What is BECCS?
BECCS is typically envisioned as the cultivation of one type of crop, a monoculture, over a large
area (a carbon negative process) and combusting this biomass in a power plant to produce
electricity.
The CO2 from the exhaust stream is then diverted and stored, or sequestered, deep
underground in some sort of geologic formation. Thus, we have the removal of CO2 from the
atmosphere and environment by plants that are grown, which are then burned to make
electricity, and the CO2 produced from combustion is stored deep underground.
Bio energy with carbon capture and storage is any process that integrates the following :
1.
Decarbonizing effects of biomass production
2.
Energy production from biomass
3.
Carbon capture and sequestration
There are many shortcomings and engineering inefficiencies associated with this process. There’s the fact that we are growing plants to burn them in order to produce electricity, which may sound strange to many people.
That aside, we require A LOT of land, water, and energy for plant cultivation. There is also a carbon cost to transporting this biomass to the site of power generation––trucks require diesel, which combusts and produces CO2 that is emitted to the atmosphere.
Finally, there is energy required for separating CO2 from the plant exhaust stream. Separation is always an energy-intensive process.
Our Process
This process relies on agricultural and food waste, which require less water, land, and energy intervention. We turn this biomass into charcoal, or biochar, a carbon-dense material. We gasify this using the Reverse Boudouard reaction. We add CO2 to the biochar at high temperature, enhancing the carbon negativity of this process, and produce synthesis gas, which is composed of H2 and CO. CO is commonly thought of as a poison but is actually a viable feedstock for a solid oxide fuel cell (SOFC). Thus, SOFCs can be used to produce electricity and a generate a CO2-rich exhaust stream that requires far less energy intervention before sequestration.
Envisioning a better BECCS!
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Pyrolysis is the process by which biomass is heated in the absence of oxygen to break down organic structures through a series of complex thermo-chemical pathways. It generates solid, liquid, and gaseous products, and the product distribution varoes with pyrolysis conditions. All three products are valuable and have various commerical applications. In this study, the solid produc, biochar, is of value.
What differs between those feedstocks?
Ash Content
- Ash remaining after gasification (unreacted material) is a good indicator of inorganic content of biochar
- Inorganics (alkali and alkaline earth metals–Ca, Na, K) have been shown to catelyze the Reverse Boudouard reaction
- Measured ash content as percentage of biochar sample remaining after gasification
Pyrolized several bio-waste feedstocks (walnut shell, pistahio shell, pumpkin seed shell, corn cob, coconut shell) at three different temperatures: 400C, 450C, 500C. Measured mass yield increases with decreasing pyrolysis temperature. In a large scale process, we want to maximize our yield, so this is an interesting result for us to consider.