Co-firing Biomass with Coal for Power Generation Suthum Patumsawad Department of Mechanical Engineering King Mongkuts Institute of Technology North Bangkok Thailand Fourth Biomass-Asia Workshop Biomass: Sources of Renewable Bioenergy and Biomaterial November 2007, Grand BlueWave Hotel Shah Alam, Malaysia.

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

Power Generation Coal Used extensively to generate electricity and process heat for industrial applications. Poses significant world environmental problems: global warming (CO 2 ) acid gases (NO x and SO 2 )

Power Generation Biomass: as a fuel source. Steadily increasing Biomass fuels are CO 2 -neutral, hence reduce global warming effects. Biomass fuels are CO 2 -neutral, hence reduce global warming effects. The sulphur and nitrogen contents are often lower. The sulphur and nitrogen contents are often lower.

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

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. 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.

Large investment cost/MWe of electricity Large investment cost/MWe of electricity Dependent on biomass availability Dependent on biomass availability Technical issues have to be considered in design: erosion and corrosion, slagging and fouling of heating surfaces. 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) Lower plant efficiency than in large plant (scale effects) The features of a small (10 MWe) power plant

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, 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. but also as a result of the interaction of fuel reactants of different origin, e.g. biomass and coal. Co-firing

Emission reduction

Attitude to co-firing One regards coal as the problem One regards coal as the problem (carbon dioxide). The other attitude sees coal as the solution The other attitude sees coal as the solution (more stable combustion characteristics). But both attitudes are environmentally sound.

Co-firing: merits Some biomass fuels can be grown on redundant agricultural or set-aside land, improving local economics and creating jobs. 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. Increased plant flexibility in terms of fuels utilised. Improved plant economics through the use of zero/low cost fuel feedstocks. Improved plant economics through the use of zero/low cost fuel feedstocks.

Co-firing: merits Fuel feedstocks may be available locally, reducing transport costs. 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. 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. 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.

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. 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.

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. 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. 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. 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. 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.

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

Direct co-firing

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

Biomass co-firing via pre- gasification (Indirect)

Indirect co-firing for gas- fired boilers

Parallel co-combustion (steam-side coupling)

Drivers of co-firing biomass Reduces the emissions of greenhouse gases and other pollutants Reduces the emissions of greenhouse gases and other pollutants Co-firing in coal plants would strongly increase biomass use Co-firing in coal plants would strongly increase biomass use Lowest capital cost option for increasing the use of biomass to produce electricity 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 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 Improves combustion due to the biomass higher volatile content Jobs creation Jobs creation

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

Lessons learned

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

Slagging and fouling can be reduced with appropriate fuel blending.

Co-firing provides means for emissions reduction Reducing NO x emissions Reducing NO x emissions Biomass blending decreases SO2 emissions Biomass blending decreases SO2 emissions Trace organic compounds Trace organic compounds Particulates Particulates

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 Lower investment and operational cost Increased fuel flexibility Increased fuel flexibility Lower emissions Lower emissions Increased reliability and efficiency Increased reliability and efficiency

Thank you