Method for detecting content of ammonia in condensate of ammonia synthesis process

Abstract

The invention relates to the technical field of chemical engineering, in particular to equipment and a method for detecting the content of ammonia in condensate of an ammonia synthesis process. The invention relates to an online detection method for ammonia content in a condensate in a synthesis ammonia process, which is characterized by comprising the following continuous steps of: A) leading out a sample flow from a condensate pipeline of a synthesis ammonia device at constant pressure, and attenuating the pressure and temperature at a sampling position to obtain a condensate to be detected in a normal-pressure and normal-temperature state; b) introducing the condensate to be measured into a conductivity measuring cell, measuring the conductivity value of the condensate in real time, and collecting the temperature of the sample at the same time; c) according to a pre-established conductivity-ammonia concentration calibration curve and in combination with a temperature compensation coefficient, converting the measured conductivity into ammonia concentration; and D) outputting the converted ammonia concentration to an upper system in an analog quantity or digital quantity mode for process adjustment and alarm interlocking. The invention aims to provide equipment and a method for detecting the content of ammonia in condensate in an ammonia synthesis process by utilizing conductivity.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, specifically to an apparatus and method for detecting the ammonia content in the condensate of ammonia synthesis process. Background Technology

[0002] Currently, most factories and available data use conductivity to directly reflect ammonia leakage data in the condensate of the ammonia synthesis process. However, due to interference from other impurity ions in the condensate, temperature variations, and differences in the degree of ionization of NH3·H2O in the condensate, the conductivity measurement cannot directly reflect the ammonia content in the condensate. Our company's AT-601 analyzer at the outlet of the ammonia washing tower water cooler in the ammonia synthesis unit originally used an ammonium ion measurement method to measure the ammonia content in the washing tower process water. The ammonia nitrogen analyzer at the outlet of the washing tower water cooler used an ion-selective electrode to directly detect ammonium ions to determine the ammonia concentration. The ammonia nitrogen sensor consists of a potassium ion-selective electrode, a pH electrode, and a temperature electrode, forming an integrated electrode. However, this method is affected by factors such as temperature, pressure, and membrane sealing during the process, often resulting in inaccurate measurements. Furthermore, it requires significant maintenance, the instrument is expensive, and this leads to substantial maintenance costs. Additionally, the electrode can only measure normally at one standard atmosphere; exceeding the standard atmospheric pressure will damage the electrode, rendering it unable to measure and causing it to malfunction. Given this situation, by studying and demonstrating the mathematical relationship between conductivity and ammonia concentration, the method was modified to use conductivity to measure the ammonia concentration in the synthetic ammonia condensate. When proposing the technology of "detecting ammonia content in condensate using conductivity in synthetic ammonia process," a comparison was made with similar domestic technologies. The comparison revealed that the original ammonia nitrogen analyzer at the outlet of the ammonia washing tower water cooler used an ion-selective electrode to directly detect ammonium ions and determine the ammonia concentration. However, this electrode was unsuitable for our company for three main reasons: First, the electrode and membrane head were plug-in type, which could not be sealed for a long time, causing corrosion damage to the electrode lead plug-in contacts; second, even after solving the first problem, it was found that temperature influence made measurement impossible; third, potassium ions in the synthetic ammonia process condensate caused significant interference, and even with potassium ion compensation, the measurement requirements could not be fully met. (Note: The pretreatment system was designed according to process requirements.) The permeate membrane of this electrode can only be used under conditions of pressure below 0.2 MPa and temperature below 40℃, which the synthetic ammonia process cannot meet. Summary of the Invention

[0003] The purpose of this invention is to provide an apparatus and method for detecting the ammonia content in the condensate of ammonia synthesis process using conductivity, so as to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, this invention provides the following technical solution: a device and method for detecting ammonia content in the condensate of a synthetic ammonia process. Laboratory multi-point analysis shows that the conductivity of the condensate during normal synthetic ammonia production is between 0.6-0.9 μS / cm. When ammonia leakage occurs, the conductivity of the process condensate rises sharply, and this change in conductivity can promptly reflect the leakage concentration of ammonia (as confirmed by the laboratory). Relatively speaking, the conductivity of the synthetic ammonia process condensate is an easily measurable and highly accurate data point. Therefore, by obtaining a correct conductivity reading and performing calculations or searching based on curves and tables, the ammonia concentration data can be easily obtained. Furthermore, the conductivity analyzer can be flexibly calibrated online, further improving the accuracy of the measurement.

[0005] When selecting instruments, the Rosemount 1056 transmitter and its matching 228 model electrode were chosen. Its advantages are: (1) The electrode is a conductivity electrode. When the selectivity coefficient is set to 10-5 during measurement, there is very little potassium ion interference, which greatly eliminates potassium ion interference. Potassium ions in the condensate will not affect the conductivity value, ensuring the stability of the measured value. (2) The Rosemount 1056 transmitter has a built-in curve setting, which can directly convert the conductivity value (us / cm) into the ammonia concentration value (ppm), which more intuitively reflects the ammonia content in the condensate.

