Cofiring is a near term, low-cost option for efficiently and cleanly converting biomass to electricity by adding biomass as a partial substitute fuel in high-efficiency coal boilers. It has been demonstrated, tested, and proved in all boiler types commonly used by electric utilities.

1. COFIRING OF
BIOMASS

2.  Green house gases from burning fossil fuels have
caused the Earth's temperature to rise.
 Increasing the temperature of the earth or global
warming causing numerous disasters due to climate
change in a number of places on earth.
 When greenhouse gases not controlled then the result
of damage to the environment of the earth will be more
severe.
 Therefore, efforts were made to reduce greenhouse
gases as the cause of environmental problems.
INTRODUCTION

3. There are four common scenarios to prevent the global
warming effect of CO2 in the atmosphere gradually
 Increasing the efficiency so that the fossil fuel
consumption decreases
 Mix of renewable fuels with fossil fuels so that
fossil fuel consumption has also decreased
 Substitution of fossil fuels with renewable fuels
 The absorption of CO2 in the atmosphere so that the
concentration of greenhouse gases can be reduced.

4. Based on the origin and the effect that CO2 in the
atmosphere there are some basic terms
1.Carbon positive
2.Carbon negative
3.Carbon neutral

5. CARBON POSITIVE, CARBON NEUTRAL
AND CARBON NEGATIVE

6. CARBON POSITIVE
 Fossil fuel or fuel mines are grouped into
Carbon Positive fuel
 This is because the burning of this fuel
would make gas content in the atmosphere,
especially CO2 will increase. So this is
termed as carbon positive
 Increased CO2 in the atmosphere is the
source of global warming

7. CARBON NEGATIVE
 Biochar or agricultural charcoal is an example for
carbon negative
 The biochar is used to fertilize the soil by placing
it on the ground is a material that can absorb
CO2 from the atmosphere as well as increasing
the soil fertility, because its nutrient content and
media for microbial breeding
 Technology in the group Carbon Capture and
Storage (CCS) is a Carbon negative technology

8. CARBON NEUTRAL
 CO2 gas in the atmosphere
does not increase due to the
generation of energy from an
energy source it is said that
energy sources Carbon Neutral
 Renewable energy sources
such as biomass, wind, water
and sun are Carbon Neutral
 Material substitution of fossil
fuels with renewable fuels
included in the Carbon Neutral
scenario

9. COCOMBUSTION OR COFIRING
 Cofiring (also referred to as co-combustion) is
the combustion of two different fuels in the same
combustion system
 Fuels can be solid fuels or liquid fuels or gaseous
fuels and its source either fossil or renewable

10. COFIRING
 Process of replacing a portion of coal in power
plant boiler with biomass
 This can be done by either mixing biomass with
coal before fuel is introduced into the boiler, or
by using separate fuel feeds for coal and
biomass.
 Up to 15% of coal can be replaced with biomass
with little or no loss in efficiency.
 Very low cost; only small adjustments need to be
made to original facility

11. POWER GENERATION
Coal
• Used extensively to generate electricity and
process heat for industrial applications
• Poses significant world environmental problems
o global warming (CO2)
o acid gases (NOx and SO2)
Biomass: as a fuel source steadily increasing
 Biomass fuels are CO2-neutral, hence reduce
global warming effects
 The sulphur and nitrogen contents are often lower

12. BIOMASS CHARACTERISTICS
 Lower density
 Higher moisture content, often up to 50%
 Lower calorific value
 Broader size distribution, unless pre-conditioned
by screening, crushing or pelletizing
 The variability of the material as a fuel will be
greater

13. BIOMASS CHARACTERISTICS
 Such variations in fuel quality, compared to coal,
may have a number of implications for plant
applications that include process design and
operation, and potential of plant availability

14. INTEREST IN COFIRING WITH BIOMASS
 Due to increasing social concern about global
warming and Green House Gases (GHG) emissions,
cofiring is regarded as a great opportunity for
replacing coal (solid fossil fuel) used for power
generation with renewable fuels (biomass) with lower
costs and a direct decrease in green house gas
emissions

