Asphalt industry reduces emissions

RSS

The asphalt industry is responding with innovative solutions to the call for reductions in emissions. Patrick Smith reports

The current economic climate and the push to reduce all types of emissions while increasing the use of recycled materials have put pressure on industry to come up with answers.

Asphalt production is no exception, and it is tackling these issues vigorously with innovative solutions, including the increasing use of warm asphalt mixes in Europe (a trend that is now catching on in the USA and elsewhere); plants that can use high quantities of reclaimed asphalt pavement (RAP), and plants that can be retrofitted with the necessary accessories.

At the recent World of Asphalt conference and exhibition in Cincinnati, USA, Matthew Corrigan of the US 3796 Federal Highway Administration said that 20 technologies such as additives, foams, special types of bitumen or a combination of these methods, along with equipment, could now be used during the production of warm asphalt in the country, including the European Shell WAM Foam, which was trialled in Norway some years ago. As with traditional asphalt, RAP can be incorporated into the mixture, which achieves lower operating temperatures by combining both soft and hard grade bitumen (soft bitumen is mixed with the aggregate to precoat it and then the hard bitumen is introduced into the mixture as foam).

3774 Shell claims its WAM Foam production and laying process (its production temperature is 115°C) leads to a temperature reduction of about 50°C, resulting in a reduction in emissions, dust and fumes, while at the plant during production there is a 30% reduction of CO₂; CO (25%), Nox (60%) and dust (more than 50%): at the site while laying, fumes are down to almost nil.

Other claimed benefits are savings in energy consumption; greater workability offering a longer construction season and an extended workability window; "performance and quality at least equivalent to that of hot mix asphalts", and it is suitable for base and surface layers.

383 Ammann Group claims that the two decisive aspects of a greener asphalt industry are lower operating temperatures and the use of as much recycled asphalt as possible.

"It is usually possible to lower the mixing temperature by at least 20°C and sometimes by as much as 70°C," said the company.

Indeed, it said that the first asphalt mixing plant capable of producing quality aggregate from 100% RAP using a special parallel drum has been put into operation in North Germany where an improved drying and heating process increased efficiency and enabled fuel savings of around 10%.

The New Top Tower TT4000 model from the 3798 Fayat Group's Italian Marini line-up offers greater production capabilities than previous units in this range and is also capable of producing all types of hot, warm and half-warm materials, with or without recycled materials, as these methods are the only sure ways to guarantee the reduction of CO₂ emissions in the future.

The TT4000 uses some of the features from the Top Tower TT3000 unit launched last year but now offers a throughput of 260tonnes/hour. This new plant comes in addition to existing plants, which have outputs of 180-200tonnes/hour.

According to sales and marketing manager Jacques Bonvallet: "This machine is not only bigger, the design is basically the same as the TT3000 but is now able to facilitate retrofits coming in the next few years."

He explained that as asphalt technology is evolving, Fayat is keen for its machines to have capabilities for further modifications as required. The TT 4000 has been designed so that it can meet the needs of customers for the next 20 years in mind and allow changes as they are developed.

3607 Astec's Double Barrel Green System for lower temperature warm mix now has a second generation model (unveiled at the World of Asphalt). The new design is now standard for both the Double Barrel Green System and for the Green Pac warm mix systems, which can be retrofitted to continuous mix and batch plants from any manufacturer.

Astec said that the Double Barrel Green system saves energy and eliminates smoke and emissions without compromising mix quality and uses water to produce foamed warm mix asphalt that is odourless, smokeless and longer lasting. The company claims that with the Green Pac System an operator can decrease fuel consumption 14% by decreasing the mix temperature while having the ability to run higher percentages of RAP.

3652 Terex also offers a warm mix system, and it uses water rather than additives to lower mixing temperatures by a claimed up to 32°C. "The foamed asphalt warm mix system can be installed on parallel flow plants as well as any brand of unitised counterflow drum mixer. It is capable of lowering mixing temperatures on a wide variety of mix designs, including those incorporating RAP," said Terex.

Terex's warm mix system features an in-line installation, so both hot and warm mix liquid AC is sent through a single pipe into the drum, a new set up that is said to offer several advantages for producers with extremely congested plant layouts.

Turkish manufacturer 3797 ÇESAN claims its mobile asphalt plant, featuring a five-floor screening system is a world first. The plant, with a capacity of 280-300tonnes/hr, also features a 4tonne mixer volume and stone mastic unit and with standard road dimensions can be transported on roads worldwide. The company said its plants can mix a minimum 15% RAP into the asphalt mix.

"CESAN plants can reduce energy consumption, greenhouse gas emissions and improve efficiencies by reducing fuel consumption with its completely self-designed dryer, which operates on the basic principle of heat transfer to the aggregate. From this point for each 1tonne of asphalt a minimum of 1litre of fuel can be saved," said the company.RSS