|FIRE CUBES - COOKING WITH BIOMASS|
Fire Cubes are biomass fuel briquettes made from anything that will burn well enough to provide domestic cooking and heating. Typically such briquettes are made from paper and sawdust. The mixture is compressed in a manual machine and dried out as far as possible. These can be used as a wood or coal substitute.
Made in Swaziland since about 1992, 'paper bricks' have slowly gained acceptance as an alternative to collecting fuelwood from the forests and farms. One operation in Hlatikhulu has had orders as large as 5 tons and some producers export 'paper bricks' to South African townships near the common border.
Equipment is available to make between one and sixteen briquettes at a time.
One Method of Production
1. Soak and pulp the paper you have available. One kilogramme will do for a start.
2. Add three kilogrammes of sawdust and mix well.
3. Pour (slosh!) the mixture into the mould(s) filling them evenly if there is more than one cavity.
4. Squeeze the plunger(s) into the mould to press out as much water as you can. Some models require you to turn the unit upside down to get the water away from the compressed briquette.
5. Eject the briquettes.
6. Remove the pin(s) that produce the hole(s).
7. Slide the briquettes off the base plate and store until dry.
Lighting the Briquettes
1. Experience shows that these briquettes will not burn well until they are hot enough to support an open flame. This translates into a need for 'kindling' to warm them up. Light a small kindling fire using twigs or paper and put the Fire Cubes on top of them. They are shown burning in a Basintuthu Stove which can optimize the combustion.
2. When the fire starts, it will smoke quite a bit as the Fire Cubes heat up. When they start to burn the fire grate heats up and secondary combustion begins to consume the smoke.
3. The secondary combustion produces additional heat by reducing the CO to CO2 and burning wasted carbon, soot and ash. The visible smoke virtually disappears.
4. The picture sequence show a typical cooking experience using biomass fuel briquettes made as described above. The pot is a 6.8 Kg cast iron flat bottomed Falkirk pot with 3 litres of water in it. The water and pot temperature was 23 deg C when starting off. When the briquettes were buring without the assistance of any kindling (after the fire was established) the pot was put on top of the stove. There was a brisk wind blowing at the time.
5. The flame temperature inside the secondary combustion was about 820 degrees C which is similar to that achieved with a wood fire in the same stove.
6. The boiling point in Matsapha is 95 deg C because of its altitude. The water took 18 minutes to come to a rolling boil using only the briquettes as a fuel. The consumption of fuel was at a rate of about 1 unit per 5 minutes.
7. The heat content of a briquette averages 0.77 MJoules so the combination of the briquette fire and Basintuthu Stove is equivalent to a 2.5 KW electric heating element.
8. The bare cost of production of the briquettes using the largest scale manual equipment available is approximately US$0.0052 per MegaJoule which is about half the local cost of electricity and one third the local cost of charcoal.
9. It is acknowledged that the local cost of coal generated electricity (in South africa and some surrounding countries) is the second lowest in the world. However, locally made waste biomass briquettes can still compete with this.
Heat Value of Wood = approx 13-20 MJ/Kg
Heat Value of Paper varies, newspaper is also about the same
Briquette sizes range from 40 to 250 gm each.
Paper Briquette density ranges from 0.18 to 0.3 gm/cm^3
Cattle dung has been effectively used in the RSA as a binder for charcoal dust.
Coal dust can be used if it has a high volatiles content.
Briquettes made entirely from paper have been made and sold on the East Rand for many years however we consider that to be a waste of binding material.
Waste paper-bound sawdust fuel briquettes using an entirely manual production process (South African Patent Application 2002/0689).
At a dry weight of 45 grammes average per briquette and making 16 at a time, you will process 540 kg per 8 hour shift. This is a consumption of 430 kg of sawdust and 110 kg of soaked newspaper (or other paper) as the binder.
For 10 Kg of dry inputs it uses 55 litres of water for the pulping and mixing. About 40-45% of the water is recovered in the moulding process and can be recycled. This means that it uses 2.75 litres of new water per kg of product. At a production of 12 tons of briquettes you will use (and evaporate from the wet briquettes) 33 cubic metres of water per month.
Per ton of output you will need about 200x25 litre plastic containers of water stored at all times (soaking paper). For 540 kg of briquettes per day, you need 90 containers which will be cycled every 4 days. They can be stacked 2 high and it requires something like 1.2 x 4 metres of floor space to do it. The sawdust is not soaked.
The sawdust and paper have to be mixed together. This can be done completely by hand or with a hand operated mixer. 540 kg of output will require 2 hand operated mixers.
There is a large amount of space required to dry the briquettes. The area depends on the local climate. They can be racked, and solar heating is advised, under a simple cover. We are not prepared to estimate the time for drying as it depends on many factors. It takes several days (3-8). If it takes 6 days there will be 540x6 kg of briquettes in the drying area (about 72,000 units).
Heat Content and Value
The heat content is 1.3 MegaJoules per briquette. In terms of electricity, it is worth 11.7 cents per briquette for its heat value. It is estimated that they will sell for about 1/2 to 3/4 of that (6 to 9 cents ea). Producing 12,000 briquettes per shift represents a retail value of R720,00 at 6 cents each. It will take 8 to10 people to produce this.
At this time, we are quoting R20,000 for a set of equipment that in fact varies depending on the installation it the figure is not exact. It is quoted to give people an idea of that might be involved. The process consists of:
- soaking and pulping the paper (containers, hand tools)
- mixing in the sawdust (mixers, barrows)
- moulding the briquettes (moulding table, pressing table x 2, ejecting table, water collection trough) - carrying off the finished product for drying (carts, racks, barrows)
- drying (drying shed, racks?)
- packaging and distribution (bagging, labelling)
The use of the technology is permitted in return for a monthly royalty of R80. This fee gives up to 1 hour per month of telephonic technical support (per set of equipment in the licencees' possession), general advice and upgrades of the process (information) should they emerge. The use of additional production lines, whether purchased from us or others, requires the payment of an additional fee per machine to use the process.
Cold, it will burn only when a flame is applied. Otherwise it 'charcoals' with a lot of smoke:
Start the fire with kindling under the briquettes. It will produce smoke while heating up:
When the briquettes get hot, secondary combustion begins, consuming the smoke and providing additional (free) heat. Note that the flames are not really coming from the surface of the cubes, but from the combustion of smoke from the fire lower down in the grate. The Basintuthu Stove provides pre-heated air injection to make this type of highly efficient combustion possible. The photo clearly shows a dense, bright orange flame from primary combustion of a briquette near the top of the grate. The clearer, darker orange flame is secondary combustion of the smoke:
A peek under the pot: secondary combustion at 800+ deg C.:
Measurements were done with a digital 1000 Deg pyrometer. Note the small lick of secondary flame on the leeward side of the pot (the wind is blowing from the right) and the steam which is visible in the high resolution picture (click on this one). The pot weighs 6.820 Kg when empty and contains 3 litres of water:
Less than 20 minutes later, a full rolling boil in spite of the mass of the cast iron pot.
The local boiling temperature is 95 Deg C.: