| Medium consistency technology(MC technology) is an environmentally friendly, energy-saving and high efficiency pulping technology, which is the development tendency of the pulping process in the world and the medium consistency pulp pump is the core equipment of medium consistency technology. Due to that consistency pulp suspension is a complex mixture of solid, liquid and gas phase composition. With the consistency increasing gradually, the paper pulp will lose fluidity;the gas in the suspension increasing gradually,the pulp suspension can not be carried out by ordinary centrifugal pulp pump.According to above reasons, medium consistency pulp pump must have the ability of making medium pulp fluidize. So, it is of great importance in engineering application to rheological characteristics of medium consistency pulp suspensions and gas-liquid separation performance study on the MC pump.In this these, the MC pump testing bed was built, and the operation and performance characteristics of MC pump in different conditions were studied using sonar flow meter and monitoring system. By numerical simulation, the non Newtonian fluid model for medium consistency pulp is established on the basis theoretical and experimental study on the flow characteristics of medium consistency pulp,then it is studied to effect law of MC pump performance on physical parameters of the model and characteristics of MC pulp suspension. Effect law of MC pump performance on The flow rate, speed, inlet pressure and vacuum degree is studied by using the numerical simulation method and is compared with the experimental results.By altering pulp pump impeller exhaust hole size and location, it is studied to effect law of MC pump performance on exhaust hole.The main contributions and creative achievements of this work are presented as follows.1.The gas-liquid two phase flow in MC pump is studied by numerical simulation and established mathematical model of medium consistency pulp suspension.Based on Euler-Euler two phase flow model, choosing different nonNewtonian fluid models as the liquid phase medium,gas-liquid two-phase flow is calculated by numerical simulation method. The calculation results and test are compared and choose reasonable non Newtonian fluid model as pulp suspension liquid phase model. The results show that mathematical mode of the Herschel Bulkley fluid is more close than others compareing the experimental result. Ordinary water two-phase flow compared to the Herschel Bulkley fluid two-phase flow fluid,relative velocity changes larger;turbulent kinetic energy dissipation rate changes smaller;streamline is irregular in some region.2.MC pump external characteristic and the effect law of gas-liquid separation are studied on characteristics of MC pulp suspension by numerical simulation.Based on Euler-Euler two phase flow model and Herschel Bulkley fluid mathematical mode,MC pump external characteristic and the effect law of gas-liquid separation are studied on non Newtonian fluid model parameters, gas fraction and bubble diameter of MC pulp suspension.The results show that under medium consistency pulp suspensions gas fraction established, increasing bubble diameter, pump gas-liquid separation performance increases significantly, liquid fraction of pump outlet and gas fraction on the exhaust hole increases gradually, the head and the efficiency increases gradually. In the bubble diameter established, with medium consistency pulp suspensions gas fraction increases gradually, liquid fraction of pump outlet decreases gradually, the exhaust hole gas fraction on the exhaust hole increases gradually, the pump head and efficiency decreases.3.According to results of the experiment, three kind of concentration7.52,9.3,12.1% medium consistency pulp suspension fluid mathematical models are established and study effect of MC pulp pump external characteristic and the influence law of gas-liquid separation on operating conditions. Using Herschel Bulkley fluid mathematical mode, MC pulp pump external characteristic and the influence law of gas-liquid separation are studied on medium consistency pulp pump operation flow, speed, inlet pressure and vacuum degree using numerical simulation and method Euler-Euler two phase flow model, and the results is compared with the experimental results.The results show that liquid fraction of pump outlet increasesgradually with the speed, inlet pressure and vacuum degree increasing and descends gradually with flow increasing;gas fraction on the exhaust hole increases with flow and speed and descends gradually with inlet pressure and vacuum degree increasing.When transporting different concentration of the pulp, liquid fraction of pump outlet decrease gradually gas fraction on the exhaust hole decreases gradually with the increase of pulp concentration;the volume ratio of air in the impeller increases gradually, the pressure gradient distribution in the impeller is reduced grand the speed of the pulp in the volute is reduced.Under the same vacuum degree, the pump head, efficiency decreased gradually with the increase of the pulp concentration when transporting different concentrations of pulp, this consistent with the experimental results.4.By the method of numerical simulation, effect law of MC pulp pump external characteristic and the effect law of gas-liquid separation on impeller exhaust hole.By altering pulp pump impeller exhaust hole size and location, using Herschel Bulkley fluid mathematical mode, gas-liquid two phase flow steady numerical calculation is carried based by Euler-Euler two phase flow model. It is shown that under the certain condition,liquid fraction of pump outlet and gas fraction on the exhaust hole increases gradually, the head and the efficiency increase first and then decrease with increasing of hole size; under the radial position of the exhaust hole established,liquid fraction of pump outlet and gas fraction on the exhaust hole increases first and then decreases,the head and the efficiency decreases gradually when exhaust hole from the back surface of the impeller to acting face;under the circumferential position of exhaust hole established,liquid fraction of pump outlet and gas fraction on the exhaust hole increases first and then decreases,the head and the efficiency decreases gradually when exhaust hole moving hub towards flange. |
PDF Full Text Request