According to one or more embodiments, olefins may be produced by contacting a hydrocarbon feed stream with a particulate solid in a reaction vessel. The reaction vessel may be connected to a riser. The riser may extend through a riser port of an outer shell of a particulate solid separation section such that the riser may comprise an interior riser segment and an exterior riser segment. The particulate solid separation section may include a gas outlet port, a riser port, and a particulate solid outlet port. The particulate solid separation section may house a gas/solids separation device and a solid particulate collection area. The riser port may be positioned on a sidewall of the outer shell such that it is not located on a central vertical axis of the particulate solid separation section. The particulate solid may be separated from an olefin-containing product stream in the gas/solids separation device.