Research On The Exergy Of Air Separation Unit In Iron And Steel Manufacturing Process

The air separation unit (ASU) products is an important secondary energy medium in the production process of steel enterprises. Because of the differences in ASU processes as well as their operation levels, the significant variances for energy consumption levels exist in different companies. Reducing ASU energy consumption and improving the operational economy of ASUs have been important issues faced by the steel industry.On the basis of the traditional energy saving balance research according to the first law of thermodynamics, the second law of thermodynamics is further introduced in the thesis. The exergy analysis is employed as a theory tool to study the energy saving of ASU energy consumption:The comprehensive investigations, analyses and calculations are carried out on the roles of ASU gas products in the modern iron and steel production. It points out that the ASU process is an indispensable process for modern steel enterprise. The power consumption for air product makes up more than10%of the whole enterprise power consumption. In the oxygen steelmaking process, calorific values from element oxidized are about4～5times of oxygen generation energy consumption.Based on the comprehensive investigation on the iron and steel production of Tangshan Iron&Steel (TI&S) and current oxygen using situation, it is learned that the oxygen consumption is about56m3per ton steel, which is little more than the theoretical value, and the redundancy is around5.0%; the oxygen enrichment rate for blast furnace iron making is40～45m3per ton iron; the total integrated oxygen consumption is closed to100m3per ton crude steel.With the help of the physical property parameters calculation software, the exergy for40000m3/h ASU of TI&S is analyzed. The quantitative effect law for the exergy efficiency with different production yields is achieved:when the total yield of liquid production is increased by9%(300m3), the general exergy efficiency can be increased by0.7%to1.0%. When the yield of liquid argon is increases, the exergy efficiency can be improved. When oxygen (gas) yield is increased by10%, the general exergy efficiency can be increased by1.3%. Exergy efficiency varies with different combinations of products. An optimal value can be determined among these combinations. In view of the exergy analysis, the oxygen/nitrogen interchangeable variable load flexible operation with the combination of internal and external is put into effect. It points out that the liquefaction plant, of which the greatest liquefied oxygen amount is14000m3/h, should be configured in TI&S, which can improve the general exergy efficiency of the system, and reduce the oxygen or nitrogen emission rate.Based on the theoretical guidance of the exergy analysis, modifications to the steelmaking oxygen delivery system are carried out. The delivery pressure is reduced from3.0MPa (G) to1.5MPa (G) on the premise of keeping steelmaking oxygen pressure in constant. On account of the research, the obvious effects of energy saving and synergism are obtained by the gas company of TI&S, and the patented inventionis also gained, which win a favorable review in the metallurgical industry.