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Embracing Coal: Cleaner Combustion Techniques for Domestic Stoves

This position paper by Crispin Pemberton-Pigott presents an insightful discussion on the perception and realities of coal as a fuel source. It emphasizes the need to rethink coal's classification as a "dirty" fuel, highlighting its historical context as old biomass and its efficiency in energy production. The paper outlines the challenges of coal combustion, particularly with improper stove designs that cause emissions. It introduces innovative combustion methods like Top-lit Up-draft (TLUD), Bottom-lit Down-draft (BLDD), and End-lit Cross-draft (ELCD) that significantly reduce particulate emissions and enhance energy efficiency.

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Embracing Coal: Cleaner Combustion Techniques for Domestic Stoves

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  1. Workshop Session onSolid Fuel Combustion or How I stopped preaching to the CHOIR and learned to love COAL Position paper: Crispin Pemberton PigottNew Dawn Engineering Workshop on Domestic StovesInternational Conference on Domestic Use of Energy: DUE 2011, Cape Peninsula University of Technology, Belville, 12 – 13 April 2011

  2. What COAL is not • is not a dirty smoky fuel any more than paraffin is (and it is not) • does not contain ‘smoke’ • does not contain carbon-monoxide (CO) • does not contain particulate matter • does not cause radiation burns or radon gas or any nuclear threat not already present in bananas (which contain Potassium 40)

  3. What COAL is • it is very old biomass – the old green • it is (usually) a high energy fuel per kg • it is relatively low in O2 compared with new biomass • it is widely used by poor people for almost all their energy needs • it is widely vilified as a ‘dirty fuel’, in fact it has been demonized as the very definition of dirty fuel

  4. Why do COAL stoves smoke? • because the stove does not burn all the fuel • or all the CO • or all the smoke • because the stove was not designed to burn coal • It is the STOVE which smokes, not the COAL!

  5. Baseline Stove Emissions of PM 2.5

  6. Clean ways to burn COAL • Fluidised beds? Not really, at least no so far. • In a cast iron coal stove? Not really, so far. • Co-fired with wood? Bad experience so far. • Gasifier, yielding coke? Big energy losses. Only three methods found so far • Top-lit Up-draft (TLUD) stoves • Bottom-lit Down-draft (BLDD) stoves • End-lit Cross-draft (ELCD) stoves

  7. Why do these three methods work? • They have common elements in their design: • Only a small portion of the fuel is ignited at once • Newly evaporated volatiles are passed through a bed of hot coke • The volatiles are cracked to make producer gas • Ash is cleared from the places where gases burn • Excess air is limited => good air:fuel ratio • Correct primary:secondary air split (not the same as the correct air:fuel ratio)

  8. Hopper-fed cross draft stove

  9. The gas path is long

  10. ELCD PM2.5 Reduction PM 2.5/m3 & Mass burned Time (minutes)

  11. Crossdraft PM 2.5 Reduction PM 2.5/m3 & Mass burned Time (minutes)

  12. TLUD PM2.5 reduction PM 2.5/m3 & Mass burned Time (minutes)

  13. Hopper + crossdraft PM 2.5 reduction PM 2.5/m3 & Mass burned Time (minutes)

  14. Comparison of 20 stoves PM 2.5 Official Target 2008: 30% reduction Unofficial Target: Target: 98% reduction Achieved March 2011: 5 successful products >98% reduction Best: >99% (3 products) PM 2.5 perNet MJ “Improved” stove 2000 Baseline 1000 Really improved! 500

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