Lime Kiln

Introduction to the Lime Kiln

Lime kiln is a kind of construction or equipment that is used for producing lime. Lime kiln is mainly composed of one or more lime furnaces. Limestone will be decomposed into carbon dioxide and Calcium oxide through burning, and the Calcium oxide is called quick lime. Quick lime is a kind of important building material that is widely used in construction, agriculture, industry and other fields.

High temperature and corrosive gases can cause serious damage to the inner wall of lime kiln, Therefore, refractory materials are widely used in the lime kiln construction and maintenance to extend service life.

AGRM Refractory is one of the most professional refractory material production enterprises in China, and we are a comprehensive solution provider for high-temperature kilns that integrating production, trade, and research. We provide one-stop service from design, product manufacturing, furnace construction and related products provision.

rotary lime kiln
rotary lime kiln

Types of Lime Kilns

Lime kilns are primarily categorized based on the raw materials and fuel types, with examples including gas-fired lime rotary kilns, coal powder-fired lime rotary kilns, and others using various fuels. The nomenclature of lime rotary kilns often reflects the specific fuel used, such as diesel-fired lime rotary kilns. Additionally, lime kilns are classified by capacity, with designations like 100-ton lime kilns, 150-ton lime kilns, 300-ton lime kilns, 400-ton lime kilns, 600-ton lime kilns, 800-ton lime kilns, 1200-ton lime kilns, and so forth.

Another classification criterion is based on the material transport method, leading to distinctions like car kilns, roller kilns, and pusher plate kilns. A more general classification considers the physical state of the calcined product and the production method used.

The kiln types of lime kilns are widely used in the construction materials industry. Many of them have a history of being used in the cement industry, where they were originally designed for the calcination of clinker in cement kilns. In recent years, China has introduced and developed various advanced kiln types suitable for lime production by importing foreign technologies. These advancements have expanded the range of options available for lime production in the country.

AGRM Refractory is one of the most professional refractory material production enterprises in China, our refractory products are widely used in construction of different types of lime kilns. There are several different kinds of lime kilns classified by structure, rotary kiln, vertical kiln, double chamber vertical kiln, sleeve kiln, and mixing kiln. And you should select the appropriate refractory material to suit the different kinds of lime kilns to ensure normal operation.

Rotary Kiln

Rotary kiln is a large, cylindrical, and inclined industrial furnace-like structure that is used for various thermal processes. Rotary kilns are commonly used in the production of cement, lime, alumina, and other materials. The main components of a rotary kiln include the kiln shell, support rollers, thrust rollers, and drive system. Refractory materials play an important role in the operation of rotary kilns. The kiln shell is lined with refractory materials to protect it from the high temperatures,  chemical reactions, and mechanical stresses encountered during the thermal process. Therefore, It is essential to select the suitable refractory materials to suit the specific conditions and requirements of rotary kilns. 

The domestically developed series of lime rotary kilns with vertical preheaters and vertical coolers have been widely promoted in China. The designed production capacity ranges from 250 tons per day to 1200 tons per day, catering to the diverse needs of various enterprises. Rotary kilns can utilize commonly used domestic fuels such as coal powder, calcium carbide furnace gas, coke oven gas, natural gas, mixed gases, and various combinations of gas and coal powder for combustion. This flexibility allows production enterprises to meet the requirement of utilizing locally inexpensive energy sources.

rotary lime kiln
rotary lime kiln
rotary lime kiln

Vertical Kiln

A vertical kiln (also known as shaft kiln) is a stationary, vertically oriented cylindrical lime kiln. It can be categorized into mechanical vertical kilns and conventional vertical kilns. Conventional vertical kilns involve manual feeding and unloading or mechanical feeding with manual unloading, while mechanical vertical kilns have both mechanical feeding and unloading.

Compared to conventional vertical kilns, mechanical vertical kilns operate continuously, with higher production output, better quality, and increased labor productivity. In recent years, China has independently developed fully automatic, mechanized, environmentally friendly, and energy-efficient vertical kilns for active lime production. The performance indicators of these kilns are approaching those of various advanced kiln types developed abroad.

Refractory materials for vertical kilns have specific requirements due to the unique design and operating conditions. Therefore, It is important to select the appropriate refractory material based on the specific conditions and requirements.

Double Chamber Vertical Kiln

The double chamber vertical kiln also called twin-shaft vertical kiln is a new type of environmental lime kiln for energy-storing, It has two chambers and adopts an alternating calcination process. When one kiln is calcined, the other chamber stores heat. And the heat from the flue gas can be transmitted to the other kiln chamber through the channels. The twin-shaft vertical kiln, considered one of the advanced lime kilns, is characterized by its counter-current heat storage and calcination principle. It boasts the lowest recognized thermal consumption in the lime production industry. Currently, domestically designed twin-shaft vertical kilns have a capacity ranging from 120 tons per day to 800 tons per day. The gas fuel consumption is as low as 850 x 4.18 kJ/kg, with an electricity consumption of 40 kWh/t. The heat sources, utilizing coal powder and coal gas, are safe and reliable, and the key lining of the kiln can have a lifespan of 3 to 6 years. The structure is so complex that requires professional technical personnel to install and maintain. Therefore, It is important to select the appropriate refractory material based on the specific conditions and requirements.

