1. Recent Developments in the Clean Combustion of Coal
Crispin Pemberton-Pigott
International Technical Consultant – WB CSI Projects
Presented at Warsaw, Poland
30 May 2017
Session: ‘Solutions – Part 1’

2. tHeory of smoke Production
Coal is placed top of a fire.
The coal is heated and volatile gases are given off.
Unburned gases produce ‘smoke’ which consists of condensed volatile matter, other combustible gases and unburned carbon.
Generally, a coal with a higher volatile content creates more smoke.
The result is terms like “high” and “low” quality coal  inappropriate
Clean Combustion of Coal

3. tHeory of smoke Production
‘Coked’ coal is ordinary coal that is roasted using a process called ‘destructive distillation’.
Known in China since the 9th Century that coking coal produces in a ‘low smoke fuel’.
In the mid 1800’s in the UK, train engines were required to “consume their own smoke”. So they had to burn coke.
Removing some volatiles produces a ‘semi-coked’ coal-based fuel: easier to light than coke.
Coke and semi-coke are often rejected as a domestic fuel, usually over ignition
Clean Combustion of Coal

4. Smoke Combustion
Stoves that burn all the volatiles make very little smoke.
Top-lit Updraft – load once, ignited on top, flames go upwards (Pat 1707?)
Bottom-lit Downdraft – coal loaded continuously from the top, ignited at the bottom, flames go downwards then upwards (Pat. 1688)
End-lit Cross Draft – coal loaded on the side, ignited on the bottom, gases move laterally through a coke bed and then rise as a gas fire (Pat. 1742).
Clean Combustion of Coal

5. CROSSdraft Stove Coal bunker on one side Fire at the bottom1 2 3 4 5
CROSSdraft Stove
Coal bunker on one side
Fire at the bottom
Flames rise from other side
Cooking and heating functions are relatively easy to arrange 3 1 2
CPP – GTZ 7.1, 2010
Clean Combustion of Coal

6. smoke COMBUSTION Solid fuel fires are “gas fires”.
All stoves burning all fuels create “smoke” within the fire.
If the smoke is not burned we see it coming out.
Some stoves burn most of the smoke – it depends on the stove architecture.
In theory a stove could burn all the smoke…
Clean Combustion of Coal

7. CROSSDRAFT STOVE Coal supply Pyrolysing zone Semi-coking zone1 2 3 4 5 6 1
CROSSDRAFT STOVE 5
Coal supply
Pyrolysing zone
Semi-coking zone
Coke burning zone
Gas burning zone
Cooking zone
Unlike a TLUD, it can be refueled while burning without affecting the emissions. 2 4 3
Clean Combustion of Coal

8. CROSSDRAFT STOVE Raw fuel Dehydration, devolatilisation starts1 2 3 4 5 6 1
CROSSDRAFT STOVE 5
Raw fuel
Dehydration, devolatilisation starts
Semi-coking with lots of smoke
Smoke ‘cracking’ inside the coke
Gas burning with secondary air
Heat transfer to pot
All processes continue indefinitely.
It is a miniature semi-coking factory! 2 4 3
Clean Combustion of Coal

9. 1 2 3 4 5 6 1
Crossdraft stove 5 1
The challenge is not to do it, it is to sustain this set of fuel processing and burning conditions.
4 The coke burns and shrinks, dropping ash into the ash drawer below
3 Pyrolysed coal drops down the grate
2 Semi-coked fuel falls into the space
I Coal in the bunker falls down 2 4 3
Clean Combustion of Coal

10. 1 2 3 4 5
Crossdraft stove 6 1 5
The depth of fuel in (4) determines the level of secondary air.
The gap under the bridge (3) combined with the grate angle controls the depth of the fuel.
The width of the grate (6) sets the fire- power level.
The volume of fuel in the bunker (1) determines the duration of the burn. 2 4 3 6
Clean Combustion of Coal

11. IMPACT – Indoor Air Quality
Clean Combustion of Coal

12. LAB TESTS – Mongolian Baseline 26.6g PM2.5 emitted in 2 hrs
Clean Combustion of Coal

13. LAB TESTS – GTZ 7.4 59 mg PM2.5 emitted in 3 hrs
Clean Combustion of Coal

14. LAB TESTS – KG4.0 100 mg PM2.5 emitted in 6 hrs
Clean Combustion of Coal

15. IMPACT – Indoor Air Quality
Clean Combustion of Coal

16. IMPACT – Indoor Air Quality
Clean Combustion of Coal

17. IMPACT – Indoor Air Quality
Clean Combustion of Coal

18. IMPACT – Indoor Air Quality
Clean Combustion of Coal

19. IMPACT – Indoor Air Quality
Clean Combustion of Coal

20. IMPACT – Indoor Air Quality
Clean Combustion of Coal

21. IMPACT – Indoor Air Quality
Clean Combustion of Coal

22. Conclusions AND ADVICE OVERALL PERFORMANCE
These stoves are at the pre-production prototype stage – more refinement needed
They heat and cook much better than all the traditional stoves
They have controllable heating and cooking power
They provide hot water 24/7
They all but eliminate indoor smoke
They provide 40% more heat burning 40% less fuel
They are made by artisanal welders ‘on the street’ for $160 (2 sheep)
Clean Combustion of Coal

23. Conclusions AND ADVICE CONCEPT OF ‘CLEAN’
The concept of ‘clean coal’ as currently used is inappropriate
The concept of a ‘polluting fuel’ as currently used is inappropriate
The concept of a ‘clean stove’ as currently used is inappropriate
Only a fuel + stove + user behaviour can deliver a ‘clean solution’
which means things are only really clean in a context
Accepting this this has far-reaching policy implications
Clean Combustion of Coal

24. Conclusions AND ADVICE INHERENT EMISSIONS - TOXINS
Some species of wood are highly toxic. We do not ban all biomass combustion. Come coal contains what might be, may be, dangerous levels of: Fluorine, Arsenic, Sulphur, Uranium, Mercury, Chrome… Do not use them as a domestic fuel if exposure cannot be managed. It is not reasonable to project that very real danger onto all coals of all types from all sources in the world – don’t generalize. This mischaracterisation of all coal’s inherent emissions is not sustainable.
Clean Combustion of Coal

25. Conclusions AND ADVICE INHERENT EMISSIONS REDUCTION
Inherent Emissions are not the result of poor combustion – it is in the coal Same fuel Improved stove Insulated home Fuel  Stove with 2x efficiency  House with 1/3 of heat demand = 1-(inherent emissions per kg x 0.5 x 0.33) = 83% reduction This applies to CO2, SO2, Hg, Cr6, U, etc …without fuel processing? Fuel is slightly processed – it is ‘sized’ to the stove’s requirements,10-25mm
Clean Combustion of Coal

26. Thank You! QUESTIONS
Clean Combustion of Coal