Fermentation tank
The fermentation tank is one of the main equipments for beer production. The tank is filled with more than one hundred tons of wort. The cooling yeast produces chemical reactions in the tank to generate heat, which increases the temperature of the wort in the tank. There are three temperature measurement points in the tank. The sensor uses Ptl00 thermal resistance (RTD). The platinum resistance probe is inserted into the irrigation tank about 0.5 meters. The outer wall of the tank is provided with upper, middle and lower cooling jackets and three two-position electric valves. The electric valve regulates the flow of the cold medium in the cooling jacket to control the temperature of the wort in the tank. A factory's cold media use liquid ammonia to cool down. The upper, middle and lower three electric valves can be independently switched. The condition of the factory is rather special. The upper valve switch mainly affects the central temperature, the middle valve switch mainly affects the lower temperature, and the lower valve is installed near the exit, that is to say, There is no one-to-one correspondence between the three temperature measurement points and the three sets of cooling jackets. If the upper temperature measuring point is too high and the body of wine (the liquor in the fermentor consisting mainly of wort and yeast is called a wine body) is shallow, the measured temperature is the temperature of the gas-liquid mixture, so it is generally not As a controlled quantity, because the yeast is also deposited on the bottom of the cone of the fermenter, the lower temperature is not suitable as a controlled quantity. Therefore, it is mainly to control the temperature, taking into account the temperature under the warm, in order to control the main valve, supplemented by the valve. During the fermentation process, the temperature is constantly rising. When the upper limit temperature is reached, the refrigeration equipment is opened and the temperature in the tank is lowered by circulating the alcohol in the cooling tube. When the fermentation temperature is lower than the temperature required by the process, the refrigerant is turned off, and the beer continues to be fermented according to the process requirements. The entire fermentation process is completed in about 20 days. Therefore, controlling the temperature and the rate of rise and fall of beer during beer fermentation is the key to the quality and production efficiency of beer.
2 Cone Fermenter Temperature Control System
2.1 beer fermentation temperature control system design
According to the structure of the fermenter and the characteristics of the fermentation process, a cascade control system is adopted to give full play to its advantages and measure and control the temperature of the fermenter reasonably and accurately.
In the design of the system, it is necessary to understand the choice of primary and secondary controlled parameters; the design of the secondary loop; the relationship between the primary and secondary loops; and the choice of the primary and secondary regulators' control law and the determination of the positive and negative actions.
2.1.1 Selection of main and subordinate controlled parameters of fermentation temperature control system
When designing a controlled system, the selected parameters must effectively reflect the process conditions. The main parameter of the process is the temperature of the wort in the fermenter. The selection of secondary parameters is the key to the cascade control system. The rationality of the secondary loop design determines whether the characteristics of cascade control can be used. According to the design principle of the secondary loop, the choice of secondary controlled parameters should be such that the time constant of the secondary loop is small, the control channel is short, the response is sensitive, the secondary loop contains the main interference received by the controlled object, when the object has a long pure delay time , should try to include the pure lag part in the main object.
2.1.2 Selection of regulation rules for primary and secondary regulators
The type of primary and secondary regulators in the cascade control system is selected based on the control requirements.
(1) Selection of main regulator regulation rules
In the cascade control system, the main parameters are the main indicators of the production process, directly related to the product quality, and the process requirements are relatively strict. Because the main controlled parameter is the temperature of the fermenter, the capacity of the object control channel lags behind. In order to overcome the capacity lag, we must use PID regulation.
(2) Selection of regulation rules for secondary regulators
The purpose of setting the secondary parameters of the cascade control system is to ensure and improve the control quality of the primary parameter. The secondary loop is a follow-up system, and its given value changes with the output of the primary regulator. When selecting the flow rate as the secondary controlled parameter, because the proportional regulation law is sensitive to noise, in order to keep the system stable, the proportionality must be chosen larger and the proportional control function is weaker. To this end, the integral action is introduced and the PI regulation law is adopted.
2.1.3 Selection of positive and negative modes of primary and secondary adjustment
In order to ensure the normal operation of the cascade control system, the positive and negative actions of the primary and secondary regulators in the cascade system must be properly selected. The positive and negative actions of the secondary regulator are only related to the secondary loop and have nothing to do with the primary loop. According to process requirements, in order to ensure product quality, the control valve selects the closed form, and its amplification factor is "-". When the valve opening increases, the flow into the cooling jacket increases, then the sub-object amplification factor is "+" according to the The principle that the sign of the ring amplification coefficient is "+" and the sub-regulator is "-", so the positive action mode is selected.
