Xanthan Gum Fermentation Process Intelligent Control

It's predicted that biochemical project will develop rapidly in the 21 century. With the development of the biochemical fermentation, people pay more and more attention on the monitor and the control of the process, while improving the technics and the equipments. Automation of biochemical fermentation has won the eyes of fields from both academy and industry, also many theories and methods and techniques have come to being. However, the control of the process is far more unformed than that of other industrial processes.The process of biochemical fermentation is a large complex system, containing physical process, chemical process and biological process. Each subsystem is of a confusing essential mechanism, which shows the uncertainty, the nonlinearity of the model and the coupling of the parts of the object to be controlled. It's a hard work to model mathematically for a microbial fermentation.In this dissertation, automation of the process of the xanthan-gum fermentation is discussed, especially the adjustment and control of the environmental parameters, such as the temperature, the pH value, the concentration of the dissolved-oxygen, and the pressure inside the reactor, taking the object of one of a new type of SMG airlift reactors as an example. Temperature control is of crucial importance in the fermentation, and every kind of certain microbe need an exact temperature to live and grow. So we must control it perfectly. The pH value of the fermentative solution will affect the growth and propagation of the thalli and the compound of the metabolite, consequently the efficiency and quality of the product, which demands a high grade control. In an oxygen-friendly biochemical reaction, if oxygen that is necessary is not enough, the growth and the metabolism will be spoiled and this will cause a slow speed and a bad quality of the product also. We must keep a certain concentration of the dissolved oxygen during the process. However, a lower pressure in the fermentor will bring a pollution of bacterium; and a higher pressure will make much more carbon dioxide in the solution and then get toxic thalli. Therefore, we must keep a certain pressure in the reactor. Much foam always floats up on the solution during the cultivation of microbe, which is due to help thalli grow partly and unevenly or to prevent the outcomes from synthesizing normally. Even the foams can leak out of the reactor through gas-out pipes, and hence cause leakage of the solution or take the risk of being polluted by bacteria. So we must hold back too much foam.Routine control alone cannot deal with the above problems satisfactorily because it is difficult to build an exact model for the fermentation process. Intelligent control is a subject that studies human control behaviors and how to substitute machine for human in future. As an unconventional control method, it simulates human intelligence better than before. It's characterized that it adjusts the controller's output according to control behaviors (such as error and its changing ratio) other than the mathematic model of the object. And the means begins with how to simulate human control behaviors by controllers, which can be used widely and perfectly in the control of industrial processes.We will be faced with difficulty of building an exact model of the object if we control the temperature by means of series control with the main parameter of the temperature of the reactor and the secondary parameter of the temperature of the water in the outside jacket. Fuzzy control is a new kind of computer control measure based on mathematics of fuzzy set theory, fuzzy language variable and fuzzy logical reasoning. As a nonlinear control method, fuzzy control can be provided with both systematic theory and many practical backgrounds. Fuzzy control depends little on the object model, with the advantages of good dynamic performance, small overshoot and super robust. But fuzzy control has only limited grade values as to bring static error and poorer precision. In order to ensure the system to hav...