Eco-friendly wood dryer humidifier

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clasou
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by clasou » 07/05/10, 13:11

No, me eco drying, it's been miles outside, all summer.
But the idea is still to make a dryer, kind that there was on it can be done, but not done yet.
a + claude
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dedeleco
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by dedeleco » 07/05/10, 14:29

for economical drying, a condenser is required
(which recovers calories from evaporated water)

perfectly accurate, but you need an airtight container for wood (finely divided) where hot and dry air circulates and in the same room the cold condenser which recovers liquid water and its heat of condensation, method rarely respected by dryers ordinary commercial linen !!!
Otherwise in a warm room, the water evaporated from the wood in the open air will partially condense on cold surfaces (windows) and restore its calories to the hot room, if the air circulation to the outside, VMC or air intake for combustion is not strong !! otherwise we lose this heat with the air charged with steam leaving and the cold dry air with the same flow returning !!
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bernardd
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by bernardd » 07/05/10, 19:40

There is also the solution of finding a watertight container, and making a sufficient vacuum (10mb?) There for the water to vaporize at 20 ° C.

But I cannot find precise technical information on the rate of evaporation of a fixed quantity of water.

And I don't have enough vacuum pump yet to test it myself :-)
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by dedeleco » 07/05/10, 20:47

Under complete vacuum, evaporation is very fast (speed of each molecule at more than 1000m / s or at least the speed of sound 330m / s but the quantity removed (speed multiplied by the number of molecules, like the inverse of the pressure) is limited by the pumping capacities in m3 / s at low pressure and as in addition the vacuum pumps do not have good performance (at least the small ones), this is not very useful except for drying and freeze-drying foods like mushrooms, etc., but not for firewood.
If the water is liquid it is that of the vapor pressure at the boiling point, very fast, if the pump is powerful enough, almost instantaneous and the cold produced (ice) stops evaporation!
http://www.trs-online.com/conc.php
http://www.cyber.uhp-nancy.fr/demos/CH- ... 2_4_2.html
http://pagesperso-orange.fr/trounoir/ev ... noirs.html
You can take a water pump to pump, if you have a stream or a booster to circulate the water in a closed circuit. !!

In my opinion heating a little with the circulation of air thus dry on finely divided wood (essential) is the most economical by letting it condense on the cold windows and walls of the house or elsewhere inside and not outside! (vulgar efficient tumble dryer with condensation).
A boiler doing this before burning wet wood has a good performance !! But it's very expensive, unless you tinker with it !!!
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bernardd
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by bernardd » 08/05/10, 10:35

Thank you very much for these links, this is exactly what I was looking for and I couldn't find, with this equation in particular:
http://www.cyber.uhp-nancy.fr/demos/CH- ... 2_9_5.html

I'm looking at how to dry the sawdust for the domestic production of pellets.

The factors limiting the speed of drying without heating are:
- the arrival of thermal energy to compensate for the vaporization energy,
- the suction rate of the steam to maintain the vacuum necessary for boiling below room temperature,
- and the contact surface of the liquid water in the sawdust.

But in domestic, we are not really in a hurry either :-)

In all cases, the extracted steam must be condensed, ideally near the sawdust to recycle the heat: but this is not a problem with evaporation under vacuum at room heat.

My current question: what is the power required for the vacuum pump? But I think it will be much lower than the heating power required for evaporation at atmospheric pressure.
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by dedeleco » 08/05/10, 14:47

My current question: what is the power required for the vacuum pump? But I think it will be much lower than the heating power required for evaporation at atmospheric pressure.

Well, no there is no miracle !!
Evaporation of water requires a lot of energy and where does it come from when pumping ???
It comes partly from the pump (integral work of PV undergone by the gas to be calculated see
http://www-ipst.u-strasbg.fr/cours/ther ... /gaz-p.htm )
and heat provided by the environment, with the non-evaporated water which freezes the non-evaporated water very quickly and therefore slows evaporation exponentially by reducing the temperature !!!
So it is not more interesting energetically except the speed (with good exchanger and finely divided), unless you recover the condensation (see manufacturers on tons dried per hour)
http://www.trs-online.com/conc.php
(Read with care because manufacturers recover energy if possible and to have examples of energy balance with beautiful noisy Roots pumps)
The interest is the speed and perfection of drying, but for a small volume, not too rushed, of very dry air Usually blown on divided wood is also effective.
In very dry Sahara, the drying speed is staggering, to the point of wearing burnous and burka (with UV, the real Islamic scientific reason for the burka) !!!
Either we take dry air on dry days in summer, and we do not rewet it at night by condensation !!
Either we heat a little to make it almost dry (0 to 20 ° C in winter or 20 ° C to 40 ° C in summer) and we blow on the finely divided wood (otherwise very limiting) and we recondense the water vapors to Starting point for a very good energy balance !!!
Finally for a high speed under vacuum, you need big roots pumps and finely divide the wood on a good exchanger, otherwise we don't pump anything and we don't dry anything faster than air !!!
The aggregates dry without a vacuum pump but recover the heat and charge a good price almost fuel oil sawdust good to throw!
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bernardd
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by bernardd » 08/05/10, 17:38

