Discussion Papers, Department of Finance and Management Science, Norwegian School of Economics (NHH)
No 2007/9:
Optimized on-line process control of bleaching operations with OptCab
Patrik Flisberg ()
, Stefan Nilsson ()
and Mikael Rönnqvist ()
Abstract: To produce pulp for paper production or as market pulp is
a complicated on-line process with many integrated stages that impact the
final quality. In the bleaching plant which is at the end of pulp
production, the main objective is to increase pulp brightness within
specified limits. Here chemical treatments are applied in sequential stages
to achieve the right brightness while striving to maintain the pulp
strength as unaffected as possible. The raw material, i.e. pulp logs and
wood chips from saw mills, differ in quality and properties. Due to this,
it is important to continuously update the amount of chemicals added to the
pulp in real-time. This is typically done by experienced operators. In this
paper, we describe an on-line optimization based decision support system
called OptCab that controls the bleaching process at Billerud AB's paper
mill in Skärblacka. The solution approach is based on two phases. In phase
one, we establish approximations of each of the processes based on process
data collected on-line. These approximations are found by solving a set of
constrained least square problems and are updated every 15 minutes. In
phase two, we formulate an overall nonlinear control problem that links all
stages together and aims to minimize the cost of chemicals. This is solved
on-line every five minutes. The system has been in operation during the
last three years providing a 10% reduction in the use of chemicals.
Additional benefits include a more stable brightness quality.
Keywords: Pulp production; on-line optimization based decision support system; nonlinear control problem; (follow links to similar papers)
JEL-Codes: C61; (follow links to similar papers)
19 pages, March 27, 2007
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