Document Q9KZQDJ9zYKZwY2j424eK1Go

American Society of Heating and Ventilating Engineers Guide, 1934 corresponding height and diameter can then be determined from Equa tions 6 and 7, respectively, and the economical size will then be attained. Equations 6, 7 and 9 may be simplified considerably for average operating conditions in an average size steam plant by assuming the following conditions: Average chimney gas temperature, 500 F..... ....................... Tc = 960 Mean atmospheric temperature, 62 F.... ................................ T0 = 522 Average coefficient of friction, 0.016............................................/ = 0.016 Average chimney gas density, 0.09........ Wc = 0.09 Sea level elevation with barometer of 29.92........ Ba = 29.92 Substituting these values in Equations 9, 7 and 6, respectively, and reducing: Ve = 13.7W1/S (10) . D = 1.5W'2/5 (U) H = 190Z>r , (12) Fig. 7 gives the economical chimney sizes for various amounts of gases flowing and for required draft intensities as computed from Equations 10, 11 and 12. They are based on the operating factors used in reducing Equations 6, 7 and 9 to their simpler form. The sizes shown by the curves in the chart should be used for general operating conditions only, or for installations where the required data necessary for an exact deter mination are difficult or impossible to secure. Whenever it is possible to secure accurate data, or the anticipated operating conditions are fairly well known, the required size should be determined from Equations 6; 7 and 9. The recommended minimum inside dimensions and heights of chimneys for small and medium size installations are given in Table 1. GENERAL EQUATION The general draft equation for a steam producing plant may be stated as follows: Dt -- hi = hp + Ab + *Bd + he + hBr + hv + ho + He + Hr (13) where Dt = theoretical draft intensity created by pressure transformer, inches of water. hi = draft loss due to friction in pressure transformer, inches of water. hp -- draft loss through the fuel bed, inches of water. Ab = draft loss through the boiler and setting, inches of water. ... /iBr = draft loss through the breeching, inches of water: hv = draft loss due to velocity, inches of water. ABd = draft loss due to bends, inches of water. Ac = draft loss due to contraction of opening, inches of water. ho = draft loss due to enlargement of opening, inches of water. Ae = draft loss through the economizer, inches of water. Ar = draft loss through recuperators, regenerators or air heaters, inches of water. The left hand member of Equation 13 represents the total amount of available.draft created by the pressure transformer, that is, the natural 356 Chapter 26--Chimneys Table 1. Recommended Minimum Chimney Sizes for Heating Boilers and Furnaces f Warm Air Furnace Capacity inSqIn. op Leader Pipe Steam Boiler Capacitt Sq Ft op Radi ation 790 1000 590 690 900 900 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 10,470 Hot Water Heater Capacitt 8q Ft op Radi ation Nominal Dimen sions op Fire Clat Lining in Inches ' Rectangular Flub Actual Inside Dimensions of Fire Clay ' Lining in Inches Actual Area Sq In. Round Flue Inside Diam eter of lining in Inches Actual Area Sq In. 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 8^x13 7 xllM 81 13x13 liKxll M 127 8^x18 6% x 16)4 110 13x18 11)4x16)4 183 18x18 15)4x15)4 248 20x20 17Mxl7)4 298 20x24 24x24 17x21 21x21 24x24* 357 441 576 24x28* 28x28* 30 x 30* 28x32* 672 784 900 896 10 12 15 18 20 - 22 24 27 79 113 177 254 314 380 452 573 Height in Ft Above Grate 35 40 45 50 55 60 65 Dimensions are for unlined rectangular flues. tThis table is taken from the A.S.H.V.E. Code of Minimum Requirements for the Heating and Venti lation of Buildings (Edition of 1929). draft chimney, Venturi chimney, or fan, and is equal to the theoretical intensity less the internal lossesrincidental 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 tensity and is analogous to the total dynamic head in a water works system. For a general circulation of gases then 9a=Or where Da. = available draft intensity, inches of water. Di = required draft, inches of water (14) The draft loss through thefuel bed(hF), orthe 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 installations, the draft loss through the fuel bed is dependent upon the following factors:^ (1) character and condition of the fuel, clean or dirty; (2) percentage of ash in the fuel; (3) volume of'interstices in the fuel bed, 357