[Stoves] Heat / cook stove - proposed design

[Darren Hill]

Hello Everyone,

After this project going well onto the back burner as it warmed up here, 
the temperature we are seeing at night now is focusing my attention again.

If anyone is interested discussion about this started 29th December and 
went on until 23rd February.  The stove is about half built- I'm going 
to be working on it again on Tuesday.

I've attached a diagram of how I'm now planning to build the grate and 
throat area.  (I took the liberty of modifying the GIZ diagram Crispin 
kindly sent to explain an appropriate layout)

As I'm only going to be burning wood and in my experience of wood stoves 
all the wood burns to a light ash which would easily fall through the 
grate I am planning to have a stationary grate.   Am I making the wrong 
decision here?

I'd welcome anybodies thoughts on things as they stand.

Hoping to get it finished soon.  Considering the number of people I've 
been describing it to all year it would be good to also let them know 
how it works!!!  I've never seen anything like this in action - I'm 
thoroughly intrigued.

Best regards

Darren

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[Stoves] Building my Heat / cook stove.
Crispin Pemberton-Pigott crispinpigott at gmail.com
Wed Feb 23 21:46:01 PST 2011


Dear Darren



I think you are going to have a couple of problems with the layout as drawn
and they are solvable.



Let's look at them all:



1.       The restricted height at the entrance of the combustion area is
probably the right height, but that is for limiting the amount of fuel that
can fall onto the grate further in.

2.       The grate needs to extend into the whole area under the combustion
zone or else it will fill up with ash and you don't have a way to get it
out. The grate is correctly placed, perhaps a little steep but that can be
altered. Char and ash will fall forward (as it should) but end up in the
bottom of the combustion area.

3.       The constriction you describe well on the side is going to catch
some of the char and ash and might (or not) create a bridging problem. You
can address that if it happens.

4.       The purpose of getting the grate under all the horizontal area
solves two things: it allows a lot of controllable air to reach the far end
of the grate where there will always be less fuel. That means air gets
through and effectively becomes secondary air. If you make the grate
shakeable, you can clear the ash but you will need to have it stop at a
vertical or inclined surface or the bottom will get blocked.

5.       We are having pretty much the same layout but the restriction is
above the grate about 100mm. This allows the grate to carry enough fuel and
still have all the gases and smoke and flames come together above the fuel.

6.       We start the fire by placing some fuel on the grate, extending into
the part below the combustion area then top-light in the combustion area.
The fire works its way back to the fuel hopper it the top is left open. Then
when it is well established, close the hopper and vary the air with the
controller you indicated.

7.       The key change is the extension of the grate, perhaps at a lower
angle. We are using 15-20 degrees but there is nothing magic in that.

8.       I have attached a drawing of the GIZ 7.1 combustion chamber that
worked very well using all the principles mentioned. Note the angled piece
on the right. This protects the grate from becoming blocked from movement by
trapping something between it and the wall, when shaken.

9.       Note the constriction above the left side of the grate. It is 100 x
80mm. As you look at the side view drawing, the grate is 155 deep. That
means the moving part is about 260 x 155.



Regards

Crispin







From: stoves-bounces at lists.bioenergylists.org
[mailto:stoves-bounces at lists.bioenergylists.org] On Behalf Of Darren Hill
Sent: 21 February 2011 20:40
To: Discussion of biomass cooking stoves
Subject: Re: [Stoves] Building my Heat / cook stove.



Hello Crispin,

The bleed is at top bypassing the need for gases to go down past the heat
exchanger.

Secondary air is flowing in through some 20mm x 20mm internal diameter
square section tubing.  Is this enough or do I need more? Another 20mm x
20mm square section tube? More?

I've attached another diagram which shows things as they are currently
planned/progressing.

Looking at this diagram.  Are you saying to have some of the grate to the
left of the red line I've drawn on the diagram?

Currently this is the thinnest point (or bottle neck, or throat) and has a
vertical ceramic slab either side so that this 'throat' is not the full
width of the hopper.  Extending the grate further to the left will, in
effect, increase the area of the thinnest point.  I currently plan to have
the lowest part of the grate level with the bottom of the ceramic block
(that is the floor of the combustion chamber) so it is away from the
thinnest/hottest area.

Is it best to shift the grate to the left?
If so what % of the grate left of the red line?
Should I also raise the grate so that the its level with the top of the
ceramic block that is the floor of the combustion chamber?

I'm working on the stove today and tomorrow.  Going to build the air tight
doors today.

Best

Darren

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