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Guidelines for Energy Auditing of P C Fired Boilers

Guidelines for Energy Auditing of P C Fired Boilers. Surender Kumar Deputy Director,NPTI. Boiler Schematic. Water & Steam cycle Fuel System Air & flue gas Flow Path Ash/ rejects Handling System. Performance Parameters . Boiler Aspects For Study .

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Guidelines for Energy Auditing of P C Fired Boilers

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  1. Guidelines for Energy Auditing ofP C Fired Boilers Surender Kumar Deputy Director,NPTI

  2. Boiler Schematic • Water & Steam cycle • Fuel System • Air & flue gas Flow Path • Ash/ rejects Handling System

  3. Performance Parameters

  4. Boiler Aspects For Study • Coal quality - composition and calorific value • Coal milling aspects • Combustion and excess air • Reheaters • Heat recovery units – Economisers, air-preheaters etc. • Insulation aspects

  5. Boiler Aspects For Study • Operation and maintenance features which affect the energy efficiency • Boiler blow down aspects • Soot blowing aspects • Condition & status of boiler and their internals • Feed water system aspects • Air and flue gas system aspect

  6. Steps Involved In Boiler Energy Audit • Data collection • Observations and Analysis • Exploration for energy conservation measures • Report preparation

  7. Data Collection

  8. Particulars Unit Details at Normal cont. rating, NCR Data Collection-boiler Specifications Make XXXXXX Type Water Tube Single Drum Capacity tph 627.32 Main Steam pressure kg/cm2 155 Main Steam temperature 0C 540 Boiler efficiency % 87.16 Super heater outlet flow tph 627.32 Reheater outlet flow tph 565.6 Calorific value –GCV kcal/kg 4350 Coal consumption tph 106.2 Total combustion air tph 822 LTSH outlet temperature 0C 420 Reheater outlet temperature 0C 540 Water-economizer inlet temperature 0C 241 Water-economizer outlet temperature 0C 280 Oxygen content at Economizer outlet % 4.23

  9. Unit Design/NCR Actual Data Collection-boiler Specifications Make Type Year of Installation Main Steam Pressure kg/cm2 Main Steam Temperature oC Main Steam Flow tph Steam pressure at LTSH outlet kg/cm2 Steam temperature at reheater inlet oC Steam temperature at reheater outlet oC Steam pressure at reheater inlet kg/cm2 Steam pressure at reheater outlet kg/cm2 Steam temperature at LTSH out oC Saturated steam temperature in drum oC Super heater platen outlet temperature oC Maximum pressure drop in reheater Kg/cm2 Super heater spray tph Reheater Spray tph Ambient temperature oC Coal consumption tph

  10. Unit Design Actual Data Collection- Economiser Feed water pressure at the inlet kg/cm2 Feed water pressure at the outlet kg/cm2 Feed water flow tph Feed water temperature at the inlet oC Feed water temperature at the outlet oC Oxygen content in flue gas before/after economizer % Excess air % in flue gas before/ after economizer % Flue gas inlet temperature oC Flue gas outlet temperature oC Flue gas quantity tph

  11. Unit Design Actual Data Collection:Air Pre Heater Air quantity at APH outlet (primary) tph Tempering air tph Air heater outlet (secondary) tph Total combustion air tph Air temperature at fan outlet oC Air outlet temperature of APH – primary oC Air outlet temperature of APH– secondary oC Oxygen content in flue gas before APH % Excess air % in flue gas before and after APH % Flue gas inlet temperature oC Flue gas outlet temperature oC Flue gas quantity tph

  12. Data Collection-flue gas temperature profile Unit Design Actual Super heater platen outlet oC RH front inlet oC RH rear inlet oC SH finish inlet oC LTSH inlet oC Economizer inlet oC APH inlet oC APH outlet oC ID Fan inlet oC ID Fan outlet oC

  13. Data Collection- coal parameters Unit Design Actual Fixed Carbon % Volatile Matter % Moisture % Ash % Grindabiity index HGI Coal calorific value-HHV Kcal/kg Size of the coal to mill mm Total contract fuel fired tph

