factors affecting formation and emissions of dioxins and mercury in power and industrial boilers

8/6/2019 Factors Affecting Formation and Emissions of Dioxins and Mercury in Power and Industrial Boilers

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PCDD/PCDFs AND MERCURY IN

POWER AND HEATING GENERATION SECTOR

ANDREA SBRILLI

UNIDO CONSULTANT

ESEA FORUM

NATIONAL AWARENESS WORKSHOP FOR DEMONSTRATION

OF BAT/BEP IN FOSSIL FUEL-FIRED UTILITIES AND INDUSTRIAL BOILERS

ON PERSISTENT ORGANIC POLLUTANTS (POPS)

BANGKOK, THAILAND 13 JUNE 2011


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UNINTENTIONAL POPs AND MERCURY EMITTED

DURING BURNING PROCESS

INDUSTRIAL AND NON INDUSTRIAL BURNING PROCESSES

CAN BE THE EMISSION SOURCES OF:

UNINTENTIONAL PRODUCED

PERSISTANT ORGANIC POLLUTANTSUP-POPs

DIOXINS AND FURANS (PCDD/PCDF)

POLICHLOROBIPHENYLS (PCBs)

HEXACHLOROBENZENE (HCB)

AND

MERCURY


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FORMATION DURING BURNING PROCESS

VIA OMOGENUOUS AND HETEROGENUOS PHASE

REFORMATION DURING GAS COOLING

IN THE HEAT EXCHANGER ZONE

REFORMATION IN THE

DUST FILTERS

RELEASE FROM SCRUBBERS (DRY AND WET)

MAIN FACTORS AFFECTING

UP-POPs FORMATION AND EMISSION IN

THERMAL PROCESSES

CHORINE INPUT WITH FUEL (FOSSIL OR BIOMASS)


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LARGE, FOSSIL FUEL-FIRED POWER PLANTS

ARE WELL-CONTROLLED,THE COMBUSTION EFFICIENCY IS USUALLY HIGH,

THE PROCESS IS STABLE AND THE FUELS USED

ARE GENERALLY HOMOGENEOUS

THE CONCENTRATION OF PCDD/PCDFSSs

IN THE EMISSIONS ARE LOW,

BUT MASS EMISSIONS ARE HUGE DUE TO

LARGE VOLUMES OF FLUE GASES EMITTED

POWER PLANTS AND

INDUSTRIAL BOILERS

SMALLER INDUSTRIAL PLANTS

ARE LESS WELL CONTROLLED

EMISSIONS OF PCDD/PCDFs ARE AT HIGHER CONCENTRATIONS

BUT WITH AT LOWER MASS EMISSION

DUE TO LOWER VOLUMES OF FLUE GASES EMITTED


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RESIDUALS AND DISTILLATE OILS

HEAVY FUEL OIL MAY CONTAIN SIGNIFICANT

QUANTITIES OF ASH, NITROGEN, AND SULFUR

HOWEVER, THEY GENERALLY RESULT IN

LOW LEVELS OF ORGANIC EMISSIONS

LIGHT FUEL OIL AND NATURAL GAS

GENERATE LOW AMOUNTS OF PCDD/PCDFs

BOTH ARE VERY HIGH CALORIFIC, CLEAN BURNING

FUELS WITH LITTLE CONTENT OF ASHES

ONLY IF LIQUID OR SLUDGE WASTE IS CO-FIRED HIGHER

CONCENTRATIONS OF PCDD/PCDFs MAY BE FOUND

INFLUENCE OF FUEL


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USE OF BIOMASSES

THE COMBUSTION

OF SOME OF THEM

INCREASES

FOULING OF

SURFACES OF

BOILERS

DUE TO THE GREATINPUT OF MINERAL

MATTER AND

CHLORINE

THERE IS AN

INCREASE IN

EMISSIONS OFDUST, HYDROGEN

CHLORIDE AND

PCDD/PCDFs


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THE CHLORINE CONTENT OF UNTREATED WOOD IS USUALLY

BETWEEN 0.001 AND 0.01 % BY WEIGHT.

IN BARK IS HIGHER , 0.01 TO 0.02%

DEPENDING ON THE LOCATION, EVEN HIGHER

CHLORINE CONTENTS CAN BE FOUND

IN UNTREATED WOOD AND BARKS.

