Online standardized measurements of pulp and stock quality

Optimization and control of the pulp and paper making processes for cost-effective production requires more frequent monitoring of the relevant pulp and stock preparation quality parameters. A new quality monitoring system for pulping and stock preparation is developed. The new online L&W Pulp Tester is a complete wet laboratory with automatic sampling from different positions along the process chain. Repeatable tests are made automatically and frequently. True variations are monitored in real time and are used to secure product quality, save time, material and energy, and increase production. The online pulp tester consists of automatic standard and established tests for CSF, SR, brightness, color, fibre length, kink, coarseness etc. suitable for building up an automatic quality monitoring and optimization system in the mill. Samples from a liner mill with refining in several steps was investigated and showed a good potential for online measurement of pulp strength potential. A new automatic measurement of fibre coarseness is an important parameter for prediction of pulp strength potential in addition to the fibre morphology measurements. Accurate and repeatable measurements and classification of vessel cells is an important measurement for classification of hardwood pulps. Reliable data and high uptime of the system are fundamental requirements for online pulp quality analysers. Confidence is created by automatic measurements according to existing standards and established procedures. The repeatability is tested with automatic sampling from a tank to avoid manual steps in the test. A high uptime of the system is reached by automatic cleaning procedures, use of well proven components and robust design. The new online standardized tests are used for applications in all types of pulp and paper production. As a complement to the sampled system a new fast inline fibre quality analyser (L&W Fiber Quality Transmitter) based on image analysis is recently introduced. WHAT IS PULP QUALITY? What is the purpose of pulp quality testing? One main purpose is to predict the final product potential from wet pulp properties. If we know the impact from the pulp properties on the final product then we can optimize and control the process for best economy. But what shall we measure to characterize pulp quality? And what technique is useful in a reliable online quality testing system? Mechanical pulp For mechanical pulp the measure of freeness has been used traditionally since it is sensitive to process parameters in refining and is connected to dewatering on paper machines. Regarding strength properties of mechanical pulp,Forgacs [12] showed already 1962 that measuring only freeness was not enough for characterization of pulp. He stated that at least two parameters are needed for classification of strength properties of mechanical pulp (reinforcement and bonding or total surface). Much work has been done since that time regarding pulp quality. Automatic analysis with modern optics was early introduced in mechanical pulping. One of the absolute first successful optical devices for online process measurements was a shive analyzer with automatic sampling and sample preparation. Shives increase the probability for web brakes, linting and printability problems. The optical Shive analyzer was invented by Jan Hill at STFI 1974 [1]. The signals from two perpendicular placed detectors were multiplied. The pulse length and height resulting from passing shives were analyzed and were measures of shive length and width respectively. It was followed by a pulp quality monitor system (which became the PQM). An optical fibre fractionator was combined with the shive analyzer and a freeness tester to an automatic sampled system for monitoring of quality for mechanical pulps. Three fibre length fractions were created from three optical channels with different characteristics [4]. It is known that fiber length correlates to sheet strength like tear index and strongly influences formation.Several systems with the same concept as PQM have entered the market since then and are common in the industry today. Ferritsius[13] has summarized the quality for mechanical pulp in five steps the five star: