Partially-reduced iron producing method and partially-reduced iron producing apparatus

1. A partially-reduced iron producing method comprising the steps of:

laying an ignition carbon material to a predetermined height on an endless grate;

igniting the ignition carbon material, and then packing raw-material pellets on the ignited ignition carbon material, the raw-material pellets formed by mixing and pelletizing a reduction carbon material and a raw material containing iron oxides;

causing a flammable volatile component to be generated from the reduction carbon material in the raw-material pellets and combust, by use of a combustion heat of the ignited ignition carbon material;

causing a temperature of the raw-material pellets to further rise by use of a combustion heat of the flammable volatile component, so that a reduction reaction proceeds and a carbon monoxide gas is generated, while causing the raw-material pellets adjacent thereto to be heated by use of the combustion heat, so that a flammable volatile component is generated from the reduction carbon material in the adjacent portions of the raw-material pellets;

increasing a concentration of the carbon monoxide gas near the raw-material pellets having the temperature further raised, to a combustion range of the carbon monoxide gas by supplying an oxygen-containing gas to the raw-material pellets having the temperature thereof caused to further rise, so that the carbon monoxide gas combusts and a combustion zone is formed, the oxygen-containing gas made by circulating a remaining portion of the flammable volatile component and the carbon monoxide gas and mixing the remaining portion and the gas with air; and

moving the combustion zone sequentially in a bed height direction of a packed bed of the raw-material pellets in a period between supplying of the raw-material pellets onto the ignition carbon material and discharging thereof, so that the packed bed of the raw-material pellet is thermally reduced and a partially-reduced iron is produced.

2. The partially-reduced iron producing method according to claim 1 , wherein a laying height of the ignition carbon material is higher than 3 mm but is lower than 10 mm.

3. The partially-reduced iron producing method according to claim 1 , wherein the partially-reduced iron thus produced is put into a submerged arc furnace in a state while being thermally reduced together with a reduction carbon material to be subjected to final reduction and melting.

4. A partially-reduced iron producing apparatus comprising a partial reduction furnace configured to pack, on an endless grate, raw-material pellets formed by mixing and pelletizing a reduction carbon material and a raw material containing iron oxides and to thermally reduce the raw-material pellets, the partial reduction furnace including:

ignition carbon material supply device configured to lay an ignition carbon material layer to a predetermined height on the endless grate;

ignition device configured to the ignite the ignition carbon material layer;

raw-material pallet supply device configured to pack the raw-material pellets on the ignition carbon material layer ignited by the ignition device; and

exhaust gas circulation device configured to supply an oxygen-containing gas to the packed bed of the raw-material pellets heated by a combustion heat of the ignited ignition carbon material layer, the oxygen-containing gas made by circulating part of an exhaust gas discharged from the packed bed of the raw-material pellets and mixing the part with air, wherein

a partially-reduced iron is produced by thermally reducing the packed bed of the raw-material pellets through a combustion region for the ignition carbon material layer and a heating region for the raw-material pellets, the combustion region formed on an upstream side in a travelling direction of the endless grate by supplying the oxygen-containing gas having a predetermined oxygen concentration to the ignition carbon material layer ignited by the ignition device, the heating region formed downstream of the combustion region for the ignition carbon material layer in the travelling direction of the endless grate by supplying the oxygen-containing gas having a lower oxygen concentration than the predetermined oxygen concentration to the packed bed of the raw-material pellets.

5. The partially-reduced iron producing apparatus according to claim 4 , further comprising:

a hood provided above the endless grate and configured to form an air-tight space between the hood and the endless grate; and

a plurality of wind boxes provided below the endless grate and configured to form air-tight spaces between the wind boxes and the endless grate, wherein

the ignition carbon material supply device is disposed upstream of a raw-material pellet supply device in the travelling direction of the endless grate.

6. The partially-reduced iron producing apparatus according to claim 5 , further comprising:

partition boards provided in the hood, surrounded by the hood and the endless grate, and configured to define a space in a center portion in a longitudinal direction of the endless grate;

exhaust gas circulation device configured to discharge an exhaust gas in the space in the center portion in the longitudinal direction of the endless grate and supplying the exhaust gas to the wind boxes;

air supply device, connected to the exhaust gas circulation means, configured to supply air; and

flow rate adjustment device, provided in the air supply device, configured to adjust a flow rate of the air.