Maximising Ash Utilization for Sustainable Development

Ash is an inherited impurity of coal that will not burn. It refers to the solid residue left behind after coal is burned in a boiler, consisting of non-combustible mineral particles that separate into two main types: Fly ash and Bottom ash.

Ash Characteristics:

Parts of the ash handling system:

• Bottom ash handling system
• Air preheater ash-handling system
• Fly ash handling system

Bottom ash handling system:

The bottom ash handling system features a bed ash cooler that utilises Forced Draft (FD) air for effective cooling. Once cooled the ash is pneumatically conveyed to a bed as silo. From there, it is transported to a cement plant for grinding, where it is processed into a fine powder. This streamlined approach enhances efficiency and facilitates the reuse of bottom ash in cement production.

Fly ash system:

The ash produced from the combustion of coal, commonly called as fly ash, is transported through a pneumatic conveying system to a dedicated fly ash silo. Once stored in the silo, the fly ash is subsequently conveyed pneumatically to the cement plant, where it is utilized in the production of cement. This process not only facilitates the efficient handling of fly ash but also contributes to sustainable cement manufacturing by incorporating a valuable byproduct into the production cycle. The pneumatic conveying system ensures that the ash is moved safely and efficiently, minimizing dust emissions and maintaining a clean operational environment.

Ash management objectives:

Maximize the utilization: Maximize the reuse of ash in various applications to minimize landfill disposal and promote circular economy practices.

Enhance product quality: Improve the performance and durability of construction materials like cement, concrete, and paver blocks through the incorporation of processed ash.

Sustainability goals: Contribute to carbon footprint reduction by promoting ash-based eco-friendly products and minimizing greenhouse gas emissions.

Ash utilization in cement production:

Process overview:

• Role of ash as a pozzolanic material
• Enhance binding properties and reduce clinker use

Environmental benefits:

• Reduces CO2 emissions and energy consumption in cement production

Fly ash is widely used in cement plants as a supplementary cementitious material (SCM), contributing to both the production process and the sustainability of the cement industry. Here’s a brief overview of its usage, benefits, and sustainability impact, including typical percentage ranges.

Usage of fly ash in cement production

• Raw material component: Fly ash can replace a portion of Portland cement in the cement blend. Typically, fly ash is used in proportions ranging from 5 to 10%
• Mixing process: During the production of cement, fly ash is mixed with clinker (the primary ingredient in cement) and gypsum. The combination undergoes grinding to produce a homogeneous cement product that includes the pozzolanic properties of fly ash.
• Hydration reaction: Fly ash reacts with calcium hydroxide released during the hydration of Portland cement, enhancing the strength and durability of the final product.

Benefits of using fly ash:

• Cost reduction: By partially replacing Portland cement with fly ash, manufacturers can lower production costs. Fly ash is often less expensive than cement, thus reducing overall material costs.
• Improved performance: The addition of fly ash can enhance the mechanical properties of cement, improving workability, reducing permeability, and increasing long-term strength.
• Reduced energy consumption: The use of fly ash can lower the energy required for cement production, as the overall clinker content is reduced. This leads to lower emissions from the energy-intensive clinker production process.

Sustainability Impact:

• Waste reduction: Utilizing fly ash in cement production diverts waste from landfills, contributing to waste management and recycling efforts.
• Lower carbon footprint: Since the production of Portland cement is responsible for a significant portion of global CO2 emissions, replacing part of it with fly ash can significantly reduce greenhouse gas emissions. Studies suggest that using fly ash can reduce carbon emissions by approximately 10% to 30% per ton of cement produced.
• Resource conservation: By substituting fly ash for Portland cement, the demand for natural resources used in cement production is decreased, promoting more sustainable resource management.
• Improved durability: Concrete made with fly ash demonstrates greater resistance to sulfate attack, chloride penetration, and other environmental factors, leading to a longer lifespan and reduced need for repairs or replacements.

Incorporating fly ash in cement production not only enhances the technical properties of cement but also supports broader sustainability goals. By reducing waste, lowering emissions, and conserving natural resources, this practice contributes significantly to making the cement industry more sustainable.

Overall, the use of fly ash in cement plants exemplifies a practical approach to integrating industrial byproducts into mainstream construction materials.

Ash utilization in paver block manufacturing

Process overview:

• Ash is a key ingredient in paver block formulation.

Benefits:

• Improved durability and strength
• Cost-effectiveness due to reduced cement content

How fly ash is used to make paver blocks:

Fly ash, a byproduct of coal combustion, is effectively used in the production of paver blocks through the following process:

• Raw material preparation: Fly ash is collected and tested for quality to ensure it meets standards.
• Mix design: The mix typically includes fly ash, cement, aggregates, and water, with fly ash often comprising up to 70% of the binder materials.
• Mixing: The dry materials are thoroughly mixed with water to achieve a consistent mixture.
• Molding: The mixture is poured into molds to shape the paver blocks, followed by compaction to ensure density.
• Curing: The blocks undergo initial and final curing to promote strength and durability through hydration.
• Quality Control: Cured blocks are tested for compressive strength and water absorption to meet quality standards.
• Finishing: After testing, the blocks may be treated for aesthetics and packaged for distribution.

Benefits:

Using fly ash in paver blocks enhances sustainability by reducing waste, improving strength and durability, lowering production costs, and minimizing the carbon footprint associated with traditional cement production.

1) Ash collection and transportation

Ash collection systems:

• Mechanisms used (e.g., pneumatic conveying, mechanical handling)

2) Transportation logistics

• Efficient methods for transporting ash to the utilization sites of the cement plant & paver block plant

3) Quality control measures

Testing protocols:

• Regular testing of ash for compliance with the standard (ASTM & IS)

Quality assurance:

• Monitoring during cement and paver block production

4) Challenges & solutions

Challenges:

• Handling and storage of ash
• Variability in ash quality

Solutions:

• Advanced handling systems
• Consistent quality checks

Overview of CFBC technology: CFBC (Circulating Fluidizing Bed Combustion) is a robust, flexible and environmentally friendly combustion method that offers significant advantages over traditional systems. Its adaptability to various fuels and stringent emission regulations makes it a preferred choice in modern power generation and industrial applications.

Characteristics of CFBC boiler in Gallant Ispat Limited.

• Boiler capacity- 150 TPH
• Maximum fuel feeding – 600 TPD
• Maximum ash generation – 150 TPD
• Utilization rates:
  1. 98% in cement production
  2. 2% in paver block manufacturing

Conclusion:

The utilization of ash generated from CFBC boilers in cement production presents a compelling opportunity to enhance economic viability, reduce emissions, and promote sustainability. By transforming a waste product into a valuable resource, this approach not only lowers production costs and minimizes waste management expenses but also fosters job creation and local economic development. Furthermore, it significantly reduces the carbon footprint of cement manufacturing and mitigates greenhouse gas emissions associated with landfill disposal.

The elimination of water usage in ash management contributes to vital water conservation efforts, while the improved material properties of cement enhance the durability and longevity of infrastructure. Ultimately, this innovative integration aligns seamlessly with global sustainability goals, supporting responsible consumption and climate action. As industries increasingly prioritize sustainable practices, the effective utilization of coal ash in cement production stands out as a practical and impactful solution for a more sustainable future.

Author:

Ashwini Kumar Mishra
Vice President
Gallantt Ispat Limited