Patent ID: 6841040

Claim:
A method for feeding chemicals into a fibre suspension in the short circulation of a paper machine, between a machine screen and a headbox comprising the steps of: passing a fiber suspension flow through a pipe expansion comprising a first pipe having a first diameter which is connected at an expansion step to a second pipe of a second diameter which is larger than the first diameter, and wherein the first pipe and the second pipe are coaxial, the expansion step extending perpendicular to the direction of the fiber suspension flow; wherein the expansion step has a height defined as one-half the second diameter minus the first diameter; feeding a chemicals flow into the fiber suspension flow at a location, the location being positioned from immediately before the pipe expansion, wherein the chemicals flow is so close to the expansion step that the chemicals have no time to react with the fibre suspension before the flow enters the expansion step, to downstream of the expansion step a length up to 50 times the height; and following feeding the chemicals flow, feeding the fiber suspension flow into the headbox.