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Thermoelectric fan to filter coal smoke

You know, for your yurt
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I am just on my way home from spending 4 days in Ulaanbaatar, Mongolia.  Cold, interesting and very very smoky.  The entire city is in the bottom of a wide river valley and for the duration of winter a thick miasma of coal smoke sits over the place so thick you can't see 2 blocks and, more importantly, is a very serious health hazard.

When winter comes to Mongolia, additional poor people move into the city join their brethren who are already there all living in the circular felt tents known as "Yurts".  In the centre of each yurt is a pot-bellied stove with a single stovepipe going up through the top of the roof.  The only fuel in this mostly treeless land is crude coal which creates a lot of smoke.  The people have few choices about what to burn as nothing else is a cheap as coal and they naturally need to keep warm in the Mongolian winter.

I've been trying to think of an inexpensive way of mitigating the issue and the best I came up with is an attempt to filter the smoke before it hits the open air.  There are many inexpensive filter ingredients available such as felt, charcoal etc which the locals could make and clean themselves - although flammability will be an issue.  The problem is that smoke won't force it's way through a filter without some assistance. My proposal is to manufacture cheap Thermoelectric generators driving a fan in the stovepipe. 

Thermoelectric generation works by temperature differences and that is something the average Mongolian has lots of in winter. My device would affix to the top of the stovepipe and would only engage and divert the smoke when a thermocouple senses that the stove is up to temperature. One side of the device sources the residual heat from the smoke and the other to a pan of water/ice on top of the yurt. This powers the fan to force the smoke through the filter which can be replaced or washed out as needed. 

I'm pretty serious about coming up with an affordable solution as I can’t imagine living in those unhealthy conditions on a long term basis, let alone raising kids there. All suggestions and improvements welcome. Remember, it has to be simple and cheap

AusCan531, Dec 02 2013

Franklin stove http://en.wikipedia...wiki/Franklin_stove
Appropriate technology [8th of 7, Dec 03 2013]

Smoky Ulaanbaatar, Mongolia https://www.google....atar+smoke&tbm=isch
It's one thing to see, another to breathe. [AusCan531, Dec 05 2013]

Thermoelectric powered fan https://www.gyrosco...asp?product=ECOFAN2
Seebeck Effect. [AusCan531, Dec 05 2013]

Closer... http://www.biolites...m/about/technology/
Uses a thermoelectric fan to reduce pollution, but by improving combustion, rather than by filtering. [spidermother, Dec 05 2013]

It seems small reductions in smoke don't make much difference in health outcomes. http://www.bbc.com/news/magazine-38160671
[AusCan531, Dec 07 2016]

Cockcroft–Walton generator https://en.wikipedi...%93Walton_generator
"... generates a high DC voltage from a low-voltage AC or pulsing DC input." [8th of 7, Dec 10 2016]

Santa's Ger http://i.imgur.com/NAcDHfv.jpg
(Not a Yurt in Mongolia as that's a Russian term.) [AusCan531, Dec 12 2016]

Me visiting my Mongolian Family. http://i.imgur.com/esrDb28.jpg
[AusCan531, Dec 12 2016]

Images inside a Yurt/Ger many showing simple stove in question. https://www.google....920&bih=950#imgrc=_
[AusCan531, Dec 12 2016]

The Great Smog https://en.wikipedi...reat_Smog_of_London
Not very nice [8th of 7, Dec 14 2016]

Coalite https://en.wikipedia.org/wiki/Coalite
A typical smokeless fuel [8th of 7, Dec 14 2016]

[link]






       A more efficient stove is the answer, shirley ?   

       Some sort of secondary combustion of the smoke, using an inverted syphon, would probably be the thing to go for.   

       With a tall flue, and good convection, there will be enough pressure difference to draw extra air into the secondary chamber - possibly an annulus situated above the hearth.   

       No moving parts, just more metalwork inside the stove.   

