Solar furnace for lime and bricks

[Sourdois]

Thank you for your involvement in answering me with a lot of explanations.
I am currently collecting data from the lime producer.
I don't mind the idea of ​​creating an alternative to the solar oven. All this can be indicated in the terms of reference of the study that we are currently preparing.

What interests me today is to find the resource person (s) to do this study. It is a consultant mission with payment of fees, mission costs and air ticket supported. If your job is in this field and this project interests you, you can let me know.

All ideas are welcome to improve the terms of reference of the study and to understand what will be expected.

Thanks,

you can give information on the furnaces currently used and especially on the consumption of wood and the production of lime (or brick)

the mirror surface is expensive and the amount of scrap to build a large dish also

the solar project deserves to be studied but we must also consider progress simpler

for lime: manufacture of charcoal by pyrolysis, and continuous lime kiln where burnt charcoal mixed with limestone to be cooked: excellent thermal efficiency, consumption 10 times lower than a separate wood fireplace

making charcoal by pyrolysis produces gas, methanol and acetone, instead of smoking as it is unfortunately everywhere

the construction of a wood pyrolysis plant not only reduces the consumption of wood in the lime kiln, but also reduces the amount of wood needed for all charcoal users in Africa!

the use of charcoal is often criticized: it is however the best fuel ... it is only the (old) archaic manufacturing method which is bad

I replace old with archaic because pyrolysis is old too: we called it wood distillation in 1850 when it produced the spirit of wood, old name of the alcol to burn

in 1850 this method was not profitable for charcoal because of the high price of the necessary material

today the material is cheaper and energy becomes more expensive, it changes everything

pyrolysis of wood is also interesting to do by solar method: instead of wasting part of the wood to heat it itself, we heat by the sun and we keep all the combustible gases produced for something else: for example heating a brick at night when the sun is down

the advantage of the gas produced by the pyrolysis of wood is that it can be stored to supply the oven continuously

I tried 15 years ago to start this kind of manufacturing of charcoal in France ... but impossible to build something in France ... steeped in regulations that bite the tail

difficult to build also in africa where everything is more expensive because of the lack of everything

[Sourdois]

Thank you for all your advice.

I put in the message of Chatelot16, what we expected at the level of our feasibility study. If you also think you have the skills and that this is your job, you can also apply to carry out this study.

Our wish is really to find the competent people who can come to Burkina Faso on a mission to help us build this project in a concrete way.

Thanks,

All the advice from chatelot16 is to be listened to, with great care, to be weighed, given the scope and importance of the project, in particular, start with simple tests with simple mirrors (same plans, 20 of 1m2 are 20KW on 1m2) , on small dimensions, then, the improvement of the yield by good thermal insulation, recovery of the heat between entry and exit, enormous economy with what comes out warming what enters, and in addition, test of heat conservation at night, which requires an enormous volume in refractory rocks such as wools or pulverulent lavas, with thermal insulation, especially by the slow thermal diffusion, over approximately 0,2m in one night from 8 to 10h.

It all depends on the volume used, but from a few meters in diameter, we must be able to keep most of the temperature at night and therefore save a lot of time heating or even cooking for lime or brick, and save a lot of expenses.

So in a ball a few meters in diameter, isolated and with earth walls or rocks with low thermal conductivity (pumice, sand, etc.?) Supporting inside 900 ° C, it should be possible to keep on one night most of the heat.

So the characteristic length of thermal diffusion increases as the square root of time :
http://fr.wikipedia.org/wiki/Diffusivit%C3%A9_thermique
http://fr.wikipedia.org/wiki/Conduction_thermique
for clay coefficient of thermal diffusion approximately 1mm2 / s gives for 10h of night or 36000s a length of 1xrac (36000) = 189mm and therefore the heat only enters the wall on a few multiples of this length,
For a large hot tank put, suddenly for the night, in a large bunker made of almost cold clay or brick at the start, the heat will only go out by diffusion on a few multiples of this length of 18,9cm.

