Control system of lab spray dryer based on Pilotech LabTECH traditional design
The lab spray-drying technology can atomize the thin material and make co-current contact with the hot air, so that the moisture can be quickly vaporized and evaporated to obtain a dry product. This method can directly dry the solution into powder or granular products, which can save the process of evaporation and pulverization. Compared with other drying equipment, spray drying equipment has the advantages of high drying efficiency, good product quality and low industrial pollution. This paper discusses and studies the spray drying process and automatic control system based on spray drying technology.
In order to deal with the current situation that the control system of the domestic drying industry is not perfect, this paper is mainly based on the experimental data of the actual production of the factory, and then the control system of the lab spray dryer is improved and perfected more advanced. This test bench is based on the lab spray dryer to collect and verify the experimental data. Through the fluent simulation and experiments, various influencing factors in the production are discussed and verified, and a set of the most efficient and accurate control scheme is obtained. The data in the process is calculated and designed by using the fluid mechanics calculation formula, the calculation formula of the relevant valve and the air inlet volume is deduced, a set of accurate control parameters is obtained, and the structure of the nozzle is designed and analyzed. Calculate the head and energy loss required by the equipment, and select the appropriate feed pump. According to the requirements of the system, equipment and instruments such as sensors and electric valves are selected. Use simulink to compare the simulation effect of fuzzy controller and traditional PID control. Use LabVIEW to design and program the human-computer interaction interface of the control system. Then the fuzzy control algorithm is combined with the traditional PID control system, which can correct and adjust the control parameters in real time, making the whole control system more accurate and reliable. Finally, the fuzzy control algorithm is programmed into the single-chip microcomputer, and the spray drying equipment is installed and debugged. The fuzzy control system and the traditional control system are respectively used for sampling tests to compare the qualified rate of product quality and verify the feasibility of the fuzzy control algorithm.
1.1 Overview
Spray drying technology refers to the process of using atomizing nozzles to crush the liquid into countless tiny droplet particles, and quickly heat and volatilize the moisture of the droplets in a high-temperature drying medium to finally obtain a dry powder product. Drying consists of four steps : (1) atomization of liquid; (2) mixed contact of droplet particles with high-temperature drying medium; (3) rapid evaporation of water droplets; (4) drying The dry powder product is separated from the high temperature medium. The delivery form of the liquid can be in the form of solution, emulsion and suspension, etc. that can be delivered by the feeding pump, and the final product can be in the form of powder or granules .
For different liquids and different product requirements, the designed spray drying system is very different, but several necessary system equipment is essential in all systems, such as: liquid supply system, liquid mist chemical system, drying tower and gas-solid separation system . Figure 1-1 is the flow chart of the necessary equipment for spray drying.
1-Feeding system 2-Heating system 3-Nozzle 4-Drying tower 5-Gas-solid separator Figure 1-1 Flow chart of drying equipment
For nearly a hundred years, spray drying technology and equipment can occupy one of the many dryer equipment.
The main reason for its important position is because it has advantages that other dryers cannot compare with: (1) the drying process time is very short; (2) the liquid itself does not withstand high temperatures; (3) the quality of the product after drying Very good; (4) The drying process is not complicated; (5) The industrial pollution is small, which is beneficial to the protection of the environment; (6) The control system of the drying process is simple and easy to understand; (7) It has a wide range of applications; (8) It can be used for Multi-stage tandem drying.
