Measurement of ammonia synthesiser pressure transmitter

Project Overview

Selection and application of pressure transmitter for measuring ammonia synthesizer

Ammonia synthesis is an important link in modern chemical production, and as the core equipment of ammonia synthesis, the safe and stable operation of ammonia synthesizer is crucial. During the ammonia synthesis reaction, pressure is one of the key factors affecting the reaction rate and balance. Therefore, accurately measuring and controlling the pressure in the ammonia synthesizer is of great significance to ensure production safety and improve ammonia synthesis efficiency. As an instrument that can convert pressure signals into standard electrical signals, the pressure transmitter plays an irreplaceable role in the pressure measurement of ammonia synthesizers.

1. Working conditions characteristics of ammonia synthesizer and requirements for pressure transmitter

The ammonia synthesis reaction is carried out under the conditions of high temperature, high pressure and the presence of catalyst. Its typical The reaction conditions are: temperature 450~550℃, pressure 15~30MPa. The working environment of the ammonia synthesizer is harsh, which puts forward special requirements for the pressure transmitter:

1. And stability: Ammonia synthesis pressure changes are very sensitive, and pressure fluctuations will directly affect the yield and selectivity of ammonia. . Therefore, the pressure transmitter needs to have (generally required ≤0.25%FS) and long-term stability to ensure the accuracy and reliability of pressure measurement.

2. High temperature resistance and corrosion resistance: The internal temperature of the ammonia synthesizer is high, and there are corrosive media such as ammonia, hydrogen, and nitrogen. Therefore, the pressure transmitter must choose high-temperature resistant (generally required ≥200°C) and corrosion-resistant materials, such as Hastelloy C-276, Monel alloy, etc., to ensure that it can work stably for a long time in harsh environments.

3. Anti-vibration and impact resistance: The ammonia synthesizer will produce certain vibration and impact during operation, which may affect the measurement accuracy and service life of the pressure transmitter. Therefore, the selected pressure transmitter should have good vibration and impact resistance to adapt to harsh working environments.

4. Safe and reliable: Ammonia synthesis reaction is a high-risk chemical process. Once a leakage or explosion accident occurs, the consequences will be disastrous. Therefore, the pressure transmitter must comply with relevant national safety standards and have reliable safety protection functions to ensure production safety.

2. Commonly used types of pressure transmitters for ammonia synthesizers

According to different measurement principles and structural characteristics, the pressure transmitters suitable for ammonia synthesizers mainly include the following types:

1. Diffused silicon pressure transmitter: Its core component is a diffused silicon sensitive element made of the piezoresistive effect of silicon material. This type of transmitter has the advantages of high accuracy, small size, and vibration resistance, but its temperature resistance is relatively low, and it is generally suitable for occasions where the measurement temperature does not exceed 150°C.

2. Ceramic pressure transmitter: Its core component is a ceramic sensitive element made of the piezoresistive effect of ceramic materials. Compared with diffused silicon pressure transmitters, ceramic pressure transmitters have higher temperature resistance (up to more than 400°C) and excellent corrosion resistance, and are suitable for measuring the pressure of high-temperature and highly corrosive media.

3. AdaptationStrain pressure transmitter: Its core component is to paste the strain gauge on the elastic element, and use the principle that the elastic element is compressed and deformed to cause the resistance change of the strain gauge to measure pressure. Strain gauge pressure transmitters have the advantages of simple structure, low cost, and wide measurement range, but their accuracy and long-term stability are relatively poor, so they are suitable for occasions where measurement accuracy is not required.

4. Sapphire pressure transmitter: Its core component is a sapphire sensitive element made of the piezoresistive effect of sapphire material. Sapphire pressure transmitter has the advantages of high precision, good stability, high temperature resistance (up to 800°C and above), and corrosion resistance. It is currently an ideal choice for pressure measurement in ammonia synthesizers. However, its cost is relatively high, and it needs to be selected according to the actual situation.

3. Selection principles of ammonia synthesizer pressure transmitter

Selecting a suitable ammonia synthesizer pressure transmitter is crucial to ensure production safety and improve ammonia synthesis efficiency. When selecting, the following factors should be considered:

1. Measuring range: Select the appropriate pressure transmitter range according to the working pressure range of the ammonia synthesizer. Generally, the range of the pressure transmitter should be 1.2 to 1.5 times greater than the measured pressure value to ensure measurement accuracy and prevent overload.

2. Accuracy level: Select the appropriate accuracy level according to process requirements. For the ammonia synthesis reaction, the accuracy level of the pressure transmitter is generally required to be no less than 0.25% FS.

3. Output signal: Common pressure transmitter output signals include 4~20mA, 0~5V, 0~10V, etc. The appropriate output signal type should be selected according to the interface requirements of the control system.

4. Material: Select the appropriate pressure transmitter material according to the corrosiveness and temperature of the medium. For ammonia synthesizers, high temperature and corrosion resistant materials should be selected, such as Hastelloy C-276, Monel, etc.

5. Installation method: Choose the appropriate installation method according to the on-site installation conditions. Common installation methods include threaded connection, flange connection, ferrule connection, etc.

6. Explosion-proof level: Choose the appropriate explosion-proof level according to the level of the hazardous area on site. For ammonia synthesizers, the pressure transmitter is generally required to reach at least dⅡCT4 level.

IV. Installation and maintenance of ammonia synthesizer pressure transmitter

1. Installation precautions

(1) The installation location should be as close as possible to the measured pressure point, and avoid vibration and heat sources to reduce measurement errors.

(2) Pay attention to the cleanliness of the pressure interface during installation to prevent impurities from entering the pressure transmitter and affecting the measurement accuracy.

(3) After installation is completed, verification should be carried out to ensure that the pressure transmitter is working properly.

2. Maintenance

(1) Calibrate the pressure transmitter regularly. Generally, the calibration cycle is half a year to one year.

(2) Regularly check the pressure connecting pipeline to ensure that it is smooth and leak-free.

(3) Clean the outside of the pressure transmitter regularly to prevent dust and impurities from affecting its heat dissipation performance.

V. Conclusion

As an important part of the ammonia synthesizer, the pressure transmitter's selection and application are of great significance to ensure the safe and stable operation of the equipment and improve production efficiency. In practical applications, appropriate pressure transmitters should be selected based on comprehensive considerations of process conditions, technical requirements and economic factors, and installation, debugging and maintenance should be done well.