GH Power was recently featured in the International Journal of Hydrogen Energy.
Highlights from the Article:
- Hydrogen, heat and alumina are cogenerated from reaction of aluminum with water.
- Pressure controls the onset of reaction.
- Specific surface area of the powder has a significant impact on ignition.
- Presence of steam is necessary for ignition of larger powders.
- High specific surface area alumina powder is produced.
Abstract
Oxidation of metals in water has been explored to generate sustainable carbon free hydrogen and power. This paper studies the thermal ignition of micro aluminum powders in high-pressure deionized (DI) water for cogeneration of hydrogen, heat, and alumina. Thermal ignition (temperature runaway) is necessary to ensure achieving high reaction temperatures, past the saturation temperature, where alumina formation is thermodynamically favorable. Aluminum powders with nominal particle diameters of 1, 10 and 45 μm with spherical morphology and 2 μm with flake morphology were mixed with DI water to form slurries with equivalence ratio of 1.3 in a 100 mL batch reactor. The reactor was pressure maintained between 500 and 2000 psig using a back-pressure regulator, and heat was injected into the slurry through an electric band heater. It was found that 1 and 2 μm powders ignite in compressed water, but only the 2 μm slurries achieved temperatures above saturation temperature at pressures above 700 psig. On the other hand, 10 and 45 μm powders require saturated steam for ignition at pressures above 1000 and 1200 psig, respectively. Hydrogen volume data indicate that larger powders at higher pressures optimize reaction yield, which is likely due to delayed ignition which preserves the active aluminum content and the particle-water reaction interfaces. Scanning electron microscopy images illustrate that the byproduct particles crack upon ignition at the saturation temperature, which increases the specific surface area by an order of magnitude relative to the aluminum powders. Pore size distribution data indicates the formation of micro, meso and macropores upon the ignition. X-ray powder diffraction data indicate that reaction temperatures above 450 °C promote the formation of alumina (Al2O3) instead of boehmite (ALOOH).