Commercial MIDGE stoves are a waste of money

Not only are commercial MIDGE stoves a waste of money but they also go against the spirit of wood gasification. Self-reliance is the key to wood gasification, the ability to provide for yourself and for others in times of hardship.

If there was an energy crisis then popping down to the shop for a MIDGE stove is not an option. There won't be any. Nor will there be an Internet for you to purchase one on either.

Another reason for not buying a commercial MIDGE stove is that for some reason they come with an integral battery operated fan to produce a stronger draught. The battery operated fan also goes against the spirit of wood gasification. Where are you going to get batteries from in an emergency?

A well-built gasifier simply doesn't need a forced draught. I have boiled water and cooked meals on my MIDGE stove. That is all they are meant to do and a handmade one does the job perfectly.

Read the plans. Find some cans. Make gas!

MIDGE stove plans - The Complete MIDGE (pdf)

No-weld downdraught gasifier #3

In this section we complete the combustion tube inside the combustion chamber. Then we marry the combustion chamber to its shroud.

You will remember that we had introduced the combustion tube into the hole at the bottom of combustion chamber. Tabs were cut to hold the tube in place.

After checking that the tube has an idea fit we remove it. Four holes are drilled into the side walls of the combustion tube. These holes will take a bolt each so that they take the weight of the tube.

Next, a restraining band is made from a thin strip of steel (such as was leftover when cutting the 20-litre drum. Four holes are drilled into this band so that it can be held in place by the four bolts on the side wall of the combustion tube.

Holes are drilled into the bottom, closed end, of the combustion tube. This allows ash to fall out of the tube.

A disk of metal sheet is cut and entered into the combustion tube. It rests upon the bolt heads and acts as a throat inside the combustion tube. A hole (or holes) will be cut into this to allow char to fall into the combustion tube.

The combustion tube is placed back into the combustion chamber such that the tabs holding the tube in place are caught between the tube and the restraining band. This band holds the combustion tube firmly in place.

The combustion chamber was turned upside-down and the gap between the combustion tube and chamber sealed to prevent air from bypassing the char.

Here we can see the combustion tube sitting on top of the shroud we made in section #1. On top of the combustion chamber sits a hopper. Details of the hopper will be given in section #4.


No-weld gasifier sections:

#1 - Introduction - materials and tools, building the combustion chamber shroud

#2 - Building the combustion chamber

#3 - Completing the combustion tube

No-weld downdraught gasifier #2

In this section we detail the construction of the combustion chamber. This is where air from the outside meets hot char to form wood gas.

The combustion chamber is made from two ends of a 20-litre vegetable oil drum. A whole drum is too big so we just cut off what is needed from either end and then join the two ends together.

In the following photo we can see an old drum being cut with tin snips. Drill a hole (using a low setting on your drill) in the side of the drum so that the tin snips can be inserted into the drum wall. I won't give dimensions here. It is up to you to decide what sizes you need depending on what tins and drums you have available. Read the whole of this article before starting work.

Here we can see the two ends of the drum. Keep the strip of metal between the two ends as that will come in useful later.

The bottom end of the drum has tabs cut into its wall section. This allows the top end of the drum to be pushed over the tabs and locked in place.

Now, a hole is cut into the bottom of the drum. The hole has a diameter about 2 centimetres smaller than your chosen combustion tube.

Here we see the completed hole. The hole doesn't have to be accurate, just smaller than the combustion tube. You then cut tabs so that they can be bent up and cling to the combustion tube. This will help hold the tube in place.

Here we see the tabs bent up and clasping the inserted combustion tube. The tube is a tin of about 15 cm diameter with one end open and the other closed.

In the next section we will complete the combustion tube and show the combustion chamber and shroud joined together.

No-weld gasifier sections:

#1 - Introduction - materials and tools, building the combustion chamber shroud

#2 - Building the combustion chamber

Ferrocement resources

In a previous post we mentioned the possibility of using ferrocement as a way of building a no-weld gasifier. At the moment we are using lighter gauges of steel and bolting together our no-weld gasifier. To create airtight seals we are using fire cement.

It is not too far a step to start using ferrocement to seal the gasifier from air and wood leakages. There are also advantages to using ferrocement as a way of protecting the lighter steel gauges from excessive heat, which cause buckling.

For the time being we will continue without ferrocement and consider its use after a test run.

Ferrocement - resources

Electricity generator running on wood gas

This is a very good presentation about what can be achieved with a simple wood gas powered generator.