  14. Data Collection-boiler heat balance Unit Design Actual Ambient temperature oC Excess air % Dry gas loss % Hydrogen loss % Moisture in fuel loss % Moisture in air loss % Unburnt combustible loss % Radiation loss % Un accounted loss % Gross boiler efficiency on HHV %

  15. Unit Requirement at NCR Actual Remarks Data Collection- mills and burners performance No of coal burners No Primary Air Fuel tph No of mills in operation No Mill loading % Air temperature at mill inlet after tempering oC Air – fuel mixture temperature after leaving mills oC Total coal fired tph Air – Fuel Ratio

  16. Data Collection- coal mill specifications Type of mill ______________ Make _________ Capacity __________tph at coal ________grind Fineness ___________% through ________mesh Motor rating ____________kW Motor voltage ________ V No of mills :__________ Running /Standby _________/________ Design coal parameter Moisture _____% Ash _____% Volatile matter _____% Fixed carbon _____% HGI _____%

  17. Type Number Data Collection: Soot Blowers Soot blowers for furnace Soot blowers super heaters Soot blowers for reheaters Soot blowers for air preheaters Medium of blow Steam pressure before reduction Steam pressure after reduction Steam consumption

  18. Data Collection:Case Example of 210/500 MW Unit

  19. Main Boiler NCR Data Collection: Boiler Specifications Make Natural Circulation, balanced draft, double pass, single drum, single re-heat, direct pulverized coal/oil firing, dry bottom type, tangential firing Type XXXXXX (210 MW) XXXX (500MW) Capacity tph 700 1681 Main Steam pressure kg/cm2 154.9 177.2 Main Steam temperature 0C 540 540 CRH Pressure kg/cm2 43.09 HRH Pressure kg/cm2 40.99 CRH Temperature 0C 341.6 HRH Temperature 0C 540 Boiler efficiency % 87.3 88.1 Super heater outlet flow tph 645 1524.27 Reheater outlet flow tph 571 1372.42 Calorific value –GCV kcal/kg 3500 3750 Coal consumption tph 139 299 37.2 38.7 333 540

  20. Total combustion air tph 791 1853 Data Collection: Boiler Specification LTSH outlet temperature 0C 398 Reheater outlet temperature 0C 540 540 Water -economizer inlet temperature 0C 246 253 Water-economizer outlet temperature 0C 292 314 Pressure drop in reheater Kg/cm2 1.5 2.1 Super heater spray tph 3.2 0 Reheater Spray tph --- Ambient temperature oC 27 28

  21. ECONOMISER Data Collection: Economiser Feed water pressure at the inlet kg/cm2 169 193.1 Feed water pressure at the outlet kg/cm2 167.3 191.03 Feed water flow tph 659.4 1524.27 Feed water temperature at the inlet oC 246 253 Feed water temperature at the outlet oC 292 314 Oxygen content in flue gas before economizer % 3.54 3.59 Excess air % in flue gas before economizer  % % 20 20 Flue gas inlet temperature oC 493 356 Flue gas outlet temperature oC 351 136 Flue gas quantityt APH I/L tph 2032 %

  22. Air Pre Heater Data Collection: Air Pre Heater Air quantity at APH outlet (primary) tph 175 257 Tempering air tph 91 283 Air heater outlet (secondary) tph 483 1263 Total combustion air tph 791 1853 Air outlet temperature of APH – primary oC 320 326 Air outlet temperature of APH– secondary oC 324 326 Oxygen content in flue gas before APH % 3.54 3.59 Flue gas inlet temperature oC 351 356 Flue gas outlet temperature oC 136 136 Flue gas quantity tph 2032

  23. Flue Gas Temperatures Data Collection Flue Gas Temperature profile Super heater platen outlet 1165 1119 RH front inlet 1008 1034 RH rear inlet 864 905 SH finish inlet 754 LTSH inlet 637 788 Economizer inlet 493 561 APH inlet 351 356 APH outlet 136 136 210 MW 500 MW Unit 0C 0C 0C 0C 0C 0C 0C 0C

