Guidance on increasing gas velocity in pipes

[Cleanboy]

I need some guidance on the above topic.
A need has risen in a petrochemical plant to increase fuel gas velocity from the present 35m/sec to a higher velocity. This is to enable a higher through-put, and increase production. There is therefore a need to understand the impact of such an increase and the regulations/standards that we can reference for guidance. One consideration is a possible of eroding the pipes due to increased gas velocity. However, this is not a major issue because the pipes are thick enough to withstand the increased velocity over a specific period. Further, the fuel gas is free of particles and moisture. The other consideration is increased noise, but this is also not a serious issue, given that the pipes circuit is in close proximity to other noisy equipment.
What other factors should I consider? What should be the velocity limit? What codes or standards should I reference for guidance?
Thanking you in advance for your support.

 

[LittleInch]

The highest I've seen in a standard for clean dry gas is 40m/sec, but in reality if you have very clean dry gas then sonic velocity is your physical limit. Hydrogen systems are going higher up to 60m/ sec.

How much higher?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[RVAmeche]

The caveat of "the gas is free of particles and moisture" needs to be very, very well defined and documented. It may be intended to be that way, but is it really? Always? Is this a smooth steady state increase or periods of high flow that may cause hammering or FIV?

I get its the cheaper route when increasing capacity and we have limited data, but this smells like a bad or short sighted idea.

 

[LittleInch]

Could you not raise the pressure and stick in an extra regulator at the far end?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Check pressure drop and see if any pressure control loops are affected. Use isothermal or adiabatic compressible flow expressions. Control valves may not have sufficient Cv, and pressure sensing impulse lines may need to be relocated.

 

[shvet]

What codes or standards should I reference for guidance?

Make sure the fluid is guaranteed total gas phase. This is critical. As per my experience refinery fuel gas is considered as "dirty, wet, sour" environment.

para. 2.5 API 14E or para. 5.5 ISO 13703

https://publishing.energyinst.org/t...n-induced-fatigue-failure-in-process-pipework

https://onepetro.org/SPEATCE/procee...13ATCE/D031S032R004/172738?redirectedFrom=PDF

6 Line sizing criteria
6.1 General
When sizing piping, the following constraints shall be addressed:
• required capacity/available driving pressure;
• flow induced forces;
• noise/vibration;
• pressure surges;
• material degradation - erosion, corrosion, cavitation;
• liquid accumulation/slug flow;
• sand accumulation.
Line sizing criteria in the sub clauses below shall be adhered to for design of new installations. For modification of existing installations, additional considerations shall be given to life cycle cost, and increased velocity and/or pressure drop may be accepted if mechanical integrity can be documented, e.g. ρV2 > 200 000 kg/ms2 for a line in the flare system.
In general, sizing of lines should be in accordance with ISO 13703.
...

6.3 Sizing of gas lines
6.3.1 General
When sizing gas lines the sizing criteria will be a compromise between the maximum velocity (see 6.3.2) and allowable pressure drop, see 6.3.3. Piping with gas at the dew-point and/or with some droplets shall be designed as gas lines.

6.3.2 Maximum velocities
In lines where pressure drop is not critical, gas velocity shall not exceed limits which may create noise or vibrations problems. As a rule of thumb the velocity should be kept below:

(4)
where
V is the maximum velocity of gas to avoid noise in m/s
ρ is the density of gas in kg/m3
or 60 m/s, whichever is lowest.
In order to avoid excessive dispersion of noise in lines connected to pressure control valves, the valve manufacturer shall be consulted.
For anti-surge lines, the constant 175 in the formula (4) may be replaced with 200 during process upsets, if the noise level is acceptable. However, during normal recycle, the velocity should be limited to the velocity as given by the formula (4).
If solid particles exist, special attention shall be given to particle erosion.

6.3.3 Recommended pressure drop
Where pressure drop is critical (e.g. when it results in unacceptable liquid drop out in suction lines between scrubber and compressor suction, inlet lines to turbo expanders and contactors etc.), the guidelines in Table 4 should be used. The pressure drop should be prorated between the operating pressures given.
Table 4 – Recommended pressure drop for single phase gas process lines