The first major audit results to emerge from ABB's 'Six Step Plan' for
energy conservation have been revealed by one of its Drives Alliance
Partners, Sentridge Control, following a highly successful project at
Mayflower Vehicle Systems' huge manufacturing plant in Coventry. Les Hunt
reports
Donald Campbell's Bluebird land speed record car was built there; it was
a strategically important manufacturing site during the Second World War;
now they make aluminium and steel skin panels and structural components
for, among others, Rolls-Royce Motor Cars, MG, Ford and Jaguar, as well
as key body parts for the Aston Martin Vanquish. Mayflower Vehicle
Systems' (MVS') Coventry site is around 80 years old and is, by any
standards, huge. It is also a big user of energy.
Committed to reducing CO2 emissions, following its adoption of the ISO
14001 environmental management system standard, and faced with the burden
of the Climate Change Levy, MVS had already placed an energy audit high
on its list of priorities, when local firm, Sentridge Control - one of
ABB's seven nation-wide Drives Alliance Partners and a specialist in
energy saving control strategies - was called in to provide some timely
advice. Sentridge's sales director, Paul Stafford picks up the story:
Our strategy in these cases is to audit the current position, identify
and quantify potential savings, prepare an action plan, then implement it
and monitor the results; we call this our 'Sea Change' initiative. But
with MVS, getting started posed a big challenge. Just where do you start
on such a big site? Working on the premise that 80% of the site's energy
is used up by just 20% of its applications, narrowed the field somewhat,
and Sentridge focused its attention on five key areas of the plant,
identified as having the highest savings potential. Past experience and
the local knowledge of site staff helped in this exercise.
The audit quickly revealed the first 'culprits'. Three 30kW
phosphate/alkali rinse pumps, serving a critical stage in the sheet metal
pre-treatment process, were running continuously up to ten hours per day
even though they are required for only two out of every eight-minutes of
the pre-treatment cycle. The system was effectively throttled using
valves, because on-off control at this frequency would have led to
premature motor failure. Sentridge suggested placing one of the motors
under inverter control to determine the ‘before and after’ energy
consumption levels. An inverter was actually ‘borrowed’ for this trial
from Sentridge’s own stock. With the inverter in place, the motor was
switched off between rinse cycles and then ramped up to speed at the
start of the duty. The savings achieved provided the catalyst for action
in other areas of the plant.
“We were cynical about the huge savings that were being claimed at the
beginning of this exercise,” recalls MVS’ facilities manager, Pat
O’Sullivan. “Now, thanks to the inverter installation on this rinse duty
we have cut the running costs of these pumps by 87.9% - even higher than
the original estimate.” Faced with these facts, senior MVS management was
persuaded to grant an unbudgeted £30,000 for drives installations in this
and other areas, including six units for the phosphate and alkali rinse,
chemical and soap pumps, and a further eleven drives for other pumps and
cooling tower fans, ranging from 2.2 to 55kW. The projected annual
savings for the entire installation was calculated at £19,000. Incidental
benefits of inverter control include a reduction in valve gland packing
requirements and a lower frequency of motor bearing replacement.
At the earliest stages of this project, Sentridge encouraged full MVS
technical involvement. Key staff overseeing the operation and maintenance
of the drives were given a one-day intensive course at the system
integrator’s ‘drives school’, and they passed on their newly acquired
k