CO-COMBUSTION (COFIRING) OF

WASTE WITH FUELS

Jan Nadziakiewicz

The need of co-combustion

The increasing consumption of fuels creates the need to use

some other substances as fuels.

Especially interesting from technological point of view is co-

combustion of fossil/renevable fuels with some amount of

waste.

The co-combustion process requires special systems of gas

cleaning and monitoring of emission to the environment.

Special emission standards must be observed.

Most popular is using waste in cement industry and power

systems.

Various types of waste can be applied as fuel.

The purpose of using waste as fuel

Energy recovery,

Saving of fossil fuels and bio-renevable fuels,

Reducing amount of waste to be landfilled,

Reduction of environment pollution.

Waste types possible to use as fuels for co-combustion or

production of rdf

Waste

codes Waste types for RDF production LCV MJ/kg

20 01 01 Paper, cardboard 15

20 01 10 Cloth 16,3

20 01 11 Textiles 16,3

20 01 25 Oils and edible fats 20 - 30

20 01 38 Waste wood 15,8

20 01 39 Plastics 30 – 40

20 01 99 Other elective collected fractions 14

THE TYPICAL PARAMETERS OF RDF PRODUCED FROM

MUNICIPAL SOLID WASTE

No. Parameter Unit Limits

1 Lower Heating Value kJ/kg 18 000

2 Ash content % < 20

3 Sulfur content % < 2

4 Chlorium content % < 0,7

Tanner diagram for mixture of municipal solid

waste + 30% sludge

FUEL MARKMunicipal Solid WasteSludge 30% humidityMSW + Sludge 30%Sludge 80% huidityMSW + Sludge 80%Hard coal

CO-COMBUSTION INSTALLATION

… it is the installation producing energy or other products in

which the fuel is used with some additional amounts of

waste or fuel from waste, with the aim of their energy

recovery or incineration (utilization).

This installation must fulfill the special requirements

provided in a regulation dealing with the incineration

systems.

Possible arrangements of co-combustion

MOST POPULAR WASTE USED AS

ADDITIONAL FUELS

Used tyres,

Waste rubber,

Waste from paper processing,

Used oils,

Waste wood,

Municipal sewage sludge,

Industrial sewage sludge, (paper pulp)

Plastics,

Used solvents.

Advantages and disadvantages of cofiring

of waste with fuel

Use of biomass in co-firing incorporate environmental, socio-

economic and strategy advantages regarding the use of

biomass in dedicated biomass plants.

In the case of waste residues the combustion may change

the emission regulations to satisfy more strict standards

For example, limits in emissions for large scale

combustion facilities are more permissive than regulations

for incineration plants.

The bio-fraction of waste reduces emission of CO2 to

atmosphere – determination of this fraction is a key issue.

Advantages and disadvantages of cofiring

of waste with fuel

Specific investment (per unit of installed power) is reduced

in comparison with conventional biomass facilities since

plant using fossil fuel already exists and only diverse

modifications are required.

Power generation with better efficiency: generally biomass

power plants produce electricity with relative low efficiency (18

to 22%) compared with the huge coal units (32 to 38%) with

optimised cycles given the economy of scale.

Flexible operation: original plant can operate still at 100%

load with fossil fuel. Co-firing facility is less sensitive to

seasonality in biomass production and to biomass

availability and price.

Advantages of co-combustion of waste

Modernization of existing installation and infrastruccture is not

necessary.

No need for special training of staff operating the installation.

Much easier approval of ecological and social organizations.

Producing „green energy” with some extra income.

Disadvantages of co-firing of waste with

fuel

There are technical problems with the proper mixing of

biomass/waste with coal.

The addition of biomass lowers the softening temperature of

ash causing the deposits on the boiler structure and

worsening the heat transfer.

Aplying the RDF instead of raw waste reduces this effect to

some extent.

European countries have proven the promotion of co-firing

is a key for the development of biomass markets as well as

for the creation of expertise on biomass handling and

combustion.

Disadvantages of co-combustion of waste

Needed higher efficiency of gas cleaning installations inexisting boiler systems.

More restricted emission standards for co-combustion than forcombustion itself.

Only cement kilns are fully prepared for o-comustion of waste,but they have special restrictions (LHV, Cl, metals).

Only waste/RDF of defined properties can be added to coal inindustrial installations.

