By Ed Misajet
The word “innovative” is often tossed around loosely in today’s asphalt industry. Sometimes, what manufacturers describe as an innovative design is nothing more than a copy of some similar idea that already existed. While embracing new technology can be an enormous risk, such risks can pay big dividends, if pursued correctly.
One such technological innovation may be a recycling system built by Burke Heating Systems of Shelbyville, Kentucky. Known as the RapSaver™, this patent-pending design is a completely self-contained recycling system that assists the main asphalt plant increase production, lower operating costs and reduce emissions.
The first prototype of the RapSaver was erected three years ago in Carrollton, Ohio.“The goal was to provide first operation data for maximum process capacity, temperature levels, moisture removal potential, maintenance wear factors, and overall performance efficiency,” says Jerry Collette, chief engineer for the RapSaver project.
Why This New System?
The use of reclaimed asphalt pavement (RAP) has become more prevalent. More contractors are recognizing the substantial benefits of utilizing this resource. Costs for fuel, aggregate and liquid asphalt have skyrocketed since the mid-80s. Many federal and state specifications now allow RAP in a variety of applications. So, many hot mix asphalt (HMA) producers are looking for ways to maximize the use of RAP, while working to minimize some of the problems normally associated with using RAP, such as blue smoke and other environmental concerns.
How Does it Work?
The RapSaver is a unique design when compared to most standard recycling systems. Most RAP systems simply size the material and introduce it directly into the production process; Burke’s system is different. The RapSaver is a preheating system comprised of a continuously fed, sealed conductive heating system. This approach allows cold, wet RAP to be heated and dried using a slow moving, hollow screw heating auger and a heated trough. Heat exchange fluid is brought to a temperature of about 600ºF with a direct-fired tube-in-tube exchanger or helically coiled hot oil heater.
The hot fluid is pumped through the hollow jacket and the hollow auger flights, slowly elevating overall RAP temperatures to 165º to 185ºF with a portion of the smaller particles reaching 350ºF.In a single pass, with variable 4- to 12-minute dwell times, a process flow rate of 80 to 100 tons per hour can be achieved, depending upon moisture content. With inlet RAP moisture contents of 5 percent or less, RapSaver has been able to dry the RAP to 1 percent or less moisture in a single pass.
A Shared Interest
The Shelly Company, a subsidiary of Oldcastle Materials Group, a large HMA producer, with 47 plants in the state of Ohio, had shown keen interest in the RapSaver prototype. After several factory visits to Burke’s manufacturing facility, president, Jim Tharp, and operations manager, Paul Protengeier, were impressed with the RapSaver concept and production capacity. They decided to install one at their plant site in Columbus, Ohio. “RAP is here to stay and we felt that we need to know, and do, more about using it,” stated Protengeier.
The Shelly Company recently purchased a Wiz Bang crushing plant manufactured by Astec in order to maintain maximum control of material sizing. “We wanted a very uniform product and utilizing the Wiz Bang to pre-crush the RAP before sending it to the RapSaver is ideal,” said Protengeier.
The RapSaver unit operating at Shelly’s plant has a 24-foot, 48-inch diameter screw with a heat exchanger firing-potential of 9.3 million BTUs. The unit operates under a hot oil heater permit and does not produce odors or particulate emissions. A portion of the heated air from the exhaust stack of the heat exchanger is ducted back into the head space above the rotating auger. This “heated sweep air” removes the moisture in the RAP as steam to the atmosphere or sends it back into the inlet of the thermal oxidizer system. The oxidizer system is a component part of the heat exchanger combustion zone and assures emissions quality at all operating temperatures and capacities.
“We knew, when we saw the test at Carrollton, that the RapSaver system had the potential to allow us to pre-heat and pre-dry a portion of our RAP feed stream going in to our 450 tons per hour (tph) Astec Double Barrel plant,” said Protengeier. Shelly runs anywhere from 350 to 450 tph, depending upon moisture contents of the virgin aggregates and RAP. The RAP contents range from 25 to 40 percent, again depending upon moisture and mix design parameters.
“We are hoping that RapSaver will boost the overall productive output capacity of the plant while allowing us to consistently run the highest RAP percentage that we can. It had been very wet during the start-up phase. And we have really given the unit a tough run. We ran actual moisture samples on what we call our ‘black sand’ which is 1/2-inch minus material. One day we were at 8.0 percent moisture, but it has generally been running 6.5, 6.6 and 6.7, due to these daily showers we have been getting,” according to Protengeier.
Average summer moisture contents in central Ohio run around 3.5 to 4.5 percent. “The steam was flying everywhere and the unit did a pretty good job of keeping up, but that high of a moisture was clear out of sight. We can’t ask it to perform to capacity with this kind of moisture during heavy rainfalls. But we wanted to see how well it did under extreme conditions while we had the opportunity,” said Protengeier.
Shelly plans to run the unit 10 to 14 hours per day in order to get a good baseline on the system. “This is the first continuous, high production installation of the unit and we intend to stretch it out. If all goes well during the next two months, we are discussing plans to expand the system in 2007 so we can run 200 tons per hour to serve more than one plant. The guys at Burke have been great during installation, and the bad weather made it even tougher. They are staying with us to complete testing, and gathering operating data through the 2006 season. If it performs as we think it will, it’s going to give us a whole new perspective on the value of recycling RAP,” said Protengeier.
|Ed Misajet is the principal of Infinite Images Inc. in Louisville, Kentucky.|