Integration of Air and Gas Flow Paths P

Integration of Air and Gas Flow Paths P M V Subbarao Professor Mechanical Engineering Department Establish a Continuity from the Beginning to the End….

A General Layout of Steam Generator

Air and Gas flow diagram

Fluid flows in A Rotary Regenerator

Development of Air & Flow Circuits

Draft Required to Establish Air Flow Air in Flue as out

Natural Draft Zref p. A = pref + p Hchimney Tgas Tatm A B

Natural Draft • Natural Draft across the furnace, • Dpnat = p. A – p. B The difference in pressure will drive the exhaust. • Natural draft establishes the furnace breathing by –Continuous exhalation of flue gas –Continuous inhalation of fresh air. • The amount of flow is limited by the strength of the draft.

Mechanical (Artificial)Draft : Induced Draft Essential when Natural Draft cannot generate required amount of breathing through various obstructions. p. A = patm + atm *g *Hchimney p. B = pfan, s Tatm A B B Tgas

Mechanical (Artificial)Draft : Forced Draft Hchimney p. B = patm + gas *g *Hchimney p. A = pfan Tatm A Tgas B

Mechanical (Artifical)Draft : Balanced Draft Hchimney p. A = pfan. b A Tatm p. B = pfan, s B B Tgas

Balanced Draught System

Resistance to Air & Gas Flow Through Steam Generator System

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210 MW POWER PLANT SG Boiler drum Reheater Final Super heater Platen Super heater LTSH Economizer Coal bunker Wind Box Secondary air duct Furnace PA duct APH Flue gas duct F D Fan P A Fan Coal feeder Coal Pulverizer

Pressure drop in Air and Gas Duct Systems Mechanical Energy equation – pressure drop across a flow passage Frictional resistance along flow path: where f = coefficient of friction L = length of the duct, m ddl = equivalent diameter of the duct, m ρ = density of air or gas calculated at the mean gas temperature, kg/m 3 u = cross section average velocity of air or gas in the duct, m/sec

Equivalent diameter for rectangular duct is given as where a and b are sides of the duct, mm. The coefficient of friction for flow through tubes can be approximated as shown below, for 5000 < Re<108, 10 -6< (k/ddl)<0. 01

Minor Losses Calculation of Local pressure drops: where Δp = local pressure drop K = local resistance factor, = density of air or gas at the position of the pressure drop calculated, kg/m 3 u = velocity of air through the fittings m/s.

Pressure drop across a burner pa K = 1. 5 for tangential burner 3. 0 for swirl burner

Pressure drop across heating surfaces Pressure drop across tube bundles: Inline arrangement: K = n K 0 Where n = number of tube rows along the flow direction K 0 = loss coefficient for one row of tubes K 0 depends on σ1 = s 1/d, σ2 = s 2/d , Φ = (s 1 - d ) Where s 1 is lateral pitch & s 2 is longitudinal pitch If σ1 <= σ2 : S 1 K 0 = 1. 52 (σ1 – 1) – 0. 5 Φ – 0. 2 Re – 0. 2 S 2 If σ1 > σ2 : K 0 = 0. 32 (σ1 – 1) – 0. 5 (Φ – 0. 9) – 0. 2 Re – 0. 2/Φ

Staggered Arrangement The loss coefficient is obtained as K = K 0 (n+1) Where K 0 is the coefficient of frictional resistance of one row of tubes K 0 depends on σ1 = s 1/d, Φ = (s 1 - d ) / (s 2 l - d ) Where s 2 l is the diagonal tube pitch given by s 2 l = √ ( 0. 25 s 12 + s 22) and K 0 can be written as, K 0 = Cs Re-0. 27 Cs is design parameter of the staggered banks S 1 S 2

For 0. 17 <= Φ <= 1. 7 and σ1 >= 2. 0, Cs = 3. 2 If σ1 < 2. 0, then Cs given as Cs = 3. 2 + (4. 6 – 2. 7 Φ)(2 - σ1) For Φ = 1. 7 – 5. 2, Cs = 0. 44(Φ+1)2

Pressure drop through rotary air heater Corrugated plate-corrugated setting plate Re >= 2. 8 x 103 f = 0. 78 Re-0. 25 Re < 2. 8 x 103 f = 5. 7 Re-0. 5 Corrugated plate- plane setting plate Re >= 1. 4 x 103 f = 0. 6 Re-0. 25 Re < 1. 4 x 103 f = 33 Re-0. 8 Plane plate- plane setting plate Re >= 1. 4 x 103 f = 0. 33 Re-0. 25 Re < 1. 4 x 103 f = 90/ Re

Ash Collectors • Following Table is used to estimate the pressure drop in Ash collectors. • Cyclone: 15 – 20 m/s 70 – 90% 500 – 1000 Pa • ESP: 1– 2 m/s 99% 100 – 200 Pa

Pressure Drop through Stack where pst = stack pressure drop, Pa f = friction factor Lst = height of the chimney, m D= diamter of the chimney , m Kc = resistance factor at the stack outlet = gas density in the stack, kg/m 3 uc= gas velocity at the chimney outlet, m/s