[0006] The specific operation steps are as follows: Menu—Program—Measurement Parameters—Sensor 1—Measurement—Custom Curve—Custom Settings—Configuration—Unit. At this time, select PPM as the unit and 5 data points. Then return to the previous menu and select to input the data points. Inputting the nomograph data obtained from the experiment will intuitively reflect the ammonia content in the condensate. (3) This model of instrument has a temperature compensation function, which can eliminate the influence of temperature on the conductivity value, thereby ensuring the accuracy of the ammonia concentration value in the condensate.

[0007] The compensation principle is as follows: the resistance of a solution decreases with increasing temperature; that is, when the concentration of the solution is constant, its conductivity increases with increasing temperature, by approximately 2%℃. Furthermore, for the same type of electrolyte, the temperature coefficient varies with different concentrations. At low concentrations, the relationship between conductivity and temperature is expressed by the following formula: L1 = L0[1 + α(t-t0) + β(t-t0)2]. Since the value of the second term β(t-t0)2 is small, it can be ignored. The relationship between conductivity and temperature at low temperature can be expressed by the following approximation: L1 = L0[1 + α(t-t0)]. Therefore, temperature compensation must be added in actual measurement. For most ions, the temperature coefficient of conductivity is approximately +1.4% °C to 3% °C. For H+ and OH- ions, the temperature coefficients of conductivity are 1.5% °C and 1.8% °C, respectively. These values ​​are generally 1% or better than the accuracy requirements for conductivity measurements. The correlation between electrical conductivity and temperature can often be expressed as the slope of the conductivity versus temperature curve, written by the equation: Where T0 is the reference temperature, T is the measurement temperature, σ is the conductivity of the substance, σ0 is the fixed reference conductivity of the substance at the reference temperature (usually at room temperature), and α is the temperature compensation slope of the substance. Mathematical relationship between ammonia concentration (represented by A) and conductivity (represented by D): . K is the ionization constant of ammonia. DD will be used as a substitute below. X 2 =(AX)K=AK-KX X 2 +KX-KA=0 . The unit of the above result is gram equivalents per liter. After multiplying by 17000, its unit becomes mg / L. . In the above formula ppm 1.497 13.761 51.282 112.563 197.604 306.405 540.54 1206.81 Figure 1 Nomograph of conductivity versus ammonia concentration

[0008] In the experiment of "using conductivity to detect ammonia content in process water of ammonia washing tower," after multi-point analysis and repeated experiments in the laboratory, the ammonia concentration values ​​measured at five points (30, 60, 90, 120, and 150) on the nomograph were found to be the most accurate. Therefore, inputting these five points into the "custom curve" option can accurately and intuitively reflect the ammonia content in the condensate. The conductivity of the condensate in the ammonia synthesis process is an easily measurable and highly accurate data point. Therefore, by calculating based on the conductivity data or searching according to curves and tables, and correcting for relevant interference data, we can easily obtain the ammonia concentration data. Furthermore, the conductivity analyzer can flexibly perform online calibration, further improving the measurement accuracy. This is very significant for the current operating conditions of ammonia synthesis production. The unit of electrical conductivity DD is μS / cm. Obviously, once you obtain electrical conductivity data, you can calculate the ammonia content in the water. Since conductivity is greatly affected by temperature, it increases when the water sample temperature rises and decreases when the water sample temperature falls. The instrument we selected is the Rosemount (1056) conductivity analyzer, which has an online temperature compensation function. We set its compensation temperature to 25°C. The ammonia ionization data were obtained at 25°C, so the conductivity data should also be obtained at the same temperature. In the actual verification process, eight concentration values ​​were measured in the laboratory, and their corresponding conductivity was calculated according to the formula. At the same time, the influence of temperature change was corrected, thus obtaining a correspondence between concentration and conductivity. This relationship was then input into the conductivity custom curve to create a nomograph. 1 2 3 4 5 6 7 8 Us / cm 10 30 60 90 120 150 200 300

[0009] Compared with the prior art, the beneficial effects of the present invention are: it solves the problems of high process requirements, unstable measurement values, and large maintenance workload in the operation of ammonia concentration analyzers, and can intuitively reflect the amount of ammonia leakage in the condensate of the ammonia synthesis process. It also has the characteristics of simple structure, low investment, energy saving, safety and high practicality. Attached Figure Description

[0010] Figure 1 This is a screenshot showing the installation complete.

