Low Volatile Doosan Babcock

Burner Developments for the Wall Firing of Low Volatile CoalsBritish Flame 1-Day Technical Meeting: 28 November 2007

Euan CameronResearch and Development CentreDoosan Babcock Energy

Burner Developments for Wall-Firing of Low Volatile Coals

• Background

• Aim of development

• Description of test facilities

• Summary of results

• Conclusions

Outline

Burner Developments for the Wall-Firing of Low Volatile Coals

• Difficulties associated with low volatile coals– Ignition– Combustion stability (over load range)– Combustion efficiency

• Causes– Lack of volatile material in the coal to support ignition– Rate of volatile matter release– High ignition temperature– Low reactivity of remaining char

• Solutions– Finer pf grading– Longer furnace residence times– Careful air admission– Furnace refractory cover where appropriate

Background: Key Issues


Background: Downshot firing system

Cyclone concentration of pf and low primary air velocity for rapid ignition

Primary combustion zone for early ignition and NOx control

Secondary combustion zone, long residence time for burnout

Recirculation of hot flue gas stabilisescombustion

High secondary air velocity for development of long flame

Single point tertiary air injection for good mixing


Background: Downshot firing system

• Cost– High capital cost (10% to 15%) of downshot firing compared to wall fired systems

• EnvironmentalDownshot firing generally results in poorer emission levels

– High NOx emissions (order of 1000 to 1100 mg/Nm3 at 6% O2)– Unburnt loss typically 2 to 4% GCV loss


Background: Wall firing system

Burner & OFAlevels

NOxReduction Zone

BurnoutZone

COMBUSTION AIR

PRIMARY AIR + FUEL

COMBUSTION AIR

PRIMARY AIR + FUEL

FurnaceConfiguration

Low NOx Burner Design

Low NOxBurnersIn operation


Background: Downshot vs. Wall Fired Boilers

Generally a wall fired furnace is smaller compared to a similarly rated downshotfurnace

Typical 350MWe units


• Wall firing low volatile coal– Predominately in former Soviet Union with generally poor results

•Excessively high unburnt loss (typically 8 to 13% GCV loss)•High NOx emissions (order of 1000 to 1300 mg/Nm3 at 6% O2)•Poor stability and turndown performance

– Some testing in Germany•Maximum of 30MWt•A range of coals down to 8% (dry) volatile matter•Stable flame achieved but requiring gas support or high primary air temperatures

Background: Previous Experience


Background: Our Experience

70

80

90

100

0 5 10 15 20 25

Dry, Mineral Matter Free Volatile Matter %

Dry

, Min

eral

Mat

ter

Fre

e F

ixed

Car

bo

n %

Anthracite

Semi Anthracite

Meta Anthracite

Low Volatile Bituminous

Pha LaiLiaocheng

Yue YangHeze

Wangqu

Downshot Firing Wall FiringWall Firing Capability Improvements

UK Site

Castle Peak’ B’


• Demonstrate combustion performance of a burner for wall firing of low volatile coals– Testing of a full-scale burner in a single burner test facility

•Limit of coals that can be fired•Turndown

• Extrapolate test results to full scale plant performance– With regard to NOx and burnout

Aim of development


Single Burner Test Facility

• 90 MW Thermal Input

• Capability to Fire a Wide Range of Fuels– Coal– Heavy Fuel Oil– Natural Gas– Orimulsion


Single Burner Test Facility

• 17m long / 5.5m wide / 5.5m high water jacketed furnace with partial refractory lining

• Downstream boiler and economiser

• Full Emission monitoring

BURNER DEVELOPMENTS FOR THE WALL-FIRING OF LOW VOLATILE COALS

• Test burnerAdvanced low NOx burner design modified to ‘suit’ low volatile coals.

• Test coalsChinese low volatile coal (13% dmmf volatile matter)UK low volatile coal (9% dmmf volatile matter)UK low volatile coal (8% dmmf volatile matter)

• Test programmeEstablish unsupported stable flameDetermine optimum firing setting with respect to NOx and burnout by varying:

– Secondary and tertiary air flows (high, medium or low)– Secondary and tertiary swirl generation (high, medium or low)– Economiser exit oxygen (2.5% to 5.0% O2)– PA/Coal ratio (high, normal or low)

Determine turndown performance

Single Burner Testing


• Successful ignition and combustion of coals with 13%, 9% and 8% volatile matter content in a wall-fired burner without the use of a support fuel.

