14rs compressed air

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O N L I N E R E S O U R C E

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Educational institutions have realized the need oremphasizing the basics, sometimes reerred to as the threeRs reading, riting and rithmetic. Tere are also several

basic Rs to be kept in mind i you want to install, operate,and maintain an efficient compressed air system:

1. reduce leakage losses2. reduce pressure at points o use3. reduce pressure at source (compressors)4. reduce system pressure fluctuations using adequately

sized and located air receivers and controls5. reduce number o partially loaded compressors to only one6. remove inappropriate applications7. reduce system pressure drop losses with properly sized

piping and valves

8. remove moisture content o compressed air with theproper type and size o dryers

9. remove condensate without loss o compressed air10. reduce downtime through preventive maintenance11. record system data and maintenance12. review air usage patterns regularly13. recover heat14. reduce energy costs (return on investment and cost o

operation).

R #1 REDUCE LEAKAGE LOSSES

In a typical plant, compressed air

leaks amount to 20-30% o the totalo all compressed air produced. In

worst case scenarios, where no detection and repair pro-grams exis t, leakage levels can be more than 50%.

A -in. leak in a 100 psi system having a pressure o 100

psig, will al low more than 3 million f o ree air to escapein one month. At an average specific power o 18 kW/100cm, this amounts to 107,000 kWh o lost energy or $10,700in energy cost per year at $0.10/kW. Tis problem is wors-ened in systems operating at even higher pressures.

Leakage rates drop with lower operating pressures. I thesystem pressure could be reduced to 80 psig, or example,the leakage flow, and energy use in a well-controlled system,would drop by 17% not including additional savings due tocompressing to a lower pressure, which could amount to ad-ditional savings o 10%.Leaks can be both intentional and unintentional.

Intentional leaks include open condensate drain cocks andvalves.

Unintentional leaks include leaking pipe joints and valves,

damaged hoses, and inexpensive, poor-fitting quick-dis-connect couplings.

Equipment not in use may also be using some compressed

air. Such equipment should be isolated rom the distribu-tion system by a valve.One way to determine the leakage rate in a system is to do

special testing when all the production equipment in the plantis shut down. I the compressors can be run in load/unloadmode, the time loaded as a percentage o total running time

will represent the percentage o total capacity going to leaks.Alternatively, or compressors with other than load/unload

Install, operate, and maintain a system that makes the best use of resources

By David M. McCulloch, Frank Moskowitz, and Ron Marshall, Compressed Air Challenge

Tis is the first of a multi-part series of articles on installing, operating, and maintaining an efficient compressed air system,

written by members of Compressed Air Challenge (www.compressedairchallenge.com).
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controls, you can do a volume bleed down test. Tis methodrequires the use o a pressure gauge downstream o the re-ceiver and an estimate o total system volume, including anydownstream secondary air receivers, air mains, and piping(V, in cubic eet). Te system is then started and brought to

the normal operating pressure (P1), and the compressor isturned off. Measurements should then be taken o the time() it takes or the system to drop to a lower pressure (P2),which should be a point equal to about one-hal o the oper-ating pressure. Leakage can be calculated as ollows:

Leakage (cm ree air) = [V x (P1-P2)/(x 14.7)] x 1.25Where:V is volume in cubic eetP1 and P2 are starting and ending pressures in psigis time in minutes

Te 1.25 multiplier corrects leakage to normal systempressure, allowing or reduced leakage with alling systempressure to 50% o the initial reading. Again, leakage ogreater than 10% indicates that the system can likely beimproved. Tese tests should be carried out once a monthas part o a regular leak detection and repair program. Adescription o these tests can be ound at www.compresse-dairchallenge.org/library/actsheets/actsheet07.pd.

Unfortunately, leaks are not a problem with a one-time cure.

Maintaining a lower leak level requires ongoing vigilance anda mindset that will not allow leaks to be tolerated. Recognizedleaks must be tagged and repaired as soon as possible.

CASE STUDY

At a large automotive manuacturing plant, an energy teamconsisting o volunteers, mostly union labor rom the shopfloor, was led by an energy coordinator. Te first step ininitial mission was to reduce energy waste by targeting airleaks. Baseline data was gathered during normal productionand during a Christmas shutdown. From this inormation,a leak reduction program was developed and approved bymanagement, based upon estimated potential savings.

