Hydrogen Production from Waste using Pyrogasification
Pyrogasification in a few words:
Pyrogasification is a result of breaking long chains of molecules like cellulose of wood or polymers thermo-chemically in very weak presence of oxygen to obtain gases which we call syngas. Syngas is a mix of hydrogen (H2), carbon monoxyde (CO), carbon dioxide (CO2), methane (CH4) mainly. Hydrogen can be further isolate by means of pressure swing absorption (PSA) or membrane or a mixte both technics.
We can produce hydrogen from multiple waste sources;
1-Biomass only from forest, agricultural (Biogenic)
2-Urban biomass like contaminated paper or cardboard which cannot be recycled, or construction wood waste. (Biogenic)
3-Mixte of urban biomass ( construction wood) and plastics mixte (non-biogenic) unrecyclable at the sorting center.
Biomass only:
Biomass gasification is a mature technology pathway that uses a controlled process involving heat, steam, and oxygen to convert biomass to hydrogen and other products, without combustion. Because growing biomass removes carbon dioxide from the atmosphere, the net carbon emissions of this method can be low, especially if coupled with carbon capture, utilization, and storage in the long term. Gasification plants for biofuels are being built and operated, and can provide best practices and lessons learned for hydrogen production.
What Is Biomass?
Biomass, a renewable organic resource, includes agriculture crop residues (such as corn stover or wheat straw), forest residues, special crops grown specifically for energy use (such as switchgrass or willow trees), organic municipal solid waste, and animal wastes. This renewable resource can be used to produce hydrogen, along with other byproducts, by gasification.
How Does Biomass Gasification Work?
Gasification is a process that converts biogenic or non-biogenic carbonaceous materials at high temperatures (>700°C), without combustion, with a controlled amount of oxygen and/or steam into carbon monoxide, hydrogen, and carbon dioxide. The carbon monoxide then reacts with water to form carbon dioxide and more hydrogen via a water-gas shift reaction. Adsorbers or special membranes can separate the hydrogen from this gas stream.
Simplified example reaction
C6H12O6 + O2 + H2O → CO + CO2 + H2 + other species
Note: The above reaction uses glucose as a surrogate for cellulose. Actual biomass has highly variable composition and complexity with cellulose as one major component.
Water-gas shift reaction
CO + H2O → CO2 + H2 (+ small amount of heat)
Pyrolysis is the gasification of biomass in the absence of oxygen. In general, biomass does not gasify as easily as coal, and it produces other hydrocarbon compounds in the gas mixture exiting the gasifier; this is especially true when no oxygen is used. As a result, typically an extra step must be taken to reform these hydrocarbons with a catalyst to yield a clean syngas mixture of hydrogen, carbon monoxide, and carbon dioxide. Then, just as in the gasification process for hydrogen production, a shift reaction step (with steam) converts the carbon monoxide to carbon dioxide. The hydrogen produced is then separated and purified.
Why Is This Pathway Being Considered?
Biomass is an abundant domestic resource.
In the Canada, there is more biomass available than is required for food and animal feed needs. A recent report projects that with anticipated improvements in agricultural practices and plant breeding, up to 1 billion dry tons of biomass could be available for energy use annually.
Biomass "recycles" carbon dioxide.
Plants consume carbon dioxide from the atmosphere as part of their natural growth process as they make biomass, off-setting the carbon dioxide released from producing hydrogen through biomass gasification and resulting in low net greenhouse gas emissions.
Challenges of biomass gasification?
Biomass from the forest are far from the center where hydrogen is needed, collection of the biomass in the forest and transportation is challenging and costly. We prefer to target the construction wood waste consider biomass or papers and cardboard mixte from sorting centres that are not suitable for recycling or contaminated.