NASA
Trust NASA to figure this one out: how to start a fire with water. Astronauts onboard the International Space Station are now in the second round of experiments designed to shed light on this counter-intuitive but very real process, and the implications are significant.
The key in using water to start a fire is that the water isn’t regular drinking water. It’s supercritical water, a state that’s hard to achieve but has some really interesting properties. To become supercritical, water has to be compressed to 217 atmospheres and heated to above 703 °F. At that temperature and pressure, water ceases to be a liquid and becomes something between a liquid and a gas, a sort of superdense gas. Add organic material to that supercritical water and the immediate chemical reaction is oxidation, which is basically a fire without flames.
Mike Hicks, a researcher from the Glenn Research Center in Ohio who has been working with supercritical water for years, explains that "the International Space Station provides a unique microgravity lab for studying [its] properties.” Starting a flameless fire with supercritical water in space is neat, but is it something that could ever benefit those of us on the Earth? Absolutely. Supercritical water could be a fantastic tool in getting rid of unpleasant organic materials like sewage since human waste contains a fair amount of water.
Hicks explains that when a stream of wet waste is pushed above the supercritical point, the supercritical water breaks its hydrocarbon bonds and reacts with oxygen. In short, the compressed and heated sewage ignites, burning cleanly and producing water and carbon dioxide as byproducts instead of the typical toxic products of an ordinary fire. Cities like Orlando, which has already established a supercritical treatment plant for municipal waste streams, farms, ships at sea, and manned spacecraft could all benefit from this clean disposal of human waste.
But there’s one challenge to overcome and that’s the effect of salt content in that liquid waste. Salt, which is easily dissolved in water at room temperature, ceases to be soluble in water that has gone supercritical. Any salt in supercritical water will agglomerate and precipitate out of the water mixture, heading for a cooler area that might be the side of a test tank. If the supercritical water is stored in a metallic tank, the salt could start to line the walls and corrode this tank, and that’s where the problem lies. Before supercritical water can be used as a waste disposal tool, scientists will have to figure out how to deal with supercritical water’s salt content.
And this is just what astronauts are studying on board the ISS right now. It’s part of the Super Critical Water Mixture experiment, a joint effort between NASA and the Centre National d’Études Spatials (CNES, the French space agency). The experiment is using French-made hardware installed in the ISS’s Japanese Experiment Module. "By studying supercritical water without the complicating effects of gravity, we can learn how precipitating salts behave on a very fundamental level," says Hicks. "We might even be able to figure out how to draw salt away from corrosion-sensitive components.”
There are some key questions Hicks, as Principal Investigator, and his team are seeking answers to with the SCWM experiment: How is salt transported in supercritical water free from the influence of gravity? What happens when a salt/water mixture is heated and compressed beyond the critical point? How will the salt escape the supercritical mixture and at what point will it start to clump together so salt crystals are actually visible inside the water mixture?
Answers to these questions are still pending since the experiment is only about half finished; begun in July of 2013, the test involves six runs lasting 15 days done over the course of a year. But when scientists do figure out how to deal with the salt in supercritical water, it will make dealing with the unpleasant byproducts of humans a lot more pleasant.