  24. Heat Balance 210M  500MW Data Collection: Heat Balance Ambient temperature oC 27 28 Excess air % 20 20 Dry gas loss % 4.77 4.64 Hydrogen loss % 5.83 5.54 Moisture in fuel loss % Moisture in air loss % 0.12 0.16 Unburnt combustible loss % 1.2 0.60 Radiation loss % 0.11 0.29 Un accounted loss % 1.11 0.40 Total Losses % 13.14 11.50 Heat Credits % 0.44 0.20 Guaranteed efficiency % 87.28 88.10 [c1]Manufacturer Margin ).5%

  25. Recommended FW limits Unit Feed water Boiler Water Data Collection: Recommended Boiler Water Parameters Hardness Nil pH at 25oC 8.8-9.2 9.1-9.6 Oxygen – maximum ppm 0.007 Total iron- maximum ppm 0.01 Total silica – maximum ppm 0.02 Conductivity at 25oC Micor s/cm 0.3 30 Hydrazine residual ppm 0.01-0.02 Total solids – maximum ppb 15 chlorides ppm Copper – maximum ppm 0.005 Permanganate consumption ppm Nil

  26. Fuel Parameters – Ultimate Analysis 500 MW Data Collection: Fuel Parameters Carbon % 37.03 Hydrogen % 2.26 Sulpuer % 0.33 Nitrogen % 0.85 Oxygen % 6.53 Total moisture % 12.0 Ash % 41.0 Gross calorific value Kcal/kg 3500 3750 Fuel Parameters – Proximate Analysis Fixed Carbon % 24.0 28 Volatile matter % 23.0 24 Total moisture % 12.0 8 Ash % 41.0 40 Unit 110 MW

  27. Measurements and Observations • Average GCV of coal • Coal analysis – ultimate and proximate • Coal consumption details • Performance parameters of coal mills • Boiler efficiency • Steam parameters of main steam, reheat, super heater, LTSH (flow, pressure and temperature) • Air – flow, temperature, pressures • Flue gas – Flow, temperature and pressure • Flue gas analysis • Coal consumption pattern

  28. Measurements and Observations • Ambient temperature • Boiler loading • Motor electrical parameters (kW, kVA, Pf, A, V, Hz, THD) etc. • Surface temperatures of insulation and boiler surfaces Other important Parameters • Unit load of the plant • Date & time of measurement • Instruments used for measurement • Frequency of the measurement

  29. Measurements and Observations • Availability factor • PLF • Coal consumption (tons and kg/kWh) • Oil consumption in ml/kWh • Boiler efficiency • Past performance trends on boiler loading, operation, PLF, efficiency • Major constraints in achieving the high PLF, load or efficiency (Input from plant personnel) • Major renovation and modifications carried out in the recent past • Coal – quality and calorific values aspects • Operational failures leading to in efficient operation such as tube failures, constraints for efficient heaters operation

  30. Measurements & Observations • Soot blowers operation • Tripping • Performance of economiser, air preheaters, LP / HP heater from past records • Combustion control system – practice followed • Mills performance • If plant has online and off line tools for performance evaluation of main equipment and BOP equipment – then details of these tools • Plant side initiatives to improve the performance and efficiency of the boiler

  31. Instruments Required For Boiler Auditing

  32. Instruments Required • Power Analyser: Used for measuring electrical parameters such as kW, kVA, pf,V, A and Hz • Temperature Indicator & Probe • Stroboscope: To measure the speed of the driven equipment and motor • Sling hygrometer or digital hygrometer • Anemometer • Available On line instruments at the site ( Calibrated )

  33. Instruments Required • Digital Manometer of suitable range and appropriate probes for measurement of pressure head and velocity head • Additional pressure gauges with appropriate range of measurement and calibrated before audit • Flue gas analyzers / orsat apparatus • Infrared pyrometers • Pressure gauges • Steam trap tester / Ultra sonic leak detectors

  34. Pre audit Checks • Trials are conducted at least for two hours and measurements are to be taken every fifteen minutes • Ensure during Auditing: • Load on the boiler to be by and large constant and represent average loading and normal operation • No soot blowers operated • No intermittent blow down • Preparedness for simultaneous data measurements and collection of various parameters. • Demo exercise for one set of measurement and observation

  35. Measurement Locations • Flue gas analysis at air preheaters inlet / out let • Temperature of flue gas at air preheaters inlet / out let • Fly ash sampling at the economiser outlet and ESP hoppers for unburnt carbon in fly ash • Sample of bottom ash from hopper or scrapper • Sample of raw coal from RC Feeder of the mill for proximate and ultimate analysis of fuel and gross calorific value. • Pulverised coal samples from each mill for sieve analysis. • Sample of mill rejects for GCV.

