About Downdraft Gasification

If you are new to the waste conversion using downdraft gasification or just looking to brush up on your knowledge, here are some of the more critical things to know about waste conversion via gasification. Keep in mind that all material contains a degree of latent energy, how we capture that energy and convert it is critical.

Overview of Downdraft Gasification

Gasification is a process that uses a feedstock, often municipal, commercial or industrial waste, for a thermo chemical conversion of waste using high heat. This is done is a low oxygen, also known as an oxygen starved environment that causes material to breakdown at its molecular level. Once the molecular breakdown occurs, the gasification process recombines them to form a producer or syngas - a gas similar to natural gas, and biochar - a carbon rich charcoal type material, which is explained below. The following cart is a high-level process flow summary of waste conversion using downdraft gasification.

Downdraft Gasification Reduces Landfill Volume, Fees, and Handling Costs

Landfills remain as the most common way to dispose of municipal and industrial waste. While the recycling rate of some forms of waste has steadily increased, so has overall volumes in general. In Australia disposing of waste can be very costly — whilst it varies by region and state, it can vary from being free to over $400/t, especially in those states that maintain a waste levy, and landfill sites fast approaching critical mass and closing as they reach their limits. This means continual increases in corporate and municipal budgets while landfills and the amount of waste generated continues to increase also. Waste gasification provides a much needed opportunity to divert waste from landfills and use it in clean energy production, keeping landfills from growing and reducing landfill fees.

Electric Power Generation through Combustion of Syngas

As organic materials like wood and sewage sludge are gasified, the chemical process creates a clean syngas, a fuel that can then be used like natural gas. Compared to other waste-to-energy methods like burning, or incineration, the gasification process allows the syngas to be cleaned of contaminants prior to its use. Incineration plants do attempt to clean their emissions, but it is done “post-combustion, making it harder to capture and isolate hazardous emissions. Creating syngas through gasification is almost like closing the circle, or closing the loop, on waste’s lifecycle and maximises the latent energy. The energy embedded in the waste can be used to power engines that generate electricity.

Lower CO2 and Greenhouse Gas Emissions

Gasification can be one of the tools used in our shift to a lower carbon economy. In particular, the gasification process releases no GHGs as landfilling and incineration of waste do. When trash/waste sits in a landfill it releases significant amounts of methane as it decomposes. If this methane isn’t captured, it goes into the air where it is 30X –- 3000% – more potent as a heat trapping gas, which is an averaged figure. Methane in fact can trap up to 100 times more -10,000% more - heat in the atmosphere than carbon dioxide within a 5 year period, and 72 times more within a 20 year period. The landfill process also requires a lot of trucking of waste materials, which also contributes to its greenhouse gas emissions. If gasification plants can tap into readily available waste nearby, they can reduce emissions from trucking as well.

No Burning or Incineration

Gasification can be one of the tools used in our shift to a lower carbon economy. In particular, the gasification process releases no GHGs as landfilling and incineration of waste do. When trash/waste sits in a landfill it releases significant amounts of methane as it decomposes. If this methane isn’t captured, it goes into the air where it is 30X –- 3000% – more potent as a heat trapping gas, which is an averaged figure. Methane in fact can trap up to 100 times more -10,000% more - heat in the atmosphere than carbon dioxide within a 5 year period, and 72 times more within a 20 year period. The landfill process also requires a lot of trucking of waste materials, which also contributes to its greenhouse gas emissions. If gasification plants can tap into readily available waste nearby, they can reduce emissions from trucking as well.

Byproduct is a Valuable High-Carbon Biochar

Another benefit of gasification is that it outputs two usable materials. The first, clean syngas mentioned earlier. The second, a “high-carbon biochar.” In a downdraft gasification process, such as the one we deploy and developed by Aries Clean Energy, 95% of the input waste is converted into syngas. 5% becomes biochar, which can be used again. Here are just a few examples of its applications and uses:

  • Fuel for kiln type operations or where a solid fuel type is required
  • Filtering media in a number of industries and varied applications from liquids, gases and odours
  • Growth foundation for in marine applications such as reef regeneration
  • Increases water retention, thus reducing irrigation volumes
  • Increases beneficial microbial activity and so crop yields whilst reducing fertiliser use, costs and resultant excess nutrient run-off
  • Moderates soil acidity
  • Reduces leaching of nitrogen into ground water
  • Improves cation-exchange capacity

 In contrast to other waste-to-energy options like incineration, downdraft gasification does not produce ash. Incineration on the other hand, produces an ash that is sometimes used to cover landfills, but must be carefully controlled to manage leaching of harmful chemicals.

 Again, downdraft gasification helps close the loop on waste materials by creating a byproduct with another valuable life.

Energy Benefits

One of the main priorities in closing the loop on waste is losing as little energy in the process as possible. Of course, given the laws of nature, this is hard to do. Thankfully, downdraft gasification has allowed the approach to waste-to-energy to get an upgrade. On average, conventional waste-to-energy plants that use mass-burn incineration can convert one ton of waste to about 550 kilowatt-hours of electricity. With downdraft gasification technology, one tonne of waste can be used to produce up to 1,100 kilowatt-hours of electricity. If this waste were to sit in landfills, we’d certainly lose a lot of the energy it contains.

Downdraft Gasification provides us with a huge energy benefit – we can reclaim more energy while powering a cleaner world.