ISSN 0104-6632                         

Printed in Brazil 

www.abeq.org.br/bjche 

 

 
    Vol. 27,  No. 02,  pp. 275 - 288,  April - June,  2010

 

 
*To whom correspondence should be addressed  
 
 
 
 

Brazilian Journal 

of Chemical 
Engineering 

 
 

OPTIMIZATION OF WATER REMOVAL IN THE 

PRESS SECTION OF A PAPER MACHINE 

 

D. M. D. Drummond

1

, M. T. M. Rodrigues

1

, I. E. Grossmann

2

 and R. Guirardello

1*

 

 

1

State University of Campinas, College of Chemical Engineering, 

Campinas - SP, Brazil. 

E-mail: dmdd@feq.unicamp.br, E-mail: maite@desq.feq.unicamp.br, 

*

E-mail:

 

guira@feq.unicamp.br 

2

Carnegie Mellon University, Department of Chemical Engineering, 

Pittsburgh - PA, USA. 

E-mail: grossmann@cmu.edu 

 

(Submitted: October 2, 2008 ; Revised: February 5, 2010 ; Accepted: February 18, 2010) 

 

Abstract - An optimization problem regarding water removal in the press section of a paper machine is 
considered in this work. The proposed model tries to minimize a cost function comprising the replacement of 
the felts in the press section, the cost of energy to operate the press and the cost of energy in the drying 
section, while satisfying the constraints of water mass balance in the process. The model is classified as a 
mixed-integer nonlinear program (MINLP) in which the most important decisions are: a) the sequence of 
paper to produce or when to produce the paper; b) the need to exchange the felts; and c) when to exchange the 
felts. Numerical examples are presented to illustrate the performance of the model. 
Keywords: Optimization; Schedule; GAMS; MINLP. 

 
 
 

INTRODUCTION 

 

With increasing interest in optimizing parts of paper 

machines in recent years, there has been much work 
addressing the solution of these problems. Most of the 
investigations that have been reported have focused on 
different parts of a paper mill, for example on paper-
converting (Westerlund et al., 1980). Also, several 
authors have studied water removal in the press section, 
as investigated by Wahlstrom (1960), who reported the 
water removal by a vertical flow at the NIP (contacting 
zone between two rolls). Different mathematical 
models for this part of a paper machine are reported by 
Kerekes et al. (1991). 

The paper manufacturing process is basically the 

same for any plant. Initially the mass of paper is 
prepared; it goes to the formation section, and then to 
the press section for water removal, and finally to the 
drying section. In a paper machine, specifically in 
the press section, there are two important points: the 

felts, whose function is to carry the wet web through 
the press nip (Farouk, 1991), and the NIP, which is 
the contacting zone between two rolls, where the 
water is transferred from the web to the felt. In the 
press section, which is the object of this work, the 
average life of a felt depends on its type, ranging 
from 35-45 days. 

The press section is an important part of the 

machine, affecting the properties of the paper, as 
well as having an impact on the manufacturing cost. 
Low efficiency in this section causes difficulties, like 
reduction of the tensile strength, increase of the 
steam consumption in the drying section of the 
machine and, in many cases, the loss of productivity 
due to the reduction of the speed of the machine. 
According to Reese (2006b), it is more economical 
to squeeze water from the web in the press section 
than to evaporate water in the drying section. A 
reduction of 1% humidity in the leaf usually results 
in a reduction of steam consumption of around 4.5% in