Gas Blending in a Pipe
Gas Blending in a Pipe
(OP)
Hi guys. Hope you are all well in this new year. Question. Client wants to blend three gas streams for use as fuel in a steam generator. The streams are: 1000 Btu/scf pipeline utility gas, 600 Btu/scf casing gas, and 1300 Btu/scf raw gas from a well. I maintain that I can insert all three of these streams into a pipe and as long as I provide sufficient turbulence, I will obtain complete mixing of these gases in a few diameters, due to turbulence and Brownian motion. I might throw in a static mixer for fun. Client says no, you need a big vessel to do the blending.
Have you guys ever seen a correlation or rule of thumb for blending gases to achieve complete mixing in X pipe diameters downstream of the blend point?
Thanks guys! Pete
Have you guys ever seen a correlation or rule of thumb for blending gases to achieve complete mixing in X pipe diameters downstream of the blend point?
Thanks guys! Pete





RE: Gas Blending in a Pipe
RE: Gas Blending in a Pipe
It all depends on Reynolds Numbers (both velocity and density have control). The 600 BTU casing gas is probably about 20% CO2 and has a SG around 1.3? The raw gas is probably around 0.8 SG? The commodity gas is 0.6 SG. So you have a pretty good range of densities. If the velocities are very different then you have a serious mixing problem and probably need a static mixer. On the other hand if your Reynolds Numbers are below 3,000 or above 6,000 and within about 5% of each other you may not need the mixer. It all depends on relative velocities and densities. If all three gases were put into a vessel at separator velocity then they would surely blend quickly, but just bringing three pipes together can easily get velocity stratification that can take a while to work itself out.
David Simpson, PE
MuleShoe Engineering
In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual. Galileo Galilei, Italian Physicist
RE: Gas Blending in a Pipe
Brownian motion isn't going to mix anything in a couple of diameters. Maybe it would work in a thermos bottle over night. Turbulence is what you want. A vessel is proably the way to go, so that you can limit high velocities to short distances within maintainable equipment. It would avoid higher pressure drops and well stream particle erosion from affecting a long pipeline.
Reaction to change doesn't stop it
RE: Gas Blending in a Pipe
If you look at things like injection of chemicals, using a centre quill or injection point would be best rather than a tee or branch connection.
Then maybe 40 - 80 D to get complete mixing.
If you stuff it through a static mixer or a control valve then maybe 10D downstream of that.
Wholly dependant on velocity, pressures, quantities, line size, SG.
Yu would be waiting an eternity for Brownian motion though, especially with that level of difference of SG
I have seen some fancy transient modeling for different liquids (condensate into Crude Oil. CFD modeling could be used.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
RE: Gas Blending in a Pipe
Tank mixing is usually more expensive, but has the significant advantage of maintaining an accurate proportion down to zero flow.
One issue is that an expensive control setup will be required:
http://www.controlglobal.com/articles/2010/control...
Another issue is that the gas to the boiler should have a consistent Btu.
RE: Gas Blending in a Pipe
Thanks again guys. Pete
RE: Gas Blending in a Pipe
Reaction to change doesn't stop it
RE: Gas Blending in a Pipe