Low-pressure pipeline connected to high-pressure pipeline
Thread Content
Suppose there is a water pipeline at 25°C and 0.7 MPa, with a flow rate of 20 liters per hour; the pipeline is 100 meters long and has a diameter of 100 mm, and it leads into a container at atmospheric pressure. There is already another water pipeline at 25°C and 0.4 MPa, with a flow rate of 20 liters per hour. It is possible to connect this pipeline to the aforementioned pipeline using a tee at a point 50 meters away, right? Is that feasible? It’s definitely possible to create a new opening in the tank. Additionally, when using the mixer module in HYSYS, there are two options regarding the pressure after combination, which is not very clear
It’s simple – just measure the pressure at 50m and then decide
It’s okay to use the 2 pipelines at different times! Valve switching must be done!
This can be achieved by installing a control valve on that high-pressure pipeline. To determine what type of control valve is needed, it is necessary to calculate the pressure required in the pipeline downstream of the valve.
According to Bernoulli’s equation, the pressure drop at point 50 is very small; it doesn’t even need to be measured – it’s definitely above 0.6 MPa
With the control valve added, the essence of the problem disappears. Let’s change the question: for a pipeline at 0.7 MPa that extends 100 m before reaching a tank at atmospheric pressure, how should the pressure at the nozzle be considered? (There are two explanations I’ve encountered so far; the first one is that the starting point for 100m is 0.7 MPa, while it is 0 at the tank inlet, with the value decreasing gradually) ； The second option: 0.7 at the 100m starting point; it becomes the pressure drop in the pipeline from 0.7 to 100m before entering the tank, and the pressure is released to 0 at the moment of entry into the tank
There is a saying that when high pressure and low pressure are combined, the resulting pressure is low pressure. That’s how MIX in HYSYS is handled; I don’t know why
Direct pressure reduction cannot be achieved without valves; to reduce the pressure, pressure-reducing equipment is necessary. It’s necessary to calculate the material balance. Throughout the entire process, there must be a point where pressure reduction is carried out. When facing such problems, don’t get stuck in details and assume things without thinking
Measured values also include the opening degree of the inlet valve. Low and high pressure pipelines should not be used simultaneously.
This post was last edited by Southeast Branch_NEHV on 2021-3-24 at 17:28. 1. The pressure at the meeting point must be lower than that of the two other pressures; therefore, the maximum pressure at the meeting point is 0.4 MPa； 2. It can be inferred from 1 that the resistance at 0.7 MPa 50 m before the convergence is greater than that at 0.3 MPa ； 3. If the flow rate in both cases is 20, then the flow rate after they combine will be 40. Since the resistance over a distance of 50 meters is greater than 0.3 MPa, no calculations are necessary; it’s clear that the resistance in that section of pipe will be greater than 0.3 * 2 * 2 = 1.2 MPa ； 4. It can be concluded from the above that the outlet pressure is complex ； 5. Therefore, the high-pressure pipeline must have a resistance adjustment device before convergence