A Clear Market Vision.
Andrew Pettingale – MD of BG Europa talks about a highly technological solution for long-term storage of asphalt from Astec…
Having a clear market vision is anything but simple, especially at a time when trends and responses are rapidly changing.
The evolution of market demand requires an increasing flexibility with how asphalt mix is produced and also stored, based on the relatively limited shelf life of the finished product. To be successful, producers need to formulate a strategy that meets the demands of the market, while limiting excess production of unused asphalt mix and enhancing production efficiency.
Andrew, commented, “The desire to embrace more environmentally responsible technologies, together with the economic advantages of inclusion of high levels of recycled products within asphalt mix is encouraging producers to evaluate their production methods. However, to enhance the economic and environmental benefits requires production equipment to be utilised at maximum efficiency. This is often in conflict with a requirement to fulfill small orders. Especially when different mix designs are required for these smaller orders, which are difficult to manage in a rational way, but often represent an important part of the overall volume the producer turns out.”
A problem that is difficult to solve:
The biggest problems relate to the preservation of the mixed material when stored for long periods of time, associated with:
- The demands of a market often presenting a fragmentation of supplies to many jobs each requiring small or medium amounts of asphalt mix, making it difficult to efficiently satisfy every single request.
- The proliferation of mixes often requiring the production of the same product on multiple occasions throughout the day. Together with the costs associated with either starting or cleaning out of the production plant to satisfy this requirement.
- The increasing frequency of night and weekend works requiring mix outside the normal operating hours of production facilities and the support network for such.
- The requirement for mix within conurbations and the difficulties associated with the operation of production facilities close to these sites of product requirement.
Andrew, continued, “Opportunities exist for producers to satisfy changing market requirements, providing their customers with a ready supply of quality mix. Astec long-term storage silos have particular characteristics which allow the producer to insulate the material for four days with the guarantee of preserving the technical characteristics of the mix.”
Technology and potential:
At first sight they look simple silos, however within they contain sophisticated technology that comes from a deep knowledge of the material, the dynamics of oxidation and loss of the mix’s physical and chemical properties.
Astec long-term storage silos allow producers to use the silos as a conventional surge bin during the busy time of day. At the end of the day time-consuming start/stop operations can be avoided and silo filling can commence while continuing loadout. The next working day, mix can be sold straightaway from full silos, without awaiting plant startup. Nobody needs to wait for mix and any delays to production plant startup can be mitigated. Uninterrupted production runs allow producers to maximise equipment efficiency and reduce material waste.
Incorporating multiple silos into production plant layouts ensures producers are ready to meet customer needs for a number of different mixes. Whilst reducing operating costs and improving plant operating efficiency
In addition, the potential to store mix for four days* without loss of mix quality, is guaranteed by Astec in writing. This allows producers to further optimize and rationalize production facilities by utilizing the concept of satellite storage; providing customers with a readily available supply of high-quality mixed material, in areas unsuitable for location of production facilities either due to environmental concerns or economic constraints.
Much more than simple silos:
The Astec long-term storage silos are not just insulated containers but a storage system in which all the elements, starting from the loading hopper, passing through the elevator conveyor and the transverse conveyor up to the silo batcher to the silo and lower cone, are designed to optimize the process.
The main elements that make it a unique technology are:
300mm of insulation at silo tops, 100mm around the cone, and 150mm along the cylinder keep the mix hot. Batchers are insulated as well, because uninsulated batchers are a major source of heat loss. Two layers of stiff sheet insulation are staggered to eliminate heat-leaking seams along the silo-cylinder. Astec uses thick, full R-value, non-compressed insulation.
In storage mode, the cylinder-operated gate at the top of the batcher is completely sealed. The gate runs in rails which tightly wedge it against a ring of grease. This forms a tight seal and keeps air from entering at the silo top.
