Page 505 - Industrial Wastewater Treatment, Recycling and Reuse

Simulation, Control, and Optimization of Water Systems in Industrial Plants 475

12.2.2 Power Plants (Thermal and Nuclear), Coal Handling,
and Other Utilities

Globally, power plants are one of the largest users of fresh water. The major
pollutants from power plants are dissolved solids in cooling water, boiler
blowdown, coal drainage, and radioactive material from nuclear power
plants. Mathematical models help to identify the water reuse and recycling
options in these plants. This practice saves water charges for the plant and
effluent discharge costs for treatment.
In addition, certain classes of online advanced control technology can
also be used for real-time optimization of the facilities, thus further reducing
the usage of precious resources like water as well as creating less effluent due
to reduction in specific coal/energy consumption.

12.2.3 Pulp and Paper
The paper-making process is one of the most water-intensive industrial pro-
duction processes. This is because, without the physical properties of water,
it would not be possible for a consistent structure to be achieved when the
constituents of paper are processed in sludge. A high level of water con-
sumption is inevitable in the processing of natural raw materials (wood,
cellulose vegetable fibers) and also in the process of recycling waste paper.
This creates a high level of wastewater for processing. The residues in the
wastewater are a problem, particularly in the case of deinking—the process
of recycling printed waste paper.
A large volume of process water becomes contaminated from
contact with raw materials, by-products, and residues in paper and pulp
industries. Basic wastewater sources are evaporator condensate, bleach plant
pulp, washer filtrate, condensate from recovery evaporators, and heat
exchangers.
The modeling tool uses for this kind of process allow a detailed analysis of
the process, including determination of different variables and visualization
of the complexity of the process without making direct changes. The appli-
cation of simulation methodology to study fresh water consumption reduc-
tion in the plant contributes to significant saving in water uses.
Closed-loop systems are particularly popular because they enable the
pulp and paper industry to recycle and reuse water as well as recover excess
pulp fibers in the wastewater. Through the integration tool, water minimi-
zation and reuse limits can be established, considering their individual need
specificities.