AU2011203327A1

AU2011203327A1 - Metallurgic use of biomass

Info

Publication number: AU2011203327A1
Application number: AU2011203327A
Authority: AU
Inventors: Michael Archer; Peter Samuel Vogel
Original assignee: Individual
Current assignee: Individual
Priority date: 2010-03-19
Filing date: 2011-07-07
Publication date: 2011-10-06

Abstract

An improved system for steel production wherein biomass is utilised as stag forming and slag foaming agent, recarburiser, reducing agent or fuel.

Description

Metallurgic use of biomass FIELD OF THE INVENTION 5 The present invention relates to use of biomass in the production of ferrous metals. BACKGROUND OF THE INVENTION A popular method of recycling steel utilises an electric arc furnace to melt scrap. In this process, graphite electrodes are plunged into a furnace charged with scrap metal 10 feedstock and the electrical energy applied to the electrodes causes arcing which melts the scrap, In most cases, the electrodes are kept submerged in the molten metal in order to maximise energy transferred to the melting mass and minimise heating of the furnace walls. Oxygen is injected into the molten mass, which reacts with elements including 15 aluminium, silicon, manganese, phosphorus, carbon and iron. These reactions are exothermic and supply additional energy to aid in the melting of the scrap. The oxides form slag on the surface of the molten metal. It is advantageous if the slag foams as it provides some insulation between the buried electrodes and the furnace walls, minimising damage to the furnace and minimising wasted energy. To promote 20 foaming, carbon and oxygen are injected into the molten mass. The iron oxidises and reacts with carbon to form carbon monoxide which foams the slag. The carbon monoxide also helps remove excess nitrogen and hydrogen from the steel. In some cases the carbon content of the steel falls below the desired level and extra carbon must be introduced. This is typically done using recarburiser coke. 25 In US patent application 11/574,649 (incorporated hereinto by reference) inventor Veena Sahajwalla teaches the use of un-agglomerated carbon-containing polymer as a slag foaming agent. Sahajwalla also teaches that the combustion residue of the polymer can act as a reducing agent or function as a recarburiser. The use of polymers in such a manner has certain advantages, including reduced electricity 30 consumption and disposal of end-of-life tyres or other wastes. However the prior art of Sahajwalla has the limitation that polymers are not a renewable resource and even though waste materials such as tyres are inexpensive, there are significant costs in transporting and processing them. 0 SUMMARY OF THE INVENTION It is an object of this invention to provide an improved system for steel production wherein biomass is utilised in ferrous metal making. 5 In one aspect, the invention provides a method of steel production wherein biomass is charged into the charge in an electric arc furnace. The biomass acts as one or more of slag foaming agent, recarburiser, reducing agent or fuel. In some embodiments, charging is achieved by injection into the molten metal. In other embodiments, the biomass is mixed with the solid material charged into the furnace 10 before melting. In yet other embodiments, the biomass is introduced into the body of the furnace and dropped on top of the charge. In one embodiment of the invention, the biomass is mechanically processed to make it suitable for charging into the furnace. For example biomass can be chopped or milled to reduce the particle size sufficiently to allow it to be blown in with air or other 15 gas. In some cases the biomass can also be dried as part of the processing. In another embodiment, the biomass is thermally or chemically processed before charging into the furnace. For example, certain unwanted fractions of the biomass can be removed. In another example pyrolysis can be used to convert the biomass to char which is then charged into the furnace. 20 In some embodiments of the invention, the biomass originates from plants grown without the use of fertilisers. It has been found that plants grown without fertilisers have lower concentrations of certain elements which can be detrimental to production of some metals. For example, excess of sulphur, phosphorus or nitrogen can be detrimental in steel. 25 In some embodiments of the invention, the biomass originates from plants of the genus Triodia. In other embodiments of the invention, the biomass originates from wood. For example, it has been found that chemical composition of combustion products of mallee is compatible with formation of good quality foamy slag. 30 In some embodiments of the invention, other sources of carbon are charged into the furnace in addition to the biomass. The invention also consists in apparatus adapted to perform the method of the invention described herein. 