A steel-making user of DEAR air separation set up their air separation plant in the early stage. At that time, due to the small amount of nitrogen required by the process and in order to reduce the investment, the molecular sieve adsorption purification process of 1:1 oxygen and nitrogen was adopted. There was no water chiller equipped, and a large amount of crude nitrogen was extracted to the water cooling column to reduce the temperature of cooling water.
With the improvement of steel-making process and the increase of steel-making capacity, the amount of nitrogen is increased, and the product structure and production capacity of the original air separation plant can no longer meet the production demand of steel-making process. The investment in new plant is large and there are many related problems. Through investigation and analysis, it is decided to transform the old air separation plant to meet the nitrogen demand of the user.
When the ratio of oxygen to nitrogen is 1:1, the ratio of nitrogen from the cold box to crude nitrogen is 1:3. It is found that the ratio of nitrogen from the cold box to crude nitrogen can reach 3:1 under a certain amount of processing air.
Due to the limitation of reconstruction cost and construction period, it is decided to use the original heat exchanger and pipeline in the cold box to interchange the corresponding interface of main pipeline of nitrogen with crude nitrogen in the cold box on the upper column. Compared with the process that all the original crude nitrogen is drawn out from the top of the main heat exchanger, the crude nitrogen gas pipe from the molecular sieve adsorber outside the cold box is connected to the main pipe of the original nitrogen out of the cold box, and the main pipe of the original crude nitrogen out of the cold box is connected with the nitrogen pipe network of the user.
After reconstruction, the amount of crude nitrogen out of the cold box is less, which basically meets the demand of molecular sieve regenerating gas, while the amount of nitrogen to the water cooling column is greatly reduced, so it needs to add the chiller is to supplement the lack of cooling capacity. The load of the chiller is determined by the demand for new nitrogen. The greater the demand for new nitrogen, the greater the cooling capacity of the chiller is needed. Compared with the original process that part of the crude nitrogen is drawn out from the middle of the main heat exchanger to the molecular sieve purifier, the crude nitrogen is drawn out from the top of the main heat exchanger after the transformation, and the temperature is higher than that before the transformation. Through the transformation, it can pass a pipe of chilled water from the water chiller to the aftercooler at the booster end of the expander, and reduce the temperature of the cooling water entering the aftercooler, so as to reduce the temperature of charge air entering the cold box, then to reduce the temperature of the crude nitrogen out of the cold box after transformation.
Through the above series of transformation, the user has fully exploited the potential of the original air separation plant with small investment and short cycle, and achieved the purpose of greatly increasing the nitrogen output.
