[Stoves] Burning unhealthy gases improves efficiency (Re: Philip, Crispin, Paul)

Fri Sep 8 21:09:58 CDT 2017

Dear Philip and Nikhil

While concurring with both the evolution of the 'solid fuels kill' theology and the driving off of volatiles, there is an aspect of making this work which applies to any solid fuel. It is that the gases produced are far better broken down (long chains shortened‎ to small molecules) if the volatiles/evaporated portions are passes through a hot bed of burning coke/char.

The stove were testing yesterday and the day before is a new iteration of the GTZ-7 from 2010 and features an 'error' in design that has the entire hopper heated outside by hot gases resulting from combustion. This is not all that helpful for burning high volatiles fuel but is aesthetically pleasing and simple to construct. In both Bishkek and Ulaanbaatar we found the performance improves when four bricks are placed in the gas-space against the outside of the hopper/bunker ‎to limit the heat getting into the hopper walls.

The trick to making this system work is to maintain a coke bed while pyrolysing ‎fresh fuel on a slow but continuous basis.

The MN4.01 in question is burning out the coke bed without properly maintaining the mass of fuel on it. This is caused by the clearance (gap) between the 'bridge' and the grate. The bridge holds up the divider between the fire and the hopper. It will be cast iron, and was carved from a brick. In the interim I am using a welded steel bridge.

If it is raised, fuel falls more easily ‎onto the lower grate, maintaining its depth. I have to raise it perhaps 5mm. This will reduce the excess air level as more coke is burning at once.

The goal is to get 8% O2 with coal and 10%, maybe 9% burning wood. (coal is more predictable so it can be run closer to the limit).

A second problem with that version is that the top was not screwed down tightly and I think quite a bit of air is leaking through, spoiling the draft, at least partly. That may affect the way the fuel falls onto the lower grate. Not much has been done to characterise that. We'll see.

The report from Bishkek is that the combustion is stable throughout the burn with the bricks in place: 28 MJ/kg ‎bituminous Kara-Keche. We didn't have a perfect burn with Baganuur (17 MJ/kg lignite) for the reasons mentioned. Altanzul is work on options in the coming week.

The MN4.01 has chambers for coal and fire made only of the plastic refractory materials (phosphate bonded) and they seem to perform well. Hard, strong, hold a great deal of heat and are thermal shock resistant.

Photo of the stove before the top is put on is attached.

Regards
Crispin

‎
Philip:

Thank you for the comment, "I think the remark about “Solid fuel stoves that cook the fuel are much cleaner, generally, than those which don't.” has to do with the removal of the volatile fraction of the fuel, which, for instance in bottom-lit fires, is driven off by heat as “smoke”."

I don't know why I misread it the first time; my eyes must have faced smoke. I should have interpreted it the way you describe.

I think Paul characterized it similarly - "making and burning gases". Except that it probably is not as much as "removing" the volatile fraction, but giving it the right amount of air and releasing it in gaseous form so it can burn cleaner.

About the 24MJ/kg coal you burnt -- was it high-vol to begin with and had it been ground finely? In a way, a pulverized coal furnace in a power plant, with exhaust gases being passed through a baghouse or an ESP to capture the very fine particulates, does the same thing, no?

Why do you call it a "working hypothesis", I wonder? This was the coal chemistry (and physics, due to different grinding index values) and combustion link I learnt.
++++

Here is a conundrum -- before 2000 or so, Kirk Smith used to discuss individual components of air emissions from "uncontrolled combustion of  unprocessed solid fuels" and claim that exposures amounted to smoking 400 cigarettes a day. Most of these were PAHs that could be just burnt away better (hence his qualification about "uncontrolled" and "unprocessed"; controlled combustion of either raw or processed fuels can achieve more complete combustion, depending on design and operational factors.)

Then he took a sharp turn sometime in the mid- to late 2000s and stuck only to "PM2.5" indiscriminately which he assumed to be equitoxic. (The only justification advanced is that "we don't know if that is not the case", which to me is irrational, given no causal links to disease patterns.)

Voila, "improved combustion" was out the window as a technical solution. "Solid fuels" became "dirty by definition", LPG became "clean by definition". "Killing by definition" followed logically, given the Integrated Exposure Response assumption.

