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Waste Heat Boilers Downstream Flash Smelting and Outokumpu/Kivcet Process
Flash smelting of copper and nickel concentrates takes place in a furnace with reaction shaft (Outokumpu flash smelting process). The process gases are cooled in a special waste heat boiler. The products are traditionally processed further on in a converter. The horizontal waste heat boiler downstream of the Outokumpu flash smelting process consists of a radiation chamber in which the gas is cooled down to 600 °C – 800 °C and an adjacent convection part in which convection heating surfaces are installed. The waste heat boilers are equipped with membrane walls, bulkheads and bundle heating surfaces. To avoid corrosion in the waste heat boilers, the water/ steam-side operating pressure is typically set between 40 and 70 bar.
This ensures that the temperature of the boiler surfaces lies significantly above the sulfuric acid dew point, as required depending on the SO2/SO3 concentration in the process gas.
In order not to exceed the maximum permissible gas temperature for the downstream filter unit, Oschatz offers a highly efficient and patented cleaning system (hammering system) for the boiler surfaces.
Another flash smelting process is the Kivcet process for lead smelting. The process gases are cooled down in two waste heat boilers to around 350 °C, with one boiler located above the melting furnace, the other one above the electric furnace.
The radiation chamber of each of the boilers consists of two vertical shafts and one horizontal convection part. The typical gas outlet temperature is 350 °C.
The successful handling of the thermal expansion of the boilers in smelter conditions is an essential factor for maximum uptime and for avoiding leaks. This is achieved by means of flexible pendulum supports that minimize horizontal forces at the side of the boilers.
The overall concept also takes account of the ease of maintenance; this is provided by means of the boiler top, which is easily accessible.