The heat recovered could serve to preheat boiler feed water, thus providing an energy savings. The membranes have also shown effectiveness in using molecular sieving to separate hydrogen from coal-derived synthesis gas and from refinery gases.

As gases and effluent are transported via molecular diffusion, the nanopore membranes separate constituents from the flow by Knudsen diffusion, molecular sieving, capillary condensation, surface flow, or a combination of these transport mechanisms.

The inorganic membrane developed by the researchers at ORNL features pore diameters as small as 0.5 nm to 20,000 nm; the support structure and layer for the membrane can be made of a variety of metals and ceramics. For example, porous metal layers applied to tubular porous stainless steel supports yield filters with pore sizes from 0.05 to 1 μm. The mechanical, thermal, and chemical stability can be tailored by a choice of materials.

The key to the design is permeance and separation factors, ORNL notes—a balance between the volumetric flow rate per unit surface, per unit of transmembrane pressure, and the ratio of flow of two gases in a binary gas mix.

In the exhaust system, water condenses by capillary action,—as opposed to thermodynamic condensation that cools the air to produce water—in the pores.

This water is constantly drawn off from the outside of the tube, allowing more water to be condensed from the exhaust passing through the center of the tube at a given temperature. Capturing water vapor via this continual displacement method leads to an approximate 100-fold reduction in contaminants, Borla says. The contact time between water-soluble gases such as nitrogen dioxide and the condensed water is eliminated.

This water reclamation system is energy neutral and designed to simplify water management operations. It permits a greater quantity of water to be removed at a given temperature compared to traditional direct condensation methods. It also limits water-gas contact time, reducing dissolution of gas-phase contaminates present in diesel exhaust and further enhancing this method’s use in obtaining high-purity water fit for human consumption.

Borla’s muffler/membrane reclamation unit could be installed on troop vehicles as part of the exhaust system will generate water at the point of use. A Humvee, which has about a 25-gallon fuel tank, could provide enough water for roughly three soldiers per tank of fuel burned.

Besides reclaiming drinkable water from fuel to hydrate combat troops, the military could also benefit from Borla’s device for any power plant platform. Borla plans to commercialize the device to a wide scope of potential military and commercial target markets including transport and stationary power plants such as generators, water pumps as well as marine, cars and trucks.

Resources

• Novel Nanopore Membrane Technology Recovers Energy from Industrial Effluents