22 CRISTINI Process measurements that


lead to quality improvement The optimisation of quality and the saving of energy on high-speed board machines has been achieved at Cristini by using integrated on-line microwave sensors clusters. Luca Canali* explains


W


ith many mills having successfully implemented


Cristini microwave meters, others are now deciding to invest in the measuring system, aiming for superior board quality by the control of the web consistency in the forming section and the exit of the press section. As a computer cluster, the measuring system can be seen as a set of tightly-connected sensors that work together so that, in many aspects, they can be viewed as a single system. It is well known that the rate


of water removal in the forming section, as well as the direction of the water removal, will affect the distribution of the fines in the z-direction of the sheet. Quantifying that rate is not an easy task without the proper measuring tools. Real time data from microwave


gauges are used as a source of cost savings in the forming section. Vacuum is an important factor in the forming section of a paper machine as it is a huge component in the mill energy equation. Continuous control of sheet dryness is the major task in order to optimise the energy consumption. In board machines, the


dewatering distribution inside each individual ply has a direct impact on the quality of the final product. Optimum conditions


July/August 2019 Figure 1 – Cristini’s microwave sensor cluster layout


at the top formers and bonding lead to better fibre distribution and cohesion.


Application based on the microwave technology FiberScan and SmartScan are highly accurate, on-line microwave metres, that are non-radioactive, easy to install, and are used for measuring consistency and water mass on paper and pulp machines. The system is based on


a patented microwave technology and algorithm which enable precise consistency measurements of the paper thickness, up to 64mm (or 64.000gsm). The proprietary measuring process allows the


output of conductivity measured by the sensors. The reduced sensor dimensions make measurements in extremely confined spaces and harsh conditions possible. SmartScan, featuring a


dedicated cooling system, can perform accurately even in the dryer section, withstanding an air temperature up to 95 deg C. The system makes it easier to


evaluate machine and/or process changes in real time as operators can view changes instantly on the DCS/QCS screens.


Improving product quality The direct measurement of water on the wire and the web provides visibility of drainage


rates and the effects of stock preparation (raw material quality, chemicals/additives) and former/presses set-up. This information can help to improve product quality, forming fabric performance and process efficiency while reducing the energy consumption of the forming, pressing and drying operations. Advancements in


instrumentation have opened new avenues for effective use of vacuum table elements to control sheet consistency for a variety of paper making applications including dandy rolls for improved formation, multiple formers for optimum formation, coverage and ply bond as well as numerous


Pulp Paper & Logistics


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