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Generation and Control of Vacuum in Furnace P M V Subbarao Professor Mechanical Engineering Department Safe and Efficient Combustion Needs Appropriate Furnace Pressure…

Development of Air & Flow Circuits

Total gas side pressure drop Pa where p 1 = total pressure drop from the furnace outlet to the dust collector, Pa p 2 = pressure drop after the dust collector, Pa = ash content in the glue gas, kg/kg pa v = average pressure of the gas, Pa pg o = flue gas density at standard conditions, kg/Nm 3

The ash fraction of the flue gas calculated as, where f h = ratio of fly ash in flue gas to total ash in the fuel A = ash content of working mass, % Vg = average volume of gas from furnace to dust collector calculated from the average excess air ratio, Nm 3/kg of fuel

The pressure drop from the balance point of the furnace to the chimney base is prest = pexit + pgas – pnd where pexit = pressure drop up to the boiler outlet

Draught Losses Total losses p Furnace, SH & RH Losses Economizer Losses Ducts & dampers losses Percent Boiler Rating

ID fan power calculation ID fan power is calculated as:

Air Pressure Losses Total losses p Burner Losses APH Losses Ducts & dampers losses Percent Boiler Rating

Modeling of 210 MW Draught System Duct APH Duct Furnace Back pass Duct APH ESP Duct FD Fan Duct • Pressure drop calculation in air & gas path and its comparison with design value. • Assessment of ID and FD fan power as a function of furnace pressure. ID Fan Chimney

Important variables along air and gas path

Pressure Variation FD Fan uct SCAPH Duct APH D Duct Wind Boiler APH ESP ID Fan Box

Off Design Pressure Variation in Air & Gas Path at Part Load 2500 2000 Pressure (Pa) 1500 1000 500 0 -500 FD Fan Duct SCAPH 1 2 3 4 5 Boiler Duct Wind Box Duct APH 6 7 8 APH 9 ESP ID Fan 10 -1000 -1500 -2000 Path Element Calculated (168 MW) Design (168 MW) 11 12

Operational Data of 210 MW plant

Effect of Furnace Vacuum on Boiler Efficiency

The net effect is saving in energy of 117. 32 k. W due to increase in furnace vacuum from 58. 9 Pa to 230. 6 Pa.

Duct APH Duct Furnace Back pass Duct APH ESP Duct FD Fan Duct New Ideas for Future Research ID Fan Chimney

Analysis of Flue Gas at the ID Fan Inlet • • • Partial pressure of each constituent in flue gas, p. CO 2 = 16. 366209 k. Pa p. O 2 = 1. 138404 k. Pa PN 2 = 68. 142138 k. Pa p. SO 2 = 0. 036081 k. Pa p. H 2 O = 13. 363218 k. Pa Mass flow rate of each constituent in tons/hour is: Mass flow rate of O 2 in the flue gas =13. 2867 tph Mass flow rate of CO 2 in the flue gas = 262. 646 tph Mass flow rate of N 2 in the flue gas = 695. 893 tph Mass flow rate of SO 2 in the flue gas = 0. 84219 tph Mass flow rate of H 20 in the flue gas = 118. 33 tph

Energy Audit of Flue Gas • Temperature of flue gas = 136 ºC – 150 o. C • Dew point of water is (obtained based on partial pressure of 0. 1336 bar) 51. 59 ºC • Cooling of the exhaust gas below the dew point will lead to continuous condensation of water vapour and reduction of flue gas volume and mass. • The temperature of the flue gas in order to remove x% of the available moisture can be obtained using partial pressures of water.

