GB2255350A

GB2255350A - Production of ferromanganese

Info

Publication number: GB2255350A
Application number: GB9208417A
Authority: GB
Inventors: Nicholas Brian Busby; Richard Brian Smith
Original assignee: British Steel PLC
Current assignee: British Steel PLC
Priority date: 1991-04-24
Filing date: 1992-04-16
Publication date: 1992-11-04
Anticipated expiration: 2012-04-16
Also published as: GB9108778D0; GB2255350B; GB9208417D0

Abstract

The invention is concerned with the production of ferromanganese in a blast furnace. By the injection of a proportion of the manganese ore as fines in the region of the blast pipes the operating conditions of the furnace may be considerably improved. Particularly oxygen and heat may be liberated in the reaction zone. <IMAGE>

Description

PRODUCTION OF FERROMANGANESE This invention relates to the production of ferromanganese, and in particular to the production of ferromanganese in a blast furnace.

Ferromanganese is an alloy of iron and manganese, in the proportion of 70-85% manganese and 5-8% carbon. It is commonly used in steel making to add manganese to steel. The manufacture of high carbon ferromanganese is conventionally undertaken in blast furnaces used for the production of iron, with the addition of ores rich in manganese dioxide in the burden. However, the blast furnace regime when producing ferromanganese is substantially different from that encountered when producing iron, and in particular high levels of oxygen enrichment in the blast are required. The high temperatures, high fuel rates and low efficiencies of normal ferromanganese production are largely the result of the thermodynamic properties of manganese oxides.

When MnO2 (manganese dioxide), the most commonly used manganese ore, enters the furnace it very quickly decomposes to Mn304 with the liberation of oxygen. This oxygen is liberated at the top of the furnace and reacts with any available fuels at the top of the furnace to heat the top. Unfortunately this heat is not easily used, and in general is wasted. As the Mn304 descends through the furnace the Mn3O4 is further reduced to the manganese monoxide by reaction with the carbon monoxide in the furnace. This reaction is highly exothermic so the stack is heated more and provides an opportunity for what is known as the Boudouard reaction to occur. This is the reaction of carbon or coke with carbon dioxide to produce carbon monoxide. This results in the unnecessary consumption of coke in the upper levels of the furnace with little benefit.It is therefore an object of the present invention to provide an improved method of making ferromanganese in blast furnaces.

According to a first aspect of the present invention there is provided a method of production of ferromanganese in a blast furnace in which ore fines rich in manganese dioxide are injected into the blast furnace in the region of the blast pipes and whereby oxygen and heat are made available by the decomposition of said manganese dioxide in the active reaction zone of the furnace. Preferably said ore fines are injected using the hot blast to blow them into the furnace. Preferably said injected ore fines are used to replace part of the manganese ore supplied via the top of the furnace.

The invention will now be described with reference to the accompanying drawings of which Figure 1 is a schematic drawing of a blast furnace in use for producing ferromanganese, and Figure 2 is a graph of the oxygen enrichment required for the production of ferromanganese.

Turning to Figure 1 the blast furnace shown schematically is of a conventional type. The blast furnace 1 is supplied in the normal manner with a charge of the appropriate composition for the production of ferromanganese through the conventional bell feed arrangement at 2 and produces a burden 3. A proportion of the manganese ore is injected into the furnace as fines by being injected into the blast stream 4 as shown diagrammatically at 5. As the fines are injected they immediately decompose, in the same way they will do if introduced into the top of the blast furnace, and liberate oxygen. This oxygen is available for the heating of the reaction zone 6, and although additional oxygen enrichment is required, this oxygen liberated by the decomposition of the manganese does contribute some small amount to the supply.It should be added that in fact there is an increased oxygen requirement over the normal operation of ferromanganese production because of the injection of cold solid material (the manganese ore fines).

After the manganese ore has decomposed into Mn 0 and oxygen 34 the more stable Mn304 is further broken down by reaction with carbon monoxide to produce manganese monoxide. This reaction is, as has been explained, highly exothermic, and the heat available from this reaction contributes to the heating of the reaction zone, instead of as in the previous case simply heating the burden and unnecessarily consuming coke. The MnO is itself reduced to manganese by the coke in the reaction zone and the required ferromanganese in a molten state drips onto the hearth from where it it tapped as required through the tap hole 8.

As was mentioned, an increased oxygen enrichment of the blast is required principally to maintain the flame temperature despite the addition of cold solid material (the fines) in the raceway region. Also the MnO reaction in which it is reduced to manganese requires heat to be added. In Figure 2 is shown a model graph of the oxygen requirement to maintain for a nominal 30000C flame temperature for a blast temperature of 100000 with oxygen at ambient temperature. The manganese fines rate in kilogrammes per ton of hot metal is shown as the abscissa, and the oxygen rate required to maintain the given flame temperature 3 in Normal cubic metres/ton hot metal (Nm /tHM) is shown as the ordinate.

Despite this increased oxygen enrichment requirement the overall operation can be more economical because there are savings in the fuel or coke employed. Furthermore, although this is an economic consideration which may vary from time to time, manganese ore fines are less expensive than lump manganese ore itself and normally the lower cost of the fines could only be obtained by going to the additional trouble and expense of sintering the manganese ore fines in a sinter plant before they were top charged.

Claims

1. A Method of producing ferromanganese in a blast furnace in which manganese ore fines are injected into the blast furnace in the region of the blast pipes.

2. A method according to Claim 1 in which the ore fines are rich in manganese dioxide.

3. A method according to any proceeding claim in which oxygen and heat are made available by the decomposition of the manganese ores in the active reaction zone of the furnace.

4. A method according to any proceeding Claim in which the ore fines are injected using the blast.

5. A method according to any preceding Claim in which the injected ore fines are used to replace part of the manganese ore supplied via the top of the furnace.

6. Ferromanganese prepared according to a method in any preceding Claim.

7. A method of producing ferromanganese substantially as described with reference to the accompanying drawings.