For spray drying control systems, most of the general temperature control systems are single-loop
Yanshan University Engineering Master’s Thesis
PID control method [5], although this method has good control effect and robustness for many industrial production, and this control algorithm is easy to understand and easy to use, its theoretical research system is relatively mature, with It has clear application significance of physical parameters and rich practical application experience; but it also has many shortcomings. Among these shortcomings, a relatively important one is the PID parameter correction problem. First, the traditional PID controller is only suitable for application in the control system with clear parameters and accurate mathematical and physical models, and it is also limited by the system parameters, that is to say, once the system parameters are determined, it can only be applied in this control system. in a special case. However, for most of the systems in which the industrial production process is nonlinear, the parameters change at any time, and the time domain characteristics are not determined, only having a fixed set of parameters is far from being able to meet the needs of the industrial production process. Second, the traditional PID parameters can only meet the needs of one of the aspects of the production process control objectives, but these two basic requirements can be obtained even if the set value and input tracking and the disturbance input characteristics are suppressed. In most cases, the requirements cannot be met, resulting in an unsatisfactory control effect of the control system. In addition, the temperature control process of spray drying is a multi-parameter control process. The conventional single-loop control method only needs to control a single system parameter to adjust the entire control system. However, this control method basically does not. To meet the requirements of the control system accurately, there are many interference factors in the control process of spray drying, and it is also a nonlinear control process. Therefore, only using the traditional PID controller is far from being able to meet the ideal control effect for this control system without an accurate mathematical model and with many disturbance factors.
For many conventional control systems, the key factor affecting the accuracy of the control effect is the accuracy of the dynamic mode of the control system. To sum up, the conventional PID control system has various problems and deficiencies, so this paper adopts the PID control mode of fuzzy control algorithm to improve the traditional control system. The first point is that the fuzzy control rule base is established based on the actual worker experience. It is not only robust, interference, and parameter changes have little impact on the control system, but it is also very suitable for nonlinear and relatively lagging control systems. In this paper, a fuzzy control algorithm based on PID is designed . According to the current production experience, the fuzzy rule library and the function of automatic adjustment and correction of PID parameters are established. For the key parameters in the spray drying process, for example, The temperature, flow rate, etc. are corrected and adjusted in real time, and then the control of the spray drying equipment is realized based on the powerful data processing function of the 51 series single-chip microcomputer. With display control, real-time display of the drying system and correction of the working parameters of the entire system, which can change and improve the shortcomings of the traditional PID control system, make the spray drying control technology more mature and improve the efficiency of industrial production .
The same spray drying technology also has some shortcomings and shortcomings :
(1) The volumetric heat transfer coefficient of the spray drying tower is relatively small, and for those liquids that cannot be dried with a high-temperature heat carrier, the drying tower used is obviously too large. Moreover, when operating at low temperature, the consumption of medium required for the drying process is huge, so the consumption of required power and energy also increases.
(2) Spray drying has relatively strict requirements on the drying of gas-liquid mixtures. For powder products with tiny volumes, the precision requirements of the separation device are relatively high, so the production efficiency and environmental pollution are greatly improved.
It can be seen from the above that the spray drying process also has certain shortcomings. However, compared with other drying equipment, spray drying still has incomparable advantages. The reason why the shortage of spray drying is listed is that we need to consider when designing the spray drying system. In view of these shortcomings, a more reasonable and effective design should be carried out, so as to avoid the adverse effects of these shortcomings on the spray drying process.
The automatic control system is of great significance to the spray drying tower. It can not only ensure the smooth and effective progress of the spray drying process and the quality of the dried products, but also help reduce the work intensity of factory workers and improve the product quality. Production efficiency has great economic and social benefits . In the field of the control system of the dryer, the domestic drying tower has a considerable distance compared with the foreign drying tower. The foreign drying tower has a high degree of automation, as shown in Figures 1-2 and 1-3. It is mainly manifested in:
(1) Automatic detection, control and alarm of the feed inlet temperature of the drying tower can be realized;
(2) Automatic detection, control and alarm of the air outlet temperature of the drying tower can be realized;
(3) The automatic detection, control and alarm of the feed liquid and hot air flow rate of the drying tower can be realized;
(4) Automatic detection, control and alarm of the temperature of some main components of the drying tower can be realized.
So far, the degree of automatic control of drying towers is still very low, basically most of them are
PID control and it is only based on one of the variables or parameters. However, the drying process in the actual production process is quite complicated, with many input and output variables, and each variable is highly correlated.
Improving the control system according to the fuzzy control algorithm is a popular advanced intelligent control method in recent years. This algorithm imitates the human thinking mode and is based on the work experience accumulated in human production. It has good control reliability and robustness. In this paper, on the basis of referring to foreign advanced drying tower equipment, combined with the produced spray drying tower, a new product combining fuzzy control algorithm technology and traditional spray drying tower is designed.
