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July
2020
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HYDROCARBON
ENGINEERING
T
he cleaning of cooling systems is usually quite a
complex and complicated task. It requires a
shutdown of the related production line or even
the whole plant, which leads to enormous
production losses and costs.
To keep the system shutdown as short as possible, the
cleaning process has to be well prepared and coordinated. It
requires experts and specific equipment on site. These do not
only cost additional money but are also quite a threat to
safety, health, environment and quality (SHEQ). While
cleaning the different parts of the plant, it also important to
ensure that all construction, dismantling, and cleaning actions
are carried out safely. Besides, during these processes, various
types of hazardous cleaning chemicals are used, which also
need to be reviewed and approved from a SHEQ standpoint.
During a cleaning process, specific parts of a system are
dismantled and cleaned one after the other. This is typically
done either with a hydro jet or specialised chemical cleaning
solutions. Unfortunately, in most cases, these cleaning
methods will not only remove the deposits from the surfaces
but also the desired corrosion protective layers. These
cleaning procedures also generate a large number of different
waste solutions which need to be disposed of properly. As
such, these complicated procedures can cause additional
workloads, which can be costly and reduce plant efficiency.
The cooling labyrinth
In a cooling system, there are a lot of different types of
materials used. Starting from different kinds of metals and
alloys as piping or for heat exchangers, but also including
materials such as concrete in the cooling tower basin or
delicate plastic parts as the cooling tower filling material.
The filling material of a cooling tower ensures the easy
exchange of the heat to be removed from the cooling water
through evaporation. As the capacity of heat exchange
through evaporation is a direct function of the available
surface, the cooling tower filling materials are engineered to
offer the largest possible surface on an as small as possible
volume. Therefore, these cooling tower fillings have large but
difficult to reach inner surfaces.
On the top of a cooling tower, the warm water is
distributed through a spraying system onto the filling
packages. Here, the water enters a kind of labyrinth starting at
the top, and the only exit is the basin at the bottom. The
water itself flows down by gravity as a relatively thin layer on
the large surface of the filling. In addition, the filling
construction is made in a way to allow the cooling water long
contact time with the air, resulting in slow flow velocities of
the water on its way down to the basin.
Counterflowing to the water, on its way through the
labyrinth, is the air. The airstream ensures partial evaporation
of the cooling water, which results in the actual cooling
effect. As the heat exchange itself is achieved by partial
evaporation of the warm cooling water into the air stream,
the evaporation also leads to a concentrating effect of the
minerals and salts in the cooling water.
Fresh water that is used to keep the concentration
effect in a reasonable balance is called makeup water. The
relation of the balance between the amount of evaporated
water and the makeup water is generally expressed as
Rainer Haug, Javier Martinez, and Pere Izquierdo, Kurita Europe,
examine a new
technique for combatting biofouling in downstream cooling systems.