How To Choose Lime Kiln For Your Project

Lime kiln is an industrial device that is mainly used in lime calcination. Quick lime is widely used in cement, chemical, metallurgy, and environmental protection industries. When it comes to the types of lime kilns, we all know that there are many types of lime kiln to choose from in the lime calcination plant. Common ones include lime rotary kiln, vertical lime kiln, annular shaft kiln, etc. These lime kilns each have their own advantages. How do you choose the most suitable lime kiln based on the application field?

Rotary kilns and annular shaft kiln each have their unique characteristics and applications. Rotary kilns are suitable for large-scale continuous lime production, with high production efficiency and adaptability, but high investment and maintenance costs. Annular shaft kilns are suitable for small and medium-sized production that requires precise temperature control, and have the advantages of energy conservation, environmental protection, and high product quality. However, their production capacity is relatively low and their structure is complex.

According to the report data of the Lime Association, the energy consumption comparison of several lime kiln processes is as follows:

It is easy to see that, except for mechanized vertical kilns (not active lime kilns) and Melz kilns, the energy consumption of other kilns is higher than that of annular shaft kilns, and rotary kilns are only suitable for producing small particle lime with a size of 10-40mm. Therefore, the use of annular shaft kilns for lime production is the best after a comprehensive comparison with advanced vertical kilns such as annular shaft kilns, Melz kilns, and Fukas kilns.

Today we compare rotary lime kiln and annular shaft kiln from the view of structure, working principle, advantages and cost.

Selection guide of lime kiln

The selection of lime kiln projects should comprehensively consider factors such as the utilization of raw fuel resources, static investment of the project, product quality, and operating costs of the lime kiln. At the same time, it should also take into account its own raw fuel conditions and consider the requirements of local environmental protection departments for low-carbon economy and sustainable development.

It is understood that the lime kiln in industrialized countries mainly consist of new vertical lime kilns and rotary lime kilns. Domestically speaking, metallurgical enterprises are building new lime kilns, forming a situation where rotary kilns and new vertical kilns are on par.

Among the new vertical lime kilns, the most commonly used ones are still the annular shaft kiln and the Melz kiln. The technical advantages of the annular shaft kiln include high thermal efficiency, large particle size range of raw materials entering the kiln, small footprint, full negative pressure operation throughout the process, and safe and stable operation.

Structure features and working principle of lime kiln

A rotary lime kiln is driven by an electric motor to rotate the kiln body, causing materials to slowly move along the axial direction inside the kiln and complete physical and chemical reactions inside the kiln. The rotary kiln is usually divided into preheating zone, firing zone, and cooling zone, and the heating process of materials is controlled by different temperature zones.

Structural characteristics of rotary lime kiln

• Cylinder: The main body of a rotary kiln is a long cylindrical rotating container, usually made of steel plates and lined with refractory materials.
• Transmission device: including main reducer, auxiliary transmission device, electric motor, etc., used to drive the kiln body to rotate.
• Supporting device: The kiln body is supported by several supporting wheels, usually equipped with a stop wheel device to prevent axial movement of the kiln body.
• Sealing device: In order to prevent air leakage, sealing devices are usually installed at the kiln head and tail.

The materials inside the annular shaft kiln are heated in different sleeves in stages, and the materials are lowered inside the sleeves by gravity, completing preheating, calcination, and cooling during the process. The temperature and atmosphere of each section can be independently controlled, and the heating curve of the material can be precisely adjusted.

Structural characteristics of annular shaft kiln

• Sleeve shaped structure: The annular shaft kiln is composed of multiple sleeves, each of which is equipped with a heating device and a material conveying device.
• Segmented control: It can independently control the temperature and atmosphere of different segments.

Investment of lime kiln

According to the current domestic price level, the investment for a 500t/d automated annular shaft kiln is 50 million yuan, for a 600t/d Fukas kiln, it is about 45-50 million yuan, for a 600t/d Merz kiln, it is about 70 million yuan, and for a 1000t/d rotary lime kiln, it is about 120 million yuan. Therefore, the advantage of investing in an annular shaft kiln is obvious.

Operation cost of lime kiln

From the above table, it can be seen that, except for the Fukas kiln, the cost of producing active lime in the annular shaft kiln is the lowest. It should be noted that the above data is the product cost when using recycled gas from within the steel plant. For example, if a rotary kiln uses coal powder as fuel, the cost of lime per ton will increase by about 100 yuan. Therefore, the economic benefits of using annular shaft kilns to produce activated lime in steel mills will be more significant.

Quality of finished product

The quality of active lime produced by the annular shaft kiln is the best, and the specific comparison is as follows:

1. The finished product has high activity. Advanced lime kiln has an activity level of over 350mI, which can meet the requirements of steelmaking production. However, during rotary kiln production, small-sized limestone is prone to burning; Both the Melz and annular shaft kilns have co current combustion zones, which result in better quality than the Phocas kiln; At present, the production quality of domestic rotary kilns is generally good, with an average activity of nearly 400ml.
2. The finished product has a low sulfur content. According to the report data analysis of the Lime Association, the sulfur content of lime produced by rotary kilns, Fukas kilns, and annular shaft kilns is all below 0.02%. The sulfur content of the Maerz kiln is generally high, and its combustion mechanism causes low sulfur content in the exhaust gas. Therefore, according to the material balance, most of the sulfur content enters the lime, that is, sulfur is stored while storing heat, and the technical guarantee value is difficult to achieve less than 0.02%; The quality of lime produced by Maerz kiln is difficult to meet the requirements of modern steelmaking and smelting process;

Raw material and fuel options

1. From the perspective of raw material usage, annular shaft kilns and rotary kilns complement each other. In the process of limestone mining, qualified limestone blocks with particle sizes of 40-80mm account for about 50%, 20-40mm account for about 20%, 20-10mm account for about 20%, and those below 10mm account for about 10%.
   At present, mining resources are becoming increasingly scarce, and we must make reasonable combinations of lime kiln types in order to improve the comprehensive utilization rate of limestone resources and fully extend the life of mines. In this way, the procurement cost of limestone is reduced.
2. In terms of fuel usage, both annular shaft kilns and rotary kilns have their own advantages. The rotary lime kiln can directly use the low calorific value fuel produced by steelmaking – converter gas. However, rotary kilns must use high calorific value fuels such as coke oven gas, blended gas, or natural gas. The advantage of rotary kiln is that it can directly use coal powder as fuel, which has a wider adaptability to fuel.

In summary, considering the characteristics of an annular shaft kiln, such as simple control, easy maintenance, full negative pressure operation and good environment, especially the characteristic of using converter gas as fuel alone, we believe that annular shaft kiln is one of the most advanced lime kilns in current technology.