What Burnt Toast and WWII Can Teach Us About Waste Management
Plastic and organics are America’s waste management weak points. Thermochemical conversion can help.
We’ve all witnessed one solution to our waste problem when we’ve made toast. Yes, I mean toasting bread.
When you put bread into a toaster and apply heat, you’re putting the organic matter of that bread through a thermal process. Depending on the temperature you have set on your toaster, the more char—some might say burnt—your toast will become.
The chemical reaction of applying heat to food in your kitchen is the best example of pyrolysis.
Pyrolysis is a technology being evaluated as a potential solution to our waste problem, along with gasification. Both of these processes fall under the definition of thermochemical conversion. Two other thermochemical processes include combustion and solvent liquefaction.
Each of these technologies functions at a different level of oxidation, temperature, heat-rate and reaction time to produce valuable resources such as electric power, heat, liquid fuels, and chemicals.
Unlike their biochemical conversion cousin anaerobic digestion (AD), pyrolysis and gasification have yet to achieve mass commercial scale adoption. Still, several manufacturers are offering different versions of pyrolysis and gasification equipment solutions.
While the consumer waste problem is not going away, both of these promising technologies are worth looking at as possible solutions to implement a circular organic waste management strategy.
Exactly how they can help calls for some nerdy explanation. That’s my cue.
How Pyrolysis Tackles Plastic Waste
Let’s size up those stubborn plastics first.
Plastics are polymers, meaning they’re made up of large molecules bonded together. Pyrolysis is a thermal chemical reaction that occurs on the molecular level. It’s also one step of the gasification process, but we’ll get into that later.
When heat is applied at the appropriate temperature—typically between 400 – 1,400°F—and oxygen is restricted, the molecules start vibrating and break down into smaller molecules. These smaller molecules can be liquid or gaseous, with syngas being a result. At the end of this process, there is typically leftover biochar and ash as a residual.
Pyrolysis can also be applied to organic waste. Typically in an organic pyrolysis implementation, the process is in the absence of oxygen since oxygen at high temperatures would cause combustion. This is why if you leave bread in your toaster too long on a high setting, you get burnt toast.
With control over oxygen, biomass can be an appropriate feedstock for pyrolysis conversion, but you can see how it’s a bit more complex.
However, with a standard feedstock of plastic waste, pyrolysis appears to be one good potential solution for our plastics problem. The technology also has the potential to deliver hydrogen, drop-in diesel, and other valuable hydrocarbon fuels and polymers. How cool is that?
Now, let’s go back in time to see how gasification is a master of organics.
Wartime Pressure Unleashes Gasification Potential
In World War II Europe, fossil fuels were in short supply and rationed. Luckily around two decades prior, a German engineer named Georges Imbert developed the Imbert generator. His invention took previous wood gasification models that were used for permanent fixtures like street lights and made the technology what we might call “mobile-friendly” to be used in vehicles.
Less than 10,000 vehicles employed the Imbert generator in Europe in the 1930s. Fast-forward to 1945 and half a million were going strong in Germany alone, with thousands more across Europe. You can still find them in use around the world today. These are known as wood gas or producer gas vehicles. As the name wood gas suggests, fueling up meant stopping for firewood. Imagine that!
Necessity is the mother of invention – some old proverb
A producer gas automobile, circa the 1940s. Source: Low Tech Magazine
Whether it’s employed in a producer gas vehicle or commercial gasification facility, the gasification process is the same.
Like pyrolysis, gasification is a thermal process, but it operates at much higher temperatures. Typical gasifiers introduce a small amount of oxygen but operate at a range of 900-3,000°F. Advanced gasifiers operate at a higher pressure and temperatures between 2,000-4,000°F.
The gasification process has four main stages when applied to organic waste.
1. Heating and drying to reduce the moisture content
2. Pyrolysis, to convert the organic waste to vapors and gasses (AKA thermal decomposition)
3. Gas solid reactions, or the partial combustion of some of the gasses, vapors and char
4. Gasification of the decomposed products
The catalyst required for gasification typically consists of air, oxygen, steam or a mixture of those three.
We continue to see gasification as an option for biomass waste conversion to generate electrical energy, renewable natural gas, or liquid fuels. One of the primary benefits of this technology is the flexibility to accept a wide variety of organic biomass feedstocks. This efficiency makes it a prime choice for organic waste management.
Thermochemical Conversion Is Still Cooking
Developers working in this sector wanting to implement pyrolysis and gasification as potential solutions are still early in the adoption curve. Investors are interested, but many are still waiting on first movers and early large scale facilities to be constructed and operational.
While these projects also lean on many of the same incentive programs that AD has available, the higher capital expenditure without the historic operating history makes both of these investments a higher risk investment.
The Diffusion of Innovations theory adoption curve. Where are you now? Source: Wikipedia
Wartime Europe turned to gasification when they were facing fossil fuel shortages. They had no choice but to adopt the technology quickly. With climate change putting us under pressure, it’s only a matter of time until these technologies—or other technologies—become accepted solutions to our waste crisis. As an active example, California is employing thermochemical conversion to manage the supply of waste from its organic waste bans.
There is no black and white solution at this time for an all-encompassing waste-to-value clean-tech solution. In today’s landscape, understanding your feedstock is the most important starting point for any waste to value development or investment. Once you know your fuel, you can claim your place in the landscape of the sustainable future of waste management infrastructure.