SIGNIFICANTLY HIGHER VALUES CAN BE FOUND

IN WOOD MATERIALS CONTAINING PLASTICS (PVC)

INFLUENCE OF CHLORINE


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FLY ASH FROM BIOMASS COMBUSTION HAS

TO BE LANDFILLED DUE TO ITS HIGH HEAVY METAL CONTENT.

COMBUSTION OF CONTAMINATED WOOD SHOULD BE LIMITED TOINCINERATION PLANTS WITH EFFICIENT EMISSION CONTROL SYSTEMS

MAX.

CONCENTRATION

PERMITTED

0.1 ng ITEQ/m3


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DIOXINS AND FURANS EMISSION FACTORS FOR

FOSSIL FUELS AND BIOMASS BURNING

12

IT IS EVIDENT THAT THE TYPE OF PLANT

AND TYPE OF EMISSIONS CONTROL DEVICES

ARE NOT CONSIDERED

UNEP TOOLKIT


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DIOXINS AND FURANS EMISSION FACTORS FOR

BIOMASS POWER PLANTS


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LITERATURE DATA

EMISSION FACTORS (EF)

IN INDUSTRIAL COAL FIRED BOILERS

FLUIDIZED BED BOILER FIRED WITH COAL (OLD)EF = 100-300 g TEQ/TJ

FLUIDIZED BED BOILER FIRED WITH COAL (NEW)

EF = 1 g TEQ/TJ

10% ADDITION OF BIOMASS TO COAL AS FUEL

CAN INCREASETHE EMISSION FACTOR (EF)

ABOUT 10 TIMES

CO-COMBUSTION OF COAL AND WASTES

GIVES VERY HIGH EMISSION FACTORS


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INDUSTRIAL BOILERS FIRED WITH WOOD (WITHOUT BARK)

EF = 1,600 g TEQ/TJ

INDUSTRIAL BOILERS FIRED WITH WOOD (WITH BARK)

EF = ABOUT 10 TIMES HIGHER

EF = 16,400 g TEQ/TJ

WOOD PELLETS FIRED BOILERS WITH CONTINUOUS OPERATION

HAVE EF 10 TIMES LOWER THAN THOSE WITH

DAILY SHUT DOWNS AND RE-STARTS.

OLD BOILERS FIRED WITH WOOD PELLETS HAVE

EF 10 TIMES HIGHER THAN

NEW BOILERS FIRED WITH THE SAME FUEL

LITERATURE DATA

EMISSION FACTORS (EF)

IN INDUSTRIAL WOOD FIRED BOILERS


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DIOXINS AND FURANS EMISSION FACTORS

CONSIDERED IN THE PROJECT

(AVERAGED VALUES)


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MAIN DESIGN AND OPERATION PROBLEMS IN BOILERS

LOW TEMPERATURES (UNDER 900-1000

DO NOT DESTROY POPs

LOW TURBULENCE OF EXHAUST GASES

NON CONTINUOUS HOMOGENUOUS BURNING

INSUFFICIENT AIR - OXYGEN CONTENT IN

COMBUSTION PROCESSES

INSUFFICIENT ON-LINE INSTRUMENTATION

FOR COMBUSTION CONTROL

(TEMPERATURE, OXYGEN, CO, DUST),

FORMATION OF DIOXINS AND FURANS

DURING COMBUSTION PROCESS


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NOT OPTIMIZED BURNING PROCESS


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UNIFORM HIGH COMBUSTOR TEMPERATURE

GOOD MIXING WITH SUFFICIENT AIR

MINIMIZE ENTRAINED, UNBURNT PARTICULATE MATTER

FEED RATE UNIFORMITY

ACTIVE MONITORING AND CONTROL OF CO AND TOTAL

HYDROCARBONS

PARAMETERS TO BE CONTROLLED

TO REDUCE PCDD/PCDFs EMISSIONS


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THE CONDITIONS INSIDE THE GAS COOLING SECTION

COULD FAVOUR PCDD/PCDF FORMATION

COOLING SECTION

TEMPERATURES VARYING IN THE RANGE 250-400 C

ACCUMULATION OF PARTICLES ON

THE COLD SURFACES OF THE TUBES

POSSIBLE CLOGGING-CONDENSATION OF FLY ASHES

PERIODICAL CLEANING OF TUBES IS RECOMMENDED

( MANUAL, MECHANICAL, STEAM INJECTION)


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COAL COMBUSTION IS THE MAIN SOURCE (>60%)

OF MERCURY EMISSIONS TO THE ATMOSPHERE.

