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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.