       "Another early example of an inverted siphon was a stove that was exhibited in 1686 at a fair in St. Germains, France. Its inventor, André Dalesme (1643–1727), called it a smokeless stove (furnus acapnos). The stove consisted of an iron bowl in which the fuel was burned. A pipe extended from the bowl's bottom and then upwards into a chimney. Shortly after starting a fire in the bowl, hot air would begin to rise through the pipe and then up the chimney; this created a downward draft through the bowl, which drew the fire and its fumes down into the bowl. Once the draft was initiated, it was self-sustaining as long as the fire burned.[11] Dalesme's stove could burn wood, incense, and even "coal steept in cats-piss" yet produce very little smoke or smell.[12][13] These results showed that fires could be used inside a room, without filling the house with smoke."   

       <link>
8th of 7, Dec 03 2013
  

       Sounds good to me 8th. I will have a read when I get home and my legs under me. All I know is that something needs to be done.
AusCan531, Dec 03 2013
  

       We suggest that this idea is somewhat redundant as smokeless stoves are WKTE, although the thermoelectric fan is sufficiently overcomplicated, expensive and unnecessary to justify the idea per se as halfbaked.
8th of 7, Dec 03 2013
  

       //coal steept in cats-piss   

       That's obviously some specialist market there...
not_morrison_rm, Dec 03 2013
  

       I'm just home but from my quick reading, the "smokeless" part of the smokeless stoves described in the Wikipedia are designed to reduce/eliminate the smoke getting into the house. I'm trying to reduce the amount of smoke getting into the outside environment (without increasing the house smoke).   

       As [8th] mentioned in his anno, secondary combustion of the smoke would help - but that would only apply to new stoves whereas I'm trying to cheaply retrofit the existing units - unless of course a secondary combustion unit could be cheaply retrofitted. I am concerned that the Seebeck power generation system might be a bit anaemic to push the smoky air through a filter.
AusCan531, Dec 04 2013
  

       Filters aren't the way to go. If they're effecient enough to make a difference, they'll also clog fast. Then you have a filter full of pyrolised coal products (nasty) to get rid of.   

       If you want a cheap, low-maintainance solution, it's going to have to implement more efficent primary combustion, i.e. hotter and more stoic. That will also mean more heat from the stove, a benefit for the user, and less smoke.   

       Then you need to re-burn the combustion products, with added air to get the stoichometry right, which will fully oxidise particulates and as a bonus produce even more heat.   

       Some sort of reflow syphon with air entrainment which replaces the stovepipe above the existing stove would be a possibility. But not filters; maybe some sort of catalytic reactor, but catalysts are notoriously easy to poison, particularly with sulphur.
8th of 7, Dec 04 2013
  

       AusCan wins the 'furthest traveled baker with the most obscure destination of the year' award.   

       Given the presence of the Heat source and water source from the river, I see some kind of a cheap kettle-top stirling engine that could also double as a humidifier.
RayfordSteele, Dec 04 2013
  

       //hotter and more stoic//   

       stoichiometric, perhaps?
MechE, Dec 04 2013
  

       No, produces more heat, and doesn't complain.
8th of 7, Dec 04 2013
  

       //Filters aren't the way to go. If they're effecient enough to make a difference, they'll also clog fast.//   

       I suspect that you're quite correct here. If we were only talking a few kilos of smoke particulates it wouldn't be an issue. I was pondering charcoal or similar (powdered coal? - flammability hazard?) which could be dumped into the stove when full and help achieve 'secondary combustion' that way.   

       For interest's sake, I've posted a link to Google Images of the situation in Ulaanbaatar. I've also posted a link to a Seebeck effect fan although I'm not sure it would have the oomph to perform the task needed. Perhaps it could just draw the smoke back down to be injected into the stove body for couple iterations before being released to the outside? Good heat retention there.
AusCan531, Dec 05 2013
  

       I'm wondering about the filtration capability of dried yak poo, if modified in some such fashion. Most is probably burned for fuel. But maybe some could be spared?   

       Or perhaps a weaving of yak hair...   

