With the free time from the bank holiday, not wanting to spend the whole weekend inside I decide to devote sometime to my BioGas project. Having considered the last run a success, apart from producing a lot of smoke the gas produced did eventually light, leading me to believe that the reactor was working and just needed to continue to warm up to operating temperature.

 I loaded the base full of charcol and get started again. Within minutes the base was hot and I loaded the chamber with wood pellets – sealing the top.

After 5 minutes the colour and quantity of the smoke changed and I used my blow torch to ignite the smoke.  Instantly I was presented with a hot yellow flame, while the flame was not able to maintain itself I believe this is due to the water content and lack of mixed air – a problem soon to be fixed.

Below is a ‘basic’ drawing of the setup

I have installed flare stacks at all the post-process points so that I can check the output of the gas – The last thing I want to do is do all this work and end up with something that doesnt ignite!

So project one complete, I can successfully make flamable gas from waste wood! Next step – Clean, Condense and find a use for the wood gas.

*UPDATE 14th October 2012*

Having now purchased my own air compressor (yay!) I was able to fire up the reactor again and do an extended test. Below is a snippit of video I was able to record:

Wood Gas Reactor

Project 2: Cleaning & Condensing

Fresh from the reactor the gas is still very hot and contains dissolved in the smoke a number of unhelpful substances – water being the biggest. In its highly energised state the gas moclules lack density and compressing them would be very difficult.

From my research I have found several methods of cooling hot gas (the top 2 being):

  • Heat Exchanger / Radiator
  • Water bubble tank

To keep things simple I opted to use a sealed water bubble tank. This is where the end of the outlet from the reactor is fed under water and the gasses are bubbled up through the water, both cooling the gas and seperating the water / water soluable substances at the same time. Keeping the water as cold as possible will hopfully force more of the waste componensts to seperate from the flamable gas cloud.

If needed a further process using hay as a filter medium can be slotted into place to absorb waste if needed – however I do not think this well be required if the ice water filter goes to plan.

 So as part of my renewal projects and drive I have been focused and interested in Biogas, in particular gas produced from the breakdown of wood at high temperature with limited oxygen.

After my experiments and success with making a biodiesel reactor and running a car off biodiesel for many years I had felt that this project fitted the natural progression. If I could make a fuel for diesel engines making a fuel for spark based engines was the alternative.

Before starting on this project I did a lot of research online.

YouTube was a fantastic resource that allowed me to see other peoples success but also how their projects have come together and the pitfalls they encountered.

BBC’s Bang goes the theory did an experiment where they used coffee grounds in a similar fashion, the link can be found here.

Another site I made extensive use of was MD Pub’s Gasifier, his research, experiments and documentation became the grounds for my own jumping off points.

So what is a Gasifier?

A Gasifier is a combustion chamber where organic substances (wood, coffee grounds or other organic substances) are burnt at high temperature with limited oxygen, this causes the organic and volatile compounds to separate. In principle it goes like this:

Wood + Limited Oxygen = Carbon Dioxide + Carbon Monoxide + Carbon + Water + Hydrocarbons + Heat

The wood (or organic substance) becomes unstable and breaks down into less complex substances – otherwise known as Pyrolysis (Wikipedia Link).

Once this process has happened the gas is in a raw and almost ‘dirty’ state, at such a high temperature it contains moisture and tars that were not thermally broken down, before it can be used in any combustion engine the gas must be cleaned and impurities removed.

I have broken my project up in to two sections.

  1. Gas production device
  2. Gas cleaning device

This post focuses on Part 1, the manufacture of a BioGas production system.

From the research I did, it seems the most successful projects were ones that used compressed air, injected into the combustion chamber at the hottest point. I chose to make a ‘injection ring’ where 5 copper pipes inject air into a steel cylinder. To get started I needed a base:

Using an old 25 litre chemical drum, I cut the top off, leaving the pressed steel rim intact, This gave me a large working area to easily fit parts and get my hands into areas needed for screwing / working. For my combustion chamber I found compliments of eBay an old fire extinguisher – yes I’m aware of the irony.

I cut the base off the extinguisher:

and removed the razor sharp edge left by the cutting tool:

You can see from the positioning the plan, filling the now top of the chamber with the reaction occurring at the neck with the gas and ash flowing out of the bottom.

The next step was to drill holes and fit the air injection pipes. The drilling of the holes and fitting of the pipes was very simple, with a small jig setup to prevent the drill from travelling on a circular edge. Once I had the pipes fitted I made a ring of copper pipe around the outside and connected all the injection tubes to the ring. This gave me a single point where I could connect an air hose and apply compressed air.

From some of the learning’s from MD Pub’s pages, he had major trouble with gas tar and water escaping from the gaps between the pipe and the cylinder. So I decided before moving on that I would seal the pipes to the cylinder. My original idea was to weld or braze the gap, but after watching numerous videos on how to braze and following the pack instructions to the letter, I was unable to form a solid bond that couldn’t be chipped off with a finger nail – see photo

So my next idea was to use chemical metal. A two part compound that when combined becomes tough and bonds metal together. Fab I thought. After cleaning the remains of brazing rods off the copper and steel I set about trying to glue the gaps up. What a success! The glue set, didn’t shrink and all the gaps were filled. All my problems were solved – or so I thought!

I left the project for a week or so, coming back everything looked good, the glue hadn’t fallen off and holding the base up to the light resulted in no pin pricks of light shining through. Then I dropped it (the fire extinguisher) and the glue shattered. Being so brittle and so inflexible all of the joints immediately failed I needed a better idea, a more flexible idea.. Re-reading MD Pub’s pages he talked about using a flexible high temperature silicon sealer to fill in all the gaps. So a quick trip down the local hardware store saw me back in business.

After sealing all the gaps and joints I moved onto making a lid, making friends with a local metal workshop I had a rummage around the offcuts bin and found a sheet of metal that would be perfect. Cutting a doughnut shaped ring out from the metal and fitting it too the inverted fire extinguisher with a little silicone seal in place around the gaps:

Fab! So now I have fitted my chamber up, secured a constant stream of compressed air for the reaction to occur. All that was next was to test my Gasifier.

Loading up my reaction chamber with wood and charcoal I sealed the chamber (with the now lid, ex base of the fire extinguisher). Once the airline was attached and a constant stream of air was being forced into the chamber I felt the Gasifier immediately heat up, plenty of smoke was being product from the exit port but nothing flammable. This went on for 20 minutes and as the temperature increased so did the quantity of non-flammable gas being produced. Sadly the seal of the combustion chamber failed soon after, resulting in a small fireball about the size of a football coming out from the combustion chamber. This has shown me two things, One: Gas was being produced, Two: I need a better seal on my gas chamber.

My plan for the rest of this project is to find / design a better heat proof seal for the combustion chamber and to replicate the experiment. I believe I’m on the cusp of making this project work, so a few more steps particularly in the name of safety shouldn’t be a problem.