# Thread: Common mistakes in process design/simulation

1. Junior Member

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## Re: Common mistakes in process design/simulation

Invaluable information. Much appreciated. Thanks

2. Spons Circuit
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3. Member

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## Re: Common mistakes in process design/simulation

hi

I had problem in the pipe phase software. when I simulating the natural gas at 715 psi and 66 deg C in the transmission line, my velocity is gradually reducing , normally as per ideal law of gas the actual volume of gas should be increase due to reduction in pressure loss. when I doing the same model with natural gas at 300 psi and 66 deg c the velocity is gradually reducing in the line due to friction loss. I am not able understand this behavior in the software, ca any one explain the solution to overcome this situation.

4. -

5. Member

Join Date
Sep 2007
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## Re: Common mistakes in process design/simulation

hi

I had problem in the pipe phase software. when I simulating the natural gas at 715 psi and 66 deg C in the transmission line, my velocity is gradually reducing , normally as per ideal law of gas the actual volume of gas should be increase due to reduction in pressure loss. when I doing the same model with natural gas at 300 psi and 66 deg c the velocity is gradually reducing in the line due to friction loss. I am not able understand this behavior in the software, ca any one explain the solution to overcome this situation.

6. Member

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## Re: Common mistakes in process design/simulation

Remember that any expansion of a gas normally entails a temperature reduction, at least heat transfer with the surroundings is fast enough to hold constant temperature.

7. Member

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## Re: Common mistakes in process design/simulation

Much appreciated. Thanks

8. wyb
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## Re: Common mistakes in process design/simulation

The conversion from SCFM to ACFM can be expressed as

ACFM = SCFM [Pstd / (Pact - Psat Φ)](Tact / Tstd) (1)

where

ACFM = Actual Cubic Feet per Minute

SCFM = Standard Cubic Feet per Minute

Pstd = Standard absolute air pressure (psia)

Pact = absolute pressure at the actual level (psia)

Psat = Saturation pressure at the actual temperature (psi)

Φ = Actual relative humidity

Tact = Actual ambient air temperature (oR)

Tstd = Standard temperature (oR)

Correct ?

9. Member

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## Re: Common mistakes in process design/simulation

Actual to standard volumes can be calculated using the Combined Gas Law:

P1.V1/z1.T1 = P2.V2/z2.T2

10. Active Member

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## Re: Common mistakes in process design/simulation

what does actual & standard conditions have to do with humidity?

11. Junior Member

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## Re: Common mistakes in process design/simulation

In my exper., gas compt until c7+ is enough for eq. Sizing but for flow assurance & compre. Will give another concern

12. Junior Member

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## Re: Common mistakes in process design/simulation

Yes, Agree.,
special for Air as fluid since AIr has humidity factor that will affect the ACFM.

Originally Posted by wyb
The conversion from SCFM to ACFM can be expressed as

ACFM = SCFM [Pstd / (Pact - Psat خ¦)](Tact / Tstd) (1)

where

ACFM = Actual Cubic Feet per Minute

SCFM = Standard Cubic Feet per Minute

Pstd = Standard absolute air pressure (psia)

Pact = absolute pressure at the actual level (psia)

Psat = Saturation pressure at the actual temperature (psi)

خ¦ = Actual relative humidity

Tact = Actual ambient air temperature (oR)

Tstd = Standard temperature (oR)

Correct ?

13. Junior Member

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## Re: Common mistakes in process design/simulation

Thanks bro mohamedellejmi for these useful information..

14. Junior Member

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## Re: Common mistakes in process design/simulation

Thanks for the info! I would like to share one more common mistake in simulation i.e Over specifying the simulation. It is the hardest one to identify.. Do not make the full flow sheet at once and then start converging unit operation one by one until you are quite familiar with the whole process. Instead of that make flow sheet bit by bit and make it converge step by step and proceed.