Document rBkwyax3Z1r000ozk0zargEMv

American Society of Heating and Ventilating Engineers Guide, 1937 Table 3. Drying Time and Conditions for Representative Materials3--Con Material Temperature Deg P Per Cent Relative Humiditt Drtinq Time Tanin and other chemicals (spray dried)................. Tobacco leaves................................................................ Varnish refrigerator boxes. ......................................... 250-300 150-200 85-130 180-200 110 110-140 120-130 120-130 120-130 Vitreous Enamel sheets before firing........................ 170 300 Wallboard fiber insulating, roller type drier.......... .300-385 Wallboard fiber insulating, truck type drier_____ 300-384 Walnuts lOO^ Wheat, com, oats, rice, barley.................................... 180 Wire cloth Japan.........................^ .............................. 200 Wool........... ...................................................................... 105 35 25-35 35-40 35-40 35-40 Instantaneous 12-96 Hrs 12 Hrs 12 Hrs 5-7 Hrs Overnight 6--8 Hrs -f 2 Hrs acclima tion 16--18 Hrs -f 4 Hrs acclima tion 20--24 Hrs -f 4 Hrs acclima tion 15-20 Min 2J4~3 Hrs 24-48 Hrs 24 Hrs 20 Min See references at end of chapter. the common constituents of fuel are shown in Table 4. The heating values of oils are shown in Fig. 7. The sensible heat in Btu contained in the products of combustion of an average fuel oil and various gases is given in Fig. 8. The problem of securing complete combustion in a heater is , important, in order to secure efficiency and the absence of soot formation, ; but unlike the ordinary power or heating boiler, excess air need not be i maintained at a minimum in most cases. Excess air is generally admitted , either in the heater or before the products go into the drier. DESIGN ? In all drying problems, data regarding temperatures, time, and hu- 3 midity must be obtained by experiment or previous experience. Experi- 3 ments are best performed at the temperatures, humidities, and velocities ) to be actually used in the full sized drier, and with full size samples. > The following nomenclature and explanation of terms will be used in j the discussion of drying calculations: j H humidity of air, pounds of water vapor per pound of dry air. G pounds of dry air supplied to' the drier per unit of time, S pounds of stock dried per unit of time in a continuous drier. .S' : pounds of stock charged per batch to a discontinuous drier, 0 time. Q total heat supplied to the drier. 750 Chapter 41--Drying Systems ; = air temperature. ( = stock temperature. = average stock temperature over short time interval, in a batch drier. = wet-bulb temperature, ji = specific heat of the stock. B = total radiation and conduction losses per unit time. 10 = pounds of water per pound of dry stock. r = heat of evaporation of water. j = humid heat of air, heat necessary to raise 1 lb of dry air + H lb of steam IF. Subscript (1) designates conditions at. the point where the material in question (air or stock) enters and (2) where it leaves the drier. Air driers may be divided into two classes, those in which all moisture evaporated from the stock leaves the drier as vapor in the effluent air, and those in which part or all of the moisture is condensed from the air in the drying equipment itself. In any continuously operating drier of the first type the relation between moisture content of the stock and quantity of air required for the drying operation is given by the equation: G (H, - Hi) = S(wi - w,) (2) Table 4. Gas Combustion Constants3 Gab Carbon M olecular W eig ht Heat or Combustion Lbs per Lb or Combuotiblb Cu Ft !sgi per Lb Btu per Lb Required for Combustion Flue Products 0 Gross Net Os AT, Air COt ffsO N, c 12.000 14,140 14,140 2.667 8.873 11.540 3.667 8.873 Hydrogen H, 2.015 187.723 61,100 51,643 7.939 26.414 34.353 8.939 26.414 Oxygen Nitrogen Os 32.000 11.819 Nt 28.016 13.443 Carbon Monoxide CO 28.000 13.506 4,369 4,369 0.571 1.900 2.471 1.571 1.900 Carbon Dioxide Methane co2 44.000 8.548 ____ ____ ch4 16.031 23.565 23,912 21,533 3.992 13.282 17.274 2.745 2.248 13.282 Ethane C.Jh 30.046 12.455 22,215 20,312 3.728 12.404 16.132 2.929 1.799 12.404 Propane C,H$ 44.062 8.365 21,564 19,834 3.631 12.081 15.712 2.996 Sulphur Dioxide SO2 64.060 5.770 Water Vapor HjO 18.015 21.017 Air -- 28.900 13.063 1.635 12.081 All gas volumes corrected to 60 F and 30 in. mercury barometric pressure dry. 751