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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

Guidelines for Energy Auditing ofP C Fired Boilers

Surender Kumar

Deputy Director,NPTI

boiler schematic
Boiler Schematic
  • Water & Steam cycle
  • Fuel System
  • Air & flue gas Flow Path
  • Ash/ rejects Handling System
boiler aspects for study
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
boiler aspects for study5
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
slide6

Steps Involved In Boiler Energy Audit

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

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

data collection boiler specifications9

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

data collection economiser

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

data collection air pre heater

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

slide12

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

slide13

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

slide14

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

%

data collection mills and burners performance

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

data collection coal mill specifications
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 _____%

data collection soot blowers

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

data collection boiler specifications19

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

data collection boiler specification

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

data collection economiser21

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

%

data collection air pre heater22

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

data collection flue gas temperature profile

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

data collection heat balance

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%

data collection recommended boiler water parameters

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

data collection fuel parameters

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

slide27

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
slide28

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
slide29

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 observations
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

slide32

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 )
slide33

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
slide34

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
slide35

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.
slide37

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
slide38

Data Sheet

Boiler Efficiency Evaluation

slide39

Data Sheet

Boiler Efficiency Evaluation

slide40

Data Sheet

Boiler Efficiency Evaluation

slide41

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 %

slide42

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:

slide43

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:

efficiency evaluation of boiler

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

%

slide45

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)

energy audit coal milling system47
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 system48
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 system49
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 system51
Energy Audit- Coal Milling System

Coal fineness

Mill rejects

slide52

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.
slide53

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

slide54

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 outlettemperature from the inlet. Temperature head is obtained by subtractingair inlet temperature from gas inlet temperature.

slide55

Total air = PA+ SA+ Seal air

tph

PERFORMANCE OF AIR PREHEATERS

Theoretical

slide56

EXPLORATION OF ENERGY CONSERVATION OPPORTUNITIES

Boilers:

  • Steam and water parameters ( flow, pressure andtemperature )
  • 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 Measurementinaccuracy or unbalance
  • Dry flue gas loss
  • Insulation
  • Air infiltration to flue gases
  • Water quality, Blow down and its control
slide57

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…..
slide58

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.
slide59

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.
saving analysis with improvement in efficiency
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 fuel

PLF = plant load factor as a fraction

optimization of excess air
Optimization of Excess Air
  • 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

optimization of pa to sa
Optimization of PA to SA

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