Design of automatic control scheme for concentration equipment in traditional Chinese medicine extraction workshop

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This post was last edited by Liang Zhanhui on 2021-3-25 at 14:09. The concentration stage is a very common and important part of the automation projects in traditional Chinese medicine extraction workshops. In newly built traditional Chinese medicine extraction workshops, the concentration stage has largely achieved automated production, eliminating the need for on-site operators to intervene extensively during the production process. The control points and the general instrument configuration in the concentration section will be explained below. I. Design of the automatic control functions for the concentration process 1. Feeding control: The feeding valve and the vacuum control valve are opened to allow feeding through vacuum extraction; a level gauge is used to monitor the liquid level. When the level of the liquid reaches the set value, the feeding valve is closed to terminate feeding. The instruments required for the entire feeding process include: level gauge, feed valve, vacuum control valve, and pressure transmitter ； 2. The vacuum level is controlled by a vacuum control valve in conjunction with a vacuum pressure transmitter, to keep it within the set range. The instruments required are: vacuum control valve, pressure transmitter. 3. The temperature control steam cut-off valve is interlocked with the steam control valve; pressure transmitters and temperature transmitters are used to regulate the temperature during the concentration process ； The pressure transmitter measures the jacket pressure and can adjust the steam pressure. The instruments required include: steam cut-off valve, steam control valve, drain bypass valve, temperature transmitter, and pressure transmitter. 4. Foam elimination control: A foam sensor is used for online foam detection; the temperature and pressure control modules (including the valves used to regulate temperature and pressure) are employed to reduce foam formation. If necessary, a vent valve is activated to carry out the foam elimination process and prevent material loss. The instruments required include: bubble detection electrodes, vent valves, and valves for controlling temperature and pressure. 5. When the material transfer control reaches a certain stage, the two-stage concentration process is no longer able to meet the temperature requirements for concentration; it is necessary to transfer the material to the first-stage concentration chamber. Break the vacuum in the second stage; open the discharge valves at the bottom of the tanks in the first and second stages, and use vacuum to draw the liquid from the second stage into the concentration chamber of the first stage for concentration. The instruments required include: the secondary vacuum cut-off valve, the secondary vent valve, and the dump valve. 6. Determination of the concentration completion point: An online density meter is used to measure the density of the concentrated solution; once the measured density falls within the range specified by the process requirements, the system indicates that concentration is complete ； Or a rough assessment can be made by the liquid level in the first-effect evaporation chamber during the concentration process. The instruments required are: a densitometer or a level gauge. 7. After manual confirmation that discharge is possible (it is recommended to have manual confirmation again at the end of concentration), open the vent valve and the discharge valve to carry out the discharge operation. The instruments required are: the first-effect vent valve and the liquid discharge valve. 8. The drainage of the liquid receiving tank controls the condensate from the concentration process, which enters the collection tank; it is necessary to drain this liquid without affecting the concentration process. Once the level gauge detects that the liquid level has reached the set value, it controls the vent valve, the connection valve, and the transfer pump to discharge the liquid. The instruments required include: a level gauge, a drain valve, a vent valve, a liquid connection valve, a gas connection valve, as well as a safety interlock system with overpressure alarm capability and an emergency steam cut-off valve ； Alarm when liquid medicine temperature exceeds the upper limit, and steam cut-off valve is activated ； Alarm when liquid level is too high, and the inlet valve is shut off ； II. Precautions for the concentration section: 1. The concentration equipment in the traditional Chinese medicine extraction workshop includes double-effect concentrators, single-effect concentrators, scraper concentrators, MVR concentrators, etc. Among these, MVR concentrators have a high degree of integration; they are generally controlled via PLCs, which then communicate with the DCS system ； Two-effect concentrators and single-effect concentrators are still mainly integrated by system manufacturers ； 2. The difference between a double-effect concentrator and a single-effect concentrator is that the former has an additional evaporation chamber; the hot steam generated in the first evaporation chamber is used to heat the second evaporation chamber, which makes it more efficient and energy-saving. However, the automated control system required for it is more complex ； Compared to a single-effect concentrator, a double-effect concentrator introduces the following aspects that require control: (1) Since the second evaporator in a double-effect concentrator is heated by the steam from the first evaporator, the condensate water resulting from this steam needs to be discharged (the heating source for the first evaporator is steam, and the condensate water is steam condensate); therefore, valves must be installed for discharging this liquid (if the container for storing the condensate is large enough, it is also possible to discharge the liquid manually after each batch of material has been concentrated) ； (2) After the second stage of concentration in the double-effect concentrator is completed, the material needs to be transferred to the first stage for further concentration (the second stage uses the hot steam from the first stage for heating, resulting in a lower concentration efficiency than that achieved in the first stage); therefore, additional transfer pipelines and valves are required, making the control system more complex ； 3. If the extraction process involves alcohol extraction, the condensate from the concentration stage generally needs to be recycled ； If the extraction process is aqueous extraction, the condensate from the concentration stage (i.e., wastewater) can be discharged into the sewage pipeline ； 4. When dealing with materials prone to forming bubbles, foam electrodes with multiple detection points can be used for bubble detection; by adjusting the control strategy, the degree of bubbling can be controlled to prevent material leakage ；