In the next step, leaks were identified and tagged or repair.Te results o the efforts were published each weekend, and

news of the success spread through the plant. Each team mem-ber was given a red Energy Team jacket. ey developed a

procedure or all employees to report leaks and be rewarded ortheir eorts. Bulletin leak boards were installed, and progress

in fixing leaks was posted. Messages were displayed on Vmonitors throughout the plant. Soon, everyone was aware andinvolved in the program, which produced a cultural change.

Te initial baseline showed a compressed air usage rateaveraging almost 12,260 cm. Within our years, this haddropped to 6,250 cm, saving approximately $2,000 perday. Te reduced rate remained relatively constant with theincreased awareness.

R #2 REDUCE PRESSURE AT POINTS OF USE

Many plants use a single common

compressed-air distribution system tosupply a variety o end-use applica-tions. When this is the case, the totalsystem must maintain a pressure high

enough to satisy the equipment having the highest pressurerequirement, even though the majority of the equipment might

require a much lower pressure. Tis higher pressure causesall the unregulated compressed air equipment in the plant touse more air, and also increases the power required by the aircompressor by 1% or every 2 psig in higher pressure.

When speciying new equipment requiring compressed air,its ofen possible to speciy a lower required operating pressure,

such as 70 psi, to minimize the system pressure requirements.It also may be possible to retrofit existing equipment or lowerpressure operation by replacing less-than-optimal components.On existing equipment, once retrofits are done, it is ofen pos-sible to progressively reduce the main air supply pressure todetermine the minimum pressure at which the equipment willoperate efficiently. For equipment that cant be optimized, it maythen be possible to segregate equipment onto a separate system,

so the majority of the compressed air system can be operated at

a lower pressure. Te portion requiring a higher pressure couldthen be supplied by a dedicated-compressor system or by abooster compressor drawing air rom the lower pressure system.

RELATING DISCHARGE PRESSURE

TO ENERGY CONSUMPTION

For systems in the 100 psig range, for every 2 psi

increase in discharge pressure, energy consumptionwill increase by approximately 1% at full output flow

(check performance curves for centrifugal and two-

stage lubricant-injected rotary screw compressors).

There is also another penalty for higher-than-needed

pressure. Raising the compressor discharge pressure in-

creases the demand of every unregulated usage, includ-

ing leaks and open blowing. Although it varies by plant,

unregulated usage is commonly as high as 30-50% of

air demand. For systems in the 100 psig range with

30-50% unregulated usage, a 2 psi increase in header

pressure will increase energy consumption by about

another 0.6-1.0% because of the additional unregu-lated air being consumed (in the worst-case scenario,

the extra flow could cause another compressor to start).

The combined effect results in a total increase in

energy consumption of about 1.6-2% for every 2 psi

increase in discharge pressure for a system in the

100 psig range with 30-50% unregulated usage.

PRODUCTION/COMPRESSED AIR
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Te pressure drop across air treatment equipment at the enduse must also be taken into account and should be monitoredto prevent a orced increase in compressor discharge pressureor an unintended decrease in pressure at the points o use.

Filters, in particular, should have element pressure drop moni-tored and changed regularly.

A major consideration is how accurately the minimum

desired pressure at the point o use can be maintained.Fluctuating system pressure can cause production qualityproblems, including torque variations o tools and incon-sistent paint spray. Pressures that are higher than necessarycan be caused by compressor control problems and, whenthey occur, can boost end-use air flows by causing artificialdemand. Artificial demand occurs because unregulated enduses will use more air at higher pressure.

CASE STUDYA lumber mill sorting machine had various kicker and lifercylinders installed to move the lumber into position andperorm additional lifing operations. It was ound that mosto the machine actuation cylinders required a power strokein one direction only and the unloaded return stroke neededmuch less power. Pneumatic circuitry was installed that sup-plied 100 psi air to the cylinders on the power stroke, but only40 psi air was used or the retract stroke. Tis operation wasound to use 60% less air on each retract stroke and 30% lesscompressed air overall.

R #3 REDUCE PRESSURE AT SOURCE (COMPRESSORS)

Real savings will not be realizedunless the discharge pressure at thecompressors can be reduced. A rule

o thumb commonly used or a typi-cal 100 psi compressed air system is

that the energy requirement o the compressors is reducedby 1% or every 2 psi decrease in system pressure. In somecases, due to undersized piping, some o these savings maybe lost because o increased velocity at the lower pressure,through dryers, filters, and piping.

