68
J. Wood et al.
Improvement 2: Increasing Oxygen Enrichment
Oxygen enrichment has long been employed in smelting process applications to
reduce fuel consumption, offgas generation rates and to increase productivity. In
oxidising processes such as copper smelting, energy liberation from the feed materials, combined with Ausmelt lance operation with high levels of oxygen enrichment,
means that little, if any auxiliary fuel introduction is required to regulate the bath
temperature. In reducing process applications such as zinc residue fuming, for which
there is no energy provided by the feed, fuel introduction via the Ausmelt lance is
used to supplement the process heat balance. Fuel combustion at the lance tip ensures
higher energy efficiency than in other bath smelting processes and also allows for
independent control of the bath temperature and oxygen potential, which is critical
in achieving low concentrations of Zn and Pb in the final slag. This method of fuel
introduction does, however, impose limitations around the maximum level of oxygen
enrichment able to be sustained without impacting lance integrity. Use of oxygen
enrichment for the Ausmelt process in fuming applications has typically been limited to approximately 45 vol. % due to elevated combustion/flame temperature at the
lance tip and high operating temperatures required in these processes [7].
A key improvement enabling operation with increased enrichment in the Ausmelt
fuming process has been the development and commercial-scale implementation of
a patented fluid-cooled lance design. By decoupling the lance cooling duty from the
energy generation duty, a step change in oxygen enrichment can be achieved.
Improvement 3: Reducing Feed Moisture
Zinc leach residues are quite challenging materials to dewater to low moisture levels
by thickening and filtration only, meaning that residue cakes are commonly characterised by moisture levels as high as 35 wt% and only rarely, less than 20 wt%. Due
to their fine particle size, these residues often result in significant dust generation
when dried to less than 20% moisture. Outotec has considerable experience in the
injection of feed materials via the Ausmelt lance, with a good example of where
this has been applied being the injection of granulated Ni-PGM matte at the two (2)
Anglo Platinum TSL converting furnaces in South Africa [7]. Whilst the introduction of dry feeds via the Ausmelt lance necessitates additional equipment for drying
and injection, for the processing of high-moisture content feeds such as zinc leach
residues, the benefits are substantial.
Table 2 on the following page illustrates the considerable benefits achievable
by tailoring the process configuration and operating conditions for processing a
particular feed input (composition and throughput).
J. Wood et al.
Improvement 2: Increasing Oxygen Enrichment
Oxygen enrichment has long been employed in smelting process applications to
reduce fuel consumption, offgas generation rates and to increase productivity. In
oxidising processes such as copper smelting, energy liberation from the feed materials, combined with Ausmelt lance operation with high levels of oxygen enrichment,
means that little, if any auxiliary fuel introduction is required to regulate the bath
temperature. In reducing process applications such as zinc residue fuming, for which
there is no energy provided by the feed, fuel introduction via the Ausmelt lance is
used to supplement the process heat balance. Fuel combustion at the lance tip ensures
higher energy efficiency than in other bath smelting processes and also allows for
independent control of the bath temperature and oxygen potential, which is critical
in achieving low concentrations of Zn and Pb in the final slag. This method of fuel
introduction does, however, impose limitations around the maximum level of oxygen
enrichment able to be sustained without impacting lance integrity. Use of oxygen
enrichment for the Ausmelt process in fuming applications has typically been limited to approximately 45 vol. % due to elevated combustion/flame temperature at the
lance tip and high operating temperatures required in these processes [7].
A key improvement enabling operation with increased enrichment in the Ausmelt
fuming process has been the development and commercial-scale implementation of
a patented fluid-cooled lance design. By decoupling the lance cooling duty from the
energy generation duty, a step change in oxygen enrichment can be achieved.
Improvement 3: Reducing Feed Moisture
Zinc leach residues are quite challenging materials to dewater to low moisture levels
by thickening and filtration only, meaning that residue cakes are commonly characterised by moisture levels as high as 35 wt% and only rarely, less than 20 wt%. Due
to their fine particle size, these residues often result in significant dust generation
when dried to less than 20% moisture. Outotec has considerable experience in the
injection of feed materials via the Ausmelt lance, with a good example of where
this has been applied being the injection of granulated Ni-PGM matte at the two (2)
Anglo Platinum TSL converting furnaces in South Africa [7]. Whilst the introduction of dry feeds via the Ausmelt lance necessitates additional equipment for drying
and injection, for the processing of high-moisture content feeds such as zinc leach
residues, the benefits are substantial.
Table 2 on the following page illustrates the considerable benefits achievable
by tailoring the process configuration and operating conditions for processing a
particular feed input (composition and throughput).