Process plant layout has received interest in the processing industry because of its impact on the installation costs and process safety. This work proposes a model to allocate process units in tri-dimensional (3D) space, based on a non-overlapping projection approach represented as a disjunctive model; the modeling equations include both multi-floor and safety constraints. The mathematical formulation undergoes a disaggregation procedure, so that the model becomes an MINLP problem. The solution of the MINLP model uses the GAMS modeling environment. Four case studies make it possible to show the scope of this non-overlapping model. Besides, the results obtained undergo comparison against a real process allocation and previous reports from the literature. The comparison reveals that the proposed approach is a competitive alternative to get the 3D process plant layout solution. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.