Dense gas-solid flows have been the subject of intense research over the past decades, owing to its wealth of scientifically interesting phenomena, as well as to its direct relevance for innumerable industrial applications. Dense gas solid flows are notoriously complex and its phenomena difficult to predict. This finds its origin in the large separation of relevant scales: particle-particle and particle-gas interactions at the microscale (< 1 mm) dictate the phenomena that occur at the macroscale (> 1 meter), the fundamental understanding of which poses a huge challenge for both the scientific and technological community. This proposal is aimed at providing a comprehensive understanding of large-scale dense gas-solid flow based on first principles, that is, based on the exchange of mass, momentum and heat at the surface of the individual solid particles, below the millimeter scale. To this end, we employ a multi-scale approach, where the gas-solid flow is described by three different models. Such an approach is by now widely recognized as the most rigorous and viable pathway to obtain a full understanding of dense-gas solid flow, and has become very topical in chemical engineering science. The unique aspect of this proposal is the scale and the comprehensiveness of the research: we want to consider, for the first time, the exchange of heat, momentum and energy, and the effects of polydispersity, heterogeneity, and domain geometries, at all three levels of modeling, and validated by one-to-one experiments. These generated insight and models will be extremely relevant for the design and scale-up of industrial equipment involving dispersed particulate flow, which is currently a fully empirical process, involving expensive and time-consuming experimentation.