Brown Stock Washing Analyzer

The Brown Stock Washing Analyzer Solution: This solution optimizes any countercurrent Displacement or Diffusion washing process. The mathematics of the very complicated dynamic characteristics of this process have been solved. However, attempts to control this kind of washing system have generally not been very successful. This is due to the lack of reliable measuring instruments and analyzers, which are necessary to provide the critical information needed for the optimization and control of this process.

Of the total Pulp Mill Sodium Losses, 94% of the Free Sodium (as NaOH, Na2CO3, Na2S, Na2SO4 and small amounts combined with organic matter), are lost as carry-over or “Washing Loss.” Looking at overall operating cost and efficiency the following should be considered: 1) the cost of make-up chemicals to replace the losses, 2) maximizing the “Solids Yield” for its heating value at the Recovery Boiler, 3) minimizing the “Dilution Factor” to save steam at the evaporators and monitoring the shower solids at the remaining stages to quickly detect possible washing problems. In the case of an evaporator limited mill the solids and dilution factor issues are amplified. Also for bleach mills, no bleaching action can take place until the excess sodium in the pulp has been neutralized adding the cost of expensive bleach chemicals.

Application Technology
The hardware package being offered combines both the Duralyzer-NIR analyzer and rotary consistency analyzers specifically designed for reliability and low-maintenance. For the consistency analyzers, dilution flow measurement and control must be available or added. Retractable gate valve assemblies are provided for the consistency analyzers and sampling systems for the Duralyzer-NIR. A Consulting Service for the mandatory process study to develop the mathematics that need to be programmed to the existing DCS System (or an auxiliary computer) is also included.

All the critical Brown Stock Washing Plant Indicators, like Weight Ratio (W), Relative Yield (Y), Relative Washing Loss (1-Y), Washing Liquor Ratio (R), Dilution Factor (DF) and the entire plant Efficiency Factor (E) are being calculated by the Duralyzer. All of the critical factors needed to optimize any countercurrent washing plant are continuously displayed, recorded and are at the operator’s disposal for optimum operation.

The last washer Fresh Water Flow is controlled based on a combination of the above information. In a well instrumented Washing Plant, the upstream shower flows are automatically controlled to maintain steady Seal Tank levels, as well as Washer Vat levels to control the drum speed. To monitor the performance of each washer, the filtrate shower total Dissolved solids is measured in order to detect and alarm in case of plugged or partially plugged filtration, excess soap formation or any other disturbance of the process. For the Kraft Process, guide lines have been established between Weight Ratio (W) and Yield (Y) to arrive at the optimal operating point; therefore the System will be able to suggest to the operator the changes needed for the best efficiency that is available for any individual Washing Plant

Manufacturer: R.E. Hodges; Auburn, Alabama

Brown Stock Washing Application:

Of the total Pulp Mill Sodium losses, 94% of the free sodium, as well as some combined with the organic matter are lost as carry-over or "Washing Loss." Looking at overall operating cost and efficiency, the first consideration is the cost of make-up chemicals to replace these losses.

The second consideration is maximizing "Solids Yield" due to its heat value in the Recovery Boiler and minimizing "Dilution Factor" to save steam at the evaporators. Additional considerations are evaporator limitations in many mills and overall chemical consumption at bleachable grade mills.

With all the measurements available as shown below, the critical Brown Stock(B.S.) Washing Plant Indicators, like Weight Ratio (W), Relative Yield (Y), Washing Liquor Ratio (R), Relative Washing Loss (1-Y), Dilution Factor (DF) and the entire plant Efficiency Factor (E) can be calculated. The critical factors to optimize any countercurrent washing plant are continuously displayed as shown in an example below. The last washer Fresh Water Flow is controlled based on the above information and the traditional B. S. Washing instrumentation is left to the user.