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The introduction of urea using DCS control technology has brought great convenience to production. Based on the characteristics of the urea production process, the author has put forward preliminary ideas for upgrading the existing DCS control system. 1 CO2 compressor: The proper operation of the CO2 compressor has a direct impact on the stability of processes such as synthesis and circulation. At the same time, when the CO2 compression unit is in operation, it generates a high amount of heat, and it is also noisy, resulting in a relatively harsh operating environment. Some manufacturers have set up operation rooms, but in such rooms there is generally only monitoring of the pressure at the primary inlet of the CO2 unit, with no other monitoring instruments. CO2 compression units require monitoring operation; a single inspection per hour is not sufficient. If the monitoring signals from the CO2 units can be fed into a microcomputer, allowing them to be monitored from the main control room and subject to partial adjustments, it facilitates better control and adjustment of the system by the operators in the main control room, while also improving the level of operation and management on site. 1.1 Introduction of detection signals for the 4M12CO2 compressor: The main detection signals of the CO2 compressor are fed into the microcomputer, such as the inlet pressure at stage 1 (PI—101), the exhaust pressure at stage 1 (PI—102), the exhaust pressure at stage 2 (PI—202), the inlet pressure at stage 3 (PI—301), the exhaust pressure at stage 3 (PI—302), the exhaust pressure at stage 4 (PI—402), the exhaust pressure at stage 5 (PI—502), and the pressure in the main supply pipe for cooling water (PI—701). There are also temperature detection signals: TE—101 (primary intake air temperature), TE—201 (secondary intake air temperature), TE—301 (tertiary intake air temperature), TE—401 (quaternary intake air temperature), TE—501 (quinary intake air temperature), etc. Of course, other parameters such as oil temperature and cylinder return water temperature can also be fed into the microcomputer, allowing for centralized monitoring, management, and partial operational control from the main control room. 1.2 Automatic control of the primary inlet air volume: The pressure at the primary inlet of the CO2 compressor must meet certain process requirements – it cannot be too low (as this can lead to negative pressures), but it also cannot be too high. Especially in small urea plants, the oxygen supplied to the CO2 compressor inlet is provided by a Roots blower; if the pressure at PI-101 is too high, it will result in a reduction in the amount of air supplied. In severe cases, no air will be able to reach the system, which will affect the corrosion process in the urea tower. Therefore, PI—101 pressure monitoring is very important. The existing vent valve at the primary inlet shall be replaced with a control valve assembly, using PI-101 as its control parameter; a setpoint (the normal pressure value for primary inlet air) shall be manually specified, and its control system shall be integrated into the DCS system. This allows the automatic control to be maintained at a predetermined pressure for the primary inlet air in the main control room. 1.3 Remote control adjustment of CO2 compressor load: In 4M12-type CO2 compressors, load adjustment is generally carried out on-site by the operator using a control valve (some also use a clearance valve for this purpose). There are many problems associated with regulating the load using one valve per cycle (or on-site clearance valves): one of them is the impact of human factors on the accuracy of load regulation. The second reason is that unit vibration can cause changes in the opening degree of the primary circuit valve, affecting the authenticity of the load. Thus affecting the stability of the synthesis and circulation systems. Replace the single valve per circuit with a control valve bank, using the pressure at the first-stage outlet as a parameter, and feed its signal into the microcomputer. The control operator adjusts the set value (primary outlet pressure), which causes one of the compressors’ regulating valves to act, thereby achieving the purpose of increasing or decreasing the load. When the production load is constant, it can be placed in automatic control mode, thereby achieving a stable load and remote control, while also avoiding any impact from human factors or other elements on the accuracy and stability of the load. 1.4 Automatic control of oxygen addition at the primary inlet: Oxygen addition to the feed gas is done for the purpose of preventing corrosion in the urea tower. A low oxygen addition level is detrimental to corrosion prevention, while a high oxygen addition level is harmful to