MILL OPTIMIZATION

8/11/2019 MILL OPTIMIZATION

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www.AsianSBCUsers.comI 2011 Conference

Presented By:

Richard Storm

Innovative Combustion Technologies, Inc.

Optimizing boiler and coal millperformance

2367 Lakeside Drive, Suite A-1Birmingham, Alabama 35244

(205) 453-0236
http://www.asiansbcusers.com/http://www.asiansbcusers.com/


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OXYGEN AND AIR:

Stratified oxygen at the furnace or boiler

exit

Air heater leakage greater than 10%

Combustion air distribution to theburners exceeds10%

Air in-leakage through the ash hoppers

Air in-leakage through the nose arch,

penthouse or convection pass areas

FOULING AND SLAGGING

Furnace exit S.H. inlet slagging

Fouling of the convention pass and/or the air

heater baskets

Burner eyebrows and waterwall slagging

HIGH GAS TEMPERATURES

Flue gas temperature at the furnace exitis greater than 2,150F (1177C) peak

Stratified flue gas temperatures

Economizer gas outlet temperaturegreater than 750F (399 C Respectively)

Overhead tube metals in the superheater

and the reheater

FANS AND DAMPERS:

I.D. fan capacity inadequate

I.D. and F.D. fan clearances are not

optimum

Damper, register, and fan control

louvers are not timed from 0-100% on

the operating drive or hand control

BOILER DRUM

LEVEL

Uneven furnace

heat release can

contribute to non-

uniform steamgeneration in the

waterwall circuits,

resulting in varied

steam by weight in

the furnace circuitry,

and sometimes tube

failures or steam

purity problems

STEAM AND STEAM

TEMPERATURE CONTROLS

High de-superheating spray

flows

Higher or lower steamtemperatures than design

PULVERIZER AND BURNER LINES FUEL DISTRIBU

TION:

Fuel Imbalances

Primary airflow for the Air/Fuel ratio is not correct

Poor fineness (Less than 75% passing 75 micron & >0.3% not passing 300 micron

Fuel temperatures less than 135F (57C)

Pulverizer rejects high

Mechanical tolerances are out of specification and the burners are not within 1/4

FLYASHFlyash unburned carbon

(LOI) greater than 5% for

bituminous coals and

greater than 0.5% for

subbituminous coals

Electrostatic precipitator

performance reduced due

to ash conductivity or

high carbon content

Symptoms of a Boiler Needing Combustion Optimization


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The Definition of Optimum Combustion is at least these factors:

BlueHighlighted parameters are environmentally driven factors

Highlighted in Greenare heat rate factors of optimum combustion

Completed combustion within the furnace (no Secondary combustion at the Superheater)

Acceptable NOX

Acceptable CO Fly ash unburned carbon satisfactorily

Full load capability and meet all environmental and fuel quality requirements

De-superheating spray water flows minimal

Design Steam temperature attained

No reducing atmosphere in the lower furnace causing waterwall wastage

Primary airflow is optimized No furnace slagging

No convection pass fouling

Minimal Pop corn ash

Burn lowest quality (least expensive) fuel with no adverse consequence

Flames stable and satisfy flame scanners

Satisfactorily low LOI so that ESP performs satisfactorily for minimum opacity


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Common boiler tests to optimize combustion and boiler reliability


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13 Prerequisites For Optimum Combustion

(Ensures Proper and Optimum inputs)

Furnace exit must beoxidizing preferably, 3%.

Fuel lines balanced byDirty Airtest to 5% orbetter.

Fuel lines balanced infuel flow to 10% orbetter

Fuel line fineness >75%

passing a 75 Micronscreen. 300 Micronparticles


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High furnace exit gas temperatures

contribute to overheated metals,

slagging, excessive sootblower

operation, production of popcorn

ash, fouling of SCRs and APHs

Coal pulverizer spillage

from pulverizer throats

that are too large

Non optimum primary airflow

measurement and control ;

Excessive NOXlevels

Flyash Carbon losses

High primary airflows contribute to

unnecessarily high dry gas losses

and also poor fuel distribution and

poor coal fineness.

