Natural Gas BTU reduction

[RHoyt]

I didn't want to post a long drawn out question, so I will stick to the basics unless more details are needed.

I work for an oil company that sells the natural gas we produce. We are having a hard time keeping the BTU's below the 1150 cut off. It seems like the heat of the day causes us to have an increased amount of BTUs, I've noticed the vapor recovery runs a lot more.

I was wondering what we can do to reduce our BTUs. Will cooling the gas down reduce the BTUs? Changing pressures? Trying to keep the wash and stock tank from heating up during the day?

Any help will be greatly appreciated, and if you need more information just let me know.

 

[zdas04]

You have a problem that is common in old oil fields that start producing the gas cap without any real understanding of the differences between oil production requirements and gas production requirements. For the last 100 years, gas has been treated as a waste product that has to be gotten out of the way to produce oil. Gas facilities in these fields have tended to be inadequate.

The best thing would be to send the rich gas somewhere to recover the very valuable NGL stream. That is probably not an option.

Next best is to lower the temp of the gas to condense all of the condensable gases you can into somewhere you can stabilize and sell them. If you are just dumping the liquids from your VRU back into a tank, you are spending a lot of money to capture liquids that will immediately flash back into the stream when they warm up.

If you can't do either of those, then you can inject CO2 up to the total inerts limit of the pipeline--2-3% will lower your BTU, it could be enough.


David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

Remember, being ignorant isn't your fault; staying ignorant is.

 

[bcs5274]

around here they are gettin more stringent on hydrocarbon dew point, we have been installing refrigeration skids and also jt skids to get the dew points in line, the ngl are being used to cut parrafins in their oil wells

 

[dcasto]

as we say in the front range "To Air is Human", Remember it.

To lower BTU's you'll need to cool the gas off and condense the C3+, its that simple. But as bcs is learning, there are still a lot of C2 and C3's in casinghead gas.

If you are close to 1150 BTU and thats the cut off, just compress the gas to over 400 psig, cool it down with a chilled water system that you see on buildings (well, depending on the amount of gas that may a chiller from the sears tower. Your gas buyer should have a dew point limit, typically 30F, so you only need to cool to this temp, hence the water chiller system.

If you have gas like bcs has, you may need a propane refrig unit, JT plants are way over rated for use on casinghead gas with BTU's over 1300 when you only need to meet dew point or minor BTU decreases.

You'll knock out some high BTU stuff and you can drop that back into the tank. Some of it will flash and go through the whole process again. To save energy, you back exchange the chilled gas with the fresh hot gas.

Google natural gas dew point control plants.

If this fails remember my opening line. Oh, hire a gas gatherer to help you, we are plentiful and in the phone book, just pick up the phone and whistle