May 2012

A clean sweep

Vale will overhaul smelter to reduce atmospheric emissions

By Peter Diekmeyer

Vale is pumping $2 billion into sulphur dioxide and dust emission reduction initiatives at its Copper Cliff smelter in Sudbury, Ontario. The move has copper-nickel operations, procurement and project personnel rolling up their sleeves and sharpening their pencils.

“It’s one of the largest environmental investments in Ontario’s history,” says Dave Marshall, an engineering manager at Vale who has been involved in development of the project over the past five years. “The new sulphuric acid plant will cut projected sulphur discharges by some 120,000 tonnes. Greenhouse gas emissions will also go down, as we will be using 3.5 million cubic feet of natural gas less each year. So naturally we are all very excited.”

Vale’s new initiative, dubbed the “Clean AER (Atmospheric Emissions Reductions) project,” is impressive in many ways. In all, it will create close to 1,300 new jobs at peak construction and, in addition to the building of the new acid plant, a secondary baghouse and a wet gas cleaning plant will involve a complete overhaul of the Copper Cliff smelter’s converter aisle.   

Saleable gains

According to Marshall, about 60 per cent of the project’s efforts will be channelled into the smelter modifications and the new sulphuric acid plant that will process gasses captured in the Sudbury smelter. The plant will transform sulphur dioxide gas to liquid sulphuric acid through a chemical process that involves its exposure to a catalyst at high temperature, which will convert the sulphur dioxide to sulphur trioxide.

The sulphur trioxide will then be absorbed into water, creating sulphuric acid. The sulphur dioxide gas goes through two separate stages of conversion and absorption to increase the efficiency of the process, and the end product, one of the world’s largest commodity chemicals, can be easily sold on the open market.

The project’s converter wet gas cleaning plant will play an important role as well. The facility removes dust and cools process gasses from the sulphur dioxide gas stream, which is collected from the pyrometallurgical process of the converters prior to being transported to the acid plant.

In the gas cleaning plant, the hot gasses from the converters will first be cooled with water to remove large dust particles and condense gaseous metals to a solid form. The metals will then be collected in wet electrostatic precipitators, and the clean gas will then be transferred to the acid plant. The dust and metals must be removed from the gas to ensure the acid produced is of a quality that can be sold to other industries.   

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