Carbon molecular sieve for PSA nitrogen generator
2022-08-19
As we known, about 78% of the atmosphere is nitrogen, which is an inert protective gas and is widely used in our daily life and industrial production. The general process of obtaining nitrogen is either cryogenic air separation or PSA. Today we are going to talk about PSA nitrogen generator, which we usually call nitrogen generator. The adsorbent that needs to be used in the process of PSA nitrogen production is called carbon molecular sieve. Carbon molecular sieve is a kind of non-polar carbon material, and its appearance is usually small black cylinder.
For more applications of adsorbents, please consult the manufacturers of activated alumina and molecular sieves.
PSA nitrogen generator working principle
Carbon molecular sieve pressure swing adsorption is an automatic equipment that uses carbon molecular sieve as adsorbent, and uses the principle of pressure adsorption and decompression desorption to adsorb and release noir gas from the air, thereby separating nitrogen. Carbon molecular sieve is a kind of columnar granular adsorbent full of micropores on the surface and inside, which is black in color. The pore size distribution characteristics of carbon molecular sieves enable the kinetic separation of O2 and N2. Such a pore size distribution allows different gases to diffuse into the pores of the molecular sieve at different rates without repelling any gas in the mixture (air). The separation effect of carbon molecular sieve on O2 and N2 is the slight difference in the dynamic diameter of the two gases. The diffusion rate, the kinetic diameter of the N2 molecule is larger, so the diffusion rate is slower. The diffusion of water and CO2 in compressed air is not much different from that of oxygen, but the diffusion is slower. The mixture of N2 and Ar is finally enriched from the adsorption tower.
Analysis of common faults of carbon molecular sieve in nitrogen generator
The main phenomenon of carbon molecular sieve leakage in the nitrogen generator is that black smoke is emitted from the evacuation management during the operation of the nitrogen generator, and even the molecular sieve particles are sprayed out. The direct cause of powder leakage.
1.1 Poor quality of carbon molecular sieve
Carbon molecular sieve is an adsorbent that separates nitrogen and adsorbs oxygen. Its quality directly affects the performance of the nitrogen generator and the purity of the gas supply. Carbon molecular sieves with good quality have better dust resistance, moisture resistance, strength, and adsorption properties than molecular sieves of ordinary quality.
1.2 Improper filling of carbon molecular sieves
The nitrogen generator does not have professional filling vibration equipment when filling with carbon molecular sieves, resulting in low packing density of molecular sieves inside the machine. When the nitrogen generator is running, the compressed air flow rises through the bottom of the tank, and after the oxygen is adsorbed by the molecular sieve, the nitrogen is transported to the downstream pipeline. Due to the frequent impact of the airflow, the wear of the internal carbon molecular sieve is intensified, and the material level of the molecular sieve gradually decreases. When it reaches the lower limit of the top cylinder, the cylinder no longer presses and restricts the molecular sieve, thereby accelerating the pulverization of the molecular sieve and causing the powder to penetrate the filter screen. , emptied with oxygen enrichment.
1.3 Air source pressure
The purified compressed air enters the bottom of the nitrogen generator tower, and the pressure of the supply air source affects the working condition of the nitrogen generator. Due to the high frequency of pressurization and decompression of PSA nitrogen production equipment, the impact of the pressurized gas on the molecular sieve is very honorable and causes the wear of the carbon molecular sieve. All the pressure and flow rate of the gas source should be strictly controlled. If the pressure of the air source is too large, at the moment when the pneumatic valve is opened, the impact force of the air source on the molecular sieve is large, which increases the friction between the molecular sieves. The force is also relatively large. If the gas source pressure is too small, the time for the molecular sieve to adsorb oxygen to reach saturation is longer, in other words, the working time of the nitrogen generator to output qualified nitrogen is prolonged, and the friction time between the molecular sieves becomes longer, which accelerates the pulverization of the molecular sieve.
1.4 The pneumatic valve is not strict
The pipeline of the nitrogen generator is equipped with pneumatic quick-opening butterfly valve group, pressure equalizing valve group, exhaust valve group and vent valve group. Any valve group that is not tightly closed and leaks may be generated in another nitrogen generator that is temporarily not working. Air flow, the surging of the air flow will also increase the static friction between the molecular sieves and aggravate the pulverization of the molecular sieves.
1.5 Intake water and oil and gas are too large to cause failure
The front-end intake source of the nitrogen generator is equipped with multi-stage filtration facilities and drying facilities. This set of equipment mainly includes an air source purification system composed of a cold dryer, an over-efficiency filter, an alumina heating dryer and a precision filter.
The filter element and alumina ceramic ball in the air source purification system need to be replaced regularly. If the filter element is damaged or not replaced in time, it will cause water and oil and gas in the air source, but water and oil are the most important factors that affect the quality and service life of molecular sieves. .
1.6 The top cylinder is not pressed tightly
Low instrument air pressure, damage to the cylinder and low material level of the nitrogen generator are the reasons why the top cylinder is not tightly pressed. When the top cylinder is not tightly pressed, the cylinder no longer restricts the molecular sieve. After the airflow enters, the molecular sieve has a larger space for movement, which increases the impact force between the molecular sieves, accelerates the pulverization of the molecular sieve, and affects the internal structure of the equipment in serious cases. firmness, aggravating the damage to the internal components of the equipment.
1.7 Cracked strainer and coconut pad
Due to the long-term impact of the airflow and the molecular sieve, the filter screen and the middle part of the coconut pad were damaged, causing the molecular sieve to fall into the bottom of the tank and leak out with the oxygen-enriched effluent pipe. If the damaged filter screen and coconut pad are not replaced in time, a vicious circle will be formed, which will affect the purity and flow of product gas, and seriously affect the stability and safety of equipment operation.
Tracy Chen 
