Bio Char

This week we had our first fire of Winter. A bit later than usual, but then the days have been warm and the nights mild. We benefitted from the excellent insulation of our house and made sure we closed up and drew curtains early in the afternoon to retain the warmth. Then finally some rain came and everything cooled just that extra few degrees.

The by-product of having a wood heater is that there is plenty of ash during the cold months. Which is handy spreading around the garden. Pure wood ash consists of calcium, potassium and magnesium. Because it contains calcium it will raise the pH of the soil, and can be used on acid soils instead of lime. Here and here is some further information.

But there is another by-product. Just before we go to bed we dampen the fire by turning down the air slide which slows the burning. The next morning there is always a reasonable amount of charcoal remaining on and in the white ash.

The morning after

Bio Char is charcoal that has been burnt in a low oxygen atmosphere. Therefore every morning the  firebox is cleaned out and the material stored in a metal container. Sometimes the charcoal is still smouldering hence the metal container. This process also causes whatever remaining charcoal to be buried in ash which limits its Oxygen.

After it has cooled it is emptied into a feed bag for storage. By the end of Winter there is usually half a dozen bags of this material. The charcoal pieces can be quite large and to break them down they would be sieved through some bird wire which has holes about 12mm diameter and then the larger bits placed in a metal drum and pulverise with the end of a large piece of wood (3 x 2).

This was time consuming and time was in shortfall. The solution was the Chipper/Mulcher. Extremely quick but messy as a dust cloud spreads for about 5 metres around the work area. Not something to do next to the laden clothesline. And a good face mask compulsory.

The end result was that with minimal effort there was 120-150 litres of Bio Char and wood ash.

Whenever compost is being made this mix of Bio Char and ash is sprinkled lightly every few layers.

On Mulcher/Chippers, Shell Grit and Bio Char

Since our Mulcher/Chipper was out and dirty from making the NZ Compost it was deemed a good time to knock out some Bio Char. I'd used the last of the previous batch yesterday.

Last Winter we had cleared out the wood heater every morning and stored the contents. The reason for a daily clean was to ensure that we collected not only the ash but also any charcoal that remained unburnt. If we had not cleaned out that charcoal would have been consumed in the next fire.

Some of these lumps of charcoal are very large. The simplest way to break them into Bio Char is running them through the Mulcher/Chipper. Dead simple and quick. The only thing to remember is to wear breathing protection and don't do this near the washing line. The amount of fine dust is incredible. Leaves you with a blackened face. If desired a solution is to wet the contents.

Bio Char exiting the Mulcher/Chipper

A better view of sizes against the grass background

The final volume was about 100 litres of Bio Char from about 6 feed bags of fireplace cleanings. Enough to keep us going for 12 months.

Now that the mulcher/chipper was really filthy we went for broke. We have three 70 litre garbage bins that were almost completely full of Oyster Shells. That is a lot of Oysters. We digested these ourselves i.e. the Oysters not the shells.

Oyster Shells

With the mulcher/chipper rolling at full speed the shells are slowly fed in to the entry schute and the output collected in feed bags at the bottom. We get a fairly good variety of sizes especially if the material is allowed to build up in the out schute slowing down the exit speed and allowing the shells to bang around in the mulcher/chipper innards.

Fairly good mix of Fines and Coarse

The final result was two very full feed bags which should see the girls producing very hard eggshells for some time. These were stored in an old plastic garbage bin.



Final Result

It is just as well we completed all our mulching tasks because just as I was giving it a good hose out, one of the main bearings supporting the flail system disintegrated.  Ah another workshop job.

Bio Char

Our Wood Heater yields a bucket of ash and charcoal every morning We've been keeping it and building up a stockpile until the end of the cold season. Initially it's scooped into a steel bucket and later when cool stored in feed bags. Once the warmer weather has arrived the Chipper/Mulcher is relocated away from the house and all the collected ash and charcoal is fed into the Chipper/Mulcher. A large feed back is used to catch the fine material. We wear a face mask when operating for this process because the dust is fine and prolific. All the collected material is stored in a plastic drum and used liberally on the vegetable garden and especially when building the NZ Compost. Our wood heater yielded almost 200 litres of material last cold season.

Charcoal in the Fireplace

Charcoal Cooled and Bagged

Mulched Ash