PetroSun(NASDAQ:PSUD) is an energy company specializing in oil and gas exploration and algae fuel. It headquarters are in Scottsdale, Arizona, USA.

PetroSun's website describes a process called "carbon negative energy production". Organic matter is burnt in a kiln with limited oxygen (pyrolysis). This produces carbon dioxide, hydrogen and charcoal (which PetroSun calls "biochar").

The carbon dioxide is used as a feedstock to grow algae for biofuel. The hydrogen is burnt to generate electricity. The biochar, which contains a lot of carbon, is used as a fertiliser.

If the feedstock is plant matter which fixed atmospheric carbon dioxide, and part of its carbon becomes fertiliser which will not be burnt to re-release the carbon into the atmosphere, the net result is a reduction in atmospheric carbon, i.e.. an overall carbon-negative process.

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