Research On Pulping Process Control System For Medium And High Speed Tissue Paper Machine

In recent years,with the continuous improvement of living conditions,the demand for tissue paper has been increasing year by year,which has also led to the vigorous development of the tissue paper industry.Meanwhile,under the background of vigorously advocating environmental protection,energy saving or consumption reducing,and low-carbon economy,the medium and high speed tissue paper machine with high levels of automation,high productivity and low energy consumption is the industrial trend.However,there be the higher speed of tissue paper machine,there be more strict requirement for the quality of stock,then the good automatic control technology is to be the necessary means of ensuring the pulp quality in the pulping process.Therefore,it is a significant topic to make application study of control technology for the tissue paper pulping process,which is of great significance to improve the quality of tissue paper and to upgrade the production of the tissue paper manufacturer.Under the funding support of Shaanxi Science and Technology Co-ordination Innovation Project(2016KTCQ01-35),this thesis expands the study of technical application focused on the pulping and beating process control,based on the DCS project of pulping line for medium and high speed tissue paper machine in a tissue paper plant in Guangdong.The main works are presented as follows.(1)Study on the sequential cycle control strategy of pulper and the solution of layering between pulp and water in the storage towerIn view of the problems of bad automation,heavy workload and labor cost and unstable pulping quality in the traditional intermittent control of pulper,the sequential cycle control strategy of D-type hydraulic pulper was designed.Aimed at the problem of layering between pulp and water in the storage tower,the self-dilution scheme by using water layer was put forword via combining the mechanical device design and automatic control,and the interlocking logic control strategy of the twin tower was designed.(2)Multi-objective optimization control strategy of series beating processA multi-objective optimization scheme was proposed with the object of refining quality,productivity and cost.Taking the flow rate,concentration of pulp and the current(or power)of refiners as the decision variables,modelling of the soft-sensor of beating degree and wet weight for the series beating process was finished via combining the SEL beating mechanism and model identification method,using the models to rapidly evaluate the quality objective in the optimization and predict online in the production,and then the multi-objective optimization model with the best beating quality,highest productivity and lowest cost was constructed.To solve the multi-objective optimization problem,achieve the optimal compromise between the three objectives,and obtain the optimal control set point of decision variables,an improved global optimization algorithm,simulated annealing algorithm(SAA),was proposed.(3)Research and design of the series beating process control logicOn the basis of digesting the exclusive control logic of Andritz company of Austria,aimed at the requirements of the domestic triple-disc refiner and actual process control,the refiner-body and peripheral interlocking protection control logic of the series beating process were redesigned.The refiner-body control logic includes group ready,start and emergency stop logic of the main motor,and the forward and reverse,fast and slow speed and stop logic of the adjustment motor,the peripheral interlocking control logic includes sequential start-up,stop and refiner flushing logic,which all can effectively protect refiners and the periphery equipments,reduce handling complexity,improve the beating quality and automation level.(4)Design and implementation of the pulping process control system based on PCS7 and S7-400PLCBased on the overall system layout and implementation framework,by using Siemens S7-400 PLC and PCS7 respectively as the control hardware and software platform,the DCS of pulping process and the implementation scheme of advanced optimization algorithm were designed according to the control requirements of pulping process and related strategies in thesis,and the DCS was applied to actual production.The DCS designed in this paper was put into operation at a paper plant in Guangdong in October 2017.Because of the sequential cycle control strategy,the number of operators of single pulper reduced from 2~3 to 1,the pulping time of single tank shortened about 1/2 and the pulping quality is more stable.According to the user's preliminary statistics and feedback,the yield of refining increased about 15.7% and the cost per ton pulp declined about 2.6%,the rate of inferior paper produts reduced about 3%,the main parameters are controlled stably with a high level of automation,which obtained the user's high praise.