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close this bookBoiling Point No. 43 - Fuel Options for Household Energy (ITDG - ITDG, 1999, 44 p.)
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The Fulgora sawdust burning stove

by Harold Bland c/o Intermediate Technology Development Group, Schumacher Centre for Technology and Development, Bourton Hall, Bourton on Dunsmore, Rugby, Warwicks CV23 9QZ or E-mail <haroldbland@green555.freeserve.co.uk>

Le foyer Fulgora utilisant les sciures

Cet article traite d'un foyer appelulgora qui avait commercialise. Le principal usage de ce foyer ciures est le chauffage des locaux, les aspects techniques du foyer y sont dits.

This is a brief article based on personal experience of using sawdust waste to heat a workshop. The Fulgora was a patented sawdust burner commercially produced in Battersea, London (patent No 595869, now expired)*. The smaller model, described below, was purchased in the 1970s, and has been in intermittent use ever since. It is fairly simple in construction, but very effective.

* The author would be interested to hear what became of the design and the Company subsequently.

Material:

Mild steel sheet: 2 mm thick for legs and lid, the rest 1.2 mm thick.

Finish:

Natural (light rust).


Figure 1: Schematic drawing of Fulgora stove

H Bland


Figure 2: Removable inner bin with hole through to air chamber below

H Bland

Output:

A few kW for 4 to 8 hours with an air door opening 20 to 30 mm. The burn rate increases near the end of the sawdust charge, as the burning core expands out to reach the inner container walls. Up to 7 kW can be produced, but at this output the case glows red-hot, so inflammables must be kept well away, and the fuel charge does not last long.

Operation:

The heater comprises two concentric bins. The removable inner bin has a hole through the bottom to the air chamber below. This allows hot gases to be drawn downwards through the hole to where combustion occurs. The hot gases rise between the inner and outer walls of the heating stove, providing good heat exchange to the room as they pass between the two chambers before passing out of the room through a flue (Figures 1 & 2).

Fuel range:

Sawdust is best. Shavings or chip-pings will work provided they do not collapse down the airway. They work better mixed with sawdust, but have the effect of making it burn faster and hotter.

Burn time:

Fuel charge lasts 3 to 8 hours according to output and sawdust density. The fire has to burn right out before refuelling.

Flue size:

Minimum 2 or 3 m long to give adequate draw (Figure 3). Minimum diameter 100 mm, since it does not produce tar, a thin metal flue seems adequate, such as a stainless steel flue liner. However some water vapour may condense in the flue and run out at the base as a brown liquid

Smoke:

After the initial lighting period of a few minutes, it is completely smokeless, and was given an Agrement Certificate as a smokeless burner. Because it burns out- wards from the core, all the smoke from the smouldering sawdust has to exit into the stream of hot excess air rising up the core, and so is burnt off, yielding negligible smoke or tar. Other smoky fuels can be incorporated into the sawdust, and will then burn smokelessly.


Figure 3: Flue should be 2 or 3 metres long, leading out of doors

H Bland

Cooking:

A saucepan or kettle may be heated rapidly on the central, level area of the lid which gets very hot even on low settings because it is above the burning gases rising up the central core. Chapatis can be cooked on the cooler outer sloping parts of the lid.


Figure 4: Ensure that the core is kept central (top view)

H Bland


Figure 5: Sawdust should stay in position when core is removed

H Bland

Lighting the stove

The following has been found to be the best method for lighting:

· Open the air door full.

· Remove the lid.

· Insert the removable core tube.

· Pour in the sawdust, keeping the core tube central (Figure 4)

· Compact the sawdust by pressing it when half full and again when full.

· Remove the core tube by twisting and lifting straight up. The sawdust should stay put, leaving an airway right through from the air inlet below (Figure 5)

· Refit lid.

· Warm the flue by burning half a sheet of newspaper through an inspection hatch at the base of the flue. This creates a draw to help lighting and reduce any tendency to leak smoke during the initial warm-up period. If necessary, the lid may be temporarily sealed against smoke leakage by wrapping a strip of felt pipewrap round the lid edge while the flue warms up and creates a draw.

· Light two or three sheets of newspaper in the air chamber below the sawdust, taking care not to block the airway up to the core. Feed in further sheets until it is drawing well (Figure 6).

· Close the air door to give an airway 20 to 30 mm wide to control the output to a few kW. Remove any temporary lid seal before it catches fire.


Figure 6: Light a few sheets of paper to heat the flue

H Bland