Reclaiming water from diesel fuel to hydrate combat troops

Soldiers need water, but it’s not always easy to keep combat troops hydrated. In an effort that could curb the number of dangerous treks needed bring water to fighting soldiers, researchers at Oak Ridge National Laboratory are developing a system that would reclaim drinkable water from diesel exhaust.

Melanie Moses DeBusk of the lab’s Materials Science and Technology Division explained the technology in a recent interview. Here are excerpts from our talk:

How does your work solve the problem of getting water to combat soldiers?

If we generate the water at the point of use, we reduce vulnerability and tactical use.

The fuel that’s being used is essentially hydrocarbons. The way engines work, [the hydrocarbons] get mixed with oxygen in the air. The fuel is ignited. The combustion of hydrocarbons in the presence of oxygen is going to produce CO2 and water. Water is not necessarily already in the fuel. It’s being produced when you combust the hydrocarbons in the presence of oxygen. To reclaim water that’s being pumped into the air, we pass it through porous, tubular membranes. We create conditions so the water in the exhaust condenses in nano-pores along the inner surface of the tube. We pull [the water] through the walls of the tube to the outside. Now, you’ve got your condensed water on the outside and your exhaust is continuing to flow through the center of the tube.

Is the water drinkable?

Our initial work on contamination has shown a 100-fold reduction in the amount of nitrogen dioxide that condenses in the water. Our current testing suggests we are going to significantly reduce any contamination that would dissolve into the condensed water because we’re limiting the contact time of the exhaust and the water. There is less time for these contaminants to dissolve into the water.

We’re still in lab-scale testing. Not all the hydrocarbons are necessarily combusted, but there is commercial technology that can be put in line right after the engine to remove un-combusted hydrocarbons by oxidizing them or filtering out the particulates and soot.

[With any kind of technology like this, you're going to have to integrate some check. Even if it's working optimally the majority of the time, we would have to have sensors in place so there's an indication to everybody that it is working properly.]

How did you develop this idea? Was this expanding on technology that was already out there?

Quite a few years ago, some people in our group had been asked by a U.S. Army representative if we could use our porous inorganic membranes to reclaim water from exhaust. Understanding how capillary condensation works, our group members considered whether the nano-pores in the membranes would be able to act as capillaries and effectively condense. From there, it was a matter of getting funding and proving the concept in the laboratory. We proved in a small project that we are able to capillary condense water from a wet gas stream and improve our condensation efficiency.

Understanding the limitations encountered in previous attempts by others to reclaim water from exhaust by other methods, we’re also working to incorporate other components to our proposed system. [This includes] trying to incorporate graphite foam, which is a highly-conductive, lightweight material. [In our system it could] aid in the cooling process without adding any significant weight or bulk and limit the additional energy requirements.

What’s the next step for this work?

Currently in the lab, we’re working on optimizing the conditions under which it works best. We’re also working to incorporate the graphite foam. Our next step is going to be modeling the system’s effect on a generator to understand how it affects engine operations. From there, we need to secure additional funding to take this to the full-scale demonstration.

Photos: U.S. Army; Melanie Moses DeBusk