Abstract: This paper introduces an automatic alkali addition control and management system for fermenters based on configuration software and PLC. The system automates the management of the entire fermentation process in the fermenter and maintains constant pH value, improving the stability of product quality, facilitating enterprise management, and reducing the labor intensity of operators. Currently, the system has been practically applied in three xanthan gum production workshops with good control results.
Keywords: Configuration software, PLC, fermenter, automatic feeding, constant pH control, batch management
Abstract:This article describes automatic alkali control and management systems based on configuration software and PLC, which can achieve PH constant control and automatic management in entire fermentation process, improve the stability of product quality, ease labor, the system has good control effect in three xanthan gum production plant practical application.
Key words:Configuration Software PLC Fermenter PH constant control Batch control
1. System Introduction
1.1 Original Alkali Addition Process Description
Fermentation is a crucial process in xanthan gum production, directly impacting product quality and yield. During fermentation, the fermenting material produces a large amount of acid, hindering bacterial growth and normal fermentation. Therefore, alkali solution is added to neutralize this acid. Currently, the method for adding alkali during fermentation typically involves operators taking samples at the sampling port every 1.5 hours, measuring the pH value of the sample, and manually opening the alkali valve when the measured value is lower than the target value, while simultaneously timing the valve opening with a stopwatch. This method introduces several problems: first, the sampling time is too long, leading to unstable pH values within the fermentation tank; second, the amount of alkali added depends on operator experience, resulting in different estimated addition times for the same test value; third, adding too much alkali at once causes significant pH fluctuations within the tank, negatively impacting fermentation; and fourth, the measured pH value of the sampled material is affected by temperature changes and dynamic/static measurement factors, leading to discrepancies between the measured value and the actual pH value of the material within the tank, affecting measurement accuracy. Furthermore, human error often influences the viscosity of the fermented material, thus affecting product quality.
1.2 Self-controlled alkali addition solution
To overcome existing problems, the system installs a pH electrode on the fermenter to collect the pH value of the material in the fermenter in real time. The alkali addition cycle time is set on the industrial control computer software. When the set cycle time arrives, the PLC compares the real-time pH value with the set target pH value. If the real-time value is lower than the target value, the PLC automatically calculates the required alkali addition time based on the difference between the real-time and target pH values, and opens the solenoid valve according to the calculated time, completing one alkali addition cycle. The alkali addition cycle time can be set by the operator according to the viscosity of the material at different fermentation stages. In the early stages of fermentation, when the viscosity is low, the alkali addition cycle time can be shorter; in the later stages, when the viscosity is high, the cycle time can be longer. The alkali addition cycle time is generally set to 3–10 minutes.
In addition to automatic alkali circulation, the system also retains a manual alkali addition function on the host computer for each fermenter. Operators simply need to switch from automatic to manual mode using the mouse, and then click the manual alkali addition button to open the solenoid valve for alkali addition in any fermenter, with the addition time displayed. Regardless of whether alkali addition is manual or automatic, if the pH value of the material exceeds the target pH value during alkali addition, the system will close the solenoid valve to prevent excessive alkali addition.
To facilitate enterprise management and querying, after each batch of fermentation is completed, the system allows users to click a button to export the pH value data of the entire fermentation batch and generate an independent batch file.
2 System Design
2.1 Hardware Components
2.1.1 System Block Diagram
The system block diagram is shown in Figure 1.
The on-site data acquisition and control unit consists of a PLC, an AD module, electrodes, instruments, and a solenoid valve. The pH value of the fermenter is sent to the PLC through the AD module. The PLC compares the acquired pH value with the target pH value and calculates the time for adding alkali. Based on this time length, the solenoid valve is opened to add the alkali solution into the fermenter.
The remote management system consists of an industrial control computer (ICC). The ICC interface displays the operating status of all fermenters in the workshop. Parameters set and commands issued by operators are downloaded to the PLC via the ICC, which then executes the corresponding actions according to the program. The ICC software can export and save pH data for each batch, facilitating enterprise query and management. Enterprise computers can connect to the ICC via a local area network to remotely monitor workshop production.