This animated figure shows this slowing down, in square root of time, which allows to keep a high proportion of the heat over a finite time, by the slow diffusion of heat and T, in a cold wall, brutally brought into contact with the hot :

There is a loss of heat and of T as the ratio of the thermal capacities of the hot tank to that of the wall over its diffusive thickness.
All the basic equations are on and the wikipedia links in it:
http://fr.wikipedia.org/wiki/Conduction_thermique
A very large tank, almost sphere or cubic cylinder of 5m in diameter, will thus keep most of its temperature.


It’s often overlooked, but even allows to keep the heat underground between summer and winter as realized at www.dlsc.ca to heat the winter.

See on ggogle all the theories and realizations of solar power plants with planar mirrors with tracking or parabolic.
What limits the T max is the infrared radiation from the heated surface like T ^ 4, which is therefore very strong at 900 ° C., and therefore very difficult to obtain (surface very red to white), requiring a large number of mirrors.
Basis for this radiation not black at all at 900 ° C:
http://fr.wikipedia.org/wiki/Corps_noir
and all the links in
http://fr.wikipedia.org/wiki/%C3%89nerg ... _thermique

Also perhaps, it is better to see it as a means of greatly reducing the consumption of wood or fuel oil.

[dedeleco]

It is good to know what is currently working, for ovens used with wood, size, power required (quantity of dry burnt wood, at 4KWh per kilo burned), to understand the difficulty of a system that only exists very little, if any, elsewhere.

Our wish is really to find the competent people who can come to Burkina Faso on a mission to help us build this project in a concrete way.

is very difficult, because those, having carried out solar ovens, will not see possible, that their technique which they know, and which is perhaps not necessarily adapted to your country, which requires simple means, usable by its inhabitants .
The high T is a real difficulty for a simple realization (high concentration necessary, minimum to calculate, the law in T ^ 4 gives very roughly, a factor of ((900 ° C + 273) / 300) ^ 4 = 256, that is 256 mirrors sending their light on a single identical surface, hole in the oven, (I took 273 = 300 since it is very coarse), just to compensate for the losses by radiation at 900 ° C)

Simple plane mirrors with each simple, cheap, fairly precise tracker (lots of electronic plans on the internet) could do this, to send sunlight into a hole in the oven and at least help with heating.

In my opinion to achieve progressively simple small, inexpensive, low T, on a small oven, to identify local difficulties, and gradually move to large, warmer and more complex.
Beware of specialists who have produced very efficient, complex, and who risk being locally unsuitable, with failure?

Real functional realization:
closest to your pottery oven need:
http://fr.wikipedia.org/wiki/Four_solaire_de_Mont-Louis
http://www.capcir-pyrenees.com/articles.asp?id=5506
http://www.reseauculturel.fr/articles.a ... FR&id=5011
http://four-solaire.fr/
http://four-solaire.fr/marocains.htm

but be wary, tourist curiosity, too !!

Exchange of know-how with the city of Safi in Morocco. The Mont-Louis solar oven is engaged in a process of technology transfer to the countries of the South. Its goal is to install on a village scale a solar oven that will cook pottery, plates for eating, bread, construction materials, melt any metal to make pots or tools for cultivation 4.

and parabolic at unknown price:

http://energie.cnrs.fr/2008/DOCS/cogene ... -01-08.pdf
https://www.econologie.com/mini-centrale ... -4063.html

Multiple variations are possible, but T = 900 ° C requires a high minimum concentration to be specified, not necessarily parabolic.

The ultimate achievement:
http://fr.wikipedia.org/wiki/Four_solaire_d%27Odeillo

[Sourdois]

We look forward to seeing you!
I have already been in contact with Development of a solar oven. But I wish to widen my sources and also widen the study starting from your observations for example. I am still awaiting data on the production of lime and the conditions of this production.

More concretely, are you interested in this mission?
At the current stage I must prepare terms of reference and submit them to the cooperation which will agree to finance the study.
Everything is still open.

It is good to know what is currently working, for ovens used with wood, size, power required (quantity of dry burnt wood, at 4KWh per kilo burned), to understand the difficulty of a system that only exists very little, if any, elsewhere.

Our wish is really to find the competent people who can come to Burkina Faso on a mission to help us build this project in a concrete way.

is very difficult, because those, having carried out solar ovens, will not see possible, that their technique which they know, and which is perhaps not necessarily adapted to your country, which requires simple means, usable by its inhabitants .
The high T is a real difficulty for a simple realization (high concentration necessary, minimum to calculate, the law in T ^ 4 gives very roughly, a factor of ((900 ° C + 273) / 300) ^ 4 = 256, that is 256 mirrors sending their light on a single identical surface, hole in the oven, (I took 273 = 300 since it is very coarse), just to compensate for the losses by radiation at 900 ° C)

Simple plane mirrors with each simple, cheap, fairly precise tracker (lots of electronic plans on the internet) could do this, to send sunlight into a hole in the oven and at least help with heating.

In my opinion to achieve progressively simple small, inexpensive, low T, on a small oven, to identify local difficulties, and gradually move to large, warmer and more complex.
Beware of specialists who have produced very efficient, complex, and who risk being locally unsuitable, with failure?

Real functional realization:
closest to your pottery oven need:
http://fr.wikipedia.org/wiki/Four_solaire_de_Mont-Louis
http://www.capcir-pyrenees.com/articles.asp?id=5506
http://www.reseauculturel.fr/articles.a ... FR&id=5011
http://four-solaire.fr/
http://four-solaire.fr/marocains.htm

but be wary, tourist curiosity, too !!

Exchange of know-how with the city of Safi in Morocco. The Mont-Louis solar oven is engaged in a process of technology transfer to the countries of the South. Its goal is to install on a village scale a solar oven that will cook pottery, plates for eating, bread, construction materials, melt any metal to make pots or tools for cultivation 4.

and parabolic at unknown price:

http://energie.cnrs.fr/2008/DOCS/cogene ... -01-08.pdf
https://www.econologie.com/mini-centrale ... -4063.html

Multiple variations are possible, but T = 900 ° C requires a high minimum concentration to be specified, not necessarily parabolic.

The ultimate achievement:
http://fr.wikipedia.org/wiki/Four_solaire_d%27Odeillo

[Sourdois]

One point to clarify:

We have a partnership with DW
www.dwf.org/
He works on small ceramic ovens that save up to 80% of wood.
But the problem of lime production is different given the quantities to be produced.

I just put a picture of an oven currently in use.
https://www.econologie.info/share/partag ... ypu2Gh.jpg

It is good to know what is currently working, for ovens used with wood, size, power required (quantity of dry burnt wood, at 4KWh per kilo burned), to understand the difficulty of a system that only exists very little, if any, elsewhere.

Our wish is really to find the competent people who can come to Burkina Faso on a mission to help us build this project in a concrete way.

is very difficult, because those, having carried out solar ovens, will not see possible, that their technique which they know, and which is perhaps not necessarily adapted to your country, which requires simple means, usable by its inhabitants .
The high T is a real difficulty for a simple realization (high concentration necessary, minimum to calculate, the law in T ^ 4 gives very roughly, a factor of ((900 ° C + 273) / 300) ^ 4 = 256, that is 256 mirrors sending their light on a single identical surface, hole in the oven, (I took 273 = 300 since it is very coarse), just to compensate for the losses by radiation at 900 ° C)

Simple plane mirrors with each simple, cheap, fairly precise tracker (lots of electronic plans on the internet) could do this, to send sunlight into a hole in the oven and at least help with heating.

