magnesium metal rotary kiln

Magnesium Metal Rotary Kiln

Our magnesium metal rotary kiln shells range in size from Ø1.6 × 32m to Ø4.0 × 80m. Available with matching vertical preheaters (YRQ04-YRQ20) and vertical coolers (LSF36-LSF112), they can meet production needs of varying capacity scales.

Capacity: 2-20t/h

Specifications: Ø1.6 × 32m - Ø4.0 × 80m

Applicable Materials: Dolomite calcination for magnesium metal production lines

Magnesium Metal Rotary Kiln Product Introduction

The magnesium metal rotary kiln is a specialized rotary kiln developed specifically for the calcining characteristics of dolomite and the process requirements of the Pidgeon process for magnesium smelting. It is a key piece of equipment in the dolomite calcining system. The calcined dolomite produced by this kiln features stable and uniform quality, high activity, and low loss on ignition, fully meeting the process requirements of the Pidgeon process. This results in high magnesium extraction and silicon utilization rates, reducing magnesium production costs and making it an ideal piece of equipment for calcining dolomite in the magnesium industry.

Highlights

1. The rotary kiln consists of a cylinder, support assembly, transmission mechanism, and seals for the kiln head and tail.

2. The kiln's aspect ratio is reduced from the traditional 20-25 to 14-15, minimizing heat loss from the kiln surface.

3. The drive system utilizes a variable-frequency motor equipped with an inverter, offering advantages such as a wide speed range and heavy-load starting.

4. Heat-resistant steel flake seals at the kiln head and tail replace the original seals, reducing air leakage and ensuring durability.

Working Principle

 Dolomite is fed into the kiln through a chute at the kiln tail (high end). Due to the inclination and slow rotation of the kiln drum, the dolomite rolls circumferentially while moving axially from the kiln tail (high end) toward the kiln head (low end). Fuel is injected into the kiln through a burner at the kiln head for combustion. Heat is transferred to the dolomite through radiation, convection, and conduction. Within the kiln, the dolomite undergoes preheating, decomposition, and sintering, ultimately becoming calcined white before being discharged from the kiln head.

1. Raw Materials

1) Dolomite

The particle size requirement for dolomite is 10-40mm. The portion exceeding the upper limit of 40mm and the lower limit of 10mm must not exceed 5%.

Chemical Composition of Dolomite:

MgO: 19-21%; CaO: 30-33%; SiO₂ <0.5%; Fe₂O₃ <0.5%; Al₂O₃ <0.5%; Na₂O <0.005%; K₂O <0.005%; Mn <0.0005%; CaO/MgO = 1.394 (mass ratio), CaO/MgO = 1.0 (molar ratio).

2) Ferrosilicon

Ferrosilicon should be 75# ferrosilicon containing ≥75% Si, i.e., 49.92% Si and 50.08% FeSi₂.

3) Fluorite Powder

Fluorite powder contains >90% CaF₂ and has a particle size of 200 mesh.

2. Production Process

★. The magnesium smelting process utilizes the mature, reliable, and rational Pijiang process. Qualified dolomite is calcined in a rotary kiln. The calcined dolomite, fluorite, and ferrosilicon are then mixed in a specific ratio, ball-milled, and pressed into pellets. The pellets are then placed in a reduction tank and subjected to high-temperature thermal reduction under vacuum conditions to produce crystalline magnesium. The crystalline magnesium is then remelted and refined to produce magnesium metal. The process includes raw material storage, dolomite calcination, grinding and pelletizing, reduction, and refining.

Raw Material Storage

★. Dolomite is crushed to the required particle size at the mine and stored in the plant's dolomite stockpile. Ferrosilicon and fluorite are stored directly in the plant's warehouse. The storage capacity is based on two weeks' worth of production.

Dolomite Calcination Workshop

★. An energy-saving and environmentally friendly rotary kiln with a vertical preheater and cooler is used. Imported dolomite that meets the required particle size and quality is unloaded into the material yard, where it is stacked and reclaimed by a loader. After screening by a vibrating screen, the 10-40mm dolomite is transported by belt to the top silo of the rotary kiln's vertical preheater. It then enters the preheater through a material pipe, where it exchanges heat with the high-temperature flue gas flowing from the rotary kiln, preheating the material to over 800°C. After falling into a transfer chute, it enters the rotary kiln and is calcined at 1250°C to produce activated calcined white. It is then unloaded into a cooler, where it exchanges heat with cold air blown in by a fan, cooling the activated calcined white to below 100°C while the air is preheated to over 600°C. The cooled activated calcined white is discharged from the cooler and transported to the pelletizing workshop via a slab conveyor.

The main reactions are as follows:

★. CaCO₃·MgCO₃ = CaO·MgO + 2CO₂

The high-temperature flue gas generated by the rotary kiln undergoes heat exchange with the dolomite in the preheater, reducing its temperature to below 220°C. It then enters a bag filter, where dust is removed and discharged into the atmosphere via a high-temperature fan. The dust concentration in the exhaust gas is less than 30 mg/m³. The entire production line utilizes a technologically advanced and reliable PLC control system, with centralized operation and management in the main control room.

Ball Making Workshop

★. The calcined dolomite is fed by an elevator to silo #1 for storage. Ferrosilicon is crushed to less than 20 mm in a jaw crusher and then hoisted by an elevator to silo #2 for storage. Fluorite powder is hoisted by a single bucket to silo #3. The three raw materials stored in the silo are continuously batched and fed into the ball mill under computer control for mixing and grinding. The particle size requirement is <100 mesh. The mixed powder then passes through the elevator, silo, and buried scraper conveyor before entering the briquetting press to form pellets. The batching system utilizes an intelligent control system, and the entire process is fully automated with computer monitoring. The ball mill is driven by a 10kV high-voltage motor, reducing power loss compared to the previous 380V low-voltage distribution system. The pelletizing workshop is equipped with three dust removal systems: the C1# dust removal system for the ferrosilicon crushing area, the C2# dust removal system for the batching grinding area, and the C3# dust removal system for the pelletizing area. This comprehensive dust removal system significantly improves the operating environment of the pelletizing workshop compared to traditional workshops, enhancing the working environment for workers.

Reduction and Refining Workshop

★ The reduction furnace utilizes high-temperature air rapid reversing regenerative combustion technology. The regenerative reduction furnace is continuously heated using coal gas. Pellets are fed into the reduction tank within the reduction furnace via a feeder. Magnesium vapor generated in the reduction tank is condensed into crystalline magnesium (crude magnesium) in an end condenser. The crude magnesium is then removed and sent to the refining and alloying production lines.

The magnesium rotary kiln primarily consists of a transmission system, supporting rollers, supporting and stopping rollers, a kiln drum, a kiln head, a kiln tail, and sealing devices. Its key structural features are:

1. Mechanical or hydraulic stop rollers are selected depending on the kiln type; both offer high precision, reliability, stability, and ease of adjustment.

2. The kiln has two to four pivot points (most have three), making it easy to ensure the contact surface between the supporting rollers and the kiln belt is parallel to the drum axis during installation.

3. The support system utilizes rolling bearings, significantly simplifying the supporting roller structure, reducing wasted power loss during kiln operation and facilitating maintenance and inspection.

4. Heat-resistant steel flake seals replace conventional labyrinth seals at the kiln head and tail, resulting in superior sealing performance, increased reliability, a longer service life, and easier replacement.

5. To facilitate installation and commissioning, and to ensure kiln operation during main drive system maintenance or other abnormal conditions, and to prevent bending and deformation of the kiln drum during cooling, a slow kiln rotation mechanism is provided.

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