Introduction
BALAS® is a steady state simulation package for chemical processes with emphasis on pulp and paper.
The software has been developed at
Technical Research Centre of Finland
over the last 20 years and several Finnish paper mills, engineering companies and equipment manufacturers
currently use it. The list of current users can be found here.

Figure 1.

Screen shot of BALAS®.

BALAS® operates under Windows operating systems and it is equipped with a graphical user interface
(Figure 1.). Typical applications are
 Calculation of mass and energy balances
 Analysis of heat integration and heat recovery
 "What if" analysis
 Process optimisation
 Development of unit operation modules
Unit operations and model libraries
BALAS® has an extensive selection of unit operation modules. These unit operation modules enable
the user to model the whole paper mill including mechanical pulping, heat recovery, utilities and
wastewater treatment. New unit operations, including unit operations for kraft pulping process, are
under development. A selection of readymade model processes, which are listed below, are supplied with
the software:
 TMP
 PGWS (News)
 PGW70 (SC, LWC)
 DIP
 Paper machine (uncoated)
 Debarking plant
 Effluent treatment plant
 Water preparation plant
 CHP power plant
 Multieffect evaporator
These model processes have been parameterised using typical industrial values. These processes can be
pasted to any process model. Using these processes as a basis for modelling one’s own processes can speed
up the modelling task considerably.
Calculation modes
Steadystate simulation
Process behaviour with predefined model parameters can be calculated using simulation mode. Two optional
solvers are available for simulation calculations.
Design
Design (rating) calculation mode is used when one needs to define unit model parameters based on known
output values based on e.g. mill measurements. In design mode any number of output values (e.g.
temperatures) are fixed to their known value and an equivalent number of parameters (e.g. heat transfer
area) are freed. During design calculation values for the parameters are sought to meet the given output
requirements. Any number of design constraints can be introduced, and they are solved simultaneously with
the rest of the process.
Dynamic simulation
Elementary dynamic simulations can be performed in this calculation mode. BALAS® is currently
equipped with two dynamic process elements, which enable modelling dynamic behaviour of tanks and time
delays caused by piping. Tank dimensioning and examination of process variability are typical
applications of this feature.
Optimisation
BALAS® has a solver for nonlinear optimisation problems. For these problems an objective function
(the function to be minimised or maximised), equality (design) and inequality constraints, and free
variables (design parameters) can be defined. The solver manipulates the values of free variables to
obtain the optimal value for the objective function. Typical applications of this feature are water
allocation problems and parameter optimisation problems.
Parameter estimation
A solver has been added to handle exclusively parameter estimation problems. In this mode sets of
measured data (e.g. contaminant concentrations) in various parts of the process can be supplied. The
free variables and constraints are given in similar fashion as in optimisation mode. The solver
manipulates the variables to obtain the best possible fit between the measured data and simulated values
using a leastsquare type of algorithm. A typical application of this feature is to estimate sources and
sinks for dissolved and colloidal substances in processes.
Excelinterface
BALAS® comes with a readymade link to Microsoft Excel. This link allows the user to access and
manipulate all BALAS® parameter and stream data and run any process within Excel. Excel tools can
then be used for visualisation and analysis of calculated data (Figure 2.).

Figure 2.

Visualisation of process data using Excel.

Selected applications
Mass and energy balances
Several mills have been modelled using BALAS®. Typically the models have been set up to
investigate mass and energy balances (Figure 3.). The model in the Figure is a socalled Total
Site model, which includes all the major processes and their interconnections.

Figure 3.

Simplified diagram of a Total Site model.

The model includes external cooling and heating needs, process water requirements and effluent
production of every major process. It also includes water preparation, effluent treatment and CHP power
plant. With this model following aspects can be studied for any season or operational scenario:
 Water balance
 External heating and cooling needs
 Need for external fuel
Energy studies
Numerous energy studies have been conducted with the help of BALAS® software. These studies have
ranged from typical energy saving studies to integration of new, efficient technology into an existing
process (Figure 4.).

Figure 4.

Comparison of different drying technology options on a mill.

Modelling dissolved and colloidal substances (DCS) in paper making processes
BALAS® can handle modelling of DCS and nonprocess elements. Generation and adsorption/desorption
of these elements has been modelled using userdefined reactions. These reactions can be readily defined
in some unit operation models, e.g. refiner and bleaching tower, and there also exists a generic reactor
module that can be used elsewhere in the process.
Measured concentrations of nonprocess elements can also be transformed into source and sink terms using
the parameter estimation mode in BALAS®. Measured data from various parts of the process are given
as data set(s) for the solver and reaction parameters are manipulated to achieve the best possible
agreement between the measured and simulated concentrations (Figure 5.).

Figure 5.

Conversion of measured concentrations to sorption terms and process parameters.

Water use reduction studies
These types of problems arise when we are considering reusing slightly contaminated process water in
other parts of the process in order to reduce the fresh water demand. The main objective is to allocate
process water in such a way that the intake of fresh water is reduced as much as possible without
exceeding contaminant concentrations in critical parts of the process, like bleaching.
The optimising solver in BALAS® can be utilised to solve these types of problems. One needs to
build a structure containing all the possible connections between water sources and sinks (a socalled
superstructure). The objective function is to minimise the fresh water intake and constraints can be set
to ensure that contaminant concentrations do not exceed their maximum values in given parts of the
process. The flowrates between the water sources and sinks are the free variables, which the optimisation
routine manipulates to achieve the optimal solution. In Figure 6 is shown typical results of water
use reduction studies performed by
Technical Research Centre of Finland.

Figure 6.

Influence of increased recycling on buildup of dissolved substances.
