V-Pack ASTEC THE V-PACK TM
TM In today s market, many asphalt producers are now producing a wide range of mixes at a single plant. Switching between virgin and high RAP mixes, hot mix (HMA) and warm mix (WMA), open-graded and dense graded mixes or significantly varying tonnage rates can cause large swings in stack temperatures. If these temperature swings exceed the limits of the baghouse, adjustments to the flighting arrangement must be made to prevent damage to the baghouse. These changes can be costly and time consuming, especially if new changes will be made when the mix type changes. Astec s V-Pack stack temperature control system uses v-flights and a drum VFD (Variable Frequency Drive) to help facilitate producing many different types of mixes, while controlling stack temperature without the added cost and time of flight changes. V-Pack U.S. Patent No. 8,863,404 B1
Control Stack Temperature Achieve Wider Veil of Aggregates Eliminate Hot Spots Change Mix Designs Easily With No Flight Changes Increase Drum Efficiency Veiling With Competitor s Flights Occurs Only at Tip When a competitor s flight is partially filled, it has to rotate further before the material reaches the tip of the flight. This can cause over showering and a hole in the veil, with the hot gases bypassing the material. TM Veiling With ASTEC s V-Flights Occurs at Tip and Notch With a v-flight, the material begins to veil through the notch sooner, eliminating hot spots. Additionally, the veil on the v-flight is wider. Instead of just showering from the tip, v-flights shower along the edge of the notch as well as the tip. A wider veil increases the effectiveness of the veil by exposing more material to hot gases. The Notch in ASTEC s V-Flights Allows for a More Even Veil of Material The v-flight differs from a standard veiling flight in that it is slightly larger than a standard flight and has a v-shaped notch. The increased size allows the v-flight to carry the same amount of material as a standard flight. The notch allows the flight to more evenly veil at both higher and lower tonnage rates. Open graded and high RAP mixes can have high stack temperatures, which can potentially damage the baghouse and limit production. Increasing the speed of the drum increases the number of times the aggregate can veil through the gas stream. This increases heat transfer and lowers stack temperature. When running large varieties of mixes, utilizing v-flights and VFDs allows producers V-Flight Showering Zone to quickly switch mixes without the need for costly and time consuming flight changes between mixes or less than optimal flighting that compromises efficiency.
TM How Drum Speed Changes Effect Stack Temperature 3 If the actual temperature is different from the set point, the drum speed is adjusted. Control Schematic 2 Actual temperature is compared to the baghouse set point temperature. The control loop established from the baghouse stack temperature probe to the control software to the variable frequency drive maintains the baghouse stack inlet set point temperature similar to an automotive cruise control. If the actual temperature is above the target temperature, the software increases the rotational rate of the drum. Increasing the drum speed increases the number of times the material is veiled through the hot gas stream. Because more particles are in the gas stream, heat transfer from the hot gas to the material increases. The result is that more heat ends up in the material and exhaust temperature decreases. If the actual temperature is below the target temperature, the software decreases the rotational rate of the drum. This decreases the amount of time the material is in the hot gas stream, which reduces the heat transfer from the hot gas to the material. The result is increased exhaust temperature. A 50 F (28 C) Drop in Stack Temperature EQUALS 3% Fuel Savings 1 Baghouse stack temperature is measured at the baghouse inlet. 4 The software instructs the variable frequency drive to increase or decrease drum speed to match the baghouse temperature set point. ASTEC Double Barrel Drum ASTEC Baghouse
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