MERCURY IS PRESENT IN COAL IN TRACE AMOUNTS

(0.011.8 mg/kg).

CONCENTRATION IN CRUDE OILS

SHOW WIDE RANGES (0.01-30 PPM).

IN RESIDUAL OILS HIGHER CONC. THAN DISTILLATE OILS

NATURAL GAS HAS VERY LOW AMOUNTS (0.020.2 ppb)

SMALL COMBUSTION PLANTS AND

RESIDENTIAL COAL BURNING

ARE ALSO SIGNIFICANT MERCURY SOURCES

MERCURY EMISSION SOURCES


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MERCURY CONTENT IN SOME TYPES OF COAL


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ESTIMATED

MERCURY

EMISSION

FACTORS

(mg/TJ)

FOR DIFFERENT

TYPES OF FUEL

IN SMALL

BOILERS INEUROPE

REF: Costs and environmental effectiveness of options for reducing mercury emissions to

air from small-scale combustion installations.AEA Technology / NILU-Polska 2005


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MERCURY EMISSIONS

MERCURY EMISSIONS FROM COMBUSTION SOURCES

OCCUR IN THREE FORMS:

SOLID PARTICULATE-ASSOCIATED MERCURY (HGP )

GASEOUS DIVALENT MERCURY, (HG2+)

AND GASEOUS ELEMENTAL MERCURY, (HG0)

AT HIGH TEMPERATURES IN BOILERS, MERCURY

IS RELEASED AS ELEMENTAL MERCURY (HG0).

IT IS THEN OXIDIZED BY CHLORIDE ACID, SO2AND FLY ASH IN FLUE GAS IN HG2+. THIS IS SOLUBLE AND

ASSOCIATES WITH THE PARTICLES IN FLUE GAS TO FORM HGP.

HG2+, HGP AND HG0 HAVE VERY DIFFERENT

PHYSICO-CHEMICAL CHARACTERISTICS AND, CONSEQUENTLY,

DIFFERENT EMISSION PATHWAYS


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CONTROLLING MERCURY EMISSIONS FROM BOILERS

INVOLVES 3 SEPARATE STEPS;

PRE-COMBUSTION CONTROL,

PRE-CLEANING AND PRE-TREATMENT OF RAW COALS

AND IMPROVEMENT OF THEIR QUALITYTO REDUCE THE ASH CONTENT, SULPHUR CONTENT

AS WELL AS CHLORINE AND MERCURY

IN-FURNACE CONTROL

LOW EXCESS AIR COMBUSTION,AMMONIA INJECTION, AND UREA INJECTION.

POST-COMBUSTION CONTROL.

USE OF EMISSION ABATEMENT DEVICES

MERCURY REDUCTION


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INFLUENCE AND EFFICIENCY OF ABATEMENT

DEVICES FOR PCDD/PCDFS AND MERCURY

THE SIZE OF THE UTILITY BOILERS ALLOWS

TO HAVE SIGNIFICANTECONOMIES OF SCALE,

THAT ARE NOT AVAILABLE TO INDUSTRIAL BOILERS.

FEW TECHNICAL OPTIONS EXIST FOR SMALL BOILERS

PCDD/PCDFs ARE REMOVED IN A LARGE EXTENT BY

FILTERING SYSTEMS COUPLED WITH

ADSORBERS MEDIA (ACTIVE CARBON)

AND CATALYTIC DEVICES (SCR)

MERCURY IS REDUCED IN A LESSER EXTENT BY

MECHANICAL SEPARATORS

DESULPHURIZATION DEVICES

FILTERING SYSTEMS COUPLED WITH

ADSORBERS MEDIA (ACTIVE CARBON)


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FLUE GAS

DESULPHURIZATION DEVICES


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PCDD/PCDFs IN WET SCRUBBERS

USED IN LARGE BOILERS

OPERATING TEMPERATURE IS 45-80 CUSUALLY TWO STAGES ARE USED (ACID AND BASIC)