1.2.1 Development of spray drying technology
The concept of spray drying technology was first proposed by Basler, who proposed the working principle of spray drying technology and the realization method of this principle as early as 1888. Spray drying technology is to use atomizing nozzles to crush the original liquid into small droplets, and use hot air to quickly dry the moisture near the volatilized droplets to obtain a dried product. The material to be dried is not only a solution but also a suspension. Dried products can be produced in a variety of ways, such as powder products, hollow sphere products and agglomerate products can be produced. At present, spray drying has obvious advantages, such as “quick work”, “good product quality” and “efficient production”. By 1935, it has been widely used in dairy products, pharmaceutical industry, detergents, dehydrated food and Agricultural fertilizers and other fields. Many of the most common products in life today are spray-dried products, such as instant coffee, milk powder, and soups for fast food. The spray drying technology started late in China and has not developed for a long time. It was first introduced around 1955 when the spray drying equipment tower of the former Soviet Union was used for drying experiments on dyes and streptomycin. In the 1950s, the Harbin Songhuajiang Milk Factory produced milk powder for the first time using the centrifugal spray production method . Since then, the technology of spray drying in the dairy and pharmaceutical industries has been promoted and applied to a certain extent, so that the spray drying technology has a steady development in China.
1.2.2 Domestic Development Status
So far, the research on spray drying technology in China mainly focuses on the improvement and development of the mechanical properties of the spray drying tower, and the development and research on the control theory of spray drying has just begun. From 1960 to
Beginning in 1980 and 1990, talents from some domestic enterprises and colleges and universities gradually put various conventional
And more mature control methods are applied in other production fields. For example, the control method of PID controller is applied to the control system of spray drying tower equipment. Since then, the automatic control system of spray drying tower has been developed and improved.
For China, the automatic control level of the spray drying process has also developed. Although many automatic control methods have been proposed by researchers in recent years, there are very few that can be really applied to actual industrial production. Researched by Sun Guoguo, Wang Weiying and Liao Chuanhua of Nanjing University of Technology, they conducted a detailed research and analysis on the overall control process of spray drying. A control method based on regulating the amount of bypass air. A method for automatic control of spray drying process based on PLC fuzzy logic control proposed by Shen Jinfei and Yan Wenxu of Jiangnan University, this method can well solve the time lag in the control process. The oscillation problem of the overall control system has better control performance compared with the previous conventional control algorithm. A set of spray drying tower equipment based on computer control was proposed and established by Tu Yuanzhao and Ren Xiaohong. Based on a self-correcting fuzzy control module in Siemens PLC, the control process of spray drying can be adjusted and controlled. Although the above-mentioned methods do not have a leaping effect on actual industrial production, they have played a certain role in promoting the control of the domestic spray drying process to a certain extent. After that, a fuzzy algorithm controller based on Fuzzy-PID was proposed by Yin Zhiyu , which was actually applied in the temperature control of hot water boilers, because the fuzzy controller has a self-correction function, this method Compared with the previous conventional control method, there is a more obvious control effect. In the domestic spray drying research field, Beijing Chemical Industry Research Institute independently designed and developed a micro lab spray dryer for scientific experiments. Its overall drying control effect has been greatly improved, but this kind of drying has not been seen. The machine is widely used in industrial production.
1.2.3 Status Quo of Foreign Development
Many people think that as early as 1810, people’s exploration of spray drying technology has already begun. In 1865, LaMont first proposed to apply the spray drying method to the production of egg products. However, the invention made by American Samuel Percy later had a more profound impact on the development of spray drying technology. In the early 1870s, he invented a patent titled “Improvement of Drying Operation and Concentration of Liquid Materials by Atomization”, in which the principle of spray drying technology was clearly given.