In my opinion to achieve progressively simple small, inexpensive, low T, on a small oven, to identify local difficulties, and gradually move to large, warmer and more complex.
Beware of specialists who have produced very efficient, complex, and who risk being locally unsuitable, with failure?

Real functional realization:
closest to your pottery oven need:
http://fr.wikipedia.org/wiki/Four_solaire_de_Mont-Louis
http://www.capcir-pyrenees.com/articles.asp?id=5506
http://www.reseauculturel.fr/articles.a ... FR&id=5011
http://four-solaire.fr/
http://four-solaire.fr/marocains.htm

but be wary, tourist curiosity, too !!

Exchange of know-how with the city of Safi in Morocco. The Mont-Louis solar oven is engaged in a process of technology transfer to the countries of the South. Its goal is to install on a village scale a solar oven that will cook pottery, plates for eating, bread, construction materials, melt any metal to make pots or tools for cultivation 4.

and parabolic at unknown price:

http://energie.cnrs.fr/2008/DOCS/cogene ... -01-08.pdf
https://www.econologie.com/mini-centrale ... -4063.html

Multiple variations are possible, but T = 900 ° C requires a high minimum concentration to be specified, not necessarily parabolic.

The ultimate achievement:
http://fr.wikipedia.org/wiki/Four_solaire_d%27Odeillo

[dedeleco]

I limit myself first to basic and sometimes forgotten physicist remarks.

The details of the needs, power and size of current ovens are essential. (how much wood burned by weight in each batch of how many days and how much power in KW, 10, 100, 1000 KW ???? )
I imagine that it is big and therefore difficult, for 900 ° C.
First make preliminary simple, small, much less hot, then hot and small, even to just transform a simple little pebble into lime !!.

It is a big project, very useful, but easily complex, which requires a strong study by collecting all the various varied opinions, especially those having carried out a similar system, T = 900 ° C, rare, and to compare the complexity for country, with few means and little knowledge.

We must then weigh the advantages and disadvantages of the various embodiments.

[Sourdois]

Hello,

I took a little time to respond, but with the situation in Mali, I was busy and I also left the country to reach Burkina by road.

Here are the elements on the ovens and current production:
- Ovens constructed of baked bricks
- Capacity: 20 tonnes of quicklime on average
- Average wood consumption: 100 steres
- Cooking time: 1 week without interruption
- Quality of the stones: CaO of 56,4% on average; average block size 30x50cm
- Lime production in 2010: 25 tonnes

The objective is to increase production. I posted a photo of an oven.

Thanks,

I limit myself first to basic and sometimes forgotten physicist remarks.

The details of the needs, power and size of current ovens are essential. (how much wood burned by weight in each batch of how many days and how much power in KW, 10, 100, 1000 KW ???? )
I imagine that it is big and therefore difficult, for 900 ° C.
First make preliminary simple, small, much less hot, then hot and small, even to just transform a simple little pebble into lime !!.

It is a big project, very useful, but easily complex, which requires a strong study by collecting all the various varied opinions, especially those having carried out a similar system, T = 900 ° C, rare, and to compare the complexity for country, with few means and little knowledge.

We must then weigh the advantages and disadvantages of the various embodiments.

[dedeleco]

I indicate some thoughts on the scope of the project:

Capacity: 20 tonnes of quicklime on average
- Average wood consumption: 100 steres
- Cooking time: 1 week without interruption

indicates the current yield:
20 tonnes of calcium

gives an idea of ​​current performance
50 tons of wood gives 200000KWh consumed, (4KWh / Kilos)
over 7 days at 168h gives 1190KW of power.
The megaWatt, like Odeillo:
http://michel.hubin.pagesperso-orange.f ... olaire.htm

Then with the difference enthalpies between Ca0 and CaCO3 on
http://en.wikipedia.org/wiki/Calcium_carbonate
http://en.wikipedia.org/wiki/Calcium_hydroxide

this gives per gram of CaO 2,97KJ / gCa0 (not identical not g of caCO3 74/100 ratio)

which gives about 3million / 3600 = 826KWh / ton CaO
either at 4KWh / kilo of wood, you need mini 206Kilos of wood per ton or for 20 tonnes, 4 tonnes of wood mini to dehydrate in CaO, and therefore to heat to 900 ° C, recoverable if exchanger, I count double 8 tonnes wood / 20 tonnes of CaO.