For centuries and all over, humanity has tinkered with flow of air, temperature of combustion, fuel feed methods, shape and materials of stoves and furnaces of many a size, to improve efficiency and burn off volatile fractions (and water in some cases).

I have never known Prof. Smith to bother with metal content in solid fuels that is ash (or solid waste of combustion) or char left unused. He single-handed brought about a millennial intellectual revolution -- all solid fuels are dirty per se. No use bothering with improved combustion.

I submit this theology is at the root of the SDG that sets as goal a reduction in the % of households that use solid fuels as the primary energy source for cooking, and generates aDALYs so Gold Standard Foundation can collect fees by fooling the gullible.

Mere science has huge political consequences. Prof. Smith has driven a stake in the heart of "more complete combustion" -- "More Complete Union of Carbon and Oxygen", I used to say - that I suppose is the core mission of this group. I support his call for transition to LPG and electric induction stove, but I think it is still worthwhile to do better of what we know how to do better anyway.

Volatile matter has higher heating value, and more complete combustion not only burns off unhealthy gases but improves efficiency. If I had any objection to Crispin's statement, it is probably just that small solid fuel stoves for cooking are not as versatile as gas stoves, which meet user preferences for control and time-saving and leave no ash.

I wonder if cooking some foods releases PM2.5. Prof. Smith would declare not just that cooking kills, but food kills. (Which some do, but that is another tale.)

Nikhil

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On Wed, Sep 6, 2017 at 6:19 AM, Philip Lloyd <plloyd at mweb.co.za<mailto:plloyd at mweb.co.za>> wrote:
Nikhil, Crispin

I think the remark about “Solid fuel stoves that cook the fuel are much cleaner, generally, than those which don't.” has to do with the removal of the volatile fraction of the fuel, which, for instance in bottom-lit fires, is driven off by heat as “smoke”.  I recall our experiments with a 24MJ/kg coal burned bottom-lit, and the “smoke” collected on a small electrostatic precipitator we built. The ESP soon clogged! The material recovered from it was 33MJ/kg. Pyrolysing the coal at ~400 deg C until the volatiles were reduced to ~8% gave a 21MJ/kg fuel that emitted <5% of the smoke that came off the unpyrolysed coal under the same conditions.

Preheating the fuel, as happens in Crispin’s “cross-draft” stove, must help to release the volatiles early.  Well mixed with primary air, they then burn cleanly, and there is no smoke.

It’s only a working hypothesis; it would be interesting to sample the atmosphere in the fuel bed at the bottom of the preheating zone.

Philip

From: Stoves [mailto:stoves-bounces at lists.bioenergylists.org<mailto:stoves-bounces at lists.bioenergylists.org>] On Behalf Of Nikhil Desai
Sent: Wednesday, September 6, 2017 4:36 AM
To: Crispin Pemberton-Pigott
Cc: Discussion of biomass cooking stoves
Subject: Re: [Stoves] News: National Geographic on promotion of gas stoves over improved woodstoves - in Guatemala

Crispin:

I am humble, not a humbler. Of course I won't have heard of "Guidance Unto the Ignorant". I learnt some 25+ years ago, "You don't know more, you just know different things." (From a 4-year old. I celebrate her as my teacher.)

Of course "pride of ownership" matters and factors into "price of ownership" users are willing to pay. That was the point of my "Modern Cooking" piece five years ago - moving away from purely "scientific" metrics and placing the cook in the center.

I don't know how much coal is used in cookstoves; in India, limited to one or two states, more in rural China. I don't know about Indonesia, Colombia, Korea, Mongolia any longer. But I agree there is more potential in coal than general biomass (dung, straw, wood waste) simply because coals are regionally specific and can be made consistent quality by price premia for quality. Same can be applied to wood. All depends on how much fuel is self-generated (farm waste, dung) and collected.

All the "cookstoves and health" literature has failed to collect any data on stove type (the song goes "three stone fire or other traditional stoves"), fuel collection (scavanging or self-produced), dwelling type or size/quality of ventilation. If we bothered to define the context, we would have a better definition of the problems than theorizing in air-conditioned hotel rooms.

