3 replies to this topic

[Zauberberg]

Good day to everybody,

Please see attached granulometry analysis of sand particles from a gas production system. As you can see, more than 25% of the particles is smaller than 40 micrometer (threshold for visibility with a naked eye).

I have a discussion with the wellhead compressor vendor, regarding the required efficiency of the sand removal system upstream of the field compressors (gas engine driven, piston type, single-acting, suction 6 barg, discharge 15 barg), and it seems like we cannot reach an agreement with regards to the practical limits of size of sand particles that should be retained by the existing separator/strainer system upstream.

The issue is that I do not want to use a set of cartridge filters in gas field production environment, which is recommended by the vendor. This thing will get clogged on a daily basis. What we can consider logical is adding a fine mesh strainer (mesh 300 or 400) in series with the existing system (Manifold strainer is #200 Mesh = 70 microns), to keep the paricles larger than 40 or 50 micrometer away from the compressor. Production stream consists of Methane-rich gas, produced water, and sand.

Based on your experience, what is the best way to proceed forward?

 

Regards

Attached Files

•  Sand.bmp   1.62MB   18 downloads

[Art Montemayor]

Zauber:

 

It’s nice to hear from you.  However, it seems like you’ve been challenged again in the field.

 

You've got a very serious and potentially expensive problem this time – as my experience would indicate.  Regardless whether you have a reciprocating or a screw compressor, you can’t tolerate any of the sand particles in your analysis – no matter how small they may be.  I have had that same tiger by the tail and the only method I have found to justify compressing the resultant gas is to employ wet scrubbing – lots of it.  You may use the produced water, depending on its quality , quantity and local conditions.  I never tried a liquid ring compressor because of the small capacities available.

 

I don’t know who you are dealing with as to compressor manufacturer and vendor, but I totally agree with your refusal to employ mechanical filters to produce a “clean gas”.  You will wind up buying all the filter elements you can find and you still will have to put up with continuous shutdowns and filter element replacement as well as line clean-outs.  You and I both know that your compressor –and its lube system – can’t tolerate any solid particles.  Even “fine powdered” particles will act as emery and soon mechanically wear out all your metal-to-metal parts – such as bearings, pistons, rings, valves, rods, packings, etc., etc..  Gas compressors and solid particles – no matter how small – don’t mix.  And any attempt to deal with the situation by applying mechanical separation is, in my opinion, a futile attempt.  You are perfectly correct in not going down that path.  Your vendor is simply doing what he/she has to do in protecting their product’s best interest.  The compressor was not designed to handle ANY solid particles and, as such, has to be protected from these.  A cartridge filter – as used in the upstream oil and gas business -is strictly designed to handle LIQUIDS and GASES – not solids.  The term “filter” is a misnomer here.

 

However, this leaves you out on a limb.  You’ve probably got a “dirty” wellhead that produces 3 phases: gas, liquid, and solids and you have to process the gas.  I have employed a well oversized 3-phase separator wherein I try to bring about maximum contact between the liquid phase and the solids, making the solids go into an emulsion and precipitate at the first stage of the separator where I employ sand removal nozzles and internal spay headers.  I also have employed a “wash tower” employing simple, ceramic Raschig Rings and recirculating wash water.   These worked well, but eventually required clean outs.  A lot of the problems involving sand particles revolve around the TYPE of basic material it is composed of.  Silica is one thing, clay is another.  One is abrasive, the other is sticky and difficult to handle.  I always remember what my Unit Operations professor in college told me: the worse Unit Operations are the ones involving solids.  And I have lived long enough to confirm it.

 

Are you still in Peru?

[gegio1960]

Zauber,

I'm not an expert of this field and I appreciate Art approach.

Anyway, I've heard of a similar problem in a Lybian Gas Plant that, after several unsuccessful tentatives, was solved by the application of a 

wringing separator. The application is described at the following link http://www.wringingi...tions.php?sel=2.

Maybe it's interesting for you. Let me know....

Kind regards and good luck,

gegio

[Zauberberg]

@ Art,

 

Thank you very much for your reply. Spot on, as always.

There isn't much we can do now with regards to additional separation. We are stuck with the existing facilities upstream (which have zero or little automation and containing a lot of accumulated sand and sludge) but if the problems persist we will definitely going to follow one of your recommendations - a separator with the internal sprinkler system being quite an attractive one). This also gave me an idea to use sprinklers in the production separators in another project dealing with sand and clay particles.

 

What we are going to do for the time being is to try to clean the existing system through fine mesh strainers (300 Mesh in the manifold and 400 Mesh conical strainers in compressor suction), and perhaps go even for a finer Mesh. See attached materials - the mesh strainers are made of sintered wire cloth and can be made up to the size of 5 microns. Do you have experience with this ultra-straining?

 

@ Gegio,

 

Thank you very much for the reference. Depending on the outcomes of commissioning, I will contact the supplier and ask for more detailed information regarding fields of application of wringing separator.

 

Best regards

 

Attached Files

•  Bopp Strainers.pdf   1.34MB   21 downloads