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Ammonia is a promising hydrogen carrier to transport green hydrogen from overseas to Japan at lower cost and resulting in lower lifecycle CO2 emission. Low carbon ammonia will be produced by fossil fuel reforming with CCS or EOR at the early stage of the introduction of ammonia fuel to the market. Green ammonia production from renewable sources is the ultimate goal, but there are some issues to commercialize. The low capacity factor, which is caused by the fluctuation of solar irradiation or wind speed, is a big issue which leads to ammonia production costs.
In this presentation, we would like to explain the results of optimization studies of capacity and operation of units that comprise the ammonia production process using photovoltaic generation as a renewable power source. In addition, we will introduce the demonstration test results of the operation of the demonstration plant of ammonia synthesis that simulates the fluctuation of hydrogen supply.
In the case of green ammonia production using a photovoltaic power source, it is necessary to absorb the fluctuation of hydrogen production caused by solar radiation during the day and weather change, and supply a certain amount of hydrogen to the ammonia synthesis plant. For this objective, a battery and a hydrogen storage tank can be introduced, but these devices are expensive. Hence, we optimized the capacity of these units and operation methods. As the results, we found the scheduled load change operation of the ammonia synthesis unit with the prediction of hydrogen production is effective to reduce the ammonia production cost.
In Japan, the government funding project SIP, Strategic Innovation Promotion Program, supported the research, development, and demonstration of “Energy Carriers” from 2014 to 2018. Under the project, we developed a new Ruthenium-based ammonia synthesis catalyst which has excellent activity in lower pressure and temperature conditions. Also, we constructed an ammonia synthesis demonstration plant in FREA, the Fukushima Renewable Energy Institute, AIST. From April 2018, the plant started operation to evaluate the performance of the developed catalysts and acquire the engineering data for scaling up.
During this demonstration test, we performed a load change operation test which simulated the change of hydrogen flow rate from the hydrogen production unit using renewables. In this test, the feed hydrogen flow rate changed between 100% and 40% of its capacity. The ammonia synthesis process responded smoothly according to the feed hydrogen flow rate and stabilized within one hour without instability. This result indicates the possibility of flexible load change operation of the ammonia synthesis process using hydrogen from renewable energy.
This demonstration and study are supported by the Council for Science, Technology and Innovation (CSTI), Cross-Ministry Strategic Innovation Promotion Program (SIP), “Energy Carriers” (Funding Agency: Japan Science and Technology Agency).