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Total rectification of argon is to separate oxygen from argon in a crude argon column to obtain crude argon with oxygen content less than 1×10-6 directly, and then separate it from fine argon to obtain fine argon with purity of 99.999%.

With the rapid development of air separation technology and the demand of market, more and more air separation units adopt the process of producing argon without hydrogen to produce high purity argon products. However, due to the complexity of argon production operation, many air separation units with argon did not lift argon, and some units in operation of argon system were not satisfactory due to the fluctuation of oxygen use condition and the limitation of operation level. Through the following simple steps, the operator can have a basic understanding of producing argon without hydrogen!

Commissioning of argon making system

* V766 in full opening process before discharging coarse argon column into fine argon column; Liquid blowout and discharge valves V753 and 754 at the bottom of crude argon tower I (24 ~ 36 hours).

* Full opening process argon out coarse argon tower I defining argon tower valve V6; Non-condensing gas discharge valve V760 at the top of the argon tower; Precision argon tower, liquid blowing at the bottom of precision argon measuring cylinder, discharge valves V756 and V755 (precooling precision argon tower can be carried out at the same time as precooling coarse argon tower).

Check the argon pump

* Electronic control system — wiring, control and display are correct;

* Sealing gas — whether the pressure, flow, pipeline is correct and does not leak;

* Motor rotation direction — point motor, confirm the correct rotation direction;

* Piping before and after the pump — check to make sure the piping system is smooth.

Check the argon system instrument thoroughly

(1) Rough argon tower I, Rough argon tower II resistance (+) (-) pressure tube, transmitter and display instrument is correct;

(2) Whether all liquid level gauge (+) (-) pressure tube, transmitter and display instrument in argon system are correct;

(3) Whether the pressure tube, transmitter and display instrument are correct at all pressure points;

(4) Whether the argon flow rate FI-701 (the orifice plate is in the cold box) (+) (-) pressure tube, transmitter and display instrument are correct;

⑤ Check whether all automatic valves and their adjustment and interlocking are correct.

Main tower working condition adjustment

* Increase oxygen production under the premise of ensuring oxygen purity;

* Control the lower column oxygen-rich liquid empty 36 ~ 38% (liquid nitrogen restricts into the upper column valve V2);

* Reduce the expansion amount under the premise of ensuring the main cold liquid level.

Liquid in coarse argon column

* On the premise of further precooling until the temperature of the argon tower no longer drops (the blowout and discharge valves have been closed), the liquid air is slightly opened (intermittently) and flows into the condensing evaporator valve V3 of the crude argon tower I to make the condenser of the crude argon tower intermittently work to produce backflow liquid, cool the packing of the crude argon tower I thoroughly and accumulate in the bottom part of the tower;

Tip: When opening the V3 valve for the first time, pay close attention to the pressure change of PI-701 and do not fluctuate violently (≤ 60kPa); Obact the liquid level LIC-701 at the bottom of crude argon tower I from scratch. Once it rises to 1500mm ~ full scale range, stop precooling and close V3 valve.

Precooling argon pump

* Stop valve before opening the pump;

* Blow out the valve V741 and V742 before opening the pump;

* slightly open (intermittently) the pump after blowing off valve V737, V738 until the liquid is continuously ejected.

Tip: This work is carried out under the guidance of argon pump supplier for the first time. Safety issues to prevent frostbite.

Start the argon pump

* Fully open the return valve after the pump, fully close the stop valve after the pump;

* Start argon pump and fully open the back stop valve of argon pump;

* Observe that the pump pressure should be stabilized at 0.5 ~ 0.7Mpa(G).

Crude argon column

(1) After starting the argon pump and before opening the V3 valve, the liquid level of LIX-701 will decrease continuously due to the liquid loss. After starting the argon pump, the V3 valve should be opened as soon as possible to make the condenser of the argon tower work and produce backflow liquid.

(2) V3 valve opening must be very slow, otherwise the main tower conditions will produce large fluctuations, affecting the purity of oxygen, crude argon tower after work to open the argon pump delivery valve (opening depends on the pump pressure), the final delivery valve and return valve to stabilize the FIC-701 liquid level;

(3) The resistance of two crude argon columns is observed. The resistance of normal crude argon column II is 3kPa and that of crude argon column I is 6kPa.

(4) The working condition of the main tower should be closely observed when crude argon is put in.

(5) After the resistance is normal, the main tower condition can be established after a long time, and all 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) At the initial stage of argon column operation, the extraction amount of process argon should be reduced (15 ~ 40m³/h) in order to improve the purity. When the purity is close to normal, the flow rate of process argon should be increased (60 ~ 100m³/h). Otherwise, the imbalance of argon column concentration gradient will easily affect the working condition of main column.

