Energy Conservation in Compressed Air

System.

Mechanical Utility Systems.

Roll Nos. – 1120717 - 1120715 - 1120714 - 1120716 - 1120719

Compressed Air : “Compressed air is air which is kept under a pressure that is greater than atmospheric pressure.”

Advantages of Compressed Air :

• Wide Availability of Air & its compressibility.

• Easy Transportability in Long pipes & its storage in pressure

vessels.• It is free from fire hazards.• Ease of handling with control of pressure,

force, motion, etc.• Reliability of operation and remote

controlling.• Easier maintenance & cost effectiveness.• It does not cause any pollution

Disadvantages of Compressed Air :

Compressed air is not cheap as power medium and it is not as safe as considered.The main reasons are :-

• Loss of compressed air power due to inefficient control and leakages.

• Loss of Energy due to poorly maintained transmission and distribution.

• Damage may occur due to over pressure in storage vessel.

• Valves may seize at freezing temperatures due to presence of moisture

in compressed air.

Industrial Uses of Compressed Air : To operate reciprocating tools e.g. in

riveting ,hammers ,paving breakers ,diggers ,etc. To operate rotating tools e.g. air

motors ,drills ,reamers ,grinders ,wrenches ,etc. In Vehicle propulsion (compressed air vehicle). Compressed Air Energy Storage. In Air Braking Systems:-Railway braking & Road vehicle

systems Refrigeration using a vortex tube. Air-start systems in engines. In Operation & Control of valves & instruments. Use of air cushion to reduce friction to minimum level in

hovercrafts and air lift conveyors ,pneumatic elevators ,as fluidizer for aerating solid product for reduction in apparent density.

Process gas compressing ,controls , and actuators in petroleum Industry.

Air Compressors : Air compressors account for significant amount of electricity used

in Indian industries. Air compressors are used in a variety of industries to supply

process requirements, to operate pneumatic tools and equipment, and to meet instrumentation needs.

Only 10-30% of energy reaches the point of end-use, and balance 70-90% of energy of the power of the prime mover being converted to unusable heat energy and to a lesser extent lost in form of friction, misuse and noise.

Types of Air Compressors :- Packaged rotary air compressors are most

commonly used because of their low noise levels and maintenance costs. There are different types of packaged rotary air compressor, including:

rotary screw, which is the most widely used type as it is reliable, efficient and only needs basic routine maintenance & rotary sliding vane. Reciprocating compressors are often used for small

industrial applications. Their specific energy consumption is equal to or better than rotary compressors. However, they can suffer from reduced performance levels if not maintained properly.

Centrifugal compressors are generally used for applications that need a high volume of air. At high flow rates, the centrifugal compressor is by far the most energy efficient.

Components of Compressed Air System :-Compressed air systems usually consist of the following components :-

compressor air cooler air receiver tank filter dryer condensate trap distribution system The compressor produces compressed air at the required pressure. The air receiver tank acts as a reservoir to store and cool the

compressed air and helps make sure the system can cope with variations in demand.

The air cooler, filter and dryer all treat the air at different points in the system. They remove impurities such as water, dirt and oil from the air taken in by the compressor, as well as those added by the compressor.

Compressed air may be fed to various uses on a site via a distribution system. These distribution systems can be relatively straightforward or very complex.

Compressor Performance :- Capacity of a Compressor : “The capacity of a compressor is represented as Free Air Delivery (FAD),i.e. air at atmospheric conditions at any specific location.It represents the actual rate of volume of air compressed and delivered at atmospheric conditions represented as cubic meter per minute (cmm).”

Compressor Efficiency :-Several different measures of compressor efficiency are commonly used: volumetric efficiency, adiabatic efficiency, isothermal efficiency and mechanical efficiency.

Why & How to Conserve Energy in Air Compressed Systems ??

Electric Energy, The Big Cost.

Analyze the total cost of a compressed air system and you’ll realize that power cost is significant.

In just one year it could exceed the cost of the compressor itself.

Over a period of ten years, this could consume 70% of your overall costs.

That’s why it is important to investigate energy efficiency when considering a new compressor.

70% of Your Long-Term Compressor Cost is Electricity

WHY ?

Electric Energy, The Big Cost.

76%

12%

12%

Compressed Air Cost in PerspectiveCosts over 10 Years

ElectricityMaintenanceEquipment

70% of Your Long-Term Compressor Cost is Electricity

Cost Of Production Matters

It takes 7-8 HP of electricity to produce 1 HP in an air tool.

Power consumed in producing compressed air will impact the competitiveness of production units.

Ways to Conserve energy & Improve performance of compressed air systems :

HOW ?

1. Location of Compressors :• The location of compressor & use of filters plays an important role on the amount of energy consumed.• The lower inlet temperature to compressor results into lower energy input.• It is observed that “Every 40C rise in inlet air temperature results in a higher energy consumption by 1 % to achieve equivalent output”.• Since the compressor room has higher temperature than the surrounding air temperature, it is essential that intake pipe to L.P. compressor must be extended outside the compressor room in a shade.

