7 replies to this topic

[aanita]

Air blower suction and discharge condition are as follows:

Blower Suction Pressure : 960 mbara
Suction Temperature : 45 Deg. C
Suction Flow : 62000 KNm3/hr

Blower Discharge Pressure : 0.87 barg
Discharge Temperature: 226 Deg.C
Discharge Flow : 48000 Nm3/hr


Antisurge valve is fully closed and confirm not passing. All the instrumentations (pressure, temperature, flow meter ) are checked found reading are correct. I try to convert suction flow using Boyel’s- Charles’s law (P1V1/T1=P2V2/T2) also giving error. Am I correct to convert suction flow or how can I convert it to discharge flow?

Thanks in advance.
Aanita

[Art Montemayor]

Aanita:

Your query doesn’t make sense in the manner that you express it. Are you stating that you expect the blower gas volume in the discharge of the blower to be smaller than that in the suction because it is at a higher pressure? If so, then you are correct in your logic – EXCEPT THAT the gas volumes that you compare should both be at the same, ACTUAL CONDITIONS. In other words, the gas volumes are actual when measured at the ACTUAL pressure and temperature.

There is a huge mistake in what you have written (or you simply made a typo error). Normal cubic meters (Nm³) of a gas is defined as the gas volume at a pre-defined state of pressure and temperature. Allow me to expound on what I believe is the basis of your error:

There are two different terms used in defining base conditions for gases. These are "Normal" and "Standard" conditions.

"Normal" conditions are usually used where metric or SI units are used. Before 1990 everyone understood Normal conditions to be 0 ºC and 1 atmosphere (absolute), and this was at least one basis that was (almost) universally accepted. This well-established situation was thrown into turmoil when IUPAC changed their definition of Normal conditions to 0 ºC and 1 bar (absolute). All textbooks and handbooks published prior to 1990 gave the old definition, and all engineers and scientists who had studied prior to this had the old definition firmly imprinted in their memories.

Standard Conditions are also arbitrary and vary from industry-to-industry, as well as from country-to-country.

The important thing to bear in mind in your query is that ALL the air mass that goes into your blower must also exit out through the discharge nozzle – unless you have significant leaks in your blower. The mass of gas (which I don’t know since you don’t tell us the gas molecular weight) represents a certain amount of gas moles and these represent a certain amount of Nm³ and this should be the SAME for both the suction and the discharge – regardless of what the temperatures and pressures are at the suction and discharge.

You state that Suction Flow = 62,000 KNm³/hr and Discharge Flow = 48,000 Nm³/hr (without any recycle from discharge to suction). This just cannot be true.

Are you, perhaps, mistaking actual volume flow rate with Nm³ flow rate?

[aanita]

Dear Art Montemayor

Thank you for your reply.

As a new operation engineer what I found in the FT (Flow Transmitter), I write it. After calibration of FT I found no remarkable changes in the flow. Flow is measuring in Nm³/hr and not in actual volume flow rate or any other unit. In fact, I am confused about these readings also. Moreover, it is not matching a Steady state flow. Sorry for typing error.

Thank you very much.

Aanita.

[AA Mishra]

Being operations engineer it pains not to believe instrumentation.

You check the nameplate capacity of the blower and power consumption.

You check the actual power consumption.

You take instrumentation along to derive the actual flow rate from these data.

In case, the blower is running at max. load, 80% of design flow is considered for the purpose of accounting.

Good to see operations engineer throughly checking system leakages first.

Regards

[aanita]

It is a steam turbine driven blower.
Supplier data sheet showe that suction capacity( rated) is 63500Nm3/hr and discharge( not related with supplier) show blower capacity is 54500 Nm3/hr. Power consumtion not given. I can find the steam consumtion. But efficiency I have to guess.
All the suction air is going to the flowmeter which readinfg not matching.

Thank you for your time.

[kirangparihar]

What is the type of Flow-meter that you are using?
Pl. check for Temperature & Pressure Correction Factors used.
Also you can use velocity meters for double checking the suction flow rates.
In any case, Suction & Discharge Flowrates should be same (in Nm3/hr) unless there is a big leakage!

[pawan]

Dear Anita,

1. First learning should be that Nm3 flow is a standard condition as mentioned by Art - It doesnt depend on actual P & T so by definition itself it should be same for suction & discharge.
2. Secondly the very common practical mistake from instrument side is that people generally install FT without correcting its parameters in Math Unit.
3. Since both FT comes as a part of standard package (Blowers, compressors etc are package items generally), it is general perception that their data will be same.
4. Whereas the actual case is different because they both operate at different P & T.

So My first suggestion would be to check the Design P, T & MW of both FTs separately.

Get Raw DP value from FT (Instt deppt will help you on this).

Convert this DP to actual M3 flow based on design data of FT.

Convert this actual M3 to Nm3 using actual P & T whcih are different for suction & discharge

Finally you will get slightly higher Suction Nm3 than discharge due to minor leakages if its a new machine.

Let me know your findings to help you further.

[pawan]

Anita
I suspect that both flows are in actual M3. Just check it from your instt deptt how they are presenting these figures from math units.