Pneumatic energy is converted into solid particle kinetic energy as a solid-particle-entrained gas flows downward through a vertical nozzle. For the conditions studied, the solid particles serve as a heat exchange medium to enable a gas expansion that is nearly isothermal. Also, the kinetic energy associated with the two-phase fluid is predominantly that associated with subsonic solid-particle motion. The kinetic energy of the solid particles is converted into other forms using a low-speed turbine. A theoretical description of the process is presented, and the initiation of an experimental effort to study the process is described. Experimental gas phase temperature measurements indicate the realization of isothermal expansion. Experimental turbine erosion rate measurements indicate that relatively low erosion rates occur for the conditions studied.