The positive and negative action of the main regulator only depends on the main object magnification factor sign. The input signal of the main object is the supply flow of liquid ammonia, and the output signal is the temperature of the internal area of ​​the fermenter. When the flow rate of liquid ammonia increases, the temperature in the corresponding area of ​​the tank falls, so the main objective magnification factor is "-", and the main regulator's amplification factor is "-". So the main regulator selects the positive action mode.
2.2 Cascade system tuning
There are many ways to set the cascade system, step-by-step approach, two-step setting method, and one-step setting method. The order of the tuning is the entire primary ring after the entire secondary ring.
The one-step setting method is adopted here. The so-called one-step setting method is based on experience. First, the sub-regulator parameters are set well and no longer change. Then the main regulator parameters are directly set according to the setting method of the general single-loop system. The specific steps are as follows:
1. According to the secondary parameter type, the secondary regulator parameter is selected according to the corresponding empirical value and placed on the secondary regulator. When the sub-controlled parameter is flow, the sub-regulator ratio is set to 40~80, and the sub-regulator ratio is set to 2.5~1.25.
2. After the cascade system is put into operation, the main regulator parameters are directly set according to the single-loop system tuning method.
3. Observe the control process, according to the principle of K value matching, properly adjust the parameters of the main regulator, so that the quality indicators of the main parameters meet the specified quality requirements.
4. If the system oscillates, it can be eliminated by simply increasing the proportionality of the primary and secondary regulators. Twice until you are satisfied.
2.3 Control Algorithm
2.3.1 Characteristic Analysis of Control Algorithm
In the beer production process, the fermentation process has the characteristics of large inertia, time lag, and nonlinearity. Therefore, it is difficult to obtain ideal results using conventional control algorithms. This is also an important reason that restricts the quality and efficiency of beer production. Therefore, in order to meet the requirements of beer production fermentation process control, we strive to make the identification-free adaptive control algorithm applicable to complex industrial process control with large lag and difficult modeling, without increasing the requirements of the process model. For the controlled object's characteristics, the system uses two control algorithms.
2.3.2 Conventional PID Controller
The conventional PID adjustment method is proportional, integral, differential control law. It is a simple adaptive control method that is widely used and most maturely studied in industrial production. Even in advanced industrial countries such as Europe, the United States, and Japan, the number of loops using modern advanced control algorithms is only a small percentage. The proportion of more than 90% of the control loop is basically still using PID control algorithm. The main reasons are as follows:
1. PID control does not require strict mastery of the mathematical model of the controlled object, and modern control algorithms are based on an accurate mathematical model.
2. The PID control algorithm is simple in structure, good in stability, clear in physics concepts, etc. It is easily accepted by field engineers.
3. In the course of the development of PID algorithms in the past half century, the vast number of engineers and technicians have accumulated rich experience and have found a series of methods for setting PID parameters.
Although PID control has obtained a series of research results and application experience, people's understanding and improvement of PID are still far from being completed. So far there has not been a thorough and comprehensive analysis of the PID mechanism, scope of application, and robustness. In fact, PID is not a universal controller. In systems with complex dynamic characteristics such as multiple variables, time-varying, large time-lag, and strong interference, it is difficult for PIDs to obtain ideal control effects and even cause instability. Therefore, it is necessary to carry out a comprehensive analysis of the control mechanism of PID, and propose an improved method for the application in the above-mentioned occasions.
One of the key problems in PID control is PID parameter tuning. The traditional tuning method is to set the PID parameter value according to certain tuning principles based on the mathematical model of the controlled object. However, the actual industrial production process often has non-linear and time-varying uncertainties, and it is difficult to establish an accurate mathematical model. The application of conventional PID control can not achieve the desired control effect. In addition, in the actual production site, PID parameter tuning and self-tuning methods are many, but often difficult to implement or not ideal, conventional PID controller parameters are often poorly tuned, poor performance, poor adaptability to operating conditions. Therefore, further research is needed in the tuning and self-tuning of PID parameters.
3 instrument selection
(1) Temperature sensor
Industrial assembled thermal resistors are usually used to display instruments and computers, and directly measure the temperature of liquid, vapor, and gas media and solid surfaces in the range of -200 °C to +500 °C in various production processes . I plant production of thermal resistance in line with ICE international standards and national regulations, there are two types of platinum thermal resistance and copper thermal resistance, platinum resistance is divided into mica skeleton, ceramic framework, thick film resistors and thin film resistors. The skeleton of the copper resistor is made of polycarbonate. Platinum resistance grade number Pt100 , copper resistance index No. Cu50 . BA1 , BA2 , Pt100 platinum resistance and Cu100 copper resistance can be customized. Here we choose Pt100 .
