furnace. Step 2: Sample Pretreatment The extracted raw process gas sample is transported to the sample gas pretreatment unit; This unit adjusts and preprocesses the physical state of raw gas samples under high temperature and high pressure, removes interfering factors that are not suitable for direct detection, extracts the test medium that meets the detection conditions, and outputs it stably. Step 3: Ammonium nitrate concentration detection The pretreated test medium enters the ammonium nitrate concentration detection unit (3); this unit performs online analysis of the ammonium nitrate component in the test medium, measures its ammonium nitrate concentration in real time, and converts the measured concentration information into a data signal for continuous output, thereby realizing online and real-time detection of ammonium nitrate concentration at the physical level; Step 4: Data Processing and Control Analysis The data processing and control unit (4) receives concentration data signals from the ammonium nitrate concentration detection unit (3) in real time; the unit performs conversion, storage and logical analysis on the received data, evaluates the current ammonium nitrate concentration level and its change status at each radial position and height point, and generates corresponding control logic and command signals based on the analysis results; Step 5: Alarm and Linkage Execution The alarm and linkage execution unit (5) receives the instruction signal from the data processing and control unit (4); when the data analysis results show that the ammonium nitrate concentration is abnormal or reaches the preset triggering condition, the unit immediately executes the alarm action to prompt the operator, and simultaneously outputs the linkage control signal to drive the external related process equipment to make adjustments, thereby completing the closed-loop response from monitoring to control.

Images