Whether in chemical manufacturing, electronics, laser cutting or the food and beverage industry, a safe and reliable supply of industrial gases is critical. The demand for nitrogen is essential in the production process in many fields. The main purpose is that nitrogen can be used for explosion protection and corrosion protection and to ensure process and production safety.
Some enterprises and factories have found that the purity of nitrogen gas will decrease after the nitrogen generator is used for a long time in industrial production, so what factors affect the purity of nitrogen gas. This article will focus on the common problems and solutions of nitrogen generators whose purity is not up to standard.
Nitrogen flow exceeds the standard
Fault description:
1. The indication number of the qualified nitrogen flowmeter is greater than the rated flow rate on the nameplate
2. The impure emptying flow rate is greater than the rated flow rate and cannot reach the set purity
3. Excessive regeneration gas flow
4. Switching timing error
Solution:
1. Adjust the ball valve to limit the qualified nitrogen flow to the rated value
2. Adjusting the ball valve to limit the impure nitrogen flow to 2/3 of the rated value
3. Observe the opening of the regenerated balloon valve, which is 1/5 of the normal opening
4. The switching period of the nitrogen generator is too short/too long, and the pressure equalization is generally 2-3 seconds.
Compressed air intake pressure is too low
Fault description:
1. The inlet air pressure of the nitrogen generator is lower than 0.6mpa
2. Cold dryer, suction dryer, filter blockage/fault cause low intake pressure
3. The opening and closing degree of the ball valve/stop valve for air intake and air outlet is unreasonable
solution:
1. Check the exhaust pressure of the air compressor/the pressure gauge of the primary air compressor pipe to confirm whether the pressure is greater than 0.6mpa
2. Check the front and rear pressure of the cold dryer, remove ice blockage, check whether there is abnormal exhaust of the dryer, and whether the outlet dust filter is blocked by dust
Whether the opening/closing degree of air intake/outlet/regeneration/solenoid valve air source ball valve is reasonable.
3. Equipment failure
Fault description:
1. Barometer failure
2. Pneumatic valve failure, solenoid valve failure, coil burning, valve core stuck
3. The PLC is faulty, the contacts are burned, and the solenoid valve cannot be powered
4. Molecular sieve sinking alarm, muffler spray black powder
solution:
1. Check the pressure gauge, calibrate or replace the pressure gauge
2. Jog inspection can judge whether the switch indication and action of the solenoid valve/pneumatic valve are normal at the same time
3. The PLC contact is burnt. Through the indicator light and multimeter check, the PLC has a backup point. If a contact is damaged, it can be quickly replaced to the backup point.
4. Molecular sieve sinks and alarms. Molecular sieve loosens, causing pulverization and black smoke. It is necessary to stop the machine in time and contact the manufacturer to deal with it.
Regarding the relationship between the nitrogen impurity of the nitrogen generator and the mechanical failure of the equipment itself and supporting systems, as well as the resulting impact and solutions, we will further share dry goods from external factors in this article: equipment operating environment temperature, compressed air dew point (water content), compressed air residual oil on the purity of the nitrogen machine and equipment performance.
Nitrogen-generating equipment is designed with the stable working environment of the equipment in mind, usually in the range of 0-45°C, which means that the equipment can perform normally within this temperature range. On the contrary, if it is operated outside the designed ambient temperature, it will bring problems such as performance degradation and high failure rate.
When the ambient temperature exceeds 45°C, the exhaust temperature of the air compressor will be too high, which will increase the load on the freeze dryer. At the same time, it may cause the high temperature trip of the freeze dryer. The dew point of the compressed air cannot be guaranteed, which will seriously affect the performance of the nitrogen generator. effect. Under the premise of the same purity, the flow rate of nitrogen production will drop by more than 20%; if the flow rate of nitrogen production remains unchanged, the purity of nitrogen gas will not meet the design requirements. Through laboratory high and low temperature testing, we found that when the ambient temperature is lower than -20°C, some electrical accessories cannot be started, or the action is abnormal, which will directly cause the nitrogen generator to fail to start and work.
Solution
To improve the environment of the computer room, the ventilation system should be improved in summer, and the heating conditions should be increased in winter to ensure that the ambient temperature of the computer room is within a reasonable range.
The moisture content (pressure dew point) in the compressed air has a direct impact on the nitrogen generator/carbon molecular sieve, so the nitrogen generator has strict requirements on the quality of the compressed air at the front end.
The actual case of the impact of the water removal and water separation effect of the cold dryer on the nitrogen generator:
Case 1: A user did not install an automatic drainer on the air storage tank of the air compressor, and did not drain water regularly, resulting in a large moisture content in the air intake of the cold dryer, and the third-stage filter at the air inlet and outlet of the cold dryer did not install a drainer And regular manual drainage, resulting in super high water content in the system, causing the activated carbon filter installed at the rear end to absorb water and form blocks to block the compressed air pipeline, and the intake pressure is reduced (insufficient intake), resulting in the purity of the nitrogen generator not meeting the standard. The problem was solved by adding the drainage system after the transformation.
Case 2: A user's cold dryer water separator is not good, resulting in the cooled water not being separated in time. After a large amount of liquid water enters the nitrogen generator, 2 solenoid valves are broken within a week, and the piston of the angle seat valve is completely damaged. It is liquid water, which causes the piston seal to corrode, causing the valve to operate abnormally, and the nitrogen generator cannot work normally. After replacing the freeze dryer, the problem was solved.
1. There are micropores on the surface of the carbon molecular sieve, which are used to adsorb oxygen molecules (as shown in the figure). When the water content in the compressed air is too heavy, the micropores of the molecular sieve will shrink and the dust on the surface of the molecular sieve will fall off, which will block the micropores of the sieve, resulting in a loss of unit weight. Carbon molecular sieves cannot produce the nitrogen flow and nitrogen purity required by the rating.
2. It is recommended that users install an adsorption dryer at the inlet of the nitrogen generator to reduce the water content of the compressed air and ensure that the carbon molecular sieve is not polluted by heavy oil and heavy water. Generally, the service life of the molecular sieve can be extended by 3-5 years (according to the purity level).
03. Effect of oil content in compressed air on nitrogen generator/molecular sieve:
1) For any type/form of molecular sieve, the unnecessary components are screened out through the micropores on the surface of the molecular sieve to obtain the substances we need. But all molecular sieves are afraid of oil pollution, and residual oil pollution is completely irreversible pollution to molecular sieves, so the inlet of the nitrogen generator has strict oil content requirements.
2) As shown in the figure above, oil stains will cover the micropores on the surface of the molecular sieve, causing oxygen molecules to be unable to enter the micropores and be adsorbed, resulting in a decrease in nitrogen production, or under the premise of ensuring the original flow rate, the nitrogen purity will be unqualified within 5 years.
Improvement methods for the above problems: Pay attention to the ventilation of the machine room, reduce the ambient temperature, and reduce the amount of residual oil in the compressed air; strengthen protection through cold dryers, suction dryers, filters, and activated carbon degreasers; regularly replace/maintain the front-end equipment of the nitrogen generator, Ensuring the quality of compressed air can greatly protect and extend the service life of nitrogen generators and the performance of carbon molecular sieves.
04. To sum up: external factors such as the ambient temperature of the machine room, the water content and oil content of the compressed air will affect the performance of the nitrogen making equipment, especially the cold dryer, suction dryer and filter at the front of the nitrogen making machine will directly affect The use effect of the nitrogen generator, so choosing high-quality and efficient dryer equipment is particularly critical for the nitrogen generator.