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Total Number of Subscribers: 426 |
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Posted to the desk of %FNAME% |
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Date: 17 June 2008 |
Compiled by Mr. M. Sathya Kumar |
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Energy Audit — Case study Background
: The top management of a conglomerate with diverse business and
multiple factories across the country with a turnover of Rs.3000 crores has
an internal audit group, but lacks technical members in the group. It has
recently been listed on a stock exchange after a successful issue at premium.
The Managing Director in his earlier organisation knew a consulting group
specialising in energy audits and invites them for discussions for conducting
energy audits in his factories. During discussions, it is agreed that the
in-house Chief Audit Executive (CAE) would hire two engineers in the internal
audit department, who would be observers and learn energy audit techniques
from the consulting group, so that subsequent to the initial review by the
consulting group, the in-house internal audit team would be able to carry out
‘energy audits’. The Managing Director accepted the suggestion. The focus of
energy audit will be :
Methodology and Observations Based on the above background, the CAE hires two engineers, one
electrical engineer and one mechanical engineer, and also deputes one Cost
Accountant to be a part of this team. The following are energy savings achieved during the
audits/reviews at factories : (a) Energy savings by use of energy-saving motors — Motors were tested and found to be inefficient and
recommendations made to use energy-saving motors : Blower : Normal Kirloskar Motor Present motor details : Capacity
= 7.5 HP Efficiency
= 84*% Voltage
= 402 V PF
= 0.84 Current
= 11.91 A Power consumed = 7.52 KWH Blower replaced with energy-efficient motor : Capacity
= 7.5 HP Voltage
= 416 V PF
= 0.893 Current
= 8.93 A Power consumed = 6.10 KWH Energy saving calculation : Power consumption by Standard
Motor
= 7.52 KWH Power consumption by EF
Motor
= 6.10 KWH Unit
saving/hour
= 1.42 KWH Saving @ Rs.3.5/Unit for 8000
hrs
= Rs.28,000 Cost of EF
Motor
= Rs.12,200 Payback
= 6 months (b) Energy convertion proposals mooted in terms of
compressed air systems : 1. Arrest air leaks in the compressed air system 2. Reduction in internal cooler temperature 3. One-time overhauling of compressors and adhering to
maintenance standards for all compressors 4. Other energy conservation measures like airpressure control,
reduction in suction, pressure drop in process air compressor 5. Reduce blower capacity by change of motor pulley 6. Reduction in suction air temperature for all process air
compressor by using return chilled water circulation 7. Replacement of heatless drier with refrigerated type Arrest air leaks in compressed air systems :
Compressed air system was tested for air leaks by reliable
soap-solution method and leakage points were identified and tags were put
indicating clearly the type of leak. The leaks were categorised as small,
medium and big. Small and medium leaks were identified, based on quantity of
air bubbles. Leaks with heavy noise and large bubbles are categorised as big
leaks. (c) Savings in oil : 1. Proper storage and handling of oil is the perquisite for
efficient combustion, as it ensures continuous supply of clean oil at
required temperature and pressure. 2. The oil storage tank should have provision for preheating.
The tank should have a horizontal gradient of 20mm/metre. A drain pipe should
be provided at the lowermost point of the tank. 3. Oil spillage to be avoided during loading and unloading. 4. Oil to be filtered in stages before entering into the burner. 5. For proper combustion, oil to be preheated. The preheating
will reduce the viscosity, which will in turn reduce the power required for
pumping. 6. For efficient automation, the viscosity of the oil at the
burner should be 2- - 25 centistokes. 7. As furnace oil contains up to 1% of water, it should be
removed periodically from the tanks. (Savings were achieved with less oil being consumed after
following the above recommendations). (d) Steam generators/boilers : 1. Ensure correct temperature and pressure of fuel oil at the
burner. 2. Efficient combustion requires suitable controls on firing
equipment in order to maintain highest possible efficiency at all loads. The
objective is to trim combustion air for complete combustion with minimum
excess air. Particular attention to be paid to draught control. 3. Employ blowdown (auto/manual) periodically. 4. Use the flue gas to preheat the feed water. 5. Provide adequate instrumentation to monitor fuel
consumption/steam generation/distribution. 6. Analyse flue gas and try to achieve the optimum of CO2 and O2
levels. 7. Consideration should be given to waste-heat recovery for
preheating feed water/combustion air by economiser/recuperators. 8. De-aerator temperature and pressure to be maintained to avoid
carry over of oxygen in feed water. (This led to increase in efficiency for boilers and less
consumption of oil). (e) Electrical energy : 1. Improve power factor by providing correction capacitors to
reduce kVA, which will in turn reduce the maximum demand. Instal capacitors
near the load. 2. Purchase only energy-efficient motors. 3. In rewound motors, it is observed that there is an energy loss
of 5%. Hence if at all to be used, should be used on low duty cycle
applications. 4. Match motor’s rating with driven load properly. 5. If the load fluctuations are high, use of soft starters are
to be considered. 6. If the load on motor is always less than 40%, a changeover
from Delta to Star connection can be considered. 7. Use variable frequency drives, fluid coupling for variable
speed applications, such as fans, pumps in place of inlet guide
vanes/dampers. 8. Operate transformers at more that 75% load. (f) Illumination : 1. Use electronic chokes for fluorescent tubes as they are
energy-efficient. 2. The use of timer switches or photo cells to switch-off light
during unwanted hours to be considered. 3. Lighting to be minimised in non-productive areas. 4. Translucent corrugated roof-sheets to be used to allow dry
light inside the factory. Conclusion : The key observations arising from the above exercise was tabled
at the Audit Committee. The Board and Audit Committee members appreciated the
efforts by the CAE and the outside energy audit consultants. They specially
appreciated the the efforts made by the CAE to induct engineers and develop
understanding of energy conservation efforts. This team had truly added value
to operations. The Managing Diectror appreciated the results of ‘internal audit group’ being a contributing
partner of the company’s management. The Audit Committee being satisfied with the results directed
that ‘energy audit’ should be incorporated into the annual internal
audit plan. Article
by Deepjee Singhal Manish Pipalia Chartered Accountants |
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