Development & Key Components Research On Dilution Water Headbox Of Modern Paper Machine

This paper is around the "Eleventh Five Year" National Science and technology support project "domestic high speed paper machine research" subject of "the development of dilution water headbox", dilution water headbox is the key equipment of high speed paper machine, its performance directly affects the performance of paper machine, evenness of paper, deviation of basis weight in cross direction, stability of various performance indicators, the main goal is to develop advanced dilution water headbox, its fiber has good dispersion, flow is uniform and stable, convenient and reliable regulation and deviation of basis weight in cross direction reaches the international advanced level, which creates good conditions for the dehydration forming.For a long time, the paper-making machines that required high speed or high paper quality, the whole machines imported or at least imported the headbox.The reason was that the traditional development methods complex, investment large, control level low. Another reason was due to the complexity of headbox mechanism, once molding, its performance was determined, price wsa usually higher, ould not be able to change arbitrarily, so must be careful for the design and selection. These huge difficulties made a large number of domestic colleges and universities, research institutes and production enterprises difficult to establish a professional and effective development base for a long time. Headbox technology has been simple imitation of foreign, but difficult to analyze the principles and characteristics in-depth. It was said that not only in the paper industry, but also in the design, development and production of the headbox, domestic level was behind the western countries.The purpose of this study is to break the traditional simple absorption and imitation of foreign technology, through collecting more comprehensive and accurate technical data of similar foreign products(including the introduction of technological data, related samples, patent technology), analyze in-depth its development process, design principle, technical characteristics and application, compare advantages and disadvantages, carry out advanced numerical simulation and experimental research on the key part, analyze the most advanced hydraulic headbox and the properties of key components, provide theoretical support for high-speed headbox design. The key part:slurry distribution components-- pulp distributor; slurry leveling component-- turbulence generator; horizontal quantitative regulating device--dilution water device, so the main content of this paper as follows:First, according to the characteristics of the pulp suspension fluid, necessary conditions of fiber dispersion and flow stability requirements, sum up the major suppliers of international upstream headbox, especially the product structure features, development process, advantages /disadvantages, application scope of Beloit, Metso, Voith, compared the structure and parameters of main parts(such as pulp distributor, turbulence generato, dilute water device, floating type);Beloit Corporation comcept-IV headbox is an important symbol in the history of the headbox development, is still one of the object of development in our country.Second, through comparative research and practical experience, make sure the turbulence generator is the key part of high speed paper machine. Mainly using the method of computational fluid dynamics, carry out numerical simulation.According to different structures, inlet velocity and geometry, turbulent velocity distribution and pressure distribution as measure, evaluate the effects of related factors on the pulp, and on this foundation, designed and manufactured a set of experimental equipment, study laser particle measurements on the unit element ladder pipe of turbulence generator, further research on its hydrodynamic characteristics, explore design optimization and guidance significance for the headbox.Third, the other key is diluted water device, mainly study the effect of dilution water added to the mainstream on concentration and flow, the study on the model of the modeling and the numerical simulation calculation, by comparing moisture content to judge the concentration distribution, make it possible to achieve uniform concentration distribution, single point addition of dilution water as control, in order to improve the adjusting banner quantitative differences, so as to improve the paper quality, the results show that the lateral concentration distribution is in positive normal distribution, but the steady flow chamber and the turbulence, the slurry flow has better mixing and uniform distribution.Fourth, in accordance with the requirements of dilution water head box, analyze the overall structure, such as parameter setting, pulp distributor, stepped hole plate, turbulence generator, dilution water adjusting device, lip structure, thermal equilibrium device, discusses the design principle and points, especially deduce in detail in view of the wide high-speed headbox pulp distributor classic design principle, point out its insufficient place, and put forward some improvements of the new design method. Also analyze the influence on the dilution water added position in theory, and combined with the international mature experience to determine the structure of the headbox dilution water device. Finally in order to enable the developed headbox on the machine run successfully, also designed a set of narrow headbox and simulative running system, mainly through the observation to ensure the ejected plasma flow uniformity, stability and disturbance, lay a solid foundation for the final design.Fifth, based on the analysis of current evalution for basis weight, a new method for more comprehensive evaluation is proposed. According to type and position of CD basis weight variety, the adjusting is possible with dilution advice. For random basis weight variety, changing turbulence generator is the only way for improving this property.Numerical simulation and PIV experimental results show that the method is effective for complicated ladder type turbulence generator, helpful for the analysis of principle, flow field, turbulence characteristics, can better guide the design structure and velocity parameters of turbulence generator, meet the actual requirements, the research results also indicate that the export for rectangular shape of ladder type diffusion, under the proper flow rate and structure size, the flow field distribution is more uniform, the turbulence intensity distribution is more reasonable, at the same time, study the influence on the concentration distribution by adding dilution water, master the distribution rules, is very helpful to design dilution water adjusting system and reduce the banner yield difference.Through the study of main parts and dilution water device, combined with the structure and function of the existing headbox system, comparison and analysis of the principle, through flow pattern simulation and model observation, completely develop technical data on dilution water headbox of high-speed paper machine, have a powerful role in promoting the domestic high speed paper machine and headbox technology development.