Optimal design and operation of ammonia decomposition reactors

Abstract

The design and steady-state operation of a packed bed reactor with tubular geometry is optimized. Direct optimal control methods are used. Two objective functions are considered: (i) minimization of the ammonia mass fraction at reactor outlet and (ii) minimization of the heat flux necessary to reach a predefined value of the ammonia mass fraction at reactor outlet. The optimization process is performed by using different controls, that is, the space distributions of (1) tube wall temperature T w , (2) circular tube diameter D tube , and (3) diameter d p of the catalyst spherical particles. Results for the first objective function are as follows. The optimal distribution of T w along the reactor consists of a constant temperature or a U-shaped space temperature distribution, respectively, depending on the allowed range of variation of T w . The optimal space distribution of D tube (or, in other words, the shape of the reactor tube) depends of T w . For smaller values of T w the tube is narrower at inlet and larger at outlet while the reverse situation happens for larger values of T w . For lower T w values, particles with smaller diameter d p are placed at reactor inlet while when higher values of T w are considered, particles with larger d p are placed at reactor inlet. When both D tube and d p are used as controls, the optimization results are generally different from the results obtained from one-control optimization. Results for the second objective function are as follows. The optimal space distribution of T w starts with high values at reactor inlet. Next, the temperature decreases abruptly towards a minimum (which is lower for longer tubes). Finally, the temperature increases smoothly towards a maximum near the reactor outlet. The required heat flux slightly decreases by increasing the tube length. The optimal D tube ranges between its maximum allowed value (at reactor inlet) and its minimum allowed value (at reactor outlet). The best performance is obtained for catalyst particles of the smallest allowed diameter. K E Y W O R D Sammonia decomposition reactor, minimum heat consumption, optimal design, optimal operation

Multi-objective performance optimization of ammonia decomposition thermal storage reactor

“…In the FTT studies of ammonia decomposition reactors, Hu et al [8] developed a one-dimensional ammonia decomposition reactor model and determined the reactor diameter and length for the highest ammonia decomposition rate. Badescu et al [9] obtained the optimum distribution of temperature along the pipe wall, the pipe diameter and the catalyst particle size distribution with the objectives of maximizing the ammonia decomposition rate and minimizing the heat flux under a predetermined ammonia decomposition rate.…”

Ammonia deep chemical looping combustion on perfect and reduced Fe 2 O 3 : A theoretical account

“…Ammonia (NH 3 ) has almost twice the bulk energy density of liquid hydrogen, acting as a promising energy carrier to reduce CO 2 emission, 1‐4 but traditional aerobic combustion of NH 3 inevitably produces a large amount of NOx, polluting environment 4‐11 . Differing from the traditional aerobic combustion, chemical looping combustion (CLC) uses metal oxide (M x O y ) as the oxygen carrier (OC) to oxidize the fuel (C n H 2m ), to avoid the direct interaction between C n H 2m and air, which can reduce NOx emission 12,13 .…”

Modeling And Optimization Study of PEMFC Fueled With Ammonia Reforming Gas

“…Hunter et al established an ammonia-reforming gas-PEMFC demonstration platform to demonstrate the feasibility of PEMFC using ammonia reforming gas directly [7]. Meanwhile, there have been numerous studies for the efficient decomposition of ammonia [8,9], but there are few studies on the effect of high nitrogen concentration on PEMFC. Previous studies have shown that nitrogen affects the diffusion and transport of hydrogen in the flow channel, but when pure hydrogen is used as fuel, its final accumulation is not high as it is regularly discharged regularly with anode purging.…”