In this paper we present a representation scheme for chemical unit processes. The representation is based on a topological and a phenomenological abstraction of the process. The topological abstraction decomposes the process into control volumes and boundaries. The phenomenological abstraction represents the phenomena in the process using three general process characteristics, i.e. transport, reaction/generation and accumulation of mass and energy. For these entities we define a consistent set of graphical symbols that will be connected together in a network according to the modelers understanding of the process, giving a representation of the process. We further suggest to employ this representation in the development of a modeling methodology, where the symbols are related to differential and algebraic equations in order to represent a complete and consistent mathematical model. The methodology is successfully applied to two industrial processes, a ferromanganese furnace and an aluminum electrolysis cell. The latter will be used as an example. Simulations of the aluminum cell focusing on AlF3 dynamics are included.