Bottom ash

carbon content

High furnace exit gas

temperatures contribute to high

de-superheating spray water

flows that are significant steamturbine cycle heat-rate

penalties.

Overall Plant Performance Opportunities

(>50% are Related to the Pulverizers)


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Consequences of Non-Optimum Burner Belt

Performance:

The inputsmust be Optimal

No control of air and fuel after it enters the boiler

High spray water flows to S.H. and R.H.

Tube metal over heating and reliability

problems Slagging and Fouling

Higher NOx

PopcornAsh

SCR Fouling

APH Fouling

Elevated economizer outlet gas

temperature

Burner Belt Performance is never Optimalwith less than perfect Pulverizer Performance


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1. Evaluate Coal Factors that influence mill capacity (Raw Coal

Size, HGI, Moisture, HHV, Fineness, Hp/Ton)

2. Fuel Loading & Feed Rate Control

3. Clean Air Balance within + 2%4. Dirty air flow Balance within + 5%

5. Measured Primary air Hot K Factor calibrations +2-3%

(measured vs. actual)

6. Mill temperature Control, Damper Control and Responsiveness

to Load Control

7. Air-Fuel Ratio /fuel ratios are required for Optimum FlameLengths and Carbon Burnout

8. Total air flow Measurement / Control Optimized ; Balance of

Mass Air & Fuel Flow

9. Fuel line fineness and distribution testing by air/fuel ratio

sampling & ensuring optimum fineness levels of >75% thru 200

mesh (75 micron) & 99.7% thru 50 Mesh (300 Micron)

10. Fuel line balancing through classifier changes or fuel line

distribution modifications to achieve +10%

11. Blueprinting of tolerances, mechanical settings and control

settings

Optimizing Mill and Burner Performance

8


9/45


Poor Pulverizer Performance Increases FEGT by Delaying Combustion

Increased Slagging and Lower Performance

Poor fuel fineness and

distribution aggravates high

center of combustion

Good /uniform mixing in the

burner zone. Burner

mechanical tolerances,

fineness, fuel/air balance

and PA flow proper and

precise

Molten slag on

the furnace wall

Reducing areas w/fuel

stratifications and excessive

CO levels

Sticky plastic slag deposits on

pendants. Slag temperature at or

above ash softening temperature

Excessive de-superheating

water sprays, for both S.H.

and R.H.

Air inlet & outlet flue

gases higher than

design

Tube spacing permits slag

bridging between the tube

assemblies, when the ash is

soft, sticky and/or molten

9


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Importance of Fineness

Higher fineness levels always promote more even distribution of fuel between a mills

separate burner lines.

Better distribution promotes better combustion, inherently lower NOx emissions and lower flyash L.O.I. or carbon content.

Better than 10% fuel balance is not achieved until better than 70% passing 200 Mesh (75

micron) is achieved.


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Major Factors Related to NOX Production

Fixed Factors:

Boiler Design

Fuel Factors

Burner Configuration/Design

Variable Factors:

Pulverizer Performance

Fuel Line Balancing

Combustion Air Balancing and Proportioning

Air In-Leakage


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Thermal NOX

Accounts for approximately 20 - 30% of NOXproduced

Formed from the nitrogen in the combustion air (>2800F)

Fuel NOX

Accounts for approximately 70%-80% of NOXproduced

Formed from the nitrogen in the fuel

Sources of NOXLow NOXPulverized Fuel Firing


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Higher coal fineness will promote less slagging

When combustion is completed lower in the furnace cavity, the water walls

have increased time to absorb heat released from the fuel

Increased heat release in the lower furnace results in a higher proportion ofheat absorbed by the waterwalls

Higher heat absorption by the waterwalls relates to a reduction in furnace

exit gas temperature

Reduction in furnace exit gas temperature resulting from completion ofcombustion in the lower furnace with higher fineness results in lower

slagging propensities and lower NOx.

