Compressed Air (The Invisible Thief)

Compressed air is probably going the most costly utility in your plant or store. To guage the power effectivity of your system, you will need to first look at the various components affecting the effectivity.

4 of those components can be: 1. The right compressor sort choice. 2. The compressor management system. 3. The right air after therapy choice. 4. Decide the extent of your air leaks.

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1. The right compressor sort choice.

There are a big number of compressor varieties obtainable to be used in trade as we speak. Within the household of displacement compressors, there are:

· Reciprocating (piston sort)

· Rotary screw

· Rotary vane

· ‘Roots’ sort blowers.

Within the household of dynamic compressors there are:

· Radial

· Overhung pinion design

· Axial Movement

· Ejector.

Every sort of compressor has a spread of purposes the place it’s best suited, in relation to last stress, air high quality and quantity. Each may have a particular management system based mostly upon that utility. It’s usually accepted that multi-stage compressors are extra energy environment friendly than single-stage compressors, nonetheless, preliminary buy price for multi-stage compressors is larger. The 2 commonest causes for multistaging compressors are:

· To succeed in the next stress

· To extend power effectivity

After figuring out which compressor design would finest fit your necessities, the subsequent query is “which management system is suitable for my utility”? The best way this management system is used will decide the ability effectivity of your compressors, however not your compressed air ‘system’. We’ll use the commonest industrial compressor utilized in trade as we speak as the topic of examination. That’s the rotary screw sort. These kinds of compressors can be found in single-stage and two-stage variations, oil-free and oil injected varieties We should settle for that two stage compressors are extra thermally environment friendly, as a number of the warmth of compression is eliminated half approach via the compression cycle.

2. The Compressor Management System

There are 5 primary management strategies for these kind of compressors:

1. Load/No-Load

2. Modulation (inlet throttle management)

3. Mixture of Load/No-load and modulation

4. Rotor size adjustment (Spiral Valve, Flip Valve or Poppit Inlet Valve)

5. Variable Pace Drive/Variable Frequency Drive.

Load/no-load management is the commonest capability management obtainable, as additionally it is used extensively on reciprocating compressors. This management permits the compressor to construct stress within the community till a pre-determined stress restrict has been reached within the compressed air discharge pipe (100 psig). Bear in mind, the one option to obtain a constructive stress in a piping system of any form is to provide extra compressed air than you eat.

One Load/No-load situation can be: The air demand within the plant is lower than the availability obtainable from the compressor, and the plant air community has risen to a 100-psig stage. That is the utmost setting on the compressor stress change. The stress change senses this backpressure and permits the compressor to unload. Which means that the compressor will not be delivering any compressed air to the system. This doesn’t imply that the compressor has shut down. The compressor will run for a predetermined period of time in an un-loaded state (set on a timer) whereas it waits for the plant system air stress to drop to some extent. As soon as the system stress drops to the low stress set level on the stress change, (e.g. 90 psig) the compressor would begin to load, and once more begin supplying compressed air to the piping community Within the unloaded state, the compressor consumes between 15-25% of the put in break horsepower (BHP).

The principle function of operating the compressor unloaded is to forestall the compressor motor from ranging from a locked rotor (stopped) beginning place every time the community requires extra air. That might have a detrimental impact on the motor within the type of temperature improve. With bigger motors, the motor producers have suggestions as to the variety of “chilly begins” which can be acceptable. Locked rotor beginning present is far better and far more costly than the present that’s required by a motor which is already turning (operating unloaded) In abstract, the compressor consumes both the complete load ranking of the electrical motor whereas at full load, and 15-25% of the complete load ranking at no load, utilizing a standard load/no-load sort management. One other think about operating unloaded is the low part-load motor efficiencies whereas the compressor is in an unloaded state. Each time the compressor reduces the sump stress whereas it’s operating unloaded, it takes extra HP to re-pressurize the tank again to working stress. The extra cycles the compressor goes via, the extra power penalty there’s. To keep away from extreme biking, the producers suggest that a big air storage receiver tank be put in downstream of the compressor.