  36. Data Analysis

  37. Observations & Analysis Operating efficiency of the boiler: • Heat loss due to dry flue gas losses • Heat loss due to moisture in fuel • Heat loss due to hydrogen (moisture of burning hydrogen) • Heat loss due to combustibles in refuse • Heat loss due to radiation • Un accounted losses as per the contract with the Boiler Supplier

  38. Data Sheet Boiler Efficiency Evaluation

  39. Data Sheet Boiler Efficiency Evaluation

  40. Data Sheet Boiler Efficiency Evaluation

  41. Computation of Boiler Losses 1. Dry flue gas loss: Theoretical Air Requirement Actual Air Requirement Dry Flue Gas Quantity (Wd), Kg/Kg of fuel Dry flue Gas Loss Ldfg %

  42. Computation of Boiler Losses 4. Loss due to hydrogen in fuel: Where H2 – kg of H2 in 1 kg of fuel 2. Loss due to unburnt carbon in ash: 3. Loss due to moisture in fuel:

  43. Computation of Boiler Losses 5. Loss due to moisture in air: Where AAS=Actual mass of air supplied Humidity = humidity of air in kg/kg of dry air 6. Loss due to CO in flue gas:

  44. Particulars Unit Design Value Actual value % Deviation Remark Efficiency evaluation of Boiler Date & time of the test Load MW Fuel GCV kcal/kg Loss due to hydrogen in fuel % Loss due to Dry Flue gases, Ldfg % Loss due to moisture in Air % Loss due to unburnt carbon in ash, Luca % Loss due to moisture in fuel, Lmf % Loss due to carbon monoxide, Lco monoxide % Radiation losses % Unaccounted losses & manufacturers margin % Total losses % Boiler Efficiency %

  45. BoilerHeat Balance 5.5% Heat loss due to dry flue gas BOILER 4.2% Dry Flue Gas Loss Heat loss due to wet flue gas 1% Heat from Fuel Heat loss due to moisture in fuel 100% 0.3% Heat loss due to moisture in air 1% Heat loss due to unburnts in residue 1% Heat loss due to radiation & other unaccounted loss 87% Boiler Efficiency (Heat in Steam)

  46. Energy Audit- Coal Milling System

  47. Energy Audit- Coal Milling System Objectives of energy audit : • To evaluate specific energy consumption (kWh/ton of coal) • To establish air to coal ratio of the mills (ton of air per ton of coal) • To evaluate specific coal consumption of the unit (kg /kWh) • Compare the actual consumption with design/pg test values • Suggest ways to optimise energy consumption

  48. Energy Audit- Coal Milling System • Overview of system includes mills, RC feeders, PA fans, seal air fans,mill reject handling system and associated ducts, piping, valves and dampers, lubrication system, thermal insulation status of mills/pa fans ducts/piping etc. • Samples of raw coal, pulverised coal, mill rejects,mill gearbox oil, fly ash and bottom ash

  49. Energy Audit- Coal Milling System • Raw Coal: • GCV, ash content, volatile matter, fixed carbon, total moisture,and HGI value of coal. • Pulverised Coal: • Mill fineness (% passing through 200 mesh), Running hours of mill grinding elements with material composition of each part, Individual RCF coal integrator readings be compared with overall coal integrator readings. • Mill Reject Coal: • Ash content and gross calorific value of mill rejects, FlyAsh, Bottom Ash and Combustibles in fly ash and bottom ash & GCV. • Mill Gear Box Oil: • Viscosity, moisture, mechanical impurities and appearance of lubricating oil of mill gearboxes.

  50. Energy Audit- Coal Milling System Observations

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