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Co-funded by the Intelligent Energy Europe
Programme of the European Union
Introduction - Theory - Exercises - Business Case - Summary
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Overview
Introduction
Theory Approach (some remarks)
Main components
Compressed air flow rate
Inappropriate air users
Leakage
Parameters that influence consumption
Exercises
Business Case
Summary
Introduction - Theory - Exercises - Business Case - Summary
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AIR IS FREE….BUT COMPRESSED AIR ISN’T FREE
ENERGY EFFICIENCY OF MOST OF
COMPRESSED AIR PLANTS IS QUITE
LOW
COMPRESSED AIR CAUSES A COST THAT ISN’T ALWAYS TAKEN
IN ACCOUNT
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Electric energy costs
Leakage costs
Maintenance cost
Plant modification cost
The costs of electric energy reach the 73% of total cost during the life
of air compressed system.
REASONS FOR EXCESS COST
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Reasons for exces consumption
Excess consumption through technical issues:
– Use of outdated and low efficiency electric engines
– Air distribution system not appropriated
– To high air leakage
– Compressed air engines fed with hot air
Excess consumption through behavioral issues:
– Use of too high pressure
– Compressed air engines turned on unnecessarily
– Use of compressed air to do the cleaning
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Optimizzation of air
compressed system will
deliver savings of up to 35
%.
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Approach (some remarks)
1. Identify how much air flow and
pressure each user machine needs
2. Find the right place for each user
machine
3. Identify the right place for compressed
air machines
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MAIN COMPONENTS
1. Air inlet filter
2. Air compressor, electric
motor and panel control
3. Air treatment (oil separator,
dryer, filtration)
4. Storage tank
5. Distribution Network Fonte: Improving air system performance DoE - Energy Efficiency and Renewable Energy
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Compressed air flow rate
- inappropriate air users
- leakage
The flow rate produced a direct bearing on
consumption.
The compressed air flow rate depended on
requirements.
Therefore must be avoided:
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Inappropriate air users
Transport of powders at low pressure
Ventilation
Agitation liquids
Cleaning in general
Removal of defective products from a line
Blowers
Mechanical arm
Electrobrushes
Mechanical agitators
Fans; Blowers
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LEAKAGE
• Accurate assessment with specific equipment
• Rough estimate
If more than 5% requires action!!
How to assess the losses?
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Parameters that influence
consumption
• L is the work
• M is the mass flow rate of air
• R is the universal gas constant,
• T1 is the inlet air temperature (°K),
• β is the ratio between the compression end pressure and beginning of compression,
• m is the exponent of the transformation,
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Choose an appropriate level
The increase of a bar of produced air pressure causes an
increase of about 7% of the energy consumption
If the process requires two pressure levels is good to evaluate the installation
of two compressors instead of one (with the need to achieve the lowest
pressure by reducing valves).
Parameters that influence consumption Maximum pressure
The operating pressure of a compressor directly affects the power consumption
and energy consumption.
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• Increase in operating costs
• Small diameters, lower installation costs, more losses and hence higher
operating costs
The pressure drop of the network (pipes) should never result in a pressure
drop greater than 0.1 bar
• The level of surface finish of the tubes affects the load losses
Parameters that influence consumption Pressure drop
The pressure drop of the network (pipes) should never result in
a pressure drop greater than 0.1 bar
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• The minor work is assured in the case of an isothermal transformation m = 1
• The work is greater in the case of an adiabatic m = 1.4
Parameters that influence consumption Type of transformation
To get closer to an isotherm must carry away heat during
compression
The removed heat can be used
• Only 10% of the electricity consumed by a compressor is converted into
useful energy to compress the air
• 90% of the electrical energy is converted into heat to be eliminated, but that
can be recovered (heating environment, pre-heat combustion air, heating hot
water, pre-heat process water)
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The work made by the compressor for compressing the air increases with
increasing temperature of the inlet
• The temperature of the input should be as short as possible, consistent with
current environmental conditions
• Do not take air from the compressor room or another, it is always best to take
air from the outside
• The starting point must be taken possibly in the north and in the shaded area
Parameters that influence consumption Inlet air temperature
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The air quality depends on its content:
• Particulate.
• Water (expressed in temperature of the dew point of the air pressure)
• Oil (measure)
• Material of the network and its state
Parameters that influence consumption Air quality
Air quality must be adapted to the needs of the process
Air quality has a greater cost.
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Water
The water comes from atmospheric moisture in the air
Removing water from the air can be done:
- At central Referigeration
- At the local level Steam Traps
The refrigeration is more efficient, but more expensive from the point of view of
plant and exercise.
