A new industrial-scale spout-fluid mixer (H = 3.4 m and I.D. = 0.8 m) was proposed for mixing 18.75 t/h of biomass (p(b) = 400 kg/m(3), d(b) = 2 mm) and 28125 t/h of heat-carrier (P-c = 2600 kg/m(3), d(c) = 0.5 mm), and the corresponding three-dimensional computational fluid dynamics approach, facilitated with the Eulerian-Eulerian multiphase fluid model (CFD-TFM), was developed to simulate the three-phase mixing behaviors in the mixer. The performance of the mixer and effects of operating parameters were numerically investigated. It was found that the mixing effectiveness, Me, can reach over 80% under the proposed industrial operational conditions (for example, a spouting gas flowrate Q(s) = 0.067 kg/s and fluidizing gas flowrate Q(f) = 0.035 kg/s), and the flow pattern in this case is a "jet in the fluidized bed with bubbling". Increasing Q(s) will increase the sizes of bubbles, as well as their generation frequency and rising velocity, which are conducive to the mixing of heat-carrier and biomass particles. However, a too large Q(s) will affect the falling solid flows in the distribution region and transition region of the mixer. Conversely, increasing Q(f) will aggravate the swaying and leaning of bubbles or jets towards the mixer walls, leading to a slight decrease of Me. (C) 2016 Elsevier B.V. All rights reserved.