Energy Efficient

Compressed Air Systems

Workgroup Meeting July 2014

Abdul Qayyum “Q” Mohammed

Engineer

Why is this important ?

Almost all Manufacturing Facilities use Compressed Air (CA)

These are large systems Smaller systems draw about 40 kW (50-hp)

X 40

Expensive Resource

Compressed Air (CA) is a very expensive resource The most expensive in many cases About 90% of the input energy is lost through the system

Energy In

Work Out

Only 9% !

Source: David Vanderbeek, 2011 Power Smart Forum

HeatPurges And Drains

Conversion

Why use Compressed Air ?

Simple : Its easy to use

Can be used for a wide variety of applications

All you need is a new hose for a new application

In many cases it is the economically feasible option

Well what’s the problem then?

Its ease of use makes it ……. …..the most misused resource

CA Fundamentals

Before we get into energy savings opportunities lets briefly look at Types of air compressors

Reciprocating Screw Centrifugal

Different control strategies for the compressors

Pros and Cons

Reciprocating Compressors

Simplest and oldest compressor type Size: 1 – 600 hp

Recips: Part Load

Good part-load performance Very close to ideal compressor

Ideal

Recips: Pros and Cons

Pros: Simplest and oldest compressor type Comparable full load efficiency Very good part load efficiency

Cons: Higher maintenance costs compared to

the new compressor types (for larger compressors)

Screw Compressors

Currently the most commonly used compressor in industry Sizes 5 – 700 hp

Screws: Part Load

Multiple control options Combinations of controls available with each

compressor Gives large scope for optimization

*VFDs have lower full-load efficiency

They are very efficient between45% to 80% capacity

Screw: Pros and Cons

Pros: Low maintenance Different control options work well within

different systems Proper sizing is critical

Large cost range depending on Control options Other additional options (oil free, integrated dryers etc.)

Cons: Optimization is often neglected (or done poorly)

which degrades system part-load performance

Centrifugal Compressors

Larger compressors (these are dynamic) Sizes 125 – 6,000 hp

Centrifugal: Part Load

Can be the most inefficient compressors at part loads

Combination of controls are available Control optimization is necessary for efficiency

Centrifugal: Pros and Cons

Pros: Very high full-load efficiency

Very good for systems that have a high base load Low maintenance if operated properly

Customizable Can be built to match client needs

Oil freeCons: Slightly higher cost Can be the worst at part-loads

Blow-off should be minimized Dynamic nature limits turn down ratio (to avoid surge)

Energy Saving Opportunities

There can be endless opportunities in a system. It can take couple of hours to go through them all.

So, Let’s just look at the BIG hitters Inappropriate uses Leaks Pressure Staging

Other opportunities Air Drying Storage Filters Heat Reclaim

These are things we look for when we have limited

time with the client.

Inappropriate Uses

Questions to ask..

Is CA even necessary ? It is a VERY Expensive resource

Is there an alternative that can eliminate CA use?

Is CA being used effectively ? Can CA use be reduced ?

Pressure Timing

Let’s look at some examples.

In-appropriate use Examples

To blow off a product. Good idea?

www.thoritedirect.co.uk

Air Saver nozzles use about 70% less CA

CA to cool off product. …. Good Idea?

Energy Efficient Process Cooling – Dr. Kissock, University of Dayton

In-appropriate use Examples

200x more expensive than cooling towers

Personal Cooling (We just saw cooling costs)

www.safetyposters.com

In-appropriate use Examples

Occupational Safety and Health Administration (OSHA) safety violation

Drains are used to remove condensate from the system

But do we need to lose air?

www.airbestpractices.com

Open valve: Always loosing air. Timed Drain: Timing set for peak, often results in air loss

No-loss Drain: Zero air loss

www.isccompressedair.com www.ingersollrand.com

In-appropriate use Examples

Need low pressure air (20 psig) ? => Use Blowers !

Blowers use about

5x less energy

www.spx.com

www.aircompressorsdirect.com

In-appropriate use Examples

List of Common Inappropriate Uses

Blow-Off Applications  Air knives  Dust collector purges  Cleaning with CA  Personal cooling  Process cooling   Continuous CA Use Applications  Aeration  Agitation  Atomization (mixing)  Transport of material  Air motors /hoists  Diaphragm pumps  Air vibrators  Electrical cabinet cooling  Vacuum generation  Vortex coolers  Air Cylinders  Air Operated vacuum cleaners 

Energy Saving Opportunities

There can be endless opportunities in a system. It can take couple of hours to go through them all.