Some air compressors are purchased with a pressurerating substantially higher than required at the pointso use. Running the compressors at an elevated pressuremay compensate or pressure drop across ilters and dry-ers and negate any restriction in the dis tribution piping

and valves. However, to save energy the control pressureset points and their operating band should be set a s lowas is practicable, not to the maximum allowable.

Te pressure drop across individual components andsections o the distribution system should be measured todetermine i they are within acceptable limits. Tese pres-sure drops orce compressor discharge pressures higherto compensate. Corrective action should be taken whereindicated. Tis may include changing types or size o pipes,

valves, dryers or filters. Te pressure drop rom the com-pressor discharge to the points o use should not exceed10% o the compressor discharge pressure.

Changing a main filter element at a pressure differentialo 6 psid instead o the typical 10 psid will save energy costsduring the time the drop would have been above 6 psid.

Tis change would save about 1% i it results in lowercompressor discharge pressure.

The Compressed Air Challenge (www.compresse-

dairchallenge.org) is a voluntary collaboration of

manufacturers, distributors, and their associations;

industrial users; facility operating personnel and their

associations; consultants; state research and develop-

ment agencies; energy efficiency organizations; and

utilities. The mission of the CAC is to be the lead-

ing source of product-neutral compressed air system

information and education, enabling end users to

take a systems approach, leading to improved ef-

ficiency and production and increased net profits.

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Tis is the second of a multi-part series of articles on installing, operating, and maintaining an efficient compressed air system,

written by members of Compressed Air Challenge (www.compressedairchallenge.org). Te first three Rs appeared previously.

Educational institutions have realized the need oremphasizing the basics, sometimes reerred to as the three Rs reading, riting and rithmetic. Tere are also several basicRs to be kept in mind or an efficient compressed air system.

R #4 REDUCE SYSTEM PRESSURE

FLUCTUATIONS USING ADEQUATELY

SIZED AND LOCATED AIR RECEIVERS

AND CONTROLS

Systems with inadequately sized receivers and distributionpiping can experience significant fluctuations in systempressures and can have problems with compressor cyclingthat waste considerable energy.

Reciprocating air compressor pressure pulsations canbe dampened by an air receiver close to its discharge. Tereceiver also shields the compressor and the system rom

fluctuations in demand or compressed air that momentarilyexceeds the capacity o the compressor. Other compressortypes also benefit rom a receiver close to the discharge.

An air receiver placed beore a compressed air dryer canprovide effective radiant cooling and promote the allout ocondensate and entrained lubricant. However, since the dryeris normally sized to match the output rom the compressor, ademand or compressed air in excess o the compressor anddryer rating will result in the dryer being overloaded by airflow rom the ully loaded compressor and the air stored inthe receiver. An air receiver placed afer the dryer will containalready dried air; during peak demands the dryer sees only

the output rom the compressor, so is never overloaded.

Sizing o the primary air receiver is extremely importantand can affect the choice o compressor capacity controlsystem. Figure 1 shows the effect o different receiver sizeson an installation with a lubricated rotary screw compres-

sor having a load/unload capacity control system. Tecalculations include the time necessary to blow down thesump/separator vessel to prevent oaming o the lubricant(40 s) and the time to re-pressurize the vessel (3 s). A ullyunloaded bhp o 25% is used, but this can vary dependingon the compressor cooling method and the condition o thecompressor unloading controls. Receiver capacity is shownper unit o compressor capacity.

One can see on the graph that a compressor with only 1gal o storage per cm output consumes more than 80% oits ull load power when loaded at only 40% capacity. Tesame unit with 10 gal o storage per cm would consume a

much lower 60% of full load at the same ow. Unless thereis ample receiver capacity and/or very light load demand,load/unload may not be the most efficient means o capacitycontrol. With multiple ully loaded compressors, and onlyone part loaded unit, the required receiver capacity relates tothe capacity o the partly loaded (trim) compressor, not thetotal capacity o all the compressors.

A properly sized receiver close to the compressors is es-sential but might not be sufficient to prevent erratic systempressures. Intermittent demands or relatively large volumeso compressed air can draw down the pressure o the wholedistribution system in a short period o time, causing prob-

lems or other applications requiring stable pressure.
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An air receiver located close to these points o use can pro-vide the required demand with stored air, which will preventthe large demand rom significantly affecting the overall systempressure. Tis allows more stable system pressure and moreresponse time to replenish the air receivers more efficiently.

