| Due to the restrictions on the resources, environment, and benefit, the modern pulp and paper industry is developing towards high efficiency, high quality, low consumption, low pollution, and low emission to achieve sustainable development. In recent years, our country has issued many relevant policies to compel pulping companies to use medium consistency clean bleaching technologies. The medium consistency(MC) pump is the key equipment in the medium consistency bleaching technology that our country has not been broke through for many years. In this paper, the influence of turbulence generator’ structure on the performance of MC pump, and automatic control methods of the level of MC Dropleg had been studied. It was aimed to provide some theoretical and practical experience for the domestic design of MC pump.This paper improved the medium consistency pulp fluidization test equipment based on the previous studies. The modern high speed PLC control system was used to collect the process data during the test, so that the data accuracy could be ensured. The results showed that the fiber changes during the shear process had significant influence on the experiment results. The shape of shear rotors had little influence on the flow properties of pulp suspensions in the shear room when the diameter of the rotors were equal. As long as the rotational speed achieved a critical point, pulp suspension could realize fluidization. Besides, the diameter of rotor should not be too small, otherwise the fluidization could not be realized.This paper analyzed the working mechanism and summarized the design method of turbulence generator. The diameter of turbulence generator was calculated based on the medium consistency fluidization mechanization. By using the “bind/expand” order in the UG software, it was easily to design turbulence generator blade’s structure. Six turbulence generators that covered complicated and simple structure were designed, and provided the basic conditions for the numerical simulation and test verification.CFD numerical simulation method was used to simulate the flow field of six different structures turbulence generator. The results showed that when the simulated was carried out in the single turbulence generator flow field, linear-type turbulence generator had the worst performance, while the variable spiral-type turbulence generator had the best. The smaller blade-angle of the turbulence generator blade, the better gas-liquid separating effects. When the simulation was performed in the full MC pump flow filed, the structure of turbulence generator hardly had influence on the performance of MC pump. The viscosity of pulp suspension had great impact on the performance of MC pump, increasing MC pump working speed could increase pump head obviously, but little efficiency.The MC pump performance test platform was built to study the influence of turbulence generator structure, diameter of turbulence generator, pulp viscousity, running speed, and vacuum pressure on the operating performance of MC pump. The results showed that the structure of turbulence generator had little influence on the performance of MC pump when MC pump was working in high speed, while the MC pump equipped with screw-type turbulence generator had the best performance when the MC pump was working in the low speed, and this phenomenon decreased with the decreasing pulp consistency and increasing rotational speed. The decreasing of turbulence generator diameter would worse the MC pump performance, when the MC pump was working at low rotational speed and large flow rate, pulp maybe could not be pumped. The MC pump performance decreased with the increasing pulp consistency, when consistency increased from 12% to 14%, MC pump performance decreased sharply. The rotational speed had great influence on the performance of MC pump. The better head and efficiency could be obtained at high working speed. When the rotational speed was lower than 2100 rpm, the MC pump had bad performance. The vacuum pressure had little influence on the performance of MC pump, as long as the vacuum was higher than a critical value. Overincreasing vacuum would not increase pump performance, but increased fibre lose when the flow rate was low.This paper also built an automatic control test perform for the level control of MC Dropleg, wrote relative program and stuied the effect of PID frequency regulation and PID valve regulation. The test results showed that PID frequency regulation was better than PID valve regulation, having more stable regulation for the level of MC Dropleg. The flow rate sensitivity to rotational speed was lower than valve opening size. An automatic control manner for the MC Dropleg level was designed based on the test results and related experience. The partition level control method was proposed to adjust the level of Dropleg by automatic switch PID frequency regulation and PID valve regulation at corresponding level range. Besides, this paper also designed control logic and safety interlock in the MC pump automic control process.By the piolt tests, it was explored that the structure of turbulence generator had little influence on the performance of MC pump. It was also practiced that the turbulence generator which was made by using welding method can fully satisfy the technical requirement. Besides, this paper also explored the automatic control method for the operation of MC pump. All the work have an important guiding significance on the further development of MC pump. |
PDF Full Text Request