JMP Engineering (Corporate)

Causticizing – