Efficient and consistent drying is one of the biggest challenges in operating an asphalt plant. For example, open-graded friction course (OGFC), stone mastic asphalt (SMA), or High RAP and RAS can cause high baghouse temperatures.
Furthermore, virgin or low RAP mixes, dense graded mixes, and warm mix cause very low baghouse temperatures. For these reasons, plant operators have found it very hard to do everything without physically changing the drum flighting—plus the consequences of these temperature changes can spell real trouble.
Watch the Temperature
If a plant’s dryer exhaust is too cold, then one or more of several problems can arise. Mud can build up in cold end flights, on the bags, in screws, or on walls. Also, the corrosive effects of acid attack can accelerate drum wear.
Conversely, if the dryer exhaust is too hot, then the plant wastes fuel while shortening bag life. Additionally, the plant runs a greater risk of baghouse fires. In either case, without the proper exhaust temperature, the plant suffers from reduced production capacity.
All of this highlights the problem of traditional dryer flighting systems having no flexibility, and adding flights for one mix only causes problems for another. Depending on the mixes a plant has to make, there may be no acceptable balance. In the past, operators have had limited—and often impractical—options when addressing this problem.
Swap flights? Adjustable flights? Air dilution? Adjustable slinger? Duct burner? Is the answer to simply not make certain mixes—or is there a better way?
Patented V-Pack System™
Astec says the solution is its patented V-PackTM system. Designed to enable the plant operator to manage independent control of stack temperature, the V-Pack system reduces fuel consumption, increases production capacity, and allows for greater RAP/RAS utilization and longer bag life. When compared against the traditional limitations stack temperature places on a plant’s operation, the patented V-Pack system is an unfair advantage. The V-Pack allows the plant to run mixes that tend to cause high stack temperature, including high RAP mixes, without loss of speed or fuel efficiency. There is no need to adjust flights regardless of mix designs, which saves significant time and money.
Traditional Flights Cannot Eliminate Spots
Traditional flights must rotate further before angle of repose reaches the tip of the flight. Therefore, hot gas bypassing occurs on one side of the drum. However, V-Flights provide an even veil, and with no holes in the veil, thus hot gas cannot bypass the material. Additionally, V-Flights produce a wider overall veil. Whereas the veiling for standard flights occurs only at the tip, veiling for the V-Flights occurs at the tip and the notch.
Control Veil Density
When used in conjunction with a variable frequency drive (VFD), V-Flights work to control veil density—another benefit of the V-Pack system. Utilization of a VFD enables running mixes ranging from virgin WMA to high RAP and open grade mixes without flight changes. Use of a VFD with V-Flights gives the operator control of the veil density just by changing drum rotational speed.
C. R. Jackson
A C. R. Jackson plant in Columbia, South Carolina, was experiencing a stack temperature of approximately 385 degrees F (196 degrees C). A dilution air damper was opened to cool the baghouse, but this limited production to 150 TPH (136 MTPH) per hour.
Working with Astec, C.R. Jackson installed a V-Pack system and placed it in operation. As expected, the stack temperature dropped, and the dilution air damper was closed. This increased production to 350 TPH (318 MTPH) per hour. Stack temperature remained consistent between 290 and 300 degrees F (143 and 149 degrees C).
The patented V-Pack system from Astec enables a plant to run a broader range of mix types, resulting in making more total mix, and improves production rates while saving fuel. For those plants looking for a competitive advantage over traditional flights, the V-Pack system changes the rules of the game.BACK TO ISSUE