3.igen ea boiler
DESCRIPTION
HEAT EXCHANGERS m.pptTRANSCRIPT
Guidelines for Energy Auditing of
P C Fired Boilers
Surender KumarDeputy Director,NPTI
Boiler Schematic
Water & Steam cycle
Fuel System
Air & flue gas Flow Path
Ash/ rejects Handling System
Performance Parameters
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
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
Boiler Aspects For Study
Steps Involved In Boiler Energy Audit
Data collection
Observations and Analysis
Exploration for energy conservation measures
Report preparation
Data Collection
Data Collection-boiler SpecificationsParticulars Unit Details at Normal
cont. rating, NCRMake 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
Unit Design/NCR Actual
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
Data Collection-boiler Specifications
Unit Design Actual
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
Data Collection- Economiser
Unit Design Actual
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 afterAPH
%
Flue gas inlet temperature oC
Flue gas outlet temperature oC
Flue gas quantity tph
Data Collection:Air Pre Heater
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
Data Collection-flue gas temperature profile
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
Data Collection- coal parameters
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
%
Data Collection-boiler heat balance
Unit Requirement at NCR
Actual Remarks
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
Data Collection- mills and burners performance
Type of mill ______________ Make _________
Capacity __________tph at coal ________grind Fineness ___________% through ________mesh
Motor rating ____________kWMotor voltage ________ V No of mills :__________
Running /Standby _________/________ Design coal parameter
Moisture _____% Ash _____%Volatile matter _____%Fixed carbon _____% HGI _____%
Data Collection- coal mill specifications
Type Number
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
Data Collection: Soot Blowers
Data Collection:Case Example of 210/500 MW Unit
Main Boiler NCR
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
Data Collection: Boiler Specifications
333
540
38.7
37.2
Total combustion air
tph 791 1853
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
Data Collection: Boiler Specification
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
Data Collection: Economiser
%
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
Data Collection: Air Pre Heater
Flue Gas Temperatures
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
Data Collection Flue Gas Temperature profile
0C
0C
0C
0C
0C
0C
0C
0C
210 MW 500 MWUnit
Heat Balance 210M 500MW
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
Data Collection: Heat Balance
Recommended FW limits
Unit Feed water
Boiler Water
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
Data Collection: Recommended Boiler Water Parameters
Fuel Parameters – Ultimate Analysis
500 MW
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
Data Collection: Fuel Parameters
Unit110 MW
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
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
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
Measurements and 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
Measurements & Observations
Instruments Required For Boiler Auditing
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 )
Instruments Required
Digital Manometer of suitable range andappropriate 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
Instruments Required
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
Pre audit Checks
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.
Measurement Locations
Data 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
Observations & Analysis
Data SheetBoiler Efficiency Evaluation
Data SheetBoiler Efficiency Evaluation
Data SheetBoiler Efficiency Evaluation
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 %
Computation of Boiler Losses
2. Loss due to unburnt carbon in ash:
)%()%(,
/
,
BAshBACFAshFACGCVfuelofGCV
kgkcalincarbonofvalueCalorific
LashincarbonunburnttodueLoss uca
GCV
ABTFGTM
LfuelinmoisturetodueLoss mf
100584)(45.0(,
3. Loss due to moisture in fuel:
4. Loss due to hydrogen in fuel:
GCV
ABTFGTH
LfuelinhydrogentodueLoss hf
100584)(45.0(
9, 2
Where H2 – kg of H2 in 1 kg of fuel
Computation of Boiler Losses
5. Loss due to moisture in air:
GCVABTFGThumidityAASLairinmoistureintodueLoss ma
100)(45.0,
Where AAS=Actual mass of air suppliedHumidity = humidity of air in kg/kg of dry air
GCV1005744
%CO%COC%CO
L,xidecarbonmonotodueLoss2
co
GCV100
574428h/kginnconsumptiofuel10ppminCO
L,monoxidecarbontodueLoss
6
co
6. Loss due to CO in flue gas:
Computation of Boiler Losses
Efficiency evaluation of Boiler
Particulars
Unit
DesignValue
Actual value
% Deviation
Remark
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 inAir
%
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 %
BOILER
Boiler Efficiency (Heat in Steam)
Heat loss due to dry flue gas
Dry Flue Gas LossHeat loss due to wet flue gas
Heat loss due to moisture in fuel
Heat loss due to unburnts in residue
Heat loss due to moisture in air
Heat loss due to radiation & other unaccounted loss
5.5%
4.2%
1%
0.3%
1%
1%
87%
100%Heat fromFuel
BoilerHeat Balance
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
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
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.
Energy Audit- Coal Milling System
Energy Audit- Coal Milling SystemObservations
Energy Audit- Coal Milling SystemCoal fineness
Mill rejects
COMBUSTION CONTROL, EXCESS AIR AND COLD AIR INGRESS
While conducting the study, the following need to be verified:
Present excess air and comparison with PG test or design value
Combustion control systems installed and status of operation,
calibration systems
Monitoring and controlling mechanism for oxygen, excess air and reporting systems in place
Effect of excess air on boiler performance
Excess air with respect to boiler load variation
Cold air infiltration in to the system – observe the present method of measurement, estimation, frequency of measurement for estimating the losses and control mechanisms initiated.
