Production of SHG Zinc From 100% Recycled Materials
81
Waelz Kiln Feed Preparation and Control
The critical feed criteria for good Waelz kiln operational control and performance
include: (a) blending various sources of EAF dust, (b) conditioning EAF dust with
water for lime hydration, (c) agglomeration of EAF dust or EAF dust/carbon blends,
(d) accurate proportioning with carbon reductant, and (e) consistent control of kiln
feed rate.
AZR’s Barnwell facility contains several important features that optimize feed
proportioning and control:
• PD & Vacuum Railcar EAF dust unloading to mass-flow silos on load cells
• Independent control of EAF dust silo feed rates for consistent kiln feed zinc content
and V4 ratio
• Coal/coke proportioning using a weigh-feeder and PID control to a target %C in
kiln feed
• Pre-conditioning of kiln feed with water in a twin-screw blender
• Nuclear and mechanical scales on the pelletizer feed belt downstream of the blender
• This is the primary point of control for kiln feed rate and coke proportioning
• Agglomeration on a pan pelletizer with multiple independently controlled sprays
• Return of dust catcher recycle material to the kiln feed upstream of the blender.
The results of these feed system improvements include:
• Zinc productivity consistently ~2.2 tons/operating hour or 459 MT Zn/yr/m
3
charge bed volume
• Waelz oxide (WOX) quality at < 2% Fe and > 65% Zn
• Coal/coke consumption ~1.0 tons coke/ton Zn in WOX
• Improved length of campaigns between cleanouts; fewer kiln accretions.
At the Rockwood plant, where feed pelletizing is not available, agglomeration of
dust catcher recycle material using a pug mill has resulted in improved WOX quality
and fewer feed and temperature excursions.
Oxygen-Enrichment and Productivity
AZR has applied oxygen-enrichment of the air-blast stream to promote iron oxidation
and combustion of residual carbon in the charge bed. The system is engineered for
safe, controllable application of the oxygen to preheat the kiln draft air, accelerate
upstream zinc and iron reduction reactions, and increase kiln productivity all without
causing charge melting, entrainment of bed particles, or overheating of the off-gas
system (Fig. 5).
The current oxygen-enrichment configuration is improved over the previous generation (early 2000 s) in that (a) enrichment is limited, (b) the air-blast/oxygen mixture
81
Waelz Kiln Feed Preparation and Control
The critical feed criteria for good Waelz kiln operational control and performance
include: (a) blending various sources of EAF dust, (b) conditioning EAF dust with
water for lime hydration, (c) agglomeration of EAF dust or EAF dust/carbon blends,
(d) accurate proportioning with carbon reductant, and (e) consistent control of kiln
feed rate.
AZR’s Barnwell facility contains several important features that optimize feed
proportioning and control:
• PD & Vacuum Railcar EAF dust unloading to mass-flow silos on load cells
• Independent control of EAF dust silo feed rates for consistent kiln feed zinc content
and V4 ratio
• Coal/coke proportioning using a weigh-feeder and PID control to a target %C in
kiln feed
• Pre-conditioning of kiln feed with water in a twin-screw blender
• Nuclear and mechanical scales on the pelletizer feed belt downstream of the blender
• This is the primary point of control for kiln feed rate and coke proportioning
• Agglomeration on a pan pelletizer with multiple independently controlled sprays
• Return of dust catcher recycle material to the kiln feed upstream of the blender.
The results of these feed system improvements include:
• Zinc productivity consistently ~2.2 tons/operating hour or 459 MT Zn/yr/m
3
charge bed volume
• Waelz oxide (WOX) quality at < 2% Fe and > 65% Zn
• Coal/coke consumption ~1.0 tons coke/ton Zn in WOX
• Improved length of campaigns between cleanouts; fewer kiln accretions.
At the Rockwood plant, where feed pelletizing is not available, agglomeration of
dust catcher recycle material using a pug mill has resulted in improved WOX quality
and fewer feed and temperature excursions.
Oxygen-Enrichment and Productivity
AZR has applied oxygen-enrichment of the air-blast stream to promote iron oxidation
and combustion of residual carbon in the charge bed. The system is engineered for
safe, controllable application of the oxygen to preheat the kiln draft air, accelerate
upstream zinc and iron reduction reactions, and increase kiln productivity all without
causing charge melting, entrainment of bed particles, or overheating of the off-gas
system (Fig. 5).
The current oxygen-enrichment configuration is improved over the previous generation (early 2000 s) in that (a) enrichment is limited, (b) the air-blast/oxygen mixture