As published in World Cement
By Kevin R. Peterson
The Benefits of Fly Ash in Cement Blends
Fly ash is a fine powder composed mostly of silica. It is a byproduct created when ground coal is burned by coal-fired energy plants.
Adding fly ash to Portland cement blends offers many benefits, including:
- Improved workability – Fly ash particles are spherically shaped and act like miniature ball bearings in the mix. This reduces frictional losses during the pumping process and makes it easier to work the concrete as it is being finished.
- Water demand – When fly ash is concentrated at approximately 20 percent of total cementitious compounds, water demand is reduced by approximately 10 percent.
- Reduced heat – Fly ash can reduce the heat of hydration in concrete.
- Increased strength – Fly ash reacts with lime to make the cement harder.
- Reduced permeability – The decrease in water usage decreases permeability.
- Improved durability – A decrease in free lime, increase in cementitious compounds, and reduction in permeability creates a more durable concrete.
Market Outlook: Fly Ash
About 43% of fly ash is upcycled by the cement industry. Much of the remaining fly ash is disposed of in local landfills.
While fly ash is beneficial to the cement industry, coal-fired energy plants are often not geographically close enough to cement producers. As a result, the added transportation negates the cost-effectiveness for obtaining fly ash.
Case Study: Fly Ash Transloading
A coal-fired energy plant in California, USA performed a feasibility study to explore the possibility of establishing a truck transloading terminal, used to supply fly ash to the local cement industry. Doing so would:
- Create a larger market, so that more fly ash could be upcycled and less had to be disposed of; and
- Create a centrally located source of supply, opening up new demand opportunities for local cement producers.
To bring this concept to fruition, the coal-fired energy plant considered leasing an existing rail terminal and converting it into a truck transloading terminal.
The coal-fired energy plant consulted Ball Sales and Engineering to further consider the feasibility of this opportunity. Matt Brady, a sales engineer at Ball Sales and Engineering, traveled on-site to the proposed rail terminal to assess the application. He made several observations about the rail terminal’s existing infrastructure:
- A ceiling separates the storage silos from the loading bay. Chutework extends from the silos down into the loading bay through openings in the ceiling.
- Substantial space was available between the silo discharge and the ceiling of the loading bay.
- There was an existing dust collection system in the silo area.
Brady advised that though the project was feasible, several factors must be considered. Those included:
- Fly ash’s high silica concentration poses many critical health and safety risks. The terminal would require loading spouts equipped with dust collection at the loading point.
- Each spout would require a maintenance gate, process gate, and plug valve, used to control the flow of fly ash as it is aerated and discharged from the silo through the spout.
Brady consulted one of Ball Sales’ equipment manufacturers, Vortex, to discuss this retrofit project further. They concluded:
- Though the spouts could be mounted on the ceiling in the loading bay, mounting them on the floor beneath the silo would be easier and less expensive.
- Because the spouts would be extending and retracting through holes in the floor, there was a concern that the spout sleeve and cones could become damaged as they traveled through the existing openings. The solution was a 4 ft | 1.2 m tube extension between the feed inlet and the retractable portion of the spout.
- The remaining space was sufficient for the valve stack up that would be between each silo and its spout.
Over the next months, Brady was an important resource as the client finalized its plans for the truck transloading terminal. Almost a year later, Vortex slide gates and loading spouts were installed at four load-out points.
The initial gate below each silo discharge is a Vortex Maintenance Gate.
- Manual hand crank actuation.
- Designed to be open for the majority of the time. It is only closed when maintenance of downstream equipment is required, or in the case of an upset condition.
- Designed to close through a standing column of material, if necessary.
- Round-to-square inlet transition contains an ANSI #150 pattern to connect to the silo. The inlet transition was extended to take up some of the extra space within the overall stack up.
Below each maintenance gate is a Vortex Titan Slide Gate, being used as a plug valve.
- Double-acting pneumatic air cylinder actuator. Equipped with a manually adjustable threaded rod stop, used to limit the opening stroke of the blade. This feature is used to control flow rates into the rotary feeder below.
- On the sides of the gate, a milled access slot allows for bonnet seal replacement while the valve remains in-line. As new bonnet seals are driven into the slot, the worn bonnet seals are simultaneously ejected out the other side of the gate.
- Fine material modifications – The gate contains a smoother 304 stainless steel blade and a secondary silicone rubber bonnet seal. Additionally, the bonnet area is air purged to discourage fine material accumulation in the gate body.
Beneath each rotary feeder is a Vortex Loading Spout.
- Equipped with a dust take off port, allowing the spout to be connected to the existing dust collection system. Material handling fans effectively remove dust created during the loading process. The fans transport dusts into the dust collectors, located at the top of each silo.
- Because the spouts were mounted to the floor, they are easily accessible for inspection or maintenance.
- Equipped with a four cable hoist system. This means that, if a cable should wear or break, the spout will still be operational until maintenance finds time to replace it.
- CNC-machined pulleys with radius edges and precision cable grooves, to significantly reduce cable wear. For this reason, Vortex lifting cables offer a 10 year warranty.
Remaining Stack Up
Flanged inlet and outlet transitions make up for the remaining space in the stack up.
Because of a new market opportunity this coal-fired energy plant envisioned:
- Area power plants now have a broader market for selling their fly ash;
- Local cement producers are able to access a much-needed ingredient at a more reasonable price; and
- A new business unit was established for this coal-fired energy plant.
The result is a win-win for fly ash and the cement industry.
About Ball Sales and Engineering
Ball Sales and Engineering was involved with this project from inception to completion. As a result of their knowledge and expertise, the proper equipment was selected and installed in this particular application.
Ball Sales is a manufacturers’ representative located in Huntington Beach, California, USA. With 30 years of experience, Ball Sales offers bulk material handling equipment and process solutions for a variety of industries.
For more information, please visit www.ballengineering.com.