(421c) Techno-Economic Optimization of a Microwave-Assisted, Low-Pressure Ammonia Synthesis Process with Novel Separation Technologies

Ammonia is a key chemical for production of fertilizer and storing and transporting energy [1-3]. However, the traditional process for ammonia production is still the Haber-Bosch process that operates at very high temperature and pressure leading to high energy penalty and capital investment. It currently accounts for 1-2% of energy consumption, about 5% of natural gas consumption, and 1.6% of CO2 emissions worldwide[4]. The microwave (MW)-assisted ammonia synthesis process offers a viable and attractive alternative to the Haber-Bosch process, as the synthesis can occur at near atmospheric pressure and moderate temperature. MW-reactors are highly modular thus making distributed production of ammonia technically and economically feasible. Furthermore, MW reactors can be rapidly started and shutdown thus making it possible to run these systems directly with intermittent renewable energy systems. However there is currently no study on modeling, synthesis, and techno-economic optimization of the MW-assisted processes. This talk will present kinetic modeling of a MW-reactor, development of the plant-wide model, and techno-economic optimization of a modular scale ammonia synthesis process.

Our in-house lab-scale experimental data from a MW-assisted reactor is used for kinetic model development. Kinetic parameters are optimally estimated by using the experimental data. The model is validated by using the experimental data. The reactor model is then scaled up to the desired modular scale. One of the major challenges of low-pressure ammonia synthesis is the separation of ammonia from unreacted nitrogen and hydrogen at low pressure. Separation technologies such as flash separation under ambient or mildly cold conditions used in high pressure Haber-Process process are not economically viable under low pressure separation as much colder temperatures are needed for flash separation. As a result, several novel separation technologies are investigated- solid-sorbent based separation, membrane-based separation and cryogenic separation. Rigorous first-principles models of these separation technologies are developed and integrated with the MW-assisted reactor for separating and recycling unconverted reactants.

An economic model of the process is developed by using the in-house cost data for the MW-assisted reactors. Design and operating variables of the plant-wide process are optimized by an equation-oriented approach using the sequential quadratic programming approach. Since the adsorption/desorption processes used in the solid-sorbent base separation are dynamic, a surrogate model is to be used for steady-state optimization. Various economic measures such as net present value, internal rate of return, and payback period are studied by simulating a number of scenarios including the selection of separation technology, cost of reactants, and efficiency of the MW-assisted reactor.

REFERENCES
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