• Performance

* Lowest load at which stable operation was demonstrated without oil support

Single Burner Test Results

% load

% GCV

vppm @ 3% O2

mg/Nm3 @ 6% O2

(vppm @ 3% O2)

Turndown *

Unburnt Loss

CO

NOx

8% dmmf Coal9% dmmf Coal13% dmmf Coal

538(315)

436(255)

597(350)

275640245

707050

6.411.74.3


Pilot-Scale Test Facility

• 160 kW Thermal Input

• 5m Long, 0.5m Dia. Vertical, Refractory lined, Water-Jacketed, Furnace

• Low NOx Burner, Downward Firing

• Internally air staged burner designed for bituminous coals


Pilot-Scale Test Facility

SECONDARYAIR HEATER

SECONDARYAIR FAN

PRIMARYAIR HEATER

PRIMARYAIR BLOWER

SPRAY COOLERWATER SUPPLYFROM MAINS

WATER TO DRAIN

P.F.FEEDERPRIMARY AIR

AND P.F. SUPPLY

MAINBURNER

SECONDARYAIR SUPPLY

NATURAL GASSUPPLY

START UPFUEL (GAS)

GAS

P.F.VENTURI

AFTER AIRSUPPLY

ASHBOX

SPRAYCOOLER

ESP

FURNACE

COOLING WATERSUPPLY

COOLING WATER RETURN

FLUE GAS TOATMOSPHEREFLUE GAS TOATMOSPHERE

IDFAN

NOxStarREACTOR 2

FLUE GASCOOLER 2

FLUE GASCOOLER 1

NOxStarREACTOR 1

NH3 SLIPANALYSER

SCR REACTOR

SORBENT INJECTION

NH3 SLIP ANALYSER

COMPRESSEDAIR SUPPLY

COMPRESSEDAIR SUPPLY

• In-Furnace (Primary) NOx ReductionTechnologies

– Air Staging, Overfire Air (OFA) Injection– Gas and Coal Reburn

• Post-Combustion (Secondary) NOxReduction Technologies

– Selective Non-Catalytic Reduction (SNCR)

– Selective Catalytic Reduction (SCR)

• Electro Static Precipitator (ESP)


• Testing of a 2nd Chinese low volatile coal (7% dmmf volatile matter)

• Established the effect of the main operating variables on NOx under baseline and air staging conditions

• Test programme considered the effects of:– excess air– primary zone stoichiometry– primary zone residence time

Pilot-Scale Testing


• Single stage baseline – NOx of 810mg/Nm3 @ 6%O2

• Two stage combustion– primary zone stoichiometry of 1.0 => NOx of 644mg/Nm3 @ 6%O2

•25% reduction– primary zone stoichiometry of 0.9 => NOx of 477mg/Nm3 @ 6%O2

•Additional 25% reduction, 40% reduction overall

• Using low NOx burner technology with air staging gives significant NOx performance improvements

Pilot-Scale Test Results


• Engineering model– Plant geometry– Fuel quality and fineness– Temperature– Stoichiometry

• Model used to extrapolate demonstrated test rig performance data to modern plant design

• Showed that NOx of <650 mg/Nm3 and unburnt loss <2.0% GCV is achievable for this type of fuel in commercial plant.

Extrapolation of test data to full-scale plant


• Firing of low volatile coals in wall fired burner successfully demonstrated

– Successful ignition and firing of coals with:•13% dmmf volatile matter•9% dmmf volatile matter•8% dmmf volatile matter

in a wall-fired burner without the use of a support fuel and/or high primary air temperatures

– Appreciable NOx reductions (25%+) are achievable with air staging

– Extrapolation to full scale plant shows that acceptable performance will be achieved in terms of NOx and unburned loss.

Conclusions


• Wangqu Power Station (new build)– 2 x 600MWe– Once Through Supercritical wall fired

boilers with air staging– Firing Chinese low volatile coal with 12

to 15% daf volatile matter– Commercial operation in 2007– NOx guarantee of

650mg/Nm3 @ 6%O2

– Best Performance being achieved•NOx of 580mg/Nm3 @ 6%O2

•Unburnt loss of 1.2% GCV

Commercial Application


End of presentation

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