Optimal power distribution in a P2A plant

In Power-to-Ammonia (P2A) plants the ammonia reactor is required to operate over a wide operating window between 20% to 125% of the nominal load. We formulate a rigorous model for an ammonia synthesis loop with a three-bed adiabatic quench-cooled ammonia reactor. Given a steady-state solution to the ammonia synthesis loop, we evaluate the total power input for the P2A plant composed of the electrical utility for H2 and N2 production, and compression work. The total power input and the electrical efficiency for storing electrical energy in NH3 are evaluated over a wide range of reactor H2 flow, N2/H2-ratio and recycle-ratio of the reactants. In this way, we can identify the optimal reactor flow for a given power input to the P2A plant. The optimum is revealed to be at a significantly greater N2/H2- and recycle-ratio than used in conventional ammonia plants. This reflects the very expensive production of H2 via electrolysis in P2A compared to conventional production via steam-methane reforming.