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. An example of complex technological network, investigating the process flow of an ammonia plant (AP) is presented. 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, it is found that the resultant AP tree exhibits excellent allometric scaling. (c) 2007 American Institute of Chemical Engineers.