GB2118976A

GB2118976A - Direct reduction of iron ore

Info

Publication number: GB2118976A
Application number: GB08307651A
Authority: GB
Inventors: George Clifton Carter
Original assignee: Davy McKee AG
Current assignee: Davy McKee AG
Priority date: 1982-03-25
Filing date: 1983-03-18
Publication date: 1983-11-09
Also published as: GB8307651D0

Abstract

To reduce iron ore to iron, bituminous coal is carbonised to form char and combustible gas and a quantity of iron ore and a quantity of the char in substantially stoichiometric proportions are introduced into a kiln where some of the combustible gas produced from the volatile materials in the coal is burnt to raise the temperature of the iron ore and the char sufficiently to cause reduction of the iron ore to metallic iron to take place. <IMAGE>

Description

SPECIFICATION Direct reduction of iron ore This invention relates to a process of, and apparatus for, the direct reduction of iron ore.

The direct reduction of iron ore to iron using bituminous coal as the only source of fuel and reductant in a kiln is known. The heated coal gives off volatiles, some of which are burned in the presence of oxygen to raise the temperature of iron ore. After the volatiles are given off from the coal, there remains a mainly carbon material which is referred to as a "char". The char reduces the heated iron oxide by combining with the oxygen and leaving the iron in metallic form.

In an existing process for the reduction of iron ore in a rotary kiln using coal as the sole source of fuel and reductant, the coal can be added either at the feed end of the kiln or at the discharge end or both. The use of coal added at the feed end results in the volatiles being driven off in the first or preheat zone of the kiln by the heat from the gas stream which travels countercurrent to the coal and iron ore. The gas is drawn off at the feed end and must be either burnt prior to flaring to atmosphere or used for the generation of steam in a waste heat boiler. The volatile matter from the coal puts extra calorific value into the gas stream, necessitating a greater expenditure on gas handling equipment and occasioning a greater loss if the gas is flared.

An object of the present invention is to provide a process for the direct reduction of iron ore in which this difficulty is at least partially overcome.

According to a first aspect of the present invention, bituminous coal is carbonised to form char and combustible gas; a quantity of iron ore and a quantity of said char are introduced in substantially stoichiometric proportions into a kiln and at least some of said gas is introduced into the kiln where it is burnt to heat the iron ore and the char to cause reduction of the iron ore to take place.

According to a second aspect of the present invention, apparatus for reducing iron ore comprises a carbonising plant for converting bituminous coal into char and combustible gas, a kiln having a feed inlet and a discharge outlet, means for introducing char from the carbonising plant and iron ore into the feed inlet of the kiln, means for introducing combustible gas from the carbonising plant into the discharge outlet of the kiln, and means for introducing air into the kiln.

By employing char with low residual volatile content as the reductant, then the reducing effect is obtained without any overloading of the gas handling system. Most, or all, of the combustible gas produced from the coal carbonising plant is introduced into the discharge end of the kiln. This gas together with any carbon monoxide arising from the reduction process is burnt in air which is added at suitable regions along the length of the kiln. By this means, the bed of iron ore and char is heated by convection and radiation under controlled conditions and able to meet the requirements of the process.

The process is extremely controllable and the thermal efficiency of the process can be arranged to be very high and, in addition, there is the further advantage that the temperature within the kiln, because of the improved control, can be somewhat lower and hence maintain a greater margin between the kiln temperature and the fusion temperature of the ash in the char thus preventing the formation of accretions within the kiln.

A further advantage which relates to subsequent use of the directly reduced iron is that, by minimising the char content at the discharge end of the kiln, it becomes easier to put a carbon bearing material into the kiln near the discharge end to introduce a small percentage of carbon into the product. This is a desirable feature for subsequent processing in an electric arc furnace.

The main advantage of the invention, therefore, is that, not only can the char and the combustible gases be used in the best way for the reduction process for any value of volatile matter in the coal within the range of suitable values), but the gas and char, once produced, can be used in the ratio required by the reduction process and the balance of the one which may be in surplus can be used elsewhere in the plant or made available for sale.

This aspect of the invention has the virtue of making the process capable of maintaining its output and high efficiency even when the volatile content of the coal being used changes from that which was used for the basic design of the plant.

This can readily be seen as a major advantage in maintaining output and efficiency or preserving the commercial advantage of flexibility in coal supplies.

Referring to the accompanying drawing, which is a flow sheet of the process of the invention, a rotary kiln 1 is inclined and has a feed inlet 3 at its upper end and a discharge outlet 5 at its lower end. Iron ore in granular or pellet form and char in substantially stoichiometric proportions are introduced into the feed inlet of the kiln.

Combustible gas is introduced into the kiln at its discharge end and air is added to the kiln at regions along its length. The gas is burnt and the products of combustion pass upwardly through the kiln and leave by a gas discharge 7 at the feed end of the kiln. The ore is reduced to metallic iron which leaves the kiln through the discharge outlet 5. The char and the combustible gas are produced in a coal carbonisation plant 9 to which bituminous coal is supplied and the char and the volatile materials are obtained. If the quantity of char produced by the plant 9 is in excess of what is required in the reduction process, then some of the char can be sold and, similarly, if the combustible gas produced by the plant 9 is in excess of that required for the reduction process, then the gas can be used for industrial uses in other parts of the instailation.

