4 replies to this topic

[tribleprince]

Hi

I am designing a compressed air system of 30 bar pressure. in the system there are some pneumatic valves and other miscellaneous pneumatic equipments to be operated by compressed air.
How can i calculate air consumption? and on the basis of this consumption i can define storage capacity of air receiver/storage cylinder (storage pressure is 30bar)?
How can i calculate pressure in air receiver if some pneumatic equipments are in use?

Thanks

[ankur2061]

tribleprince,

Use the "search" feature of the forums using key words such as "compressed air" "instrument air" "air receiver" to find out several posts related to compressed / instrument air consumption and sizing of air receiver.

Regards,
Ankur.

Edited by ankur2061, 18 September 2012 - 03:03 AM.

[jrtailor09]

Tribleprince,

May i know for which system are u going to use 30 bar pressure of instrument air?

There are standard from the vendor supplier regarding air requirement for individual pneumatic valve & equipment.

Regards,

[tribleprince]

Basically i am intended to use Compressed air system in a small ship and the system consists of pneumatic valves, equipment and mainly the Ship engines (2 in no) are air started at 24bar pressure.
Is it correct to size an air receiver at 30 bar to fulfill all air demands at ship?. Plz guide me if 24 bar pressure (along with all other pneumatic equipments) is used to start the engines then how much air pressure is left in air receiver (simple p1-p2? or anyother formula)? and air consumption calculation?

Thanks

[Art Montemayor]

Tribleprince:

Depending on what air pressure you really need to start the diesel (?) engines – and how much, and how often – you have a hard decision to make.

Do you really need 30 barg (note that I have to insist you use the precise type of pressure you mean – absolute or gauge; I am going to assume gauge is what you intend to use) or 24 barg? You must make up your mind. We don’t have the slightest idea of what you need to start your ship’s engine. That is YOUR responsibility to know. You should refer to your operating manual or even to the manufacturer of the engines.

The pressure level makes a difference because you are – in my opinion – close to the borderline of using a 2-stage or 3-stage reciprocating air compressor. This makes a big difference – depending on the capacity you require – in capital costs and installation and additional equipment required. A multi-stage compressor is going to need an intercooler. Depending on the capacity, you may – or may not – be able to get by with an air-cooled intercooler. But either way, you will need a water separator in between stages and drain valve capabilities. For a 3-stage machine, this starts to get cumbersome. I hope you see my point here, before going any further.

The reason for a multi-stage compressor is the acceptable compression ratio for the compressor. At 30 barg discharge, you have an overall compression ratio of 31. This approximately requires a 3-stage machine with a compression ratio of 3.14 between stages or a 2-stage machine that uses a compression ratio of 5.57 between stages. The higher the compression ratio between stages, the higher the discharge temperatures – and the higher the safety risk. At 24 barg discharge, you can use a 2- stage machine with a compression ratio of 5 between stages.

Therefore, it is up to you to make the basic decisions on what size and type of scope of work you require or want.