Abstract: A method for manufacturing mechanical pulp. Raw material of the mechanical pulp is introduced. The raw material is refined in a first refining stage to form the mechanical pulp. The pH of the mechanical pulp is adjusted to between 9 and 11 in a process step in which a first process delay is arranged. The first process delay is at least 0.5 hours. The mechanical pulp is sorted into a first accepted stock and a first rejected stock. The first rejected stock is ozonated. The pH of the first rejected stock is at the start of the ozonation process is between 9 and 11. The ozonated first rejected stock is refined in a second refining stage so that at least a part of the ozonated first rejected stock will belong to a second accepted stock. The first accepted stock and the second accepted stock are combined. The mechanical pulp may be used.

Abstract: Bleaching device for pulp includes a container to which a supply of pulp and bleaching chemicals containing peroxide as well as discharge of bleached pulp are connected. The device comprises an oxygen measuring device a temperature measuring device and/or a carbon monoxide measuring device, which are arranged to measure oxygen concentration, temperature and/or carbon monoxide concentration, respectively, from the contents of the container such as from the gas volume of the same, or from a substance flow coming from the container, such as gas flow. The measuring device is connected to a data processing unit which is coupled to a controller for automatic control of the process. The process is especially a high consistency pulp bleaching of mechanical pulp, in which the consistency of pulp in the reaction area is at least 25%, advantageously at least 30%.