Drip Pot Separators 1

[sdv325]

Well i am hoping to gain a little insight on how these work. Recently a catadyne heater manufacturer brought up the idea of implementing a "drip pot" system before fuel gas enters a catadyne heater. The problem is that wet gas is knocking out a heater even after a separator and fuel gas scrubber. The issue really presents itself in winter when the moisture freezes and knocks out the heaters, which takes out most of the process equipment. The fuel gas take off is before the main line dehydrator.

Has anyone had any experience with "drip pot" systems? Or might be able to elaborate a little more on them?

Thanks
Shaun

 

[gr2vessels]

Can you please provide the name and contact details of the catadyne heater manufacturer who brought up the idea of implementing a "drip pot" system? I will send them and email and ask them to provide an answer to your question, then I'll forwar it to you.
To me the problem seems to be the separator and the scrubber, not the wet gas. Why don't you check first the existing equipment to establish why don't they knock out the moisture/water from the gas and then quantify the additional water to be removed.
Drip-pots, condensate pots, condensate drain-pots, drain-boots, pipeline drains, drop-pot, pots, etc. (same device) have been used for over 100 years in vapor systems to remove liquid and solid build-up from a pipeline. They are employed in steam, natural gas, pneumatic, petrochemical vapor systems, etc. These devices are simple drains of varying size and capacity, installed on the bottom of the pipe, allowing gravity to separate the heavier fraction, which then can drop into a deep pot, like an extended tee of various sizes, for removal. In a flowing system, the liquid fraction must be channeling on the bottom of the pipe for effective removal. This flow regime is known as stratified, where the liquid fraction flows along the bottom and the vapor on top.
These drip pots are not for sensitive areas like fuel gas drier or moisture separators. If you are stuck with the existing ineficcient separators, then you may consider an inline, high efficiency separator as last resort to eliminate any moisture from your gas. There are many on the market, select the one with serious guarantees, provided you are able to provide correct process data on the moisture to be removed.

 

[zdas04]

gr2vessels,
That is an excellent discussion of the common wisdom. Unfortunately, this is a case where the common wisdom is as wrong as possible. Historically, pressures upstream of the fuel system were high (over 10 bara) and at those pressures it was quite reasonable to ignore evaporation. As pressures came down, evaporation became a bigger and bigger factor. At 3 bara and 28C, natual gas holds nearly 300 lbm/MMCF. This water vapor is a gas (molecules are 40% smaller than methane molecules) and mechanical separators will not touch them.

Then comes winter and the gas out of the separator gets colder than the dewpoint of the water vapor in the separator and condenses. A drip pot can help with this, but most of them do not have automatic dumps and every one I've ever been to has been full of water--a drip pot without an automatic dump is far worse than worthless.

Nothing wrong with you separator (most likely), and a standard drip pot is worthless. I've had good luck with something called a "cold finger" which you put on the line where you take off your fuel gas. This device encourages condensation by providing a very large surface area to the cold before the regulator. I have a drawing if you're interested.

David

 

[sdv325]

Thanks for the ideas guys, looks like there are some pro's and cons to a drip pot system. Only reason i considered the idea because the man who brought up the method said its very common process in Alaska during the harsh winters to solve the exact same problem. Im thinking the gas is quite wet at times considering there are over 100 well sites that have dehydrators along separators. So if there is no automatic process for dumping the water removed then its a pretty useless process as it wouldnt be able to left running for the long winter months.

If all else fails it looks like running the heaters on propane over the winter months might be cost effective.

 

[gr2vessels]

Yes David, you are right. In my warm environment, we are looking only to heat up the fuel gas after it cools down in the pressure letdown, to prevent freezing in the pipe.