Record keeping. We all hate the task but it’s important in a well-run business. Without it we wouldn’t be able to track expenses, payroll, or our most important asset: profits. While most of us tend to think of offices when we think of record keeping, there’s another place where it is useful. The asphalt plant.
Daily asphalt plant reports provide information not always readily available to management, like fuel consumption, oil percentages and plant “idle” time. They also provide an inventory record of oil and fuel in case the plant operator isn’t available to ask.
A plant report also is a powerful tool to the alert operator. It can indicate problems with the burner, or with the asphalt oil delivery system. For example: On June 8, a Boeing drum plant belonging to Continental Paving produced 2,970 tons of hot mix. In doing so, it burned 4,455 gal of diesel for a rate of 1.5 gal per ton. Cold feed samples indicate a moisture content of 5.4%. The fuel rate seems high to the operator, so he goes back through his plant reports to May when he first fired the plant after its winter maintenance regimen.
On May 10, he produced 2,125 tons of hot mix, burning 2,550 gal of fuel for a yield of 1.2 gal per ton. A glance at the report indicates cold feed moisture was 5.9%. It’s now obvious to the operator that something has changed and he needs to be looking into it.
A check of fuel filters on the burner reveals a partially plugged filter, which caused a drop in fuel pressure resulting in a higher burner setting to yield the same amount of heat, thus higher fuel consumption. The plugging happened so gradually that the operator never noticed the progressively higher settings he was using on the burner controls.
Without the plant reports to reference, he might have soldiered onward, blissfully unaware that he was wasting 3/10 gal of burner fuel per ton. At $.70 per gal, that equals $.21 per ton wasted. That’s a total of $623.70 for the day.
Spotting oil content problems
Daily plant reports also can point out problems in oil content. Let’s use a Stansteel, RM-80 batch plant as an example. On Aug. 12, the second day of a major state contract, All State Paving received the results from state sample #4, sublot 1. As its predecessor did, the sample shows an oil content of 6.7%, a tenth of a percent out of spec and in penalty territory. The previous day’s samples indicated a range of 6.3% to 6.5%.
Because the target value was 6.1%, the plant operator reduced the batch menu oil content by .3%, expecting a 6.0% on his next test. When this didn’t happen, he fell back on the traditional asphalt plant operator’s defense: The state got a couple of inaccurate tests or the nuke gauge is faulty.
In the example above, an investigation later revealed that the oil content listed by the state was correct. This particular plant uses an external oil weigh pot. The problem was traced to a build-up of asphalt/aggregate in the hole under the oil distribution bar where it enters the pug mill. The material restricted the downward movement of the scales as they loaded up, causing the scale outputs to indicate a weight lighter than reality. This forced an excessive amount of oil to be loaded in order to satisfy the batching computer’s demand for a set weight.
Because this condition did not occur overnight, it is a fair assumption that if the operator had kept daily records of oil consumption he would have noticed that his tank stickings were indicating a progressively higher yield than his plant’s computer was requesting.
In both of the examples cited, a daily plant report proves to be a valuable asset in operations. While the actual amount of dollars saved by a plant report program can be hard to estimate and likely varies from plant to plant, few people would argue that the potential is great.
Other useful information
The plant report also can contain other useful information, like venturi pressure drop, water pressure and gallons per minute for the wet systems. Baghouse data can be substituted where needed. Plant reject and mix wasted also can be tracked. By including a section for operator comments, plant down time also can be recorded. If the plant’s temperature “chart recorder” disk is included a very accurate picture of daily operations emerges.
These forms are not difficult to generate. Modifying one to fit your company’s needs is just a matter of a few minutes on your computer. Because converting most HMA facilities to the metric system requires expensive modifications to ratio and batching computers and existing plant owners aren’t likely to rush to spend unwarranted funds on such things, these forms use Imperial measurements. Feel free to convert them as needed.
Once the form has been finalized to fit a particular company, it can be sent off to the printer. A hard copy with two carbons is a good choice. One copy is for the main office, one for the plant superintendent and the hard copy stays at the asphalt plant. In some states, asphalt plants are required to provide asphalt tank measurements and mix produced tonnages to the plant inspectors at the end of each day. For this purpose, a third carbon can be added, with inappropriate data like fuel consumption and operator comments blanked out. A word of caution: Only provide the information required. It’s amazing how unnecessary and poorly understood data in uneducated hands can sometimes come back to haunt you.