Pressure/flow controls can be placed afer the primaryreceiver to maintain a stable downstream system pressurewithin +/- 1 psi. Because o the accurate pressure, the effecton product quality alone is well worth the initial investment.Te constant system pressure also allows lowering o pres-sure at points o use and at the compressors, with consider-able reduction in energy requirements. In some cases, acompressor can be shut down.

CASE STUDY

A mineral processing acility was experiencing inefficientcompressor operation because o a poor compressor control

strategy. Te acility had one large base 350 hp and twotrim 150-hp compressors installed, but only 400 gal o mainsystem storage. Because the storage was inadequate, the trimcompressors could not be run in the more efficient load/un-load mode. Larger storage o 4,000 gal was installed, whichresulted in better compressor control; however, when theplant maintenance personnel tried to lower the pressure,some problems were experienced at a baghouse that neededa large pulse o air at a high pressure to work properly.Investigation revealed low pressure at the baghouse mani-old was caused by a high flow o air requirement passingthrough small baghouse eed lines afer each cleaning pulse.

Local storage o 60 gal was added at the baghouse manioldthat was protected with a check valve and restricted througha needle valve. Tis restriction reduced the flow so the newstorage tank charged slowly, but still allowed a large pulse oair to flow to each cleaning pulse. Te local storage providedenough air that the baghouse could operate at 60 psi, allow-ing the main system pressure to be turned down.

R #5 REDUCE NUMBER OF PART-LOADED

COMPRESSORS TO ONLY ONE

Te specific power (kW/100 cm)o a compressor increases at partial

loads, regardless o the type ocapacity control system used. In thepast, water-cooled, double-acting re-

ciprocating compressors were readily available and generallyhad discrete steps o capacity output that achieved very goodenergy turndown at partial loads. Inlet valve unloadingallows steps o 100%, 50%, and 0%. Te addition o clear-ance pockets can provide additional steps o 75% and 25%.Tis offered the best mode o trimming overall capacity withother compressor types operating at ull capacity. Newer,more modern variable-speed drive (VSD) compressors arenow available that have turndown ranges equal to or better

than multistage reciprocating compressors, making thesecompressor a good choice or trim duty.

Where oil-injected rotary screw compressors are

operating in parallel, each with inlet valve modulation,it is very ineicient to have all o them modulating atthe same t ime. Controls should be set to have all but onecompressor on load/unload control, with the set points

arranged so that only the one compressor at a time wil ltrim. his provides the most eicient control mode. Caremust be taken to ensure t hat the compressors on load/un-load control are capable o ull capacity up to the unloadset point. he compressors on load/unload control alsoshould have a timer to stop the compressor when it hasbeen running unloaded or a period o time, usually 10min, to avoid too-requent starts, but keep the compres-sor armed or automatic start i the compressor is needed.

Centriugal air compressors are best used as base-loadcompressors, with another type to accommodate the loadswings. Te use o inlet guide vanes is more efficient than an

inlet butterfly valve on centriugal compressors, but provi-sion is still needed to start blowing off air at partial loads toavoid surge. Centriugal compressors operating in dischargebypass control, blowing excess capacity to atmosphere toavoid surge, waste a significant amount o energy. Wherepossible, unloading the compressor is preerred.

e majority of new compressors of all types are equipped

with microprocessor controls, which can be arranged ormore precise monitoring and control. Most modern controlsreadily allow sequencing and can be tied easily in with cen-tralized plant control systems. Tey also allow better track-ing o required maintenance and more energy savings.

CASE STUDY

A large aerospace manuacturer had a system o three350-hp, 1,500-cm centriugal compressors eeding itslarge aircrat parts plant. he plant had typical loads av-eraging 750 cm during the day and 350 cm during nightand weekend operation. Due to a very high low when theplant illed its autoclaves or parts, curing 3,000 cm ocompressed air or 10 to 15 min was required. Fill opera-tions happened less than 10% o the time during the mainshift. Unfortunately, because of the characteristics of the

compressors, this il l required two running compressors

all the t ime because compressor ailures occurred whenthey tried shutting down one o the compressors on au-tomatic start. he compressors would not run reliably inload/unload mode, so the units ran in ineicient modu-lation mode with blow-o. Operation in th is controlmode made the system speciic power 55 kW/100 cm, anextremely ineicient level.

Te plant replaced these compressors with a system oour rotary screw compressors, two o which used VSDtechnology. Te system used an efficient master compres-sor controller that matches the compressors to the load.Te peak loads are now being supplied by a high-pressure

storage system. Te new specific power or the system is 21kW/100 cfm. e project is saving 2 ,380,000 kWh/year.



