The impact of pipe diameter changes on the overall operation of the pipeline
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Will connecting a DN2200 pipe in the middle of the DN2600 low-pressure coal gas pipeline affect the overall operation of the pipeline? The original gas pipeline has a pressure of 4 kPa, a medium temperature of 60°C, and a flow rate of 200,000–250,000 m3/h. To connect the two pipelines, an additional pipe is to be installed in between; however, in order to save costs, it is not desired to use a DN2600 pipe. Is it feasible to use a DN2200 pipe instead?
It’s not impossible, but local resistance should be calculated: the drag coefficient method. Local resistance plays a decisive role in the pressure drop in pipes; there is definitely a limit to how much it can increase. The flow rate certainly remains unchanged; when the pipe diameter suddenly decreases, the flow velocity of the fluid in the pipe increases by a factor of 1.13. The formula used to calculate pipeline resistance is related to the square of the flow velocity – that is, 1.13 squared equals 1.27, meaning the resistance increases by 27%. You can calculate the pressure drop yourself to see whether it meets the requirements of the subsequent processing steps
I thought the pressure would be very low and wouldn’t have much impact, so I didn’t give much thought to the pressure issue. I was mainly concerned about whether, with a constant flow rate, the high flow velocity of the fluid inside the pipe could affect its operation. But from what you say, it seems that pressure does have a significant impact as well, right?
It is necessary to consider the pressure drop in this pipe to see if it will affect gas transportation. Additionally, impurities accumulate at the diameter change points.
If your flow rate is 250,000 units under operating conditions, which corresponds to a gas flow velocity of 18 m/s, then choosing a DN2200 pipe for you will be no problem! Calculate the resistance based on the length of your pipeline transmission; if the resistance meets the requirements, it’s fine to replace all of your DN2600 pipes with DN2200 ones in order to save costs
I calculated the flow rate of the medium, which is why I chose a pipe diameter of DN2200. The client initially suggested DN1800, but I thought that the flow rate shouldn’t be too high, so I felt that DN2200 was more appropriate. The length of the pipeline isn’t very large – it’s only 28 meters. As long as the pipeline resistance is acceptable, there should be no problem, right?
Only 28m? There’s no need to calculate the resistance; it definitely won’t be a problem