Asphalt Industry Incorporates Sustainability at Asphalt Production Plants – Part I
BY Malcolm Swanson, P.E.
Editor’s Note: During the National Asphalt Pavement Association (NAPA) annual meeting on Marco Island, Florida, February 2019, a committee on which I serve discussed the fact an elected representative had asked our industry how we could improve sustainability. The representative wanted to know how the asphalt industry would work to lower greenhouse gas (GHG) emissions, address climate change and so on. The asphalt industry already works with sustainable practices to lower GHGs and keep an already low carbon footprint in check. Recently, a member of the Astec Inc. family, Malcolm Swanson, P.E., gathered information for an 11-page document outlining some of the industry’s sustainable practices. For this warm-mix asphalt (WMA) edition of AsphaltPro, we’ll share Part I of Swanson’s paper, which includes information on our industry’s use of WMA.
If you do a Google search on “sustainability,” you will find many different definitions. Among those you will find it stated that the most common definition is, “Meeting the needs of the present without compromising the ability of future generations to meet their own needs.”
If we view our business operations by that definition, it means that we will operate in such a manner as to be able to continue to operate uninterrupted indefinitely as far as that is affected by the availability of resources and environmental conditions….I think you will agree that operating with sustainability as one of our key principles is not burdensome, but it hugely beneficial in several ways.
The asphalt paving industry already had a great record and story to tell concerning sustainable operating practices before sustainability was seen as having the level of importance that is attributed to it today. The industry did not need the threat of climate change to adopt certain sustainable operating practices, because these practices just made good business and common sense. Some of the most notable examples are as follows:
- Recycling old asphalt pavements
- Paving with warm-mix asphalt
- Using better combustion systems
- Enhance/improve energy use
- Enhance/improve material use
Because asphalt pavements are 100 percent recyclable, reclaimed asphalt pavement (RAP), is a valuable raw material that is relatively inexpensive and readily available, particularly in urbanized areas.
Warm-mix asphalt (WMA), as contrasted with traditional hot-mix asphalt (HMA), went mainstream after 2004 and now accounts for a major share of all new pavements. As the name suggests, WMA is made and laid at considerably lower temperatures than HMA. The reduced temperature means it can be made with less fuel.
Conservation of energy resources and less combustion-source emissions are natural outcomes of replacing HMA with WMA. The use of WMA also virtually eliminates evaporative emissions from the liquid asphalt cement (AC) at the asphalt plant, during the truck haul to the job, and in the paving operations. The road-building industry ha moved rapidly into WMA because it makes sense.
Another good example of applying common sense to a sustainability issue is the advent of fundamentally better combustion systems. When the 1970 Clean Air Act became law in the United States, many combustion processes suddenly had to be cleaner. Industry responded with the introduction of combustion modification technologies such as Exhaust Gas Recirculation (EGR), also referred to as Flue Gas Recirculation (FGR), staged combustion, water injection, ammonia injection, and post combustion treatment technologies like after burners, regenerative thermal oxidizers (RTOs), and catalytic oxidizers. These technologies, though fairly effective in reducing emissions of carbon monoxide (CO) and oxides of nitrogen (NOx), tended to cause decreases in fuel efficiency and power output. Therefore, they actually caused increased GHG emissions.
The design of burners used in drying stone aggregates in the paving industry were not much affected by the Act, due to the industry’s relatively small size and environmental impact, until the passage of the Clean Air Act of 1990 in the United States. About that time, Astec Inc. received an order for a very large asphalt plant to be built in Southern California. Empowered by the new Act, California’s South Coast Air Quality Management District tightened its limitations on NOx emissions to the point that there were no burners available to the industry that could stay under the annual NOx and CO emission limits for such a large plant. Although Astec had recently manufactured other asphalt plants for California paving contractors, successfully using FGR for NOx reduction, the NOx reduction levels required for the new plant were not achievable with FGR.
Astec engineers designed a completely new burner that did a fundamentally better job of combustion than traditional burners. It was a version of a pre-mix natural gas burner that did a better job of mixing fuel and air, and used aerodynamic stabilization and flame shaping to produce a compact flame. The improved combustion did the NOx reduction job without FGR or any of the other combustion modification technologies and it was more fuel efficient than conventional burners. This burner was the predecessor of today’s Astec Phoenix® Phantom and Phoenix® Talon II burners.
Better efficiency means the contractor’s fuel bill was less than it would have been otherwise. It also cleaned up the CO emissions to almost nothing. It made good sense to do well what had not been done so well before.
As a society and as an industry, we do not seem to fully recognize the synergy between practicing sustainability and our profitability. There are probably things done in the name of sustainability and climate change mitigation that do not meet the test of common sense or business sense; but as far as I have seen, such ideas are usually not good for sustainability either. In most instances, the things we would do to try to slow climate change make good common sense and business sense even without a climate change issue. If we run our businesses better, including being wise with our use of energy and materials, we will improve our profitability and, at the same time, we will operate in a more sustainable way.
I think the plants in the industry are generally run wisely; nevertheless, as I travel around the United States and abroad, I continue to see overlooked opportunities. Why not look at asphalt plants and how they should be operated through the lens of sustainability? I have found that, when I look at the design of even mature tried-and-true equipment from a different perspective, I see opportunities I had not seen before.
In Part II of this article, appearing in the August issue, we’ll discuss some of those opportunities in depth. We’ll take a look at additional ways to reduce combustion source emissions while reducing the fuel spend through the enhanced and improved use of energy and materials at the plant.
Malcolm Swanson is the vice president, innovative products, for Astec Inc., Chattanooga.