WO1999051710A1

WO1999051710A1 - Carbon pellets

Info

Publication number: WO1999051710A1
Application number: PCT/NO1999/000105
Authority: WO
Inventors: Egil Auganes; Inger Johanne Eikeland; Roger HAUKØY; Jan Mohaug; Oddbjørn PAULSEN; Thor SØNSTELIEN; Halvard Tveit
Original assignee: Elkem ASA; Elkem Materials AS
Current assignee: Elkem ASA
Priority date: 1998-04-06
Filing date: 1999-03-29
Publication date: 1999-10-14
Anticipated expiration: 2000-10-06
Also published as: BR9909450A; EP1088046A1; NO981548L; AU3346999A; NO981548D0; NO306786B1

Abstract

The present invention relates to pellets for use as a reduction material in metallurgical reduction processes for the production of metals and alloys. The pellets comprise 40-95 % by weight of biomass produced by treatment of woodchips and optionally paper with water vapour under high pressure and 5-60 % by weight of one or more fine particulate carbon materials containing a substantial amount of elemental carbon.

Description

Title of invention: Carbon pellets.

Technical Field The present invention relates to carbon-containing pellets for the use as reduction material in electric smelting furnaces for the production of metals and alloys, more particularly for the use in electric smelting furnaces for the production of pig iron, ferro alloys and silicon.

Background Art

In the production of pig iron, ferro alloys and silicon, fossile carbon in the form of lumpy coal or coke or biocarbon in the form of lumpy char coal and in the form of wood chips are used as reduction material. It is further known to use agglomerates in the form of briquettes or pellets of pulverized coal or coke, optionally with addition of iron oxide or other metal oxides.

From Norwegian patent No. 300094 it is known a method for the production of so-called biomass from organic materials such as wood and paper, where wood chips optionally together with paper is treated with water vapour under high pressure and is thereby transferred into a biomass where the main constituents of the wood, cellulose, hemi cellulose and lignin are made available. This biomass can after drying be pressed into pellets where the lignin acts as a binder. Pellets having a diameter between 5 and 15 mm can thereby be produced without addition of any external binder. Biopellets produced in this way are, however, costly and have for this reason not found any use as a reduction material in metallurgical reduction processes even though the pellets show an acceptable reactivity.

Pellets as described above which only contains biomass produced from wood chips and paper, further have the disadvantage that they have a high volume compared to the content of fixed carbon and it is therefore difficult to substitute a major part of reduction material based on fossile carbon with this type of pellets.

In order to reduce emissions of CO₂ originating from fossil carbon it is a wish in the metallurgical industry to substitute as much as possible of fossil carbon with reduction materials based on biocarbon. The only biocarbon sources which up till now have been used as reduction material in smelting furnaces for the production of pig iron, ferro alloys and silicon, is char coal and wood chips. Char coal is, however, very costly compared to fossil carbon sources such as coal and coke, while wood chips only can be used as a small part of the reduction material due to its very high volume in relation to its content of fixed carbon.

Further, there is available large amounts of fine particular fossil carbon sources such as coal, metallurgical coke and petrol coke which due to their fine particle size are not suited as reduction materials in electric smelting furnaces. When lumpy fossil carbon sources like coal and coke are used as reduction materials fine particulate material has first to be removed by screening. This fine particulate carbon materials thus presently represent an economical loss. In addition there is available fines from charcoal which are not suited as a reduction material. Finally carbon black, which is a very fine particulate carbon material is available. Carbon black agglomerated in conventional way has, however, a very low reactivity and has for this reason not found any use as a reduction material in electric smelting furnaces.

Disclosure of Invention

By the present invention one has now arrived at a carbon-containing pellet which is mainly based on biocarbon which pellets have a very high reactivity when used as a reduction material in metallurgical metal reduction processes. Accordingly, the present invention relates to pellets for the use as a reduction material in metallurgical reduction processes for the production of metals and alloys, said pellets comprising 40 - 95 % by weight of biomass produced by treatment of woodchips and optionally paper with water vapour under high pressure and 5 - 60 % by weight of one or more fine particulate carbon materials containing a substantial amount of elemental carbon.

According to a preferred embodiment the biomass is produced by treatment with water vapour under high pressure of a mixture comprising 90 - 99.5 % by weight of wood chips and 0.5 - 10 % by weight of paper, preferably 96 - 99 % by weight of wood chips and 1 - 4 % by weight of paper.

According to another preferred embodiment the pellets comprises 50 - 70 % by weight of biomass and 30 - 50 % by weight of fine particulate carbon material.

As fine particulate carbon material containing a substantial amount of elemental carbon it can be used coal, coke, char coal and carbon black having a particle size below 5 mm and preferably below 3 mm.