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R #6 REMOVE INAPPROPRIATE

APPLICATIONS

In general, it takes the equivalento 7-8 hp at the air compressor toproduce 1 hp o shaf output at a

compressed-air-powered tool. At best, this means the use ocompressed air or end uses is about 10-15% efficient, andmuch less i leakage is included. Because o this inefficientconversion o energy, its expensive to use compressed air in-appropriately or uses that could better be powered by some

other energy source.Tis applies to end uses that use high-pressure air or a

low-pressure requirement. Te energy used to compress airis not recovered when passed through a pressure regulatoror outputting a lower pressure. Where the pressure has tobe reduced below 80% o the compressor discharge pressureor a specific application, the application should be reviewedor an alternative air supply at a reduced pressure.

Equipment requiring air at 22 psi or less should be sup -plied by a blower rather than rom a compressed air line.Tis includes air lances, agitation, blow guns, mixing, and

pneumatic conveying. Blowers also may be used or regen-eration o desiccant type dryers.

Fans, rather than vortex tubes, should be used or coolingelectrical cabinets.

A vacuum pump should be used rather than a compressedair venturi tube.

An extensive list o potentially inappropriate applicationscan be ound at www.compressedairchallenge.org/library/tipsheets/tipsheet02.pd.

CASE STUDYA large cabinetry plant was using compressed-air-powered

vortex coolers on various electrical control panels to preventoverheating. Each cooler consumed 20 cfm continuously 24/7

at about 100 psi. An industrial engineer studied the coolers andound they were consuming the equivalent o 5 kW/cooler cost-ing $3,140/year to operate. Te engineer replaced the com-pressed-air-powered coolers with thermostatically controlledrerigerant-style cabinet coolers that had the equivalent Btucapacity cooling, yet consumed only 0.5 kW, costing $135/yearto run. Simple payback on the conversion was 1.3 years.

1 gal/cfm

3 gal/cfm

5 gal/cfm

10 gal/cfm

Ideal Compressor

120

100

80

60

40

20

0

0 20 40 60 80 100 120

Percent Capacity

PercentkWI

nput

Figure 1. With multiple fully loaded compressors, and only one part loaded unit, the required receiver capacity relates to the capacity of

the partly loaded compressor.

AVERAGE KW VS. AVERAGE CAPACITY WITH LOAD/UNLOAD CAPACITY CONTROL

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R #7 REDUCE SYSTEM PRESSURE DROP LOSSES WITH

PROPERLY SIZED PIPING, VALVES

Many existing compressed airsystems werent designed or their

present states, but simply grew tomeet plant expansion needs, result-ing in systems that arent adequate-

ly sized or current demand. Many distribution pipingsystems are based upon the size o the discharge connec-tion at the compressor and may be totally inadequate orthe flow rate and length o pipe.

Air velocity at any point in the distribution piping shouldnot exceed 50 f/s (ps). o avoid moisture being carried be-yond drainage drop legs in main distribution lines, branchlines having an air velocity o 50 ps shouldnt exceed 50 f inlength. Hoses and their connections ofen are sized inad-

equately, causing excessive pressure drop.Te operating pressure drop between the air compressor

discharge and the points o use shouldnt exceed 10% o thecompressors discharge pressure. A loop-type distributionsystem is recommended. Gate valves are preerred or theirminimal pressure drop.

Afercoolers, dryers, and filters should be sized or the ullcapacity o the compressors, and pressure drop across eachitem should be minimal. Particulate and coalescing-typefilter pressure drop should be monitored regularly, and ele-ments should be replaced beore the pressure drop becomesexcessive with substantial energy loss. Early element replace-ment costs can be recovered quickly by energy savings.

CASE STUDYA fiberglass parts manuacturer was having productionissues with some air-powered cutters used to ree thefiberglass parts rom their molds. ool perormance wasadequate at the start o the cut, but the production rate ellsteadily in a short period o time, especially i more than onecutter was used at the same time.

