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Application of advanced control technology in the carbonization section 1. Key technologies used in the advanced control system This project uses the following control technology owned by Zhejiang Zhongkong Software Technology Co., Ltd. they are: 1.PC-Adcon: Multivariable robust predictive control and local optimization technology will be used for multivariable control and local optimization of important unit equipment or equipment groups in ammonia-alkali plants. 2. PC-PFC single variable predictive function control technology, which will be used to improve the control level of key loops in ammonia-alkali plants. 3.APC-Sensor: Online real-time soft measurement technology based on methods such as neural network and principal component analysis will be used to calculate online the quality indicators and process parameters of ammonia-alkali plant products and be used by multi-variable controllers. The overall framework of the advanced control system is shown in the figure below: 2. Software and hardware environment of the advanced control system 1. Hardware interface According to the new line DCS system SIEMENS PCS 7, the advanced control system must make maximum use of existing hardware equipment, not only to ensure the advancement of the advanced control system, but also to consider the economy of project implementation. The DCS system provides a standard OPC interface, which can realize data exchange between the DCS system and APC-Adcon and other advanced control series software. The hardware structure after realizing the advanced control system is shown in the figure below: Advanced control system hardware structure figure 2. The software interface support software is planned to select Windows 2000 Professional version operating system. APC-Adcon advanced control software has an OPC interface and can directly exchange data with the OPC server. The OPC interface is a standard software interface that is independent of the device. Accessing process data through the OPC server can overcome differences in various network structures and network protocols, making the APC-Adcon advanced control software widely applicable. In this project, the OPC server is responsible for data exchange between the advanced control software and SIEMENS PCS7. The data exchange structure based on the OPC interface is shown in the figure below. The data exchange structure APC-adcon based on the OPC interface is an advanced multi-variable predictive control software package developed by Zhejiang Zhejiang University Central Control Software Co., Ltd. for industrial processes. Each functional module of the advanced controller is a standard part of the controller, packaging different advanced control algorithms and functions. It has nothing to do with the programming language and can be plug-and-play. Moreover, according to on-site requirements, the control device must correspond one-to-one with the advanced control algorithm. The componentized framework just meets this requirement, simplifies programming, and greatly increases the stability of the control system. APC-adcon advanced control software structure principle 3. Carbonization device control scheme adopts multi-variable robust predictive control technology to implement the following advanced control scheme: The control technology is multi-variable robust predictive control and local dynamic optimization technology APC-Adcon. In the process of making alkali, the controlled variable CV, the manipulated variable MV and the interference variable DV are as shown in the following table: Carbonization station controlled variable 4 CV CV1 A~J TIC401A~J Carbonization extraction liquid temperature adjustment CV2 aj/3 TR401a-j/3 T0401a-j Twelve circles temperature CV3 aj/2 TR401a-j/2 T0401a-j (medium temperature) Seventeen circles temperature CV4 aj/1 PTT-401a~j-1 PTT-401a~j-1 (tower pressure) 4 manipulated variables MV MV1 aj FRC-411a-j Carbonized liquid flow record adjustment MV2 aj/MV3~J LV401a-j/TV-401 Feeding threshold and cooling seawater threshold MV4 aj FRC401a-j Middle gas branch pipe flow indication record adjustment disturbance variable 2 DV2 DV1/DV2 FIC403/FIC411a~j Lower section gas volume and alkali output carbonization section production advanced control variable table 1. Lower section gas control: The carbonization section has two groups of 12 carbonization towers in the south and north. Currently, the gas volume in the lower section is insufficient for the overall production requirements. The specific volume distribution of each tower is related to the difference between the tower pressure and the gas main pipe pressure in the lower section. When the main pipe pressure is close to the tower pressure, the gas intake volume in the lower section of the tower will decrease. ； For a single tower, the tower pressure is related to the liquid level and the air pressure at the top of the tower. Since the tower pressures of each tower are inconsistent, the gas volume entering each tower from the main pipe is also different. In order to ensure that the gas volume in the lower section can be evenly distributed to the ten alkali production towers, it is necessary to ensure that the tower pressure of each tower is maintained at the same value as much as possible. ； At the same time, in order to ensure the amount of alkali produced, it is also necessary to ensure the liquid level requirements of each tower, so there are certain requirements for the tail gas pressure. In normal production, in order to maximize the alkali produced in this shift, the operator will release a large amount of the alkali produced in the tower before changing shifts. When the actual liquid level drops, in order to ensure the tower pressure requirements, the tail gas pressure will be increased, causing the liquid level of the tower to drop and the working conditions to deteriorate. After the process transformation, a self-regulating valve will be added to the tail gas adjustment, which can be used to control the tail gas to ensure the tower pressure and tower liquid level requirements. In this way, the tower pressure is stabilized while ensuring the exhaust gas pressure, and the tower liquid level is also controlled stably. During the tower inversion process, due to the influence of alkali discharge, the stability of each tower is not very good. During this period, the idea of advanced control is to stabilize the production status of each tower as much as possible. A large drop in gas volume will lead to large temperature fluctuations. Since the alkali discharge towers are reduced from ten to nine, the alkali output is reduced. The reduction in the amount of alkali sent for calcination leads to a reduction in the total gas volume in the lower section. When the gas volume decreases, the lower gas main pipe pressure This will lead to a decrease