Hot Metal

Hot Metal Hot metal (HM) is the output of a blast furnace (BF). It is liquid iron which is produced by the reduction of descending ore burden (iron ore lump, sinter, and pellet) by the ascending reducing gases. HM gets collected in the hearth of the BF. From the hearth, the HM is tapped from the taphole of the BF after an interval of time. Normally in large BFs, HM tapping rates of 7 ton/min and liquid tapping velocities of 5 m/sec, in tap holes of 70 mm diameter and 3.5 m long, are typically encountered. The tapping rate of HM is strongly influenced by the taphole condition and taphole length. Generally the temperature of tapped HM varies in the range of 1420 deg C to 1480 deg C. The tapped HM is handled in the two stages namely (i) handling of the HM in the cast house i.e. from taphole to the hot metal ladles (open top or torpedo), and (ii) transport of HM ladles to the point of HM consumption. Presently most of the HM is consumed within integrated steel plants for steel making. The HM is transferred to the steel melting shop for making of steel. The HM which is not sent for steel making is cast into pig iron in pig casting machine for use in steel making later as cold charge or is sold to foundries or to mini steel plants having induction furnaces as merchant pig iron. HM can also be granulated by a process which is known as ‘Granshot’ process. Presently the Granshot plants for the production of GPI are working at six places namely (i) Uddeholm, Sweden, (ii) SSAB Lulea, Sweden, (iii) Voest Alpine, Donawitz, (iv) Saldanha steel, South Africa, (v) SSAB Oxelosund, Sweden, and (vi)...

Probes, Instruments and measurements for Monitoring of Blast Furnace Jun28

Probes, Instruments and measurements for Monitoring of Blast Furnace...

Probes, Instruments and measurements for Monitoring of Blast Furnace A blast furnace (BF) works with the principle of countercurrent gas to solid heat exchange from tuyere raceway to the stock line and of a countercurrent oxygen (O2) exchange from fusion zone to the stock line. Solid burden materials consisting of ferrous materials (iron ore, sinter, and pellets), coke, and fluxing materials are charged into the top of the furnace, while air normally enriched with O2, and sometimes with auxiliary fuels is fed through the tuyeres near the bottom of the furnace. The usual retention time of the ferrous burden materials in the furnace may be as long as 8 hours, while that of the gas is a few seconds. However, the residence time of the coke in the hearth is much longer usually ranging from 1 week to 4 weeks. The liquid hot metal (HM) and liquid slag are tapped at regular intervals through a number of tapholes situated at the bottom of the furnace. The slag is separated from the hot metal which is handled through HM ladles. A blast furnace need to be operated with high productivity and low fuel rate in a flexible, stable and high efficiency manner and must have a long campaign life. The blast furnace is often referred to as black box because of the terms such as the furnace condition and furnace heat level which is currently in dominant use as well as since the blast furnace process has many unknown areas. The reason seems to be due to the difficulty in measurement, because, in a blast furnace, three phases of gas, solid, and liquid coexist, the reaction proceeds non-uniformly in radial direction, the process is accompanied by a time dependent variation, and the parameters to be...

Fire Resistant Steels...

Fire Resistant Steels Steel is inherently a noncombustible material. It loses strength when heated sufficiently.  Steel structural properties and its yield strength considerably decrease when it is heated to temperatures seen in a fire scenario. The critical temperature of a steel structural member is the temperature at which it cannot safely support its load. Building codes and structural engineering standard practice defines different critical temperatures depending on the structural element type, configuration, orientation, and loading characteristics. The critical temperature is often considered the temperature at which its yield stress has been reduced to 60 % of the room temperature yield stress. Fire is a chemical phenomenon that occurs as a result of thermal processes. When a steel section is exposed to a fire then the level of temperature increase on the face of steel section depends on thermal inertia, exposure of surface area and the protective coating. As the rate and amount of heat flow from the fire environment to steel section increase, the temperature, and thus the risk of failure for the steel section also increases. Since the steel has a very high thermal conductivity, exposed surface of the steel section easily transmits the conveyed heat from the fire source to the other members of the whole structure in a short period of time. Heat is transmitted in between the steel sections from high temperature sections to low temperature sections by way of conduction, radiation or convection modes. Steel sectional properties and its yield strength considerably reduce as it absorbs heat upon exposure to a high temperature level. A steel structural member may easily collapse during a fire if the temperature is allowed to reach a critical value. The fire resistance of the steel member is related to some important factors including the section size, the perimeter...