In an interview today, Dr. Yaoli Zhang from Xiamen University in Fujian Province discussed the case for integrating ammonia production with nuclear power. Dr. Zhang is currently a Visiting Professor at the Massachusetts Institute of Technology in Boston.
The idea would be to harness both unused generating capacity and waste heat to produce ammonia with a near-zero carbon footprint. The ideal for a nuclear plant is to produce electricity at a constant rate regardless of the time of day. However, nighttime demand is low relative to the day with the result that plant output often falls to 30 percent of rated capacity. This means that electricity can be generated incrementally in this period at very low cost. Zhang envisions using incremental electricity to produce hydrogen via electrolysis and then producing ammonia via Haber-Bosch synthesis.
Zhang said that conventional nuclear plants produce waste heat with a temperature of approximately 300 degrees C. He speculates that this is too low to provide significant thermal support for the ammonia synthesis reaction (which is typically conducted at 400 degrees C and above.). However, he pointed out that gas-cooled nuclear reactor technology, which is currently under development, would produce waste heat with a temperature as high as 800 degrees C.
Zhang talked about the need for comprehensive design integration of the electricity generation and ammonia production aspects of the plant. He said that nuclear plants are such finely tuned systems that it would be cost-prohibitive to try to integrate an ammonia production module on a retrofit basis. His focus, therefore, is on the design of new plants built for this purpose. He has two graduate students at Xiamen University working on specific aspects of the integration.
Zhang is also working on a further innovation. This is siting nuclear plants in the ocean, at a distance from population centers sufficient to avoid opposition from neighboring populations. Ammonia produced at such facilities would enable the transport of energy by ship in addition to transmission cable.
Zhang’s work fits within the field of nuclear-renewable hybrid energy systems. These are defined in a 2013 survey paper as “integrated facilities comprised of nuclear reactors, renewable energy generation, and industrial processes that can simultaneously address the need for grid flexibility, greenhouse gas emission reductions, and optimal use of investment capital”. Zhang himself started with an interest in the integration of nuclear power and biofuel production. He took up the idea of ammonia production based on interest in ammonia energy on the part of his colleagues at Xiamen University. Research in nuclear-renewable hybrid energy systems is being conducted within the national laboratory system of the United States, among other places.