[Stoves] CARITAS stove model TJ4B

Sat Mar 19 00:04:37 CDT 2016

In India during winter months there were quite a number of such deaths.
This was mostly true in 1950s and 60s when coal stoves were common.

Nimbkar Agricultural Research Institute (NARI)
Tambmal, Phaltan-Lonand Road
P.O.Box 44
Phaltan-415523, Maharashtra, India
Ph:91-2166-220945/222842
e-mail:nariphaltan at gmail.com
           nariphaltan at nariphaltan.org

http://www.nariphaltan.org

On Sat, Mar 19, 2016 at 10:04 AM, Frank Shields <franke at cruzio.com> wrote:

> Dear Crispin,
>
> It always seems scary to me to have a small coal burning stove inside a
> home due to possible CO poisoning. Seems all one needs is a cold stack that
> reduces air flow, wet coal or the top covers are not closed tightly - and
> problems. So is there a lot of deaths during the night with people burning
> coal?
>
> Regards
>
> Frank
>
>
>
>
>
> On Mar 18, 2016, at 7:15 PM, Crispin Pemberton-Pigott <
> crispinpigott at outlook.com> wrote:
>
> Dear Frank
>
> This type of stove is designed to operate continuously. It is very likely
> to go out overnight in most homes.
>
> There is no need to dump the ash out of the combustion chamber. The ash
> will drop through the grate and if it doesn't the gaps will be widened. The
> amount of ash is dependent on the coal composition. Nothing else.
>
> The CO in the stack is directly measured by the analyser so it is very
> low. When it is hot it is about 200 ppm. As the fire dies of course it
> rises bit there is a significant reduction if the bricks are heat
> conductive. Provided they bring stored heat ‎to the fire fast enough the CO
> can be kept burning far longer into the late fire.
>
> This aspect of combustion is not much discussed because it isn't sexy. The
> effect is this: the lengthened late burn gives the impression that the
> stove has stored a great deal of heat and people really like that. In fact
> it is still burning at low power. ‎Because of the extra burn quality there
> is very little unburned char at the end, maximising fuel efficiency.
>
> The CO/CO2 ratio of a dying fire stabilises at about ‎14%, sometimes as
> low as 12. It will in be high (30%) only in hot, air-choked combustion ‎or
> when dumping cold fuel on a hot fire.
>
> Regards
> Crispin
>
> Dear Crispin,
>
> Is it easy to stop and re-start the stove? Or do you need to dump and
> refill with new material? and how much ash is produced? I would think the
> CO would be extremely high in the stack?
>
> Thanks
>
> Frank
>
>
> On Mar 18, 2016, at 3:12 PM, Crispin Pemberton-Pigott <
> crispinpigott at outlook.com> wrote:
>
> Dear Friends
>
> Sorry for the poor quality photo but I wanted to show it to you with the
> hopper open. This is a coal stove with a hopper based on the GTZ-7 stove
> from Ulaanbaatar (2010). The model is a GTZ-7.6 but both the GTZ name has
> changed and the model 7.6 was designed never built in Mongolia.
>
> So, it gains life in Tajikistan. It is a cross draft stove with a hopper
> feeding coal onto a grate inclined down (away and to the left as seen here)
> at 30 degrees from the horizontal.
>
> <image003.jpg>
> CARITAS TJ4B Cooking and chimney heating stove
>
> The stove is little more than a metal shell with one central divider to
> facilitate the location of the bricks. It contains 19 good quality high
> temperature bricks recovered from old furnaces. In operation, the fire is
> lit in a TLUD style inside the section directly under the cooking plates.
> It is lit with split dry wood surrounded by a small amount of coal chips.
> These chips are easily ignited and fall onto the bed of coal lying
> underneath. This in turn lights the fuel at the bottom of the hopper. Air
> crosses through the lower hopper creating a continuously pyrolysis of fuel
> near the bottom of the grate. It functions a bit like a downdraft stove
> with the gases forced to pass through a cup of red hot coke stationed to
> one side. The flames then run upwards vertically to the cooking area. The
> gas path then passes out the far end of the stove body into a chimney elbow.
>
> If the firepower drops below the desired range, the ring on the movable
> grate can be shaken in and out. This causes additional fuel to fall onto
> the lower portion of the grate increasing the burn rate.  The door is
> normally completely closed and holes up the grate. If it is opened fully,
> the grate can be removed by pulling it straight back. Anything sitting on
> it is dropped into the ash drawer below.
>
> Here is the performance:
>
> <image005.png>
> As this stove is supposed to heat via a metal chimney, it is important to
> find two things: a high gas temperature and an efficiency that is not so
> high as to leave little heat available. If the efficiency is high and the
> gas temperature low, there is little more than can be extracted. This stove
> should be operated in the >85% efficient range (by adding horizontal
> chimney pipes).
>
> The two fire-related numbers are the excess air level (about 100% which is
> in the ideal range) and a low CO/CO2 ratio (≈0.2% sustained).
>
> With a space heating efficiency of about 53% it leaves another >30%
> available for heating a second room using the chimney. The cooking
> efficiency is typically 25% for this design, and that heat is considered
> part of the space heating contribution.
>
> Once the fire is established, the performance continues as shown above
> pretty much indefinitely. As long as the ash is not lumpy, it will fall
> through the grate which should be shaken occasionally, say, per 4-6 hours
> depending on the coal.
>
> The hopper can be refuelled at any time. It does not disturb the
> performance unless the fire is nearly out.
>
> Constructed from new materials, this stove costs about $50 to make. It
> will last well because nearly everything that gets really hot is made from
> bricks.  The heating power is about 3.5 kW from the stove with another 2 kW
> available from the chimney. It really needs a cast iron top, held on by
> screws. The bricks can be replaced by the owner if a lower quality brick
> was used. The ones lining the fuel hopper do not all have to be such good
> ones.
>
> Regards
> Crispin
>
>
>
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