       Both probably too flammable to be considered.
RayfordSteele, Dec 05 2013
  

       Not as big of health outcomes as one would expect. [Link]
AusCan531, Dec 07 2016
  

       what about electrostatic.
FlyingToaster, Dec 08 2016
  

       Auscan, did you get to see one of these stoves close up? I picture them like a Franklin stove. Is air for combustion outside air drawn by a dedicated inflow circuit, or warm inside air?   

       In general, though, I despair of any prospect than an individual would spend a penny of his own on any endeavor which contributes only to the common good. Such endeavors are the job of government.
bungston, Dec 10 2016
  

       // contributes only to the common good. Such endeavors are the job of government. //   

       <Inscribes [bungston]'s name on the list of pinko commie crypto-Maoist hand-wringing tree-hugging liberal woofters, to be Put Up Against A Wall And Shot When The Revolution Comes*>   

       *21 January 2017, or nearest practicable date thereafter.
8th of 7, Dec 10 2016
  

       /pinko/ more of a delicate puce. That is one syllable: puce. The e does not get its own syllable.   

       That said; schemes. The problem with smoke is soot: macroscopic particles. I envision the Mongolian winter air as cold and very dry.   

       1. I assert here that if humidified these particles will be weighed down and will fall from the air more readily. A water reservoir will be attached to the chimney and heated by the waste heat from the chimney, humidifying the passing soot such that it precipitates out more readily onto outdoor surfaces. In an ideal situation this could be augmented by an extra tall metal chimney pipe, the walls of which would act as a condenser. Sooty steam would condense and then run back down and fall into the stove for another chance at combustion to CO2.   

       I am aware of a thing called London Pea Soup and am not able to reconcile my idea that humidified soot will precipitate out more rapidly with the existence of fog / smoke hybrid. One would think the two would be enemies.   

       2. Different scheme! Charged particles are sticky. I propose that an electrostatic generator, attached to the chimney and turned by the emissions, can impart charge to the soot as it emerges. These devices can be simple, involving something rubbing electrons off of some different thing. Charged soot will stick to other soot and anything else around, rapidly leaving the air. I think there exist electrostatic air cleaners which work this way. I remember seeing on in a restaurant, its charge emitter pointed at a wall where there had formed a huge black splotch.   

       While I was typing this FlyingToaster had the same idea. I conclude the idea is good.
bungston, Dec 10 2016
  

       Scheme 3: spiral stovepipe. The exhaust pipe spirals around tightly as it exits the stove. Radiator wings are placed on it, up above the floor level. It is attractive to the users because a given load of fuel has more chance to unload its heat into the living space. Also because the government gave it to them. It is harder to clean because one cannot use a brush on a stick - one must drop a brush pig on a weighted string and pull it thru.   

       The spiraling of the smoke will give more chance for particulates to be deposited within the pipe. I can see the water tray scheme (#1) integral to the pipe but people would never remember to fill it.   

       The spiral pipe wraps around a central straight pipe. This straight pipe descends down through the stove to the bottom and then off to one side. It is an air intake. The spiraling exhaust heats incoming air for combustion. One does not use warm inside air for combustion. The yurt is warmer as a result.   

       I could not think of a way for the air intake to capture soot from the exhaust without capturing the rest of the exhaust.
bungston, Dec 10 2016
  

       // attached to the chimney and turned by the emissions, can impart charge to the soot as it emerges. //   

       Use a thermopile to generate electrical energy. Use a semiconductor switcher and a C-W multiplier ladder <link> to generate the EHT for the precipitator.   

       But since the problem is // Mongolian winter air as cold and very dry. // then shirley the answer is a very, very long intake pipe to draw air from warmer, moister latitudes ?
8th of 7, Dec 10 2016
  

       Leave the thermoelectric-powered fan, but use it to increase the speed of the smoke even more. Then pipe it through a long flu on the ground with no filter, giving the soot time to settle out. You'll still have acid in your lungs on foggy days, but the soot will be taken care of. Design the flu to be easily opened for shoveling out the built-up soot.
Voice, Dec 10 2016
  

       Soot, being largely amorphous carbon, is combustible - so collecting it and re-burning it makes sense.
8th of 7, Dec 10 2016
  

       <Michael Caine voice> They aren't called yurts. Yurt is the Russian name for them, in Mongolian it's "Ger". Not a lot of people know that</MC>
not_morrison_rm, Dec 11 2016
  

       How to route the air intake thru the exhaust so it sweeps up the soot and carries it back in?   