The steam traps have a lower cost of installation, but require higher maintenance
costs and leads to losses of air.
Parameters that influence consumption Air quality
Particulate matter can be removed by input filters
The oil can be removed by filters or at the source, using oil-free compressors.
The two solutions should be evaluated as a function of the different costs.
The oil-free compressors increase the cost of installation
The filters increase the costs of operation and maintenance
The filters should be checked regularly
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1. Start - stop (power 5-10 kW)
2. Running load - idling - stop (power> 10 kW)
3. Speed control of Compressors
Regulation system are influenced by:
• Oversized Compressor
• Control of the compressor speed
• The presence of a storage tank
Parameters that influence consumption Regulation system
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•Meets sudden demands for air
•Allows for greater stability in the level of pressure on the network
•Reduces Stop & Go of the compressor
•Provides sizing the compressor below the maximum values pressure
• The option of installing secondary tanks near the isolated users and / or highly
intermittent can be consider
Sizing of the storage tank
•The size of the tank depends on the extent of changes in the demand for air.
The size should be at least 10 times the volume of air produced by the
compressor (l/s)
•The size of the tank affects the sizing of the compressor
Parameters that influence consumption STORAGE TANK
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• Do not oversize the compressor
• Storage Tank
• Control of the compressor speed
• Type of compressor
• High efficiency engine
Parameters that influence consumption Compressor & control
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Acquisition of data on consumption of electricity
• Can I make special measures? (High cost, more accurate)
• Can I use the data available? (low-cost, lower precision)
Parameters that influence consumption How to handle the compressed air system
Evaluate the cost of compressed air
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LEAKAGE REDUCTION
What is the effect of a hole of 10 mm in
a compressed air network (@ 7 bar
pressure)
Introduction - Theory - Exercises - Business Case - Summary
a.Up to 10 kW loose
b.Up to 40 kW loose
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HOLE (mm)
Flow rate @ 7bar (l/s)
Power loss (kW)
1 1,2 0,4
3 11,1 4
5 31 10,8
10 124 43
Introduction - Theory - Exercises - Business Case - Summary
LEAKAGE REDUCTION
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HIGH EFFICIENCY ENGINES
How much to save by replacing a
standard engine with a high
efficiency engine?
a. Up to 1%
b. Up to 5%
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Power [kW]
HIGH EFFICIENCY MOTOR
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REDUCTION OF AIR SUCTION
TEMPERATURE
How much energy savings can be
obtained with the cooling air inlet 5°C?
a. Up to 2%
b. Up to 10%
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Technical literature reports that a
reduction of 5 °C of compressor input air
temperature (with respect to usual
temperature) would allow saving of 2%
of yearly consumed kWh.
REDUCTION OF AIR SUCTION
TEMPERATURE
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Practical example Porsche industry
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Description:
In 1997, the system of compressed air production of "plant2 " of the German
automobile factory Dr. Ing hc F. Porsche AG near Stuttgart was constituted by a
screw compressor - cooled water (22,2 m3/min, FAD) plus four reciprocating
compressors water cooled from 15 m3/min each.
The maximum operating pressure was 8.7 bar.
An analysis on the compressed air system, carried out by specialists of a factory
compressors, noted compressed air demand varies between 15 and 65 m3/min.
By processing all relevant data has been defined a new compressed air system
with optimized use of energy.
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Action taken:
The new system was divided into two stages comprising only air-cooled screw
compressors.
Load peaks were satisfied with the use of three machines with a 5.62 m3/min
FAD each, while the base load was covered with four compressors with a FAD of
16.4 m3/min each.
All seven compressors are managed by a centralized control system.
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Results:
The optimization of the compressed air system allowed us to calculate the cost
of energy and make energy savings.
the operating pressure was lowered from 8.5 to 7.5 bar and the specific power
of the overall compression station has been reduced from 8.19 to 6.19 kW /
(m3/min).
The total savings amounted to 483000 kWh of electricity per year.
Furthermore have been spared approximately € 55,000 in savings for non-
consumption of cooling water.
The optimization of the compressed air system has been realized with a
reasonable payback time
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Excess energy consumption through compressed air is
caused by technichal as well as behavioural issues.
Through the optimization of the compressed air plant savings
of up to 35 % are possible.
The leakage reduction can effect up to 20 % energy saving.
Adoption of high efficiency engines can effect up to 5 %
energy saving.
A reduction of 5 °C of compressor input air temperature
would allow saving of 2% of yearly consumed kWh.
Repetition
Introduction - Theory - Exercises - Business Case - Summary