Pure argon column

(1) After the oxygen content of process argon is normal, the V6 valve should be gradually opened to turn down the V766 and the process argon is introduced into the fine argon tower;

(2) the liquid nitrogen steam valve V8 of argon tower is fully open or cast automatically to control the nitrogen side pressure PIC-8 of the condensing evaporator of argon tower at 45kPa;

(3) gradually open the liquid nitrogen into the condensation evaporator valve V5 of the argon column to increase the working load of the argon column condenser;

(4) When V760 is properly opened, it can be fully opened at the initial stage of the precision argon tower. After normal operation, the flow of non-condensable gas discharged from the top of the precision argon tower can be controlled within 2 ~ 8m³/h.

The negative pressure of PIC-760 precision argon tower is easy to appear when the working condition fluctuates slightly. The negative pressure will cause the wet air outside the cold box to be sucked into the precision argon tower, 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 and V760).

(6) When the liquid level at the bottom of the precision argon tower is ~ 1000mm, slightly open the nitrogen path valve V707 and V4 of the reboiler at the bottom of the precision argon tower, and control the opening according to the situation. If the opening is too large, the pressure of PIC-760 will be increased, resulting in the decrease of the flow rate of the process argon Fi-701. It is better to control the PIC-760 precision argon tower pressure at 10 ~ 20kPa if it is opened too small.

Argon content adjustment of argon fraction

The content of argon in the argon fraction determines the extraction rate of argon and directly affects the yield of argon products. The proper argon fraction contains 8 ~ 10% argon. The factors affecting the argon content of argon fractions are mainly 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, the greater the risk of nitrogen plug;

* Expansive air volume — the smaller the expansion air volume, the higher the argon content of 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 smaller the load, the higher the argon content of the argon fraction, but the smaller the load, the smaller the argon production.

Argon production adjustment

When the argon system works smoothly and normally, it is necessary to adjust the output of argon product to reach the design condition. The adjustment of the main tower shall be made in accordance with Clause 5. The flow of argon fraction depends on the opening of V3 valve and the flow of process argon depends on the opening of V6 and V5 valve. The principle of adjustment should be as slow as possible! It can even increase the opening of each valve by only 1% every day, so that the working condition can experience the purification system switching, the change of oxygen consumption and the fluctuation of the power grid. If the purity of oxygen and argon is normal and the working condition is stable, the load can be continued to increase. If a working condition has a tendency to get worse, it indicates that the working condition has reached its limit and should be adjusted back.

Treatment of nitrogen plug

What is a nitrogen plug? The load of the condensation evaporator decreases or even stops working, and the resistance fluctuation of the argon tower decreases until 0, and the argon system stops working. This phenomenon is called nitrogen plug. Maintaining stable working condition of main tower is the key to avoid nitrogen jam.

* Slight nitrogen plug treatment: fully open V766 and V760 and appropriately reduce the oxygen production. If the resistance can be stabilized, the whole system can resume normal operation after the nitrogen entering the argon system is exhausted;

* serious of nitrogen treatment: once appear steep fluctuations in crude argon resistance, and in a short period of time into 0, shows that the working condition of argon tower collapse, at this time should be fully open V766, V760, seated argon pump sends out the valve, then fully open after argon pump backflow preventer, seated V3, try to make the liquid argon tower in argon tower, in order to avoid further damage of oxygen purity appropriate down oxygen production, such as working condition of main tower into argon tower again after returning to normal.

Fine control of argon system operating condition

① The boiling point difference between oxygen and nitrogen is relatively large because the boiling points of oxygen and argon are close to each other. In terms of the difficulty of fractionation, the difficulty of adjusting argon is much greater than that of adjusting oxygen. The oxygen purity in argon can reach the standard within 1 ~ 2 hours after the resistance of the upper and lower columns is established, while the oxygen purity in argon can reach the standard within 24 ~ 36 hours after the normal operation after the resistance of the upper and lower columns is established.

(2) The argon system is difficult to build and easy to collapse in the working condition, the system is complex and the debugging period is long. The nitrogen plug may appear in a short time in the working condition if there is any carelessly. It will take about 10 ~ 15 hours to establish the resistance of the crude argon column to reach the normal purity of oxygen in argon if the operation can be carried out according to the rule 13 correctly to ensure the total amount of accumulated argon components in the argon column.

(3) The operator should be familiar with the process, and have a certain foresight in the debugging process. Each minor adjustment of argon system will take a long time to be reflected in the working condition, and it is taboo to frequently and greatly adjust the working condition, so it is very important to keep a clear mind and a calm state of mind.

(4) The yield of argon extraction is affected by many factors. Because the operation elasticity of argon system is small, it is impossible to stretch the operation elasticity too tight in the actual operation, and the fluctuation of working conditions is very unfavorable to the extraction rate. Chemical industry, non-ferrous smelting and other equipment with oxygen extraction rate is stable than the intermittent use of oxygen steel-making higher; The argon extraction rate of multiple air separation networks in steelmaking industry is higher than that of single air separation oxygen supply. The argon extraction rate with large air separation was higher than that with small air separation. The extraction rate of high level careful operation is higher than that of low level operation. The high level of supporting equipment has high argon extraction rate (such as the efficiency of expander; Automatic valves, accuracy of analytical instruments, etc.).