       Maybe if the exhaust entered a chamber at an angle such that it produces a vortex? But could incoming air come thru the center of the vortex and carry back in the particles?
bungston, Dec 11 2016
  

       You'd need a vortex separator in the outflow, and some way of passing the particulates back into the intake stream … like a Buchner pump, for solids ?   

       <later>   

       Vanes on a shaft inside the vortex separator could turn a smalll worm drive to shift the particulates through a non-return valve into the intake, or the combustion chamber.
8th of 7, Dec 11 2016
  

       Push them as a solid using a screw! Nifty.
bungston, Dec 11 2016
  

       // Soot, being largely amorphous carbon, is combustible - so collecting it and re-burning it makes sense //   

       Seems like this leads back to your earlier suggestion of doing secondary combustion on the smoke rather than getting the soot to settle out, collecting it and burning it. I guess it is easier to re-burn if it isn't mixed with a large quantity of oxygen-depleted air.
scad mientist, Dec 12 2016
  

       //did you get to see one of these stoves close up?//   

       Not a 'real life one' although I've attached a pic of a very special one I did visit. I also picture a simple Franklin stove in the middle. [not_morrison_rm] is quite correct about the Yurt/Ger thing.   

       BONUS LINK I've also attached a picture of me visiting my Mongolian family courtesy of Photoshop and a smart-arse employee.
AusCan531, Dec 12 2016
  

       heh.   

       Assuming smoke is heavier than air - in the sense that it can be centrifugalized - we can push it to the wall of the column, where incoming air within the outside pipe collects it through the venturi effect.   

       What about volatiles ?
FlyingToaster, Dec 12 2016
  

       // smoke is heavier than air //   

       That's more a function of temperature; the hot air "carries" smoke particles better due to the more vigorous motion. Volatiles ? Again, the heat keeps them vapourized.   

       Cool the smoke to ambient. The volatiles condense out and are absorbed by the clumped particulates. Et viola ! Burnable solid fuel.
8th of 7, Dec 12 2016
  

       /cool to ambient/ If this could be done inside the living space it would have the added benefit of maximally transferring heat energy.   

       Another benefit of the spiral stovepipe - outgoing smoke is cooled by incoming air for combustion down the center pipe.
bungston, Dec 12 2016
  

       //Another benefit of the spiral stovepipe - outgoing smoke is cooled by incoming air for combustion down the center pipe.//   

       As long as the stovepipe continues to draw air out of the structure....
AusCan531, Dec 12 2016
  

       While one batch of coal is burning, the next can be improved through pyrolysis - draw off the water and low-temperature volatiles, the latter sent into the flames for a more complete combustion than otherwise, perhaps with its own draw of air.   

       Doing it in the oven has the advantage of producing the cleanest coal. Doing it on the stove top has the advantage of not accidentally setting the yurt on fire by opening the lid before the contents have cooled below their ignition point.
FlyingToaster, Dec 13 2016
  

       Not that I meant to stuff a shoe into the ongoing heat-exchange conversation, just that better coal means a hotter flame means less smoke to deal with in the first place.   

       I'd suggest insulating the outside of the heat-exchange smokestack. Premise is that the more convective air currents in a room the greater the heat loss through the walls.
FlyingToaster, Dec 13 2016
  

       /improved thru pyrolysis/ very nice idea. There can be a bin inside the stove. Close it up - a hole in the bottom allows vapors out into the burn chamber. Next load cooks while current load is going.   

       /insulating the outside of the heat-exchange smokestack/ I dont get this. The outer spiral is hot and you want some of that heat into the room if you can get it.   

