FINES INJECTION

Abstract: A method of injection ore fines into a blast furnace which comprises the steps of mixing the ore fines into a slurry with fuel oil and injecting hte slurry of fuel oil and ore fines into the furnace.

Description: FINES INJECTION The invention relates to the injection of ore fines into a blast furnace for the smelting of iron. In a conventional blast furnace the fuel, fluxes, and additives have traditionally been added from the top of the furnace and a blast of air or oxygen, often heated is injected at the bottom. The process is well known, and will not be described further. In recent years the injection of materials other than air and oxygen has been suggested and in many cases is successful and economic. For example the injection of coal using oxygen as a blast gas obviates the need to turn the coal into coke before charging, and oil and oil/coal mixtures have also been injected. Ore fines - that is finely divided iron ore - have also been injected. The injection of ore fines has been found to be particularly advantageous, since it has been found experimentally that very large amounts of the fines can be injected without adversely affecting the performance of the furnace, and this is accompanied by an increase in the permeability of the furnace charge. The fines are generally cheaper than the ore and do not have to be sintered before being used. However the methods of injecting the ore fines into the furnace have until now required them to be dried and this is a process that has consumed energy. Also the injection of fines by using the blast has required complicated design of the injection apparatus in order to achieve an even distribution of fines around the furnace; furthermore the fines are abrasive and require careful selection of the materials of which the system is made. It is therefore an object of the present invention to enable the injection of ore fines into the blast furnace in a manner which overcomes or at least substantially reduces these problems. According to the present invention there is provided a method of injecting ore fines into a blast furnace wherein the fines are first mixed into a slurry with fuel oil and the fuel oil and fines slurry is injected into the furnace. The ore fines may comprise in part iron oxide recovered from the processing of steel and the processing of steel may be the hot rolling thereof. The invention will now be described by way of example. In blast furnaces (as has already been explained), many materials are now injected into the furnace. Solid materials may be ground into a powder or granules and injected into the tuyere using the blast system, although various modification of this may be necessary. The design of the injection mechanism so as to achieve a good injection can be quite difficult; also solid materials can be abrasive and in many cases special attention is necessary to the engineering and materials of the handling system so as to enable the system to work well for acceptably ling periods. Liquids also can be injected at the tuyeres, and can of course be pressurised so that they do not require the assistance of the gas blast in order to enter the furnace. Particularly fuel oil has been injected as a fuel to reduce the amount of coke that has to be charged from the top, and oil/powdered coal slurries have been injected to form a combined fuel. Ore fines have been injected, to reduce the amount of prepared ore needing to be charged from the top, and in practice it has been found that large quantities of fines can be injected without significantly affecting the blast furnace performance. 300Kg per tonne of hot metal have been injected without trouble, and it has been found that the permeability of the blast furnace charge increases as the rate of ore fines injected from the bottom increases. However, (as has been explained) the injection of solids in the blast requires special design and engineering of the handling system, and the fines have needed to be dried beforehand so as to be entrainable in the blast gases. We have now developed a method of injection iron ore fines into a blast furnace which significantly deals with these problems, in that we mix the fines in an undried state with a fuel oil to form a slurry. The slurry is composed typically of equal weights of ore and oil and is fed to the blast furnace by a ring main so that it may be injected by a series of lances, possibly via the blast tuyeres, around the blast furnace. The rates of injection of the slurry are typically for a large blast furnace about 45-70Kg of oil per tonne of hot metal. The injection system for the slurry is the one that is used for the injection of fuel oil already present in many furnaces and therefore modifications to the furnace are minimised. Furthermore the low velocities of the slurry obviate to a large extent the problems of wear and abrasion in the supply system- As so far described the slurry has been made solely by mixing ore fines with fuel oil. However, a somewhat similar mixture is already available which can, with suitable processing, be added to the slurry. In the processing of steel and particularly steel strip in rolling mills, large quantities of mill waste, such as in the form of scale are removed from the surface of the steel as it is being processed. This scale is recovered as an oily and wet mixture which is difficult to dispose of. The larger pieces can be recycled through the blast furnace sinter plant, but a considerable amount of very finely divided iron oxide mixed with water and with hydrocarbon oil must be disposed of. It has been found that this iron oxide and indeed low grade iron oxide generally (such as processed waste from pickling tanks for example) can be mixed with the fuel oil/ore fines slurry after it has been de-watered and re-injected into the blast furnace without adversely affecting the process of the invention. De-watering can be carried out simply by allowing the waste to drain from a <_. pile thereof, possibly placed over a sieve. In this way the invention provides a means of recycling a steel processing waste product that up to now has proved troublesome and expensive to dispose of.

Claims: Claims 1. A method of injection ore fines into a blast furnace comprising the steps of mixing the ore fines into a slurry with fuel oil and injecting the slurry of fuel oil and ore fines into the furnace. 2. A method as claimed in claim 1 in which the ore fines are in a de-watered state, but undried state, before mixing with the fuel oil to form the slurry. 3. A method as claimed in claim 1 or 2 wherein the slurry is composed of approximately equal weights of ore fines and fuel oil. 4. A method as claimed in any one of claims 1, 2 or 3 including the steps of adding to the slurry of fuel oil and ore fines iron oxide recovered from the processing of iron products. 5. A method as claimed in claim 4 wherein the iron oxide added to the slurry comprises iron oxide recovered from the hot roll processing of steel, such additional iron oxide being added as oil mixed mill waste, and being de-watered prior to adding to the slurry. 6. A method as claimed in any one of the preceding claims wherein the slurry is fed to the blast furnace by means of a ring main around the furnace and injected into the furnace by means of a series of lances around the ring main. 7. A method as claimed in claim 6 wherein the slurry is injected into the blast furnace via the blast tuyeres. 8. A method as claimed in claim 6 or 7 in which the slurry is injected into the blast furnace at a rate of between about 45 to 70kg of fuel oil per tonne of hot metal production of the furnace.

Inventors: BUSBY NICHOLAS JAMES, CAMPBELL DAVID ARMOUR, RAVINDRAN SIVAGNANAM, SMITH RICHARD BRIAN, BUSBY, NICHOLAS, JAMES, CAMPBELL, DAVID, ARMOUR, RAVINDRAN, SIVAGNANAM, SMITH, RICHARD, BRIAN
Applicants: BRITISH STEEL PLC, BUSBY NICHOLAS JAMES, CAMPBELL DAVID ARMOUR, RAVINDRAN SIVAGNANAM, SMITH RICHARD BRIAN
Application year: 1993
Main classification: C21B5
IPC codes: C21B5