Control of Moisture Content for Paper Manufacturing
- Principal Investigator: Perry
Y. Li
Mechatronics and Intelligent Control Laboratory
Department of Mechanical Engineering
Co-Investigator: Shri Ramaswamy
Wood and
Paper Science Department
Project Summary
Paper manufacturing in the U.S. is a $150 billion industry
and is the 3rd largest comsumer of energy in the nation. The paper
making process is mainly concerned with the removal of most
of the water in a dilute suspension of fibers to form the final product.
Approximately 200 kg of water has to be removed to make 1 kg of paper.
Water is removed successively via gravity dewatering, vacuum dewatering,
mechanical press, and thermal drying. Uniform moisture content is
critical for paper to be curl free, cockle free and not cause printers
/ copiers to jam. Since water removal is potentially an energy intensive
process, the proper control of moisture content is important to reduce
energy use.
Current process control strategy monitors the moisture content of the end product at the end of the process and adjusts the dryers to remove more or less water. This strategy is plagued with long deadtimes, and does not detect out-of-specification products until they have already been produced. The limited sensing and long deadtimes pose fundamental limitations on the control performance in terms of disturbance rejection and robustness. In addition, because thermal drying (which is the most energy and capital intensive process) are the process control actuators, the control strategy uses more energy than is strictly necessary.
This research develops a new process control strategy in which 1) the moisture contents of the paper as it is being manufactured are estimated from a set of surrogate measurements, and 2) vacuum dewatering participate in the closed loop process control. Preliminary studies suggest that airflow through the sheet is a strong candidate for the surrogate measurements. The new control strategy overcomes the fundamental limitation of the current strategy because: a) it allows deviations of moisture content to be detected early on so that they can be corrected downstream pre-emptively; and b) the vacuum dewatering process provide control actuators which are more energy efficient. To develop this control strategy, the research tasks to be carried out include: 1) Development of a vacuum dewatering model; 2) Determination and modeling of feasible surrogate measurements; 3) Design, analysis and optimization of the control algorithms; 4) experimental validation of the models and testing of the control scheme.
This research is expected to lead to significant improvement in moisture
content control performance and energy efficiency in paper manufacture.
This will maintain the U.S.competitiveness in this industry. New fundamental
understanding on vacuum dewatering
will help design and optimize next generation of paper machines with
even better control and efficiency. Since the control strategy is quite
general, it is expected that other sequential manufacturing processes,
such as in thermal material processing, will also benefit. Educationally,
this reserach generates industrially relevant examples for dynamic systems
and control courses. It also involves students in cross-disciplinary reserach
with both theoretical and experiment contents.
Students
Sponsors:
- TAPPI Foundation
- National Science Foundation Design, Manufacturing, and Industrial Innovations Program.
- Center for Advanced Manufacturing, Design and Control (CAMDAC) of the University of Minnesota.