Process for production of elemental iron

This patent application claims the benefit of European patent application No. 07121142.9, filed Nov. 20, 2007 and U.S. Provisional Application 60/991,162, filed Nov. 29, 2007, both of which are incorporated herein by reference.

The invention is directed to a process to prepare elemental iron by contacting an iron ore feed with a reducing gas comprising synthesis gas, wherein the reducing gas is prepared by a partial oxidation process.

Direct reduction of iron (DRI) generates metallic iron in a solid form by removing oxygen from the iron ore by using a reduction gas that can be provided from the synthesis gas obtained by gasification of carbonaceous feedstock. Industrially applied DRI processes include MIDREX, HyL and FINMET, as described in “Development of Reduction Process for the Steel Production” by M. Gojic and S. Kozuh, Kem. Ind. 55 (1) 1-10 (2006).

EP-A-0916739 describes a process wherein the reducing gas for the DRI process is obtained by gasification of a coal slurry. The reducing gas fed to the DRI includes a recycle gas stream that has exited the DRI, and wherein acid gases have been removed from the recycle gas stream.

U.S. Pat. No. 5,871,560 describes a process wherein synthesis gas is mixed with an off-gas produced in a DRI process to be used as a reduction gas and wherein H₂S is fed to the reducing gas.

U.S. Pat. No. 2,740,706, as filed in 1951, describes a process for reducing metal oxides by contacting with a reducing gas. In its examples the reducing gas is prepared by partial oxidation of natural gas in admixture with carbon dioxide to obtain a reducing gas having two to three times as much volume of carbon monoxide for each volume of hydrogen. The reason, according to this publication, to add carbon dioxide to the natural gas is to achieve such high contents of carbon monoxide. Coal is mentioned as a possible feedstock instead of natural gas. In this process sulphur is removed from the reducing gas by contacting the gas with sponge iron.

The so-called entrained-flow gasification process for coal as described in “Gasification” by C. Higman and M. van der Burgt, 2003, Elsevier Science, Chapter 5.3, pages 109-128 was developed after 1970 (see page 5 of this reference).

It would be an advancement in the art to provide a process that has a higher efficiency than the above-described processes.

The above is achieved by the following process. Process to prepare elemental iron by contacting an iron ore feed with a reducing gas to obtain iron and an off-gas, wherein the reducing gas is prepared by performing the following steps

(a) partially oxidizing a mixture comprising a sulphur containing solid carbonaceous fuel and gaseous CO₂ as carrier medium with oxygen, by supplying an oxygen containing gas and the solid carbonaceous fuel to a burner, thereby obtaining a gas comprising H₂, CO, CO₂ and H₂S;
(b) removing CO₂ and H₂S from the gas obtained in step (a) to obtain the reducing gas comprising H₂ and CO and a first stream comprising CO₂ and H₂S;
(c) reducing the content of H₂S in the first stream comprising CO₂ and H₂S obtained in step (b) in a liquid redox type process and
(d) recycling at least part of the CO₂ obtained in step (c) to step (a).

Applicants found that by recycling part of the CO₂ to step (a) a more efficient process is obtained. A further advantage of the present invention is that, for a given amount of carbonaceous fuel to be partially oxidised in the gasification reactor, a smaller reactor volume can be used, resulting in lower equipment expenses, as compared to a situation wherein no CO₂ is present in step (a). A further advantage is that the removal of CO₂ and H₂S is performed in one step, namely step (b), while in the process of U.S. Pat. No. 2,740,706 this removal takes place in two steps. The separation of H₂S from the first stream comprising CO₂ and H₂S by means of a liquid redox process is much more efficient than removing H₂S from the entire effluent of step (a) as in the process of U.S. Pat. No. 2,740,706.