Fully Automatic and Online: Dirt Count for pulp lines
October 1, 2006 By Pulp & Paper Canada
Today, dirt count is most commonly determined offline in the laboratory with specific equipment. Although several dedicated measuring systems are on offer, as of today, no dedicated tool for the onlin…
Today, dirt count is most commonly determined offline in the laboratory with specific equipment. Although several dedicated measuring systems are on offer, as of today, no dedicated tool for the online calculation of the dirt count is available. As a result, at most pulp manufacturers, dirt counting is done in laboratories.
A new technology development, an online dirt count sensor, detects and measures all dirt spots on a strip of the manufactured pulp web. The classification software will then assign these dirt spots to various size categories. Based on this, the ISO and TAPPI numbers for the finished pulp drops/bales are calculated.
By means of various practical tests and studies, special arrangements of illumination and camera settings have proven successful. Process obstacles such as unintended surface structures, caused for example by the felt roll, can be overcome with a customized inspection sensor. Two illumination beams are used, both of which deploy diffuse yellow light sources. Due to this setup, more illumination angles can be realized for better illumination of the complete pulp strip. Additionally, the illumination cross web is optimized. Thus, heavy surface structures can be suppressed in the images captured by two cameras with a resolution of 160m x 160m. This resolution also guarantees the detection of very small specks.
Practical tests have shown that the corrosive environment strains the common sensor used in surface inspection. Now, stainless steel beams ensure that the sensor can withstand the environmental conditions of a pulp mill.
The results of the pulp strip detection will be processed subsequently in a software module based on the classification and post-processing of dirt spots. A software module calculates the ISO/TAPPI numbers for each drop, based on the dirt spot images delivered by the detection technology. The single dirt spots are classified according to their size. Also, shives are separated from the dirt spots by means of a well-trained classifier. The ISO/TAPPI numbers are then displayed in the operator software. Additionally, if the current count of shives of wood exceeds a fixed threshold, alarms can be sounded in order to direct the inspector’s attention towards this problem.
With the activation of a TCP/IP telegram for each drop, the optimal result transmission to the process computer will be guaranteed. Also, the optical data transmission via an OPC interface is possible.
The automatic dirt count solution enables the operators to realize the dirt count calculation online during the production. Thus, results are immediately available and the production can be adjusted accordingly: If the number of dirt spots is too high, the operators at the pulp machine still have the opportunity to adjust the machine settings and thus enhance the pulp quality.
The results of the online method correlate to the required standards, which have been set by the laboratory measurement methods. Current laboratory dirt count typically reaches 10m2 per drop, whereas the online solution inspects more than seven times as much. Hence, statistically more consistent and reliable results are delivered with this method.
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