I am not yet ready to endorse your view that "Solid fuel stoves that cook the fuel are much cleaner, generally, than those which don't." Because the quality and relative cost of fuels and stoves, and user preferences, matter.

After all, cookstoves are for cooking meals, not merely generating heat. The heat that matters comes from spices and conversations.

Nikhil

On Tue, Sep 5, 2017 at 9:35 PM, Crispin Pemberton-Pigott <crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>> wrote:
Dear Nikhil

As paid up members of Humblers Anonymous we should carry on offering what we can to whoever will accept it. Have you heard of the book from the 1800's "Guidance Unto The ‎Ignorant"? That guy should join our club.

Regarding 'cool inventions': inventors want their creations to be considered as cool as they think they are. Customers often have a different concept of what is cool.

In some markets 'pride of ownership' is about what others think is cool. It rates highly, number 3 or 4, in ranked purchasing decision contributors.

For solid fuels and generating some sort of broad revolution, I hold far more hope for coal burners than wood because in a large fraction of places where coal dominates domestic energy, there is no option, or the option is limited and in the process of being actively conserved. It is far easier to burn coal cleanly than indeterminate wood. Animal dung is quite predictable but requires some basic processing in many cases.

For biomass, processed wood and slash holds promise but the 'exciting' developments are (largely) in the grip of the char-makers with their own agenda to which the users should bend their lives. How often does that work?

If I advised the TLUD promoters I would suggest getting widespread adoption of the devices before trying to hornswaggle funding mechanisms for char buy-back ideas. If gasifiers generate twice the heat of charmakers from a kg of fuel‎, that is serious competition against the alternative.

Solid fuel stoves that cook the fuel are much cleaner, generally, than those which don't. That's a fundamentally different approach and qualifies in my book as a shift as great as introducing kerosene.

Regards
Crispin

Crispin:

In all humility, may I suggest that your answer "Ignorance about how to invent cool stuff and get it adopted" comes across as a bit arrogant?

Under conventional stereotype, where women are the principal home workers and hold exclusive responsibilities and powers over cooking and feeding (if not on purchase of food ingredients), I submit that cooking is about (a) women's time and energy allocation; and (b) the overall human environment, in and around the homes.

There is perhaps not a single "cool" invention in solid fuel cookstoves does not seem to hold much promise for the Third World masses the way it happened with, say, Primus or Nutan stoves using kerosene some 60-80 years ago, or LPG/electric stoves and other thermal appliances over the last 50 years to this date. (There are fancy wood cookstoves in the Western markets as well).

Then again, who knows, wood or pellet stoves with electric assist may change a lot.

I do agree there is a wide chasm between the users and the inventors, and the overall context of fresh and waste biomass with considerable variation in economic geography, that may be said to limit success with solid fuel stoves in the past.

Remember, the current fraction of humanity, the Bottom Half, is more variegated structurally from the upper half than was the case 50 or 100 years ago. And the bottom 20% if much farther apart in assets and income from the top 20% than ever, at least in the last 100 years.

Population and human capital (health, education/skill-base, employment, security) dynamics are far more complicated than the simple mindsets of the 1960s to 1990s suggest (and which is what lies within many of us).

Thank you so much for the pithy "Hence, the current mess."

As GACC slides into the last three years of its plan, it's worth revisiting "the mess". Reformed thinking and institutional apparatus are necessary.

Nikhil

On Mon, Sep 4, 2017 at 11:59 AM, Crispin Pemberton-Pigott <crispinpigott at outlook.com<mailto:crispinpigott at outlook.com>> wrote:
Dear Gordon

- What are people trying to do?

Invent cool stuff and get it adopted to help save the world.

- What problems are getting in the way of your success?

Ignorance about how to invent cool stuff and get it adopted.

- What collaborations are possible?

The best one would be for the ‘stovers’ to approach social scientists to find out in much clearer detail why people behave the way they do when they use domestic energy and apply it in their lives.

There is usually a gulf between the wanna-be designers and the potential users, as large as the gap between marketing people and the self-same designers.

A three-way collaboration between marketing, design/engineering and behavioural scientists would produce products that would naturally attract funding.

At the moment people seek funding first, technical solutions second, marketing expertise third, and a deep understanding of the users last.

Hence, the current mess.

Regards
Crispin

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