Guidelines for Energy Auditing of P C Fired Boilers

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
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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

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Steps Involved In Boiler Energy Audit

• Data collection
• Observations and Analysis
• Exploration for energy conservation measures
• Report preparation

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Data Collection
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Data Collection-boiler Specifications
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Data Collection-boiler Specifications
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Data Collection- Economiser
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Data CollectionAir Pre Heater
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Data Collection-flue gas temperature profile
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Data Collection- coal parameters
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Data Collection-boiler heat balance
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Data Collection- mills and burners performance
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Data Collection- coal mill specifications
Type of mill ______________ Make _________ Capac
ity __________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 _____
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Data Collection Soot Blowers
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Data CollectionCase Example of 210/500 MW Unit
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Data Collection Boiler Specifications
37.2
38.7
333
540
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Data Collection Boiler Specification
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Data Collection Economiser

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Data Collection Air Pre Heater
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Data Collection Flue Gas Temperature profile
210 MW
500 MW
Unit
0C
0C
0C
0C
0C
0C
0C
0C
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Data Collection Heat Balance
 c1Manufacturer Margin ).5
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Data Collection Recommended Boiler Water
Parameters
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Data Collection Fuel Parameters
Unit
110 MW
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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

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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

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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

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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

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Instruments Required For Boiler Auditing
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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 )

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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

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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

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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.

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Data Analysis
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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

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Data Sheet Boiler Efficiency Evaluation
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Data Sheet Boiler Efficiency Evaluation
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Data Sheet Boiler Efficiency Evaluation
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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
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Computation of Boiler Losses
2. Loss due to unburnt carbon in ash
3. Loss due to moisture in fuel
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Computation of Boiler Losses
5. Loss due to moisture in air
Where AASActual mass of air supplied Humidity
humidity of air in kg/kg of dry air
6. Loss due to CO in flue gas
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Efficiency evaluation of Boiler
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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)
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Energy Audit- Coal Milling System
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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

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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

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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.

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Energy Audit- Coal Milling System
Observations
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Energy Audit- Coal Milling System
Coal fineness
Mill rejects
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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.

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PERFORMANCE OF AIR PREHEATERS
Air leakage estimation in APH The following
gives the air leakage in to the (APH) system
if the 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
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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.
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PERFORMANCE OF AIR PREHEATERS
Theoretical
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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

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EXPLORATION OF ENERGY CONSERVATION OPPORTUNITIES

• 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..

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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.

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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.

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Saving Analysis with improvement in efficiency

• Fuel Saving
• S (?new- ?asis)100/ ?new
• Annual energy savings
• Annual cost savings

?as is the actual system efficiency CMWh
Fuel costs in Rs/MWh where MWh1 refers to energy
in the fuel PLF plant load factor as a fraction

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Case Study1. Optimization of Excess Air 2.
Optimization of PA to SA
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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

• Observation
• Excess Air and cold air
• Ingress also causes ID fan loading
• Excess FG temp. at APH

• Causes Actions
• Worn out seals and heat Transfer
  elements-Attended
• Leakage through peep/port
• holes-Attended
• Soot formation on the heat
• transfer area- S B done

• Results
• 2.83 effciciency impr. in
• Reduction Coal consumption By 74490 T/A
• Rs.63.09 saving (Rs. 847 /T)

Efficiency Evaluation of 500 MW unit
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Optimization of PA to SA
Observation (120MW unit) Higher PA to SA ratio
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 1480
Fan regulation type Inlet damper control Inlet damper control Blade pitch control Blade pitch control
Fan motor rating kw 900 900 400 400
Operating parameters Operating parameters Operating parameters Operating parameters Operating parameters Operating parameters
Air Flow M3/sec 65.27 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
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
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Thanks