January 15, 2016
Science Friday - Carbon negative energy
Welcome back to Science Friday — our weekly blog post that links you to the most recent and relevant academic research on carbon removal. This week, we're focusing on the energy sector. Take a look at some of the research fresh from the new year and don't forget to let us know your thoughts in the comments!
Nature Energy released their first issue and with it came two important pieces with thoughts on carbon removal.
First, this piece from Daniel L. Sanchez and Daniel M. Kammen explores a commercialization strategy for carbon-negative energy through the advancement of bioenergy with carbon capture and storage (BECCS). Citing the few BECCS facilities in existence today and the flexibility of thermochemical conversion of biomass, Sanchez and Kammen not only call upon government and industry to take action to develop and refine these technologies, but also give them a policy/technology roadmap to do so. This short piece is worth a read!
Next, David Reiner's research explores the world of CCS demonstration projects, outlining how far we have come and what work still needs to be done to meet global climate commitments. Reiner calls for a renewed commitment to CCS demonstration despite high costs, and emphasizes the need for a globally coordinated portfolio of demonstration projects that "learn through diversity." While not solely focused on carbon-negative CCS systems, Reiner's research could be important to the future of BECCS technology as the world begins to bring down costs of and de-risk CCS generally.
In Nature Climate Change, Pete Smith et. al,in "Biophysical and economic limits to negative CO2 emissions," lays out the needs for and limits to carbon removal systems generally. With some great graphics, Smith emphasizes the distinctive constraints between carbon removal technologies, particularly when it comes to the differences between BECCS and direct air capture systems. Read more about the water, economic, land use, energy, and nutrient tradeoffs in his article.
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Nutrient balance is an important and interesting question, but not simple.
Imagine collecting straw or corn stover for power generation, vs. letting it rot on the field. If left, then of the three major nutrients, K, P and N: phosphorus can be expected to stay in place. However, many soils have an excess of phosphate, enough in some areas to pose a health issue if it impacts drinking water supply. Potassium may return to the soil, but might be transported in runoff, depending on local precipitation patterns and very local topography. Nitrates are subject to runoff, and can be reduced back to nitrogen by bacterial action on surface biomass, notably in the spring (which is why in some agricultural areas grass seed is aerially sprayed in the fall, to move the nitrate in the grass, above the soil level, until spring plowing buries the grass). Hence the loss of nutrients from biomass collection is subject to local analysis.
Biomass processing moves the nutrients away from the field. Ash can be recycled, at a cost, although not if char is buried (assuming the ash remains in the char). Nitrogen would have to be made up. If a dollar value is placed on carbon emission avoidance or negative carbon, it will overwhelm the cost of the incremental nitrogen requirement, since for agricultural crops there is already a fertilizer application, only the dosage is increased: the sole cost is the nitrogen itself.
Peter Flynn, P. Eng., Ph. D.
Emeritus Professor and Poole Chair in Management for Engineers
Department of Mechanical Engineering
University of Alberta
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