Technical Paper T-140
Heating and Storing Asphalt at HMA Plants
Publication No. T-140
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Pages: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
13, 14, 15, 16, 17, 18, 19, 20, 21
This technical paper is published by Heatec, Inc. of Chattanooga, Tennessee, a division of Astec Industries. (Originally published in print in 1999. Revised 11-24-03. HTML version April 2008)
It is hoped that the information contained in the paper will benefit the hot mix asphalt paving industry as a whole. Individual copies may be obtained free of charge by contacting the company.
This paper reflects the considerable experience and knowledge of several individuals at Heatec. Chief contributors were as follows:
- Jim May
- Tom Wilkey
- Michael Swanson
- Jürgen Daub
- Gene Farrow
- John Clayton
- Dave Clum
- Mark Moon
- Bryan Eley
- Frank Eley
The contributors have endeavored to provide factual information in an unbiased way. However, the statements and recommendations are strictly the opinions of the individuals and are not in any way intended as a warranty of the products or materials described.
Hot mix asphalt producers face numerous choices when buying heating and storage equipment for liquid asphalt. Making the right choices is not always easy because there are many things to consider. The first concern is usually the initial cost of the equipmenteven when ample financial resources are available. Although production volume is usually a major factor in equipment costs, it’s by no means the only one. Other factors include such things as whether the equipment needs to be moved frequently, how much land area it will occupy, whether mixes will include polymers, allowable emissions, restrictions on ground water pollution, the types of fuels or energy readily available, and operating costs.
This paper discusses all of these factors. We believe that contractors should have a good understanding of these subjects before purchasing equipment. That way the contractor can buy with confidence, without fear of costly surprises later.
It is easy to focus on the initial cost of equipment and overlook how much it will cost to operate over its life. The life expectancy of the better equipment sold today is 20 years or more. So, operating costs can add up to a lot of money over 20 years and may greatly exceed the initial cost of the equipment. Consequently, where there is a choice of equipment with different operating efficiencies, the possible savings in operating costs may significantly outweigh its higher initial cost.
Perhaps the most cost effective way of obtaining higher operating efficiencies is by the appropriate use of insulation. Insulation reduces heat loss significantly, especially on asphalt storage tanks and asphalt piping operating at temperatures of 325 degrees F. Thus, insulation reduces the amount of energy required to replace heat losses, thereby reducing energy costs. So, when there is a choice of insulation thickness, it usually pays for contractors to obtain equipment with the thickest insulation offered.
Contractors should also pay close attention to the thermal efficiencies of heaters. The better heaters offered today have thermal efficiencies of 80 percent and higher. If a plant has an old heater with an efficiency less than 80 percent it may pay to replace it with one of higher efficiency. This is especially true if the plant operates throughout most of the paving season each year.
The more a contractor knows about these many subjects, the more apt he is to get the right equipment and to be satisfied that he made the right decisions. Likewise, he is less likely to be duped into buying equipment that does not fully meet his needs.
AMBIENT TEMPERATURE AND WIND
Please note that calculations for heat losses and heating requirements can vary widely depending upon the assumptions for weather conditions. Calculations in this document are based on an ambient temperature of 70 degrees F and a wind of 10 mph. We consider these conditions to be appropriate for general use. However, it may more appropriate to use a different ambient temperature and wind for a specific area or region. In any case, the reader should understand that the data presented in this document may not be the most appropriate for a specific location even though it is suitable for comparisons within the document.
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