Understanding the Effects of Coal Fineness

on NOXand/or Slagging


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Burner Stoichiometry differs when fuel is not balanced and NOXis higher

1.17

0.87

0.760.72

1.10

0.90

0.7

0.8

0.9

1

1.1

1.2

1.3Stoichiometry

Fuel

Lean

Fuel

Rich

Fuel

Lean

Fuel

Rich

Very High NOX

Lack of Excess Air to

these burners will yield

secondary combustion

Very High NOX

14


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Effect of Mill Air Flow on NOx, 500 Mw Wall Fired Boiler

Decreasing Mill Air Flow (Primary Air Flow)

NOXreduced by:

Optimized mill air flow

Air flow was high due to

oversized vane wheels coal

spillage with proper air flow.

Improvement in coal fineness.

15


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1. Better Fuel Bound Nitrogen Release (Majority of NOx is fuel derived).

2. Better Fuel Distribution.

3. Permits lower Furnace Excess O2without complications.

Mill Fineness Improves NOx in at least (3) ways

Release of Fuel Bound Nitrogen in the

De-Volatilization Zone

Fuel

Nozzle

Good Fineness Poor Fineness

N

N N

N

N

N

N

N N

N

N

N

N

N

NN

N

N

N

NN

N

N

NN

N

N

N

N

N

N

N

d l l l h


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Secondary air flow

measured to ensure

uniform and proper total

air to fuel ratio between

burner elevations

Pulverizer air flow

measured within 3%;

Critical for best NOX,

slagging and exit gas

temperature

Proper and Optimum Boiler Air Flow Management is Essential to Achieving Lowest NOX

without upper or lower furnace slagging, 725 Mw boiler firing subbituminous coal


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Precise measurement & management of all airflow inputs

to the boiler is ideal


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Proper O2in the right places is needed because combustion must

be completed and carbon to CO2in ~1 to 1.5 seconds at full load


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The Importance of Fuel Preparation

& Furnace Residence Time

Ignition

Major De-volatilization

0.000 0.200 0.400 0.600 0.800 1.00

Heating & Minor De-volatilization

Carbon

Burnout


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Common Mistake:

Low or No CO at Economizer = Optimized Air and Efficiency

Can be false if there are large furnace imbalances or boiler setting air ingress; COcan continue to burn into the convection pass.

1.0% O2

8,000 PPM CO 1.9% O2

500-1200 PPM CO

3% O2

150 PPM CO

0.5% O2> 30,000 PPM CO


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Difference Between Complete and

Incomplete Combustion

C

O

O

OC

Products of Complete Combustion

Products of Incomplete Combustion

(CO2)

(CO)

+

+

14,540 Btu

4,350 Btu


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Incomplete combustion at the furnace exit results in a hazy furnace, stack opacity,

and measurably high CO. It also contributes to boiler exit flue gas temperatures

being too high, and therefore, can contribute to super-heater tube overheating,

super-heater, and boiler generating bank tube plugging.

Due to Non Optimal Lower Furnace Heat Absorption

Resulting in Upper Furnace Short or Long Term Failures`

The Inter-Relationship of Combustion and Tube Reliability


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Inspect tubes for corrosion

or wear, check for any

problems with alignment

bars and tube shields.

* Thoroughly inspect and repair all

ductwork and expansion joints

Optimize air heater seals,

basket cleanliness, check

and repair sector plates

and all moving parts

* Verify damper strokes (all

dampers to be verified frominside ducts)

PA, FD, ID Fan

clearances and

damper/inlet vane

checks

Rebuild pulverizer

grinding elements

Refurbish burners todesign dimensions,

Dampers and/or tilts

synchronized

Air-in leakageinspections and

repairs

Typical Outage Opportunities


25/45


Slagging will occur if furnace exit gas temperatures (F.E.G.T.) exceeds the fusion

temperature of ash from the coal being fired.

F.E.G.T. should be 100F to 150F below the ash softening temperature.

Higher fineness, proper primary (pulverizer) airflow and good fuel balance reduceFEGT by allowing combustion to complete lower in the furnace. combustion in

completed lower in the furnace, the waterwalls absorb a higher amount of total

heat release by the fuel and FEGT is reduced.

