Improving efficiency in mixing technology

By Helen Wright17 July 2012

The 200 tonnes per hour Dillman Voyager asphalt plant.

The 200 tonnes per hour Dillman Voyager asphalt plant.

There are many strands to the latest developments in mixing technology for both concrete and asphalt, but they are united by the need to meet demand for more economical machines that are safe and intuitive to operate.

The big news in terms of asphalt mixing technologies has been the development warm mix asphalt (WMA) processes which allow producers of asphalt pavement material to lower the temperatures at which the material is mixed and laid.

Instead of production temperatures of 140°C to 180°C for traditional hot mix asphalt (HMA), today's warm mixes are created at 90°C and 150°C.

Such reductions have the obvious benefits of cutting fuel consumption and decreasing emissions. In addition, engineering benefits include better compaction on the road, the ability to haul material for longer distances, and extending the paving season by being able to pave at lower temperatures.

Marini - a subsidiary of Fayat - said two main techniques for producing WMA have emerged. One involves the addition of either solid or liquid bituminous binders, and the other involves the use of additive-free foamed bitumen.

The manufacturer is championing the foam route, and has developed the new Aquablack foam generator which it claims is a low cost, emissions-free device that can be easily installed on a metering line of a new plant or a plant to be upgraded.

The Aquablack consists of three main elements - an independent memory card, which manages production data, a foam gun or online foam generator and a mass flowmeter equipped with an online heater.

The additive-free foam (consisting of hot bitumen and 3% water on average) is created in the foam gun just before the point at which bitumen is injected into the mixer. Using Aquablack allows warm mix asphalt to be produced at 150°C, if not lower, according to the company.

Other developments for both asphalt and concrete mixing technology have centred on transportability and improvements to plant controls and data logging technology as well as environmental concerns such as emissions and noise.

Cemen Tech has developed user-friendly controls for its concrete dispensers, and has introduced a new style of control panel for its Mobile Concrete Dispenser line.

The new panel is lighted for night time operations and incorporates controls for the hydraulically powered water pump and the water flow control valve directly at the operator's panel to make adjustments easy and convenient.

In addition, water flow meters and admixture flow meters are all centrally located in the panel for easy operation. The panel also has a multi section hydraulic control valve which reduces hydraulic hosing and allows for easier maintenance, according to the company.

Customised control

On the asphalt side, meanwhile, Astec has also developed a new control system for its plants. The PMIII system consists of individual modules for burners, silos, motor controls, blending and loadout. The modules can be installed together as a package or individually, allowing operators to customise the controls at an asphalt facility.

Astec designed the PMIII interface with minimal graphics on each screen so as not to appear overcrowded, and the system has built-in diagnostics which are said to minimise plant downtime by helping operators identify the source of any problems.

Data logging is another area of focus for Astec, which has also launched the Data Acquisition System Hub (DASH), which is compatible with the company's TCII, PMII and PMIII control systems.

This new system provides a real-time snapshot of operations by gathering information from all plants, displaying it in interactive charts and making it accessible via web browser, or flash compatible devices such as Android tablets and smartphones.

Production data collected from each plant includes mix totals, raw material usage, current production rates as well as moistures and mix temperature. Fuel consumption can also be monitored for plants that have fuel meters connected to the plant control system.

DASH also collects sales data, which can be aggregated across plants to show totals shipped to a job or sold to the same customer from multiple plants. The idea is to speed up the resolution of any production problems, and allow management decisions to be taken more quickly.

It has been a busy year for Astec, whose other launches include a new V-Flight drum design as well as a new portable asphalt plant. The company described its new drum design as a "breakthrough", and said it would now be a standard component on all new drums and made available as retrofits.

The V-Flights are said to provide greater aggregate uniformity during the drying process, resulting in better heat transfer, a reduction of fuel use and increased productivity. Astec claimed that a reasonable expectation for fuel savings on a high recycled asphalt pavement (RAP) mix or open-graded mix would be about 10%.

Using the V-flights in conjunction with an optional variable frequency drive (VFD) also adds flexibility by extending the range of mixes that can be produced without requiring that the flights be adjusted. With the VFD, a plant operator will also have the ability to control exhaust temperatures regardless of the mix design.

For the highest level of regulation, Astec is introducing a stack temperature control system package that incorporates the V-flights along with the VFD controls. This system automatically modulates the drum speed to maintain a set temperature, and Astec claimed it would allow customers to use more RAP in mixes as a result.

