Direct reduction process for iron oxide-containing materials

Details Direct reduction process for iron oxide-containing materials Direct reduction process for iron oxide-containing materials

1997-01-15

1999-01-05

Andrews, Melvyn

Specialized metallurgical processes, compositions for use therei

Processes

Process control responsive to sensed condition

75450, 75505, 481983, 266156, 266172, C21B 1300

Patent

active

058556435

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a process for the direct reduction of iron-containing material, wherein synthesis gas, preferably reformed natural gas, is mixed with top gas forming in the direct reduction of the iron-containing material and is used for direct reduction as a reducing gas which does not crack at reduction temperature, as well as a plant for carrying out the process.
2. Description of the Prior Art
A process of this type is known, for instance, from U.S. Pat. No. 2,752,234, U.S. Pat. No. 5,081,251, and EP 0 571 358.
From EP 0 571 358 it is known to carry out the reduction of fine ore not exclusively via the strongly endothermic reaction with H.sub.2 according t o lower the operational costs involved.
However, in metallic plant parts that get into contact with CO-containing reducing gas are subject to a high stress due to corrosion. The result is metal decomposition, which is denoted as "metal dusting" in the technical literature. Metal dusting occurs to an increased extent at elevated temperatures, plant parts that get into contact with hot CO-containing reducing gas, thus, being particularly jeopardized. With a plant for carrying out the initially mentioned process, these are primarily the reactors employed for direct reduction and the gas heater heating the reducing gas to reduction temperature.
With a process according to the prior art, difficulties may occur when the reducing gas has a water content that is either too high or too low. If the water content is too high, the reduction potential of the reducing gas decreases. As a result, a higher amount of reducing gas is required for direct reduction than would actually be necessary in accordance with the chemical potential of the reducing gas. A further difficulty arises if the water content of the reducing gas is too low, because too dry a reducing gas causes metal dusting to an increased extent. In order to minimize both of these drawbacks, it is necessary to adjust the optimum water content with great accuracy.


SUMMARY OF THE INVENTION

The invention aims at avoiding these disadvantages and difficulties and has as its object to provide a process of the kind initially desired, and a plant for carrying out the process by which the occurrence of metal dusting is minimized or prevented in a simple manner despite an elevated CO content of the reducing gas. The goal is achieved in a procedurally and structurally simple and cost-saving manner, so that the service life of metallic plant parts will be considerably increased while utilizing the chemical reduction potential of the reducing gas to the optimum degree. Thereby, the energy demand, particularly the demand of reducing gas, is to be minimized.
In accordance with the invention, the object is achieved in that an H.sub.2 O content of between 1 and 2 Vol. %, preferably amounting to about 1.5 Vol. %, is adjusted in the reducing gas by subjecting a partial volume of the top gas to CO.sub.2 scrubbing prior to being used as a reducing gas, wherein the top gas subjected to CO.sub.2 scrubbing is mixed with the synthesis gas and is brought to a predetermined temperature by direct irrigation while being saturated with H.sub.2 O. After direct irrigation, the gas is heated to a temperature above the saturation temperature by admixing CO.sub.2 -unscrubbed top gas, and subsequently is used as a reducing gas.
By directly cooling or directly heating by means of irrigation the top gas subjected to CO.sub.2 scrubbing and the admixed synthesis gas to a predetermined temperature, it is feasible to saturate this gas mixture with water, the temperature being chosen as a function of the desired water content. By adjusting a given temperature of the reducing gas, which is very simple to realize in terms of control and accuracy without great expenditure, it is feasible, to adjust the water content in the reducing gas with very high accuracy, i.e., at a substantially higher accuracy level than is achieved, for instance, by blowing in a vapor through tuyeres

REFERENCES:
patent: 2752234 (1956-06-01), Shipley
patent: 3844766 (1974-10-01), Beggs
patent: 4150972 (1979-04-01), Price-Falcon et al.
patent: 4880459 (1989-11-01), Coyne, Jr.
patent: 5082251 (1992-01-01), Whipp
patent: 5370727 (1994-12-01), Whipp

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