15. ADVANTAGES IN COFIRING BIOMASS
 Cofiring biomass also has the potential to reduce
CO2 emissions, as biomass can replace 20 to 50%
of coal
 Steadily increasing
 Biomass fuels are CO2-neutral

16. TYPES AND SOURCES OF BIOMASS
 Biomass fuel is defined as any organic material which
can be burned and used as a source of fuel
 It includes plant matter, animal and human waste,
industrial and municipal waste, waste products from
agriculture and industries can be used for this
purpose
 wood waste is a most popular biomass is used either
in pelletised or direct form used in co-firing
 This could be due to availability in large quantities
and in a suitable form for combustion with minimum
pre-processing


17. TYPICAL BIOMASS TYPES WITH THEIR
PROPERTIES COMPARED TO COAL
Fuel Calorific value MJ/kg
Coal 23 – 28
Sawdust/wood waste 9 – 12
White wood pellets 15 – 16
Black wood pellets 20 – 24
Rice husks 13 – 15
Wheat husks 17 – 19
Coffee grounds 21
Bagasse 17 – 18

18. PRETREATMENT OF BIOMASS
 Pre-treatment of biomass involves changing it into a
form which can be integrated into the fuel chain of
the generation plant without much change to the plant
itself
 It is generally unfeasible to reduce biomass to the
same size or shape as coal
 Pre-treatment includes pelletization or torrefaction

19. PELLETISATION
 Pelletisation is a process to physically densify fine
wood particles (sawdust, rice husk) into compact,
low-moisture capsules by applying pressure and heat
 Advanced (black) pellets can also be used
 Pellets of biomas have the same characteristics as
coal lumps and can be handled easier in the milling
process

20. TORREFACTION
 This consists of heating biomass in the absence of
oxygen, with reduced moisture and increased
energy density
 After torrefaction, biomass can be milled and
compressed to very dense pellets (black pellets)
 The energy density of torrified wood can be on the
order of 30% higher
 Because torrefied wood is brittle, it can be
pulverised and burned with coal

21. RATIO OF BIOMASS TO COAL
Depending on the plant set-up and the chosen
co-firing technology, substitution of more than 50%
of coal can also be achieved
 However, in most cases co-firing levels are below
5%, exceeding 10% on a continuous basis
 The co-firing mix also depends on the type of
boiler available
 In general, fluidised bed boilers can substitute
higher levels of coal with biomass than pulverised
coal-fired boilers, simply because of the larger
range of particle sizes which can be used

22.  Large investment cost/MWe of electricity
 Dependent on biomass availability
 Technical issues have to be considered in design:
erosion and corrosion, slagging and fouling of heating
surfaces.
 Lower plant efficiency than in large plant (scale
effects)
FEATURES OF A SMALL (10 MWE) POWER
PLANT

23. Definition: simultaneous combustion of different
fuels in the same boiler to achieve emission
reductions
This is
 not only accomplished by replacing fossil fuel
with biomass, also as a result of the interaction
of fuel reactants of different origin (biomass and
coal)
COFIRING

24. EMISSION REDUCTION

25. ATTITUDE TO COFIRING
 One regards coal as the problem (carbon dioxide)
 The other attitude sees coal as the solution (more
stable combustion characteristics).
But both attitudes are environmentally sound

26. MERITS OF COFIRING
 Some biomass fuels can be grown on redundant
agricultural or set-aside land, improving local
economics and creating jobs
 Increased plant flexibility in terms of fuels utilised
 Improved plant economics through the use of
zero/low cost fuel feedstocks
 Fuel feedstocks may be available locally, reducing
transport costs
 Replacement of part of the coal feed can reduce
dependence on imported fuels and help maintain
strategic national reserves of coal

