A total lignin measurement solution by BTG as basis for overall bleach plant control.
Kraft pulp bleaching is a cost-intensive process that must be well measured and controlled to produce on-spec pulp with a minimum of bleaching chemicals. The proven answer is in BTG’s BLT-5500 inline sensor which is a highly simplified approach to bleach plant instrumentation and the basis of optimized process control. Because of its measurement versatility, traditional, post chemical addition brightness and chemical residual measurements are no longer required. It is currently in use in full BTG bleach plant instrument packages – called the Optical Bleach Plant - and is the cornerstone measurement in BTG Process Solutions control implementations. These solutions are providing savings to customers of $2 to $3 per ton in chemical costs. Production increases are also documented.
Total lignin measurement
The BLT-5500 is a unique solution to the lignin measurement problems associated with traditional kappa analyzers which measure the kappa number of fibers in a washed pulp sample. But that is only part of the lignin load that consumes bleaching chemicals. The dissolved lignin in the brown stock filtrate remains an un-measured disturbance. To compensate for these disturbances it is common to install a residual and brightness transmitter after the chlorine dioxide addition and before the bleaching tower. This is not the case with BLT-5500.
The BLT-5500 is an inline sensor that measures the total amount of lignin in a process line regardless of whether it is attached to the fiber or is dissolved in the filtrate. As a result, the amount of lignin dissolved in the filtrate is no longer an unmeasured disturbance. Additionally, there is no longer a need to install brightness probes and residual transmitters after chlorine dioxide addition. The BLT-5500 can take the place of the fiber kappa measurement, the residual transmitter, and the brightness transmitter at both the “feed to bleach” location and the “CEK/DEK” position after the first extraction stage. Since the BLT-5500 can be calibrated to measure brightness as well as a total lignin measurement, it can be used at the CEK position to provide a lignin measurement for feedback control and a brightness measurement for a feedforward control signal. This is a total measurement and control solution in one sensor.
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