Crispin Pemberton-Pigott, April 6, 2010

This is a stove seen by Dulguun Basaandavaa at Suhkbaatar Square which is a huge plaza in downtown Ulaanbaatar. There was a demonstration of stoves in yurts (gers) a few days ago.

This one is particularly interesting for the reason that it is the first small scale Mongolian coal gasifier spotted in the wild. It has a fan so it may be modelled on a much larger device. I have no idea at all how it works. Perhaps someone far more knowledgeable about gasifiers can spot and name the components.

In all more than 10 new stoves were shown nearly all of which are downdraft stoves, or which can be started in updraft mode and switched to downdraft.
One of them was the previously reported BLUD stove from Inner Mongolia that rotates and becomes a TLUD during the ignition cycle.

TLUD Vesto Grasifier
Crispin Pemberton-Pigott, New Dawn Engineering, Swaziland, April 2, 2010

Dear Roger and TLUD Fans (the other kind)

Crispin Pemberton-Pigott (New Dawn Engineering) with Prof Sereeter Lodoysamba (National University of Mongolia),
Sod Dulam (Energy consultant, Ulaanbaatar) and Altangadas Tsegmid (Heat and Power Systems consultant, MonEnergy)

This stove was seen in operation in 6 and 8th March 2010 by in the home of Demberel in Ulaanbaatar, Mongolia.

It is a form of top lit updraft (TLUD) stove part of the time. The combustion chamber is a (ceramic?) lined square box with a grate enclosing the top and the bottom. It is mounted in a fairly standard brick-lined steel box with a heat exchanger at the back. The overall dimensions are approximately 500 W x 600 L x 500 H.

The unusual burning sequence is:

  1. Open the stove, push the top grate out of the way (towards the back).
  2. Build a wood fire in the combustion chamber and wait until it has burned to the point of being substantially charred.
  3. Load coal on top of the burning wood. At this point it becomes a bottom lit, updraft (BLUD) burner.
  4. The coal is left to be heated on top of the burning/smouldering wood. The top grate is pulled over the coal closing the box. It is now a square box with a grate on the top and bottom.
  5. When flames emerge through the coal and appear above the top grate, the box is flipped over using the handle on the front of the stove. At this point it becomes a TLULD burner because the charcoal has been moved to the top. The smoke arising from the hot coal below has to pass through the charcoaled wood on top and is ignited.
  6. The charcoal finishes burning during which time the coal gets fully ignited, de-volatilised and coked. After that it is an ordinary coke fire.

The coke fire burns until it expires. During the first visit it was tested with a combustion analyser during the later portion of a burn. There was nothing unusual about the fire. On the second visit gas samples were taken during ignition and for a period of one hour afterwards. The sample point was where the gases leave the mass wall and enter the bottom of the short chimney passing through the roof. Gases were analysed with a certified TSI CA-6203 combustion analyser.

Initially the CO/CO2 ratio was 20% to 40% as the fire got going. The ratio after one hour was just over 4% and 12 % late in the fire. At all times there was a high excess air ratio, 900% on high power and 1500% on low. This is higher than a traditional stove which runs 400-1000%.

The system efficiency was negatively affected by the high excess air level: from 40 to 50%. The system efficiency of a traditional stove is about 70%. The major portion of the particulates are emitted during the first 45 minutes in both stoves.

The 'heating wall' is a heat storing brick structure that condenses the combustion and fuel moisture thereby retaining the latent heat of condensation. They are gaining popularity. In spite of condensing the moisture and the low gas exit temperature (70-90 Deg C) the system efficiency is not high because of the great quantity of warmed air passing through the system. The openings are large and the stove is generally leaky, for example the cast iron top on the one we tested is not bolted onto the body (see the picture near the end of the video).

A moveable flat plate with a few holes in it is provided over the top grate that limits the rate of combustion. The burn rate is quite high for a domestic stove (because of the large area of the grate). It is probably able to reach 40 kW thermal output. The flat plate is pulled over the top grate and interferes with the airflow, extending the burn. A full charge of coal will reportedly burn for 8 hours in that condition and still have some hot coals left with which the next fire can be started. That is a major consumer demand - burning through the night.