An air auditor studied how the tools were connected tothe system. He ound that the plant designers preerred touse long 50-f hose reels to provide compressed air to thetools. Tese reels were connected to the main distributionsystem using quick-connect couplings at the input to the reel

and at the tool.Te tools were rated to provide ull perormance at a

pressure o 90 psi at the tool. o test the actual pressure,the auditor made up a pressure test gauge so the tool couldbe connected in series. Te pressure at the tool with no airflowing measured about 110 psi. When the trigger o one othe cutters was pulled, the pressure ell to 55 psi, much lowerthan the tools needed. Te pressure at the tool was improvedto 90 psi through optimization o the connectors and hoseseeding the tool by removing component, shortening hoses,and increasing the size o the components.



manufacturers, distributors, and their associations;

industrial users; facility operating personnel and their








IN GENERAL, IT TAKES THEEQUIVALENT OF 7-8 HP AT THEAIR COMPRESSOR TO PRODUCE

1 HP OF SHAFT OUTPUT AT ACOMPRESSED-AIR-POWERED TOOL.



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Tis is the third of a multi-part series of articles on installing, operating, and maintaining an efficient compressed air system,

written by members of Compressed Air Challenge (www.compressedairchallenge.org). Te first seven Rs appeared previously.

Educational institutions have realized the need oremphasizing the basics, sometimes reerred to as the threeRs reading, riting and rithmetic. Tere are also severalbasic Rs to be kept in mind or an efficient compressed air

system. Te first seven Rs were covered in parts I and II othis series. Tey include:1. reduce leakage losses2. reduce pressure at points o use3. reduce pressure at source (compressors)4. reduce system pressure fluctuations using adequately

sized and located air receivers and controls5. reduce number o partially loaded compressors to only

one6. remove inappropriate applications7. reduce system pressure drop losses with properly sized

piping and valves.

R #8 REMOVE MOISTURE CONTENT OF COMPRESSED AIR

WITH THE PROPER TYPE AND SIZE OF DRYERS

Different applications require di-erent levels o pressure dew point.Air should be dried only to the levelrequired by a specific application. Sys-tems ofen have a dryer immediately

afer the compressor, drying all o the compressed air toa level not needed at many o the points o use. Tis is anunnecessary use of energy. Each application should be re-

viewed to determine the amount o drying necessary. Very

ofen a rerigerant-type dryer having a pressure dew point

of 38 F is adequate for the majority of applications, al-though consideration must be given to distribution pipingand drains, which may be exposed to temperatures belowreezing. Only the air going to an application requiring a

lower pressure dew point should receive urther treatment.Te location o a dryer relative to an air receiver is debat-

able. An air receiver between the compressor and the dryermay provide some radiant cooling and separation o con-densate and lubricant. However, an intermittent demand orcompressed air in excess o the compressor and dryer ratingwill result in the dryer being overloaded and an increase inthe pressure dew point. Location o the air receiver afer thedryer ensures that the air flow through the dryer doesntexceed its rating and dry air is stored in the receiver to meetany intermittent demand. In some systems, a receiver atboth locations can be worth the investment.

Te pressure drop through the dryer also should be de-termined and monitored as the resulting back pressure cancause the air compressors to cycle more requently, resultingin less efficient operation.

A rerigerant-type dryer may not require any filtrationbeore or afer it, whereas a desiccant-type dryer requires acoalescing filter beore it to protect the filter bed and a par-ticulate filter afer it to stop carryover o desiccant fines. Tesefilters cause additional pressure drop and must be main-tained. Desiccant-type dryers also require the use o purgeair or regeneration, and the quantity o purge air must beconsidered in sizing o the air compressors. Dew point control

systems and other strategies are available to minimize
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the amount o purge air needed. In some cases, a blower or avacuum purge system can be used more economically.

CASE STUDY

A tire shop had a small compressed air load made up othe tools and equipment required to service automobiles,large trucks, and tractors. One compressed air line wentoutdoors to eed a tire-filling station. A main desiccant air

dryer removed moisture rom all the compressed air in theshop to a level o -40, so the line would not reeze in wintermonths. An air audit at the shop showed that, whi le theaverage compressed air load in the acility was only 9 cm,the compressor actually produced an average o 28 cm.An investigation showed that the uncontrolled heatless airdryer installed in the shop was consuming an average o19 cm or 68% o the total output o the compressor. A re-rigerant air dryer was purchased and a small point-o-usezero purge air dryer was instal led or the outdoor supplyline. Te reduction in compressed air demand saved 70% incompressed air electrical costs.

R #9 REMOVE CONDENSATE WITHOUT LOSS

OF COMPRESSED AIR

Various means are used to drain offcondensate rom dryers, air receiv-ers, filters, and header drop legs. Teamount o condensate will vary withgeographic location and atmospheric

conditions o temperature and relative humidity. Draintraps should be sized or the anticipated rate o accumu-lated condensate and chosen or the specific location andanticipated contamination by lubricants being used.

