Where has the outlet pressure of the Roots blower gone?
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Our company has two Roots blowers with a capacity of 486 m3/min each, one blower with a capacity of 303 m3/min, and one with a capacity of 280 m3/min. These blowers are used to draw semi-water gas from the gas tank and send it to the compressor for the production of synthetic ammonia. The process flow is as follows: gas tank – gas washing tower – Roots blower – cleaning tower 1 – desulfurization tower – cleaning tower 2 – electrostatic coking removal tower. Recently, we’ve encountered a problem that we’re unable to resolve; we would appreciate it if everyone could help discuss it. During normal operation, one 486 m3/min blower and one smaller blower are used, and the pressure at the inlet of the desulfurization tower is kept above 350 mmHg. However, when two 486 m3/min blowers are used, the pressure drops significantly, to around 326 mmHg, despite no changes in other process conditions. We would be very grateful if someone could provide some guidance on this issue!
When you operate two large Roots compressors, the number of compressors running increases, which speeds up the gas extraction rate; as a result, the outlet pressure of the Roots compressors drops.
If all other process conditions remain unchanged and only the spare large Roots blower is put into use, then the cause must be sought in this machine: 1. The spare machine fails to operate for some reason； 2. Leakage in the return circuit of the spare unit ； 3. Backup unit reversing (unlikely, a very basic error)
1. The gas consumption in the later processing stages increases, while the gas supply to the earlier stages either does not increase or increases insufficiently; as a result, both the inlet and outlet pressures decrease. 2. Problems with the Roots blower itself, such as issues with the internal clearance gaps or clogs in the inlet and outlet filters. 3. Leaks in the pipes, or poor sealing at the connections.
In normal operation, when two identical pump units are started simultaneously, the pressure generated will be lower than that produced by starting two pumps of different capacities. Regarding the observed phenomenon, the same pressure source generated by identical units leads to a relative decrease in the outlet pressure, which is reflected as a drop in pressure on the corresponding equipment. Moreover, when two high-power compressors are used, with the air supply source for the compressors remaining unchanged, the power required to perform the same task is reduced. The inlet pressure of the compressors drops significantly, and the outlet pressure also decreases (due to the compression ratio; both the inlet and outlet pressures fall). It is a normal phenomenon.
Has LZ connected the two Roots blowers in series to see if the pressure increases? When blowers are used in parallel, only the air volume increases while the pressure does not. If both blowers are running at the same time, does the system’s air volume increase and does the wind speed go up as well? The pressure generated by increasing wind speed increases as a square. Does the pressure at the same location decrease when the system pressure drop increases? It works on the same principle as voltage.
Agree with opinion 5#. Although different fans have higher flow rates than smaller fans, it is not necessarily the case that their wind pressure is also higher than that of smaller fans! ! !
This is because the volume of gas being pumped in has increased, and the production capacity of the gas generation furnace is limited by the size of the gas tank – to prevent the tank from collapsing, it’s necessary to increase the circulation rate by expanding the secondary line; as a result, the outlet pressure decreases. :D :D :D :D :D :D
I have a slight question: If the gas supply source remains unchanged but the inlet pressure of the compressor decreases, how should this be understood? Could you explain it?
Let me be direct: the safety valve at the fan outlet has activated, causing the flow to go from the outlet back to the inlet.
For such positive-displacement fans, with the inlet pressure remaining constant (as the original poster mentioned, other process parameters also remain unchanged), there is no difference in outlet pressure between using two blowers with high airflow rates and one blower of larger size combined with one of smaller size, since the compression ratio is fixed in all cases. The poster reported that the pressure at the inlet of the desulfurization tower had decreased; therefore, it is necessary to check whether the pressure before the outlet shut-off valve of the blower has increased.