Double Chamber Vertical Lime Kiln
Double Chamber Vertical Lime Kiln
Double Chamber Vertical Lime Kiln

Annular Shaft Lime Kiln

Annular shaft kilns is a kind of thermal equipment that consists of two concentric cylinders forming an annular furnace chamber. It has characteristics of small footprint, low heat consumption, uniform product quality, high activity, and wide adaptability to limestone and fuel, it has been applied widely in many countries and regions around the world. And it has advantages of simple operation, stable product quality, more than 360ml of thermodynamic activity, 40kwh/t of power consumption is 40kwh/t. Currently, typical specifications for sleeve lime kilns in the market include 150 t/d, 300 t/d, 500 t/d, 600 t/d, and others. Sleeve kilns are characterized by relatively simple operation, stable product quality, and an activity level of 360ml or above. Gas fuel consumption is around 900 x 4.18 kJ/kg, with an electricity consumption of 40 kWh/t. The lining of the kiln can have a lifespan of 3 to 6 years.

However, there are some problems restricting the development of sleeve kilns such as complex structure, numerous irregular bricks, complex masonry, difficult maintenance, high infrastructure investment, and unsuitable use of coal powder. Therefore, It is essential to select the suitable refractory materials to suit the specific conditions and requirements of sleeve kilns.

annular shaft lime kiln
annular shaft lime kiln
annular shaft lime kiln

Mixing Kiln

Mixing kiln is one of important kiln types in the domestic lime industry. With the introduction of international advanced technology, improvement and upgrading of domestic shaft kiln processes, supporting development of key process equipment, standardization of shaft kiln operation and management technology, application of automation control energy-saving technology, and scientific matching of environmental protection and dust removal technology, the mixing kiln has formed a complete and scientific lime production technology system. It has characteristics of small investment, small floor area, low energy consumption, strong adaptability, and environmental protection emissions meeting standards. Mixing kiln is widely used in industries such as steel, non-ferrous metals, chemicals, calcium carbide, and building materials.

mixing lime kiln
mixing lime kiln
mixing lime kiln

The production capacity of various types of lime kiln equipment is determined based on the existing market value of equipment at various scales. Lime kiln types include 100 t/d, 150 t/d, 200 t/d, 300 t/d, 400 t/d, 500 t/d, 600 t/d, 800 t/d, 1,000 t/d, 1,200 t/d, and 1,500 t/d, making a total of 11 different scales.

Among them, rotary kiln equipment has a production capacity ranging from 300 t/d to 1,500 t/d, with a total of 7 different scales. Twin-shaft vertical kiln equipment has a production capacity ranging from 200 t/d to 800 t/d, with a total of 6 different scales. Single-shaft vertical kiln equipment has a production capacity ranging from 100 t/d to 600 t/d, with a total of 6 different scales. Annular sleeve kiln equipment has a production capacity ranging from 150 t/d to 800 t/d, with a total of 5 different scales. Beam-type kiln equipment has a production capacity ranging from 100 t/d to 800 t/d, with a total of 7 different scales.

Lime Kilns Classified by Fuel Type

Mixed-burning Lime Vertical Kiln

A mixed-burning lime vertical kiln generally refers to a lime kiln that uses solid fuels such as coke, coal, etc. as the fuel source. The term ‘modern, environmentally friendly, and energy-efficient mixed-burning lime vertical kiln’ implies a design with a reasonable height-to-diameter ratio, capable of implementing a three-stage thermal process within the kiln—comprising a preheating zone, a calcination zone, and a cooling zone. This design allows for the thorough utilization of fuel thermal energy. Additionally, the kiln is charged from the top, and ash is discharged from the bottom, maintaining a closed system throughout the entire operation. The exhaust gases are directed through a pipeline for dust removal, achieving pollution-free emissions. The entire process, including charging, material distribution, material level, temperature monitoring, and ash unloading, is mechanized or automated, contributing to energy savings and environmental protection.

Gas-fired Lime Kiln

Gas-fired lime kilns refer to furnaces used for lime calcination utilizing gaseous fuels. Various combustible gases can be employed for lime calcination, including blast furnace gas, coke oven gas, natural gas, generator gas, and biogas.

