Continued from Part-2
Relative market potential of various market segments; 1) “Islanded” energy storage; 2) “Non-islanded” energy storage; 3) “Islanded” fertilizer; 4) “Non-islanded” fertilizer; 5) “Islanded” energy storage and fertilizer; 6) “Non-islanded” energy storage and fertilizer. Courtesy of Prof. Bañares-Alcántara, Oxford University.
Finally, and with a global interest in the use of ammonia for power, the International Energy Agency (IEA) has recently become a promoter of ammonia for a carbon-free future. As evidenced in their study, ammonia is much less costly to store for a long time compared to hydrogen, i.e. 0.5 $/kg-H2 for ammonia compared to 15 $/kg-H2 for hydrogen over half a year, and at least three times less costly to ship on sea or land. However, the concept is not directly competing with hydrogen, only with its mobility and storage. Cedric Philibert, Senior Energy Analyst at the IEA, reflects that the production of hydrogen from renewables dates from the 1960s, but it is only recently that the increasingly lower cost it starts to make these technologies competitive for production of the chemical, thus conversion into ammonia for distribution seems the most economically competitive alternative into ammonia for distribution seems the most economically competitive alternative.
Existing Methods of Producing Energy from Ammonia (NH3)
In 1984, Alexander Kalina developed a cycle to be used as a bottoming cycle instead of the Rankine cycle in Combined Cycle (CC) power plants and demonstrated that the cycle can reach higher efficiencies than the Rankine cycle for heat recovery. The essence of the cycle is the use of an ammonia-water mixture whose change in composition affects the thermodynamics and transport properties of the mixture. Since the boiling temperature of ammonia is lower than water it can then be used for low-grade heat recovery. Moreover, designs for steam turbines can still be used with such a mixture due to the close molecular weight between water and ammonia. The use of the Kalina Cycle (KC) with this ammonia-water working fluid can bring up to 20{828d3c3f61672f5f3f915e8276d5ef35c5e0117d26b89f98a9d5e22a85a2eb78} enhancement compared to other cycles.
Related work has suggested that mixtures of 84{828d3c3f61672f5f3f915e8276d5ef35c5e0117d26b89f98a9d5e22a85a2eb78} ammonia – 16{828d3c3f61672f5f3f915e8276d5ef35c5e0117d26b89f98a9d5e22a85a2eb78} water (in mass fraction) can produce superior thermodynamic and economic benefits. It has been recognized that combinations of the cycle with mixtures between 78{828d3c3f61672f5f3f915e8276d5ef35c5e0117d26b89f98a9d5e22a85a2eb78} to 82{828d3c3f61672f5f3f915e8276d5ef35c5e0117d26b89f98a9d5e22a85a2eb78} of ammonia concentration can provide the best operating conditions in such a cycle, with some authors even suggesting concentrations as low as 50{828d3c3f61672f5f3f915e8276d5ef35c5e0117d26b89f98a9d5e22a85a2eb78} for special geothermal applications.
Further studies concluded that the use of the cycle was more expensive than the use of state-or-the-art steam Rankine cycles, presenting a difference of ∼20{828d3c3f61672f5f3f915e8276d5ef35c5e0117d26b89f98a9d5e22a85a2eb78} cost per MWh−1, studies have sought improvements of systems with both high temperature and pressure inlets (> 773 K, > 10 MPa). New numerical designs based on the number of recuperators through the cycle, turbine outlet pressure, separator inlet temperature, and the separator inlet ammonia mass fraction played an important factor to maximise cycle efficiency up to 31.47{828d3c3f61672f5f3f915e8276d5ef35c5e0117d26b89f98a9d5e22a85a2eb78} with an ammonia concentration of 80{828d3c3f61672f5f3f915e8276d5ef35c5e0117d26b89f98a9d5e22a85a2eb78}.
Dr. Augustin Valera-Medina presented a series of studies using a generic swirl burner that was fuelled using ammonia and hydrogen/methane at different concentrations. The results showed the complexity in stabilizing premixed ammonia blends, identifying a particular pattern of oxygen consumption that was followed by flame speed reduction, retarding the combustion process, and eventually pushing the flame back into the combustion chamber with inherent aeration. Also, it was recognized that the use of hydrogen injection required a new injection strategy to ensure stable combustion, as premixing eventually led to early flashback. NOx and CO were considerably lower at high equivalence ratios > 1.10, depicting a region of chemically reactive balance between methane/hydrogen and ammonia combustion, with recombination of NOx emissions with unburned ammonia, increasing OH radicals, a topic that is still under debate across the scientific community.
H Xiao has also produced data to determine the potential of using ammonia/methane and ammonia/hydrogen blends for power generation. Results showed that the use of ammonia at high pressures as those found in industrial devices can mitigate the production of NOx by increasing the recombination of species and compacting the flame front. Moreover, there seems to be a trend in terms of the production of OH radicals at high equivalence ratios, denoting the recombination of emissions with NH2 radicals in the post-flame zone, leading to the formation of nitrogen molecules, suggesting scenarios where ammonia gas turbines can become a feasible, reliable and environmental possibility.