It has surprisingly been found that the carbon-containing pellets according to present invention have a very high reactivity. It has thus been found that so- called SiO reactivity of the pellets according to the present invention is substantially higher than the SiO reactivity of both biomass and of the carbon materials as such. Further, the pellets have a good strength allowing the pellets to be transported and added to smelting furnaces without being broken to any substantial extent. Further, the pellets according to the present invention typically have a content of fixed carbon of between 30 and 40 % which is substantially higher than for biocarbon pellets having no additive of fine particulate carbon material. By use of the pellets according to the present invention as a reduction material in smelting furnaces for the production of metals and alloys, the emission of CO₂ from fossil carbon material can be reduced up till 100 % in case fine particulate material from char coal is used as fine particulate carbon material in the pellets of the present invention.

The pellets according to the present invention are produced by mixing dried biomass produced by treatment of wood chips and optionally paper with water vapour under high pressure and the fine particulate carbon material whereafter the mixture is extruded to pellets using the natural lignin content of the biomass as a binder. Thus not external binder has to be added.

EXAMPLE 1

Pellets according to the present invention containing 75 % by weight of biomass produced by treatment of 98 % by weight of wood chips and 2 % by weight of paper with water vapour under high pressure and 25 % by weight of particulate coal having a particle size less than 3,8 mm, were examined as to SiO reactivity.

For comparison purposes pellets without addition of fine particulate coal and consisting of 100 % biomass produced by treatment by weater vapour under high pressure of 96 % by weight of wood chips and 4 % by weight of paper was examined as to SiO reactivity.

SiO reactivity was measured by means of a standardized method where a gas mixture consisting of 13.5 % SiO, 4.5 % CO the remainder being argon, at a temperature of about 1650°C is passed through a bed of the material to be tested. When the gas mixture comes into contact with the carbon material in the bed, more or less SiO(g) will react with the carbon to form SiC and CO- gas. The content of CO in the gas mixture which has passed through the carbon materials in the bed is analyzed and the amount of SiO which has reacted with carbon for the formation of SiC is calculated. Based on this a reactivity number is determined. This method is described in the paper "Reactivity of reduction materials in the production of Silicon, Silicon-rich Ferro Alloys and Silicon-Carbide " by J.Kr. Tuset and O. Raaness, AIME El. Furnace Conference, St.Lois, Miss, Dec. 1979.

The results of the SiO reactivity tests are shown in figure 1 , where the arrow marked 1 shows the SiO reactivity for pellets according to the present invention and where the arrow marked 2 shows the SiO reactivity for pellets having no addition of fine particulate coal. In figure 1 there are further shown ranges of SiO reactivity for a number of conventional reduction materials. As will be evident from figure 1 , the pellets according to the present invention have a very high SiO reactivity, substantially higher than coal and also higher than pellets consisting only of biomass produced from wood chips and paper. It was very surprising that the pellets according to the invention showed a synergistic effect as to SiO reactivity.

EXAMPLE 2

Pellets according to the present invention containing 60 % by weight of biomass produced by treatment of wood chips with water vapour under high pressure and 40 % by weight of carbon black having a particle size between 200 and 300μm were examined as to SiO reactivity using the same method as described in Example 1

The result of the SiO reactivity test is shown in figure 1 with arrow marked 3. The pellets containing carbon black according to the present invention show a remarkable high SiO reactivity, taken into account that carbon black is known to have a very pure SiO reactivity. EXAMPLE 3

Pellets according to the present invention containing 60 % by weight of biomass produced by treatment of wood chips with water vapour under high pressure and 40 % by weight of fine particulate petrol coke were examined as to SiO reactivity using the same method as described in example 1.

The result of the SiO reactivity is shown in figure 1 with arrow marked 4. The pellets containing petrol coke according to the present invention show a remarkably high SiO reactivity compared both to petrol coke as such and also to biomass as such.

Claims

CLAIMS:

1. Pellets for the use as a reduction material in metallurgical reduction processes for the production of metals and alloys, characterized in that the pellets comprises 40 - 95 % by weight of biomass produced by treatment of woodchips and optionally paper with water vapour under high pressure and 5 - 60 % by weight of one or more fine particulate carbon materials containing a substantial amount of elemental carbon.

2. Pellets according to claim 1, c h a ra cte ri ze d i n that the biomass is produced by treatment with water vapour under high pressure of a mixture comprising 90 - 99.5 % by weight of wood chips and 0.5 - 10 % by weight of paper.

3. Pellets according to claim 2, c h a ra cte ri ze d i n that the biomass is produced by treatment with water vapour under high pressure of a mixture comprising 96 - 99 % by weight of wood chips and 1 - 4 % by weight of paper.

4. Pellets according to claim ^characterized in that the pellets comprises 50 - 70 % by weight of biomass and 30 - 50 % by weight of fine particulate carbon material.

5. Pellets according to claim 1, cha racterized i n that it has a fixed carbon content of at least 30 % by weight.

6. Pellets according to claim ^ cha racterized i n that the fine particulate carbon material is coal, coke, char coal or carbon black having a particle size less than 5 mm.