Lime Kiln

What is a lime rotary kiln?

A lime kiln is used to produce quicklime (calcium oxide) by the calcination of limestone which is calcium carbonate. Lime rotary kiln is the prevalent type, accounting for about 90 percent of all lime plants.

A lime rotary kiln is a long cylindrical, slightly inclined, refractory-lined furnace, through which the limestone and hot combustion gases pass counter-currently.

The lime rotary kiln is always the heart for active lime in lime plants. Ftmmachinery is a reliable lime kiln manufacturer that specializes in designing and constructing automatic, environmentally friendly lime rotary kilns.

Why choose Ftmmachinery lime kilns?

• Low energy consumption: The lime kilns are equipped with a vertical preheater and waste heat recovery system, effectively utilizing the high-temperature flue gas generated during the calcination process. This minimizes fuel consumption and reduces operating costs.
• Good sealing performance: The lime rotary kiln is designed with an advanced structure and reliable combined scale-like seals on both ends, ensuring that the air leakage coefficient remains below 10 percent.
• New technology: The main drive system adopts a new type of AC frequency conversion speed regulation technology. Compared with traditional electromagnetic speed regulation and DC speed regulation, it is more energy-saving and environmentally protection and has a wide range of speed regulation, high efficiency, high-speed regulation precision, and stable operation.
• Process control and automation: Lime rotary kilns provide precise control over temperature, fuel efficiency, key process parameters, and emissions.
• Safety features: The lime kilns are equipped with temperature monitoring systems, gas detection mechanisms, emergency shut-off systems, and other safety measures to protect personnel and equipment.
• High-quality lime products: Ftmmachinery's lime kilns ensure the even and thorough calcination of limestone through advanced burners, optimized kiln design and parameter operation, as well as detection and control systems. This makes them particularly suitable for manufacturing highly active lime used in steelmaking.

How does a lime rotary kiln work?

Lime is the high-temperature product of the calcination of limestone. It is manufactured in limestone calcination kiln by the following reaction:

CaCO₃ + heat → CO₂ + CaO (high calcium lime)

Here's a step-by-step process of how limestone is converted to lime in a kiln:

Step 1. Raw material preparation: Limestone is crushed, screened, and ground to the required particle size.

Step 2. Charging and preheating: Feed the prepared limestone evenly into the preheater. Inside the preheater, imestone is heated to about 900°C by 1150°C kiln flue gas, reaching approximately 30% decomposition.

Step 3. Calcination: The preheated limestone moves along the kiln's axis from the tail to the head, rolling along the circumference due to the kiln's tilt and slow rotation. Fuel is injected through the burner at the kiln head, undergoing combustion. And the heat is transferred to the limestone through radiation, convection, and conduction. Limestone is calcined into quicklime while moving and discharged from the kiln head.

Step 4. Cooling: The quicklime enters a lime cooler where it is cooled to below 100°C using cold air. Subsequently, it is discharged from the cooler.

Step 5. Transfer to the finished product warehouse: The cooled lime is sent to the lime finished product warehouse through the vibrating feeder, chain bucket conveyor, bucket elevator, and belt conveyor. Add screening process according to customer requirements.

Key parts of the rotary lime kiln

1. Kiln shell

The rotary kiln shell refers to the cylindrical outer structure of a rotary kiln. It is typically made of steel plates that are joined together either through welding or riveting.

The kiln shell is a vital component of the rotary kiln, and its deformation directly affects the operation rate of the rotary kiln.

Based on extensive practical experience, Ftmmachinery produces kiln shells with enhanced cross-sectional rigidity and improved longitudinal flexibility.

2. Supporting roller

The supporting roller bears the weight of the entire rotating part and provides directional support to ensure smooth rotation of the kiln shell and kiln tyres.

Ftmmachinery's supporting rollers are made of high-quality materials like ZG55 and ZG42CrMo, offering significant load-bearing capacity, excellent impact resistance, high hardness, and exceptional wear resistance.

3. Kiln tyre

The kiln tyre, also known as the kiln ring tyre or riding ring, is a circular steel ring that is placed around the circumference of a rotary kiln and is secured to the kiln shell.

As a crucial part of the rotary kiln, the kiln tyre must possess sufficient rigidity, strength and durability.

Ftmmachinery manufactures rotary kiln tyres from high-quality cast steel materials, employing strict control measures at each stage to ensure that the kiln tyres exhibit the necessary rigidity, strength, and durability.

4. Girth gear

The girth gear is a large gear ring that is mounted on the outer surface of the kiln shell. Its primary function is to transmit torque from the kiln drive system to the kiln shell, facilitating rotation.

Ftmmachinery's girth gears undergo tempering, normalization, and precise machining to meet national standards and are capable of meeting the requirements for lime rotary kilns.

5. Refractory lining

The interior of the kiln shell is lined with refractory bricks or castable refractories. These linings can withstand the high temperatures in the kiln and offer insulation to reduce heat loss. They also protect the kiln shell from the corrosive action of lime and other materials.

Ftmmachinery provides a variety of refractory materials to cater to user needs, including magnesia refractory materials, high alumina refractory materials, clay refractory materials, thermal insulation refractory materials, chromium-containing refractory materials, etc.

Choose the right refractory lining

Frequently asked questions about lime kilns

Project case: 500 t/d active lime production line in Thailand

In June 2019, a customer from Thailand inquired about the lime production line. According to his output and final product demand, we recommended this φ3.8m×58m rotary kiln to him. Specific information is as follows:

Advantages of active lime production line

• Consistent product quality: The active lime production line ensures uniform and consistent product quality by precisely controlling parameters such as temperature, pressure, and residence time.
• Environmental friendliness: The active lime production line is equipped with a dust removal system to minimize air pollution, and a waste heat recovery system to reduce energy consumption and greenhouse gas emissions.
• Cost-effectiveness: Energy-saving measures reduce fuel consumption. Continuous operation reduces labor requirements and increases overall productivity. In addition, the scalability of the production line allows adjusting capacity to meet market demand, optimizing cost-effectiveness.

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