Lime Handling System -Bucket Elevators

A lime handling system refers to the set of equipment and processes used to transport, store, and process lime (or lime-based materials such as limestone, quicklime, and hydrated lime) in various industrial applications, such as in cement production, steel manufacturing, water treatment, and other chemical processes. Lime is a critical material in many industrial processes, particularly in cement production, flue gas desulfurization, and water treatment, where it is used for pH control, water softening, and other chemical reactions.

The lime handling system ensures that lime is safely and efficiently moved from storage areas to processing units, such as kilns, mills, or reactors, and that the final product (lime) is transported to the desired point for use or further processing.

Key Components of a Lime Handling System:

1. Storage and Silos:
   • Lime (in the form of limestone, quicklime, or hydrated lime) is usually stored in silos or bins to prevent moisture absorption and ensure a consistent supply to the processing equipment.
   • Storage silos are typically equipped with ventilation systems to prevent buildup of moisture and to maintain product quality.
2. Lime Feeding:
   • Lime is fed into various parts of the plant, such as kilns for calcination (in the case of limestone) or mixing tanks for water treatment processes. The feeding system ensures that lime is delivered in precise amounts, either as bulk or in smaller quantities.
3. Conveying Systems:
   • The conveying equipment is essential for moving lime between various stages of the handling system. Lime is often bulky, heavy, and dusty, so the conveying system must be designed to manage these characteristics effectively.

Common Conveying Equipment in Lime Handling Systems:

1. Belt Conveyors:
   • Belt conveyors are widely used in lime handling systems to transport large volumes of lime, particularly in bulk or granular form. They are ideal for moving lime over long distances, both horizontally and inclined.
   • Material Characteristics: Suitable for transporting dry, granular, or powdered lime, and they can be designed with covers or dust suppression systems to control dust generation.
2. Screw Conveyors (Augers):
   • Screw conveyors are commonly used for transporting lime in smaller quantities or for moving fine materials like hydrated lime (which is a powder). The screw mechanism efficiently moves material along a tube or trough and is often used in applications where space is limited.
   • Material Characteristics: Screw conveyors are ideal for powdery or sticky materials, and they can handle both horizontal and inclined transportation.
3. Bucket Elevators:
   • Bucket elevators are used to move lime vertically. These systems use buckets to carry material up to higher levels, and they are commonly used in lime handling systems to lift lime from storage bins to silos or processing units.
   • Material Characteristics: These are ideal for handling granular or coarse lime and are particularly useful when material needs to be moved vertically in high capacities.
4. Drag Chain Conveyors:
   • Drag chain conveyors use a series of linked chains to drag lime through a trough. They are often used in lime handling for conveying coarse and heavy materials like quicklime, especially when these materials are abrasive.
   • Material Characteristics: These conveyors can handle bulk and abrasive materials, and they are used for transporting lime from storage to processing equipment.
5. Pneumatic Conveying Systems:
   • Pneumatic conveyors use air pressure to move fine lime powders (such as hydrated lime) through pipes. This type of system is highly effective for transporting fine materials over long distances with minimal dust generation.
   • Material Characteristics: Pneumatic conveying is suitable for very fine powders or materials that need to be conveyed over long distances, such as in applications where lime is mixed with other substances in a processing plant.
6. Air Slide Conveyors:
   • Air slide conveyors are used to move powdered lime or other fine materials. In this system, air pressure moves the material across a fabric conveyor bed, allowing powders like hydrated lime to flow smoothly.
   • Material Characteristics: Air slide conveyors are used primarily for dry, fine powders and are effective in managing materials that are too light for traditional belt conveyors or screw conveyors.
7. Vibrating Conveyors:
   • Vibrating conveyors use vibration to move materials along a trough or other surface. These systems are effective for bulk, granular materials like quicklime or crushed limestone and can be used for both horizontal and inclined transportation.
   • Material Characteristics: They are ideal for moving granular or coarse materials and are used in applications where a gentle, continuous flow of material is required.
8. Rotary Feeders:
   • Rotary feeders are used to control the flow of lime from silos or storage bins to processing equipment. These feeders help regulate the amount of lime fed into other systems, such as kilns or mills, and can be used in combination with other conveyor types.
   • Material Characteristics: These feeders are used to handle granular or coarse materials and are often used to prevent blockages and ensure a continuous material flow.

Key Considerations for Lime Handling Systems:

1. Material Properties:
   • Lime comes in various forms, including limestone (rock), quicklime (calcium oxide), and hydrated lime (calcium hydroxide), and each has distinct handling characteristics:
     • Quicklime is highly reactive and can be dangerous to handle, especially when wet, as it can generate heat and release caustic hydroxide.
     • Hydrated lime is typically fine and powdery, which can create dust issues.
     • Limestone is heavy and may require equipment capable of handling larger, bulkier pieces.
2. Dust Control:
   • Lime handling can generate significant dust, especially with finer materials like hydrated lime. Conveying equipment should be equipped with dust suppression systems (e.g., dust collectors or sealed conveyors) to minimize environmental impact and health hazards.
3. Capacity and Efficiency:
   • The conveying system must be designed to handle the required volume of lime without overloading equipment. Efficiency in conveying is essential to maintain consistent flow rates and prevent blockages.
4. Corrosion Resistance:
   • Some forms of lime, particularly quicklime, can be highly corrosive, requiring that the conveying equipment be made from materials resistant to corrosion, such as stainless steel or specialized coatings.
5. Temperature Management:
   • In some systems, especially those involving quicklime in processes like calcination (where limestone is heated to produce lime), the conveying system must be capable of handling high temperatures.
6. Automation and Control:
   • The lime handling system can be automated using control systems to regulate material flow, monitor inventory levels, and ensure proper operation. This reduces the risk of human error and increases overall efficiency.

Applications of Lime Handling Systems:

1. Cement Production:
   • Lime (particularly quicklime) is a crucial ingredient in the production of cement, where it is used in the kiln for the chemical transformation of limestone into cement clinker. Lime handling systems are used to transport and feed limestone to the crushers and kiln systems.
2. Steel Industry:
   • Lime is used in the steel industry for fluxing, desulfurization, and slag conditioning. Lime handling systems are used to move lime to various parts of the steel-making process.
3. Water Treatment:
   • Lime is commonly used in water treatment for softening, pH control, and removing impurities. In these applications, lime handling systems feed hydrated lime or quicklime into water treatment reactors or mixing tanks.
4. Flue Gas Desulfurization (FGD):
   • Lime is used in FGD systems to remove sulfur dioxide (SO₂) from power plant emissions. Lime handling systems move lime into slurry tanks, where it reacts with SO₂ to form calcium sulfate (gypsum).

Conclusion:

A lime handling system plays an essential role in industries that rely on lime for various chemical processes. The conveying equipment used in these systems must be capable of handling a wide variety of lime materials (e.g., hydrated lime, quicklime, limestone) while addressing challenges like dust control, material abrasiveness, and corrosion. By selecting the right conveying equipment and system design, industries can ensure efficient, safe, and continuous lime processing.