What is a Gasifier?
Gasification is the chemical process by which synthetic gas (or syngas) is produced from the thermal conversion of carbon containing materials i.e. biomass. Unlike regular combustion that occurs in an abundance of oxygen, gasification uses only small amounts of oxygen under immense pressure.
The gas composed of hydrogen, methane, little amounts of carbon monoxide and other inert gases is very flammable and can therefore be used as a substitute for natural gas. However another system uses the downdraft gasification process to mix the syngas with air (oxygen) and the resulting mixture used to run a simply modified diesel engine. When coupled with a generator, you will end up producing electricity.
This process was first put to use in the 1790s in the US to power homes and light up city streets. It was eventually overtaken by natural gas, coal produced electricity and later hydroelectricity. However with the rising oil prices and unpredictable climate changes which have contributed heavily to rising power costs, people are beginning to rediscover the advantages of using gasifiers to relieve, albeit a little, the burden of power bills.
The Downdraft Gasification Process
Step 1: Drying of fuel
For homemade gasifiers it is advisable that you use regular wood pellets since they burn relatively cleaner and they are easily available at your local store.
The wood pellets are dried at the top of the gasifier and about 80% of moisture removed.
Step 2: Pyrolysis
After drying, the wood pellets enter the second zone also known as the Pyrolysis zone where the gaseous products are partially heated. Pyrolysis occurs under controlled conditions with limited oxygen so that instead of converting the biomass into ash, the wood pellets are converted to gas and charcoal.
Step 3: Combustion
The outputs from step 2 react with more charcoal at extremely high temperatures (about 800-900 degrees Celsius). In the absence of oxygen this process produces carbon dioxide, steam and methane.
Step 4: Reduction
Here steam is reduced to produce hydrogen. Carbon monoxide is also produced.
Advantages of Gasification
- Flexibility. Any biomass/feedstock product can do
- Gasification barely produces any emissions. This means it barely has any negative impact on the environment unlike oil.
- High efficiency. A bag of wood pellets can run your generator for a long time depending on how well built your system is.
Limitations of Gasification
- Syngas has to be purified to remove carbon monoxide which is toxic if inhaled in large amounts
- A homemade gasifier will cost you about $300 which means initial setup can be a little expensive.
- Gasification cannot produce a lot of energy. It is therefore not suitable for running energy intensive tasks.