[Stoves] A Laboratory Assessment of 120 Air Pollutant Emissions from Biomass and Fossil Fuel Cookstoves

Tue Jun 11 19:22:05 CDT 2019

Dear Andrew

That is a good and relevant set of questions.

>Right so Neil honed in on this little counter intuitive snippet from that abstract, kerosene can be cleaner than LPG but is this with an optimally performing LPG stove?

The same question should always be asked!  Was the kerosene burning appliance used to decide that "kerosene is a dirty fuel" the best available on the market at the time in that community?

LPG can be burned badly - something repeated demonstrated on stage by Prof Philip Hopke when he speaks about the origin of particles. At the GACC Roadmap meeting in Thailand he did exactly that. He showed that with an inappropriate air supply, a propane torch could make a large yellow and smoky flame.

So even if the device is good, it might not be operated properly, introducing a new question: Did the user know how to get the best performance from the appliance tested?

>...why does a forced draught or insulation increase carbonyls or PAHs,

Forced draft can cause a host of problems. That is evidence for the silliness of saying, "Only forced air stove can meet Standard xxx..."

The main reason for an increase of CO is cooling of the fire with over-supply of air. An increase of NO is caused by a reduction in the residence time of the NO in a high temperature environment.  Fans help do that.  An increase in PAH can be caused by simultaneously lowering the temperature and residence time.  Black carbon is reduced with better mixing so there may be a lowering of BC and an increase of anything with a longer decomposition time.

>I can well understand (and Tami mentioned it in the past) that a fan can loft ultrafine particles of ash

Sure. And is ash as toxic as PAH's and BC and CO? Emissions are note created equal, in spite of the EPA's assumptions. I think this year we should discuss how to change that ruling and bring in a proper evaluation of the impacts - social and environmental - created by stove emissions. This "4m people die per year from breathing..." quote has to be challenged on multiple grounds. It is being repeated as if it somehow represents the truth.

>I would expect more compounds containing carbonyl groups to get oxidised to CO2 with increased temperature and mixing.

The mistake in thinking is that assume that blowing on a fire increase the temperature. Do you remember when Aprovecho first added a fan to a charcoal stove and reported here that the CO greatly increased? Blowing on a charcoal fire greatly increases the amount of heat produced, but doesn't necessarily increase the temperature of the fire. The temperature of an object in the fire can increase - like a sword being hammered - but there must be a clear separation of the temperature from the quantum of heat produced.

The CO went up because the fire was being cooled by the cold air blown by the fan. That is not a generic result, that was specific to the device. If the air had been fan-blown and preheated to 7-800 C before reaching the fire, the CO produced would have dropped.

A major problem these days is NO produced by wood burning appliances. Wood contains enough N to create more than twice the permitted NO mass. Blowing on the fire is going to make the problem worse in nearly all cases. The new giant ESKOM power station in South Africa has a serious problem with meeting the NO standard (they are unable to do it). They bought an indulgence and exceeded their indulgence. Yeah.

Fans are great for creating optimal combustion conditions immediately, controllably, and variably. Natural draft, not so much. ND is better suited to doing something that is steady, constant, unchanging, where the system stabilises and "processes" the fuel in a predictable manner.

Best regards from the sweaty palms of Johor

Crispin
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