1. A method of reducing iron ore in which

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Direct reduction of iron ore This invention relates to a process of, and apparatus for, the direct reduction of iron ore. The direct reduction of iron ore to iron using bituminous coal as the only source of fuel and reductant in a kiln is known. The heated coal gives off volatiles, some of which are burned in the presence of oxygen to raise the temperature of iron ore. After the volatiles are given off from the coal, there remains a mainly carbon material which is referred to as a "char". The char reduces the heated iron oxide by combining with the oxygen and leaving the iron in metallic form. In an existing process for the reduction of iron ore in a rotary kiln using coal as the sole source of fuel and reductant, the coal can be added either at the feed end of the kiln or at the discharge end or both. The use of coal added at the feed end results in the volatiles being driven off in the first or preheat zone of the kiln by the heat from the gas stream which travels countercurrent to the coal and iron ore. The gas is drawn off at the feed end and must be either burnt prior to flaring to atmosphere or used for the generation of steam in a waste heat boiler. The volatile matter from the coal puts extra calorific value into the gas stream, necessitating a greater expenditure on gas handling equipment and occasioning a greater loss if the gas is flared. An object of the present invention is to provide a process for the direct reduction of iron ore in which this difficulty is at least partially overcome. According to a first aspect of the present invention, bituminous coal is carbonised to form char and combustible gas; a quantity of iron ore and a quantity of said char are introduced in substantially stoichiometric proportions into a kiln and at least some of said gas is introduced into the kiln where it is burnt to heat the iron ore and the char to cause reduction of the iron ore to take place. According to a second aspect of the present invention, apparatus for reducing iron ore comprises a carbonising plant for converting bituminous coal into char and combustible gas, a kiln having a feed inlet and a discharge outlet, means for introducing char from the carbonising plant and iron ore into the feed inlet of the kiln, means for introducing combustible gas from the carbonising plant into the discharge outlet of the kiln, and means for introducing air into the kiln. By employing char with low residual volatile content as the reductant, then the reducing effect is obtained without any overloading of the gas handling system. Most, or all, of the combustible gas produced from the coal carbonising plant is introduced into the discharge end of the kiln. This gas together with any carbon monoxide arising from the reduction process is burnt in air which is added at suitable regions along the length of the kiln. By this means, the bed of iron ore and char is heated by convection and radiation under controlled conditions and able to meet the requirements of the process. The process is extremely controllable and the thermal efficiency of the process can be arranged to be very high and, in addition, there is the further advantage that the temperature within the kiln, because of the improved control, can be somewhat lower and hence maintain a greater margin between the kiln temperature and the fusion temperature of the ash in the char thus preventing the formation of accretions within the kiln. A further advantage which relates to subsequent use of the directly reduced iron is that, by minimising the char content at the discharge end of the kiln, it becomes easier to put a carbon bearing material into the kiln near the discharge end to introduce a small percentage of carbon into the product. This is a desirable feature for subsequent processing in an electric arc furnace. The main advantage of the invention, therefore, is that, not only can the char and the combustible gases be used in the best way for the reduction process for any value of volatile matter in the coal within the range of suitable values), but the gas and char, once produced, can be used in the ratio required by the reduction process and the balance of the one which may be in surplus can be used elsewhere in the plant or made available for sale. This aspect of the invention has the virtue of making the process capable of maintaining its output and high efficiency even when the volatile content of the coal being used changes from that which was used for the basic design of the plant. This can readily be seen as a major advantage in maintaining output and efficiency or preserving the commercial advantage of flexibility in coal supplies. Referring to the accompanying drawing, which is a flow sheet of the process of the invention, a rotary kiln 1 is inclined and has a feed inlet 3 at its upper end and a discharge outlet 5 at its lower end. Iron ore in granular or pellet form and char in substantially stoichiometric proportions are introduced into the feed inlet of the kiln. Combustible gas is introduced into the kiln at its discharge end and air is added to the kiln at regions along its length. The gas is burnt and the products of combustion pass upwardly through the kiln and leave by a gas discharge 7 at the feed end of the kiln. The ore is reduced to metallic iron which leaves the kiln through the discharge outlet 5. The char and the combustible gas are produced in a coal carbonisation plant 9 to which bituminous coal is supplied and the char and the volatile materials are obtained. If the quantity of char produced by the plant 9 is in excess of what is required in the reduction process, then some of the char can be sold and, similarly, if the combustible gas produced by the plant 9 is in excess of that required for the reduction process, then the gas can be used for industrial uses in other parts of the instailation. CLAIMS

1. A method of reducing iron ore in which bituminous coal is carbonised to form char and combustible gas; a quantity of iron ore and a quantity of said char are introduced in substantially stoichiometric proportions into a kiln and at least some of said gas is introduced into the kiln where it is burnt to heat the iron ore and the char to cause reduction of the iron ore to take place.

2. A method as claimed in claim 1, in which the gas is introduced into the kiln at its discharge end such that gaseous products of combustion pass through the kiln in the opposite direction to the movement of the iron ore and char through the kiln,

3. A method as claimed in claim 1 or 2, wherein carbon bearing material is introduced into the kiln near the discharge end to increase the carbon content of the iron.

4. Apparatus for reducing iron ore comprising a carbonising plant for converting bituminous coal into char and combustible gas, a kiln having a feed inlet and a discharge outlet, means for introducing char from the carbonising plant and iron ore into the feed inlet of the kiln, means for introducing combustible gas from the carbonising plant into the discharge outlet of the kiln, and means for introducing air into the kiln.

5. Apparatus as claimed in claim 4, in which the kiln is of the rotary type and is inclined upwardly with the feed inlet at the upper end andthe discharge outlet at the lower end.

6. Apparatus as claimed in claim 5, in which the products of combustion of the combustible gas burnt in the kiln leave the kiln at the upper end thereof.

7. Apparatus as claimed in claim 6, in which the air is introduced into the kiln at a plurality of regions spaced apart along its length.

8. A method of reducing iron ore substantially as hereinbefore described with reference to the accompanying drawings.

9. Apparatus for reducing iron ore substantially as hereinbefore described with reference to the accompanying drawing.