In PSA nitrogen production, the finished nitrogen will be approximately regarded as a mixture of oxygen and nitrogen. The purity of the finished nitrogen is obtained by analyzing the oxygen content first and then subtracting it.

1. Copper ammonia solution colorimetry

According to the national standard for industrial gas, when the oxygen content in nitrogen is less than 0.5%, the copper ammonia solution colorimetry is used for determination; its principle is to oxidize low-valent copper to high-valent copper, and then measure the oxygen content in the sample according to the change in gas volume. The specific operation of this method is as follows;

• Check and confirm that the instrument is well sealed.

• Ensure that the capillary between the absorption bottle and the gas measuring tube is pure nitrogen, and keep the liquid level of the absorption bottle at a marked position.

• Lift the level bottle and let the sealing liquid discharge all the gas in the gas measuring tube. Take a sample of 100 ml and shake the absorption bottle slightly to make the sample gas fully contact with the absorption liquid. Rotate the three-way piston to allow the residual gas to return to the gas measuring tube and keep the liquid level of the absorption bottle at the original marked position. Close the three-way piston, lift the level bottle, make the liquid level in the level bottle and the liquid level of the gas tube at the same level, and read the gas volume.

• Repeat the above operation until the two readings are the same, then read the reading and get the measurement result.

2. Pyrogallic acid alkaline solution absorption method

If the oxygen content in nitrogen is greater than 0.5%, the pyrogallic acid alkaline solution absorption method can be used for determination. The operation of the absorption method is similar to the copper ammonia solution colorimetry method:

• Take 100mL of sample nitrogen with a gas tube, and then send the sample into the absorber filled with pyrogallic acid alkaline solution to let it absorb the oxygen in it.

• Repeat the absorption several times. After the absorption is complete, use the gas tube to measure the amount of oxygen absorbed, and the purity of nitrogen can be directly read from the gas tube.

3. Ostwald gas analyzer

Ostwald gas analyzer is an instrument used to analyze gas content. It can be used to analyze the content of each component of a mixed gas containing oxygen, carbon dioxide, carbon monoxide, methane, nitrogen, and hydrogen.

Using this measurement method, you need to put a saturated sodium chloride solution in the gas tube and level bottle, and add 3 to 5 drops of prepared sulfuric acid and methyl orange solution for dyeing. Then put the prepared absorption liquid in the absorber.

When making formal measurements, pay attention to the following points:

• Fill the gas tube with room temperature water to create a constant temperature condition. Before and after the analysis, let the gas stay in the gas tube for 1 to 2 minutes, and then read the reading after balancing with the water temperature.

• Add liquid paraffin to the liquid surface of the absorption liquid exposed to the air to isolate the air and avoid inhaling oxygen in the air.

• Use two absorbers each time. When the amount of oxygen absorbed by the absorption liquid in one absorber is less than 50% of the oxygen content, immediately replace it with another one.