exhaust gas safety. To strictly control the oxygen addition amount to the raw gas fed into the urea tower, an \"automatic online analyzer for CO2 gas O2 content\" is generally used in new installations. However, the control of the oxygen addition amount is still done through manual adjustment of the oxygen addition control valve on-site or remotely. The “Automatic Analysis” (ARS—502) signal is interlocked with the oxygenation control valve assembly, making it a control parameter for the oxygenation valve (control valve); its control system is integrated into a microcomputer, allowing for centralized control and management from the main control room. After the modification, the oxygen addition amount to the feed gas can be automatically analyzed and adjusted within a specified range (usually between 0.4% and 0.8%, selected depending on the circumstances). 1.5 Automatic control of the inlet temperature at the fifth stage of the 4M12 type CO2 compressor: The outlet pressure at the fourth stage of this CO2 compressor is approximately 7.9 MPa, which is close to the critical pressure. If the temperature is below 32°C, CO2 will liquefy. Moreover, since the compressor must undergo compression at its fifth stage as well, this can lead to serious accidents such as liquid slugging. Therefore, the inlet temperature control at level 5 must not be lower than 32°C. However, in order to separate oil and water from the CO2 gas, inter-stage coolers, namely four-stage coolers, are installed; naturally, a lower temperature is advantageous in this case. The conditions for controlling the inlet temperature at the fifth stage of the CO2 unit (referring to 4M12) are quite stringent; to ensure safe operation, it is common to set the control temperature above 34°C, with actual operating temperatures ranging from 37 to 40°C. However, this is not favorable for the oil drainage at subsequent stages. Especially in models that do not have a fifth-stage oil drainage system, this can lead to a decrease in the purity of the CO2 entering the tower. Moreover, the oil entering the system affects the heat exchange efficiency of the heaters, can cause clogging of the nozzles, and also poses risks to the safety of the exhaust gases. It is necessary to control the inlet temperature at the five stages to be reasonable and optimal. The inlet temperature of the fifth stage of the CO2 compressor is controlled by the amount of cooling water used in the fourth stage. An additional control valve assembly is installed at the return valve of the fourth stage; using the inlet temperature of the fifth stage as a parameter, the signal is also fed to the microcomputer. This allows the inlet temperature of the fifth stage to be set to a specified value, and the control valve for the cooling water return in the fourth stage can be operated automatically, thereby achieving automatic control of the inlet temperature of the fifth stage. Similarly, the inlet temperatures at stages 2 to 4 can also be made automatically controlled using the aforementioned method. 2 Synthesis system: The ability to achieve automatic control over the three materials fed into the tower in the synthesis system (i.e., NH3/CO2 and H2O/CO2 fed into the tower) is key to realizing automatic control of the entire system. 2.1 Concept of ratio adjustment A ratio adjustment system consists of a ratio calculator that sets a ratio parameter by determining a certain ratio between one active flow rate F1 and another passive flow rate F2, thereby establishing the relationship F2=kF1. 2.2 Concept for adjusting the NH3/CO2 ratio at the inlet of the tower In a process with full circulation of aqueous solutions, the NH3/CO2 ratio at the inlet of the tower is approximately 4.0 (on a molar basis). Let F1 be the flow rate of CO2 entering the tower, and F2 be the flow rate of NH3 entering the tower; the value k is 4.0 (i.e., the NH3/CO2 molar ratio). Based on the relationship F2 = 4F1, control mechanisms based on ratio adjustment are used to regulate the load on the CO2 compressor (i.e., the flow rate F1), so that FR—203 (the flow rate of CO2 entering the tower) and FR/HIC—202 (the flow rate of NH3 entering the tower) form a ratio-based control system. Signals from this system are fed into a microcomputer, thereby enabling automatic control of the NH3/CO2 ratio at the inlet of the tower. 3 Conclusion The above modification proposals are based on the characteristics of the actual production process, and they address the issues of lack of automatic control for NH3/CO2 fed into the tower as well as the inability of the CO2 unit’s main control room to exercise control. Of course, this is just a concept; whether it can actually be applied in production still requires joint research, development, and discussion by process designers, control system experts, and software developers.