Main Equipment, Processes And Management Transformation Measures Of Air Separation Unit

Contents

1.Main equipment and processes of air separation unit
1.1 Air compressor
1.2 Oxygen compressor
1.3 Medium-pressure nitrogen compressor
1.4 Low-pressure nitrogen compressor
1.5 Air cooling tower
1.6 Molecular sieve adsorber
1.7 Air separation tower
2.Daily management measures
2.1 Cold box inspection management
2.2 Air compressor maintenance management
2.3 Process indicator control
2.4 Multi-level inspection system
3.Technical transformation measures
3.1 Transformation purpose
3.2 Transformation content
3.2.1 Conditions that the water spray system should have
3.2.2 Water spray technical description
3.2.3 Preparation before water spraying
3.2.4 Water spraying steps
3.3 Precautions
3.4 Effect after transformation
4.Conclusion

1 Main equipment and processes of air separation unit
1.1 Air compressor
Use energy-saving rotor, driven by 6kV high-voltage motor. The air is sucked in after passing through a three-stage filter (removing impurities above φ=0.3μm), and is sent to the air cooling tower after four-stage compression.

1.2 Oxygen compressor
Driven by a 6kV high-voltage motor, the oxygen from the air separation enters the compressor, is compressed to 100℃ and 3.5MPa through five sections and ten stages, and is sent to the oxygen pipeline network through the outlet valve.

1.3 Medium-pressure nitrogen compressor
Driven by a 6kV high-voltage motor, the nitrogen from the air separation is compressed to 2.5MPa and 40℃ through five sections and ten stages, and is sent to the medium-pressure nitrogen pipeline network.

1.4 Low-pressure nitrogen compressor
Driven by a 6kV high-voltage motor, the nitrogen from the air separation is compressed to 0.55MPa and 40℃ through a single-axis five-time six-stage intermediate cooling, and is sent to the low-pressure nitrogen pipeline network.

1.5 Air cooling tower
Polyethylene jet ring filler is used to reduce the air temperature to 10~14℃.

1.6 Molecular sieve adsorber
The lower layer is inert alumina, the middle layer is activated alumina, and the upper layer is molecular sieve, which is used to remove moisture, hydrocarbons and CO2 in the air.

1.7 Air separation tower
After the purified air is cooled by heat exchange, oxygen with a purity of > 99.6% and nitrogen with a purity of <2.0×10⁻⁶(V) are obtained in the main distillation tower, and liquid argon with a purity of < 2.0×10⁻⁶(V) is obtained in the argon system.

2 Daily management measures

2.1 Cold box inspection management
Establish a cold box inspection ledger, regularly check the frost and ice hanging on the cold box wall, the consistency of the valve switch position with the central control, and the integrity of the pressure pipe transmitter, judge the nitrogen filling situation in the cold box through the upper, middle and lower pressure gauges, and test and analyze the exhaust gas components and the exhaust size of the breathing hole to ensure the integrity of the cold box and the flexibility of the valve.

2.2 Air compressor maintenance management
Replace the air filter regularly to ensure the normal suction pressure of the unit; regularly spray water on the impeller to clean the dirt and maintain the vibration displacement of the unit within the normal range.

2.3 Process indicator control
Strictly monitor the process indicators, adjust them in time when they deviate, analyze the reasons and formulate measures when they cannot be adjusted, and correct them when they are stopped for maintenance.

2.4 Multi-level inspection system
It is divided into six levels: workshop leaders, safety officers, process engineers, equipment engineers, maintenance teams and operation teams. Each level finds and solves problems from different functional perspectives to achieve all-round diagnosis of the device.

3 Technical transformation measures

3.1 Transformation purpose
To solve the problem that there are still fine dust particles after the air compressor inlet filtration, which leads to dust accumulation, carbonization and corrosion of the impeller volute, thereby reducing the efficiency of the compressor and increasing the vibration value, water spray descaling technology is used.

3.2 Modification content
Desalted water is injected through the water tank inlet valve, and the ≥0.6MPa nitrogen from the medium-pressure nitrogen compressor is used as the water tank pressure gas source. The water is divided into four paths through the outlet valve and filter, and used as the first to fourth level descaling water spray.

3.2.1 Conditions that the water spray system should have

Nozzles, branch pipes, main water pipes, pressure water tanks, and water filters are intact;
Water quality, water pressure, and water volume meet the requirements;
Pipes and valves are clean, and the instrument verification is qualified;
The pipeline has been treated with anti-corrosion;
All parts of the air compressor are intact and operate normally.

3.2.2 Technical description of water spraying
Water volume 33L/min, maximum water volume 80L/min;
Water spraying pressure is shown in Table 1 (local atmospheric pressure 91kPa).

3.2.3 Preparation before water spraying
Confirm that the valve of the water spray pipeline is closed and the water filter is not blocked;
Confirm that the instrument display is correct;
The air source pressure of the pressure water tank is 0.6~1.0MPa (gauge pressure);
Reduce the discharge pressure (close the inlet guide vane to reduce the load);
Slightly open the condensate discharge valve of the air compressor intercooler;
Wash the water tank with desalted water and fill it to 50%;
Fully open the pressure nitrogen inlet valve to charge to 0.5~0.6MPa;
Record the air compressor flow, discharge pressure, inlet and outlet pressure/temperature at each level, vibration, motor current, voltage and other parameters.

3.2.4 Water spraying steps
Flush in order according to 1, 2, 3, and 4 levels, open the water tank outlet valve, fully open the first valve of the water spray pipeline, slightly open the blow-off valve to clean the pipeline, and close it after draining and cleaning;
Gradually open the second valve to fully open, and use the first valve to adjust to the water spray pressure to spray water;
Each level of water spraying lasts 3~8 minutes;
After the water spraying is completed, close the valve and open the blow-off valve to drain;
Fully close the pressure nitrogen valve, open the water tank exhaust valve and drain valve to discharge the remaining water and gas;
Open the inlet filter to drain the remaining water in the pipeline, and reset it after blowing it with air;
Close the condensate discharge port (except for the automatic discharge of the steam trap), and continue to run the air compressor for 20 minutes to dry the pipeline;
Record the data when running at full load and compare it with the data before water spraying to evaluate the effect;
Close the water tank exhaust valve and drain valve.

3.3 Precautions
During maintenance, check the nozzle direction (the first level is opposite to the air intake direction, the second to fourth levels are the same), the wear and cracking of the nozzle, and the rust of the air pipeline;
Cut off the water source at ordinary times, and add a blind plate to prevent leakage and rust when necessary;
It is strictly forbidden to spray water on the first-level impeller when the ambient temperature is < 2℃;
The best time for flushing is before shutdown, and it can also be flushed online (partially close the inlet blade regulator to reduce the load);
In winter, add steam to the water inlet pipeline, drain the inlet pipeline water when standby, and strengthen the inspection and chartering of personnel.

3.4 Effect after transformation
The impeller and volute sediments are washed away, the compressor remains in a balanced state, the operating parameters are normal, and the system is not shut down due to air compressor reasons, ensuring the long-term stable operation of the air separation system.

4 Conclusion

As an important part of coal chemical industry, the air separation unit needs to consolidate daily management and strengthen technical transformation to ensure long-term safe and stable operation, provide guarantees for coal chemical production, and maximize benefits.