Te relatively common practice o leaving a manual drainvalve cracked open shouldnt be tolerated as it wastescompressed air. For all types o drain traps, bypass piping isrecommended to acilitate proper maintenance.

Float-type drain traps. Te mechanical nature o float-type devices combined with the contaminants present incondensate make these devices an ongoing maintenanceitem, ofen neglected. Te float is connected by linkage toa drain va lve, which opens when an upper-level setting isreached and closes when the drain is emptied. Te float de-

vice varies rom a simple bal l to an inverted bucket, but thebasic principle is the same. An adequately sized drain valve

is essentia l or satisactory operation and to prevent block-

age. A float which sticks in the closed position wont allowcondensate to be drained, while a float which sticks in theopen position will allow the costly loss o compressed air.

Electrically operated solenoid valves (time cycle blow-

down).A solenoid-operated drain valve has a timing devicethat can be set to open or a specified time and at specifiedintervals. Again, the size o the valve and any associated ori-

fices must be adequate to prevent blockage. Te valve is setto operate without reerence to the presence o condensateor lack o it. Te period during which the valve is open maynot be long enough or adequate drainage o the amount oaccumulated condensate. On the other hand, the valve canoperate even when little or no condensate is present, result-ing in the expensive loss o compressed air.

No air loss or zero air loss drain valves. Tese use amagnetic reed switch or a capacitance device to detect thelevel o condensate present and operate only when drainageis called or. When an upper-level inductance sensor detects

liquid, the microprocessor opens a solenoid. A lower-levelinductance sensor signals or the drain to be closed.

Its vital to mai ntain traps and drains in good op-erating condition. I the drains and traps are clogged,condensate will ill vessels and pipes in a short period otime and be carried over into the system in the orm oliquid water, and may: cause corrosion and deposits in the air receiver

prematurely exhaust the capacities of pre-lters and desic-cant dryers

overload refrigerant-type dryers

cause moisture accumulation in the system piping, result-ing in corrosion

cause malfunction of air-operated valves, making opera-tion sluggish or erratic

wash away lubricants from operating cylinders of air-oper-ated valves or other similar equipment

cause some of the lubricants used on solenoid valve O-

rings to become sticky or gummed up, causing the solenoidvalve to become inoperable.

Also, some o the system piping may be installed outdoorsand exposed to varying ambient temperatures. Accumulatedwater may reeze during winter and cause damage to piping

and instruments.



11/1211

CASE STUDY

A timer drain at a pharmaceutical company was set todrain the air dryer water separator at regular intervalsto avoid water carryover. Te backup compressor eed-ing the air dryer had a sophisticated control designed to

sense rapid changes in pressure and start the compressorin response to ensure the compressor could rapidly loadbeore the pressure ell below its load set point. Te timerdrain had a large drain orifice that consumed a significantamount o air, enough to cause a change in pressure whenit drained. Due to this pressure fluctuation, the compressorwould start but not load. Te timer drain requency wassuch that the compressor constantly ran unloaded con-suming 90,000 kWh/year.

R #10 REDUCE DOWNTIME THROUGH

PREVENTIVE MAINTENANCE

Prevention is better than cure.Neglect can lead to costly downtimeo production equipment and moreextensive repairs. Manuacturersrecommended maintenance items

should be required, documented, and reviewed regularly orthe development o any trends.

Te use o compressor synthetic lubricants, stated to begood or 8,000 hours o operation, doesnt mean the as-sociated lubricant filter and air-lubricant separator also aregood or the same period. Te pressure drop across lubricantfilters and separators should be monitored regularly.

Records may indicate a normal interval betweenchanges, which may then be planned. Some compressormicroprocessors will signal required maintenance, andthis should not be ignored.

Automatic condensate drains must be checked regularlyto ensure satisactory operation.

CASE STUDY

A oundry making railway wheels couldnt keep the pressureup in the plant, even with all our o the compressors run-ning. Te liquid coolers in their compressors had become sodirty that the compressors couldnt run at ull load so had

to be modulated down to lower output. Te overly hot airproduced by the compressors and dirty dryer coolers causedthe air dryers to constantly trip off. Te plant loading hadincreased to a point where low pressure was a constant prob-lem. Te site was orced to rent and operate three expensivediesel compressors just to keep up.