So, Let’s just look at the BIG hitters In appropriate uses Leaks Pressure Staging

Other opportunities Air Drying Storage Filters Heat Reclaim

These are things we look for when we have limited

time with the client.

Reduce Leaks !

Leaks are lost $$$$$

Air Power Usa

www.logis-tech.co.uk

Leaks Example

Misconception “We do not have a large leak load..” On average 30%* of a facility’s compressed air is lost

to leaks Example Facility

*U.S. DOE, Compressed Air Fact Sheet #7

Avg. Leak Load = 50% !! In a two compressor system

100 kW in Non-production ~ 100 Homes

Weekend

Strategy to Reduce Leaks

Strategies we have observed: Leak reduction programs

Other Methods Use of Isolation Valves to valve off unused areas Reduced pressure during non production Turning off CA system on weekends

http://processengineering.theengineer.co.uk/

Goals for Leaks

Can I have Zero Leak Load ? Unfortunately, NO

What should I aim for ? Good rule of thumb is to reduce it by 50% We have observed facilities with leak loads

As high as 60% and As low as 7-10% - this was accomplished overtime

by reducing leaks and isolating unused areas

Energy Saving Opportunities

There can be endless opportunities in a system. It can take couple of hours to go through them all.

So, Let’s just look at the BIG hitters In appropriate uses Leaks Pressure Staging

Other opportunities Air Drying Storage Filters Heat Reclaim

These are things we look for when we have limited

time with the client.

Did we adjust pressures at end use ? Do you need line pressure ?

Reduce Pressure at End Use

0.25” @ 95 psig

Unregulated tool

Regulated tool

0.25” @ 70 psig

~ 120 acfm

~ 95 acfm

~ 20% reduction !

We recently observed a large manufacturing facility with efficient compressors…..

Almost all end uses were unregulated !!!

Reduce Pressure at Compressor

Why is a compressor used? To pressurize the incoming air stream

A compressor has to Work harder for higher Pressure

Air Compressor

Air in @ P1

Air out @ P2Power kW

Heat out

Reduce Pressure at Compressor

Common Misconception “Raising the pressure increases capacity”

Reality – It decreases compressor capacity and increases operating costs

Often times other issues are compensated with pressure, Lack of storage Improper piping

Reduced Pressure - Energy Savings

Rules of Thumb Compressor Efficiency Increases by 1% for every 2 psi

reduction in operation pressure

Energy savings Improves compressor efficiency Reduced leak load Reduces CA use at applications

Reduced pneumatic equipment fatigue Increases equipment life

Reduced Pressure - Benefits

Goals for Reducing Pressure

How low should my system pressure be?

Rough rule of thumb, System Press = Min Press + 10

We have observed a large MFG facility with CA system at 75 psig.

This was done overtime by addressing system constraints such as adding storage, increasing pipe diameters etc.

Energy Saving Opportunities

There can be endless opportunities in a system. It can take couple of hours to go through them all.

So, Let’s just look at the BIG hitters In appropriate uses Leaks Pressure Staging

Other opportunities Air Drying Storage Filters Heat Reclaim

These are things we look for when we have limited

time with the client.

Staging

This is one of THE most important opportunities

Why?

Lets look at an example (worst case) Compressor – Centrifugal with blow-off only We just reduced compressed air demand by

50% How much do we save ?

Staging

Centrifugal part load

How much do we save ? ZERO !

Staging

System Part-Load with Multiple Compressors

Very Well staged multiple compressor system

Poorly staged multiple compressor system

Staging Fundamentals

Points to remember Constant speed compressors are only efficient

at full loads

Operation at part loads should be minimized.

You NEVER* want multiple compressors at part-load

*Does not apply in special circumstances with centrifugal and VFD compressors

Eliminate (or minimize) blow-off in Centrifugal compressors

Complexities in Optimizing Staging

Need to understand System air flow requirements Compressor – full load efficiencies Compressor – individual part-load performance Effect of combination of different compressors

within a system How one staging sequence is different from the other

How ? Metering the equipment is a start Analysis of metered data

Need to apply knowledge to obtain action items

Okay, Let’s not worry about complexities.

** This is where you may want to reach out for technical assistance.

Let’s look at a few case studies to understand the potential.

Case Study 1

Pre: Two new 900-hp centrifugal compressors are operated

in base trim manner Project cost ~ $800,000

Both of them can modulate and then blow-off

Post: Compressors are operated in parallel so that

Only one compressor blows-off first

Case Study 1 (Cont)

Savings ~ $50,000/year

A facility has two compressed air systems that were put in place for two different systems

Pre As often seen

Both systems were oversized What's interesting is both systems operate at 95 psig.

