Energy Recovery for the Non-Ferrous Industry

We offer process-specific solutions for energy recovery for all pyrometallurgical processes for the recovery of metals such as lead, copper, nickel, zinc or tin in non-ferrous metallurgy.

The hot and sticky process gases, which carry significant quantities of dust, as well as the various melting and roasting processes in non-ferrous metallurgy create major challenges for our waste heat and gas cooling systems:

Layout of waste heat boilers
Consideration of furnace geometry
Determination of heat transfer taking into account the risk of fouling
Waste gas routing within the boiler layout
Determination of radiant and convection heating surfaces
Selection of reliable heating surface cleaning systems

Waste Heat Boilers Downstream Flash Smelting downstream of the 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.

Waste Heat Boilers downstream of Isasmelt / Ausmelt Process

In the bath-lance melting process for recovering copper, nickel, lead, zinc and tin, process gas with a temperature of 1,200 °C – 1,550 °C is fed directly into a waste heat boiler. By cooling the exhaust gases, sticky dust remaining from the molten phase, is kept at a safe temperature range below the temperatures at which it would begin to soften.

Depending on the design of the whole plant, the process gas is cooled down to between 600 °C and 900 °C in a two-pass vertical boiler or down to approximately 350 °C in a three-pass vertical/horizontal boiler. The dust is partly separated in the waste heat boiler.

Further dust separation takes place in a baghouse or an electrostatic precipitator. If saturated steam is not being used, the dust can be condensed in an air-cooled condenser which is installed above the steam drum.

When processing recycled material in the smelting furnace, vapor pressure and steam temperature may be set lower because the acid dew point is lower.

The adapter elements between the furnace and the waste heat boiler can also be designed with special pipe walls with an even and smooth surface, so that accretions can be removed more easily with the help of the special Oschatz hammer cleaning system.

Another specialty of the Oschatz solutions for bath lance ovens is the evaporator design of the furnace roof cooling system.

This evaporator system, which is integrated in the boiler’s water/steam circuit , operates in the temperature range above the dew point and thus achieves a longer service life compared to conventional water cooling. In addition, the furnace roof can be replaced more easily and more quickly.

A pressure relief flap is located at the highest point of the vertical boiler, which limits process gas pressure fluctuations to a maximum value.

Waste Heat Cooling Systems – Furnace- and hood cooling systems for AUSMELT process

In the in-bath lance smelting technology, the brick-lined furnaces and hoods are typically surrounded by a water cooled jacket. Oschatz supplies a furnace and hood cooling system that is integrated into the evaporation system of the waste heat boiler.

These components are designed as gas-tight welded membrane walls. In order to protect the membrane walls from excessive heat loads, they are fitted with studs onto which a thin castable layer is attached. The lifetime of these components complies with the usual average lifetime of boiler pressure components.

In contrast, the brickwork of an originally water cooled construction needs to be relined at least once a year. The engineering concept developed by Oschatz leads to significantly less downtime, resulting in significantly increased production capacity and therefore assures that the whole plant is more economical.

Waste Gas Cooling Systems downstream of Fluidized Bed Roasting – For Zinc, Pyrite (Gold) and Copper

Roasting of zinc, pyrite and copper concentrates is carried out in fluidized beds. For this process, Oschatz supplies waste heat boilers including the coils for the fluidized beds. Hot roaster gases (800 to 1,000 °C) with a high dust load (up to 400 g/Nm³) are cooled in Oschatz boilers to approximately 350 °C.

In general, these boilers are equipped with cooled tube walls, evaporation bulkheads and convection super-heater bulkheads. Because of the composition of the process gas and the corresponding dust characteristics, a steady operation of the waste heat boilers can only be achieved by means of highly efficient heating surface cleaning systems which do not require the whole plant to be shut down for maintenance.

The Oschatz hammering system has been proven to be a very successful means to clean boiler heating surfaces.