Further reductions will come about because Noranda is building a $160- million acid plant at its Horne smelter in Rouyn/Noranda, Que. The Horne accounts for roughly 70% of the company’s total SO2 emissions. Other sm elters owned in part or in whole by Noranda are run by Brunswick Mining & Smelting in New Brunswick, cez near Montreal, and Noranda’s complex on the Gaspe Peninsula. By the fourth quarter of this year, the sulphuric acid plant should be up and running, cutting sulphur dioxide emissions from the Horne smelter next year by 50% and a recently announced concentrate injection program in the smelter converter section at an additional $16-million cost will voluntarily reduce SO2 emissions by another 20% by 1995 for a total reduction of 70% of 1980 levels. Where that one smelter spewed out 552,000 tonnes of SO2 in 1980, it will emit 165,600 tonnes by 1995.
“We are four years ahead of our federal and provincial agreements which stipulated a 50% reduction by 1994,” said Hennie Veldhuizen, director of environment for Noranda. The agreements also provide for $41.6 million from each level of government in the form of repayable loans.
Rob Metka, Noranda Minerals’ project director, said the plant is among the largest and most complex of its kind in the world. “This is a state-of-the-art plant on a grand scale,” he said. The total complex, parts of which incorporated proprietary designs of Chemetics International (which was also the lead engineering firm on the project) includes a gas cleaning section and an acid plant. The feedstock consists of off-gases from Noranda’s continuous process reactor. A quenching tower, where off- gases enter at temperatures of 325 degrees C, is the first step in the gas-cleaning stage. Water cools the gases to the adiabatic saturation point (the point at which no more cooling can take place), in this case 80 degrees C. The cooling creates very fine particles (a vapor really) containing trace amounts of arsenic, cadmium, lead, zinc and all the other elements in the off-gases.
This vapor is fed to a variable throat venturi, a pipe with a tapered section that has a moveable plug to constrict the opening even further (thus, the “variable throat” designation). As the vapor flows through the venturi, the flow velocity increases. This turbulence allows the particles to combine with water droplets, which is the whole point to the exercise.
The post-venturi stage includes 2-stage condensors that cool the gases and produce a mist. The mist is collected in electrostatic mist precipitators (made by Joy Manufacturing of Kitchener, Ont.), which are vertical lead tubes about 18 ft long and 10 inches in diameter with a positively charged electrode in the middle. Mist particles are attracted to the negatively charged walls of these tubes and collected at the bottom. A mercury scrubber completes the cleaning stage.
The metallurgical acid plant has three main sections: a wet gas section where the gas is cleaned, cooled and dried; a dry gas section where sulphur dioxide is converted to sulphur trioxide; and a strong acid circuit that absorbs the sulphur trioxide to produce sulphuric acid.
The wet gas section begins with dust removal, cooling and electrostatic precipitation. The precipitator removes any remaining dust and acid mist. A drying tower washes the gases with sulphuric acid to absorb all the last traces of moisture. Dried air and sulphur dioxide are then fed to a blower with a 6-ft-diameter impeller spinning at 3,200 r.p.m.
The dry gas section includes a 3-pass converter that converts the SO2 to SO3 so that it can combine with water. (Like oil, SO2 has no affinity to combine with water.) Gases are heated in a heat exchanger and passed across a catalyst bed. After cooling, the gases are passed across the catalyst twice more. SO2 to SO3 conversion should be 97%.
The process gas then enters the absorbing tower, passing through a layer of packing counter-current to a flow of strong sulphuric acid. The SO3 contained in the process gas is absorbed by the sulphuric acid and a surplus of sulphuri c acid (H2SO4) can be extracted. Eleven acid storage tanks have been installed with a total capacity of 80,000 tonnes.
Noranda had originally slated to spend about $10 million on local supplies and contractors, but that figure ballooned to $30 million as the project progressed. Local contractors included Pamo Construction, Pilon Construction, Promec Construction, Betteridge Smith Construction and R. Blais & Fils. Structural steel was supplied by Dominion Bridge and Lords Cie, while Fibreglas piping, ducting and vessels were supplied by Fabco of Maple, Ont., Troy Manufacturing of Montreal and Abco of Nova Scotia.
The plant will have the capacity to produce 350,000 to 400,000 tonnes of sulphuric acid per year, a supply that will be sold, in part at least, to chemical companies operating on the U.S. eastern seaboard. Because the plant was conceived and built as an environmental project, Noranda is not expecting it to be a big money-maker. “We’re counting on its breaking even,” said Veldhuizen. “If we can make some money at it, that’s great. It is an environmental project. The project wasn’t constructed to satisfy the sulphuric acid market.”
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