27.  Reduced emissions of main classes of pollutants
through reduction in amount of coal burnt. This can
occur through simple dilution or via synergistic
reactions between biomass feedstocks and coal
 Several types of combustion and gasification
technology may be applicable to a particular
combination of feedstocks. These may include
pulverised fuel, bubbling fluidised bed combustion
and circulating fluidised bed combustion
MERITS OF COFIRING

28.  Feedstock pre-preparation may be required. For
instance, wood requires chipping, straw may require
chopping up resulting in increased energy requirements
 Some biomass materials have low bulk density (straw),
this resulting in the handling and storage of large
quantities of materials
 Moisture content may be high, reducing overall plant
efficiency
 Depending on the feedstock, the complexity of fuel
feeding requirements may be increased; some materials
can be co-fed using a single feed system whereas others
require a separate dedicated system
COFIRING DEMERITS

29. BIOMASS COFIRING TECHNOLOGY
 Direct cocombustion in coal fired power plant
 Indirect cocombustion with pre-gasification
 Indirect cocombustion in gas-fired power plant
 Parallel cocombustion (steam side coupling)

30. DIRECT COFIRING

31. DIRECT COFIRING
 This method uses a single boiler with either common or
separate burners to burn the biomass together with the
coal. Direct cofiring system includes
o Comilling
o Cofeeding
o Combined burner
o New burners

32. coal
Biomass Pretreatment
Burners
Boiler
COMILLING
Milling
• Primary fuel-coal
• Secondary fuel-biomass or waste
• Blended and milled in a single system
• Injected to the burners

33. coal
Biomass
Pretreatment
Burners
Boiler
COFEEDING
Coal mills
Modified
mills
• Separate treatment of primary and secondary fuels(milling)
• Incorporation of secondary fuel to main flow
• Mixture takes place downstream

34. coal
Biomass
Pretreatment
Modified coal
Burners
Boiler
Coal mills
Modified
mills
COMBINED BURNER
• Fuels are treated separately (milling) and transported to
burners
• Primary fuel uses original ports and secondary fuels uses
new ports
• Feeding does not involve fuel mixing
• Combustion stages take place simultaneously

35. coal
Biomass
Pretreatment
Coal
Burners
Boiler
NEW BURNERS
Coal mills
Modified
mills
Biomass
Burners
 Fuels use independant feeding lines
 Primary fuel-original injection system
 Secondary fuel- new burners

36. INDIRECT COFIRING
Biomass is converted to gaseous or liquid
fuels which is then burned with coal in a
boiler
Indirect co firing system include
1.Gasification system
2.Pyrolysis

37. GASIFICATION SYSTEMS
 Secondary fuel – transformed into gas by means of
gasifier
 Produced gas(producer or syngas) is injected in
coal boiler

38. PYROLYSIS
 Biomass is converted into bio char or bio oil and
then it is used

39. coal
Biomass Torrefaction
Burners
Boiler
Milling

40. PARALLEL CO-COMBUSTION
 A separate boiler is used for biomass and the steam
generated is then mixed with steam from the coal
fired boilers
Disadvantages
• Pre-preparation of
feedstock
• Handling and storage
• Moisture content will be
high
• Slagging and fouling issues

41. DIRECT COFIRING OF BIOMASS
Two methods were developed
 Blending the biomass and coal in the fuel
handling system and feeding blend to the boiler
 Separate fuel handling and separate special
burners for the biomass, and thus no impact to
the conventional coal delivery system

42. BIOMASS COFIRING VIA
PRE-GASIFICATION (INDIRECT)

43. INDIRECT COFIRING FOR GAS-FIRED
BOILERS

44. PARALLEL COCOMBUSTION
(STEAM-SIDE COUPLING)

45. DRIVERS OF COFIRING BIOMASS
 Reduces the emissions of greenhouse gases and other
pollutants
 Co-firing in coal plants would strongly increase
biomass use
 Lowest capital cost option for increasing the use of
biomass to produce electricity
 Co-firing biomass and coal takes advantage of the
high efficiencies obtainable in large coal-fired power
plants
 Improves combustion due to the biomass higher
volatile content
 Jobs creation

