There is a lot more into selecting the right compressor for an application other than the horsepower. As follows:
The flowrate required at differential pressure (discharge minus suction pressure), inlet/discharge temperatures and pressure ratios and other properties of the gas being pumped, with all inlet and outlet process data of the fluid.
What type of compressor for the application is required such as a centrifugal or reciprocating.
What special features or auxiliaries are required for the compressor for the application.
What materials are required for compatibility with the process fluid.
Normally a purchase specification with data sheet is provided to a vendor that specifies all specific requirements of the compressor to be purchased in regards to performance requirements, auxiliary/accessory requirements, and material requirements, as well as what industry standard the compressor needs to be built to. The mechanical engineer and process engineer would provide the above data to the vendor, while the electrical engineer will provide requirements and specifications for the motor.
Thank you for your help. Unfortunately l am new to process engineering and l only have the plant flow diagram as attached showing that l need 7.5Hp motor and no further information. We use compressed air to dry cake filter after filtration using the horizontal pressure leaf filter. we blow the filter with 2-3bar compressed air. So was wondering if any 7.5bar centrifugal pump stated by the designer will do the job sufficiently. And if l were to install a lower hp, does it make any good engineering judgement.? Thanks again
Longer answer is that any pump or compressor you need to know certain things in order to size it or buy it.
These are
Fluid and it's properties (density, MW, compressibility, heat capacity etc)
Inlet conditions (pressure, temperature)
Outlet requirements (pressure mainly, temperature comes from the pump or compressor)
Flowrate (volume per unit time or mass flow
Power depends on flow and pressure difference,
Pumps and compressors are really just energy transfer between incoming power (electricity) and the fluid moving with increased head or pressure.
For an air compressor you now know certain things, I.e. fluid, inlet conditions (atmospheric usually) and you have a minimum pressure.
You don't know flow.
Many air compressors come as pre packaged units, often with a 7 bar/100 psi accumulator.
So probably any 7.5kW air compressor would do the job if it supplies air at 7.5 bar.
