Application of PLC in beer fermentation temperatur

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The application of PLC in the temperature control of beer fermentation

the fermentation process of beer is a process in which some components of wort are metabolized with the participation of beer yeast, so as to transform wort flavor into beer flavor. Beer fermentation is one of the key links in the beer production process. It is also an extremely complex biochemical exothermic reaction process that occurs in the fermentation tank and releases a lot of heat. In this process, not only the fermentable sugars, amino acids and other nutrients in wort are decomposed into ethanol (C2H5OH) and carbon dioxide (CO2) by yeast cell enzymes, but also a series of fermentation by-products are produced, such as diacetyl, higher alcohols, aldehydes, acids, esters and so on. Although the content of these metabolites is very small, they have a great impact on the quality and taste of beer, and the formation of these intermediate metabolites depends on the fermentation temperature. Therefore, whether the fermentation process is normal and smooth will directly affect the quality of the final beer product. For example, if the temperature in the fermentation process changes violently, it will not only cause the yeast to precipitate, age, die, autolysis in the early stage, resulting in abnormal fermentation, but also directly affect the composition of yeast metabolic by-products, thus endangering the beer body and flavor, and the stability of beer colloid. Therefore, the control of fermentation process conditions has always been highly valued by wine makers

in the past, the control of various process parameters in the beer fermentation process was mostly realized by conventional table display, manual on-site operation and adjustment, and manual recording. However, with the continuous increase of beer production, the number of fermentation tanks is gradually increasing (some factories have reached 30 ~ 40). If the conventional method is still used, it will not only cause great inconvenience to the production and operation of workers due to the large number of instruments, but also cause the instability of production quality and even production accidents due to human factors such as negligence and mistakes. Therefore, programmable logic controller (PLC) is designed to automatically control the fermentation temperature of beer

1 beer fermentation process control

1.1 the controlled object

beer fermentation is carried out statically in the fermentation tank, which is composed of tank body, cooling belt, insulation layer and other components. The shape of fermentation tank is generally conical, with a large volume, most of which are more than 100m3 (the volume of beer fermentation tank in China is 120m3 ~ 500m3). Beer fermentation should strictly follow the process curve, otherwise it will affect the quality of beer. In order to facilitate the heat dissipation, the upper, middle and lower cooling jackets are set on the outer wall of the fermentation tank, and the upper, middle and lower temperature measuring points and three eccentric pneumatic valves are set accordingly. The ice water flow in the cooling jacket is adjusted through the valve opening to realize the control of the wine temperature. With the valve opening as the control quantity and the wine body temperature as the controlled quantity, there are three refrigerant valves to control the temperature of the fermentation tank by controlling the refrigerant flow through the cooling zone. In the process of fermentation, the temperature is constantly rising. When the upper limit temperature is reached, the refrigeration equipment should be turned on, and the temperature in the tank should be reduced through the circulation of alcohol in the cooling pipe. When the fermentation temperature is lower than the temperature required by the process, turn off the refrigerant, and the beer will continue to ferment according to the process requirements, and the whole fermentation process will be completed in about 20 days. Therefore, controlling the temperature and its rising and falling rate in the process of beer fermentation is the key to determine the quality and production efficiency of beer

1.2 beer fermentation temperature curve

the beer fermentation process curve is shown in Figure 1, including three stages: natural temperature rise, high temperature constant temperature control, temperature drop and low temperature constant temperature control. In the early natural heating stage, it is basically not necessary to control, because in the fermentation process of beer cans, the heating is carried out by the heat generated by the fermentation itself, and the natural heating is allowed; In the constant temperature stage, the temperature in the fermentation tank is kept constant by controlling the refrigerant on-off valve; In the cooling stage, the temperature is reduced at a specified rate by controlling the refrigerant on-off valve

Figure 1 Typical beer fermentation curve

according to the above requirements, a beer fermentation controller with PLC as the core is designed. Each controller controls a fermenter. The specific temperature control is realized by PID algorithm. PID control is widely used in practical industrial processes because of its simple and reliable, easy to implement, good static performance and other advantages

2 hardware implementation of the control system

the PLC control system structure of the fermentation process is shown in Figure 2, which is composed of Siemens S7 Series PLC (control station) and several IPC (operation station). The system adopts a three-level bus structure: the bottom link is PROFIBUS-DP bus, which is connected to the remote i/o rack, responsible for the connection between PLC, CPU and distributed i/o stations, and the field equipment is connected to the distributed i/o rack nearby

Figure 2 structure diagram of PLC control system of fermentation tank group

(1) control station (lower computer)

the lower computer system only needs to be configured with a set of s or SPLC system (depending on the size of the system), which mainly realizes the functions of data acquisition, automatic control, remote control and interlocking. The lower computer system has the characteristics of high reliability and convenient expansion

(2) operation station (upper computer)

the upper computer system is composed of more than two sets of industrial control computers combined with the corresponding communication interface equipment