46. TECHNICAL BARRIERS
 Thermal behavior and efficiency
 Fouling and corrosion of the boiler (alkalis, chlorine)
 Environmental constraints - emissions

47. EFFICIENCY
COMBUSTION PENALTIES INVOLVED IN
COFIRING LESS THAN 20 TH% BIOMASS
WITH COALARE RELATIVE SLIGHT,
VERGING ON THE NON-EXISTENT

48. SLAGGING AND FOULING CAN BE REDUCED
WITH APPROPRIATE FUEL BLENDING

50. COFIRING PROVIDES MEANS FOR
EMISSIONS REDUCTION
 Reducing NOx emissions
 Biomass blending decreases SO2 emissions
 Trace organic compounds
 Particulates

51. SLAGGING
Two major causes contribute to slagging
during biomass combustion
 Crystal precipitation of alkali metal elements in
the biomass fuel and
 Ash fusion during biomass combustion

52. CRYSTAL PRECIPITATION OF
ALKALI METAL ELEMENTS
 A high concentration of K in biomass fuel tends to
result in the easy formation of compounds with low
melting points, and leads to severe slagging on
heating surfaces
 A portion of the soluble K turns into gas during
combustion and escapes with the flue gas
 Cl and K first combine into KCl (g), which then
condenses on heating surfaces with coarse fly ash
and forms adhesive bondings in the tube

53. ASH FUSION TEMPERATURE
When the furnace temperature is higher than ash
softening temperature ash would melt and would come out
of the surface bottom continuously as molten slag
Ash fusion temperature regarding coal

54.  Softening temperature (wood biomass) 950–1000°C
(straw biomass) 1000°C
(seaweed biomass) <800°C
 Herb biomass has a lower Initial Deformation
Temperature (IDT) of 730°C
 Biomass generally has a lower ash fusion temperature
than coal because of the high volatile matter and Cl
content in biomass and the high K content in ash

55. FOULING
 Vaporization of volatile inorganic elements during
combustion
 As temperature decreases these elements condense on
ash particles and heating surface forming a glue
which initiate deposition

56. BIOMASS ASH EFFECTS
 Most biomass materials have low ash contents (<5%), compared
to most power station coals
 The biomass ashes are very different chemically from coal ashes,
i.e. they are not an alumino-silicate system, but a mixture of
simple inorganic compounds, of Si, K, Ca, P and S
 There are concerns about increased rates of deposition on boiler
surfaces and the surfaces of SCR catalysts
 There are concerns about increased rates of high temperature
corrosion of boiler components, with high chlorine biomass
materials
 Biomass co-firing tends to increase the level of submicron
aerosols and fume in the flue gases, and may impact ESP
collection efficiency
 There may be utilisation/disposal issues with mixed coal/biomass
ashes

57. EFFECT OF BIOMASS ASH ON ASH FUSION
TEMPERATURES AND FOULING
BEHAVIOUR
Coal ash slagging
 For coals with high ash fusion temperatures, the addition of
relatively small amounts of some biomass ashes can reduce the
DT by as much as 200ºC
 For low ash fusion temperature coals, the effect is much less
dramatic
 For predictive purposes, the normal coal Slagging Indices can be
applied to mixed biomass-coal ash systems
 Empirical correlations permit estimation of the Deformation
Temperatures of mixed ashes
Coal ash fouling
 Fouling indexes for mixed biomass/coal ashes are based on the
alkali metal contents of the fuels

58. CONCLUSION
Cofiring represents a cost effective, short term
option at a large scale. Although biomass cofiring
technologies can already be considered as proven,
there is a continuous demand for equipment with:
 Lower investment and operational cost
 Increased fuel flexibility
 Lower emissions
 Increased reliability and efficiency