Saturday, March 3, 2012
Regenerative Fuelcell- Water and Fire
In a regenerative fuel cell the results of redox reaction between Hydrogen and Oxygen, are power and water; the above reaction can be reversed in the same electrochemical process to regenerate hydrogen and oxygen. Such a system is called ‘regenerative fuel cell’. It is a perfect example of a closed circuit system. In ancient Hindu mythology there were citations that claim water came from fire and fire came from water. Two gaseous elements Hydrogen and oxygen reacts violently rather explosively resulting in cool water. Perhaps Hindu mythology terms this reaction as fire which results in water. Similarly by passing a direct current into water, it splits water into oxygen and renegenerates Hydrogen, which is a symbolic representation of Fire. Many would have watched a number of ‘you tube video footings’ on water gas. The water gas or Brown’s gas is a mixture of Hydrogen and oxygen along with undissociated water molecules liberated during the process of electrolysis. It can be lit into a flame similar to Oxy-acetylene flame and can be used even to cut metal plates. That is the power of brown’s gas, which I call Oxy-Hydrogen gas. This torch is commercially marketed for metal cuttings applications. But production of pure Hydrogen completely free from Oxygen is a matter of great commercial importance. Hydrogen is one of the lightest gases and it has a strong bondage with noble metals like Platinum and Palladium. Platinum as a catalyst with carbon as a carrier has a wider industrial applications such as Hydrogenations in fine chemicals and pharmaceuticals. The author has experience in such applications in bulk drug manufacturing such as Ephedrine and Paracetamol. In a PEM (proton exchange membrane fuel cell) MEA (membrane electrode assembly) is the heart. The Platinum catalyst coated on the surface of the ‘Nafion’ membrane reacts with gaseous Hydrogen gas. It strips the electron from hydrogen atom while the polymer membrane allows only proton to pass through. The expelled electron flows around the circuit. Flow of electron is nothing but current or electricity. The proton crosses the membrane and reacts with incoming Oxygen through cathode forming water. It is an exothermic reaction and generates heat similar to any combustion reaction, that has to be dissipated.In larger installation we can use this waste heat for a typical CHP (combined heat and power applications) such as power and steam or chilled water or for space cooling. Fuel cell (based on Hydrogen fuel) operates quietly with absolutely no emission except water, and of course, there is no smoke. It is an ideal power source for 24x7 applications such as hospitals, call centers, departmental stores and continues process industries. In the reverse process of a Fuel cell, the electrochemical devise becomes an Electrolyzer splitting water into Hydrogen and oxygen. The electrolyzer works the same way as Fuel cell but in reverse;the feed is de-ionized water and the products are Hydrogen and Oxygen. In bipolar alkaline electrolyzer, a catalyst such as potash lye is added whereas in solid polymer electrolyzers platinum acts as a catalyst similar to a Fuelcell. The generated Hydrogen comes under pressure obviating the use of an additional compressor. The Hydrogen is stored in cylinders for further usage. As I mentioned in my previous articles the power required to split water into Hydrogen and Oxygen is more than the power generated from the resulting Hydrogen by a Fuelcell.That means an input of excess energy is necessary for a regenerative fuel cell to operate successfully .Where this energy will come from depends on the cost benefit analysis to be made. Surplus Hydro power is ideal for such regenerative fuel cell applications. But we can also use various other renewable energy sources such as wind, solar, geothermal, OTEC depending upon the location and applications. The biggest advantage with regenerative fuel cell is there is no other input except the excess power to be supplied. When renewable energy is deployed on large commercial scales then regenerative fuel cell will become a clean solution of the future. I have no doubt in my mind that this will become a commercial reality. Of course the top policy makers should understand the potential and make a right decision and encourage more business and industries to deploy such systems. The energy costing model cannot be based on fossil fuel model because fossil fuel is not renewable. This is the crux of the problem. In our future articles we will present case studies of various clean energy systems that are already in commercial operation. I also welcome articles from clean energy professionals with real life project experience and problems they face. I welcome comments and feedback from business, industries and individuals.