Astec engineers were tasked with designing a plant that would maintain high production levels at a site elevation of 7,200 feet, using an aggregate supply containing seven percent moisture content.
"IT'S THE FIRST PLANT IN LATIN AMERICA WITH A V-PAC TEMPERATURE CONTROL SYSTEM." —Moises Esquivel, director of sales for Latin America and Caribbean, Astec
When a municipality shuts down its own asphalt production facility because citizens living in adjacent neighborhoods complain of the emissions, equipment agent Ramon Garcia, owner of DIMAQ, knew he would have to rely on the expertise of a plant manufacturer to convince the government that all requirements could be met with the right design and modification of the asphalt production components required.
It’s the first asphalt plant in Latin America with a V-Pac Stack Temperature Control System, according to Moises Esquivel, Astec’s director of sales for Latin America and the Caribbean. The V-Pac controls stack temperature through use of V-flights and drum variable frequency drive. This feature allows a plant operator to make changes from a RAP mix design to a virgin mix design with reduced flight changes, while increasing drum efficiency in the process. The plant also features Astec’s Phoenix Talon II low emissions burner that can be fired with either natural gas or diesel oil, with a combustion air blower silencer, which reduces excess noise during operation. It’s capable of producing mix designs with up to 50 percent recycled asphalt pavement (RAP), and is also equipped with Astec’s Green System capable of producing warm mix, which further reduces emissions by reducing the heat and fuel required during production.
Other notable components include four cold-feed bins, dual recycle feed bins, a 68,194 CFM Pulse Jet Baghouse that includes aramid fiber bags for precise dust control, a variable frequency drive compatible exhaust fan, a 350 DBL dry additive system, three 200 ton New Generation Storage Silos capable of holding mix for up to four days, a large control center equipped with PMII-B Continuous Mix Blending Controls, dual 2 MMBTU Heatec Hot Oil Heaters, three CEI 10,000-gal. AC tanks (two equipped with mixer agitators capable of storing polymer asphalt binders), and a twin pump asphalt metering system.
“The complete plant is capable of maintaining production at an operating elevation of 7,200 feet and using an aggregate supply containing 7 percent moisture content,” Esquivel says. “Most asphalt producers in Latin America rate their asphalt plant production with a 3 percent moisture content; within the US it’s 5 percent; and we rated this plant at a 7 percent because of the high moisture content in the aggregates due to the annual rainfall Mexico City receives.”
A UNIQUE OPPORTUNITY
For Garcia, the equipment agent who coordinated the plant transaction by working with Astec in addressing the specific needs of the city’s asphalt and public works operations, the project presented a unique opportunity to help the city address its asphalt needs in a way that would enhance the entire quarry site.
“The plant we replaced worked and produced the mix the city needed, but it failed to meet the environmental concerns citizens demanded. That’s why the city decided to shut it down three years ago,” Garcia explains. “It’s a very unique location in the center of city. It used to be an active quarry with four operating asphalt plants. The quarry operation was shut down 20 years ago and older batch plants were shut down since then. Eventually the one remaining continuous drum plant in operation was replaced with another continuous drum plant, and that’s the one officials shut down when the surrounding neighborhoods voiced their unhappiness.”
That action forced the Mexico City government to rely solely on independent asphalt producers to support its paving crews, but the asphalt director and public works director continued to push city officials to consider investing in another plant that would supply a large portion of asphalt for the city of 20 million residents, who expect their roads be kept in good operating condition.
"I WAS CONFIDENT ASTEC COULD DESIGN A PLANT TO MEET SITE RESTRICTIONS. " —Ramon Garcia, owner, DIMAQ
“I’ve sold Astec products (Roadtec pavers and Shuttle Buggies) for over 40 years, so I felt pretty confident their engineering people could design and build a plant that would meet the site restrictions and produce quality mix without adding unnecessary emissions to the area,” Garcia says.
The site constraints are due to the fact that the city officials wanted to use three-fourths of the quarry location for park and recreation facilities since it is surrounded by residential neighborhoods.
The production issues, on the other hand, are directly related to the high moisture content and site elevation.
“It rains five months of the year and the aggregate stockpiles have a high moisture content that has to be dealt with,” Garcia says. “The elevation is another issue. The drum and baghouse components must account for the need to move more heated air to dry the aggregate in a high-altitude environment.
“Paving operations are conducted at night when streets can be shut down. They (asphalt and public works operations) wanted a 250 TPH that could produce the quantity of material required to complete a project between 12 and 4 a.m.” he adds. “This operation has three different and distinct operations throughout a 24-hour period. During the day much of the production is for patching work. Then the plant switches over to main paving projects by producing and stockpiling mix needed before the overnight work begins.”
As Garcia points out, the new plant system allows operators to easily switch mix designs because of the automatic controls for drum rotation and the V-flights that produce a wider veil of material in the drum.
“I think the authorities involved in operating the plant, as well as the government officials who supported the acquisition of the plant, all support the advantages cutting-edge technology offers and are willing to investigate leading production and paving approaches, like warm mix and high-RAP,” Garcia says. “The plant produced approximately 500,000 tons during its first year (2017) of operation and I expect next year the demand will be much greater. They know they now have a green facility that reduces the emissions, and they will further explore increasing the use of warm mixes and high-RAP mixes to further promote an environmentally-friendly operation.”