Process flow and troubleshooting for nitrogen production using PSA nitrogen generators in the coal industry.

Nitrogenous Sea Floating and Sinking

The nitrogen generator uses high-quality carbon molecular sieves as adsorbents and employs the pressure swing adsorption principle at room temperature to separate air and produce high-purity nitrogen.

Typically, two adsorption towers are connected in parallel, with the inlet pneumatic valves controlled by a PLC to operate automatically, alternating between pressurized adsorption and depressurized regeneration to complete nitrogen-oxygen separation and obtain the required high-purity nitrogen.

(PSA) for nitrogen generation: Carbon molecules can simultaneously adsorb oxygen and nitrogen from the air, and the amount of adsorption increases with increasing pressure. Moreover, carbon molecular sieves adsorb oxygen very quickly, reaching over 90% in about 1 minute; while the amount of nitrogen adsorbed is only about 5% at this time. Therefore, the adsorption at this point is mostly oxygen, and the remainder is mostly nitrogen.

The nitrogen generator's workflow is achieved by a programmable logic controller (PLC) controlling three 2-position 5-way pilot solenoid valves, which in turn control the opening and closing of eight pneumatic pipeline valves. The three 2-position 5-way pilot solenoid valves control the left suction, equalization, and right suction states, respectively. The timing sequences for these states are stored in the PLC. In the power-off state, the pilot gas from all three 2-position 5-way pilot solenoid valves is connected to the closed ports of the pneumatic pipeline valves. When the process is in the left suction state, the solenoid valve controlling left suction is energized, and the pilot gas connects the opening ports of the left suction inlet valve, left suction gas generator valve, and right exhaust valve, causing these three valves to open and completing the left suction process. Simultaneously, desorption occurs in the right adsorption tower. When the process is in the equalization state, the solenoid valve controlling equalization is energized, and the other valves are closed. The pilot gas connects the opening ports of the upper and lower equalization valves, causing these two valves to open and completing the equalization process. When the process is in the right-suction state, the solenoid valve controlling the right suction is energized, and the pilot gas connects the opening ports of the right suction inlet valve, the right suction gas generator valve, and the left exhaust valve, causing these three valves to open and completing the right suction process. Simultaneously, the left adsorption tower desorbs. In each process segment, all valves except those that should be open should be closed. To ensure that the oxygen released from the molecular sieve due to pressure reduction is completely discharged into the atmosphere, nitrogen gas is used to purge the desorbing adsorption tower through a normally open backflush valve, blowing the oxygen out of the tower. This process is called backflush, and it occurs simultaneously with desorption.

The workflow of our nitrogen generator is controlled by a Siemens S7-200 programmable controller, which first controls the solenoid valves, and then the solenoid valves control the opening and closing of eight pneumatic pipeline valves in towers A and B respectively. The solenoid valve timing sequence is stored in the programmable controller. During the years of operation of our nitrogen generator, the main problems have been low gas production pressure and high oxygen content.

The main reasons for low stress are:

1. If the incoming gas pressure is low, the natural gas production pressure will also be insufficient.
2. High gas consumption on site, insufficient gas production, naturally leading to increased pressure.
3. Clogged or faulty filters and valves in the gas supply pipeline reduce gas flow, resulting in nitrogen production far less than gas consumption and consequently low system pressure.
4. A leak in the gas pipeline caused the pressure to drop.
5. Abnormal valve circuit control or mechanical jamming in the nitrogen generator.

The purity of nitrogen generators is generally required to be above 99.9%. High oxygen content will affect production. The main reasons are as follows, based on the operating principle:

1. The original compressed air pressure was low, resulting in poor pressure swing adsorption and ineffective deoxygenation.
2. solenoid valves or pneumatic valves controlling the left and right towers , such as delayed opening and closing times or valves that are stuck and refusing to operate, will cause gas leakage. This will lead to erratic operation of the two towers, poor nitrogen production, and high oxygen content.
3. Control the amount of gas used appropriately. Using more gas than the recommended flow rate will also result in poor nitrogen production.
4. Failure to replace the carbon molecular sieve and filter element for an extended period can also lead to high oxygen content.
5. A control circuit malfunction causes a solenoid valve malfunction, preventing it from opening and closing properly, thus resulting in an oxygen content malfunction.