       / As long as the stovepipe continues to draw air out of the structure.... — AusCan531/ Making it like a Franklin stove means the stove air is a closed circuit. I think Franklin stoves draw horizontally thru a wall but no reason they could not draw thru a separate vertical pipe that runs the same general route as the exhaust stovepipe.
bungston, Dec 13 2016
  

       So what's being advocated is a small-scale coke oven.   

       Process inputs - coal and air.   

       Run the coal through the water-gas/producer-gas reaction. The resultant gas can be used for heating elsewhere in the building.   

       Importantly, water must be condensed in the remote combustors to feed back into the water-gas cycle. Unlike in a gasworks, the tar and ammonia are fully oxidised and discharged to atmosphere.   

       The residue is coke. Just add air, for more thermal energy.   

       Finally, remove the ash and clinker, and either use it for aggregate in concrete, or dump it in a far-away hot country full of impoverished dark-skinned people who are too desperate and poorly-educated to realise what's being done to them*.   

       *Add some toxic organic waste as a binder. An extra wad of greenbacks into the president's numbered Swiss account will ensure that all environmental regulations are fully complied with.
8th of 7, Dec 13 2016
  

       Apparently the lower grades of coal are one third to one half mechanically and chemically trapped water - that's probably the most important to remove, for a higher temperature (ie: cleaner burning) flame.   

       As well as plain old thermal preprocessing, there's the Coldry process, consisting of removing the 35-45% mechanically and chemically trapped water by weight, by mechanical means. That might be suited towards the coal-providers who could save on transportation costs with a higher energy:weight product.   

       //insulating the out side of the heat-exchange smokestack// Posited is that a floor-to-ceiling hot pipe in the middle of the room will cause a major convective loop which mostly heats the roof and walls. If you have an efficient heat-exchange happening, it's not necessary to provide that much surface area in that configuration.   

       A thermoelectric-powered rotating fan washing across the top or sides of the oven might be better.
FlyingToaster, Dec 14 2016
  

       // efficient heat-exchange happening, it's not necessary to have that much surface area in that configuration //   

       Hmmmm …   

       At the start of the exchanger, that's true, but as the temperature drops the rate of flow diminishes proportionately. Heat flow is a direct function of differential temperature.   

       At that point increasing the contact area pays dividends.   

       Initially the main mechanism is likely to be radiative, but at lower temperatures, convection predominates.
8th of 7, Dec 14 2016
  

       When London outlawed dirty coal to decrease smog, what was substituted for home heat? It seems to me that was the same problem, and was solved. Minus the yurts.   

       My limited understanding is that the better grades of coal make better coke but any coal can be cooked into coke. Converting low grade coal to coke at a site remote from the end user (for example, near the mine) makes sense because 1: economy of scale 2:airborne effluent will be outside the city and as noted, 3: reduced transport cost for the lighter coke.   

       Mandating a process change by a limited number of miner / distributor companies seems more promising than trying to get the citizenry to change what they do on a wide scale. If coke started being delivered instead of coal I imagine the yurt dwellers would figure out what to do with it.
bungston, Dec 14 2016
  

       Re stove images: they must be taking in room air for combustion, which is then replaced by cold outside air coming thru cracks. I do not see where the stove gets its air, though.   

       1. External air source could be a thin pipe inside the existing stove pipe (maybe that is already there?), or second pipe along the floor to the outside. People would trip over floor pipe. Kids probably already bump into stove/ stovepipe and get burned.   

       2. Thermoelectric fan should circulate room air thru stove in sealed conduit. Radiant heating is fine but convection heating is even better.
bungston, Dec 14 2016
  

       // what was substituted for home heat? //   

       "Smokeless" coal, gas central heating, electricity.   

       <link>   

       // any coal can be cooked into coke. //   

       Hard coal, yes. Coke for steelmaking needs to have the right chemical and mechanical properties. Coke for simple fuel is less demanding.
8th of 7, Dec 14 2016
  
      
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