Is compressed air so cheap? : 2/1/2016




Simplified Energy savings


In our last article, we discussed about ensuring 24x7 drinking water to all citizens of a country. In this article we will talk about one more important utility in our life - The Air ! Air is as important for industries as it is important for comman man.  Compressed air is one of the important utilities in most of the industries. Let’s see how we can best utilize this resource efficiently & what benefits can we get by doing so.

What is Compressed Air?

Compressed air is a form of stored energy that is used to operate machinery, equipment, or processes. Compressed air is used in most manufacturing and some service industries, often where it is impractical, expensive or hazardous to use electrical energy directly to supply power to tools and equipment.

Powered by electricity, a typical air compressor takes approximately 7 volumes of air at atmospheric conditions, and squeezes it into 1 volume at elevated pressure (about 100 psig/7 bar). The resulting high pressure air is distributed to equipment or tools where it releases useful energy to the operating tool or equipment as it is expanded back to atmospheric pressure.

In the compression process, and the subsequent cooling of the air to ambient temperatures, heat and moisture are released as by-products, as illustrated in the figure below.

 



Depending on the application, excessive moisture in compressed air needs to be managed as it can cause problems with piping and end use equipment.

Compressed Air Systems :


Compressed air systems consist of a number of major subsystems and components. These systems can be subdivided into the Supply side and the Demand side.

The Supply side includes compressors, air treatment and primary storage. A properly managed supply side will result in clean, dry, stable air being delivered at the appropriate pressure in a dependable, cost effective manner. Major compressed air supply subsystems typically include the air intake, air compressor (fixed speed and/or variable speed), aftercooler, motor, controls, treatment equipment and
accessories.

The Demand side includes distribution piping, secondary storage and end use equipment. A properly managed demand side minimizes pressure differentials, reduces wasted air from leakage and drainage and utilizes compressed air for appropriate applications. Distribution piping systems transport compressed air from the air compressor to the end use point where it is required. Compressed air storage receivers on the demand side can also be used to improve system pressure stability.

As a rule of thumb, for every horsepower (HP) in the nameplate capacity, the air compressor will produce approximately 4 standard cubic feet per minute (scfm).

A simplified diagram illustrating how some of the major components are connected is shown in Figure below.

Compressed air is used for a diverse range of commercial and industrial applications. As it is widely employed throughout industry, it is sometimes considered to be the ‘‘fourth utility’’ at many facilities.

It has been common practice in the past to make decisions about compressed air equipment and the end uses based on a first cost notion. However, ongoing energy, productivity and maintenance costs need to also be considered for calculating system costs. In other words, best practice calls for decisions to be based on the life cycle cost of the compressed air system and components.

Improving and maintaining peak compressed air system optimization requires addressing both the supply and demand sides of the system and understanding how the two interact.

Optimal performance can be ensured by properly specifying and sizing equipment, operating the system at the lowest possible pressure, shutting down unnecessary equipment, and managing compressor controls and air storage. In addition, the repair of chronic air leaks will further reduce costs.

For a typical compressed air end use, like an air motor or diaphragm pump, it takes about 10 units of electrical energy input to the compressor to produce about one unit of actual mechanical output to the work.

For this reason other methods of power output, such as direct drive electrical motors, should be considered first before using compressed air powered equipment. If compressed air is used for an application, the amount of air used should be the minimum quantity and pressure necessary, and should only be used for the shortest possible duration. Compressed air use should also be constantly monitored and re-evaluated.

 

In our next article, we will discuss more about savings from compressed air.

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