This invention relates to the production of hydrogen and heat energy and more particularly to the production of hydrogen and heat energy by reacting a metal with water.
It has been proposed to replace conventional hydrocarbon fuels with cleaner burning hydrogen in internal combustion engines. Unfortunately existing methods of storing hydrogen require heavy tanks for the compressed gas or complicated vessels for the liquid that are uneconomical to use. The metal hydride, although it can be claimed as the best existing method of storing hydrogen, is still too heavy to be used as a mobile hydrogen storage medium. Additionally, the large stored quantities of hydrogen require special safety precautions. It would be desirable to provide a method of generating the hydrogen gas fuel as needed.
Some metals like aluminum, magnesium, or lithium react with water, spontaneously generating hydrogen gas and heat. Among these reactive metals, aluminum is the most abundant, cheapest and safest metal. But, the reaction between aluminum and water is not sustained at ambient temperature due to the protective oxide layer formed on the metal surface. Therefore, the use of aluminum as a fuel to generate heat and hydrogen gas requires that the protective layer be efficiently and continuously removed.
European patent No. 0 055 134 B1 (1986) discloses a method for the production of hydrogen by inducing electrical discharge between aluminum wire and aluminum drum both of which are immersed in water. When a voltage is applied between the wire and drum, an arching discharge takes place between them, inducing electro-plasmic reaction. The reaction produces hydrogen and oxygen gas and aluminum oxide. The arcing between the wire and drum helps remove the oxide layer formed on the wire tip, exposing fresh aluminum to the water. Thus, a continuous generation of hydrogen gas is possible when the wire is fed against the drum.
This process has two major disadvantages. First, since the process is slow, the heat generated from the reaction is wasted by being dissipated through the water. Second, the electrical energy required to sustain the reaction is rather high. It is estimated that around 20 KJ of electrical energy is consumed to generate about 5 liter of hydrogen gas at room temperature and a pressure of one atmosphere.