Method and arrangement for feedback based control in chemical refining of wood

A control system for controlling values of process parameters of a pretreatment process of wood particles, the control system comprising:

• a sampler;
• one or more measurement information inputs coupled to said sampler for receiving measurement information indicative of measured characteristics of samples taken by said sampler of a product flow in said pretreatment process;
• one or more control information outputs for setting values for said one or more process parameters of said pretreatment process, and
• a processing engine coupled to said measurement information inputs and said control information outputs;
• wherein said processing engine is programmed to
• obtain a sample of said product flow of said pretreatment process using said sampler after said wood particles have undergone steam explosion in a hemihydrolysis reactor,
• measure one or more characteristics of particles in said sample using a particle measurement device, wherein said one or more characteristics of particles include at least shive content in the sample, and to produce one or more pieces of measurement information indicative of the measured characteristics;
• and
• select one or more values of one or more of said process parameters using said one or more pieces of measurement information,
• wherein said using of said one or more pieces of measurement information to select one or more values of said one or more of said process parameters comprises selecting at least a value of a second residence time of said product flow in an impregnating vessel that precedes said hemihydrolysis reactor in said pretreatment and selecting at least one of the process parameters selected from:
• a third residence time of said product flow in a first soaking silo that precedes said impregnating vessel in said pretreatment, or
• a fifth residence time of said product flow in a second soaking silo that is between said impregnating vessel and said hemihydrolysis reactor in said pretreatment, and
• wherein said particle measurement device is configured to measure shive content in said sample as one of said one or more characteristics of particles, the measured shive content is compared to a default shive content to produce at least a second piece of said one or more pieces of measurement information, and value for at least one of said third residence time or said fifth residence time is selected to intensify impregnation of wood particles in said first or second soaking silo respectively in response to said second piece of measurement information indicating larger than default shive content.