Document pB6y5v19KR8kGXxL9xmdB8brd

HEATING VENTILATING AIR CONDITIONING GUIDE 1941 The left hand member of Equation 13 represents the total amount of available draft created by the pressure transformer, that is, the natural draft chimney, Venturi chimney, or fan, and is equal to the theoretical intensity less the internal losses incidental to operation. The right hand member represents the sum of all of the various losses of draft throughout the entire boiler plant installation outside of the pressure transformer itself. The left hand member expresses the available intensity and is analogous to the head developed by a centrifugal pump in a water works system, while the right hand member expresses the required draft in. . Table 1. Recommended Minimum Chimney Sizes for Heating Boilers and Furnaces8 | Steam Warm Air Capacity m Sq In. op LsADca Pipa Boiles Capacity orSqRPadti ation Hot Rbatbb 8q Ft or Radi ation Nominal DiuenFms Clat Lama in Inches Rectangulab Flub Actual aside Dimensions of FLiirneinCglay In Laches Actual Area 8q In. Round Flub Inside Diam eter of lining Inches Actual Area Sq In. 790 590 1000 690 900 900 1,100 1,700 1,940 2,130 2,480 3,150 4,300 4,600 5,000 5,570 5,580 6,980 7,270 8,700 9,380 10,150 . 1 10,470 973 1,140 1,490 1,490 1,820 2,800 3,200 3,520 4)090 5,200 7,100 7,590 8,250 9,190 9,200 11,500 12,000 14,400 15,500 16,750 17,250 834x13 7 xll^ 81 13x13 lltixllti 127 8M*18 6^x16^ 110 13x18 ilJ*xl6J* 183 18x18 15^x15^ 248 20x20 17Jixl7M 298 20x24 24x24 17x21 21x21 24x246 357 441 576 24 x 28> 28 x 28b 30 x 30b 28 x 32b 672 784 900 896 10 79 12 113 15 177 18 254 20 314 22 380 24 452 27 573 He:gt w Ft Abotb GtUTT 35 40 45 50 55 60 65 laUoi "ofth19M)S H'V`E' ^ f Minimum Requirements for the Heating and Veatt ^Dimensions are for tlnlmed rectangular flues. tensity and is analogous to the total dynamic head in a water works system. For a general circulation of gases where Da. = Dr Da = available draft intensity, inches of water. Dr = required draft, inches of water. (14) The draft loss through thefuel bed (/if) , or the amount of draft required to effect a given or required rate of combustion, varies between wide limits and represents the greater portion of the required draft. In coal-fired 176 CHAPTER 8, CHIMNEYS AND DRAFT CALCULATIONS nations, the draft loss through the fuel bed is dependent upon the ^fwrine factors: (1) character and condition of the fuel, clean or dirty; ml nercentage of ash in the fuel; (3) volume of interstices in the fuel bed, * rseness of fuel; (4) thickness of the fuel bed, rate of combustion; ~?^ype 0f grate or stoker used; (6) efficiency of combustion. ' L js a certain intensity of draft with which the best results will be htained for every kind of coal and rate of combustion. Fig. 7 gives the tensity of draft, or the vacuum in the combustion chamber required to burn various kinds of coal at various rates of combustion. Expressed in ther words, these curves represent the amount of draft required to force ihe necessary amount of air through the fuel bed in order to effect various rates of combustion. It will be noted that the amount of draft increases - .u nprrentaee of volatile matter diminishes, being comparatively low for the lower grades of bituminous coals and highest for the high grades and small sizes of anthracites. Also, when the interstices of the coal are large and the particles are not well broken up, as with bituminous coals,much less draft is required than when the particles are small and are well broken up, as with bituminous slack and the small sizes of anthracites. In general, the draft loss through the fuel bed increases as: (1) the per centage of volatile matter diminishes; (2) the percentage of fixed carbon increases; (3) the thickness of the bed increases; (4) the percentage of ash increases; (5) the volume of the interstices diminishes. In making the preliminary assumptions for the draft loss through the fuel bed, due allowances should be made for a possible future change in the grade of fuel to be burned and also in the rate of combustion. A value' should be selected for this loss which will represent not only the highest rate of combustion which will be encountered, but also the grade of coal which has the greatest resistance through the fuel bed and which may be burned at a later date. 177