20
D. Gregurek et al.
sinter plant and blast furnace); however, over the last decades, the direct smelting
reduction processes (roast-reaction) have become more important and are nowadays
state of the art [1–5]. The main vessel for zinc production from Zn leaching residues
from hydrometallurgical production, EAF dust from steel production and various
non-ferrous slags, is the Waelz kiln.
Generally, the process parameters and technology are chosen according to the
input material, i.e., present impurities and required metallurgical work. The conditions range from oxidizing for sulfur removal (roasting) to reducing for smelting,
including evaporation of metals and metal compounds with alkalis and halogens—
sometimes both in one vessel. The process temperature is generally far higher than
the metal liquidus temperature which is for lead 327 °C and for zinc 419 °C. The
temperature is even high enough for evaporation of certain metals in the form of
metals, oxides, sulfides, and halides, namely around 1000 °C. However, these high
temperatures are required in order to:
(1) obtain a liquid and reactive slag that is easy to remove in processes dealing with
liquid metal and slag, and/or
(2) achieve the desired volatilization of certain input components (slag fuming,
Waelz process).
Additionally, slag chemistry is adjusted in a way to minimize metal overheating,
as well as enhance the process chemistry and desired reactions.
Consequently, the following challenges arise for the refractory [4, 5] as a result
of the:
– Chemistry of liquid slags: varying slag composition within the system FeO–SiO 2 –
CaO and/or choice of other slag systems and additives (soda slag) causes chemical
attack.
– Chemistry of input materials: volatile compounds including metals, halides,
alkalis, etc. infiltrate the refractories and react with the refractory components.
– Furnace atmosphere and temperature: repeatedly changing atmospheres (oxidizing/reductive), as well as exposure to hot gases lead to increased refractory damage.
Overheated liquid phases (metal and slag) with resulting very low viscosity cause
deep refractory infiltration and chemical attack.
– Mechanical forces/abrasion/erosion: the flow of gas and liquid phases also mechanically attacks the refractory lining. Either directly by impact or indirectly by continuously removing protective reaction products formed on the refractory surface.
In the case of zinc Waelz kilns dealing with mainly solid materials, moving solid
material in a rotating kiln creates different challenges for the refractory lining
compared to gas or liquid phases.
A general overview of wear phenomena in lead and zinc furnaces was discussed
and introduced in several papers in the past [6–11]. Particularly in the lead industry,
a lot of work was done regarding refractory corrosion testing in different pilot-scale
and industrial furnaces [10, 11].
D. Gregurek et al.
sinter plant and blast furnace); however, over the last decades, the direct smelting
reduction processes (roast-reaction) have become more important and are nowadays
state of the art [1–5]. The main vessel for zinc production from Zn leaching residues
from hydrometallurgical production, EAF dust from steel production and various
non-ferrous slags, is the Waelz kiln.
Generally, the process parameters and technology are chosen according to the
input material, i.e., present impurities and required metallurgical work. The conditions range from oxidizing for sulfur removal (roasting) to reducing for smelting,
including evaporation of metals and metal compounds with alkalis and halogens—
sometimes both in one vessel. The process temperature is generally far higher than
the metal liquidus temperature which is for lead 327 °C and for zinc 419 °C. The
temperature is even high enough for evaporation of certain metals in the form of
metals, oxides, sulfides, and halides, namely around 1000 °C. However, these high
temperatures are required in order to:
(1) obtain a liquid and reactive slag that is easy to remove in processes dealing with
liquid metal and slag, and/or
(2) achieve the desired volatilization of certain input components (slag fuming,
Waelz process).
Additionally, slag chemistry is adjusted in a way to minimize metal overheating,
as well as enhance the process chemistry and desired reactions.
Consequently, the following challenges arise for the refractory [4, 5] as a result
of the:
– Chemistry of liquid slags: varying slag composition within the system FeO–SiO 2 –
CaO and/or choice of other slag systems and additives (soda slag) causes chemical
attack.
– Chemistry of input materials: volatile compounds including metals, halides,
alkalis, etc. infiltrate the refractories and react with the refractory components.
– Furnace atmosphere and temperature: repeatedly changing atmospheres (oxidizing/reductive), as well as exposure to hot gases lead to increased refractory damage.
Overheated liquid phases (metal and slag) with resulting very low viscosity cause
deep refractory infiltration and chemical attack.
– Mechanical forces/abrasion/erosion: the flow of gas and liquid phases also mechanically attacks the refractory lining. Either directly by impact or indirectly by continuously removing protective reaction products formed on the refractory surface.
In the case of zinc Waelz kilns dealing with mainly solid materials, moving solid
material in a rotating kiln creates different challenges for the refractory lining
compared to gas or liquid phases.
A general overview of wear phenomena in lead and zinc furnaces was discussed
and introduced in several papers in the past [6–11]. Particularly in the lead industry,
a lot of work was done regarding refractory corrosion testing in different pilot-scale
and industrial furnaces [10, 11].