Relationship between gas components and flow rate
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The circulation volume of the methanol synthesis gas compressor changes significantly depending on the gas composition: it is around 600,000 cubic meters when the carbon content is high, around 300,000 cubic meters when the hydrogen content is high, and around 350,000 cubic meters when the hydrogen-to-carbon ratio is approximately 1.98. The pressure fluctuations also remain around 4.5–6.0 MPa. I would like to ask the experienced members of the forum why this happens. I simply don’t understand why such a change would occur, given that the previous system ensured a stable gas supply.
Changes in the gas composition affect the physical properties of the gas, such as density and viscosity, thereby influencing its flow behavior and compression efficiency within the compressor. As the high carbon content in the components increases, the gas density rises, resulting in an increase in the mass of gas per unit volume; consequently, the compressor cycle volume at the same flow rate also increases. Conversely, at high hydrogen contents, due to the low density of hydrogen, the mass of gas per unit volume decreases; therefore, the circulation volume is reduced. Changes in the hydrogen-to-carbon ratio also affect this effect. Furthermore, different gas compositions can also lead to fluctuations in pressure and temperature, thereby affecting the efficiency and stability of the compressor. .
From a flow rate perspective alone, measuring flow rate requires temperature and pressure compensation. Since the flow rate is calculated by multiplying the cross-sectional area of the pipe by the velocity, even mass flow rate must be converted into volumetric flow rate—after all, it’s flowing through a pipe. Therefore, density and composition are crucial factors affecting the final result. Especially gases. The liquid is probably more or less the same. As for the 600,000 cubic meters you mentioned, I’m not sure what type of flow meter was used to measure the 300,000 cubic meters; it might not be accurate if temperature, pressure, and density adjustments were not made.
The detection of compressor gas flow rate generally involves throttling-type devices such as Annubar. Temperature and pressure compensation is typically applied. Variations in gas composition can cause a significant deviation between the actual density and the designed value, necessitating correction; otherwise, the flow rate measurement will be inaccurate.
The higher the molecular weight, the easier it is to compress. Therefore, large changes in hydrogen content can cause pressure fluctuations at the compression outlet. Compression efficiency decreases.
This gets to the core of it. For the same unit, significant fluctuations in the gas composition are not recommended.