1. Preparation before compression
Gas purification: Before compressing industrial nitrogen, it is usually necessary to purify the nitrogen. Because industrial nitrogen production may contain small amounts of impurities such as moisture, oxygen, carbon dioxide, etc. For some high-precision application scenarios, these impurities can have adverse effects. For example, in the electronics industry, moisture and oxygen may affect the performance of semiconductor devices. The commonly used purification methods include adsorption and chemical absorption. Adsorption method is the use of adsorbents (such as silica gel, molecular sieves, etc.) to adsorb water and other impurities in nitrogen gas; The principle of chemical absorption is to remove specific impurities through chemical reactions, such as absorbing carbon dioxide with alkaline solutions.
Pressure regulation: After nitrogen is produced from the equipment, its initial pressure may be low and generally needs to be adjusted to a pressure range suitable for compressor suction. This process can be achieved through regulating valves or buffer tanks. The buffer tank can also stabilize the airflow and prevent pressure fluctuations from causing damage to the compressor.
2. Principle of compression process
Piston compressor compression:
Piston compressor is a common type of compressor. Its working principle is to compress gas through the reciprocating motion of the piston inside the cylinder. When the piston moves downwards, the pressure inside the cylinder decreases, the intake valve opens, and nitrogen is drawn into the cylinder; When the piston moves upward, the intake valve closes and the nitrogen gas in the cylinder is compressed, increasing the pressure. When the pressure reaches a certain level, the exhaust valve opens and the compressed nitrogen gas is discharged from the cylinder. In this process, according to the ideal gas state equation $PV=nRT $(where $PV $is pressure, $V $is volume, $n $is mass, $R $is gas constant, and $T $is temperature), as the volume decreases, the pressure will correspondingly increase. For example, in a single-stage piston compressor, if the initial pressure is 1 atmosphere, after compression, the pressure can be increased to around 5-10 atmospheres, depending on the design and operating parameters of the compressor.
Screw compressor compression:
The screw compressor is mainly composed of a pair of interlocking male and female screws. After nitrogen enters the suction port of the compressor, the gas is gradually compressed between the teeth of the screw as the yin-yang screw rotates. The rotational motion of the screw causes gas to move from the intake end to the exhaust end, continuously reducing its volume and increasing its pressure. Compared with piston compressors, the compression process of screw compressors is continuous and the gas flow rate is relatively stable. It can increase the pressure of nitrogen from atmospheric pressure to a higher pressure range, for example, it can increase the pressure of nitrogen to 7-14 atmospheres, and its compression efficiency is high, suitable for compressing nitrogen with larger flow rates.
Centrifugal compressor compression:
A centrifugal compressor compresses gas by using a high-speed rotating impeller to do work on the gas. After nitrogen enters the impeller, it gains kinetic energy under the high-speed rotation of the impeller, and then in the diffuser, the kinetic energy of the gas is converted into pressure energy, thereby increasing the pressure. The characteristics of centrifugal compressors are high flow rate and wide range of pressure increase. It can compress nitrogen from lower pressure to higher pressure, such as from atmospheric pressure to tens or even hundreds of atmospheres. It is commonly used in large-scale industrial nitrogen compression systems, such as in the chemical and refining industries. When high-pressure nitrogen needs to be transported on a large scale, centrifugal compressors are a good choice.
3. Temperature control during compression process
In the process of industrial nitrogen compression, due to the compression of the gas, according to thermodynamic principles, its internal energy increases and the temperature rises. Excessive temperature may affect the performance and safety of the compressor, as well as cause changes in the chemical properties of nitrogen gas. Therefore, it is necessary to control the temperature during the compression process. Generally, cooling systems are used to reduce temperature, and common cooling methods include air cooling and water cooling. Air cooling is the process of dissipating heat into the air through a radiator and fan; Water cooling utilizes circulating water to absorb heat. For example, in a piston compressor, a cooling jacket is usually installed around the cylinder to remove the heat generated during the compression process by circulating cooling water, keeping the temperature of nitrogen gas within a suitable range, generally not exceeding 150-200 ℃. The specific temperature limit depends on the material and design requirements of the compressor.
4. Multi stage compression and intermediate cooling
In order to obtain higher pressure, industrial nitrogen is usually compressed in multiple stages. Multi stage compression refers to the continuous compression of nitrogen gas through multiple compressors or stages of compressors in sequence. After each stage of compression, the gas will undergo intermediate cooling. This is because after the first stage of compression, the gas temperature will increase. If it is not cooled and enters the next stage of compression directly, it will increase the power consumption of the compressor and may also exceed the temperature limit of the compressor. For example, in a three-stage compressor system, nitrogen gas is first compressed in the first stage, with a pressure increase from 1 atmosphere to 3-4 atmospheres. After the temperature increases, it is cooled to near the initial temperature through an intercooler before entering the second stage of compression, where the pressure is further increased to 8-10 atmospheres. After cooling again, it enters the third stage of compression, ultimately increasing the nitrogen gas pressure to around 20-30 atmospheres. Intermediate cooling can significantly improve the efficiency of the compressor, reduce energy consumption, and ensure the safety and stability of the entire compression process.
5. Processing and storage after compression
The compressed industrial nitrogen requires further processing and storage. If nitrogen is used in high-pressure environments, such as chemical synthesis reactions in high-pressure reactors, compressed nitrogen needs to be transported to the site of use through pipelines, and the pressure resistance and sealing of the pipelines must be ensured. If used for storage, compressed nitrogen gas is usually stored in high-pressure storage tanks. The material and design of high-pressure storage tanks must comply with safety standards and be able to withstand the pressure of nitrogen gas. For example, in some industrial gas supply stations, compressed nitrogen is stored in seamless steel cylinders or large storage tanks with a pressure of 15-20 MPa for future use. At the same time, in order to ensure the safety of storage, safety equipment such as safety valves and pressure gauges will be equipped, and the storage tanks will be regularly inspected and maintained.
