5 replies to this topic

[process85]

Hi everybody,

I have a query regarding the unit conversion for inlet flow to a blower.

I had issued a data sheet for blower with inlet flow in Nm3/hr of gas and on a dry basis.
Now vendor has asked to provide the inlet flow equivalent to air in m3/hr.

I have the inlet Pressure(P) & Temperature(T),composition and Molecular weight of the inlet gas.

My understanding is first get the Nm3/hr of gas on wet basis.Convert this value to kg/hr of air using equation : kg/hr of air = (Nm3/hr of wet gas) * (M.W of air) / 22.4

Then divide this value with density of air at inlet conditions (P&T)of blower as per:
kg/m3 of air = kg/hr of air / (Density at P&T of air)

Kindly confirm my methodology.

[Art Montemayor]

Process:

You want to transport a gaseous fluid. That is obvious. Otherwise, you wouldn’t need a blower. However, you fail to identify the gaseous fluid to us. And that is probably what is giving your blower supplier problems.

You must identify the fluid. If it is a mixture of gases (& vapors), you should give the complete composition and its pressure and temperature at the proposed blower’s suction port. I presume you have identified the blower discharge condition you require to the supplier. There is no “wet” or “dry” condition involved in specifying the suction conditions. Simply state them as theY actually will exist. It is the blower supplier’s responsibility to identify the required size of blower and the required Hp to drive the machine. But the supplier has to know WHAT – exactly – is supposed to be transported by raising it to a specified discharge pressure.

The blower’s capacity in “equivalent air” should be of no interest to you – or to the blower – UNLESS what you are proposing to put into the blower is air (and wet with water vapor!). If that is the real case, then a composition identification will take care of that. The density of the gas and its actual suction conditions are what should be of interest to your supplier. If you identify the gas, then the density can be calculated.

[process85]

Thanks Art for your reply.
However, I would like to inform you that I have given the composition of gas including the water content, inlet pressure and temperature and molecular weight of the inlet gas.Also, I have provided the discharge pressure.
Ideally, vendor should not be asking these queries, however that is the case.
In that scenario, the method I have described, is it correct?

Also my understanding is that the design temperature shall be decided by vendor only based on his estimation of the discharge temperature.
Please clarify.

[Art Montemayor]

Process:

You are correct. You don't owe anything else to the vendor. You have supplied all the basic data required needed to size and select the blower.

Now it is the vendor's turn to offer the machine that will do the job, complete with a description of what is needed as driver Hp and additional equipment. The design temperature for the machine is decided by the vendor since only he/she knows the discharge temperature. You have kept the faith. The ball is in the vendor's side of the court.

Apparently, the vendor has blowers rated for air service and not for your specific application; he now wants your estimation of the equivalent so that the existing blower can be offered to you and you take the responsibility for the size. I would not accept this kind of arrangement from a vendor. I would stick to what you have outlined: The vendor is taken as the "Expert" in this application and it is his/her call to come up with the correct machine for the application. If he/she can't, they should say so and bow out of the bidding.

[katmar]

Just to add a "hear, hear" to Art's reply. Avoid this supplier. If he can't help you with basic sizing, how will he support you when the blower gives problems later on?

[samrat]

I agree with Art. I have spent most of my career in Process Gas Compressors of various sizes in Oil,Gas,Petrochemical and Refineris. . The customer is supposed to give their requirements stating the end conditions and gas composition at the inlet. It is the Compressor Manufacturer's responsitiblity to size the compressor based on:

1. Gas Composition furnished
2. Overall compression ratio
3. Type of Prime mover required
4. Any specific code requirements such as API 11P,API 618,API 617 etc.etc.

For a given gas composition the manufacturer has to find out which Equation Of State applies to a given gas.

In short, A manufacturers' responsibility should not be trasnferred on to customer - if customer has furnished the right type of information.

Your question regarding the Expected Discharge Temperature: This depends upon the stage compression ratio and the Cp/Cv value of the gas. The actual operating discharge temperature depends upon the material of construction of the cylinder(if jacketed) and the volume flow of the cooling media.

Hope this answers your question in nutshell.
samrat