Fluid-granular flows are common phenomena in nature and industry. Here, an efficient computational technique based on the distributed Lagrange multiplier method is utilized to simulate complex fluid-granular flows. Each particle is explicitly resolved on an Eulerian grid as a separate domain, using solid volume fractions. The fluid equations are solved through the entire computational domain, however, Lagrange multiplier constrains are applied inside the particle domain such that the fluid within any volume associated with a solid particle moves as an incompressible rigid body. The particle-particle interactions are implemented using explicit force-displacement interactions for frictional inelastic particles similar to the DEM method (Cundall and Strack, 1979) with some modifications using the volume of an overlapping region as an input to the contact forces. A parallel implementation of the method is based on the SAMRAI (Structured Adaptive Mesh Refinement Application Infrastructure) library. Application of this method to simulate fluid-granular flows in pipes with a step decrease in cross-sectional area is discussed. Correlations between pressure losses and solid mass fluxes in a pipe for different particle concentrations, pipe diameters and particle sizes are studied. Results of the simulations agree well with available experimental data for the mass flow ratio vs pressure drop during conveying. (C) 2015 Elsevier B.V. All rights reserved.