The yield with 50 tonnes of wood is not very bad, around 8/50 = 16%, but could be improved, heat loss and in combustion fumes, with a lot of technology.
It is a simplistic, useful assessment to fix ideas at the outset.

The power required is per minimum ton taking twice the 826KWh / ton to dehydrate (a yield of 50% would be great with mirrors) 1600KWh / ton CaO gives over a week 604800s a power of 1600x3600 / 604800 = 9,52KW, this day and night, either sun alone 8h 3 times more, or rounded 30KW solar per ton required, min.

30 KW require 30m2 of mini mirrors per tonne processed (I would tend to double given the probable losses forgotten of all kinds) !!
These 30 to 60m2 per tonne of CaO obtained are to be concentrated by a factor of 200 at around 900 ° C according to a simplified article, for a thermal machine, but to be read carefully while removing the (1-T0 / TH):

http://en.wikipedia.org/wiki/Concentrated_solar_power
(see efficiency)

So you have to concentrate the 30 to 60m2 of mirrors 200 times on 0,15m2 to 0,3m2 of entry trapping light in the oven of the kind in Odeillo
http://michel.hubin.pagesperso-orange.f ... olaire.htm
which works 3200 ° C,
or the kind analyzed in the forum with patent:
https://www.econologie.com/forums/piege-hype ... t4917.html
http://sycomoreen.free.fr/syco_francais ... PHRSD.html

See this thesis on much simpler, as a basis for ideas:
http://esc.fsu.edu/documents/DascombJThesis.pdf

It is not a simple project, nor an easy one.

We must test on small and not too complex with small quantities, a mirror of 1m2 and a few grams of CaCO3, before.
Then bigger but for 10 to 100kilos per batch.

20 tonnes requires getting closer to Odeillo, 600m2 to 1200m2 of mirrors, mini over a week with storage at night for the heat, which Odeillo does not do at all !!

Otherwise see German commercial products with Stirling that work but are expensive, for the price of their efficiency, which can only deal with light traps in small quantities with 10KW.

[chatelot16]

100 wooden stere for 20 tone of lime: big disaster

with continuous lime kilns where limestone and coke are mixed, it consumes 100kg of coke per tonne of lime

coke is pyrolyzed coal, exactly the same as charcoal ... hence my idea to start by making charcoal

with a good means of charcoal production a small part of the wood currently consumed will be enough to make the same amount of lime

it takes nothing away from the interest of a solar lime oven ... but limestone is a very poor conductor of heat, hence the very long cooking time with limestone in large pieces: for a solar oven fast it will be necessary to break the limestone into a small piece ... it requires additional material

a solar lime oven which cooks in a few hours ground limestone in small pieces of 1cm will be useless if there is not a good grinder

I also have in project a system to make charcoal by solar pyrolysis: instead of consuming part of the energy of wood to heat it, all the energy of wood is transformed into fuel, charcoal, liquid, and gas ... wood to be pyrolyzed is only heated by the sun

gas can be used to run generator

the liquid can be used as vehicle fuel

charcoal can be used for a good lime kiln ... or for all other usual uses in Africa

there are some who criticize charcoal, almost synonymous with ecological waste ... it is only bad manufacturing that is open to criticism: as fuel it is the simplest and most efficient with the minimum material

[dedeleco]

One point to clarify:
We have a partnership with DW
www.dwf.org/
He works on small ceramic ovens that save up to 80% of wood.
But the problem of lime production is different given the quantities to be produced.