in the air intake of each tower when the tower pressure does not fluctuate greatly, which will cause fluctuations in the normal production of the tower. In normal production, in order to ensure the pressure of the lower gas main pipe, when the calcined furnace gas is insufficient, a part of the kiln gas will be supplemented to ensure the main pipe pressure. This allows each tower to have air intake. However, due to the relatively low concentration of the kiln gas charged, the concentration of the lower gas entering the tower will decrease, which will have an impact on production. The initial idea for controlling the gas in the lower section is that the tower pressures of each tower should be close to the same value, so that the difference with the main pipe pressure is close, so that the gas volume in the lower section can be reasonably distributed. And ensure that the tail gas pressure is constant, so that when the tower pressure is stable, the liquid level will also be stable, making the tower production stable. During production, the gas in the lower section of each tower is distributed in proportion according to the amount of alkali produced. 2. Mid-section air control: In the current production, the supply of gas volume in the middle section is sufficient, which can ensure production. However, there are some restrictions on the gas volume in the middle section of each tower. If the gas volume introduced is too large, it will take away NH3 in the liquid phase, thus reducing the conversion rate. Therefore, for the amount of gas introduced in the middle section, it is enough to ensure that the tower index requirements are met, rather than the bigger the better. 3. Alkali output control: There is a general range for the alkali output of each tower. In normal production, the dispatching room gives a total alkali output requirement, and then the operator determines the specific alkali output of each tower based on experience based on the working conditions of each tower. When the tower is inverted, since one alkali production tower is reduced, the alkali output of other towers will inevitably increase, but it is impossible to completely make up for the alkali output of the reduced tower, which will affect subsequent processes and reduce the gas volume of the lower section of calcination. In advanced control, a grid of alkali output requirements will be listed in the advanced control screen. This amount is given by the dispatching room. Then the alkali output of each tower is distributed in two ways.: The first is manual allocation by the operator, which is suitable for the initial stage of tower inversion. During this period, for a new alkali production tower (which has just changed from cleaning state to alkali production), its alkali output should be relatively small, such as 20m3/h. ； The second is automatic distribution. This is the normal production period. After the total amount requirement is given, the control system automatically allocates the alkali output of a single tower. The distribution principle is to ensure that the total alkali output is the required value and the alkali output of a single tower is within the allowable range of normal production. 4. Cleaning gas control: For the cleaning process, the main factors affecting the temperature of the neutralizing water are the cleaning gas volume and the cooling seawater threshold. Relatively speaking, the cleaning gas volume has a greater impact, and there are not many operations on the cooling seawater threshold, so the control of this temperature is mainly affected by the cleaning gas volume. In actual production, the cleaning gas volume fluctuates greatly. For the supply of cleaning gas, the total volume is basically constant. When the tower pressures of the two cleaning towers are different, the gas volumes entering the two cleaning towers are inconsistent. This makes the air intake volume greatly affected by the tower pressure, and the tower pressures of the two towers are inconsistent. Gas grabbing phenomenon occurs when the tower pressure of one tower fluctuates, which will cause the air inlet volume of both towers to fluctuate, causing the outlet neutralization water temperature to fluctuate. Therefore, advanced control requires stabilizing the tower pressure, thereby stabilizing the cleaning gas inlet volume, thus ensuring that the fluctuation of the outlet neutralization water temperature is reduced. Regarding the control of the temperature of the neutralizing water coming out, if the tower itself encounters an inverted tower, the cooling water will be turned off first, so that the temperature of the neutralizing water coming out will rise by about 10 degrees, that is, the fluctuation of itself is relatively large. 5. Feed neutralized water: The feed neutralized water mainly controls the liquid level of the tower (reacted through the tower pressure). When the liquid level is guaranteed, production can be normal, and the adjustment of the alkali output can also meet the requirements. At the same time, after the tower pressure is stabilized, the air intake volume of the lower section of the gas can be stabilized and reasonably distributed. 6. Main pipe pressure considerations: Since the supply of gas and liquid is affected by the upper process, the impact on the main pipe pressure is not considered in the advanced control. Once the main pipe pressure is higher or lower, the operator will contact the external process for adjustment. 7.CV (Control Variables, controlled variables) requirements: The current control idea, for the alkali production process, the control indicators of a single tower are medium temperature (17 circles), 12 circles of temperature, tower pressure and alkali outlet temperature. Among them, the temperature of 12 circles is regional control, that is, it can be guaranteed to be within a certain control range. ； For the cleaning process, the control indicators are the outlet neutralization water temperature, tower pressure and outlet neutralization water CO2 concentration. The CO2 concentration is tested once an hour, so CV is not included in the HIECON controller. 4. Conclusion The preliminary application of advanced control technology in the carbonization tower unit of our plant's new line in the past six months has achieved good results, which are mainly reflected in improving the smoothness of operation and carbonization conversion rate, realizing jamming operation, and increasing output. Facts have shown that the system technology is advanced and mature, with good control performance, strong robustness, wide adaptability, and a high degree of software engineering. The model established by the system can better reflect the dynamic characteristics of the device, conform to the actual situation of the device, and meet the actual needs of the site.

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