Plant and process for the production of pig iron and/or...

Details Plant and process for the production of pig iron and/or... Plant and process for the production of pig iron and/or...

1998-09-04

2001-02-06

Andrews, Melvyn (Department: 1742)

Specialized metallurgical processes, compositions for use therei

Processes

Producing or treating free metal

C075S446000, C266S160000, C266S172000

Reexamination Certificate

active

06183534

ABSTRACT:

The invention relates to a plant for the production of pig iron and/or sponge iron, comprising at least one fluidized bed reactor intended to receive fine ore, a reducing-gas feed duct leading to said fluidized bed reactor, an offgas discharge duct departing from the fluidized bed reactor and a discharge means, preferably a briquetting means, provided for the reduction product formed in the fluidized bed reactor, wherein the offgas discharge duct of the fluidized bed reactor runs into a purification means, such as a scrubber, subsequently into a heating means and finally into the reducing-gas feed duct of the fluidized bed. The invention further relates to a process for producing pig iron and/or sponge iron using this plant.
The processing of fine ore to sponge iron in a fluidized bed reactor, in principle, is known from U.S. Pat. No. 5,082,251. There, the reducing gas is produced by catalytic reformation of desulphurized and preheated natural gas with overheated water vapor in a reformer furnace. That process allows for the production of high-quality sponge iron from fine ore.
The invention is based on the object to improve a plant of the type initially described in such a manner that the product produced, i.e., pig iron and/or sponge iron, complies with a high quality standard at a minimum energy input, in particular exhibits a high degree of metallization and purity, such that further processing will be ensured without any problems.
In a plant of the initially described kind, this object is achieved in that the heating means is constructed such that it comprises two stages and that there are provided a heat exchanger as the heating means for the reducing gas and, connected serially therewith, a partial combustion means for the reducing gas with an oxygen feeding means.
Advantageously, a CO
2
removal means is provided in the reducing-gas feed duct of the fluidized bed reactor, for lowering the CO
2
content of the offgas formed in the fluidized bed reactor.
The process of the invention for producing pig iron and/or sponge iron is characterized in that fine ore is reduced to sponge iron with a reducing gas in a fluidized-bed direct reduction zone according to the fluidized bed method, wherein a purified offgas forming in the fluidized-bed direct reduction zone is supplied to the fluidized-bed direct reduction zone as a supplement to freshly supplied reducing gas, and that such offgas supplied to the fluidized-bed direct reduction zone is heated in two stages, preferably together with freshly supplied reducing gas, namely in a first stage through heat exchange and in a second stage through partial combustion by means of oxygen which is fed into at least a partial quantity of the reducing gas.
In order to lower the CO
2
content of the reducing gas supplied to the fluidized bed direct reduction zone to the desired measure, the offgas from the fluidized-bed direct reduction zone suitably is subjected to CO
2
removal.
Advantageously, the freshly supplied reducing gas is fed to the fluidized-bed direct reduction zone while bypassing the CO
2
removal means for the offgas from the fluidized-bed direct reduction zone.
Direct reduction in the fluidized bed process may be effected in two or several stages, as is known, for instance, from U.S. Pat. No. 5,082,251. Further, it is possible to carry out direct reduction by aid of a circulating fluidized bed, known, for instance, from EP-B-0 364 865.
In the following, the invention will be explained in more detail by way of an exemplary embodiment schematically illustrated in the drawing, wherein the FIGURE represented in the drawing illustrates the process scheme of a plant according to the invention.
The plant comprises two fluidized bed reactors
1
,
2
consecutively connected in series, fine ore being conducted via a fine-ore supply duct
3
to the first fluidized bed reactor
1
and from there via a conveying duct
4
to the consecutively connected fluidized bed reactor
2
. The material completely reduced in one fluidized-bed direct reduction zone
5
each of the fluidized bed reactors
1
,
2
(sponge iron), upon emergence from the second fluidized bed reactor
2
, is supplied to a briquetting plant
6
where it is hot- or cold-briquetted. Prior to introducing the fine ore into the first fluidized bed reactor
1
, it is subjected to an ore preparation, such as drying, which, however, is not illustrated in detail.
Reducing gas is conducted through a gas duct
7
in counterflow to the ore flow, from the fluidized bed reactor
2
to the fluidized bed reactor
1
, i.e., to the fluidized-bed direct reduction zones
5
provided in the fluidized bed reactors
1
and
2
and is carried off the first fluidized bed reactor
1
—viewed in the ore flow direction—as an offgas through an offgas discharge duct
8
.
The offgas drawn off the fluidized bed reactor
1
is cooled and scrubbed in a purification means
9
preferably designed as a wet scrubber and subsequently is mixed with the freshly supplied reducing gas by running together with a reducing-gas feed duct
10
supplying fresh reducing gas and the offgas discharge duct
8
. The mixed gas thus formed is passed through a CO
2
removal means
11
, preferably designed as a CO
2
scrubber, and is freed from CO
2
. After this, heating of the mixed gas to a temperature of about 400° C. is effected in two stages in a heat exchanger
12
. Following upon the same, there is an afterburning means
13
, in which part of the mixed gas is burnt under oxygen supply, the mixed gas thus attaining the temperature required for the direct reduction in the fluidized bed reactors
1
,
2
of up to about 850° C. This heated mixed gas then is available to the fluidized bed reactors
1
,
2
as a reducing gas.
According to a preferred embodiment, only the offgas of the fluidized bed reactors
1
,
2
is subjected to CO
2
scrubbing and the reducing gas freshly supplied via a duct
14
is mixed with the offgas only after CO
2
scrubbing of the same.
The briquetted sponge iron is processed in a compact steel works, for instance equipped with electric furnaces and converters. If necessary, briquetted sponge iron also may be charged into a melter gasifier through a conveying means and melted there. This is advantageous, in particular, if excess energy is available in a melter gasifier.
Advantageously, the heat exchanger
12
is operated with part of the offgas from the fluidized bed reduction, which is fed through a duct
15
. Offgas that is not required for the reduction process or the heat exchanger
12
is supplied to other consumers through an export-gas discharge duct
16
. The discharge duct
16
advantageously run into a gas collection tank, such as a gasometer, for the intermediate storage of the export gas. Thus, differences in gas production and deviations in pressure within the system may be checked and balanced out in an advantageous manner.
The briquetting plant
6
may be replaced with a discharge means
17
, such as, e.g., a cold discharge means.
All of the conveying means and gas ducts are equipped with control organs or compressors, respectively, in a usual manner.


REFERENCES:
patent: 5989308 (1999-11-01), Kepplinger et al.

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