1 DESCRIPTION OF PREFERRED EMBODIMENTS Embodiments of the invention will now be described with reference to the drawing Fig. 1. 5 Furnace 1 is an electric arc furnace in which scrap metal is melted and refined to make steel of a particular quality. The usual process is followed, whereby a charge of scrap metal is dropped into the furnace through a removable lid (not shown), and electrodes 2 are plunged into the solid scrap charge 3. The arc between the electrodes melts the scrap. Lance 5 is inserted into the molten metal and a gas such 10 as air (carrier 8) is blown through lance 5. Biomass 7 particles from hopper 6 are thereby blown into the molten charge, Oxygen 9 is also blown into the molten charge via lance 4. Biomass 7 reacts with the iron and oxygen to form carbon monoxide which foams the slag 10. The carbon monoxide also helps remove excess nitrogen and hydrogen from the steel. The combustion of biomass 7 also adds energy to help 15 heat the molten metal. In one preferred embodiment, the biomass is finely chopped grass of the genus Triodia. This plant has the surprising quality that its ash composition is similar to that of metallurgical coke and hence performs well as a substitute. The low sulphur content of Triodia, and other biomass, is another desirable quality. As the carbon 20 content of the plant is less than half that of coke, it is generally necessary to use at least two kilograms of Triodia for every kilogram of coke displaced. In another preferred embodiment, wood, for example the species mallee, is used as the biomass. Many species of wood, for example mallee, have surprising qualities such as high calcium content which are beneficial in slag formation and foaming. 25 As well as beneficial effects on slag formation and foaming, use of biomass according to this invention improves the overall efficiency of the metallurgical process due to the high volatile content of most biomass compared to coke. This adds directly to energy input as the volatiles are liberated and combust and also improves the efficiency of combustion of other material in the furnace. 30 Whereas some exemplary embodiments of the invention are described above, it will be understood that many variations can be made without departing from the scope of the invention. For example, although in the exemplary embodiment the biomass is introduced by injection into the molten metal, it is also possible to practise the invention in many 2 other ways, for example by mixing the biomass with the metal feedstock, or dropping it onto the charge in the furnace from above. It will also be understood that whereas the invention is described herein as utilising an electric arc furnace, it can also be practised with good results in other metal 5 making, refining or processing applications. The use of the invention is also not restricted to steelmaking, it being applicable to other metallurgical processes, particularly those where fossil carbon sources have traditionally been used. Furthermore, it will be understood that the biomass used according to this invention can be processed in various ways before being introduced to the furnace. For 10 example, to facilitate transport by compressed gas through a lance, it is desirable to reduce the biomass to small particles. This can be achieved by well-known methods such as chopping or milling. Alternatively, the biomass can be pyrolysed to char then ground. In some cases the biomass can be mixed with the metal feedstock or charged directly into the furnace, in which case it need not be reduced to fine 15 particles. In such cases it is convenient for transport and handling purposes to densify the biomass close to the point of harvest, for example by pelletising or briquetting. 3

Claims

1. A method for production of metals using a furnace including the step of introducing biomass into the furnace.

2. A method for production of metals using a furnace according to claim 1 5 wherein said biomass functions as one or more of slag forming agent, slag foaming agent, recarburiser, reducing agent or fuel.

3. A method for production of metals using a furnace according to claim 1 or claim 2 wherein said biomass is grass of the species Triodia.

4. A method for production of metals using a furnace according to claim 1 or 10 claim 2 wherein said biomass is wood.

5. A method for production of metals using a furnace according to claim 1 or claim 2 wherein said biomass is made from eucalypt trees.

6. A method for production of metals using a furnace according to claim 5 wherein said biomass is made from eucalypt trees of the species mallee. 15

7. A method for production of metals using a furnace according to any of claims 1-6 wherein another source of carbon is introduced into the furnace in addition to said biomass.

8. A method for production of metals substantially as herein described. 20 ECHIDNA ENERGY PTY LTD 6 TH March 2010 5