PERFORMANCE OF AIR PREHEATERS
Air leakage estimation in APH:The following gives the air leakage in to the (APH) system ifthe Oxygen % is measured at the entry and exit of the APH
Alternatively, if the CO2% is measured in the exhaust gases then the air
leakage is estimated by
PERFORMANCE OF AIR PREHEATERS
Gas side efficiency: The gas side efficiency is defined as the ratio of the temperature drop, corrected for leakage, to the temperature head and expressed as percentage.
Temperature drop is obtained by subtracting the corrected gas outlet temperature from the inlet. Temperature head is obtained by subtracting air inlet temperature from gas inlet temperature.
PERFORMANCE OF AIR PREHEATERS
Theoretical
Total air = PA+ SA+ Seal air tph
EXPLORATION OF ENERGY CONSERVATION OPPORTUNITIES
Boilers:Steam and water parameters ( flow, pressure and temperature )
Air and gas parameters ( flow, pressure and temperature )
Burners operation
Primary and secondary air ratios and temperatures
Air infiltration in to boilers
Unburnt loss reduction
Combustion control – boiler excess air, O2 Measurement inaccuracy or unbalance
Dry flue gas loss
Insulation
Air infiltration to flue gases
Water quality, Blow down and its control
Stack Temperature Boiler Soot Deposits, High Excess Air , Air inleakages before
the combustion chamber, Low Feed Water Temperature , Passing dampers and poor air heater seals , Higher elevation burners in service, Improper combustion…
Incomplete Combustion Poor milling i.e. Course grinding, Poor air/fuel distribution to
burners, Low combustion air temperature, Low primary air temperature, Primary air velocity being very high/very low, Lack of adequate fuel/air mixing…..
EXPLORATION OF ENERGY CONSERVATION OPPORTUNITIES
Dry flue gas loss. Air in-leakage through man holes, peep holes,
bottom seals, air heater seal leakage, uneven distribution of secondary air, inaccurate samples/analysis.
Poor automatic boiler SADC, burner tilting, O2 control….
Radiation and convection heat loss. Casing radiation, sensible heat in refuse, bottom
water seal operation, not much controllable but better maintenance of casing insulation can minimize the loss.
EXPLORATION OF ENERGY CONSERVATION OPPORTUNITIES
Blowdown.
1 % of blow down carries a 0.17% heat added, in the boiler, 0.25% heat is required to make up accounts to 0.42% so blow down to be adhered to the chemist requirement.
Scaling and soot losses.
Super heated steam with high enthalpy is used. 1% of steam may be required, contains 0.62% heat
content, to make up the loss another 0.25% heat to be added to feed water resulting total heat loss of 0.87%.
Frequency of soot blowing must be carefully planned.
Auxiliary power consumption.
EXPLORATION OF ENERGY CONSERVATION OPPORTUNITIES
Saving Analysis with improvement in efficiency
Fuel Saving S% = (ɳnew- ɳasis)*100/ ɳnew
Annual energy savings
Annual cost savings
ηas is = the actual system efficiency CMWh = Fuel costs in Rs/MWh where MWh1 refers to energy in the fuelPLF = plant load factor as a fraction
Case Study:
1. Optimization of Excess Air 2. Optimization of PA to SA
Optimization of Excess Air
Parameter Design measured
Excess air at boiler exit % 19.0 23.6
Excess air at APH exit % 28.0 55.6
FG temp. at APH exit 0c 146.0 167.6
Dry Flue gas loss % 5.08 8.89
Heat loss due to CO % 0 0
Heat loss due to moisture in air % 0.12 0.18
Heat loss due to moisture and H2 in fuel % 5.95 5.78
Heat loss due to unburnt in ash % 0.90 0.09
Sensible heat loss in ash % 0.56 0.59
Surface and unaccounted losses % 0.17 0.10
Design margin % 0.5
Total heat losses %(corrected) 12.57 14.93
Thermal efficiency % 87.43 85.07
ObservationExcess Air and cold air Ingress also causes ID fan loadingExcess FG temp. at APH
Efficiency Evaluation of 500 MW unit
Causes & ActionsWorn out seals and heat Transfer elements-AttendedLeakage through peep/port holes-AttendedSoot formation on the heat transfer area- S B done
Results2.83% effciciency impr. inReduction Coal consumption By 74490 T/ARs.63.09 saving (Rs. 847 /T)
Optimization of PA to SA
Type Unit PAF A PAF B FD A FD B
Capacity M3/sec
55 55 58.4 58.4
Total design head
mmwc
1212 1212 450 450
Fan Speed rpm 1480 1480 1480 1480Fan regulation type
Inlet damper control
Inlet damper control
Blade pitch control
Blade pitch control
Fan motor rating
kw 900 900 400 400
Operating parametersAir Flow M3/
sec65.27 56.34 24.8 68.0
Power consumption
kw 920 907 78 185
System Efficiency
% 78.6 67.0 66.5 77.5
Ratio of PA 56.7(40)
43.3(60}
Observation (120MW unit)Higher PA to SA ratio
Result
Adjustment of ratio, power consumption reduced from 2090 kw to 1760 kw
Saving of Rs. 3.22 M/A, cosidering 7500 hrs/year and Rs. 1.30 per kwh
BOILER
Boiler Efficiency (Heat in Steam)
Heat loss due to dry flue gas
Dry Flue Gas LossHeat loss due to wet flue gas
Heat loss due to moisture in fuel
Heat loss due to unburnts in residue
Heat loss due to moisture in air
Heat loss due to radiation & other unaccounted loss
5.5%
4.2%
1%
0.3%
1%
1%
87%
100%Heat fromFuel
BoilerHeat Balance