Some of the important points to be considered to reduce energy consumption are as follows :-

2. Use of Air-filters:• Air filters must be used to supply clean air at suction to

compressor to avoid wear of moving parts.• Filters should have high dust separation capacity with

minimum pressure drop since higher pressure drop across the filter increases the power consumption

3. Elevation :• The altitude of a place has a direct impact on the

volumetric efficiency of the compressor.• It is evident that compressors located at higher altitudes

consume more power to achieve a particular delivery pressure than those at sea level, as the compression ratio is higher.

4. Intercooling in between the stages :• Intercoolers should be provided in between the stages to reduce the power requirement to run the compressor.• Ideally, the temperature of the inlet air at each stage of a multi-stage machine should be the same as it was at the first stage. This is referred to as “perfect cooling” or isothermal compression.• The extent of power saved depends on the intercooling of air carried out in the intercooler.• It is observed that “An Increase in 6 degree Celcius in the inlet air temperature to second stage results in 2% of specific energy consumption”

5.Using Variable Speed Drives:• Variable speed drives should be used for capacity control of compressors to reduce power consumption.

6. By Controlling Pressure Settings :• Compressor operates between pressure ranges called as loading (cut-in)

and unloading (cut-out) pressures. • For the same capacity, a compressor consumes more power at higher

pressures. They should not be operated above their optimum operating pressures as this not only wastes energy, but also leads to excessive wear, leading to further energy wastage.

• The volumetric efficiency of a compressor is also less at higher delivery pressures.

Reducing Delivery Pressure :

“ A reduction in the delivery pressure by 1 bar in a compressor would reduce the power consumption by 6 – 10 %.”

7. Proper Arrangement of Pipe lengths & fittings :

8. Use Blowers in place of Compressed Air System :• Blowers must be used for low pressure applications instead of compressed air (e.g. in agitation, air for combustion of fuel, conveying materials in pipes.)• Misuse of compressed air should be avoided for cleaning floors , equipment cleaning, etc.

• Air Distribution system should be such that the length of pipe up to point of use in minimum and uses minimum pipe fittings and joints so as to reduce the pressure losses.• Where possible the piping system should be arranged as a closed loop or “ring main” to allow for more uniform air distribution to consumption points and to equalize pressure in the piping.

9. Reduce Leakages :

• It is necessary that the leakages in the compressed air supply &

distribution system are eliminated as far as possible.

• Leakage tests are conducted by ultrasonic leak detectors. It is done by observing & locating sources of ultrasonic vibrations created by turbulent flow of air passing through leaks in pressurized system.

• Another method of leak detection is by conducting no load test. The distribution system is supplied compressed by closing all the terminal valves of consumption points. The load on the compressor will eventually reflect that there is a leakage in the system.

10.Replace Pneumatic tools :

12.Avoiding loss of air pressure due to friction :

The loss of pressure in piping is caused by resistance in pipe fittings and valves, which dissipates energy by producing turbulence. The piping system will be designed for a maximum allowable pressure drop of 5 percent from the compressor to the most distant point of use.

Pneumatic tools such as drills and grinders should be replaced by motor driven tools where ever possible since the energy consumption is almost 5 % to 10 % of the compressed air system if these pneumatic tools are used.

Case study:- NORGREN world leader in pneumatic components and

automation systems systematic self-examination and with the help

of safety and energy saving techniques and products

directly increase overall profits, as well as making a valuable contribution to the wider issues.

Causes:- leaks, pressure drops, over pressurization,

misuse of jets and poor compressor management.

around 30% of the air produced is wasted.

Causes:- leaks, pressure drops, over pressurization,

misuse of jets and poor compressor management.

around 30% of the air produced is wasted.

leakages Causes:- Aging pipe work, Flange connector gaskets

and pipe dope, loose Fittings, Flexible hoses subjected to strain and abrasion, Couplings with damaged seals, etc.

Remedies:- planned maintenance routine that is intolerant

of leaks.

Isolate systems when not in use

Estimate the percentage of air lost to leaks.

Misuse of Jets Causes:- processes such as dusting, cooling,

separating and other tasks.

jets are left permanently running.

Remedies:-

With a suitable valve and sensor, these can be controlled automatically so they are only on when required.

Over pressurisation Causes:- Many systems run at full line pressure with the only

control being the compressor cut off switch.

high friction demands higher set pressures.

Remedies:- Use of pressure regulators at exit

Check for correct lubrication

Pressure drop Causes:- resistance to flow by localized restriction

and general friction in pipes and components.

Fitting a smaller filter Remedies:- Pipe routing should have gentle sweeping

bends where possible.

large enough filters

Compressor Management Large compressor installations are

likely to be fitted with sophisticated power and load management systems.

These use figures of expected consumption rate, storage volume and pressure to tell the compressor how long to run in an off load condition before shutting down during times of low or no demand.