Investigation revealed that inadequate management hadallowed the leak level to increase to a point where 1,100 cmo compressed air was being used on the weekend, even withno production. Poor maintenance practices had allowed thecompressor set points to drif so badly that one compressorwasnt even loading when pressure was low. Another had

developed a problem that kept its inlet valve closed, greatlyreducing its output.

Repairs, replacements, and adjustments were done to

coolers, cooling water quality, compressor controls, andleakage levels, including finding and fixing a 550 cm leak ina baghouse. Annual savings were measured at $90,000/year,not including diesel compressor uel and rental costs. Teplant is now running on three compressors.

R #11 RECORD SYSTEM DATA AND MAINTENANCE

All maintenance items should berecorded and the records analyzed,

so that timely preventive measurescan be established. In addition, re-cords should be kept o all operating

pressures before and aer major components and at strategic

points in the system. Tese will indicate potential problemareas requiring corrective action.

R #12 REVIEW AIR USAGE PATTERNS REGULARLY

Recording operating pressures at stra-tegic points throughout the systemcan reveal changes in usage but maynot adequately indicate the rate o

change o pressure due to changes indemand. Data logging can help in this area.

Over time, new production machines may be added, whileothers may be eliminated. Te person responsible or thecompressed air supply needs to be kept inormed o suchchanges, which may require upgrades to the compressed airsystem, including plant expansion, rather than waiting untila problem develops. Low pressure at a point o use may notrequire additional compressor capacity; the problem may bedue to fluctuating demand at another point o use, and theproblem could be solved by the addition o a secondary airreceiver close to that application.



manufacturers, distributors, and their associations;industrial users; facility operating personnel and their










12/12

R #13 RECOVER HEAT

e majority of rotary air compres-

sor packages are air-cooled, and itsestimated that, o the total power,80% results in heat to the oil coolerand an additional 13% to the air

afercooler. Tis provides a substantial potential or heatrecovery.

Te atmospheric air blown across radiator-type coolers canbe used or space heating o plants in cold weather conditions.An additional an may be needed to supply the necessarypressure head or ducting and distribution o this air.

In some water-cooled compressor applications, waterheating has been accomplished or use in the plant.

CASE STUDY

A small company reconditions propane bottles or resale atvarious depots throughout its territory. Te plant uses a 25-hpair compressor that produces the equivalent o about 15 kWo heat in average conditions. During reconditioning, thepropane bottles are painted and dry while hanging on an overhead conveyor. Te compressor heat is captured and redirect-ed to the propane bottles to assist in heating the make-up airand drying the paint. Te remainder o the heat is redirectedto the acility production areas to help to displace buildingheat. Te building has all electric heating so the compressor

heat displaces the equivalent kW loading. Estimated savingsare $2,500/year in electric heating costs.

R #14 REDUCE ENERGY COSTS (RETURN ON INVESTMENT

AND COST OF OPERATION)

e whole objective of e Com-pressed Air Challenge is to reducethe energy consumed by compressedair systems. Implementation o therecommendations can result in some

compressors being shut down and used or standby. Teresulting savings in the cost o operation go right to the bot-

tom line o a companys financial statement.In addition, the right amount o air at the right pressure

and o the right quality will enhance product quality, reduc-ing deects, scrap, and warranty costs. Customer satisactionwill be improved.

Following the 14 Rs results in an efficient compressed airsystem that pays dividends.

This article is based on a paper by

David M. McCulloch, retired, and modified byFrank Moskowitz, Draw Professional Services, and

Ron Marshall, Manitoba Hydro.

Moskowitz is a Compressed Air Chal-

lenge instructor for the Fundamen-

tals and Advanced levels of training,

an AIRMaster+ instructor and a De-

partment of Energy (energy savings)

expert on compressed air systems.

Hes also vice chair for ASME Standard EA-4-2010,

Energy Assessment for Compressed Air Systems,

and is a member of International Standards Organiza-

tion (ISO) technical committee for air compressors and

compressed air systems energy management.

Contact him at [email protected].

Marshall is a certified engineering

technologist in the province of Mani-

toba and has received certification

as an energy manager, demand side

management and measurement and

verification professional through the

Association of Energy Engineers. He was the first Cana-

dian participant to qualify as a DOE AIRMaster+ special-

ist and is involved as a member of Compressed Air Chal-

lenges Project Development and Marketing Committee.

Marshall is an industrial systems officer for Manitoba

Hydros Customer Engineering Services Department.

Contact him at [email protected].

mailto:[email protected]:[email protected]:[email protected]:[email protected]

14rs compressed air

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