Emission standards for SO2 for fuels

Emission standards for NO2 for fuels

Emission standards for dust for fuels

Emission standards for waste incineration

Emission standards of SO2, NO2, dust

[mg/m3u]

0

100

200

300

400

500

600

Węgiel

kamienny

Biomasa Odpady

11%

Odpady

6%

mg

/m3u SO2

NOx

Pył

Emission standards for co-combustion of

waste

0

50

100

150

200

250

300

350

400

450

0 0,2 0,4 0,6 0,8 1

C, m

g/m

3u

Udział odpadu

CSO2

CSO2

Measured parameters for waste incineration

installation: Hydrogen chloride (HCl)

Hydrogem fluoride (HF)

Nitrogen oxide (NO)

Nitrogen dioxide (NO2)

Sulphur dioxide (SO2)

Carbon dioxide (CO2)

Oxygen (O2)

Ammonia (NH3)

Water vapour (H2O)

Mercury (Hg )

Temperature

THC

VOC

Sb + AS + Pb + Cr + Co + Cu + Mn + Ni + V

WASTE INCINERATION SYSTEM

1.Bunkier na odpady komunalne2 Podajnik odpadów 3.Palenisko z rusztem 4.Kocioł: - a - komora paleniskowa- b -pęczki konwekcyjne kotła - c- walczak5. zasobnik żużla6. Filtr spalin7. Wylot spalin do instalacji oczyszczania

Co-combustion in power boilers

Power boilers fired with coal or biomass have good potential

in co-combustion of waste or fuel from waste with basic fuel.

The main advantage is their technical equipment: fuel

storage and preparation, milling systems, gas cleaning

systems etc.

Long time of residence of flue gas in the boiler (2s).

The other positive point is the formal regulations which in

most cases are fulfilled by power installations, althoug some

additional equipment should be installaed.

The basic types of boilers in power system

Grate type boilers.

Pulverized fuel boilers.

Fluidized bed type boilers.

The type of boiler influences on the possibility and cost of co-

combustion of waste with fuel.

Grate type boilers

Grate type boilers are used mainly in a small water or steam

boilers of a thermal power up to 50 MWth.

In large power systems they are usually used as peak-load

boilers.

Grate type boilers usually have very simple gas cleaning

systems (cyclones, electrostatic precipitators, no SO2 or

NOx removal systems – this is the real obstacle for co-

combustion of waste or fuel from waste.

Problems with the bottom ash – still may contaain carbon

and hydrocarbons.

OR-35N – GRATE TYPE STEAM BOILER

Boiler type: drum boiler

Combustion system: moving grate

Max. capacity: 9,7 kg/s

Steam temp. Out: 450°C

Steam pressure 4,0 MPa

Thermal efficiency: 87%

Fuel: Hard coal

LHV of fuel: 23 MJ/kg

Cieszyn electropower station

Pulverized fuel type boilers

They are most popular type of boilers in Polish power

system. The thermal power of one unit usually exceeds

500MWth.

This units are equipped in relatively sophisticated gas

cleaning installations: dust removal (electrostatic

precipitators or bag filters), SO2 removal systems (dry or

wet), NOx removal systems (SCR or SNCR).

They can be relatively easy adapted to the requirements for

co-combustion of waste.

The main problem is milling of waste to the size required by

coal transport system. The easiest type of waste to be co-

combusted in these types of boilers is sewage sludge (small

organic and mineral particles).

MAIN CHARACTERISTICS OF COAL FIRED

POWER PLANT

PULVERIZED TYPE BOILER

FOSTER WHEELER CORPORATION

Odpowiednia objętoćś komory paleniskowej w celu skutecznego spalania paliw stałych, ciekłych i gazowych

Konstrukcja MONO-WALLTM TM ze ścian membranowych zapewniajacych szczelność komory paleniskowej

Młyny misowo-rolkowe MBF i bębnowo-kulowe dla wielu rodzajów paliw.

System niskiej emisji NOx bazujący na stopniowaniu powietrza.

Technologia SCR zapewniająca najniższą emisję NOx

PULVERIZED TYPE BOILER

FOSTER WHEELER CORPORATION

WP-200 – Water boiler OP-230 – Steam boiler

Advantages of co-combostion of sludge in pulverized

type boilers

Pulverized type boilers fuelled with coal are very popular in power system Poland and they are run as basic load for many hours per year.

High capacity of these boilers (large amounts of coal burned) makes possible the utilization of large amounts of sludge.

The investment costs of modification of fuel system are not very high and are much lower than for special installation of sludge incineration..

The sluge from munisipa sewage is not corrosive and no toxic so the co-combustion process can be quite safe for environment.

Fluidal bed type boilers

This type of boilers became more popular in Poland.

There are low requirements regarding the size of fuel

particles in the furnace.

They have the possibility of SO2 removal in the combustion

process (lime addition to the fuel) and a low generation of

NOx (low temperatures – about 9000C).