: It is likely that this system will reduce start-up emissions from the point that the hot coal is under the burning wood/charcoal fire (the TLUD stage), for approximately 1/2 of the ignition cycle.

: The system efficiency is low compared with a traditional stove which means that although the rate of particulate production may be less per kg burned during part of the ignition cycle, more coal might have to be burned to provide adequate heat, possibly increasing the overall production of smoke.

The contact information for one of the local (Mongolian) promoters is:
Prof Adiyasuren Borjigdkhan

He reports that they wish to install 80 in homes around Ulaanbaatar to gather user opinions.

Submitted by
Crispin Pemberton-Pigott (New Dawn Engineering)
with Prof Sereeter Lodoysamba (National University of Mongolia)
and Sod Dulam (Energy consultant, Ulaanbaatar)
and Altangadas Tsegmid (Heat and Power Systems consultant, MonEnergy)

12 March 2010

Crispin Pemberton-Pigott and Roger Samson, February 2010

Please click Read More for a set of photos showing the construction of a prototype 125 mm diameter Grasifier Stove burning Switchgrass Pellets provided by Roger Samson (REAP-Canada).

Crispin Pemberton-Pigott and Roger Samson, January 2010


Roger Samson was here tonight and we made and tested a Grasifier: a Switchgrass burning stove based on the dimensions of the Vesto adapted to make a lower cost pellet burning stove for Haiti.

Power, 2.5 kw
Burn rate 8-10 g/min
Mass 550 g
Fuel load 600 g though it can hold 750

Lighted with two caps of paint thinners
The flame went completely blue (just before the end) then wobbled a lot and went out.
When it went out there was no smoke indicating there were no volatiles left.

Time to fabricate, about 30 minutes.

I see this as a burner that can be attached to the centre of a Haitian charcoal stove to convert it into very clean burning a pellet stove.

Char yield: 25% of the initial dry mass.
Moisture content of the initial fuel, about 7%

Ash: nearly none.


Richard's Charcoal Supplemented Briquettes
Edit Blue cells only C C Pemberton-Pigott Jan 2010

Outside Diameter 100 mm
Height 70 mm
Central hole diameter 35 mm
Volume 0.48 litres

Density of the briquette 0.40 kg/litre
Mass, Dry 0.19 kg

Contents, density assumed to be equal Portion Energy
Leaf/Straw 75% 17.00 MJ/kg

Download attached spreadsheet.
Edit only the values in the blue cells © C Pemberton‐Pigott, January 2010


Crispin Pemberton-Pigott & Christa Roth, December, 2009

Chinese Draft Enhancer

Dear Friends

Working on advice brought by Cecil Cook from Lusaka, Peter Coughlin in
Maputo has tried using a short vertical tube (about 400mm) held over the
lighting charcoal to accelerate ignition. This tool is widely used in
Lusaka. It is typically 50mm in diameter and can be made from an piece of
scrap pipe or rolled metal sheet.

Peter reports that people using it have reported faster lighting and a
reduction in emissions during ignition (which is the smoky part of a
charcoal fire).

I tried a similar though larger tube over coal in a bucket and achieved a
dramatic reduction in particulate emissions - certainly more than 90%.


This principle is not only limited to Zambia, it is pretty widely applied by other charcoal users in the region.
Though the most perfect 'chimney' I have got is from China: It came as a standard accessory packed in the carton of the Chinese coal-briquette stove marketed in South Africa under the name of 'Lotti stove'. I think the stove is manfuactured by Shengzhou. So it could be standard chinese practice. The conical shape with the two little air-holes on both sides shortly below the top works much better than a straight tube. We used one at stove camp this year on a two-can TLUD instead of the upper straight can and draft increased considerably. Foto attached, but not sure if it makes it on the list. regards, christa

Reporting of Performance- Stacked Bars
Crispin Pemberton-Piggott,May 10, 2009

Comparing Stove PerformanceComparing Stove Performance

See attached Excel Spreadsheet

Stacked BarStacked Bar

Dry Fuel Equivalent Calculator
Crispin and Nigel Pemberton-Pigott, October 2007


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