Reducing ash fusion temperatures are always lower than those in an oxidizing

atmosphere. Ash melts into a slag due to lower melting points caused by areducing atmosphere allowing slag to be formed at lower temperatures.

Root Cause of Upper Furnace Slagging

FEGT Exceeds Ash Fusion Temperature


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Typical FEGT

Measurement

Location

Controlling Furnace

Exit Conditions, one if

not the most important

factor to controlling

slagging, optimum

steam temperatures &

combustion efficiency.


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FEGT is controlled by the amount

of heat absorbed by the water

walls, FEGT is lowered when:

1. Wall blowers are blown

2. Burner tilts down on tangentially

fired units

1. Combustion is completed faster

Better fineness

Good fuel & air Balance

2. Better mixing in the lower furnace,

more uniform:

O2 Temperature

Slag deposition


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Burner Tilts in upward orientation on tangentially fired units

reduces furnace residence time


29/45


Changing FEGT with Burner Tilts

2250F 2000F 1850F

Burner Tilts (+) UP

Burner Tilts (0) Horizontal

Burner Tilts (-) Down

Low W.W. Heat AbsorptionLow Retention Time

Higest FEGT

Moderate Retention Time

Lower FEGTModerate W.W. Heat Absorption

Higest Retention Time

Highest W.W. Heat AbsorptionLowest FEGT
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30/45


Delayed combustion = reduces waterwall

absorption = high FEGT (same effect as

smaller furnace)

Air Heater

To Precip/

Bag House

Air Inlet

Relationship between FEGT and

Furnace Heat Release Rate


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Ash Fusion Temperatures

ID ST FTHT

Th F E it h ld b O idi i b


32/45


The Furnace Exit should be Oxidizing because:

1. Reducing Ash Fusion Temperatures are always lower

2. Low or No O2 increases Furnace Exit Gas Temperature


33/45


Low O2at the Furnace Exit also causes slagging

Ash chemistry changes andash fusion (melts) at lowertemperature

FEGT is higher because there isinsufficient excess oxygen to

complete combustion in thelower furnace


34/45


Poor coarse coal fineness (>300 Micron particles) can impact on the lower

furnace slope causing heavy slagging in the lower furnace


35/45


SLAGGING

ZONE

FOULING

ZONE

Tube spacing becomes

more restrictive as the

heat transfer process

changes from Radiant in

the furnace to

Convective heat transfer

in the back pass

Slagging / Fouling

20 Tips to help Prevent Slagging

Use good walk downs and/or permanent cameras to

id tif l b f it b bl i th SH th


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20 Tips to help Prevent Slagging

Good control of the furnace exit conditions to minimize

or stop slagging. (Proper & uniform O2and

Temperature) Uniform furnace exit conditions across

the furnace (F/O2) = uniform slag deposition. (Uniformslag is more easily managed. Active monitoring of the

FEGT is KEY. Operators need to be aware of FEGT to

optimize their cleaning strategies and make

adjustments. Trust but verify optical, acoustic and

calculated FEGT. High Velocity Thermocouple Testing

is the Gold standard of FEGT measurementHVT

measures bulk and discrete point temperatures.

Don

t overuse OFANOx can be too good

the benefits of over-staging will be short lived

Practice preventative

not reactive

soot

blowing by cleaning water walls, reducing FEGT

and Slagging conditions. Keeping the walls

clean and lowering furnace temperatures can

also reduce NOx, sometimes as much as 15%.

Optimize lower furnace fuel & air interactions to

maximize water wall heat absorption.

Know your coal before it enters the furnace

(Operator awareness) Control the coal quality

issues that you have control of, Plant

coal

quality control starts in the coal yard. Raw coal

sizing, moisture (coal pile management), coal

drying (mill outlet temperature) and fineness.

Pulverizer performance is critical to preventing

lower furnace slag/clinkers. Avoid the splat

factor.

identify slag before it becomes a problem in the SH, the

plant can then shift from a normal

to aggressive

sootblowing/cleaning mode of operation to manage or

remove the clinker online. Take Action rather than

waiting for a forced outage.


