Softening and Melting characteristics of iron bearing burden in blast furnace
The cohesive zone of a blast furnace is the region where the iron-bearing burden starts softening and melting after undergoing the thermo-chemical changes in the stack. The cohesive zone, an alternate layer of fused iron bearing mass and solid coke is characterized by its location, shape, thickness and coke slit width. The softening-meltdown properties of ferruginous material have very important bearing on the furnace operation including pressure drop, distribution of hot ascending gas, fuel rate, hot metal quantity etc. Accordingly, it is desirable to assess the suitability of the iron bearing raw material, prior to their use in the blast furnace, in the laboratory, under simulated conditions. A series of tests with samples from all the major steel plants of India have been conducted in a facility, installed at National Metallurgical Laboratory, Jamshedpur,
The basic purpose of the softening-melting test is to evaluate the softening-melting characteristics of iron ore and sinter sample taken in a small cylindrical graphite crucible by simulating the physical and chemical conditions in the shaft till the cohesive zone of blast furnace. This simulation study under laboratory conditions is carried out by subjecting the sample to pre-programmed time dependent variation of temperature, reducing gas composition and load. Behavior of the sample in the test can be characterized by measuring changes in the sample bed height, gas-pressure drop across the sample bed, bed shrinkage, identifying softening and melting temperatures and calculating degree of reduction and percentage non-dripped material (NDM).
High Temperature Softening Meltdown Apparatus
The parameters that are programmed/ set/ controlled in the apparatus for each experiment is as follows:
Rate of heating, that is, Time Vs Temperature – using the programmable temperature controller
Gas mass flow rate – using the mass flow controller
Temperature at which reducing gas enters the reaction tube – using the programmable temperature controller
Load applied on the sample bed – using the pressure regulator
Temperature at which the melt collection chamber changes its position – using the programmable temperature controller.
All the data/ output results are recorded with strip recorder provided on the panel as well as are acquired to PC based Data Acquisition System simultaneously and continuously, which are listed as follows:
Furnace temperature – recorded/ acquired to DAS
Sample temperature – recorded/ acquired to DAS
Pressure drop across the sample bed – recorded/ acquired to DAS
Sample bed shrinkage – recorded/ acquired to DAS
% CO, % CO2, and % H2, of the exhaust gas during the experiment – acquired to DAS
% CO, % CO2, and % H2 of the input gas mixture just prior to and at the end of experiment seen/recorded
voltage across and current drawn by the heating element – Acquired to DAS
During the experiment the molten metal / slag is collected at preset temperatures.
Plots of furnace temperature Vs Pressure drop and furnace temperature Vs % CO & % CO2 obtained from S-M experiments conducted:
Sample: 70% Sinter & 30% I/Ore
