1 the original state of the system More than ten years ago, according to the traditional general design and conventional selection, our factory has installed a liquid level measurement and control system for synthetic ammonia and cold. The liquid level meter uses the pneumatic high-pressure float level adjustment transmitter UTQ-113 of Shanghai Automation Instrument No.5 Factory. The regulating valve adopts ZMBS-320KDg6C=0.1, which is equipped with a pneumatic adjustment recorder and a sub-line board to form the ammonia fraction of the synthetic section. Cold cross high voltage measurement and control system. In order to facilitate maintenance and repair. A total of 7 Dg10 high pressure valves, two standard tees, one elbow, 15 pairs of high pressure flanges, 48 ​​high pressure bolts, 90 high pressure nuts and 5Mφ 24×6 high pressure pipes are used in each system. In order to extend the service life of the high pressure regulating valve and ensure the adjustment effect, two high pressure regulating valve series schemes are adopted. The whole system is cumbersome, the installation is large, the scene is messy, and the investment of each system is also more than 15,000 yuan (the price a few years ago). However, after the installation of these two systems, the liquid level detection reaction was inaccurate and has not been used normally. 2 Cause analysis The liquid level detection in high-pressure vessels such as ammonia separators and cold exchangers in the production of synthetic ammonia in our factory is not normally operated by the liquid level detecting device designed and installed in the form of connected pipes (float type liquid level gauge, etc.) according to the conventional method. According to the survey, it is common in small fertilizer plants. The reason for this phenomenon is that high-pressure gas-liquid separators such as ammonia and cold-crossing are not simple empty-tube containers, and the working pressure is up to 32 MPa, which are equipped with separate internal parts of different structural forms, and the outer parts of these high-pressure containers are The barrel is welded with a multi-layer coil and it is not allowed to open holes in the barrel. Therefore, the gas-phase and liquid-phase reserved interfaces installed as the liquid level detecting instrument are all opened on the upper forged high-pressure container and the lower head, that is, the gas phase interface is in the upper head and the liquid phase interface is in the lower head. It is well known that after the high-pressure medium flows through the equipment, due to the influence of equipment resistance, a pressure difference will occur at the inlet and outlet of the equipment. The magnitude of the pressure difference is related to factors such as equipment structure, flow cross section, medium flow rate, etc., and varies with the flow rate of the medium. Taking the ammonia separator of our factory as an example, the medium enters the container and flows through the separated internal parts for gas-liquid separation. The liquid ammonia accumulates at the bottom of the ammonia fraction as a product, and the gas extracts ammonia from the outlet at the upper end of the vessel into the subsequent stage device. The ammonia level and cold junction liquid level detection interface (liquid phase, gas phase) of our plant are located on both sides of the separation section, and the pressure difference generated by the separation section also acts on the liquid phase interface of the liquid level meter. According to measurements, the pressure difference of the separation section can be as high as several meters to ten meters of water column at full load. With ammonia, cold-crossing equipment structure and medium inlet position and flow direction in the separation section, two situations may occur; one is that the positive pressure side of the separation section pressure difference acts above the liquid level and the negative pressure side acts on At the gas phase interface of the liquid level meter, at this time, the gas phase and the liquid phase of the liquid level meter are the positive superposition of the pressure difference generated by the actual liquid level in the container and the separation section. Generally, the measuring range of the float level transmitter is only within 1 meter. Therefore, as long as there is a little liquid at the bottom of the container, it will quickly fill the connected tube of the external level gauge (float) under the pressure difference, so that the level gauge The full level is displayed. Unless the liquid level in the container is completely emptied, the external float level gauge always displays the full scale regardless of the change in the liquid level. In another case, the pressure difference positive pressure side of the inner part acts on the gas phase interface of the liquid level meter, and the negative pressure side acts on the liquid level in the container, and the internal pressure difference and the liquid level value are inversely superposed. Due to the pressure difference of the inner part, no matter how the liquid level in the container changes, even if the liquid level is filled with the container or even with liquid, the liquid level gauge shows zero. The original ammonia and cold cross pneumatic float level measurement system of our factory is not allowed, and it still belongs to the former type. 3 Improvement measures In order to achieve energy saving and consumption reduction as soon as possible, our factory is determined to re-engineer the synthetic ammonia and cold water level detection automatic control system. The UYB-320C built-in capacitive high-pressure liquid level transmitter, which is valued and promoted by the editorial department of "Fertilizer Industry" and "Small Nitrogen Fertilizer", is directly inserted into the equipment from the ammonia and cold-crossed liquid phase holes to detect its liquid level. The plasma double-column digital display (with upper and lower limit alarms) displays the liquid level change, and the liquid level upper and lower limit alarms and regulating valve positions are self-adjusted by a simple electronic regulator. Since the original pneumatic high-pressure regulating valve has never been used after it has been installed, it is still used for adjustment for the purpose of saving investment. Our factory used minor repairs. In less than half a day, both sets of liquid level gauges were installed. After commissioning and driving, the liquid level detection part will work normally quickly and put into operation to realize the ammonia discharge operation under the liquid level indication. Subsequently, the self-control system was debugged, and it was found that the original pneumatic control valve ZMBS had serious internal leakage. Although the two valves installed in series with cold cross were all closed, the circulation capacity was also selected very small, but the liquid level was still difficult to mention. Up, it shows that the regulating valve has been difficult to adapt to the needs of high-pressure liquid level self-control. Even so, the amount of gas run has been significantly reduced compared to manual ammonia release, and the CH4 content in the recycle gas also increases. Our factory quickly purchased two new special automatic ammonia release valves for replacement, which were used for ammonia and cold exchange systems to realize automatic ammonia release, so that the liquid level control was quickly transferred to normal, and finally solved me in a short time. The key to this production of the plant is the automatic control of the measurement of ammonia and cold high pressure liquid level. 4 implementation effect The synthetic ammonia and cold liquid level measurement and control system based on built-in capacitor high-pressure liquid level transmitter has been officially put into operation in September 1993 for more than 2 years. It has been proved that the implementation effect of the project is obvious and the benefits are significant. According to statistics, the annual direct profit is 800,000 yuan. (1) After the high-pressure liquid level detection automatic control system is put into use, the effect is remarkable (see table). The CH4 content in the circulating gas is obviously improved. Our factory is heavy oil and gasification, which has been increased from 4%~6% before installation level gauge to 11%~14%, which effectively reduces the effective gas venting and leakage of the synthetic system. (2) The ammonia and cold liquid level of the system are accurately measured, and the automatic ammonia release or manual manual ammonia release under the condition of liquid level detection is realized, and the manual manual ammonia release under the condition of no liquid level display is eliminated, which is effective. Realize safe production. (3) The application of the liquid level automatic control system frees the operators from frequent manual adjustments, greatly reduces the labor intensity of the workers, stabilizes the operation, and the temperature of the synthetic tower catalyst is stable, almost straight. (4) The liquid level gauge is extremely convenient to install, the structure is very light, and the total weight is less than 2Kg. It can be used with one flange, three bolts and three nuts. The liquid level meter measurement and control system works reliably and stably. Our factory has been in operation for 2 years and has basically no maintenance. The implementation of this project was guided and helped by Li Dezhong, a high-tech industrial company in Tuzuoqi, Inner Mongolia. I would like to express my sincere gratitude. WPC Parts, WPC Plastic Clip, WPC Joist Screw Shangyu YongSheng New Material Co., Ltd. , http://www.wpc-deckingboard.com