I just put a picture of an oven currently in use.
https://www.econologie.info/share/partag ... ypu2Gh.jpg

The DW approach seems to me, essential ecological, with simple technologies, accessible to local inhabitants and not a very high level technology, not very feasible locally (German ovens or like Odeillo, a priori essential for the 20 tons of lime, more improved with night storage !!).

The DW ovens on their site are not solar, but clever vault in mud bricks which saves 80% of wood, by not losing most of the heat in the open air, if I understood correctly:

Once enough pots are dry, they are placed in a shallow open pit, where thirty or more pots and other objects will be fired together. Dried cow dung, some wood, bark and branches - anything that will burn - is simply piled round and over the pots and set alight. Most of the heat generated escapes to the open air and a gust of wind suddenly changing the temperature in the pit makes the pottery crack or causes unsightly discolouring.
Its main focus has been on training many hundreds of village builders to use earth vaults and domes so that they no longer need to cut down scarce trees for roofs. Noticing the very uneven quality of the clay gutters used to channel water away from these “woodless” roofs, DW suggests that village builders should try building simple mud brick vaulted kilns for the women potters. The results exceeded all expectations on a number of levels.

Ten years after the first kiln went up, over 850 women in 35 villages have seen for themselves dramatic improvements in output, in quality - and above all in their income.

Using a closed kiln, a load of 148 pots weighing 670 kgs needs only half a cartload of fuel and the breaking rate is less than 3%. That's a 93% saving in fuel for a 70% increase in saleable output. Why? Because the kiln is completely sealed once the products have been put into the chamber, so there is very little heat loss and no risk of wind causing sudden temperature fluctuations. In addition, after the firing the women can recuperate about 7.5 kgs of charcoal, which they either sell or use for their own cooking needs representing a local market value of more than € 6.

To provide a group of ten women with a kiln, several potter's wheels, two terracotta tile making kits and gutter molds, and to ensure they are properly trained in how to use them most efficiently costs € 2,000 - or just € 200 per woman.

A small investment compared with providing them with a regular income for life and with skills they can pass on to their children.

Also, as Chatelot16 advises, it is better to make, in small quantities, crushed limestone, in pieces of a few cm (rapid thermal diffusion a few minutes (100s for 1cm, and 10000s for 10cm, about half the thickness of the piece, http://fr.wikipedia.org/wiki/Diffusivit%C3%A9_thermique)
using small solar ovens already efficient to obtain 900 ° C, because it is necessary to concentrate to 150 to 200 times, effective, with a fairly rapid circulation of limestone, in the light collecting oven, trying to heat the limestone which enters by cooling the lime that comes out, in a small, but efficient system, to design and develop.
The advantage is that it would only work with the sun, heating in about 10 to 15 minutes, a small amount.

The grinding could be done by solar stirling engine, actuating the crushers or breakers. .

The difficulty is that this technology is not functional in Europe, at best certain elements exist, commercial, parabola, Stirling engine, the oven much less, especially for continuous lime.

It would be necessary to try on small quantities of limestone in a simple solar oven, even of 1m, but precise of parabolic form to concentrate by at least 100:
http://en.wikipedia.org/wiki/Concentrated_solar_power
(see efficiency)

A spherical parabola on a precise metal frame, formed of 200 pieces of flat mirrors of 7cmx7cm well oriented, carefully, towards the identical aperture sensor may be suitable.
One m2 gives 1KW coming from the sun, is reduced in the oven around 100W to 250W depending on the quality of the concentration, given the radiation losses from the solar oven at its entry, in sigmaT ^ 4.
So it will form 100 to 300 grams of lime per hour, if not too much loss, with 1 m2 of relatively simple mirrors.

The Odeillo geometry, with planar mirrors moving towards a fixed parabolic concentrator seems the best.

Curves of the maximum efficiency of solar thermal collector, with perfect Carnot Motor according to the temperature of hot spring TH and concentration factor. A Stirling will be 1/4 to 0,3 of that.