Identical situation with Modulation management: The air demand within the plant is lower than the availability obtainable from the compressor, and the plant air community has began to rise to the 100-psig stage. Because the stress rises, the modulation management valve permits a circulate of air to an inlet throttling butterfly valve. This is also a ‘poppet’ sort valve as effectively. The stress sign controls the diploma of closure of the inlet valve, lowering the circulate of air into the compressor, in an try to match the air supply to the demand. Which means that the compressor will not be delivering as a lot compressed air to the system. The compressor will run this manner till the demand drops beneath the bottom flip down proportion allowed by the producer after which flip off. As soon as the system stress drops to the low stress set level on the stress change, (e.g. 90 psig) the compressor would begin to load, and once more begin supplying compressed air to the system piping community with the modulation valve absolutely opened. There are drawbacks to this sort of management system as effectively. When you have got a hard and fast stress ratio compressor, which is about to a particular discharge stress, the inlet absolute stress (psia) may have a direct influence on the stress ratio and finally the HP/CFM ratio.

By choking off the inlet to the compressor you have got created a destructive (vacuum) stress underneath the inlet valve. To compensate for this destructive stress, you will need to eat extra Horse Energy relative to the delivered CFM. Subsequently, working a modulation sort compressor at a excessive diploma of flip down ends in an inefficient manufacturing of compressed air. Essentially the most environment friendly option to run a constructive displacement compressor is at full load whatever the management strategies. In nearly all conditions the demand for compressed air fluctuates. That’s to say, as air consuming tools begin and cease, the demand will increase or decreases. To satisfy this fluctuating demand with a management system that gives the least energy penalty doable, there are three firms which have developed comparable management methods to attain this.

These management methods are known as ‘Flip Valve’ or ‘Spiral Valve’ and “Poppit Inlet Management”. They work primarily the identical approach, and provide the identical kind of financial savings. What is actually taking place with the ‘Spiral Valve’ and “Flip Valve” configuration is that as a valve is turned, ports within the compressor housing are opened to environment on the inlet aspect of the screws, successfully shortening the size of the rotors. On this place the compressor produces much less quantity with out creating the destructive stress on the inlet and consumes a decrease kilowatt draw.

With the “Poppit Valve” configuration, inlet port orifices are opened to environment successfully engaging in the identical shortening of the rotors.

There’s a relationship between energy consumption at partial load and at full load on every of the completely different management strategies. You will need to observe that the road usually representing On-line/Offline and Begin/Cease on conventionally provided graphs is often proven as a serrated line. This line needs to be a strong line as there is no such thing as a doable partial load air supply with these management strategies. Once more, we have now to recollect, there’s a energy penalty while you run an electrical motor at partial load. We should at all times consider the proportion of partial loading we are able to settle for and search options when that restrict is surpassed.

As to Variable Pace or Variable Frequency drive capability management, this might be mentioned in a future article as they’re newer management strategies than those beforehand described and apply to considerably fewer current methods. Additionally not mentioned right here is the Reciprocating compressor’s variable cylinder pocket management methodology.

Whatever the management methodology chosen, the final suggestion from the completely different producers is that an air storage receiver tank needs to be positioned downstream of the compressor to clean out the load cycles of the compressor.

The right air after therapy choice.

The subsequent consideration in evaluating your air system is the collection of an power environment friendly air dryer and filter system. Why is that this necessary?

1. Moisture in instrument air methods will foul delicate shifting components.

2. Liquid water will wash off the lubricant in pneumatic parts, resulting in untimely put on.

3. In spray paint purposes, the water will trigger blistering of the paint and injury the completed product.

4. In some industries the place molten steel is available in contact with compressed air, any liquid moisture or oil within the air could be disastrous, resulting in critical harm, or demise.

5. In chilly climates, the place the temperature of the ambient air coming involved with the compressed air piping system could fall beneath 32 levels F., the pipe, or different parts may very well freeze because of the moisture within the system.

6. Moisture in compressed air piping results in corrosion. These flakes of rust could be carried downstream by the compressed air, and into a number of the valves and cylinders, blocking crucial orifices.

7. Pipe scale and rust inside pipes creates drag (stress drop), which have to be overcome by rising the stress on the compressor. Rising the stress on the compressor will improve the horsepower consumption and decrease the CFM delivered.The target is to have the least stress drop throughout the air system parts as doable

To start with, a coalescing sort of filter is required to take away the water vapor from the compressed air. This filter needs to be positioned as near the compressor after cooler’s moisture separator discharge as doable, as these coalescing sort filters are designed to take away vapors and aerosols, not liquid flows.

As soon as this therapy has been completed, the choice have to be made as to what diploma of dryness is required by the method.

There are three primary dryer varieties to select from. Every sort has benefits and downsides.