Figure 1
2.1.2 Main Hardware Components
① Industrial PC: The Advantech IPC-810 industrial PC is used;
② Configuration software: MCGS6.2, 512 points;
③ PLC: Delta DVP48EH00R2, 24DI/24DO;
④ AD acquisition module: Delta DVP04AD-H2 module is used;
⑤ Communication module: ICP DARK I-7520 communication module is used;
⑥ pH value electrode and instrument: High temperature resistant, fermentation-specific electrode is used, and the instrument is matched with the electrode, with a 4~20mA output;
⑦ Solenoid valve: AC220 power supply, must be resistant to strong alkali corrosion;
⑧ Solid State Relay: DC24V control / AC220V output.
2.1.3 On-site plan
① Industrial control computer
The industrial control computer is placed in the workshop duty office and exchanges data with the PLC control cabinet through an RS232/485 communication module. Theoretically, the communication distance is 1.2KM, but considering the communication speed, the communication distance should be minimized.
② PLC control cabinet
The installation location of the PLC control cabinet depends on the site conditions. It is best to choose a clean environment with an ambient temperature below 40 degrees Celsius.
③pH value instrument cabinet
When installed near the fermenter, the distance between the electrode and the instrument should be less than 10m to prevent the weak signal generated by the electrode from attenuating.
④ Solenoid valve
The solenoid valve is installed between the original manual alkali addition valve and the air intake pipe. A filter screen should be installed at the inlet of the solenoid valve to prevent particulate matter from entering the solenoid valve and affecting its operation.
The scene is shown in Figure 2.
Figure 2
2.2 Software Components
2.2.1 Industrial PC Main Interface
The main interface of the industrial control computer program is shown in Figure 3.
Figure 3
The main interface of the software reflects the basic operating data and status of all fermenters. The operating data includes: target pH value, measured pH value and fermenter start time. The status data includes: start/stop status, alarm status, manual/automatic status, and alarm prohibition/allowment status.
To view the detailed operating data and status of a specific fermenter, click "Enter" on the main interface to access the corresponding fermenter interface, as shown in Figure 4.
This interface displays detailed operating data and status of the fermenter, including:
① Operating status indicator, alarm indicator, manual/automatic status, manual/automatic control button, manual alkali addition button, solenoid valve switch status, number of solenoid valve actions, and historical alarm records.
② Batch input and display, fermenter start-up and shutdown time, start-up timer, data export.
③ pH value measurement, alkali addition time coefficient, cycle detection time setting, pH target value setting, pH upper and lower limit setting.
④ Historical pH curve, real-time pH curve.
2.2.2 User Interface Operation
Figure 4
(1) Startup Operation
Step 1: Enter the batch number for this fermentation;
Step 2: Set system operating parameters;
Step 3: Select manual/automatic mode;
Step 4: Turn the selector switch on the PLC control cabinet to "Start".
(2) Stop operation
① First, turn the selector switch on the PLC control cabinet to "Stop". When in the stop state, the PLC program will not execute the program for the fermenter and alkali cannot be added manually or automatically.
(3) Data export
① When the fermenter is stopped, click "**Export pH data of this batch of fermenters**". Data can only be exported when the fermenter is stopped.
(4) Manual addition of alkali
① Select the "Manual" button, then click "Manual Alkali Addition" to open the solenoid valve. The opening time is displayed in the "Alkali Addition Timer".
(5) Automatic alkali addition
① Select the "Automatic" button, and the system will automatically cycle and detect the addition of alkali according to the set cycle time.
(6) Curve browsing
Real-time curve: Double-click the real-time curve to zoom in for easier viewing.
Historical curve: Hover your mouse over the historical curve to see the pH value at a certain point in time.
2.2.3 Protection Strategy
During the opening of the solenoid valve, whether alkali is added manually or automatically, if the measured value exceeds the target value, the system will automatically close the solenoid valve to prevent excessive alkali addition.
2.2.4 Alarm Strategy
When the measured value is higher than the upper limit alarm value or lower than the lower limit alarm value, the system will issue an audible and visual alarm after a 10-second delay. The buzzer in the PLC control cabinet will sound an alarm, and the corresponding fermenter alarm display box on the software interface will turn red and flash.
3. Conclusion
After adopting automatic alkali addition, the pH value control accuracy is: target value ±0.05, which overcomes the uncertainty caused by manual alkali addition, improves the pH stability of the fermenter, and enhances the quality stability of the product. The system integrates the management of fermenters throughout the workshop. Operators only need to be at the computer to understand and operate the working status of each fermenter in the entire production workshop, reducing the labor intensity of operators.
About the Author
Xiao Xianzong (1977-) Male Engineer, works at Invesco New Energy Technology (Shanghai) Co., Ltd.