Meanwhile Dillman, a division of Astec, has introduced the portable 200 TPH Dillman Voyager asphalt plant. The new plant is built around the Dillman unified drum and includes a 50 tonne self-erecting surge bin to ensure a quick set-up without the need for cranes.

Designed for producers which require a plant made to move several times during the paving season, the Voyager offers a straight-forward design with components that can be dismantled, moved to a new site and set up and ready for production in about five days.

Transportability

This type of highly mobile and flexible design is also reflected by other manufactures. Lintec, for instance, has introduced a fully containerised Gussasphalt plant - all the components of which (including the mixer, burner, electrical cabinets etc) are pre-installed into easily transportable containers, which have certified shipping dimensions.

Gussasphalt is a very dense type of mastic asphalt bound by a polymer modified binder. Lintec's latest plant, which has a capacity of 20 tonnes per hour, was sold to French contractor Colas' subsidiary SMAC in April this year.

Lintec claims that its containerised plant design leads to lower transport costs and handling times, with the plants up and operating after a week. No concrete foundations are required as the large bottom area of the containers give enough stability on a normal compacted site service, and the fact that all the components are housed also lowers noise, dust and heat emissions.

Noise reduction has also been a central concern for Ammann, which has developed a new silencer - the Ammapax - to help contractors tackle this. The device, which does not require any extra room as it is fixed to the chimney opening, is available in different configurations that can reduce noise levels by 10 dB, 15 dB or 20 dB, depending on requirements. It is also compatible with plants made by other manufacturers.

Meanwhile, Ammann has also developed a new module to add to its AS1 technology platform in asphalt plants - the EcoView system. This technology is designed to show at a glance how efficiently a mixing plant is working by continuously recording operating and energy-related data such as fuel, electricity consumption and CO2 emissions and presenting this in graphical form to the mixing engineer.

Comparisons with "previous performance" indicate trends and any necessary need for action. The idea is to make energy costs per tonne of asphalt as transparent as possible, and provide indicators for possible causes of an increase in energy consumption.

Ammann has also launched a new range of asphalt mixing plant - the Unibatch models, which it describes as "all rounders". UniBatch plants have a capacities range from 80 to 350 tonnes per hour and feature "future proof" designs, capable of being modified to adapt to a wide range of sites. The plants have a modular construction, with individual components transported in standard containers, and the range is compatible with all of Ammann's recycling technologies.

Similarly, Asphalt Drum Mixers' (ADM) new EX Series of asphalt plants were also developed to cope with recycled material and can process high percentages of RAP. Capable of producing between 100 and 425 tonnes of asphalt per hour, the EX Series use separate drying and mixing zones to achieve the maximum level of heat transfer and fuel efficiency.

EX Series plants are available in portable or stationary versions and can be operated by just one plant operator and one loader operator. ADM also designed the plants to reintroduce emissions back to the drum's combustion zone, making the plant more environmentally friendly.

Marini has also broadened its range of asphalt plants with the introduction of the new Top Tower 3000, which can produce 240 tonnes per hour and is capable of a recycling rate of up to 35%.

The company said the main innovation on the new plant concerned the upper part of the mixing tower and the screen in particular. The idea was to upgrade the screen and maximise the screening area (38 m² of total screening capacity and 6.6 m² for the sand screen), while keeping the dimensions down to a minimum. In addition, the screen has been optimised with new access hatches for quick and easy access to the different meshes, simplifying maintenance operations.

Furthermore, the aggregate and filler weighing hoppers on the Top Tower 3000 have been redesigned and enlarged, mainly in response to the requirements of customers producing special asphalt mixes containing high levels of filler, according to Marini.

Marini said its Top Tower models now offer a complete range covering all outputs from 200 to 300 tonnes per hour. It said each model is also capable of integrating the most recent technological developments in terms of recycling solutions, including a recycling ring, direct introduction into the mixer, combined ring and mixer solution and parallel drums, as well as accommodating warm-mix asphalt production, including the addition of foam bitumen, solid and liquid additives and the injection of wet sand.

Adaptability

Manufacturers expect to see demand for such environmentally friendly plants increase in the future, but not across all markets. As Ammann points out, plants with recycling capabilities and reduced emissions are in demand in markets where resources are tight and environmental requirements are particularly strict.

However, demand can differ significantly from region to region, and Ammann said one of its key strategies would be to improve its capacity to adapt its products to suit local customer requirements.
This tailor-made approach could become a decisive competitive factor in the mixing sector, while the trends of increased automation and transportability also look likely to continue to shape developments.

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