Energy Optimization And Control For Paper Machine Dryer Section With Closed Steam Hood

Currently, environmental pollution and energy shortage are the main factorswhich restrict the development of China’s paper industry. Under the dualpressures of the increasingly fierce market competition and strict policy ofenergy saving，paper companies have to develop a long road of clean productionand energy saving. Running status of steam condensate system and ventilationsystem for dryer section with closed steam hood have great relationship withenergy efficiency. However, for a long time, most of the research work focuseson the steam condensate system, while the energy consumption of the dryersection ventilation system is ignored. This paper is supported by Science andTechnology Coordinating Innovation Engineering Project (2012KTCQ01-19) ofShaanxi Provincial Science and Technology Department. After studying on thefactors that affect energy and energy distribution in the paper machine dryersection, energy optimization scheme of dryer section is proposed. In this paper,the study is focused on the energy model of the ventilation system, to reduceenergy consumption of dryer section through optimizing the parameters, andautomatic control system for the dryer section is designed to further reduceenergy consumption. The main work of this paper can be summarized in fouraspects as follows:(1) The direction to energy consumption optimization of dryer section witha closed steam hood is analyzed. According to the web drying process, the dryersection can be divided into the steam condensate system and the ventilationsystem. And the energy distribution and factors of the steam condensate systemand ventilation system are further analyzed. For steam condensate system, theenergy consumption is constant when steam way is not change and the cylindershave no water. For the ventilation system, the temperature and humidity of thesupply air, the temperature and humidity of exhaust air as well as the amount ofair volume change will result in a greater change of energy consumption. Therefore, in this paper the energy consumption of the dryer section is reducedby optimizing the parameters of the ventilation system.(2) The energy consumption mathematical model of ventilation system isestablished. The objective optimization between supply air temperature andenergy costs is steadied by material balance of ventilation system. The lowestcost of energy consumption for dryer section is guaranteed by using GeneticAlgorithm to find the optimal value of the supply air temperature.(3) The control strategy for ventilation system is designed. The impact onthe energy from the change of the zero，exhaust dew point and the energy supplyair temperature is analyzed. The relationships among these variables includingthe air supply, exhaust volume，the exhaust temperature and humidity aresteadied. In the premise that the amount of exhaust and air supply，the value ofair temperature are used as control variables, zero feed forward and feedbackcontrol strategy is designed. Exhaust temperature and exhaust humidity selectedcontrol system is designed to control exhaust dew point when the exhausttemperature and humidity are used to be control variables. According to thesupply air temperature of the heating process，split Control Strategy is designed.(4) The energy consumption optimization control system of dryer section isachieved. Based on the hardware of PLC of Siemens S7-300and software ofWinCC6.0&Step7, a DCS with three lays for dryer section was established. Thebasic level sets sub-control systems of pressure, level, flow and temperature,which keep the drying process work smoothly. In the linkage level, small unitsare linked to adapt the changes of production. In the optimization level, energyoptimization of drying process is achieved to ensure the lowest cost of energy inthe whole process.The content studied in this paper has been applied in one of papermakingproduction line in Sichuan Mianzhu. The application results show that energyoptimization and control systems proposed and designed in this paper havecertain feasibility. Energy consumption of paper machine dryer section can bereduced effectively.