Existing types of lime kilns include lime rotary kiln calcination equipment (referred to as ‘rotary kiln equipment’) and lime vertical kiln calcination equipment (referred to as ‘vertical kiln equipment’). Mainstream equipment types for vertical kilns include twin-shaft vertical kiln equipment, single-shaft vertical kiln equipment, annular sleeve kiln equipment, and beam-type kiln equipment. These five equipment types, with the aforementioned being the mainstream, are all reflected in the standards.

Lime kilns come in various specifications and models based on different purposes. Some examples of lime kiln specifications include Φ1.5X24 meters, Φ1.8X38 meters, Φ2.0X45 meters, Φ2.2X50 meters, Φ2.4X38 meters, Φ2.4X55 meters, Φ2.5X56 meters, Φ2.8X45 meters, Φ3.0X48 meters, Φ3.2X50 meters, Φ3.3X50 meters, Φ3.5X54 meters, Φ3.8X55 meters, Φ4.0X60 meters, Φ4.3X64 meters, Φ4.8X74 meters, Φ5.0X74 meters, Φ5.6X87 meters, Φ6.0X95 meters, and so on.

The production capacity and calcination quality of lime kilns serve as critical indicators for equipment capability, guiding users in the selection of equipment based on the required lime grade. If stable production of high-grade lime is needed, such as with an activity level exceeding 360, or even reaching 400+, the choice would be rotary kiln equipment. For normal production of low-grade lime, users may opt for specific equipment among vertical kilns.

Working Principle of Lime Kiln

The basic working principle of a lime kiln involves the decomposition of calcium carbonate in limestone, the main component of lime stone, into calcium oxide and carbon dioxide through the application of high temperatures. Lime, the end product, mainly consists of calcium oxide.

In the lime kiln, limestone and fuel are loaded (or introduced through gas fuels via pipelines and burners). The process begins with preheating at around 850°C, initiating the decomposition, and completes the calcination process at approximately 1200°C. Following cooling, the lime is discharged from the kiln, completing the production of lime products. Different kiln types have distinct methods for preheating, calcination, cooling, and ash unloading. However, certain process principles remain consistent:

  • High-quality raw materials lead to high-quality lime.
  • High calorific value of the fuel results in lower consumption.
  • The particle size of limestone is directly proportional to calcination time.
  • Lime activity is inversely proportional to calcination time and temperature.

Lime Kiln Components

The lime kiln consists of the kiln body, feeding device, material distribution device, combustion device, ash unloading device, electrical system, instrument control system, dust removal device, etc.

Material Distributor

Material distribution in mixed-burning lime kilns is a crucial component, and the choice and performance of the material distributor significantly impact the production efficiency of the lime kiln. Various types of material distributors are available, including rotary distributors, screw-shaped distributors, fixed distributors, etc. The selection principles are: ensuring uniform mixing of raw materials in the lime kiln, reasonable distribution of particle sizes, possessing high-temperature and wear-resistant characteristics, and facilitating maintenance.

Burner

The main auxiliary equipment for a lime kiln is the burner. Gas fuel is mixed with the required oxygen (air) in the burner at a certain ratio and then introduced into the furnace for combustion. Different gases require varying amounts of air, and different furnace types and heating methods demand different flame types, such as premixed, semi-mixed, external mixed flames, and oxidation flames, neutral flames, reduction flames, etc. The burner for a gas-fired kiln to some extent determines the calcination effect of the lime kiln.

Air Supply Device

Whether for mixed-burning or gas-fired lime kilns, rational air supply is essential. Combustion requires three conditions: fuel, air (oxygen), and an open flame. The amount of air is calculated based on the oxygen demand of the combustible components in the fuel. Insufficient air supply results in incomplete combustion, while excess air supply turns into surplus air, causing significant heat loss and fuel waste. The selection of a fan must consider both theoretical calculations and specific furnace types, relying on practical experience.

Dust Removal Equipment

Lime Kiln Cyclone Dust Collector – Primary Dust Removal

Suitable for high-temperature, coarse and fine dust particle separation and collection. It offers high efficiency, large processing airflow, and stable performance, making it suitable for primary dust removal from flue gas.

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Lime Kiln Baghouse Dust Collector – Secondary Dust Removal

After the reaction and primary dust removal, the temperature of lime stone dust and flue gas decreases to below 180°C, meeting the temperature requirements of baghouse dust collectors. The concentration of acidic gases in the flue gas decreases, reducing corrosion, ensuring the service life of the bags. The dust particles are dry and non-fibrous, with poor adhesion, making them suitable for baghouse dust collectors to capture fine, dry, non-fibrous dust particles. The baghouse dust collector is adaptable to changes in gas volume, can capture a wide range of dust particle sizes, has a simple structure, and operates stably.

In a word, although there are various types of lime kilns in China, the basic process principles are generally similar. The true differences lie in the specific requirements. In practical production, consideration should be given to solving kiln problems from the overall to the local level. Emphasis should also be placed on regular maintenance and optimizing supporting equipment.

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