Experiments are described on the pneumatic conveying of 2.7 mm alumina particles up a vertical riser of internal diameter 46.4 mm or 71.4 mm. The particles entered the riser from a fluidised bed, via a short horizontal pipe and a bend of radius 75 mm. Measured variables included solids flow rates, air flow rates, inlet and outlet air pressures P-1 and P-2, and the pressure profile in the riser. The solids flow rate was consistent with some earlier models of similar systems, in which the plugs of packed solids move up at a velocity of about U-U-mf, where U=superficial air velocity and U-mf=incipient fluidising velocity. Solids-wall friction is significant and suppresses fluidisation. To model the system approximately, a conveying efficiency=(power for air compression)/(rate of gain of potential energy of solids) is defined and correlated against solids flux. It was found that the conveying efficiency tended to an asymptote just above 20%. The correlation led to a tentative design formula, Eq. (6), for predicting P-1-P-2 at a given solids flow rate. P-1-P-2 is typically between 50% and 100% of the pressure drop needed to support a column of solids of height equal to that of the riser. It was concluded that plug flow pneumatic conveying is a satisfactory technology for transporting coarse particles which cannot be conveyed in leaner regimes due to the possibility of pipeline erosion or solids attrition. (C) 2012 Elsevier By. All rights reserved.