How to choose PSA nitrogen and oxygen generator

Air is composed of 78% nitrogen, 21% oxygen, and 1% rare gases and impurities. Oxygen is the gas that people rely on for survival. Nitrogen is inexhaustible and inexhaustible. Now it is more and more popular. It has been widely used in food storage, metal heat treatment, petrochemical industry, glass industry, etc. field.

Nitrogen is a colorless and odorless gas, and has a lower density than air. Nitrogen accounts for 78.08% of the total atmosphere. At standard atmospheric pressure, nitrogen is cooled to -195.8℃ and becomes a colorless liquid; cooled to -209.8℃,Liquid nitrogen becomes a snow-like solid. Nitrogen is chemically inactive, and it is difficult to react with other substances at room temperature, but it can chemically change with certain substances under high temperature and high energy conditions to produce new substances useful to humans.

Nitrogen generator

1. Cryogenic nitrogen production: It mainly uses the different boiling points of different gases to obtain liquid nitrogen through low-temperature fractionation.

2. Membrane separation for nitrogen production: similar to filters, the use of oxygen and nitrogen molecules to permeate the membrane to achieve a certain nitrogen concentration, the general concentration of nitrogen is not higher than 99%, the application range is relatively small.

3. PSA pressure swing adsorption nitrogen production: PSA gas separation technology is a non-cryogenic gas separation technology, using compressed air as raw material, carbon molecular sieve as the medium, using oxygen molecular diameter<nitrogen molecular,oxygen and nitrogen molecular size is different, molecules can enter the sieve surface pores of are adsorbed, cannot pass through gap stacked sieve,then adsorbed on desorbed by rapid emptying decompression,emptied into atmosphere.With a certain program cycle switching,purity be produced to 95-99.999%.

Selection of nitrogen equipment

1. No matter what type of nitrogen generator equipment is selected, we must know the following parameters: namely nitrogen purity, nitrogen flow, nitrogen pressure, and nitrogen dew point.

① Nitrogen purity. Nitrogen is generally used as a process gas, which is different from our compressed air as a power source. It must reach a certain pressure and gas volume. Nitrogen generally directly contacts the product to isolate the oxygen around the product. In the event of high temperature, welding, cutting, etc., it reduces the risk of oxidation and guarantees the quality of the processed product.

②Nitrogen flow rate, that is, the amount of nitrogen used by the customer (nitrogen flow unit: Nm³/h or NL/min, where N represents standard conditions, commonly known as nominal conditions: 20℃, 101325pa, which is 1 standard atmosphere) The nitrogen consumption is also guaranteed during production Must condition.

③ Nitrogen pressure is used to deliver nitrogen to the point of use. The level of nitrogen pressure affects the flow rate of nitrogen. The higher the pressure, the greater the flow rate when the conditions remain unchanged.

④ Nitrogen dew point, that is, the water content of nitrogen. Nitrogen also has a certain dew point (water content index) requirement when it directly contacts the product, otherwise it will also affect the product quality.

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How to choose supporting equipment:

1 Liquid nitrogen (forms like water, colorless liquid), the temperature is about -200℃, most industries cannot use it directly at such a low temperature. The liquid nitrogen must be gasified by an air temperature gasification device to reach normal temperature before it can be used. Because liquid nitrogen is similar to water, its volume is compressed (each ton of liquid nitrogen can vaporize 700-800Nm³; with a purity of 99.9995% nitrogen depending on the use pressure), which is convenient for transportation. A large amount of nitrogen can be quickly provided through the vaporization device, and liquid nitrogen It has a low pressure dew point (about -70℃), so the high index of liquefied nitrogen can meet the needs of all walks of life.

2 However, the requirements for the use of liquid nitrogen are also relatively high. For example, if the amount is too small, you can only buy bulk nitrogen, and the cost of bottled nitrogen is very high; liquid nitrogen requires a dedicated use site and dedicated storage equipment and gasification equipment, special equipment use registration certificate, there is a monthly minimum consumption amount, and the amount is not stable. Cost-effective. Liquefied nitrogen has the same performance index, so users with low purity (such as 99.9% purity) increase the cost of use.

3 PSA nitrogen generator can customize nitrogen production equipment of different sizes according to the consumption requirements, and at the same time configure the corresponding air compressor and dryer to obtain nitrogen. Whether it is 95%, 99%, 99.99% or 99.9995% purity, there are corresponding equipment specifications to meet. The pressure can be obtained regardless of whether it is 0.1MPa or 30MPa.

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The above figure is a set of conventional parameters (purity 95-99.999%, flow rate 1-2000Nm³/H, pressure 0.1-0.75MPa, pressure dew point -40℃ configuration diagram). Seeing the above configuration diagram, everyone’s biggest doubt is air pressure How to choose the machine? The air compressor is selected according to the purity, flow and pressure of nitrogen. The purity flow rate of nitrogen determines what type of carbon molecular sieve we choose. Different carbon molecular sieves correspond to different air-nitrogen ratios.

For example: 120Nm³/H-99.99% nitrogen generator air consumption calculation: 120/60*4.9=8.8m³/min (where 60 is 60min, 4.9 is the air nitrogen ratio. 9.6m³/min is the real-time consumption, according to the drying Air consumption of the air compressor should be enlarged by 10%-30%) If the dryer part is equipped with a suction dryer to generate air consumption, which needs to be enlarged by 30%, the air compressor should have a displacement of at least 12.5m³/min. Refer to this For flow rate, select the corresponding air compressor power of 75KW. After the air compressor flow is calculated, the gas pressure in the overall pipeline can be obtained (for example, the compressed air pressure is up to 0.8MPa, and the nitrogen pressure is up to 0.7MPa).

Email:austin@apureda.com.cn

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The drying and purification part is configured according to the dew point requirements of the finished nitrogen.

1) There is no requirement for dew point, and the cold dryer can be configured separately. Because carbon molecular sieve also has a certain role in adsorbing water molecules, the nitrogen pressure dew point of the finished product of this configuration is below -30℃. However, long-term use of carbon molecular sieve with compressed gas with relatively high water content will soften the carbon molecular sieve, accelerate its attenuation, and reduce its service life.

2) It is recommended that you install an adsorption dryer at the front end of the nitrogen generator. The pressure dew point of the compressed air after the adsorption dryer is between -30 and -40℃, with extremely low water and oil content, and negligible pollution to carbon molecules. Not counting, it can greatly extend the service life of carbon molecules and reduce the failure rate of valve parts of the nitrogen generator.

3) If you need a lower dew point, you can enlarge the dryer or customize a suction dryer with a low dew point to reach a nitrogen dew point of -50 to -70 ℃.