(585c) Analysis of Green Ammonia Production Responding to Fluctuating Renewable Energy By Using Dynamic Simulation

Ammonia is a promising hydrogen carrier to transport green hydrogen from overseas to Japan at lower cost and resulting in lower lifecycle CO₂ emissions. Low-carbon ammonia will be produced by fossil fuel reforming with CCS or CO₂ -EOR at the early stage of the introduction of ammonia fuel to the market. Green ammonia, which is synthesized from green hydrogen and nitrogen, is the ultimate goal, but there are some issues facing its commercialization.

One of big issues is the low capacity factor which is caused by the fluctuation of solar irradiation or wind speed and makes ammonia production costs expensive. Hence, at the 2019 AIChE Annual Meeting’s Ammonia Energy Conference, we introduced the results of optimization studies of the capacity and operation of units that comprise the ammonia process using photovoltaics as a renewable power source. Moreover, we also introduced the test results of the fluctuating operation in the ammonia synthesis demonstration plant. From the results of this study, it was put forward that, in order to absorb the fluctuations of solar or wind energy, the optimization of battery and hydrogen storage tank capacities and the ammonia plant load changing operation are effective for the ammonia production cost reduction. Regarding system capacities optimization, based on each equipment unit cost and specification, the optimal configuration can be determined by case-study calculation.

In this presentation, we would like to explain the results of the dynamic simulation of ammonia synthesis imitating the fluctuating renewable power source combined with a buffering system for verifying the influence of ammonia plant load changing operation. The influence, which is caused by the dynamic operation corresponding to renewable energy source fluctuation, against ammonia plant stability has to be simulated. As an example of non-steady state operation, there is a risk of overheating vis-a-vis the design temperature or oscillation of the reactor temperature caused by increasing the feed rate of hydrogen rapidly. Moreover, there is a probability of surge in the recycle compressor without actuating the anti-surge system when the feed rate suddenly decreases.

The dynamic model is a convenience to analyze the process condition and can show the plant stability without actual operation in a real plant. The objective of this study is to establish the design concept for the ammonia synthesis loop and identify the margin to instability of the ammonia reactor and relevant equipment. By a combination this study and overall system configuration optimization, we will establish the Green Ammonia Production system concept and design basis for the commercial Green Ammonia plant using renewable energy.