Aries Clean Energy
June 5, 2017
If you are new to waste gasification or looking for a brush up on your knowledge, here are the top 7 things to know about waste gasification
1.) Overview of Gasification
Gasification is a process that uses a feedstock, often municipal or industrial waste, for a thermo chemical conversion of waste in high heat. This is done in a low oxygen environment and causes material breakdown at the molecular level. Once the molecular breakdown occurs, the gasification process recombines them to form a syngas, a gas similar to natural gas, and biochar, explained below. Below is a high-level process flow summary of waste gasification:
2.) Gasification Reduces Landfill Volume, Fees, and Handling Costs
Landfills remain the most common way to dispose of municipal and industrial waste. While the recycling rate of waste has steadily increased, so has overall waste volumes in the US. Disposing of waste is costly — the average cost to landfill trash is $50/ton in the U.S. This cost has steadily grown from $8/ton in 1985 and shows no signs of dropping. This means continual increases in corporate and municipal budgets while landfills get higher and higher. Waste gasification provides an opportunity to divert waste from landfills and use it in clean energy production, keeping landfills from growing and reducing landfill fees.
3.) 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. The energy embedded in the waste can be used to power engines that generate electricity.
4.) 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 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. 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.
5.) No Burning or Incineration
In the gasification process, the input waste is not a fuel, but a feedstock for a high temperature chemical conversion process. Gasification has several advantages over traditional combustion processes for waste treatment, including that it takes place in a low oxygen environment that limits the formation of dioxins and of large quantities of SOx and NOx. Gasification is continually becoming favored over incineration because there is no burning, and significantly less toxic emissions, in the process.
6.) 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 like the one we’ve developed at Aries Clean Energy, 85% of the input waste is converted into syngas. 15% becomes biochar, which can be used again. Here are some example applications:
- Fuel for cement kilns, offsetting other raw materials
- Soil amendment that helps soil retain water and nutrients
- In production of carbon black, an industrial colorant
- As a filtering agent for liquids or gases, since it shares many chemical properties with activated charcoal
In contrast to other waste-to-energy options like incineration, 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, gasification helps close the loop on waste materials by creating a byproduct with another valuable life.
7.) 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, 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 gasification technology, one ton of waste can be used to produce up to 1,000 kilowatt-hours of electricity. If this waste were to sit in landfills, we’d certainly lose a lot of the energy it contains.
Gasification gives us a huge energy benefit – we can reclaim more energy while powering a cleaner world.