The purified compressed air enters the tower and exchanges heat with the reflux gas in the main heat exchanger. It is gradually cooled into saturated air with a small amount of liquefaction, and then enters the lower tower for distillation. Distillation is the process of obtaining pure oxygen and nitrogen through multiple partial evaporation and partial condensation in a fractionator using different boiling points of oxygen and nitrogen. The function of the lower fractionation tower is to produce liquid air and liquid nitrogen. The main condenser evaporator is used to evaporate liquid oxygen and condense gas nitrogen at different pressures under low pressure, while the upper fractionation tower is used to obtain product oxygen and nitrogen.
The equipment adopts the principle of deep freezing separation, and the process of molecular sieve adsorption at room temperature and reflux expansion refrigeration for oxygen and nitrogen production is selected. After passing through an air filter to remove dust and other mechanical impurities, the raw air enters a screw air compressor and is pressurized to 1.2MPa. The compressed air passes through an air cooler and enters an air precooling unit to cool to 5-8 ℃. The water is removed in a water separator and then enters a molecular sieve purifier to remove moisture, CO2, acetylene, and other hydrocarbons. The purifier consists of two adsorbers; One working, the other regenerating (automatic switching of the system). The regenerated gas is the dirty nitrogen discharged from the cold box, which is pressurized by an expansion mechanism driven fan and heated by an electric heater. The switching cycle of the purifier is 8 hours.
The temperature of the air exiting the purifier increases due to the adsorption heat of the molecular sieve. The purified air enters the cold box and exchanges heat with the returning dirty nitrogen, nitrogen, and oxygen in the main heat exchanger. It is cooled to the liquefaction temperature, with a small amount of air being liquefied. Then it enters the bottom of the lower tower, and the air rises one by one through the sieve tray, exchanging heat and mass with the reflux liquid nitrogen from the condenser at the top of the tower. As a result, liquid air is obtained at the bottom of the tower, and high-purity nitrogen is obtained at the top of the tower.
The liquid air is cooled and throttled by the subcooler before entering the middle of the upper tower as the reflux liquid for the distillation tower. The nitrogen at the top of the tower is completely condensed into liquid nitrogen, except for some being extracted as products. Most of it is used as reflux liquid for distillation, and a small amount is extracted as liquid products, which are discharged from the cold box through a liquid storage tank. After the product nitrogen is heated to room temperature through the main heat exchanger and air, it is output to the user as a product.
The product can be directly extracted from the bottom of the condensing evaporator.
The equipment is designed based on the principles of long-term stable and reliable operation, energy conservation, and simple and convenient operation and maintenance. The following advantages.
*Nitrogen gas has high purity and is very stable
*This process is a new development and design, and our company is able to apply this technology maturely.
*Good safety - the external compression process uses oxygen to compress in the form of gas at room temperature, while the internal compression process uses liquid oxygen to compress in the form of liquid at low temperature. The internal compression process has higher safety performance
*The startup time is short, and users can stop midway according to their actual needs. After heating, the time from starting the expander to producing qualified products is within 12 hours.
*There are few supporting units, and oxygen and nitrogen storage bags and oxygen and nitrogen compressors are not used, greatly reducing the floor area.