Post Combine the two compressed air systems

Case Study 2

Facts:Engineers like factor of safety;

Vendors like to sell larger compressors

Compressor Optimization: Case Study 2

In the new case only one compressor is part-loaded instead of two.

Savings ~ 20%

Manufacturing facility wanted to save energy They thought VFD compressor is a good idea (it is,

but..) Pre

They bought a Oversized (215 hp) VFD compressor Why ? Sales person recommendation ? Lack of analysis ?

Issue: the VFD could not trim Used a 250 hp load/unload as the trim instead

Not good

Post Bought appropriately sized (125 hp) VFD compressor

Compressor Cost ~ $150,000

And changed the control sequence

Case Study 3

Case Study 3

Big Savings

Savings ~ 24%

* Could have been achieved the first time if the VFD was

sized right.

Multiple facilities with multiple compressors

Are more compressors better ?

Is a control system better ?

Is a VFD better ?

Case Study 4

Case Study 4

Facility 1

Facility 2

Facility 3

1. Poorly Staged(Manual)- 8 similar compressors

2. Staged with VFD(Pressure based)- 8 different compressors

3. Very well staged. (Demand Based)No VFD - 8 similar but different size compressors.

Most of the savings can be achieved by effective staging Control systems are vital for optimization in large

systems

A VFD compressor can help improve your part-load performance Typically only one effective VFD is required per system

If sized correctly

Case Study 4

Summary

We discussed Importance of compressed air

Why its an expensive resource Different types of compressors and their controls

Reciprocating Screw Centrifugal

Largest Energy savings opportunities In-appropriate uses Leaks Pressure Staging

We looked at a few case studies

Its time for the Recommendations

Recommendations

Pursue all the low-cost no-cost opportunities In-appropriate uses Leaks Reducing pressure Staging with available control systems

Consult experts to evaluate best strategy with available controls

Consult technical experts before Investing Capital The last thing you want is invested capital and no savings.

New compressor installation Control system upgrade

Questions ?

Thanks for Listening!Abdul Qayyum “Q” Mohammed

www.gosustainableenergy.com

614-268-4263 x308

aqmohammed@gosustainableenergy.com

Additional Slides are available at the End for

Interested Parties

End Use: CA Diaphragm Pumps

Facilities use CA Diaphragm Pumps. Needed for extremely corrosive or volatile fluids However, in many cases diaphragm pumps are

used for fluids that can be moved with a regular centrifugal pump

www.wildenpumps.org http://www.winter-pumpen.de/

Motor Operated

pumps use about

4x less energy

End Use: Dust Collector Purges

CA is used in dust collector for purges. These purges can use significant amount of air if

not optimized properly. Control CA with solenoids to appropriately time

purgesBag house uses ~ 40% of system capacity

Distribution: Storage

Used to eliminate (or dampen) the variation of pressure within the system. Particularly important in systems with

load/unload compressors

Storage improves part load performance of a system with load/unload compressors

“Improving Compressed Air System Performance: A Sourcebook for Industry.” – US D.O.E, Nov 2003

Distribution: Storage (Cont.)

How much storage should I have ? Rule of thumb 3 to 5 gal/cfm of compressor

output Actual requirement depends on fluctuations in CA

demand and types of compressors

Optimize Compressed Air Drying

Appropriate drying technologies should be used Common drying technologies in order of decreasing efficiency

Refrigerant Dryers Cycling Non-Cycling

Desiccant Dryers Heat of Compression* (HOC) Heated desiccant

Heated with Blower purge Heated with CA purge

Heatless desiccant* HOC dryers are more efficient than refrigerated dryers

Generation: Reclaim Heat

~ 80% of input energy is lost as heat Heat can be used for various purposes

For space heating during winter For process use throughout the year

Summer

Plant

Winter

Air Compressor

Cooling Air

Compress Outdoor Air Compressed

Air To Plant

Generation: Reclaim Heat

Example Installation

Generation: Compress Outdoor Air

Outdoor air is typically cooler than a mechanical room Cooler air is denser hence easier to compress Fraction savings ~ 2% per 10 F reduction

Note: Savings are realized in oil free compressors only

In oil lubricated compressors the air is mixed with hot oil before compression. This eliminates savings.

Considerations should be made to avoid freezing temperatures

What's the benefit of Energy Savings?

We reduce emissions Helps slow down global warming

Helps Protect Out planet

What are we talking about ? Lets rephrase “What is MY benefit ?”