6 replies to this topic

[kay1]

Hi,

I am presently working on utility and instrument air receivers. The air passes from a compressor unit to a filter separator and to an air dryer. I then passes thru an after filter before going to the instrument air receiver. A stream goes from upstream the air dryer to the utility air receiver.

The instrument air will be used by control valves, oxygen strippers, hiperfilters etc. I think sizing the air receivers and others will depend on the users. But I dont have enough information on the amount of air to be used. I will appreciate any information on how to go about this and which one of the equipment to treat as proprietary.

Regard
Saheed

[Art Montemayor]

Saheed:

It’s very important to note that you are supplying two (2) different types of air usage:

1. pneumatic instrumentation; and,
2. “Utility” consumption.

If what you mean by “utility” is meant to be pneumatic tools air, breathing air, air for bag filter shakers, etc., etc., then you have a situation where the utility air will probably set the critical and peak supply demand at any given time. Additionally, bear in mind that you have not fully stated ALL the required basic data before arriving at a reasonable air receiver size. You have failed to state what type of compressor(s) you have, what is their capacity, their capacity control type, their arrangement (stand-by spare, emergency backup supply, and other local factors.

The logical first step - and what you should already have in hand - is a complete listing of all pneumatic instrumentation and the individual normal and maximum air demand of each. You should have this information on a spreadsheet with indications of which are the critical instruments and their critical air supply. You should also list all the possible utility air consumption rate demanded at any one time. Along with this, you should have a complete detailing of all the air supply capacity available to the total system. Don't forget to allow for future, possible additional air consumers.

The correct sizing of the required air receiver will depend not only on the users, but also on the maximum air flow rate fed from the compressors and the air dryers. Don’t forget that one of the priority scope of work for the air receiver is to act as a capacitance device, ensuring that a steady, dependable source of air is available to your users. That means the air receiver sizing should suit the compressors’ air capacity production. The type of compressors and their capacity control plays a factor in how you size the air receiver.

You state you don’t have enough information on the amount of air to be used and you ask for information on how to go about this. My answer is simply: get up from your desk and go out into the process and start making a detail listing of all the points of air consumption. It’s as simple and direct as that. As I said, that’s the first thing you should have already.

I don’t understand what you mean by “which one of the equipment to treat as proprietary”.

I hope this helps you out.

[kay1]

Art,

Thank you for the information. I am glad to tell you I am up from my desk and doing just as you have said. I think I have what i need for now and will definitely get in touch if I am stuck.

I really appreciate your contribution to this forum.

[kay1]

I forgot to add this. The compressor type is Rotary Screw, electrical driven, 40HP, 3600RPM. Free air delivery is 87.4scfm and pressure rating is 150psig. There are 2 in use and 2 spares.

And another question- Is plant air same as utility air?

[Art Montemayor]

Saheed:

Plant air may - or may not - be the same as utility air. The terms' local definition depends on what industry you are involved in, your specific process, or your air applications.

Plant air, for example, is termed that in the USA when we distribute it for use as motive force in pneumatic tools, hoists, air blowers (to clean work areas and tools), and even in air motors. An air motor is basically an air blower running in reverse: air is used as energy in the "air motor" to drive an agitator, a pump, or any other mechanical device in situations where electrical sparks cannot be tolerated due to explosion or other hazards.

Utility air is a term I've come across only once or twice in 47 years. On those ocasions, it meant air used to drive air motors or special tools.

Both plant air and utility air are usually saturated with water at the available distibution pressure and temperature; in other words, this air supply is not dryed.

How your applications define it is unknown to me. I don't even know where you are located.

I hope this helps.

[kay1]

Art,

Thank you. I am a young engineer located in Nigeria.

[Adriaan]

The main difference between "plant air" and "utility air" used to be that one was treated more, specifically dried (at CBN a silica gel absorber was used for that purpose) to prevent condensation in pneumatic equipment (such as control valves).

"Utility air" then is - to me at least - air used to drive pneumatic equipment and "plant air" used for things like purging, breathing, 'air bombs' on transport lines etcetera.

Given the relative costs of having a split air system (one with higher quality requirements) versus the cost of having ONE system (saving almost half the piping and pressure vessel costs) at CBN a single system is now used wherein all the air (now dried with a pair of adsorbers to a much lower dewpoint) is of the highest possible quality - relatively speaking.

A drawback in using this very dry air, however, in our experience is that pneumatic cylinders tend to last a little shorter than before, mainly because the rubber seals in them wear out it seems. It also means that the air is no longer used for breathing (hooray! A portable air unit is rented for that purpose now, delivering better quality air).