A novel vortex combustor (VC) firing various solid, liquid, and gaseous fuels was recently developed and tested for commercial heating applications. The combustor is characterized by a strong swirl and low temperature combustion environment. The paper presents numerical simulations and measurements of the isothermal and reacting gas flow and the gas-particle slip motion in the VC. The results show that the gas flow in the VC with a coaxial center tube and multiple air injection is characterized with swirling, developing, and recirculating features. The swirl intensity is affected by the combustion in the VC. Swirl provides an effective control of the gas-particle slip velocity in the VC.