Continuous Digester Analyzer

The Digester Liquor Analyzer Solution: This solution is a turnkey solution for carrying out white and black liquor analysis of the digester. The analyzer is designed to extract samples from a continuous digester at strategic locations. The system is based on industrial spectrometer. Black liquor analysis includes Residual Effective Alkali (REA), RAA, TDO(Total Dissolved Organics) and Total Dissolved Solids (TDS).

White liquor analysis provides measurements for effective alkali (EA), AA, TTA, sodium sulfide (Na2S), sodium carbonate (Na2CO3) and total Dissolved solids (TDS). The analyzer package consists of an industrial spectrometer configured for white & black liquor analysis, an acid cleaning system to remove any scale buildup from the sampling optics and all the necessary sampling hardware to interface white & black liquor lines into the system.

Up to eight samples points are brought into the system with ½” stainless steel tubing or equivalent. Sampling and cleaning is completely automated and is controlled by the spectrometer and sampling system microcontroller.

Application Technology
Reliable and accurate white liquor analysis for batch and continuous digesters is important for minimizing pulp quality variations. For both continuous and batch digesters white liquor composition needs to be accurately known to ensure that the correct effective alkali is charged for the given chip mass entering the digester.

The two primary sources of variation that interfere with charging the correct amount of alkali on wood for batch and continuous digesters are chip moisture variations and white liquor variations. If white liquor composition is accurately known then one source of variation can be eliminated. With an online white liquor analyzer the white liquor can be trimmed in real time to meet target effective alkali and sulfidity levels allowing one to maintain a constant liquor to wood (L/W) ratio for a given alkali to wood ratio. Alternatively, variations in alkali to wood ratio induced by white liquor composition variations can be compensated for by only adjusting the liquor to wood ratio. Either approach requires an accurate online analysis of the cooking white liquor.

The DURALYZER-NIR white liquor analyzer provides the required effective alkali (EA) and sulfidity measurements in a timely, accurate and reliable manner. Additionally, white liquor TTA, TDS and deadload levels are also available from the same analyzer.

Manufacturer: R.E. Hodges; Auburn, Alabama

Continuous Digester Control Application:

Monitoring black liquor REA and Lignin contents in a continuous digester provides a means for implementing advanced control schemes. NIR analysis is well suited for measuring these properties in the BL as well as the RAA and TDS.

Figure on the left shows typical sample collection points on a single vessel, hydraulic Kamyr digester. In the first step the incoming EA variations are compensated by controlling the WL flow. In the second step, most of the unknown wood/chips variations can be quickly compensated for with a feedback from TC to the White Liquor charge.

 The measured REA and Lignin profiles at the top of the digester can be compensated by adjusting the temperatures in the cooking zones. Continuous digesters fitted with liquor feed points in the cooking zones have the added flexibility of stabilizing the REA needed for the actual bulk delignification job.

• Kappa variability reduction
• Stabilized level control
• Energy savings
• Minimized emissions
• Maximized production
• Better quality fibers
• Less shives produced