7 replies to this topic

[pejmanpark]

Dear All,

I am so glad that I found this forum. I am now busy with a project which deals with the liquid carryover problem in reciprocating compressors. I would like to know if there is any device to detect the liquid at the entrance of the compressor (suction side) or inside the compressor cylinder?
I know that there are some drainage systems at the system's low points or some level measurements in the separators. However, I am wondering if there is any system or sensor which can detect this liquid.

And consequently, if the liquid is detected what is the best thing to do? Shutting down the compressor, running with lower load, ..?

Regards,
Pejman

[Art Montemayor]

Pejman:

There is a conventional, standard method of detecting, controlling, and rejecting any liquids at the entrance of a reciprocating compressor (suction side) in order to avoid these same liquids from entering the compressor. This method consists of a vapor-liquid separator (sometimes called a “scrubber”, knock-out pot, suction drum, etc.). This vessel is built to separate any liquids from the vapor or gas to be compressed subsequently, identifying its presence in the vessel with a liquid level gauge and a level controller that operates an automatic drain valve.

Once any liquid gets inside a reciprocating compressor cylinder, the potential damage has been done and it is practically too late to mitigate the potential damage or hazard. The logic on protecting a reciprocating compressor from liquid invasion is to install what I have described above. I also encourage the installation of a manual drain valve on the separator in the event the automatic level control valve fails to function or is taken out for inspection or repairs. That way, the compressor is kept on line and isn’t shut down. Operators can be assigned to manually drain the suction separators on a timely basis during their work shifts. Of course, if required, you can also install high level alarms in each of the suction separators to alert operators in some remote DCS control room.

What I describe is standard design and operating procedure for reciprocating compressors.

[Himanshu Sharma]

Art as always has given you a wonderful explanation.

From academic point of view yes water in the process gas can be analyzed by means of placing a moisture analyzer.These kinds of analyzer are typically placed in naphtha isomerization units where water is an extreme poison for catalyst.

Having said that i have till date not seen any compressor with an online moisture analyzer for machine safety and control may be it is cost prohibitive or i am unaware of issues that art or other experienced members can highlight.

[Technical Bard]

Even small amounts of liquid in a reciprocating compressor can be catastrophic. I know of two instances where this occurred in refineries. One was water carrying over the suction drum to a hydrogen makeup compressor. The second was liquid hydrocarbon carryover into a propane refrigeration compressor during a severe upset. In both cases, the head cover flange bolts failed, resulting in the release of flammable gases into the compressor building. Both of these led to explosions and fire.

[pejmanpark]

Dear All,

Thanks for your responses, esp Art. The information was very useful. My question is indeed for the cases that the separator is not well-designed or due to some strange conditions, the system is not working at its operating conditions. In these cases there might be some liquids entering the liquid (or even the chance of liquid condensation in the suction line, if the suction line is cold or long).
In these cases, is there any way to detect or prevent the liquid?
Thanks,
Pejman

[Suresh Kumar.P]

Hi,
The best thing is to have a knock out drum at the suction of compressor with a high level alarm to alert the DCS operator and high high level trip in case the action was not taken in time or the level build up rate is too fast.
As you said if the line is long and suspect any condensation, please provide steam or electrical tracing around the pipeline.

[Traverso_JR]

Dear All

I´m so glad e met this forum too. I work with lubrication in Brazil and now I'm searching and learning about lubricant losses in natural gas reciprocating compressors. This discussion is helping me a lot. I've read a paper that can give good information for all. http://www.perryequi...werMagazine.pdf to all.

[VTate]

Hello,
In addition to thorough description given by participants of discussion, I would advise vibration monitoring, namely, accelerometers installed on cylinders of reciprocating compressors. There are systems developed for such kind of monitoring and they allow to get vibration patterns as a function of crank angle. Generally, high vibration levels during compression process in compression chambers can be the indication of presence of liquids. The safety Alarm signal from this system can be sent to DCS to trigger compressor Shutdown.
Kind regards, Vitalii