OBSERVATIONS ON DRYING AND HEATING OF AGGREGATES

RESULTS ARE PRESENTED OF RECENT STUDIES ON THE HEATING AND DRYING PROCESS OF AGGREGATES FOR PRODUCTION OF HOT-MIXED ASPHALTIC CONCRETE. MOISTURE DETERMINATIONS IN AGGREGATE TEMPERATURE STUDIES WERE CONDUCTED. MOISTURE TESTS SHOW THAT COARSE AGGREGATE DISCHARGED FROM THE DRYER CONTAINS 3 TO 4 TIMES AS MUCH RESIDUAL MOISTURE AS DOES FINE AGGREGATE. TEMPERATURE OF THE SAND WAS FOUND TO BE GENERALLY HIGHER THAN THAT OF STONE AT BOTH DRYER AND HOT-BIN DISCHARGE POINTS. MOISTURE PROBLEMS APPEAR TO BE RELATED TO CONCURRENT LARGE DIFFERENCES BETWEEN SAND AND STONE BIN TEMPERATURES AND LARGE DROPS IN COARSE AGGREGATE TEMPERATURES BETWEEN THE DRYER DISCHARGE AND HOT-BIN DISCHARGE GATE. DRYER TEMPERATURE GRADIENT MEASUREMENTS DETECT THE EFFICIENCY OF HEAT PENETRATION INTO THE AGGREGATE ALONG THE LENGTH OF THE DRYER, AND ARE ALSO SENSITIVE TO CHANGES IN MOISTURE CONTENT, FEED RATES, STACK GAS VELOCITY, AND FLIGHT DESIGN. THREE ZONES OF HEAT TRANSFER EXIST IN THE DRYER, BUT BOUNDARIES BETWEEN THESE ZONES ARE NOT AS SHARP AS NOTED IN LABORATORY CURVES OF TEMPERATURE VERSUS TIME FOR HEATING INDIVIDUAL STONE PARTICLES. DATA DEMONSTRATE THAT STONE IS HEATED BY TRANSFER OF HEAT FROM THE FINE AGGREGATE, AND THAT CONSIDERATION OF METHODS OF IMPROVING SUCH A MODE OF HEAT TRANSFER MIGHT BE OF VALUE IN IMPROVING DRYER OPERATION AND EFFICIENCY. THE TIME THAT AGGREGATE IS IN THE DRYER OR RESIDENCE TIME STUDIES INDICATE THAT THEORETICAL RESIDENCE TIME AND THE PERCENT HOLDUP CALCULATED BY FRIEDMAN-MARSHALL EQUATIONS SHOW A QUALITATIVE RELATIONSHIP WITH THE ACTUAL RESULTS OBTAINED. STOICHIOMETRIC CALCULATIONS WERE MADE TO COMPUTE HEAT AND MATERIAL BALANCES. HEAT TRANSFER COEFFICIENTS DETERMINED BY HEAT MATERIAL BALANCES ARE OF VALUE IN DETERMINING DRYER CAPACITY. THE FUEL OIL REQUIRED PER TON OF AGGREGATE INCREASES DIRECTLY WITH THE MOISTURE CONTENT OF THE AGGREGATE BEING DRIED. THE VOLUME OF EXCESS AIR IN STACK GASES INCREASES AS FEED RATE AND AGGREGATE MOISTURE CONTENT DECREASE.

• Supplemental Notes:
  • Vol 34, pp 149-193, 12 FIG, 20 TAB, 33 REF
• Authors:
  • Parr, W K
  • Kole, L L
• Conference:
  • Assoc Asphalt Paving Technol Proc
• Publication Date: 1965-2

Subject/Index Terms

• TRT Terms: Aggregates; Asphalt concrete; Coarse aggregates; Driers (Devices); Drying; Fine aggregates; Fuel oils; Heat transfer; Heating (Structures); Hot mix asphalt; Mathematical analysis; Moisture content; Sand; Stoichiometry; Stone; Storage facilities; Temperature; Temperature gradients; Testing
• Uncontrolled Terms: Capacity
• Old TRIS Terms: Aggregate drying; Bins
• Subject Areas: Geotechnology; Highways; Materials; Terminals and Facilities;

Filing Info

• Accession Number: 00210812
• Record Type: Publication
• Files: TRIS
• Created Date: May 24 1994 12:00AM