[Stoves] Philips Stove. Was Re: Jatropha press cake as a fuel

Thu Jan 4 01:20:04 CST 2007

Dear Paul v.d.S.,

Thanks for the info.  So good to get things clarified by the man who really
knows.

Your explanation makes a lot of sense.  The described operation of the Philips
stove is NOT the same as either Reed's Woodgas Campstove nor the same as what
we were doing at Stove Camp 2006.

The operation as done in Reed's stove would not have any heat at the TEG until
the final minutes of the pyrolysis.  For the TEG to operate and for the fan to
blow, there needs to be heat at the bottom at the beginning of the cooking.

At Stove Camp, the method we used was strickly "trickle-feed" of small 
fuel and
we did not utilize the capabilities of the Philips stove to take in the larger
pieces of fuel and then operate un-attended.  This could be tried by 
anyone who
has one of Reed's Woodgas Campstoves, and at Aprovecho where there is one of
your stoves.  I do not know if Reed, Agua Das, and others had 
experimented with
the addition of the larger pieces of wood, but I do not recall any 
discussion of
feeding larger pieces of fuel into the Campstove after the initial 
top-to-bottom
pyrolysis of the fuel.

Although the Philips stove has the air-flow and physical 
characteristics of the
other forced-air TLUD gasifiers, the operation you describe is clearly
"bottom-lit" and up-draft.  It will be interesting to see the extent to which
the air coming in from the lower holes actually contributes to some secondary
combustion.  Also, the Philips stove is not really the same as the traditional
and larger up-draft gasifiers where there is much more fuel inside the 
gasifier
and where there are reasonably distinct layers from bottom to tip of ash, hot
char, cooler char, zone of pyrolysis, and raw fuel on top.

So, the distinctiveness of the Philips stove is confirmed in both the
use/placement of the TEG and in its recommended manner of operation.

Question:  In India, are the users of the Philips stove informed about and
instructed that the stove could be used in the standard TLUD fashion with a
full load of fuel at the beginning with ignition at the top?  I suspect not,
because there would need to be an additional set of wires from the fan to an
external battery because the TEG would not be heated.

We all wish you success with the testing of 1000 units in India.  
Please keep us
informed.

Paul A.

-- 
Paul S. Anderson, Ph.D., Geography professor - Emeritus
Telephone:  USA-309-452-7072 (residence and office)
Internet site:  www.ilstu.edu/~psanders
For my gasifier stoves info, go to:
http://bioenergylists.org/contributors#Paul_Anderson

Quoting Paul van der Sluis <paul.van.der.sluis at philips.com>:

> Dear Paul A.,
>
> The TEG generator is mounted below the fire as can be seen  in:
>
> http://money.cnn.com/popups/2006/fortune/better_living/5.html
>
>
> To prevent overheating it is insulated to such an extent, that the hottest
> fire a user can make, just does not fry the TEG.
>
>
> For explaning  your question on my  "top feed stove":
>
> Discussion in this group have focussed on 2 types (and I quote from you)"
>
> ***********
> One is the classical T-LUD method of "fill the fuel chamber, ignite at
> the top,
> let it pyrolyze, then either empty out the char or let it continue to
> consume
> the char."
> *******
> or
>
> *******
> The other is what has been discussed here at the "trickle feed" (or
> trickle
> fuel) method in which the fuel is continually added (at 20 to 40 second
> intervals?) in small amounts dropped in over the top of the stove.  The
> trickle
> of fuel could be from the very beginning or done after the pyrolysis stage
> has
> been mainly completed.
> ******
>
> I regard my stove as a hybrid. The preferred way of using the Philips
> stove is to start with small pieces of wood. To get the fire started and
> to make the stove hot.
> That should take about 5 minutes.
> One could now trickle feed the stove, but that is very unconvenient for
> the user. That is why I prefer to put relatively large pieces of wood into
> the stove. Something
> like 5 cm thick, 8 cm long pieces of branches. One piece at a time, but
> once burning a second and eventually a third piece can be added. This will
> last for 10 -  15 minutes at high power (high fan speed) or up to 30
> minutes continuous at low power (low fan speed). Gives the user freedom to
> cook or walk away.
> Larger pieces cannot be done because in that case the combustion chamber
> (fire) can cool down so much that the secondary flame (the flame burning
> the woodgas) can extinguish temporarily, resulting in large amounts of
> smoke. The stove should have enough thermal mass to be able to do this.
> The large pieces now burn in the classical T-LUD method, but not from top
> to down but from outside to the inside of a woodpiece. The pieces pyrolyze
> from the ouside to the inside and become char that is eventually consumed.
> A new piece of wood should be added before all char is gone. When you
> interrupt the combustion and cut a piece of wood into two, the
> outside-to-inside pyrolysis can clearly be seen.
> In this way you get the advantages of the clean burn from the classical
> T-LUD, combined with the advantage of continuous cooking of the trikcle
> feed. The disadvantage is that the cooking vessel should be removed to
> accomodate these large woodpieces 2 - 4 times per hour.  If that is
> unwanted, almost identical results can be obtained after splitting the
> branches length wise into two pieces, so they fit into the gap between the
> cooking vessel and the stove (which is 3 cm).
> This size of the wood also has an influence on the thermal power. If I
> need really high power (preparing meat), I  feed small pieces in a faily
> high speed into the stove with the fan at high speed. If I need lower
> power I use only 1 large piece, with low fan speed. If I need really low
> power (for simmering) I use char which I saved from the previous cooking
> run and the fan at low speed. A full fill with left over char and the fan
> at low speed lasts for more than 1 hourt of unattended simmering.
>
> It really pays in terms of cooking convenience to put a bit of effort into
> wood cutting. When I use the stove (and I cook on this stove for 2 years
> now for a family of 5) I have a box of wood pieces ready and I pick large/
> or small pieces as I need it at that particular moment. After all cooking
> runs I throw the remaining char into an air tight metal vessel for later
> use.
>
>
>
>
> *****
> Concerning the thermal efficiency of about 40%, please describe the
> arrangement
> of the pot (size, with skirt?, stainless steel?, with lid on?, etc) as it
> was
> used on the stove when the testing was done.
> ******
>
> The 40% efficiency is measured without skirt, lid on and a 30 cm flat
> bottom stainless steel cooking vessel holding 4l of water. With a skirt I
> can get efficiencies up to 80%, but who wants to use a skirt??
>
> Regards,
>
>
> Dr. P. van der Sluis
> Philips Research Laboratories Eindhoven
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