Analysis of metallurgical processes and slag utilisation in an integrated steel plant producing advanced high strength steels [Elektronisk resurs]

• Some elements in the raw materials used in iron- and steelmaking make it difficult to maintain or further improve the steel quality, but also adversely affect the composition of generated slags and other materials, thereby reducing their potential for internal recycling and/or other utilisation.A Process Integration (PI) approach was taken to analyse the dependence of the properties of a specific metallurgical slag on individual processes as well as on the interaction between processes. Analyses were made of how to obtain maximum usage of metallurgical slags without compromising the quality of the main product, i.e. crude steel. Based on a real case scenario, a number of approaches were studied with regard to the quality demands for maximised use of slags. The effects of changes in raw materials on blast furnace (BF) and basic oxygen furnace (BOF) processes were investigated. Altered composition of the raw materials affects material and BF reductant rate, generated slag amounts, slag recycling and material compositions, etc. In this study special attention was directed towards the magnesium oxide (MgO) contents in BF and BOF slags and, subsequently, the effects on phosphorus (P) refining in the BOF.The analysis of system effects of changed quality of lime raw material, i.e. limestone and consequently on-site produced burnt lime, show that an increased MgO content raises the MgO level, exceeding the set maximum permissible MgO content in both the BF and the BOF slag. The increased MgO content in burnt lime charged to the BOF will have a strong negative effect on the P refining capacity of the slag; therefore, burnt lime with an increased MgO content cannot be used without taking further measures if maximum P refining is required.Based on the results of the analysis, a number of approaches were further investigated in order to identify methods to preserve or decrease current MgO levels in generated slags and maintain, or further improve, slag utilisation potential without compromising the liquid steel (LS) quality. Analysed strategies were: diluting the MgO content in the BF slag by increased slag rate, decreased BOF slag recycling to the BF, increased P tolerance in BF produced hot metal (HM), lower MgO content in pellet mix or decreased use of dolomitic lime in the BOF. The most efficient approach to markedly increase the BOF slag recycling rate and simultaneously maintain the prerequisite MgO content in BF slag and LS quality is by increasing the tolerance of P in hot metal while at the same time excluding dolomitic lime in the BOF. 

Ämnesord

Engineering and Technology  (hsv)

Materials Engineering  (hsv)

Metallurgy and Metallic Materials  (hsv)

Teknik och teknologier  (hsv)

Materialteknik  (hsv)

Metallurgi och metalliska material  (hsv)

Process Metallurgy  (ltu)

Processmetallurgi  (ltu)