Indirect process zinc oxide, also known as French process zinc oxide, was popularized by Frenchman LeClaire in 1844. Boasting high purity and high activity, it has become the mainstream zinc oxide production process worldwide. By weight, most zinc oxide globally is manufactured via this method. Adopting electrolytic zinc ingots as raw materials, the process consists of core procedures including melting, vaporization, oxidation, cooling, and collection, yielding finished zinc oxide products with an average particle size ranging from 0.1 to 10 micrometers.
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Raw Material and Heating Section Equipment
1.1 Raw Material Related Equipment
Refined Zinc Ingot Silo/Storage Area: Used for storing qualified electrolytic refined zinc ingots, equipped with moisture-proof and dust-proof devices. It prevents zinc ingots from moisture oxidation and impurity contamination, ensures raw material purity, and supplies clean feedstock for the subsequent melting process.
Lump Coal Storage Silo: For storing lump coal used for heat supply, matched with feeding devices to provide stable fuel for coal-fired furnaces and serve as the heat source for vaporization furnaces.
1.2 Heating System Equipment
Coal-fired Heating Furnace: The core heat supply equipment is fueled by lump coal. It generates high-temperature heat to supply heat to the vaporization furnace, and the resulting flue gas can be recycled for secondary utilization. Equipped with a slag discharge device to regularly remove combustion slag and maintain efficient furnace combustion.
Air Blower (Air Supply Unit): Delivers combustion air to the coal-fired furnace to ensure full combustion of lump coal. It can adjust air volume to precisely control combustion intensity and match the temperature requirement of the vaporization furnace.
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Melting and Vaporization Section Equipment
2.1 Melting Furnace
Melting Furnace Body: Adopts a high-alloy refractory high-temperature resistant furnace structure with thermal insulation layers. Its core function is to heat refined zinc ingots to 600～700℃ to melt them into liquid zinc, providing liquid feedstock for the subsequent vaporization process. A reserved liquid zinc outlet enables steady delivery of molten zinc to the vaporization furnace.
Furnace Sealing Device: Made of high-temperature resistant sealing gaskets to seal the furnace door and feeding port. It reduces heat loss, blocks external impurities from entering the furnace to contaminate liquid zinc, and avoids premature oxidation of molten zinc.
Flue Gas Duct: Connects the melting furnace to the chimney to discharge flue gas centrally. Part of the waste gas can be recycled to improve thermal energy utilization efficiency.
2.2 Vaporization Furnace
Vaporization Furnace Body (Equipped with High-Temperature Resistant Crucible): The core gasification equipment with a refractory high-temperature resistant furnace structure, internally fitted with graphite crucibles or high-purity alumina crucibles resistant to temperatures above 1200℃. It heats liquid zinc to over 1000℃ for vaporization into zinc vapor. The crucible material features excellent corrosion resistance and thermal shock resistance to prevent erosion and damage by high-temperature liquid zinc.
Zinc Vapor Duct: Adopts high-temperature resistant ceramic or quartz pipelines to connect the vaporization furnace and oxidation furnace, delivering zinc vapor stably. With smooth inner walls and superior tightness, it prevents zinc vapor leakage and premature condensation.
Flue Gas Recovery Device: Recycles flue gas from the vaporization furnace back to the melting furnace as a secondary heat source, realizing thermal energy recycling, cutting energy consumption, and reducing exhaust emissions.
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Oxidation Reaction Section Equipment
3.1 Oxidation Furnace
Oxidation Furnace Body: Fabricated from high-alloy stainless steel lined with refractory bricks, with a temperature resistance of over 1200℃. It provides a closed reaction space for zinc vapor to react with oxygen. Zinc vapor fully contacts with ambient oxygen inside the furnace to undergo an oxidation reaction and generate zinc oxide powder, accompanied by bright luminescence and a temperature drop during the reaction.
Air Supply Blower: Delivers clean air to the oxidation furnace to provide sufficient oxygen for the oxidation reaction. Adjustable air volume controls reaction intensity and zinc oxide particle formation efficiency, preventing insufficient or excessive oxidation.
In-Furnace Zinc Oxide Collection Device: A reserved collecting outlet at the bottom of the oxidation furnace collects freshly generated zinc oxide powder. After subsequent sieving, coarse powder is sold as downgraded products, while fine powder is combined with baghouse-collected zinc oxide for integrated processing.
