EDITOR’S CHOICE
EFFECTIVE VENTILATION
AXAIR FANS
POLYPROPYLENE VS. STAINLESS STEEL AND GRP
IN WASTEWATER TREATMENT VENTILATION
Wastewater treatment plants face a number
of challenges in terms of ensuring safe and
effective ventilation. The chemicals used
during the wastewater treatment process
pass through metering equipment in a
dosing system. In the system, the solution
is at its strongest and the chemicals
and their gases are often corrosive
and can be flammable. Such chemicals
and gases include methane, ammonia,
phosphorous, pesticides and carbon dioxide.
Consequently, wastewater treatment
plants are, by nature, one of the harshest
engineering environments.
To ventilate wastewater treatment plants,
engineers have a choice of materials for the
fans and systems. Typically, these materials
are stainless steel, glass reinforced plastic
and polypropylene. The range of corrosive
gases present in the plants is so vast that it
is essential to select ventilation equipment
resistant to the largest array of chemicals
possible. The benefits and drawbacks of
each material is discussed below.
STAINLESS STEEL FANS
Benefits:
Stainless steel is a highly durable
material that can withstand some harsh
environments.
Drawbacks:
Often, a special finish, for example, marine
grade powder coating is required to
make stainless steel corrosion resistant
in environments where highly corrosive
chemicals and vapours are present. Therefore,
there is an added cost implication to what
can be a relatively expensive material.
Stainless steel is also the heaviest of the
three options, meaning there is an extra
challenge when designing the ventilation
system.
GLASS REINFORCED PLASTIC
(GRP) FANS
Benefits:
GRP, as the name suggests, is plastic
reinforced with fibreglass. It can be
manufactured in a way that makes it more
resistant to corrosion and lighter than
stainless steel.
20
PECM Issue 38
Drawbacks:
The cost of making GRP corrosion resistant
can cause it to have a considerably
greater manufacturing cost that material
counterparts like polypropylene.
Furthermore, the corrosion resistance
achieved with GRP is often not as effective
as stainless steel or polypropylene according
to the HVAC and Chemical Resistance
Handbook for the Engineer and Architect:
‘GRP equipment resisted only 29% of 109
chemicals in a satisfactory manner, thus
affecting its durability. That same rating was
higher for stainless steel (52%), and even
higher for Polypropylene (79%).’
Moreover, GRP can be subject to fibre
shedding due to the nature of the material.
This can cause problems with longevity and
overall durability.
POLYPROPYLENE FANS
Benefits:
Polypropylene is thermoplastic and many
of its properties are similar to polyethylene.
However, it offers several additional
benefits over GRP and stainless steel.
Firstly, it can be up to 30% less expensive
than other materials used for ventilation
in environment with harsh gases and
chemicals. As previously mentioned, it
usually offers more durability than most
other materials used in wastewater
treatment plants and resists the largest
number of chemicals. It is also the lightest
of the three options, making polypropylene
ideal in terms of ease of installation.
In certain circumstances, there may be other
variables to consider when selecting the
material of the ventilation system but the
polypropylene option is ideally suited to the
wastewater treatment environment due to
its lightweight, durable, affordable, corrosion
resistant properties.
Axair fan’s range of polypropylene fans have
scrolls which are moulded into a single
piece, meaning that there are no welding
joins. This improves the durability of the
fan at it eliminates the risk of welded joins
parting and needing to be repaired.
For more information, contact our
team by calling 01782 349 430,
emailing [email protected] or
visiting www.axair-fans.co.uk.