PRODUCTION NOTES |
BRANDON NOEL, EDITOR
4zevar/adobestock.com
BATCH VS. DRUM: What To Consider Before You Buy Provided by Astec Industries
Investing in new an asphalt plant? These tips can help you find the best match
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here’s nothing more important than having the right equipment for the job you’re trying to do. But what you really need is not always obvious, and neither is how to decide. In regards to the question of which type of asphalt plant you need, it might seem there are only two answers: batch or drum (continuous). However, there’s no perfect, one size fits all solution, and sorting out which is best for you and your business depends on a few things: • Type of job and production schedule that must be kept • Individual market characteristics (geography, tradition, etc) • Local and regional industry regulation • Short term and long term investment costs (equipment, maintenance, etc.) Since using search engines on the internet can sometimes provide different results every time you use them, we spoke with industry experts to get solid answers, along with pros and cons of each.
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ASPHALT CONTRACTOR SEPTEMBER 2022
THE BASIC DESIGN Before we launch into the first factor, let’s briefly establish a minimum baseline of understanding for the different models of asphalt plants available, as well as their basic designs and function. The oldest and most well-known style of asphalt plant is the batch configuration. Iterations of which were first used as far back as the turn of the 20th century and the most common elements of which are nearly unchanged. Multiple large cold aggregate storage bins hold sorted material based on its size and are drawn together into the drying drums, heated up, passed through multiple screens to re-sort them and stored in a tower of hot aggregate bins. According to the mix, the various hot aggregates are weighed alongside the required amount of sand and other fillers, as well as the binder. One batch at a time, all these weighed materials are mixed together, passed into storage and eventually transported away. Continuous plants operate in virtually the exact same manner and process, except that they bypass the mixing tower and screens, instead opting for a counterflow mixer. The sized cold aggregate is sent to the drying drums according to the design mix, heated,
blended with non-segregated RAP, fillers and the binder all in one non-stop process, that is mixed together continuously and then leaves the drum chamber and is hauled to a job site via truck. When it comes to the continuous, also called “drum” mixers, there are three common variant configurations typically available on the market. Each relates to the way in which the aggregates are introduced in relation to the heat source and air flow: • The older continuous plants are parallel flow drum mixers where the materials proceed in the same direction as the hot gases. • A later variant is the counterflow drum mixer which consists of either a counterflow dryer and a separate external mixer or an elongated combination dryer/mixer drum with the burner head placed part way into the drum to allow mixing with liquid asphalt to occur behind the burner, out of the gas stream. This reduces hydrocarbon emissions and increases fuel efficiency over the parallel flow drum mixer. • The most technologically advanced version of is a double barrel drum mixer, which provides a very uniform dryer in the double barrel drum mixer gives the highest available thermal efficiency. JOB TYPES AND PRODUCTION SCHEDULE Batch style plants may seem to be at a disadvantage, but they still offer one thing that could very well be the deciding factor right at the top: Flexibility in production, especially for small batch sizes. For the contractor who needs to satisfy multiple customers or different projects on a day-to-day or, especially,
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