FOR REMOVAL OF ACIDS AND METALS, AND SO2

LOW EFFICIENCY FOR POPs REDUCTION

POPs ARE ADSORBED ON THE PLASTIC MATERIALS

USED IN THE WALLS OF THE SCRUBBER

AND CAN BE DESORBED AT HIGH TEMPERATURE

IF POLYPROPYLENE LAYERS ARE ADDED AND

EMBEDDED WITH CARBON

PCDD/PCDF AND MERCURYCAN BE ADSORBED

REMOVAL EFFICIENCY UP TO 70%


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DRY AND SEMY-DRY SCRUBBERS

SPRAY INJECTION OF SLAKED OR WET LIME Ca(OH)2MEDIUM REMOVAL EFFICIENCY

IF ACTIVE CARBON IS ADDED

PCDD/PCDFs REMOVAL EFFICIENCY UP TO 99%

LOWER CAPITAL COSTS BUT HIGHER OPERATING COSTS

THAN WET SCRUBBERS

MORE SOLID RESIDUE

TO BE COLLECTED BY THE FILTERS

SPRAY DRY SCRUBBERS ARE MOSTLY USED FOR SMALL

TO MEDIUM CAPACITY BOILERS


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IN SMALL BOILERSUSUALLY SETTLING CHAMBERS OR CYCLONES

THEY COLLECT ONLY COARSE PARTICLES

SMALL BAG FILTERS ARE AVAILABLE

IN LARGE FACILITIESELECTROFILTERS AND FABRIC (BAG) FILTERS

CAN COLLECT FINE PARTICLES

FABRIC FILTERS AND ELECTROFILTERS

OPERATE NORMALLY AT 200 CHIGHER TEMPERATURE CAN BE

CRITICAL FOR PCDD/PCDF REFORMATION

ALL THESE DEVICES MUST BE FREQUENTLY CLEANED,

TO AVOID PCDD/PCDF RE-FORMATION

FILTERING SYSTEMS


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PARTICULATE MATTER ABATEMENT DEVICES

SMOKE RELEASES FROM STACKS


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SMOKE RELEASES FROM STACKS.

NO ABATEMENT DEVICES WORKING


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DEVICEPCDD/PCDFREMOVAL

EFFICIENCY

SETTLING

CHAMBERS

VERY

LOW EFFICIENCY

CYCLONES LOW EFFICIENCY

VENTURI WET

SCRUBBER

MEDIUM EFFICIENCY

FABRIC FILTERS

(FF)

HIGH

FOR FINE PARTICLES

ELECTROSTATICPRECIPITATORS

MEDIUM EFFICIENCY

PCDD/PCDF

REMOVAL EFFICIENCY

PCDD/PCDFs ARE MAINLY ADSORBED

ON FINE PARTICULATE MATTER


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(HG2+) IS SOLUBLE AND ASSOCIATES WITH

THE PARTICLES IN FLUE GAS TO FORM HGP.

THEREFORE, EMISSIONS OF HG2+, MAY BE CONTROLLED BY

TYPICAL AIR POLLUTION CONTROL DEVICES (APCD),

FLUE GAS DESULFURIZATION (FGD) SYSTEMS

ELECTROSTATIC PRECIPITATORS (ESP)

FABRIC FILTER (FF)

THE VOLATILE FORM HG0 CAN BE CONTROLLED

BY ADDING ACTIVE CARBON TO DRY SCRUBBERS

BECAUSE THE RELATIVE PROPORTIONS OF HG2+, HGP AND HG0

CAN VARY, THE CORRESPONDING REDUCTIONS

ACHIEVED BY APCD VARY IN WIDE RANGE

REDUCTION OF MERCURY EMISSIONS


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REDUCTION OF MERCURY EMISSIONS

THE APPLICATION OF FLUE GAS DESULFURIZATION FGD

HAS A VERY DEEP IMPACT ON MERCURY REMOVAL

THE LOW TEMPERATURE OF WET SCRUBBERSALLOW THE VOLATILE TRACE EMENTS

TO CONDENSE AND TO BE REMOVED

REMOVAL EFFICIENCY RANGE FROM 30 TO 50%

SPRAY DRY SYSTEMS COUPLED WITH FABRIC FILTERS

GIVE GOOD RESULTS

REMOVAL EFFICIENCY RANGE FROM 35 TO 85%


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THANK YOU FOR YOUR ATTENTION !

Andrea Sbrilli, UNIDO consultant

[email protected]

ESEA FORUM

NATIONAL AWARENESS WORKSHOP FOR DEMONSTRATION

OF BAT/BEP IN FOSSIL FUEL-FIRED UTILITIES AND INDUSTRIAL BOILERS

ON PERSISTENT ORGANIC POLLUTANTS (POPS)

BANGKOK, THAILAND 13 JUNE 2011

factors affecting formation and emissions of dioxins and mercury in power and industrial boilers

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