Astec’s patented discharge gate seals the bottom of the cone when the silo is in storage mode. The heated and insulated discharge gate closes to completely cover the cone opening. Oil is pumped into the gate to seal the bottom silo opening. The oil reservoir is located by the silo legs, and a motor-driven pump moves the oil from the reservoir into the gate. A sensor monitors the oil level in the gate and controls the pump.
The lower cone has a specific inclination of 66º and a higher shape, which naturally prevents segregation and build-up of the material. To prevent wear caused by the material, the interior is lined with wear-resistant steel or optionally ceramic liners can be installed.
Heating of the walls of the cone:
A silicone electric heating blanket surrounds the lower cone section. A thermostat activates the blanket when the temperature drops below set point. This sensor saves money, because the energy to heat the cone is used only when required. Hot-oil heating is available as an alternative to the electric blanket.
Transport of the material:
The drag conveyor reaches to the top of the silo. Strong, wear resistant, roller chain runs from bottom to top, with deep, steel slats attached every 300mm. This heavy slat chain assembly resists hydroplaning over the mix. Depending on required capacity, Astec offers either single or dual chain configurations. The drag conveyor discharges into a traverse conveyor atop the batchers.
The mix moves by drag conveyor or bucket elevator into a three-ton batcher atop the silo. When full, the batcher releases the slug of mix. Mix drops through the rapid-opening double clam-gate into the silo and flattens on impact. Astec’s double-clam gates are not like conventional pinch-closed style double-clam gates. Astec’s overlapping gates slice through material flow as the gate closes. This slicing action and over-lapping gates result in better gate wear resistance when compared to pinch-closed style gates. The double gates also centre the drop into the silo and form a flattened mix surface, which prevents mix segregation.
Silo pressure equalized:
As mix level rises, it displaces air in the silo. Integrated vents inside the batcher enclosure allow bi-directional airflow and equalize silo pressure as mix level changes during fill and loadout.
External coating & painting:
The outer casing is made of aluminium, completed with a coating that maintains the quality characteristics over time. The painting is either carried out in the official Astec colour or optionally in the customers colour choice.
The walls of the silo are made from rolled steel plate lined by structural weld. Jogged radial joints form a smooth inner surface, reducing wear at the joints. Standard silo legs provide 4.0m of clearance for trucks from the top of the weighbridge. Legs and the silo support frame are made of heavy, structural, wide flange beams. Silo support structures are designed to meet the site-specific design criteria at the installation location.
The advantages of a highly technological solution:
What are the advantages of a highly technological solution like the long-term storage silos from Astec
The possibility of planning plant production in a more linear way is certainly the first and most obvious advantage. By storing up to four days of material with Astec’s guarantee of the quality, producers can cope with the peak loads, small supply requirements and intelligently use production plant downtime.
Being able to logically schedule when to start a plant and when to shut it off. With the silos, it is possible to cope with the first load flow very quickly, as well as shorten the loading times thanks to the material that can be prepared continuously and loaded quickly when the trucks arrive.
The ability to store mixed material to overcome short to medium term interruptions to paving operations, without wasting mix. Where projects require high volumes of mixed material, production capacity can potentially be exceeded and necessitate the production of a buffer of material prior to the commencement of works. Disruption to paving operations either due to infield breakdown or changing weather conditions, can be mitigated by storing this material for up to four days without loss of quality.
The potential to maximise production plant capacity/efficiency. By filling either plant based or satellite storage facilities on Friday afternoon and then providing customers with high volumes of quality mix early Monday morning, without waiting for production plant startup.
Andrew concluded, “Astec long term storage silos revolutionized asphalt production methods in the USA. Allowing customers to take advantage of clean technologies for high capacity recycling of asphalt products such as the Double Barrel®, whilst maintaining the flexibility in supply to their customers. Recently our customers in Europe, by utilizing Astec silos for satellite storage applications, have taken these advantages one step further by consolidating production at highly efficient, environmentally responsible production facilities.
“Investment in long term storage solutions allows producers to position themselves differently in a competitive market, take advantage of clean efficient technologies and production methods whilst enhancing service to their customers.”
* polymer modified, open-graded and SMA mixes excluded