[0011] Figure 2 This is a schematic diagram of electrode installation. Detailed Implementation

[0012] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0013] Example 1 The conductivity method for detecting ammonia content in the process water of the ammonia washing tower operated stably during the experiment, promptly reflecting ammonia leaks and ensuring production and personnel safety. It boasts high stability and low maintenance costs, eliminating the need for replacing electrode caps and the associated debugging time associated with traditional ammonia meters every six months. This method solves the problems of high maintenance requirements and inaccurate measurements associated with existing analytical instruments, while also saving significant maintenance costs. In the synthetic ammonia production process, the conductivity method for measuring ammonia concentration saves over 20,000 yuan annually compared to the ammonium ion method. During initial operation, this technology occasionally exhibited unstable measurement values, revealing a discrepancy between the laboratory conductivity curve and the actual field curve. After correction, the instrument operated normally for 72 hours following the correction, with measured values ​​within the allowable error range (compared to laboratory measurements). Over three months of continuous operation, the instrument remained accurate with minimal deviations, all within the permissible error range.

[0014] Since the successful implementation of this solution in the laboratory, guided by the laboratory data, the online experimental modification was carried out step by step and in a planned manner. It took more than half a year to complete the experimental test. After the technology was operating normally on site, with the cooperation of manual analysis in the laboratory, the accuracy and effectiveness of the instrument detection data were detected.

[0015] Working principle: The conductivity measurement value is obtained by using the Rosemount 1056 transmitter and its matching 228 electrode. By inputting the relationship between conductivity and ammonia concentration, the Rosemount 1056 transmitter has a built-in curve setting function, which can directly convert the conductivity value (us / cm) into the ammonia concentration value (ppm), reflecting the concentration of ammonia in the condensate more intuitively and quickly.

[0016] Although embodiments of the invention have been shown, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An online detection method for ammonia content in condensate from a synthetic ammonia process, characterized in that, Includes the following sequential steps: A) A sample flow is drawn from the condensate pipeline of the ammonia synthesis unit at constant pressure, and the pressure and temperature are attenuated at the sampling point to obtain the condensate to be tested under normal pressure and temperature. B) The condensate to be tested is introduced into the conductivity measurement cell, and its conductivity value is measured in real time while the sample temperature is collected at the same time. C) Based on the pre-established conductivity-ammonia concentration calibration curve and combined with the temperature compensation coefficient, the measured conductivity is converted into ammonia concentration; D) Output the calculated ammonia concentration to the host system in analog or digital form for process adjustment and alarm interlocking.

2. The online detection method for ammonia content in condensate of ammonia synthesis process as described in claim 1, characterized in that, The constant pressure sampling in step A is achieved by a pressure-reducing sampling cup, the outlet pressure of which is not higher than 0.1 MPa.

3. The online detection method for ammonia content in condensate of ammonia synthesis process as described in claim 1, characterized in that, In step A, the sample temperature is controlled within the range of 20℃ to 35℃ before entering the conductivity measurement cell.

4. The online detection method for ammonia content in condensate of ammonia synthesis process as described in claim 1, characterized in that, Step B employs a bipolar platinum black conductive electrode or an equivalent corrosion-resistant electrode, with an electrode constant of 0.10 cm⁻¹. -1 ~1.00cm -1 .

5. The online detection method for ammonia content in condensate of ammonia synthesis process as described in claim 1, characterized in that, According to the method of claim 1, the calibration curve in step C is fitted by at least 5 different conductivity-ammonia concentration data points.

6. The online detection method for ammonia content in condensate of ammonia synthesis process as described in claim 1, characterized in that, The conductivity data point is located at 30 μS·cm. -1 ~150μS·cm -1 The range corresponds to an ammonia concentration range of 50 mg·L⁻¹ to 2000 mg·L⁻¹.

7. The online detection method for ammonia content in condensate of ammonia synthesis process as described in claim 1, characterized in that, The temperature compensation coefficient is taken as 1.5%·℃⁻¹ to 2.5%·℃⁻¹.

8. The online detection method for ammonia content in condensate of ammonia synthesis process as described in claim 1, characterized in that, It also includes an online calibration step, which involves periodically switching a standard solution with known conductivity to calibrate the conductivity measurement cell. If the deviation between the calibrated value and the theoretical value exceeds a set threshold, the calibration curve is updated.

9. The online detection method for ammonia content in condensate of ammonia synthesis process as described in claim 1, characterized in that, The analog signal output in step D is a DC current of 4mA to 20mA, and the digital signal includes RS-485 or Ethernet Modbus protocol.

10. The online detection method for ammonia content in condensate of ammonia synthesis process as described in claim 1, characterized in that, When the ammonia concentration exceeds the preset upper limit, the upper-level system triggers an audible and visual alarm or automatically shuts off the corresponding discharge valve to achieve over-limit interlock protection.

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