Dynamic simulation of a highly load-flexible Haber–Bosch plant

Abstract

The Power-to-Ammonia process has been suggested to decarbonize global ammonia production and to enable global energy trade using ammonia as a carbon-free energy carrier. Traditionally, Haber–Bosch plants for ammonia production based on natural gas have been operated near their nominal load and with slow load change rates. Power-to-Ammonia calls for more load-flexible plants to optimally utilize fluctuating renewable energy sources. This work presents a detailed dynamic model of a modified Haber–Bosch plant including feed compression, reaction, separation, and refrigeration. We conduct simulation studies demonstrating load change rates up to 3%/min and safe operation with down to 10% of the nominal feed flow rate. Three strategies are investigated utilizing an increasing number of variables to achieve favorable conditions during part-load operation. Among those, a combination of pressure reduction, reduced flow in the synthesis loop, increased ammonia fraction in the reactor feed, and omitted intercooling between the reactor beds enables the smoothest load transition and best conditions during part-load operation. We further show that a moderate pressure reduction in the synthesis loop can reduce power demand during part-load operation. • Dynamic simulation of Haber–Bosch plants down to 10% load at ramp rates of 3%/min. • Pressure control for purge-free Haber–Bosch-type synthesis loops was implemented. • Reducing reactor intercooling allows to sustain higher reactor flow at part load. • Increased ammonia fractions in reactor feed are favorable for part-load operation. • Moderate reductions in synthesis loop pressure significantly reduce power demand.

Topics & Concepts