Fly ash processing: Tailored solutions for the reclamation of harvested fly ash

Harvested fly ash is a fine, powdery substance generated as a byproduct of coal combustion in power plants. Rich in silica, alumina, and calcium, it’s a pivotal ingredient for cement production. Especially in the UK, with the dwindling availability of Coal Derived Fly Ash (CDFA) due to the closure of coal-burning stations, the importance of harvested fly ash has risen sharply. The UK has over 100 million tonnes of CDFA stored in lagoons and stockpiles, signifying a treasure trove awaiting proper utilisation.

Construction applications

In construction, harvested fly ash is incorporated into concrete, enhancing its workability, strength and durability while also reducing water demand and lowering CO2 emissions. Furthermore, using harvested fly ash in this way can help manage industrial waste, reduce landfill usage, and promote sustainable construction practices. Despite these benefits, during fly ash processing, careful handling and treatment are essential due to the potential presence of heavy metals and other hazardous substances within the fly ash.

Why harvested fly ash is important

There are several benefits to reclaiming fly ash and processing it as a by-product, including both environmental and economic advantages:

  • Securing Availability: The looming uncertainty surrounding the long-term availability of harvested fly ash from conventional sources underlines the need for alternatives. Reclaiming stored fly ash offers a sustainable solution.
  • Minimising Landfill Dependency: Recycling and processing fly ash reduces reliance on landfills, preserving crucial space.
  • Economic Advantages: Leveraging harvested fly ash as an alternative to certain materials introduces cost efficiencies, especially in construction and concrete fabrication.
  • Enhancing Concrete Quality: Harvested fly ash improves the overall properties of concrete, boosting its resilience and durability.
  • Carbon Emission Cutbacks: Integrating fly ash in concrete reduces CO2 emissions, especially when considering the carbon-intensive production of Portland cement.
  • Guarding the Environment: Properly processed fly ash ensures that contaminants like mercury or arsenic don’t compromise our environment.
  • Energy Retrieval: Some variants of fly ash, especially those from biomass plants, contain unburned carbon which could be tapped for energy.
  • Fostering Employment: The effort involved in processing harvested fly ash can stimulate job creation and economic growth.
  • Spearheading Sustainable Innovations: Embracing harvested fly ash in construction practices promotes a circular economy, championing industrial sustainability.

Read more about the huge harvested coal-derived fly ash (CDFA) opportunity.

Fly ash in concrete and building materials

The use of harvested fly ash in concrete and other building materials has gained popularity in recent years, and offers several benefits ranging from improved workability, durability, and long-term strength to significant cost savings and reductions in CO2 emissions. Good quality fly ash can increase the sustainability of concrete and cement products due to the reduction in carbon related to transport and cost compared to limestone and Portland stone alternatives.

Notably, in June 2023, Atritor and ST Equipment and Technology showcased their potential in Coventry. Using the Atritor Dryer Pulveriser and the STET separator, we demonstrated the treatment of fly ash to meet the European EN450 standards, emphasising its role in enhancing the properties of concrete.

Fly ash improves the workability of concrete, enhancing its performance and making it easier to mix, transport, and place. It also reduces the water demand, resulting in a lower water-to-cement ratio, which contributes to the strength and durability of the concrete. Using fly ash in concrete also contributes to long-term strength. It reacts with the byproduct of cement hydration to form more cementitious compounds, enhancing the concrete’s ultimate strength over time.

Fly ash concrete shows increased resistance to damage from freeze-thaw cycles and chemical attacks. This makes it suitable for structures that need to withstand harsh environmental conditions or corrosive substances.

Reduction in CO2 emissions is another benefit of fly ash in concrete. The production of Portland cement contributes a significant amount of CO2 to the atmosphere. By substituting a portion of cement with fly ash, we can reduce the carbon footprint of concrete production. Fly ash is often less expensive than Portland cement, so its use can result in cost savings for concrete manufacturers and construction companies.

Harvested fly ash processing

The process of preparing wet fly ash for usage begins with extraction and pre-screening, both crucial steps for ensuring the quality of the resulting product. During extraction, the wet fly ash, a byproduct of the combustion process in coal-fired power plants, is carefully collected for further treatment. Pre-screening then follows, serving to remove any coarse or unwanted particles and ensuring a consistent starting material for further processing.

After extraction and pre-screening, the fly ash undergoes drying, a key step in transforming the wet byproduct into a form that can be used in construction applications. The drying process reduces the moisture content of the ash, making it easier to handle and prepare for subsequent processes.

The dried fly ash is then deagglomerated, a process that breaks down larger clusters of particles into individual ones. This is particularly important in enhancing the performance of the fly ash when mixed with cement, as deagglomeration increases the surface area of the particles, thereby improving their reactivity.

The deagglomerated fly ash is then subjected to classification. Classification ensures that the fly ash particles have the required size distribution for specific uses. 

It’s important to note that processed fly ash must meet specific regulatory standards to be used in construction applications. In Europe, for instance, the standard for fly ash in concrete is EN450 Class N or S. This standard outlines the properties that fly ash must have, including its chemical composition, loss of ignition, and fineness, among others.

In the United States, the regulations are outlined in ASTM C-618 and the newer ASTM E3183. These American standards similarly define the requirements for using fly ash in concrete, ensuring the resulting concrete products’ performance, durability, and safety.

Fly ash processing equipment and solutions with Atritor

Atritor Dryer Pulveriser. Blue mechanical device with intricate gold and silver components, including rotating gears and a central axle.The Atritor Dryer Pulveriser offers simultaneous drying, deagglomeration and classifying. It is capable of a product feed rate of up to 20 tonnes per hour and evaporation rates of up to 4,000 kilograms per hour, utilising inlet gas temperature as high as 550 degrees centigrade.

We take a collaborative approach with our customers in our Pilot Plant proving facility, where we test the wet fly ash using different process setups until we achieve the right end fraction for your individual applications. The Pilot Plant testing and our considerable knowledge of fly ash gives us the knowledge to advise you on the financial viability of proceeding with a project. When specifying a project, we consider the characteristics of the fly ash as it varies depending on source, time of year extracted. The wetter the ash, the more energy it will require to dry. We also consider capital expenditure, such as civil works, and equipment. 

Our in-house design and manufacturing facilities provide you the resources for a bespoke approach. Then we install commission and train users of the plant to ensure our customers achieve a profitable end product.

At Atritor, we have 90 years of experience delivering bespoke drying and grinding solutions. We specialise in taking waste products and turning them into something valuable. From testing, design, manufacturing, installation, commissioning and training – we take care of the whole solution for fly ash processing. We have the previous experience and comprehensive testing data to apply to your feasibility study, saving you time and cost in your decision-making. Get in touch with our team and see how we can help you with fly ash processing.