Abstract: A continuous semi-dense phase conveying system comprising a vessel having a gas inlet, a particulate material inlet, and a gas and particulate material outlet, which has an operating pressure of about 15 psig or less. The system includes a rotary airlock valve for feeding particulate material into the vessel and a pressurizing gas supply which branches into a feed gas line and a bypass line. A pneumatic conveying line coupled to the gas and particulate material outlet of said the and coupled to the bypass line. The pressure of the vessel is controlled using a bypass valve on said bypass line and optimize the flow of gas and particulate matter through the pneumatic conveying line.