TURBULENCE IN NATURAL GAS 1

[JACHA2000]

Platform offshore natural gas production have the worry of having a bottleneck at admission 3 Gas Vessel, as these three flowlines and output are the same diameter (8 "ANSI 600) and can produce turbulence???. Currently it has an average of +/- 22 psi pressure differential between the production Gas Vessel and output pipeline.
As shown in the graph and it's really like we have in the field, the production test Gas Vessel and enter below and the new MBD-2020 Gas Vessel above the line output to the pipeline.

PROFESSIONAL CRITERIA WOULD LIKE TO KNOW ON THE SUBJECT THAT COULD HAVE PROBLEMS WITH THIS CONFIGURATION AND HOW WE CAN MITIGATE

 

[zdas04]

"Turbulence" is a technical term with a precise definition (i.e., Reynolds Number greater than 6000) that is used in many no-technical discussions (e.g., "the airplane experienced turbulence"). Turbulence is manifested as a random three dimensional motion imposed on the flow. The 22 psid you are talking about is not "turbulence" as much as it is "interference" or "phase interactions".

Each of your three inputs is moving at its own bulk velocity, which means it is at a different dynamic pressure (very very small differences, granted, but different nonetheless). Until these streams homogenize themselves, they will act like a multi-phase flow, which means that they will expend a lot of energy changing flow regime, just like a multi-phase stream..

The useful flow area of a line is a very complex subject, but a rule of thumb that works is 2X8"=10", 8"+10"<12", 2X10"=12". This is not obvious from combining flow area and converting the combined area to an effective diameter (e.g. 8+8=11.3), but the wetted area (i.e. the place where the no-flow boundary occurs) is 3/5 as big in the 10" which makes the big pipe more effective than the two smaller pipes. CFD runs supports that the reduction in the volume of the no-flow boundary theoretically makes the pipe more efficient. Putting two 8-inch streams into an 8-inch pipe significantly increases the velocity of the combined stream. If you had known you were going to combine these three streams at design time, the departing pipe should have been 12" instead of 10", nothing you can do about that now.

As a general rule, I would have tied the new production unit into the second stub instead of the first stub (the models show slightly better mixing with a side stream instead of a head-to-head stream, but not big enough to change it if already built, the head-to-head configuration is probably costing you 2-3 psid of the 22 you are losing. The rest is just too much gas in too little space, the reservoir will fix that for you over time.

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