Improved reliability = better energy efficiency
May 1st 2007 During the last decade there have
been a number of technical
developments by the compressed
air industry to help users reduce their cost
of generation and use of compressed air.
However, the greatest influence on the
consumption is still largely down to the
user in how the whole system is installed
and maintained, and how the compressed
air is used on site.
Many of the barriers to improving
energy efficiency of a compressed air
system are the same as for general energy
management. Compressed air is invisible
and as long as the supply is continuous
and not causing production any problems,
energy saving is low on the priority list.
Indeed few if any on site know the annual
cost of using air. Reliability is of
paramount importance and fear that
energy efficiency measures could
compromise reliability of air supply
impedes changes. Two of the largest
causes of avoidable waste in a
compressed air system are leaks and overpressurisation.
Add to this unregulated
and indiscriminate use for low grade
duties such as cleaning and cooling, and
there's significant variability and hence a
risk to supply reliability – a matter of
greater immediate concern for the
manufacturing and process industries.
However all these can be controlled by the
user.
1) Unregulated use
Review what compressed air is used for
on site, it is often misused i.e. wasted –
just because an air supply is readily
available, not because it is the most costeffective
or appropriate method.
Processes evolve and production methods
change, affecting the way compressed air
is used, so review the system and working
practices regularly.
2) Compressed air leaks
High compressed air leakage rates persist
in many systems - the leak rate on an
unmanaged compressed air system can
be as much as 40% of the compressor
output. The most common sources of
leaks are:
Manual condensate drain valves left
open
Shut-off valves left open
Leaking hoses and couplings
Leaking pipes and pipe joints
Leaking pressure regulators
Air-using equipment left in operation
when not needed.
Compressed air leaks also lead to
additional costs through:
Fluctuating system pressure, which can
cause air tools and other air-operated
equipment to function less efficiently –
potentially stalling and affecting
production
Reduced service life and increased
maintenance of equipment due to
unnecessary compressor cycling and
running time
Excess compressor capacity.
The fluctuating system pressure brings
us round to the second issue:
3) Over-pressurisation:
Compressed air systems often run at
pressures of up to 2 bar above the rated
pressure. This is usually to guarantee
sufficient air at all times for different
production processes. Not only does this
consume more energy, it also shortens life
of components due to over-pressurisation.
A 1 bar reduction in air pressure can
reduce generation costs by 6-8%. Overpressurisation
(often referred to as
"artificial demand") is usually indicative of
trying to lessen the effect of fluctuating air
pressure in the system which causes
problems such as production stoppages
and variable product quality. Poor
maintenance is often responsible for
pressure drop in a system where dryers,
filter elements and piping have all been
neglected. So, why are systems generally
over-pressurised although it costs more in
terms of electricity? The overpressurisation
cost is usually minimal
compared to potential downtime costs
should the air supply fall below the
required level.
There is a solution to creating a reliable
system where the pressure can be
lowered without compromising the
compressed air supply a paramount
requirement for manufacturing and
process industries. BCAS has applied for
Carbon Trust funding to trial pressure
control techniques together with leak
reduction programmes. Although the pilot
sectors are food and drink and aerospace,
if you have an installed capacity of 200kW
or more please contact us directly about
potential participation. Watch this space
for news and updates.
For further independent information on
energy saving, as well as compressed air
legislation and health and safety issues
visit: www.bcas.org.uk More articles from BCAS: | 
