A solids circulation system captures and transfers char or other reacting solids from a gas stream created by a first reactor, to a second reactor. The second reactor has a dense fluid bed and converts the carbon in char or residual reactants in the solids to gaseous products. The solids circulation system comprises a cyclone that receives the gas stream with solids, the second reactor, a riser and a cyclone dipleg connected to the second reactor. A conveying fluid is utilized to transport a portion of the bed media from the second reactor through the riser to mix with the gas stream containing char or reacting solids prior to cyclone entry. The addition of the bed media helps to manipulate the properties (density and mean size) of the solids mixture that is captured by the cyclone and facilitate steady or quasi-steady dense phase flow of solids down the dipleg into the second reactor. This second reactor provides additional residence time, mixing and gas-solid contact for efficient conversion of char or reacting solids.