3 software design of control system

3.1 composition of control system

temperature is one of the main controlled parameters in industrial production. The composition block diagram of temperature control system is shown in Figure 3. The controller in the figure is PLC, which designs the control program according to the PID control law. The output of PID regulator is converted into PWM, which is used to control the output relay of PLC, so as to control the refrigerant on-off valve of beer fermentation tank

Figure 3 composition block diagram of temperature control system

the temperature measuring element adopts platinum resistance with good linearity and small time constant to measure the temperature of the fermentation tank, and the temperature is converted into a voltage proportional to it by the temperature transmitter. The function of the v/f converter is to convert the voltage output by the temperature converter into a frequency proportional to it, which represents the actual temperature in the fermentation tank. Use the high-speed counter in PLC to record this frequency, so as to generate an error signal compared with the given value of temperature

the fermentation process of beer lasts for more than ten days. The most important link is to control the different fermentation temperatures in the fermentation tank in each time period. According to the requirements of the fermentation process, we design the fermentation temperature time curve and input it into the programmable controller, so that the system can automatically adjust according to the temperature given values in different time periods. The main program flow chart of the whole system is shown in Figure 4

Figure 4 control main program

the main program starts by calculating the actual fermentation time of the beer, then takes out the standard temperature value corresponding to this period of time, compares the standard temperature value with the actual temperature value, if it is equal, returns to the main program inlet again for the next round of standard value search, if it is not equal, the system calculates the corresponding PID coefficient by the CPU, and outputs a signal to control the solenoid valve, Open or close the refrigerant valve with the air circuit controlled by the solenoid valve for temperature regulation

the system can be programmed with S7 software. Using these software to configure the whole system, the structure of the whole fermentation tank system and the real-time state of each valve can be displayed at any time, the actual temperature value, liquid position and other parameters of each fermentation tank can be read out, the whole system can be monitored, and various alarm real-time displays and temperature control curve records are available, so that the operator can grasp the working condition of the system in time

3.2 realization of PID controller in PLC closed-loop control system

this system adopts SPLC of German Simens company as the control core, which can realize temperature acquisition and automatic adjustment. The system requires 12 channels of temperature control, and each circuit is controlled by a set fixed value. Select the corresponding functional modules according to the actual requirements. Among them, CPU module adopts cpu-314ifm, which has an MPI interface, integrated with 20 digital inputs, 16 digital outputs, 4 analog inputs and 1 analog output. PID control function block is integrated inside, which can easily realize PID control

pid controller is the abbreviation of proportional integral derivative control. It is widely used because it has the following advantages:

(1) it does not need an accurate mathematical model of the control system. Due to nonlinearity and time-varying, many industrial control objects are difficult to obtain their accurate mathematical models, so the design methods in control theory cannot be used. For this kind of system, using PID control can get satisfactory results

(2) it has strong flexibility and adaptability. Integral control can eliminate the static error of the system, differential control can improve the dynamic response speed of the system, and the effective combination of proportional, integral and differential control can meet different control requirements. According to the specific situation of the controlled object, various improved control methods of PID control can also be adopted, such as pi, PD, PID with dead zone, integral separation PID, variable speed integral PID, etc

(3) the structural model of PID controller is simple in program design, easy to realize in engineering and convenient in parameter adjustment

3.3 how PLC realizes PID control

when using PLC to PID control analog quantities, the following methods can be adopted:

(1) use PID process control module. The PID control program of this module is designed by the PLC manufacturer and stored in the module. When users produce products of other specifications and sizes, they only need to set some parameters, which is very convenient to use. A module can control several or even dozens of closed-loop loops. However, this kind of module is expensive and is generally used in large-scale control systems

(2) use PID function command. Now many PLCs have functional instructions for PID control, such as PID instructions of S. They are actually subroutines for PID control. When used together with analog input/output modules, they can get an effect similar to using PID process control modules, but the price is cheap

(3) realize PID closed-loop control with self-made program. Some PLCs have no PID process control module and functional instructions for PID control. Although some PLCs can use PID control instructions, they hope to adopt some improved PID control algorithm. In the above cases, users need to prepare their own PID control program

3 policy support is a beneficial guarantee for the development of recycled plastic granulator 4. PID control parameter adjustment

1 shows people a new face full of vitality and imagination Determination of sampling period TS

according to the sampling theorem, the sampling frequency should be greater than or equal to twice the highest frequency contained in the sampled signal in order to restore the original signal, that is, FS ≥ 2fmax, where FS is the sampling frequency and Fmax is the highest frequency in the sampled signal

2. Determination of parameters KP, Ki, KD

parameter tuning of PID control loop is a difficulty in analog closed-loop control. If the initial parameters are improperly selected, there may be a large overshoot, and even make the system unstable. Siemens' new generation small SPLC has the function of PID parameter self-tuning, and the v4.0 programming software STEP7 micro/win adds PID tuning control panel. The combination of these two functions enables users to easily realize PID parameter self-tuning. Self tuning can provide a set of approximately optimal tuning parameters. The PID setting control panel in the v4.0 programming software STEP7 micro/win of s monitors the PID loop graphically. The panel can also be used to start or cancel the self-tuning process, set the parameters of self-tuning, and set the recommended setting value or the setting value set by the user

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