Fuel Types for Lime Burning
As we all know, there are different kinds of lime kiln according to different types of fuels. The fuels used for burning lime are very diverse, including solid fuels, gaseous fuels, and liquid fuels. The combustion principle of modern lime kilns is to use the most economical fuel, the one that is most environmentally friendly, and the one that saves the most energy.
Currently, the most commonly used fuels are coke and gas. The most ideal fuel is gas, including blast furnace gas, converter gas, coke oven gas, carbide tail gas (gas), and producer gas, which are the best fuels for lime kilns. This is because these gaseous fuels are waste materials that can be utilized, fitting into the circular economy model. Especially for coke oven gas, which is largely vented and has abundant resources, followed by blast furnace gas and carbide tail gas. Utilizing these gases can significantly save energy, protect the environment, and more importantly, provide substantial economic benefits to enterprises.
The amount of fuel used for burning lime depends on the type of kiln and the calorific value of the fuel. The heat required for calcining lime comes from the combustion of fuel. The molecular formula for the combustion of the main component of solid fuel, carbon, is C + O2 = CO2. For gaseous fuels, the amount needed is calculated based on their calorific value. According to practical experience, producing one kilogram of lime requires about 960 kcal of heat, but this can vary depending on the production equipment and process conditions of different plants. Generally speaking, burning one ton of lime requires about 1600 m3 of blast furnace gas, about 300 m3 of coke oven gas, about 360 m3 of carbide tail gas, about 120 m3 of natural gas, and about 900 m3 of producer gas.
Mixed-fuel lime shaft kiln
A mixed-fuel lime shaft kiln generally refers to a lime kiln that uses solid fuels to burn lime, including shaft kilns that use coke, coal, and other fuels. The so-called modern environmentally friendly and energy-saving mixed-fuel lime shaft kiln refers to a kiln with a reasonable height-to-diameter ratio, capable of realizing three thermal processes inside the kiln, namely preheating, calcining, and cooling. This allows the fuel’s thermal energy to be fully utilized. The entire operation process, from loading at the top to ash discharging at the bottom, is closed, with flue gas being expelled through pipelines and filtered to achieve pollution-free emissions. From loading, distributing, material level and temperature detection, to ash discharging, everything is mechanized or automated, which not only saves energy but also protects the environment.
Gas-fired lime kiln
A gas-fired lime kiln is a kiln that uses gaseous fuels to burn lime. Currently, the gaseous fuels that can be used for lime burning include blast furnace gas, coke oven gas, natural gas, producer gas, biogas, and other combustible gases.
Solid Fuel Lime Kilns
Solid fuels are those that are in a solid state at room temperature. Common examples include:
- Coal-fired Lime Kilns: Coal is a common fuel for lime kilns, especially in areas where it is readily available and economical. Coal-fired kilns need specific design considerations for handling coal, including storage, pulverization, and feeding mechanisms.
- Coke-fired Lime Kilns: Coke, a byproduct of coal, is another solid fuel option. Coke-fired kilns have a similar design to coal-fired kilns but need considerations for the high carbon content and combustion characteristics of coke.
- Wood-fired Lime Kilns: These kilns use wood or wood-derived materials (such as wood chips or sawdust). Wood-fired kilns require considerations for feeding mechanisms and ash disposal.
- Biomass-fired Lime Kilns: Biomass such as agricultural waste, pellets, and other organic materials can be used. These kilns often have adaptations for handling and burning varied biomass fuels.
Liquid Fuel Lime Kilns
Liquid fuels are used in a liquid state, often derived from petroleum. Examples include:
- Oil-fired Lime Kilns: These use various types of fuel oils (heavy oil, light oil, diesel, etc.). Oil-fired kilns require burners designed for liquid fuel atomization and combustion.
- Waste Oil-fired Lime Kilns: These kilns burn waste oils from various industrial processes, necessitating specific handling and treatment systems to manage impurities and ensure efficient combustion.
Gaseous Fuel Lime Kilns
Gaseous fuels are those that are in a gaseous state at room temperature. Examples include:
- Natural Gas-fired Lime Kilns: Natural gas is a clean-burning fuel and is commonly used due to its availability and ease of control. These kilns require gas burners and control systems to regulate the gas flow and combustion process.
- Propane-fired Lime Kilns: Propane is used where natural gas is not available. Propane-fired kilns have similar requirements to natural gas kilns but need specific storage and delivery systems for the liquefied gas.
- Syngas-fired Lime Kilns: Syngas, or synthesis gas, is produced from gasification of carbon-containing materials. These kilns need to handle the variable composition and calorific value of syngas.
Combination Fuel Lime Kilns
Combination fuel kilns can burn multiple types of fuels, either simultaneously or switching between them. These kilns offer flexibility in fuel use and can optimize operating costs based on fuel availability and prices.
Specific Considerations for Different Fuels
- Burner Design: Different fuels require different burner designs to ensure efficient and complete combustion.
- Fuel Storage and Handling: Solid, liquid, and gaseous fuels need appropriate storage solutions to handle them safely and efficiently.
- Emission Controls: Different fuels produce different emissions. Kilns must be equipped with appropriate emission control systems (e.g., scrubbers, filters, precipitators) to meet environmental regulations.
- Heat Distribution: The method of heat transfer and distribution within the kiln can vary depending on the fuel type. For example, solid fuel kilns might have grates or fluidized beds, whereas gaseous fuel kilns might rely on flame impingement.
