In the field of coal chemical engineering, the main task of the air separation unit is to supply the required high-purity oxygen to the gasifier. With the development of coal chemical industry, a large amount of oxygen is needed, and the market demand for liquid oxygen, the air separation unit has also been rapidly developed. Reasonable design of cryogenic pipeline materials is the safety guarantee of the air separation unit. The cold box of the air separation unit is generally designed and supplied by the process contractor. NEWTEK introduces the design of cryogenic pipeline materials outside the cold box for a coal chemical supporting 80,000 m3/h air separation unit project. The process flow is briefly described. The air separation unit adopts a process flow plan of full low-pressure molecular sieve adsorption to purify air, air turbine booster expansion mechanism refrigeration, product oxygen and nitrogen internal compression, and air booster circulation. The process flow is divided into air compression system, air precooling system, molecular sieve purification system, expander system, distillation system, liquid storage standby system and public system.
The raw air is filtered by a self-cleaning filter to remove mechanical impurities such as dust. The filtered air enters the centrifugal compressor and then enters the air cooling tower. The air after the air cooling tower enters the molecular sieve purifier. The purified air is divided into three streams, one as the instrument air of the air separation unit, one enters the low-pressure plate heat exchanger and enters the lower tower after cooling, and the other goes to the booster air compressor.
This air is divided into three parts:
① After the air is pressurized by the first-stage impeller of the booster air compressor, it is extracted as instrument air and factory air.
② The air at the last stage of the booster enters the booster fan of the expander for pressurization, and then enters the high-pressure plate heat exchanger for heat exchange with liquid oxygen after being cooled to room temperature by the cooler. The high-pressure air enters the lower tower after passing through the liquid expander and throttling.
③ The air extracted from the booster enters the high-pressure plate heat exchanger, and the air extracted from the high-pressure plate heat exchanger enters the expander. The expanded air is sent to the lower tower.
After the air is initially distilled in the lower tower, liquid air, liquid nitrogen and dirty liquid nitrogen are obtained, which are supercooled in the cooler and throttled to enter the upper tower. After further distillation in the upper tower, liquid oxygen is obtained at the bottom of the upper tower, which is compressed by the liquid oxygen pump and enters the high-pressure plate heat exchanger. After reheating, it is discharged from the cold box and enters the oxygen pipeline network. Normal pressure nitrogen is extracted from the top of the upper tower, reheated by the low-pressure main heat exchanger and sent to the user pipeline network. Part of the liquid oxygen is extracted in the cooler and supercooled to enter the storage tank as a product. A certain amount of argon fraction is extracted from the middle of the upper tower and sent to the argon efficiency tower. The argon fraction is distilled in the argon efficiency tower to obtain crude argon. The crude argon is reheated in the plate heat exchanger, exits the cold box, and enters the dirty nitrogen pipeline. Liquid nitrogen is extracted from the top of the lower tower and sent to the storage tank, and then extracted from the storage tank and pressurized by liquid nitrogen and enters the high-pressure plate heat exchanger. After reheating, it exits the cold box. Part of the liquid nitrogen is extracted and supercooled in the cooler and enters the storage tank as a product. Part of the liquid in the backup system's liquid oxygen and liquid nitrogen storage tanks is loaded onto trucks for transportation, and part enters the pipeline network through liquid oxygen, liquid nitrogen pumps, and water bath vaporizers.
