JOURNAL PAPER

The LUREC^® process - key to economic smelter acid plant operation

K.-H. Daum

OUTOTEC

SYNOPSIS

Over many decades, numerous feasibility studies have demonstrated, that the production of sulphuric acid remains the most viable option of sulphur recovery from smelter off gas and abatement of SO₂ emissions to the atmosphere. This is particularly more pronounced as smaller but more concentrated off-gas flows are to be treated from smelters, and enhanced sulphuric acid processes become available.
Off-gas handling systems represent a significant capital and operating cost burden to the metallurgical operation. Modern pyrometal-lurgical smelter processes for sulphide ores based on the use of oxygen-enriched air, produce relatively small off-gas flows with high SO₂ concentrations in the smelter gas of 30-60%-vol. of SO₂. This is a prerequisite for substantial cost reductions in the smelter off-gas handling and treatment system.
As an alternative to sulphuric acid production, numerous scrubbing concepts with alkali or dual-alkali combinations as well as organic absorbents have been proposed. Also the reduction of the SO₂ to elemental sulphur has frequently been studied. Very few of those alternative processes have been built in industrial scale, but all were generally characterized by none-sustainable operation due to cost reasons, problems with issues related to chemicals used and by-products or poor availability.
Thus the traditional concept of converting the SO₂ to sulphuric acid is most common, although regarded as uneconomic, but is at least a proven, environmentally sustainable and reliable way of sulphur gas processing. With the high acid price levels these days, operating companies are even able to generate significant revenue with their otherwise 'fatal' acid.
Even though smelter gas is available at high SO₂ concentrations, in a conventional acid plant one would add large amounts of air to dilute the gas down to a suitable concentration of 12-13 (14)%-vol. SO₂. Dealing with higher SO₂ concentrations in smelter acid plants is not feasible, as the gas exit temperature of the catalytic oxidation step would exceed the allowable limit for the catalyst. Hence those conventional acid plants are characterized by the use of large equipment, i.e. high capital cost, high energy consumption and limited flexibility.
The newly developed LUREC^® process can handle off-gas with significantly higher gas concentrations, even in excess of 25%-vol. SO₂. It is entirely based on well-proven equipment and unit operations. The first industrial application, operating with 16-18%-vol. SO₂ will be presented in this paper, along with the fundamentals of the process. It will be demonstrated that the process requires inherently lower capital cost, fewer operating costs, and offers better energy recovery and lower emis-sions as compared to conventional design.
While most existing smelter acid plants would have some built-in spare capacity, any significant increase of smelter capacity, say of 30%, can basically not be accommodated without installing an additional parallel new acid plant unit. An add-on LUREC^® module can remove any such restriction, while simultaneously debottlenecking the existing acid plant. The paper also discusses the present status of the add-on technology for smelter acid plant expansions with respect to technical boundary conditions of different process alternatives as well as economic and environmental aspects.
Application of the LUREC^® process to modern smelter acid plants operating with high SO₂ gas concentration, will lead to a substantial reduction of the specific size of the gas processing equipment and equivalent savings in capital and operating cost.
The LUREC^® process is patented worldwide by OUTOTEC.

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