Compressor stonewall 1

[balaplus]

Is it true that stonewalling phenomenon in centrifugal compressors does not occur for lighter gases like nitrogen ?

 

[dcasto]

Not true. Stone walling is when the compressor cannot meet the required head and the gas can not flow and will then flow backward through the compressor until the suction p Ifressure rises enough for the head pressure gain in the compressor can over come the discharge pressure. This back and forth movement is surge.

If the compressor was designed to compress methane to a certain pressure, with nitrogen in the unit the compressor would put up more pressure (it the same feet of head, just that feet of head time gas mole wt or density is pressure).

If the compressor was designed to move freon, then with nitrogen in the system, the unit would not put up enough pressure and would stonewall.

 

[rlewis]

Stonewall actually occurs when the gas chokes in the diffuser. Lighter gases have higher accoustic velocity and therefore run at much lower Mach numbers in the diffuser and will therefore require more volume flow before they choke. The lighter the gas, therefore, the less likelyhood to reach choke velocity in the diffuser and stonewall. Nitrogen isn't however a particulaly low MW gas, and compressors designed for air or nitrogen do choke.

 

[jamesbanda]

is stonewalling the same as surging?

 

[UmeshMathur]

The term stonewall refers to the condition when the compressor fails to develop any head, as the suction volumetric flow is too high for a given RPM. (Recall that, typically, the head drops off as suction flow increases for a given RPM. Eventually, the head v/s suction flow curve becomes nearly vertical at the stonewall flow.)

Surge, on the other hand, refers to the condition when the compressor is subject to extreme flow oscillations and instability; this is caused by insufficient suction flow. The minimum flow required to avoid surge increases with compressor RPM. Antisurge control systems (using very fast acting control valves) recycle flow from the discharge back to the suction to ensure that the net suction flow exceeds the minimum required, for a given RPM, to avoid surging.

 

[MortenA]

dcasto is wrong. What he describes is surge. Stonewall is "at the other end" that is low head large volume. It is connected to the fact that wing tip speed of the impellars cant exceed the speed of sound in the medium.

The term "stonewall" is because its like a "wall of stone" with regards to capacity increase (no way around it).

Best regards

Morten

 

[dcasto]

MortenA is correct, I was applying what our operations people called it when the CCC antisurge system was tuned up.