21. COFIRING BIOMASS WITH COAL FOR POWER GENERATION.ppt
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Cofiring, the simultaneous combustion of biomass and coal, presents an effective strategy to reduce greenhouse gas emissions and mitigate global warming. By replacing a portion of coal with biomass, which is CO2-neutral, power generation can achieve lower costs and a decrease in environmental impact. Despite technical challenges, cofiring is recognized as a viable option for transitioning to renewable energy sources while utilizing existing coal power infrastructure.
21. COFIRING BIOMASS WITH COAL FOR POWER GENERATION.ppt
- 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
- 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
- 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
- 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