British Bassler, in the 1880s, he applied pressure nozzles to the spray drying process, and proposed the world-famous method of spray concentration. At the beginning of the twentieth century, the French Stauff put the nozzle atomizer with the
Combined with L-plate hot air distributor, the proposed patent is to apply spray drying technology to plasma drying.
Around the same time, Gardner invented the first spray drying equipment with airflow nozzles .
Although spray drying technology has been greatly developed during this period, there is almost no application in actual industrial production. The inability to achieve continuous atomization drying is one of the most critical factors. It was not until 1905 that a company in the United States applied Stauff’s patent to the drying equipment for the production of dairy products, and then realized the application of spray drying technology in actual production.
In the 1870s, Rayleigh put forward a very important theory through the study of non-viscous liquids in laminar flow state that “when the length of the liquid bundle is greater than its circumference, it will become unstable and lead to spalling”. Although these theoretical conditions do not exist in practice, this conclusion is often referred to in future research explorations. At the end of the twentieth century, Tyler’s exploration of mercury beams proved the feasibility of Rayleigh’s conclusion. In the 1930s, Weber developed Rayleigh’s conclusions and further developed and enriched Rayleigh’s conclusions by taking into account factors such as the surface tension and viscosity of liquids. Until the 1930s, people’s research and exploration of liquid beams reached a very high level. It was subsequently proposed by Haenlin that in the case of high-speed airflow, a rather irregular wave shape is formed on its surface and is proportional to the magnitude of the velocity. Almost at the same time, Castleman derived the correlation formula between the Reynolds number and the liquid beam based on the disturbance of high-speed airflow, and further developed this conclusion, taking into account the viscosity, surface tension and density of the liquid. When the Reynolds of the liquid is lower than the critical value, the most important effect of the atomization process is the vibration of the surface of the liquid beam; when the Reynolds number of the liquid is near the critical value, the main effect of the atomization is the movement of the wave on the liquid beam; the Reynolds number of the liquid is much larger When the critical value is reached, the liquid can be quickly crushed into small mist droplets . These are one of the simplest atomization processes. For real industrial production, the process of spray drying and the influencing factors are much more complicated than this, but many people think that the physical properties of the liquid and other factors have a great impact on the mechanism and operating conditions of the atomization process.
Applying the theory of automatic control to the process of spray drying is of great significance to the actual industrial production. The first aspect is to improve the quality of the product. At present, spray drying technology has been widely used in many fields such as food, chemical industry, forestry industry, pharmaceutical industry, construction industry, aquaculture, etc., and spray drying technology has shown an increasing trend year by year in many major industrial fields. No matter what kind of product it is, the technology of spray drying has an important impact on the quality of the product. Applying more advanced and effective control technology to spray drying technology can more accurately control the water content of the product, thereby improving the quality of the produced product.
The second aspect is in the field of energy conservation and environmental protection. For contemporary people, protecting the environment is an important issue faced by the entire human race. There will be huge energy loss in the process of spray drying. Research on emission reduction is very important [22]. The quality of the control method selected in the process of spray drying has a great impact on energy saving and emission reduction, and the most important control variable is the drying temperature. The application of different control methods, the achieved temperature response is also different, and the utilization of energy is also different. If we want to make progress in improving energy efficiency, we should choose to improve more advanced control methods. At present, the most advanced spray drying technology in the world is monopolized by large foreign companies. The control level of spray drying technology in China is relatively low. Generally, there is no special in-depth research and exploration of spray drying technology. At present, the spray drying equipment used by domestic companies all use relatively backward traditional control technology. Therefore, the research on the control system of spray drying technology has a profound impact on changing the current situation of backward domestic spray equipment.
This paper has a very broad application prospect for the research of spray drying control system. Combining spray drying technology with advanced fuzzy control algorithm, a fuzzy controller is designed based on 51 single-chip microcomputer with very high cost performance. The drying tower has many advantages, such as the advantages of small overshoot, good robustness, stable system, and fast response speed, which have a very important impact on economic benefits. The research of this paper can greatly develop the various advantages of the spray drying tower, so as to provide reliable practical experience and theoretical preparation for the technical application of enterprises and scientific research exploration in universities.