1. Absorption (Deliquescent Kind)

2. Condensation (Refrigeration Kind)

3. Adsorption (Desiccant Kind)

There are additionally a wide range of ‘level of use’ dryers which can be obtainable to deal with particular circumstances. One can be the membrane dryer, which is a novel low capability, low dewpoint dryer, with a excessive relative purge air requirement. One other can be the desiccant stuffed cartridge sort filter/dryer. Each are sometimes utilized in small circulate, crucial point-of-use purposes, requiring completely dry air.

From an power standpoint, every of those dryer varieties (aside from the deliquescent sort) consumes power both in direct electrical energy consumption or purge air consumption. The purge air requirement for these dryer varieties vary from 2% to 30% and this quantity is way from being free.

There are numerous methods to judge the power necessities of those dryer varieties, and lots of strategies of lowering the purge air necessities of some dryer varieties. All of those strategies needs to be investigated.


· Most air compressors ship 4-5 CFM/HP at 100 psig discharge stress

· Each 2 psig of stress will increase or decreases the ability draw of an air compressor by 1%

· Each 10° diploma F. change in inlet temperature impacts the effectivity about 1%. Colder temperature will increase and hotter temperatures lower effectivity.

· Energy prices for 1 HP for 3 shifts, 7 days per week (8760 hours) at 10 cents/kWh =about $654.00/yr.

· A 50 HP compressor rejects roughly 126,000 BTU/Hour. Roughly 119,000 BTU/Hour is recoverable.

Armed with this basic info, you’ll be able to estimate the price of producing the purge air necessities of the several types of dryers. Bear in mind to additionally add within the precise energy prices for parts corresponding to heaters and blowers or another energy necessities of the dryer.

Decide the extent of your air leaks

As to the topic of air leaks, this instance will inform the story very clearly:

If in case you have a 100 HP compressor, you’ll be able to assume that the capability might be about 4 CFM per put in HP, or 400 CFM at 100 PSIG as beforehand acknowledged.

The typical plant loses about 20-30% of their compressed air capability to air leaks. This is able to equate to 80 – 120 CFM @ 100 PSIG within the above instance.

Assume that the plant operates on a 2-shift, 16-hour day, 5- days per week, and 48 weeks per yr. This is able to add as much as 3840 HRS per yr.

Assume that your energy price can be $0.10 per kWh Subsequently: 80 CFM ÷ 4 CFM/HP = 20 HP 20 HP x.745 = 14.9 KW 14.9 kW x 3840 HRS x $0.10 = $7,449.60 / Yr That is equal to a leak of slightly below ¼” 120 CFM ÷ 4 CFM/HP = 30 HP 30 HP x.745 = 22.35 kW 22.35 kW x 3840 HRS x $0.10 = $8,582.40 / Yr. That is equal to a leak of simply over ¼”

Multiply the above percentages based mostly in your precise put in compressor H.P.

That is simply a sign of the price of your air leaks, and needs to be a adequate motivational device to justify their restore. Air audits can be found to confirm each the benchmark to your compressors and your air consumption via leakage. The value of this sort of audit can simply be justified via price financial savings, as soon as the leaks have been recognized and stuck.

One of many large issues is the state of the compressors. Some firms have a number of compressors all operating at partial load and a few not delivering any air in any respect. We at all times suggest that your compressor provider or restore facility examine your compressors previous to an audit.

To see extra details about audits, chances are you’ll wish to take a look at the next website online:


CFM/ Cubic Ft per Minute

SCFM / Commonplace Cubic Ft per Minute

FAD / Free Air Supply

HP/ Horse Energy

BHP/ Brake Horse Energy

kWh – Kilowatt Hour

PSIG/ Kilos per Sq. Inch (Gauge)

PSIA/ Kilos per Sq. Inch (Absolute)

As beforehand talked about. this text doesn’t tackle all the specifics of compressed air operation corresponding to variable pace drive management or poppet valve rotor size adjustment. It doesn’t go into depth on reciprocating compressors or dynamic compressors, nor does it tackle a number of driver choices corresponding to steam turbine drive or engine drivers. We’ve got simply touched somewhat on a number of the commonest points confronted by end-users of compressed air tools.

The data on this article is supposed as an summary of the fundamentals and is on the market within the public area, and has been for a few years. The data introduced is compiled in a logical format from many alternative sources and isn’t meant for particular compressor choice or system design.

For particular points with current tools onsite, please contact your native compressed air provider of alternative. For particular discussions on many of those points chances are you’ll contact: Michael J. Morel

Morel Consultants Firm

Source by Michael J Morel

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