Heating water with wood gas

I was experimenting with Big MIDGE last night. Attempting to find out the minimum amount of wood chips I would need to boil 1 litre of water. Not much was the answer. Approximately 200g is the amount of wood chips required.

It is surprising how efficient these MIDGE stoves are. They produce no smoke, can be used indoors so long as there is adequate ventilation, and produce little ash. They give off an awful lot of heat and most of it is directed precisely where you want it.

Upcoming experiments include constructing a heating coil from copper pipe and attempting to heat a larger mass of water using the thermosiphon effect. I would like to heat enough water for one or two showers, washing the dishes and a cup of coffee per day.

Ultimately I would like a larger gasifier that during the course of a day can heat a large heat store. This store would be a heavily insulated tank holding 10,000 or more litres of water. The intention would be to heat the store to provide enough heat for a week of hot water and underfloor heating.

A wood gasifier is ideal for this as it is very efficient. Most of the heat generated would go into the store. The wood chips would be simply created from waste wood mass. There would be no need to fell large trees, which could then be sold on for income rather than my burning here. Besides, chainsaw work, bucking and splitting does my back no good at all.

Operating a wood gas stove

I have created a better video of the MIDGE stove in operation. I'm no Orson Welles but I do come in on budget.

The stove is a particular type of gasifier known as an 'inverted downdraught gasifier'. Essentially, that makes it an upside-down downdraught gasifier. The difference being that the wood gas is immediately burnt in the inverted gasifier but in the normal configuration it is tapped off for running an internal combustion engine.

The inverted downdraught gasifier in its most basic form consists of one can suspended inside another. The outer can acts as a cowling permitting air to enter its primary air holes where it can pass into the inner can. The inner can has holes at the bottom, in the form a grating which aids combustion of the fuel, and a ring of secondary air holes at the top which create an air/fuel mixture with the wood gas.

Fuel consists of wood chips. This permits easy fuel collection from broken tree boughs and the sort of waste that owners of log burning fires reject. The chips are packed down into inner combustion can and a small amount of some flammable liquid (spirit or paraffin) is dripped on top so as to get the fuel to sustain a hot flame long enough for char formation.

A fire is lit on top of the fuel, which results in a char layer forming. Beneath this layer is the pyrolysis layer where wood is converted into hot wood gas. Combustion continues down through the wood chips, converting the chips into charcoal which is then reduced to wood gas. The wood gas rises up, meets hot air at the secondary air holes and ignites.

You can think of a MIDGE stove as a device for making charcoal, which is then reduced to various volatile gases and a small amount of ash. The operation is very efficient, is virtually smokeless and yields little ash.

YouTube - Wood Gas Stove

No-weld downdraught gasifier #1

Much is made of wood gasifiers being useful in emergencies. However, most are made in today's time of relative plenty. Constructors have ample time to source materials and then weld them together with state of the art equipment.

What if we were in an emergency? What if the materials available were not of a high grade? What if welding facilities were either not available or inappropriate given the materials we had? All of these questions made me think of building a no-weld gasifier, using common materials that anyone might have and tools that could easily be found.

In these times of dwindling resources, scrap metal is snapped up by scrap dealers and is hard to find. In an emergency, looking for quality scrap metal might not be an option. Here are some typical scrap tins that you might find in your house or on a rubbish tip.

Tools used were the kind that can either be found around the home or easily procured. No welding was permitted so fixings either had to be bolted together or merely rested on top of each other. Sealing to prevent gas escaping or air getting to where it shouldn't be had to be done with fire cement, which can be found in most hardware stores.

The larger tins are 20-litre vegetable oil drums and are ideal for building the main housings for a gasifier. These drums can easily be cut with tin snips but care must be taken when cutting thin steel as any jagged edges can easily scratch your skin. The metal will not clean and any dirt can enter wounds and cause infection.

This photo shows the top cut off a drum. A serrated edge can clearly be seen.

Serrated edges can be cut into tabs and then tapped down so that no sharp edges are in harm's way.

A firm surface under that part of the drum being tapped prevents the drum being put out of shape.

The result is an open-topped drum that can be used to house the combustion chamber of a gasifier. The fitting at top left of the drum is a tank connector. Any wood gas produced will be sucked out through this port.

Close-up of the tank connector. Connecting it is simply a matter of making a hole in the drum and screwing both parts of the connector either side of the drum wall. No welding required.

In the next section we will build the combustion chamber that sits inside this gas collection drum.

No-weld gasifier sections:

#1 - Introduction - materials and tools, building the combustion chamber shroud

#2 - Building the combustion chamber