3 replies to this topic

[ahme21]

Dear All,

Has any of you ever experienced or heard of Air ingress into suction of Natural Gas compressors operating at low suction pressures ( ~ 25 - 50 Psig)? Theoraticaly if there is any blockage in suction such as blocked mesh pad could cause a vacuum in suction during suction stroke. This could lead to an explosion in worst case or in case of minor ingress may creat problems in downstream process, such as contimnation of Amine solutions.

Has any of you ever experienced any thing like that?

[Art Montemayor]

Ahme21:

I have never experienced the evidence of air ingress into the suction side of a reciprocating compressor due to partial vacuum suction conditions.

But that doesn’t mean I would permit a hydrocarbon gas to go into partial vacuum in the suction side of a reciprocating compressor – or any other type of compressor. This, in my opinion is inviting an explosion to take place in the downstream process. I have been warning about this very, specific incident on our Forums for over 10 years.

In fact, I vividly recall my alarm at finding a copy of “Rules of Thumb for Chemical Engineers” by Carl Brannan being circulated within our Forums with the recommendations for suction pressure in refrigeration compressors running with hydrocarbon refrigerants and partial vacuum. I immediately wrote comments to the Forum specifically advising against this practice. I consider it totally unsafe and hazardous. I certainly hope the new editions of “Rules of Thumb for Chemical Engineers” have corrected this gross oversight.

Nowhere in the hydrocarbon industry are compressor suction pressures allowed to venture into the partial vacuum zone. In fact, suction pressures on these applications are always kept and controlled at pressures above approximately 5-10 psig – with alarms and shutdowns at pressures below these values.

[sheiko]

Dear Art,

Unfortunately, the new edition of the book you mentionned still indicates that reciprocating compressor can operate under slight vacuum at the suction side (Table 6-5).

[Dazzler]

Although not the hydrocarbon industry, I have come across two cases of positive displacement compressors (gear or lobe) handling flammable gas (mostly H2) and with partial vacuum at the suction side, in fact through most of the plant. One was in a petrochemical plant and the other in a chemical plant. I know one of those had oxygen analysers (perhaps dual redundant) near compressor suction for alarm and possibly trip. In both cases the risk of partial vacuum pulling in air via a leak was protected against or the vacuum was deemed necessary to prevent even more hazardous scenarios, such as toxic gas leak.
Dazzler

Edited by Dazzler, 03 August 2012 - 11:36 PM.