37/45


The Inter-Relationship of Combustion,

Slag and Tube Reliability

Non-Optimal furnace cleaning can significantly elevate the furnace exit gas temperature andforce heat to the convection pass

The strainer effect of the boiler tube spacing gets


38/45


Superheater

Division Panels

(8 ctrs.)

Platen

Superheater

(19 ctrs.)

Front Pendant

Superheater Final(4 ctrs.)

Front Pendant

Reheater

(9 ctrs.)

Rear Pendant

Reheater Final

(4 ctrs.)

Rear Pendant

Superheater

Economizer

Corner Firing

System

Furnace

Windbox

Preferred HVT

Traverse PlanePreferred HVT

Traverse Plane

Platen

Superheater(19 ctrs.)

Superheater

Division Panels

(8 ctrs.)

Front

Pendant

Reheater(9 ctrs.)

Rear Pendant

Reheater Final

(4 ctrs.)

Front Pendant

SuperheaterFinal (4 ctrs.)

Rear Pendant

Superheater

Economizer

The strainer effect of the boiler tube spacing gets

smaller and more restrictive between the furnace and

boiler exit

Boiler setting air ingress minimized; furnace20 Tips to help Prevent Slagging


39/45


SH/RH Heating surface areas optimized

Good steam temperatures with FEGT at or

less than ash softening temperature.

Practice prevention of slag rather than managing

slag incidents. Listen to your boiler when it tellsyou it is sick; fevers high exit gas temperatures

or FEGT, hot tubes, vomiting high spray flows,

ash spills, dark bottom ash or fly ash, Shortness

of breath ID and FD fan limitations, high DPs

and low wind box pressures.

Soot blowing technologies have also

advanced a long way from a pipe with two

holesEnsure soot blower PMs are being

completed to maximize soot blowing

effectiveness.

o e sett g a g ess ed; u ace

O2is not low with normal economizer exit O2.

Amount of heat absorbed by the water walls

regulates Furnace Exit Gas Temperature.

LOOK at the water walls; know what you

relooking for. (Slagging Conditions)

Remember the boiler is a heat engine, get

the inputs right. Fuel and air need to be in

the right places in the right amounts.

Air heater is clean & well maintained; a high

DP or Leakage doesnt lower furnace O2due to fan capacity.

Help pendant/platens clean themselves by

removing slag anchor points such as

certain types of wrapper tubes, alignment

lugs and rigid alignment/tie bars to allowsome swingingof the pendants.

p p gg g

T i l Sl i diti T ti ll fi d b il


40/45


Typical Slagging conditions on a Tangentially fired boiler

Poor Pulverizer Performance Increases FEGT due to Delayed


41/45

www.AsianSBCUsers.comI 2011 Conference41

Tube spacing permits

slag bridging between the tube

assemblies, when the ashIs soft, sticky and/or molten

Excessive desuperheating water

sprays, for both S.H. and R.H.

Sticky, plastic slag deposits onpendants. Slag temperature at or

above ash softening temperature

Reducing areas w/ fuel

stratifications and

excessive CO levels

Molten slag on the

furnace water wall

Burner tilts upward or

horizontal reduce thefurnace mixing and

elevate the furnace

exit gas temperature

Poor fuel fineness and

distribution aggravates high

center of combustion

Air Heater inlet & outlet flue

gases higher than design

From

FD Fan

To

Stack

Poor Pulverizer Performance Increases FEGT due to Delayed

Combustion, Increasing Slagging and Lowering Performance

Optimized Tangentially fired boiler


42/45


Optimized Tangentially fired boiler

No Air In-Leakage

Balanced Airflows,

Balanced Fuelflow,Fuel Fineness >75%

Passing 200 Mesh and


43/45


Typical Temperature of a Pulverizer

Between

500

F &700

F

140F - 160F

130

F140

F

Most pulverizer fires and/or puffs

are caused by coal spilling into

the high temperature area where

primary air enters the mill.

43

Typical temperature inside the mill with Coal


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Moisture of 30%



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100,000 LBS/HR Coal

X 3% Moisture

= 3,000 Moisture


Moisture of 3%

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MILL OPTIMIZATION