The main problem is formal fulfilling the requirement of the

gas temperature at least 850oC and residence time of 2 s.

FLUIDAL BOILER OFZ-230

Natural circulation

Fluidized bed circular boiler

Max. capacity: 64 kg/s

Steam temperature: 540°C

Steam pressure: 13,8 MPa

Temperature of water inlet: 158/205°C

Boiler efficiency: 91,5%

LHV of fuel: 17-20,1 MJ/kg

ELETROCIEPŁOWNIA II BIELSKO-BIAŁA

KOCIOŁ OFZ-230

”Polpharma” Starogard Gdański 2 kotły OFz-75

GENERAL REMARKS

The main restriction for applying co-combustion in power

boilers are emission standards for such process.

For relatively new boiler systems or by their modernization it

is fairly easy to adapt the gas cleaning installations to

emission standards for co-combustion.

Przykładowe obliczenia standardów emisyjnych dokonane

dla kotłów o różnej mocy cieplnej i jedynie dla trzech

podstawowych rodzajów zanieczyszczeń prezentuje

nastepująca tabela

Co-combustion in cement kilns

MAIN CHARACTERISTICS OF CEMENT

PRODUCTION PROCESS

Co-combustion in cement kilns

In many Polish cement production installations some types of waste is

burned with coal.

They are: grinded plastics, textiles, rubber, tyres, paper, wood, fuel from

municipal solid waste etc.

The method of applying the waste fuel to the kiln depends on the type of

process: (dry or wet) and the type of kiln.

The waste fuel can be fed to the main flame volume by a special burner

or to the calcinator at the end of the kiln system.

The important factor for this process is high temperature in the kiln

(1400 – 17000C), high thermal inertia and alkaline atmosphere in the

kiln.

Parameters of fuel accepted for cement kilns:

Average NHV > 13 MJ/kg (min. 12 MJ/kg in bulk)

humidity < 30 %,

CL < 0,3 %

S < 2,5 %,

Heavy metals < 2500 ppm,

PCB + PCT < 50 ppm,

Hg < 10 ppm,

Scheme of heat processes in the kiln

Heavy metals in cement kiln

Metals present in the fuel can be emitted in gas form orin a solid form.,

Solid metals are bound in the clinker with no negativeeffects neither on the procuct nor on environment.

Solid-form metals are: Cr, Be, Ba, Ni, As i Ag.

High volatile metals metals evaporate and are emitted asgas; they are: Hg and Tl.

Medium volatile metals condensate on the dust particlesand are recirculated to the process or are emitted toatmosphere; they are: Sb, Se, Pb, Cd.

The use of alternative fuels of a defined parametersdoes not change the emission level of the system.

Advantages of co-combustion in cement kilns:

Alkaline atmosphere neutralizing acidic gomponents ofgas.

Heavy metals immobilization in the clinker.

High thermal efficiency of alternative fuel combustion inthe process.

Large thermal capacity providing steady parameters ofthe process.

No solid products of combustion – they are bounded withclinker.

No special installations needed for combustion ofalternative fuel, low costs of adaptation for additionalfuel.

High performance of dust removing systems and noincrease of gas emission from the process.

Advantages of co-combustion in cement kilns:

Co-combustion of alternative fuels in cement kilns helps in reducing the volume of waste.

It reduces costs of production by recovery of energy from waste.

It saves the natural energy sources (fuels).

The rotary kiln can utilize various types of waste, which is difficult in other technologies.

Co-combustion of sewage sludge

The sludge can be utilized in grate type of boilers or in

pulverized types of boilers.

The easiest method of fulfilling the requirmrnts of

temperature and residence time are in pulverized type

boilers because of large volume and high temperatures

provided by main fuel.

The experilence show that combustion of dried sludge with

coals (up to about 10% mass) does not increase

substantially the emission from the system.

The other method is combustion of the sludge in cement

kilns.

RÓWNOLEGŁE SPALANIE BIOMASY Z

WĘGLEM

Równoczesne spalanie i

współspalanie biomasy z

węglem ze względu na dużą

zawartość części lotnych, a małą

zawartość azotu i siarki przebiega w

odmienny sposób niż samego węgla.

W rezultacie udział biomasy przy

wspólnym spalaniu z węglem

oddziałuje na emisję tlenków azotu,

dwutlenku siarki i metali ciężkich.

TECHNOLOGIE PRZETWARZANIA BIOMASY

Bezpośrednie spalanie biomasy,

Współspalanie biomasy z węglem,

Termiczna utylizacja biomasy w spalarniach

odpadów.

