Prototype Briquette gasifying stove
Richard Stanley and Kobus Venter October 2003
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Introduction
This stove is actually a natural updraft biomass gasifier. Conventional gasifiers are bottom lit and rising hot gasses needs to be drawn down assisted by some form of electric blower. By top lighting and using measured amounts of Primary and Secondary air, the result is a natural draft (Updraft) gasifier that expels volatiles and emission gases upwards without external power.
The burn direction is downward, but the pyrolysis gases move upward. A layer of charcoal is formed on top and slowly moves down as the so-called "flaming pyrolysis zone" and the unburnt fuel below this layer is heated and starts releasing volatiles which is ignited above this charcoal forming layer.
Precisely metered Primary
air is fed in through the door and into the
reaction. The volatiles are constantly being released lower
down and is then mixed with metered amounts of Secondary air higher up, and its this volatile mixture that results in a blue flame. The combustible volatiles are made up of mainly Carbon Monoxide, Methane and Hydrogen.
Description
· All components made from 3CR12 (chrome based alloy)
· Approximate weight: 15 kg
· Approximate height: 450
· Approximate width: 300 mm diam
Unique features
· Light-weight (±15 kg), therefore portable but with a wide base for stability during cooking.
· Smokeless.
· The characteristic blue flame (similar to an LP gas flame) does not blacken pots.
· No welding or electricity required during assembly and construction. All components are either pop-riveted or fixed on with bolts.
· Rust proof (Chrome based alloy material, 3CR12).
· All parts are replaceable (by drilling out the pop-rivets). This is especially relevant to parts near high heat.
· Metal components near heat source have been re-enforced (3mm) to avoid warping or quick wear.
· The combustion chamber is made of highly reflective refractory ceramics (1260°C), with a specially formulated silicon hardener mixed in during its fabrication to reduce wear and tear. This material is very insulative, reflective (of infra-red back into fuel) and light-weight and allows for stove to reach operating temperatures very quickly, yet cools down slowly to allow fuel to burn entirely to white ash, following usage. This results in low maintenance and cleaning on the part of the user.
· Long life expectancy envisaged due to aforementioned points and for the fact that no metal parts whatsoever are in direct contact with flames.
· Easy and safe batch loading refuelling system.
· The pyrolysed briquette can be immediately removed following gas burn and replaced with a fresh briquette or left to burn out completely in a conventional burn, without having to remove the pot. Alternatively charred briquette can be sold to briquette vendors or used as fertiliser.
Performance data
· High Power= 1.1 KW
· Efficiency at high power= 35.2%
Operating instructions
· Open doors and windows if used indoors.
· Place briquette on top of fuel holding plate and place kindling or starter fluid over the entire top of the briquette and inside the hole.
· Open the door fully.
· Light the briquette from the top.
· Wait for flaring yellow flame to die down (3 - 4 minutes) or for top layer of briquette to burn on its own following the completion of the kindling burn, then close the door.
· Gasification of biomass and closed coupled burn of resulting producer gas then commences with its characteristic blue flame.
·
Remove briquette
once producer gas has been extracted and burnt (±20 minutes) or
open door to allow more air in to burn resultant charred
briquette.
Contact details:
Legacy Foundation for all countries
or Venter
Forestry Services cc
for all Southern African countries