Energy Potential of Flue Gas with 10% water Recovery Partial pressure at 136 C in k. Pa Flue gas constituents Mass flow rate of each Total thermal rate of each constituent at power Enthalpy* at constituent at Enthalpy*at 49. 74 C ( released 136 C (KJ/kg) 136 C ( kg/s) 49. 74 C KJ/kg kg/s) (MW) CO 2 606. 32 3. 69075 527. 85 3. 69 0. 2895 O 2 1. 11 374. 43 72. 9572 294 72. 9 5. 8678 N 2 68. 14 425 193. 303 335. 09 193. 3 17. 3797 S 02 0. 036 487 0. 23413 430. 55 0. 2341 0. 0132 H 20 16. 37 13. 36 2752 32. 8694 2591 30. 444 11. 576 35. 1270

Energy Potential of Flue Gas with 100% water Recovery Mass flow rate of each Mass constituen flow rate Total thermal Flue gas Partial constitue pressure at Enthalpy* at t at 136 C ( Enthalpy at at 0 C ( power released nts 136 C in k. Pa 136 C (KJ/kg) kg/s) 0 C (k. J/Kg) kg/s) (MW) CO 2 606. 32 3. 69075 485. 83 3. 69 0. 444698 O 2 1. 138404 374. 43 72. 9572 248. 35 72. 95 9. 198452 N 2 68. 142138 425 193. 303 283. 32 193. 3 27. 38828 S 02 0. 036081 487 0. 23413 399. 58 0. 2341 0. 020468 H 20 16. 366209 13. 363218 2752 32. 8694 2501 0 90. 45671 127. 5086

Model Experimentation

Expected Performance of the heat exchanger Cooling capacity of the heat exchanger = 10 k. W Cooling load available with the heat exchanger = 115. 3 k. J/kg of flue gas Available rate of condensation of the present heat exchanger = 37. 85 gms/kg of flue gas.

Experimental validation Flue Gas heat exchanger measured data: DATE 1. 2. 10 2. 2. 10 FLUE WATER GAS GAS I/L O/L TO I/L JUST I/L O/L TO HEAT OUTSID TO HEAT EXCHAN E ID EXCHAN GER DUCT GER Temp °C 103 105 121 60 65 69 82 30 32 31 32 29 31 30 32 31 32 DP WAT ER FLOW QTY. OF WATER CONDEN SED cm WC 5 5 5 4. 2 LPM lt. /Hr. 12 10 12 12 1. 1 0. 9 1. 1 1

Calculation of Flue Gas Flow Rate p (cm) Tin 0 C 5 5 5 4. 2 Density (kg/m 3) 60 65 69 82 1. 051754 1. 036203 1. 024089 0. 986604 Flow rate (kg/sec) 0. 007159 0. 007106 0. 007065 0. 006355 Calculation of Condensate Flow rate Gas Flow rate (kg/sec) 0. 007159 0. 007106 0. 007065 0. 006355 MESURED CONDENSATE KG/HR 1. 1 0. 9 1. 1 1 MESURED Condensate CONDENSATE loading (gms/kg of G/SEC gas) 0. 305556 42. 67864 0. 25 35. 17994 0. 305556 43. 25126 0. 277778 43. 70829 Design rate of condensate loading using present heat exchanger = 37. 85 gms/kg of flue gas.

Combustion and Draught Control • The control of combustion in a steam generator is extremely critical. • Maximization of operational efficiency requires accurate combustion. • Fuel consumption rate should exactly match the demand for steam. • The variation of fuel flow rate should be executed safely. • The rate of energy release should occur without any risk to the plant, personal or environment.

Furnace Draught

The Control • Furnace (draft) pressure control is used in balanced draft furnaces in order to regulate draft pressure. • Draft pressure is affected by both the FD and ID fans. • The FD fan is regulated by the combustion control loop, and its sole function is to provide combustion air to satisfy the firing rate. • The ID fan is regulated by the furnace pressure control loop and its function is to remove combustion gases at a controlled rate such that draft pressure remains constant.

Furnace Draught Control

Windbox Pressure Control

Combustion Prediction & Control

The Model for Combustion Control

Parallel Control of Fuel & Air Flow Rate

Flow Ratio Control : Fuel Lead

Flow Ratio Control : Fuel Lead

Cross-limited Control System

Oxygen Trimming of Fuel/air ratio Control

Combined CO & O 2 Trimming of Fuel/Air Ratio Control

Resistance to Air & Gas Flow Through Steam Generator System