  Complex networks have attracted increasing interests in almost all
disciplines of natural and social sciences. However, few efforts have been
afforded in the field of chemical engineering. We present in this work an
example of complex technological network, investigating the process flow of an
ammonia plant (AP). We show that the AP network is a small-world network with
scale-free distribution of degrees. Adopting Newman's maximum modularity
algorithm for the detection of communities in complex networks, evident modular
structures are identified in the AP network, which stem from the modular
sections in chemical plants. In addition, we find that the resultant AP tree
exhibits excellent allometric scaling.