dedeleco wrote:Evaporation of water requires a lot of energy and where does it come from when pumping ???


Yes, precisely from the environment: the purpose of the vacuum is to bring the boiling point below room temperature so that heat can come naturally from the outside.

It remains to establish a sufficient heat conduction system.

The advantage of the vacuum is that it does not take energy to maintain it. It just takes the energy to evacuate the water vapor when it has found enough heat to be released and it has raised the pressure.
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by dedeleco » 08/05/10, 18:37

The advantage of the vacuum is that it does not take energy to maintain it. It just takes the energy to evacuate the water vapor when it has found enough heat to be released and it has raised the pressure.

No, because according to what you do precise, calculate the minimum work in PV (integral) and you find that a perfect pump needs energy, and in addition the vacuum pumps are not perfect, a lot of energy so that vacuum (the KW for 10 to 100 liters of vacuum limited by degassing), or nothing !!!!
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by Ahmed » 08/05/10, 20:26

I have a little trouble following the procedure, because the advantage of reducing the amount of water contained in firewood is to increase the efficiency of combustion, therefore the amount of heat released.
If you have to spend energy and deploy sophisticated equipment for this (an enclosure large enough to be operational and solid enough to withstand atmospheric pressure ...), this is completely illogical.
Storage in heaps under a tarpaulin or a shed allows you to achieve the desired result without other energy than that provided free by the sun.
The only cases where a drying process is used by firewood traders is on the basis of the use of manufacturing waste, which solves two problems at the same time.

For the production of pellets, it is necessary that the sawdust have a water content which is hardly possible to achieve by "air" drying; A current of hot air flows through rotary dryer tunnels which is exhausted to the outside when it becomes too humid. However, this process is energy-intensive but seems to be economically justified because it makes it possible to recover by-products from the wood industries.
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by dedeleco » 08/05/10, 22:12

hot air which is exhausted outside when it becomes too humid

whose water vapor is condensed into water to recover the heat of evaporation in a regeneration exchanger which preheats the incoming cold air to be heated.
Result, if used, this process is very energy efficient and the pellets are very profitable with sawdust initially good to throw! !
http://www.water.siemens.com/en/product ... stems.aspx
Finally, we can use a simple and simple solar drier: glass plate which heats the air below which circulates afterwards on the wood by chimney effect which will work even in winter (it suffices to heat the air a little) !!!
https://www.econologie.com/forums/sechoir-a- ... t7685.html
and many others !!!
Much better than a vacuum pump !!!
http://www.directindustry.com/prod/witt ... 46410.html
https://www.econologie.com/forums/schema-usi ... t4348.html
http://www.oliotechnology.fr/produits-s ... 00-fr.html
http://www.oliotechnology.fr/produits-p ... ts-fr.html
http://www.oliotechnology.fr/produits-p ... ev-fr.html
I am not convinced that they use the most economical means with electricity but the least tiring intellectually !!
http://pellet.over-blog.com/categorie-527999.html
http://chaudiere.pellet.over-blog.com/
http://pellet-mill.de/shop/category_2/4 ... 2AodXEB6_g
http://www.lzm-inc.com/wood-pellet-machine-c-29.html
KAHL Pelletpresse for Kleinstproduktion
http://www.akahl.de/akahl/de/produkte/c ... roduktion/
http://www.akahl.de/akahl/de/home/index.php
Randomly among an armada!
Otherwise I have the impression that pellet stoves should be improved so that they accept various qualities of divided plants from ordinary grinders. without exploding their price !!!
In my opinion a lot of heaters remain to be improved in performance and price !!
For example, include the dryer with recovery of the drying heat by condensation and clean combustion of any plant waste without exploding their price !!![/ Quote]
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