Research On Working Mechanism Of Disc Heat Dispersion To Stickies And Its Energy Consumption Modelling

In china, the waste paper has become the major paper-making raw materials at the present time. In the process of wastepaper pulping and papermaking, Treatment and control of stickies has always been a focus of investigation by worldwide researchers. But for the heat dispersion technology, a major means of dispersion technology, its dispersion mechanism is very difficult to understand deeply. It is of great significance for understanding of heat dispersion mechanism to reduce the energy consumption of heat dispersion, and improve the quality of waste paper pulp dealt by heat dispersion. On the other hand, the dispersion is also a major physical process and section during wastepaper pulping, such as pulping process, flotation, beating and heat dispersion process. Therefore, Investigation and improvement of dispersion technology is propitious to wastepaper pulping and recycling, and provide technical support for the realization of the paper industry recycling economy. As for disk heat dispersion, both internal slurry flow field and stickies dispersion mixing characteristics are investigated through theoretical analysis, visualization experiments and numerical simulations in this project. The main research content include the rheological properties of stickies, working principle and energy consumption of disc heat disperser, process and disciplinarian of stickies erosion and ruptuer dispersion, shear and cavitation in pulp flow field, and the effects of various structure parameters and operating parameters wake on pulp flow field and heat dispersion characteristics are also analyzed. The data and conclusions from the experimental measurements and numerical simulations are valuable for the design and optimization of the disk heat disperser. Although the heat dispersion process is treat as the main object, its research method and theory can apply equally to other pulp dispersion workshop section of pulping and papermaking process. Main contents and conclusions of the investigation are described in the following:(1)The very possibility of stickies dispersion process occurred in pulp flow field is analized theoretically. Analysis results show that high shearing process occurred in disc stickies heat dispersion can be described as two main two main phases, namely dispersion mixing and distribution mixing.(2)With the help of multi-phase flow theory, amathematical model stickies particle force is established. As a kind of aggregates, various forces received by stickies particle in the course of dispersion mixing are analyzed. When all of these forces are treated as dispersion force Fc, it can be described Fc as follows :(?)(3)The stickies dispersion characteristics occurred in the working region of Disc heat disperser is analyzed theoretically, and the basic principles of disc type stickies heat dispersion is put forward. It can be described as follows: As a type of aggregate, the stickies dispersion occur in two different way of rupture and erosion under the action of both shear and cavitation inside working region. Two different dispersion way will result in unlike dispersion effect. Erosion dispersion occurs in the whole course of heat dispersion, but rupture dispersion occurs only when dispersion force Fc is more than gathered strength of stickiesσc, namely Fc>σc. When Fc>σc, stickies particles will be broken into multiple smaller particles. under long time action, erosion dispersion changs constantly stickies particle into smaller. The cause of stickies heat dispersion within working region, which occurs in two way of rupture and erosion, is 4 major role. Thry are crushing force, laminar shear stress, turbulent shear stress and cavitation effect respectively.(4)Energy consumption of stickies particle heat dispersion is analyzed When heat dispersion grinding teeth is treated as a solid phase, and high speed fluidization pulpas liquid phase, with the help of multi-phase flow theory, the energy consumption model of disc heat disperser is obtained as fellow: (?)(5) A set of visualization experiment device is designed and manufactured, which can simulate multiple loading conditions, and its clearance of static and dynamic disk can be adjusted. According to the visualization experimental conditions, a set of transparent heat dispersion disk is also specially designed and manufactured. Using high-speed photography technology, several experiments of stickies heat dispersion mixed process in pulp are carried out. Both pulp and stickies movement process in disc heat disperser is recorded distinctly. Experimental results has proved that rupture and erosion dispersion principle put forward by this dissertation is fit for stickies dispersion occured in disc heat disperser. Experimental results has also recorded laminar shear, turbulent shear and cavitation phenomenon.(6) The industry experiments show that although particle size distribution of waste pulp stickies is irregularity, after heat dispersion disposal, particle size distribution will be increasingly concentrated, and small size stickies becomes smaller not any longer, but both surface and quantity of large size stickies particle will change in strong degree. experiments also show that both gap size of grinding teeth and disk dismeter will affect the heat dispersion effect, and the gap influence on stickies disersion is the most direct.(7)Combining with RNG k-εturbulence model, Discrete Phase model and particle trajectory model based on Euler-Lagrange method, a series of numerical simulations of stickies dispersion process with FLUENT software are carried out for five types of dispersion disk. The simulations are also compared with the experimental results obtained by high speed photography to validate the reliability of the computational model. The emphases of the numerical simulation are to investigate the flow field near the grinding teeth wall surface, stickies particles trajectories and pressure gradient, turbulence energy loss, shear rate and so on which cannot be got in the experimental measurements.(8)The unsteady pulp turbulent flow field inside disc heat disperser are performed by numerical simulation. Simulation results has revealed some distribution rule of physics parameters from different levels, such as velocity, static pressure, total pressure, turbulent kinetic energy, wall shear stress and shear rates distribution. At the same time, the effects of turbulent flow field wake on stickies dispersion and its rule also analyzed from aspect of inhalation flow field, pressure field, velocity field, shear rate, turbulent intensity and energy dissipation rate and so on. Analysis results has revealed the effects of heat dispersion disk structure parameters and operating parameters wake on stickies dispersion performance.(9)The results of the experimental measurements and the unsteady numerical simulations indicate that both gap size of grinding teeth and disk dismeter are two most obvious factors affecting stickies heat dispersion effect. With the teeth gap reducing or disk diameter increasing, both pressure gradient and velocity gradient will aggrandize. Correspondingly, turbulent shear, laminar shear and cavitation effect, which arouse stickies heat dispersion, will enhance, and will lead to the effect strength of heat dispersion increasing.(10)The results of unsteady numerical simulations also show that:①The pressure inside dynamic teeth channel is far higher than the static teeth channel, and the pressure gradient in the clearance static and dynamic grinding teeth increase continuously along radial direction.②When pulp flows through both static and dynamic teeth channel, a greater pressure gradient will occur along with radial and circumferential direction.③The cavitation phenomenon forming between the gap of static and dynamic disk is one of the important reasons of stickies particle dispersion.④turbulent shear occur mainly in teeth channel, but laminar shear occur mainly in the gap of static and dynamic grinding teeth.⑤The shear rate is various around the whole dispersion region. the bigger the radius, the greater the shear rate. This phenomenon of shearing rate distribution lies in all of the above five types of dispersion disk, namely, the shear rate between the gap of static and dynamic disk> the shear rate in the dynamic teeth channel>the shear rate in the staticdynamic teeth channel.