Study On Measurement And Control System Of Hood Ventilation System For A Paper Machine

The performance of the dryer section ventilation system seriously affects the machine operational efficiency, energy consumption and product quality. Its design has an important impact on the normal and stable operation of the machine as well as energy consumption. The humidity and temperature of exhaust air are important parameters in a ventilation system, which are directly related to the amount of exhaust air flow. Thus, they are closely related to energy consumption. Therefore, proper control of them is important for saving energy. The current situations of the paper machine hood control system are: the process control system is not implemented to the semi-closed hood in most mills, which means the air blower is either in full running state or controlled by fan baffle, which leads to excessive exhaust air and energy cost; As for the closed hood, although the exhaust dew control system is usually installed, it is most not in practical use, and the main reason is its control object is unclear, which results in dropping in some certain areas within the hood, and the due functionality of the control system can't be unleashed.In order to study the control method of hood ventilation system according to the survey of the semi-closed hood operating conditions and characteristics, the main research contents of this paper are as follows:Firstly, based on mass and energy balance, temperature and humidity models of the ventilation for semi-closed hood are established. Also, I succeed in validating the established models by applying operating data into Simulink of Matlab.Secondly, the real reason that they can't be put into use is that the control object is not clear enough on the basis of the existing control methods of temperature and humidity of exhaust air. Aiming to solve the problems, the combination of programmable logic controller PLC(Programmable Logic Controller), encoder and data acquisition system are used to design and develop the measurement system to gain the distribution of temperature and humidity in hoods, where the semi-closed hood in Zhongshan Yongfa Paper is an object. At the same time, three-dimensional distribution of temperature and humidity is built which enables the distribution clear and help us to find the weak points in hoods. Thus, this can provide a basis for control system's design. Again, considered the large time-delay characteristic of the hood ventilation system, feed forward and feedback control scheme is designed. Compared with the only feedback control system, the results show that feed forward and feedback control system can effectively overcome the effects brought by disturbances.Finally, based on Sinamics S120, S7-300 and humidity sensors, I design control system to expect to achieve the goals of optimizing ventilation control and reducing the energy consumption.This study gained the 3D surface of the temperature and humidity distribution within a specific paper machine hood through self-designed automated temperature and humidity measurement system, and designed the feed forward feedback ventilation control system based on the distribution, the simulated the process in Simulink. Results show that this system can control the humidity of hood exhaust in a better way, and is helpful to energy saving in a paper machine.