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Co-firing Biomass with Coal for Power Generation

Co-firing Biomass with Coal for Power Generation. Suthum Patumsawad Department of Mechanical Engineering King Mongkut’s Institute of Technology North Bangkok Thailand. Fourth Biomass-Asia Workshop “Biomass: Sources of Renewable Bioenergy and Biomaterial”

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Co-firing Biomass with Coal for Power Generation

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  1. Co-firing Biomass with Coalfor Power Generation Suthum Patumsawad Department of Mechanical Engineering King Mongkut’s Institute of Technology North Bangkok Thailand Fourth Biomass-Asia Workshop “Biomass: Sources of Renewable Bioenergy and Biomaterial” 20-22 November 2007, Grand BlueWave Hotel Shah Alam, Malaysia.

  2. Presentation overview • Introduction • Co-firing: concept and technology • Drivers and barriers • Lessons learned • Conclusions

  3. Power Generation Coal Used extensively to generate electricity and process heat for industrial applications. Poses significant world environmental problems: global warming (CO2) acid gases (NOx and SO2)

  4. Power Generation 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.

  5. Biomass characteristics • Lower density • Higher moisture content, often up to 50% • Lower calorific value • Broader size distribution, unless pre-conditioned by screening, crushing or pelletising • The variability of the material as a fuel will be greater

  6. 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 potentially, plant availability.

  7. The features of a small (10 MWe) power plant • 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)

  8. Co-firing Definition: simultaneous combustion of different fuels in the same boiler. Objective: to achieve emission reductions. This is • not only accomplished by replacing fossil fuel with biomass, • but also as a result of the interaction of fuel reactants of different origin, e.g. biomass and coal.

  9. Emission reduction

  10. Attitude to co-firing • 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.

  11. Co-firing: merits • 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.

  12. Co-firing: merits • 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. • 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.

  13. Co-firing: merits • 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.

  14. Co-firing: demerits • Feedstock pre-preparation may be required. For instance, wood requires chipping, straw may require chopping up, etc. resulting in increased energy requirements. • Some biomass materials have low bulk density (e.g. 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.

  15. Biomass co-firing (technology) • Direct co-combustion in coal fired power plant • Indirect co-combustion with pre-gasification • Indirect co-combustion in gas-fired power plant • Parallel co-combustion (steam side coupling)

  16. Direct co-firing

  17. Direct co-firing 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

  18. Biomass co-firing via pre-gasification(Indirect)

  19. Indirect co-firing for gas-fired boilers

  20. Parallel co-combustion(steam-side coupling)

  21. Drivers of co-firing 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

  22. Technical barriers • Thermal behavior and efficiency • Fouling and corrosion of the boiler (alkalis, chlorine) • Environmental constraints - emissions

  23. Lessons learned

  24. The combustion penalties involved in co-firing less than 20 th% biomass with coal are relative slight, verging on the non-existent. efficiency

  25. Slagging and fouling can be reduced with appropriate fuel blending.

  26. Co-firing provides means for emissions reduction • Reducing NOx emissions • Biomass blending decreases SO2 emissions • Trace organic compounds • Particulates

  27. Concluding remarks Co-firing represents a cost effective, short term option at a large scale Although biomass co-firing 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

  28. Thank you

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