Apparatus comprising: an in-line powder disperser, comprising: a pneumatic inlet having a first line aperture, a mixing chamber placed pneumatically downstream from the pneumatic inlet, at least a first gas injection port having an inlet responsive to a mixing gas outlet of a mixing gas source and a mixing outlet that opens into the mixing chamber, and a pneumatic outlet placed pneumatically downstream from the mixing chamber and having a second line aperture; characterised in that the apparatus further comprises: a downstream measuring device arranged to receive a pneumatically conveyed particle flow from the pneumatic outlet and configured to monitor the size of the particles in the particle flow; wherein the powder disperser is operable to break up aggregated particles and/or prevent aggregation of particles by creating turbulence in the particle flow in the mixing chamber when pressurised mixing gas is injected through the gas injection port, and wherein an injection direction of the mixing outlet of at least the first injection port is placed at an angle with respect to the flow with a first component in the downstream direction and a second larger component in an inward radial direction with respect to the conduit. an in-line powder disperser, comprising: a pneumatic inlet having a first line aperture, a mixing chamber placed pneumatically downstream from the pneumatic inlet, at least a first gas injection port having an inlet responsive to a mixing gas outlet of a mixing gas source and a mixing outlet that opens into the mixing chamber, and a pneumatic outlet placed pneumatically downstream from the mixing chamber and having a second line aperture; characterised in that the apparatus further comprises: a downstream measuring device arranged to receive a pneumatically conveyed particle flow from the pneumatic outlet and configured to monitor the size of the particles in the particle flow; wherein the powder disperser is operable to break up aggregated particles and/or prevent aggregation of particles by creating turbulence in the particle flow in the mixing chamber when pressurised mixing gas is injected through the gas injection port, and wherein an injection direction of the mixing outlet of at least the first injection port is placed at an angle with respect to the flow with a first component in the downstream direction and a second larger component in an inward radial direction with respect to the conduit. a pneumatic inlet having a first line aperture, a mixing chamber placed pneumatically downstream from the pneumatic inlet, at least a first gas injection port having an inlet responsive to a mixing gas outlet of a mixing gas source and a mixing outlet that opens into the mixing chamber, and a pneumatic outlet placed pneumatically downstream from the mixing chamber and having a second line aperture; characterised in that the apparatus further comprises: a downstream measuring device arranged to receive a pneumatically conveyed particle flow from the pneumatic outlet and configured to monitor the size of the particles in the particle flow; wherein the powder disperser is operable to break up aggregated particles and/or prevent aggregation of particles by creating turbulence in the particle flow in the mixing chamber when pressurised mixing gas is injected through the gas injection port, and wherein an injection direction of the mixing outlet of at least the first injection port is placed at an angle with respect to the flow with a first component in the downstream direction and a second larger component in an inward radial direction with respect to the conduit.