SPOSÓB PODAWANIA BIOMASY I PALIWA

DO KOMORY PALENISKOWEJ KOTŁA ENERGETYCZNEGO

Są dwie możliwości energetycznego wykorzystania biomasy wistniejących kotłach:

współspalanie bezpośrednie:- mieszanie biomasy z węglem przed układem dozowania węglado kotła (młynami),- niezależne przygotowanie biomasy – rozdrobnienie i spalanie naruszcie pod kotłem lub dozowanie do palników ewentualnie nadpalnikami węglowymi niezależnym strumieniem – w tymprzypadku możliwe jest zużycie biomasy jako paliwareburningowego;

współspalanie pośrednie:- przedpalenisko – do komory paleniskowej kotła wnoszone jestciepło ze spalania biomasy- wstępne zgazowanie biomasy – do komory paleniskowejwprowadzany jest wilgotny gaz palny.

METODY WSPÓŁSPALANIA W ENERGETYCE

z zewnętrznym paleniskiem rusztowym dla biomasy,

z wewnętrznym paleniskiem rusztowym dla biomasy poniżej przestrzeni paleniskowej,

z mieleniem lub współmieleniem biomasy i węgla,

z oddzielnym zgazowaniem biomasy i zasilaniem kotła gazem.

Z ZEWNĘTRZNYM PALENISKIEM

RUSZTOWYM DLA BIOMASY

Ko

cio

ł pyło

wy

biomasa

spaliny max

1000°C

Z WEWNĘTRZNYM PALENISKIEM

RUSZTOWYM DLA BIOMASY PONIŻEJ

PRZESTRZENI PALENISKOWEJ

biomasa

Kocioł

ruszt dla biomasy

żużel

Z MIELENIEM LUB WSPÓŁMIELENIEM BIOMASY I

WĘGLA

Ko

cio

ł

młyn

pył z

biomasy i

węgla

INSTALACJE W AUSTRII I FINLANDII

53

Elektrownie zagraniczne, jak na przykład w Lahtii w Finlandii orazw austriackim Zeltweg wykorzystują system hybrydowy doprodukcji energii elektrycznej.

Po lewej - schematelektrociepłowni w Zeltweg wAustrii o mocy 137 MW el i 334MW c ze zgazowarką drewna omocy 10 MW

Po prawej - schemat procesowyelektrowni opalanej biomasą(poprzez jej zgazowanie) orazwęglem kamiennym i gazemziemnym w Lahti (Finlandia) wgprojektu firmy Foster-Wheeler

Ruszt mechaniczny jest wyposażony w kaskadowy układ

podawania paliwa, dzięki czemu może być przystosowany do

równoległego współspalania odpadów drewna poprzez prostą

instalację drugiego układu zasilania

RUSZT PRZYSTOSOWANY DO

WSPÓŁSPALANIA WĘGLA I BIOMASY

ZE PAK ELEKTROWNIA PĄTNÓW SA

ZE PAK ELEKTROWNIA ADAMÓW SA

ZALETY SPALANIA BIOMASY

Wykorzystywanie potencjału energetycznego

biomasy,

Obniżenie emisji CO2 do atmosfery,

Proces spalania jest stabilizowany przez spalanie

węgla,

Biomasa ma niski poziom zawartości siarki,

Wysokie stężenie CaO w popiele pochodzącym z

biomasy,

Wyższa zawartość popiołu w węglu brunatnym daje

możliwość obniżenia stężenia metali alkalicznych

pochodzących z biomasy.

WADY WSPÓŁSPALANIA BIOMASY

czas przebywania paliwa w komorze

paleniskowej,

szlakowanie paleniska,

korozja wysokotemperaturowa,

niszczenie katalizatorów,

zmiana jakości popiołu,

zmiana przebiegu procesu.

PODSUMOWANIE

Współspalanie odpadów w instalacjach przemysłowych możestanowić realną alternatywę dla termicznych metodzagospodarowania różnych rodzajów odpadów.

Najistotniejsza tutaj rolę mogą odegrać kotły energetyczne ipiece cementowe służące do wypalania klinkieru, którestanowią najkorzystniejszą grupę instalacji przemysłowychdo podjęcia procesu współspalania odpadów.

Piece cementowe jako nieliczne instalacje przemysłowe mogąbez kosztownych modernizacji sprostać aktualnymprzepisom w zakresie standardów emisyjnych.

Z drugiej strony istnieje coraz większa grupa odpadów,których unieszkodliwienie powinno odbywać się metodamitermicznymi. Dokonanie tego procesu poprzezprofesjonalne spalarnie odpadów jest nadal kwestiąprzyszłości.