Useful asphalt plant formulas
Production rate
1) A plant loses about 3% of its production rate per 1,000 ft of elevation, due to the thinning of the air.
2) Plants are designed to remove 5% moisture. The higher the moisture, the lower the production rate.
3) To calculate a batch plant’s rate of production choose a weigh point on your aggregate scale (must be in a bin you are waiting on so that the pointer is rising slowly). With a stopwatch, determine the amount of time it takes the scales to return to this point. Time in seconds = (s). Divide into the number of seconds per hour (3,600). Multiply that answer by the average batch size (b). Assume the following: s = 45 seconds and b = 5,000 lb or 2.5 tons.
Example: 3,600/45 = 80 batches per hour and 80 x 2.5 = 200 tph.
4) To calculate a drum plant’s rate of production multiply the aggregate tons per hour (x) times 100% minus the moisture content (y). Add the oil tons per hour (z). Assume the following: x = 209, y = 4.3% and z = 11.76.
Example: 209 x .957= 200.01 and 200.01 + 11.76 = 211.77 tph.
5) To convert horsepower to KW multiply horsepower (h) by .7457. Assume the following: h = 350 hp.
Example: 350 x .7457 = 261 KW.
Asphalt oil
1) To find asphalt % by total mix add oil to aggregate then divide oil by total of the two. Assume the following: 250 tons aggregate used and 5 tons oil used.
Example: 250 agg + 15 oil = 265 and 15/265 = .0566% oil by total.
2) To find the number of gallons delivered on a particular “bill of lading”: Net weight in pounds (x), divide 8.328 (pounds per gal of water, which has a specific gravity of 1.0) = y. Divide y by the specific gravity (z) listed on the delivery ticket for the oil you are using. Assume the following: x = 66,920, z = 1.0273
Example: 66,920/8.328 = 8,035.54 (y); 8,035.54/1.0273 (z) = 7,822 gal @ 60 degrees F.
3) To find asphalt gallons per ton look up AC pounds per gallon at the oil’s temperature (x). Divide that number into 2000. Assume the following: x = 7.81.
Example: 2000/7.81 = 256.08 gal AC per ton at the chosen temperature.
4) To convert gallons of oil to tons look up AC pounds per gallon at the oil’s temperature (x). Multiply that number by number of gallons. Divide that number by 2000. Assume the following: x = 7.81.
Example: 7.81 ppg x 25,000 gals = 195,250 lb/2,000 = 97.625 tons of oil at (x) temperature.
5) To find out how many tons of oil are in an AC tank check the oil temperature (t). Measure liquid and convert inches to gallons (g). Find temperature on the compensation chart and get the conversation factor (f). Read oil pounds-per-gallon* @ 60 degrees (p). Assume: t = 325 degrees, g = 12,834 gal, f = .9105, and p = 8.456.
Example: 8.456 x .9105 = 7.699 ppg @ 325 degrees; 7.699 ppg x 12,834 gal = 98,811.37 lb; 98,811.37 lb/2,000 = 49.41 tons of oil. *Listed on “bill-of-lading.”
6) To figure out how much mix you can make with a given quantity of oil take the tons of oil divided by the percent of oil in mix to equal the yield.
Example: 28 tons/.055% = 509.09 tons of hot mix produced.
7) To find pounds-per-gallon of any oil: Find specific gravity listed on “bill-of-lading” (g). Multiply pounds-per-gallon of water (8.33)* by the specific gravity (g) of the oil. Assume: g = 1.0273 (actual reading for Oregon PBA-2), w = 8.33.
Example: 8.33 x 1.0273 = 8.56 lb-per-gal for the oil @ 60 degrees *Actual ppg of water.
8) To find the U.S. gallons capacity of a cylindrical tank measure the diameter (d) and the length (l). Square the diameter, multiply by length, then multiply by .0034. Assume: d = 95 in., l = 337 in.
Example: 95 x 95 x 337 x .0034 = 10,341 gal.
