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Show section. The high temperature excess enthalpy combustion, when applied to boilers, has a significant effect on the reduction of convective section of the boiler. The thermal efficiency of the boiler can be increased by incorporating the conveclive section into the heat surface area. Since the value of specific heat times the mass flow for the flue gases is larger than that for combustion air, by-passing part of the flue gases through the convective section results in maximization of the thermal efficiency for the whole boiler system. The method is called a Balanced-HRS technique. These findings are from the direct results of experimentation on a water tube boiler. The experimental results are supported by calculations using typical value of temperature for the flue gas. The incorporation of a regenerative section into a conventional boiler, results in 3 distinct sections of heat transfer for the whole system, see Fig. 3.6. Steam -<- Air 6ai Wa 0gr (1- <p )Wfi Bw j>_RjC_ 6a2 Wa ' K Ofif trcrti I Ow Ozf <pWo Regenerative Section Radiative Section 0w -Water trcrrj ±Oi_ 0s< </>wg Convective Section 0? Wf- Final Exit Gas from the Boiler Nomenclature: 6 : Temperature (° C ) (p : Bypass Ratio <P : Temperature Efficiency a : Heat Transfer Coefficient (kJ /m2' h) rj : Thermal Efficiency W : Water Equivarent (kJ/h ° C ) (Specific Heat x Mass Flow Rate ) G : Mass Flow Rate (kg/h) F : Heat Surface Area (m2) B W s : Function of W c . W m and W g B W s * : Function oi' W/i , W/r. and W g Q C G : Function of Emissivity Suffix ai : air inlet a2 : air outlet C :convective section R : radiative section g : flue gas gr : regenerative section exit gf : furnace exit 8C w s m f :convective section exit : tube wall : steam : matrix d \ w** ^ Fig. 3.6 Schematic Diagram of Heat Balance between Regenerative, Radiative, and Convective Sections For each section, the relationship between the gas temperature entering and leaving the section as well as its state can be established. This is given by the following equations: Regenerative Section: 0,, =(0ai-0J/(9^-dJ (3.1) Radiative Section: ^=^-0^(0,-6) (3.2) Convective Section: ^ = (^-^)/(^-ej (3.3) 10 11-8 |