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| Ammonia-based energy storage |
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Hydrogen is arguably the cleanest fuel because the only emission from hydrogen based energy production is water. The vision of a hydrogen society, with all its benefits for the environment, faces some technological challenges that must be addressed before it can become a reality. One of the biggest challenges, especially for vehicular applications, is finding a safe high-density storage method for hydrogen. A very attractive possibility is to store the hydrogen as ammonia. Liquid ammonia has the highest energy density (reformed) per liter among the fuels that have been considered for fuel cells. Ammonia, like hydrogen, is carbon–free, and ammonia production is a well-established economical technology. The concentration and the amount of CO2 are high enough in an ammonia production unit to make it feasible to sequester CO2. Thus ammonia has the potential to become a ‘zero-carbon’ fuel. However, ammonia is toxic, and because of very high vapor pressure of liquid ammonia (~8 bar at room temperature), there are safety concerns of using liquid ammonia in end-user applications. Amminex has developed a safe and controlled method to store ammonia in solids. The Amminex product, Hydrammine™, has an energy density similar to that of liquid ammonia. At room temperature, Hydrammine™ is a non-pressurized storage material and is - unlike liquid ammonia - not a hazardous substance for on-road transportation. It enables safe use of ammonia as an energy carrier for end-user applications. The corresponding hydrogen storage density is illustrated below. The volume needed for on-board storage on 4kg hydrogen is shown for pressurized hydrogen, liquid hydrogen and Hydrammine™. A storage capacity of 4kg hydrogen would give a fuel cell car an operating range similar to that of a standard gasoline fueled car.  Hydrammine™ for low temperature fuel cellAmminex Fuel Cells division is working to integrate the Hydrammine™ unit to an ammonia cracker to develop a ‘stand alone’ hydrogen generator in collaboration with its strategic partners. The hydrogen generator is targeted to feed PEM fuel cells. The waste heat from the fuel cell can be used to supply the desorption heat for ammonia from the storage material. The energy for the cracker will be delivered from burning a fraction of the hydrogen produced by the cracker and the unreacted hydrogen at the anode effluent. The inclusion of a cracker unit increases the size of the 'tank' in the above illustration to about 55 L.  Hydrammine™ for Direct Ammonia Fuel Cell, DAFCAmminex is involved in implementing the idea of intermediate temperature (300-400° C) Direct Ammonia Fuel Cells (DAFC). At this temperature range, ammonia can be directly fed to the anode. No cracker is needed as cracking takes place inside the fuel cell. The desorption heat for ammonia can be supplied by the waste heat from the fuel cell. In a DAFC, a proton conducting ceramic (PCC) is used as electrolyte. Unlike SOFC, because of the lowered operating temperature, the DAFC will have much less complications regarding materials. Also the startup and shut down time will be significantly reduced making it potentially applicable for mobile applications besides stationary energy production.Hydrammine™ for high temperature SOFCAmmonia is a very clean fuel for the SOFC. Because of the high operating temperature (above 600° C) of SOFC, ammonia can be fed directly to the fuel cell. Also the waste heat from the cell can be utilized to supply the desorption heat of ammonia. We are integrating our Hydrammine™ ammonia storage and delivery unit with SOFC stack in collaboration with Topsoe Fuel Cell A/S (www.topsoefuelcell.com) and RISØ (www.risoe.dk). |