By-Product Refined Zinc Recovery Device: Supporting recovery pipelines collect incompletely oxidized refined zinc by-products during the reaction, which are refluxed to the melting furnace for reuse, lowering raw material waste and improving utilization rate.
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Cooling and Conveying Section Equipment
4.1 Herringbone Cooling Conveying Pipeline
Herringbone Pipeline Body: A high-temperature resistant stainless steel pipeline designed in a herringbone structure, connecting the oxidation furnace and surface cooling unit. It conveys high-temperature zinc oxide powder while achieving preliminary cooling during transportation. The inclined structural design avoids pipeline blockage and ensures smooth powder flow.
Pipeline Thermal Insulation & Auxiliary Cooling Device: Cooling jackets can be installed on the outer wall, combined with natural air cooling to lower the temperature of zinc oxide powder inside the pipeline, reduce powder agglomeration, and relieve the load of subsequent cooling procedures.
4.2 Surface Cooling Unit
Surface Cooler / Cooling Jacket: Stainless steel cooling equipment adopting combined water cooling and air cooling to rapidly cool high-temperature zinc oxide powder below 100℃. It prevents powder agglomeration and secondary oxidation, separates partial coarse zinc oxide particles during cooling, and prepares materials for subsequent bag dust collection.
Cooling Medium Circulation System: For a water cooling configuration, supporting water pumps and cooling towers realize a recycled cooling water supply, maintaining stable cooling efficiency and avoiding water resource waste.
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Dust Collection and Finished Product Processing Section Equipment
5.1 Pulse Baghouse Dust Collector
Pulse Baghouse Precipitator: The core powder collection equipment with a filtering area matched to production capacity. High-temperature resistant needled felt filter bags (temperature resistance ≥120℃) are adopted with a dust removal efficiency of over 99.9%. It captures fine, cooled zinc oxide particles and filters impurities in the airflow to guarantee finished product purity, producing zinc oxide with an average particle size of 0.1 to 10 micrometers.
Pulse Ash Cleaning Device: Equipped with pulse valves and air storage tanks to regularly clean zinc oxide powder adhered to filter bags, preventing bag clogging, maintaining stable dust collection efficiency, and extending filter bag service life.
Hopper and Discharging Unit: A stainless steel hopper at the bottom matched with vibratory unloaders steadily conveys collected zinc oxide powder to weighing and packaging equipment, avoiding caking and discharge blockage.
5.2 Sieving Equipment for In-Furnace Zinc Oxide
Vibrating Sieve / Classifying Sieve: Stainless steel sieve machines fitted with mesh screens of different meshes. It classifies zinc oxide powder collected from the oxidation furnace to separate fine powder and coarse powder. Fine powder is merged into the main finished product stream, while coarse powder is sold as downgraded goods to realize graded product utilization and maximize economic benefits.
Screen Replacement Assembly: Facilitates quick replacement of mesh screens with different meshes, enabling adjustment of classification standards per market demand and adapting to customized particle size product requirements.
5.3 Weighing and Packaging Equipment
Automatic Weighing Machine: High-precision electronic weighing equipment for accurate metering of finished zinc oxide to comply with packaging specification standards. Matched with data recording devices for production statistics and quality traceability.
Packaging Machine: Semi-automatic or fully automatic packaging equipment fills measured zinc oxide powder into packaging bags or bulk bags, equipped with sealing units for hermetic packaging. It prevents zinc oxide powder from moisture and contamination, ensuring stable product quality during storage and transportation.
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Environmental Protection and Auxiliary Section Equipment
6.1 Waste Gas Treatment Equipment
Chimney: Connected to flue gas ducts of melting furnaces and vaporization furnaces for centralized exhaust emission. Matched with flue gas purification devices such as spray scrubber towers to remove harmful substances and ensure emissions meet environmental protection standards.
Exhaust Gas Monitoring Equipment: Online monitors installed at chimney outlets, real-time detection of exhaust emission concentrations, ensuring compliant production and eliminating environmental compliance risks.
6.2 General Auxiliary Equipment
Power Distribution & Control System: Consists of power distribution cabinets and temperature control cabinets, providing a stable power supply for full-process equipment and realizing precise regulation of furnace temperature, air volume, and cooling efficiency to guarantee stable production operation.
Maintenance & Overhaul Tools: Including high-temperature resistant tools, leak detectors, spare crucibles, and filter bags for daily equipment maintenance and emergency fault handling. It ensures continuous production and minimizes shutdown losses.