The operation of producing argon in an air separation plant is complicated.
Argon full rectification is to separate oxygen from argon in a crude argon tower, directly obtain crude argon with an oxygen content of less than 1×10-6, and then separate from refined argon to obtain refined argon with a purity of 99.999% .
With the rapid development of air separation technology and market demand, more and more air separation plants use the hydrogen-free argon production process to produce high-purity argon products. However, due to the complexity of the argon production operation, many argon air separation plants do not have argon extraction, and some of the argon systems in operation are not satisfactory due to fluctuations in oxygen use conditions and limitations of operating levels. With the following simple steps, the operator can have a basic understanding of hydrogen-free argon production!
Argon production system debugging
* V766 is in the fully open process before the crude argon column is discharged into the fine argon column;
* Fully open process argon out of crude argon column I defines argon column valve V6; non-condensable gas discharge valve V760 at the top of the argon column; precision argon column, spray liquid at the bottom of the precision argon graduated cylinder, and discharge valves V756 and V755 (pre-cooling precision argon column can be combined with pre-cooling the crude argon column at the same time).
Check the argon pump
* Electric control system - wiring, control and display are correct;
* Sealing gas - pressure, flow, pipeline is correct, no leakage;
* Motor rotation direction - click the motor to confirm the correct rotation direction;
* Piping before and after the pump - check to make sure the piping system is clear.
Thorough inspection of argon system instrumentation
(1) Whether the resistance (+) (-) pressure pipes, transmitters and display instruments of crude argon column I and crude argon column II are correct;
(2) Check whether all liquid level gauges (+) (-) pressure pipes, transmitters and display instruments in the argon gas system are correct;
(3) Whether the pressure pipe, transmitter and display instrument of each pressure point are correct;
(4) Argon flow FI-701 (orifice plate in the cold box) (+) (-) pressure pipe, transmitter and display instrument are correct;
⑤ Check that all automatic valves and their adjustment and interlocking are correct.
Main tower working condition adjustment
* Increase oxygen production on the premise of ensuring oxygen purity;
* Control the oxygen-enriched liquid in the lower column to empty 36~38% (liquid nitrogen is restricted from entering the upper column valve V2);
* Reduce the expansion amount on the premise of ensuring the main cooling liquid level.
liquid in crude argon column
* On the premise of further pre-cooling until the temperature of the argon column does not drop (the blow-off valve is closed), the liquid air is slightly opened (intermittently) and flows into the crude argon column condensation evaporator valve V3 to make the crude argon column condenser work intermittently, resulting in reflux liquid, so that the thick argon column packing is completely cooled and accumulated at the bottom of the column;
Tip: When opening the V3 valve for the first time, pay close attention to the pressure change of PI-701, do not fluctuate violently (≤60kPa); observe the liquid level LIC-701 at the bottom of the crude argon column I from the beginning. Once it rises to 1500mm~full scale, stop the precooling and close the V3 valve.
Pre-cooled argon pump
* Shut-off valve before turning on the pump;
* Blow out valves V741 and V742 before starting the pump;
* After venting valves V737, V738, turn on the pump slightly (intermittently) until the liquid is ejected continuously.
Hint: This work was performed for the first time under the direction of the argon pump supplier. Safety issues to prevent frostbite.
Start the argon pump
* Fully open the backflow valve after the pump, and fully close the pump after the stop valve;
* Start the argon pump and fully open the back stop valve of the argon pump;
* Observe that the pump pressure should be stable at 0.5 ~ 0.7Mpa(G).
Crude Argon Column
(1) After starting the argon pump, before opening the V3 valve, the liquid level of LIX-701 will continuously drop due to liquid loss. After the argon pump is started, the V3 valve should be opened as soon as possible to make the argon column condenser work to generate reflux.
(2) The V3 valve must be opened very slowly, otherwise the working conditions of the main tower will fluctuate greatly, which will affect the oxygen purity. After the crude argon tower works, open the argon pump delivery valve (the opening degree depends on the pump pressure), and finally stabilize the FIC-701 Liquid level delivery valve and return valve;
(3) Observe the resistance of the two thick argon columns. The resistance of ordinary crude argon column II is 3kPa, and the resistance of crude argon column I is 6kPa.
(4) The working condition of the main tower should be closely observed when the crude argon is put in.
(5) After the resistance is normal, the main tower state can be established after a long time, and the above operations should be small and slow;
(6) After the initial argon system resistance is normal, the oxygen content of the process argon reaches the standard for ~36 hours;
(7) In the early stage of the operation of the argon column, in order to improve the purity, the extraction amount of process argon should be reduced (15-40m³/h). When the purity is close to normal, the flow rate of process argon should be increased (60-100m³/h). Otherwise, the imbalance of the concentration gradient of the argon column can easily affect the working state of the main column.
pure argon column
(1) After the argon and oxygen content of the process is normal, gradually open the V6 valve, lower the V766, and introduce the process argon into the refined argon tower;
(2) The argon tower liquid nitrogen vapor valve V8 is fully opened or poured automatically, and the nitrogen side pressure PIC-8 of the argon tower condensation evaporator is controlled at 45kPa;
(3) gradually open the liquid nitrogen to enter the argon tower condensing evaporator valve V5 to increase the working load of the argon tower condenser;
(4) When V760 is opened correctly, it can be fully opened in the initial stage of the precision argon column. After normal operation, the flow rate of non-condensable gas discharged from the top of the refined argon column can be controlled at 2-8m³/h.
The PIC-760 precision argon column is prone to negative pressure when the working conditions fluctuate slightly. The negative pressure will cause the moist air outside the cold box to be sucked into the precision argon column, and the ice will freeze on the tube wall and the surface of the heat exchanger, causing blockage. Therefore, the negative pressure should be eliminated (control the opening of V6, V5, V760).
(6) When the liquid level at the bottom of the refined argon column is ~1000mm, slightly open the nitrogen passage valves V707 and V4 of the reboiler at the bottom of the refined argon column, and control the opening according to the situation. If the opening is too large, it will increase the pressure of the PIC-760, causing the flow of the process Argon Fi-701 to drop. If the pressure of PIC-760 precision argon column is too small, it is best to control it at 10-20kPa.
Argon fraction argon content adjustment
The argon content in the argon fraction determines the argon extraction rate and directly affects the argon product yield. A suitable argon section contains 8-10% argon. The main factors affecting the argon content of the argon fraction are as follows:
* Oxygen production - the higher the oxygen production, the higher the argon content in the argon fraction, but the lower the oxygen purity, the higher the nitrogen content in the oxygen, and the greater the risk of nitrogen blockage;
* Expansion air volume - the smaller the expansion air volume, the higher the argon content of the argon fraction, but the smaller the expansion air volume, the smaller the liquid product output;
* Argon Fraction Flow Rate -- Argon Fraction Flow Rate is the crude argon column load. The lower the loading, the higher the argon content of the argon fraction, but the lower the loading, the lower the argon production.
Argon production adjustment
When the argon gas system works smoothly and normally, the output of argon gas product needs to be adjusted to meet the design conditions. The adjustment of the main tower is carried out in accordance with Article 5. The flow of the argon fraction depends on the opening of the V3 valve, and the flow of the process argon depends on the opening of the V6 and V5 valves. The principle of adjustment is that the slower the better! It can even increase the opening of each valve by only 1% every day, so that the working conditions can experience the switching of the purification system, changes in oxygen consumption and fluctuations in the power grid. If the purity of oxygen and argon is normal and the working conditions are stable, the load can be continued to increase. If working conditions tend to deteriorate,
Treatment of nitrogen plugs
What is a nitrogen plug? The load of the condensing evaporator is reduced or even stops working, the resistance fluctuation of the argon tower is reduced to 0, and the argon gas system stops working. This phenomenon is called nitrogen plugging. Keeping the main tower in a stable working state is the key to avoiding nitrogen blockage.
* Slight nitrogen plug treatment: fully open V766 and V760 to appropriately reduce oxygen production. If the resistance can be stabilized, after the nitrogen entering the argon system is exhausted, the whole system can resume normal operation;
* Nitrogen treatment is serious: once the crude argon resistance fluctuates violently and becomes 0 in a short time, it indicates that the argon tower is in a collapsed working state. After the anti-reflux valve is fully opened, seat V3, try to keep the liquid argon tower in the argon tower, so as not to further damage the oxygen purity, and appropriately reduce the oxygen production.
Fine control of working conditions of argon gas system
①The difference between the boiling points of oxygen and nitrogen is relatively large, because the boiling points of oxygen and argon are close. In terms of the difficulty of fractionation, the difficulty of regulating argon is much greater than that of regulating oxygen. The oxygen purity in argon can reach the standard within 1-2 hours after the upper and lower column resistances are established, while the oxygen purity in argon can reach the standard within 24-36 hours after the upper and lower column resistances are established after normal operation. Build above and below.
(2) The argon gas system is difficult to build and easy to collapse under working conditions, the system is complex, and the debugging period is long. Under working conditions, a little carelessness may cause nitrogen plugs in a short period of time. If you can operate according to Rule 13 correctly to ensure the total amount of argon gas accumulated in the crude argon column, it will take about 10 to 15 hours for the resistance of the crude argon column to build up to the normal oxygen purity in argon. Argon column.
(3) The operator should be familiar with the process and have certain predictability for the debugging process. Every minor adjustment of the argon gas system will be reflected in the working conditions for a long time. Frequent and large adjustment of the working conditions is a taboo, so it is very important to keep a clear head and a calm attitude.
(4) The extraction yield of argon is affected by many factors. Due to the small operating elasticity of the argon gas system, it is impossible to tighten the operating elasticity in actual operation, and the fluctuation of operating conditions is very unfavorable to the extraction rate. The oxygen extraction rate of chemical, non-ferrous smelting and other equipment is stable, which is higher than that of intermittent use of oxygen for steelmaking; the argon extraction rate of multi-air separation network in the steelmaking industry is higher than that of single air separation oxygen supply. The argon extraction rate of large air separation is higher than that of small air separation. The extraction rate for high-level fine operations is higher than for low-level operations.