(2) Temperature transmitter
HAKK-WB series temperature transmitter is 24V power supply, two-wire integrated transmitter. The product uses imported integrated circuits to amplify the signal of the thermal resistance and convert it into an output current of 4-20mA or 0-10mA, or an output voltage of 0-5V. The armored transmitter can directly measure the temperature of the vapor or liquid. It is especially suitable for measuring the low temperature range and overcomes the influence of condensed water on the temperature measurement. Pt100 temperature transmitter is used for Pt100 platinum resistance signal need long-distance transmission, presence of strong interference source exists in the field or signal needs to be connected to DCS system. The platinum resistance temperature transmitter adopts a unique double-layer circuit board structure. The lower layer is a signal conditioning circuit. The upper layer circuit can define the sensor type and measurement range.
(3) Orifice flowmeter
HYG series orifice flowmeter (also known as throttling device, differential pressure flowmeter) is a differential pressure generating device for measuring flow, and can be used to measure the flow of various fluids in the pipeline with various differential pressure gauges or differential pressure transmitters. Orifice flowmeter throttling devices include annular chamber orifices, nozzles, and the like. The orifice flowmeter throttling device is used in conjunction with a differential pressure transmitter to measure the flow of liquids, vapors, and gases. Orifice flowmeters are widely used in petroleum, chemical, metallurgy, electric power, and light industry sectors.
The fluid filled with the pipeline, when they flow through the throttling device inside the pipeline, the flow stream will form a partial contraction at the throttling member of the throttling device, so that the flow velocity will increase, the static pressure will be low, and the flow will be generated before and after the throttling device. Pressure drop, pressure difference, the greater the flow of medium flow, the greater the pressure difference between before and after the throttle, so the orifice flow meter can measure the fluid flow by measuring the pressure difference. This measurement method is based on the law of energy conservation and the law of flow continuity.
(4) Differential pressure transmitter
The 3051X high-precision differential pressure transmitter has all the features of the EJA original meter and also extends some of the useful features. The rotary switch can clear PV value, increase clockwise, decrease counterclockwise, can be adjusted by 1μA, and can also be adjusted in a wide range. 3051X high-precision differential pressure transmitter main performance and parameters: (1) output signal: 4 ~ 20mA.DC, two-wire system. (2) Supply voltage: 12V to 45V.DC. (3) Power influence: <0.005%/V. (4) Load influence: no load effect when the power supply is stable. (5) Startup time: <2 seconds without preheating (6) Operating environment: -25°C to +70°C Relative temperature: 0 to 100%. The absolute value of the upper and lower limits after migration should not exceed the upper limit of the maximum range. (7) load characteristics: RL ≤ (u-12) / i, where: u --- supply voltage, i --- loop current. (8) Vibration effect: ±0.5%/g in 200Hz vibration in any direction. (9) Installation position: When the diaphragm is not installed vertically, it may produce an error of less than 0.24Kpa, but it can be eliminated by zero adjustment. (10) Explosion-proof type: Flameproof ExdllCT5, Intrinsically Safell CT6.
(5) Flow Totalizer
Xiamen Yu Electronics AI-708H flow totalizer controller for on-site temperature, flow and other signals collected, display, control, remote transmission, communications, printing and other processing, constitute a digital acquisition system and control system. Dual-screen LED digital display with an extremely wide range of display measurement, can display four instantaneous flow measurement values, inlet/outlet temperature measurement values, flow (differential pressure, frequency) measurement values, and the entire 11-digit flow cumulative measurement Value, 0.2% level accuracy, 0.1% level cumulative accuracy. With a variety of signal input functions, can be connected with a variety of differential pressure signal (hole plate device), linear signal (magnetic flowmeter) and pulse signal (vortex flowmeter). With two analog output transmission. Support RS485, RS232 serial interface, using standard MODBUS RTU communication protocol. The meter can carry RS232C printing function, with manual, timing, alarm print function. With DC24V feed output, field transmitter power distribution. Optical isolation between input, output, power, and communication
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(6) Electric control valve
The RC series electric control valve includes a driver that receives the driver signal (0-10V or 4-20mA) to control the valve for adjustment. It can also form an intelligent network control system according to the control needs and optimize the control to achieve remote monitoring. Â
(7) Xiamen Yu Electronics AI-808P Thermostat
LED display high-performance program table, with 50 procedures, a variety of powerful adjustment functions. It also has a large-screen digital display for easy viewing, LCD display features for interactive programming mode and parameter settings. Equipped with automatic coordination function, "SUPER" suppression overshoot function and the newly added "SUPER" hunting suppression function. The position scaling and heating/cooling modes are suitable for a variety of applications.
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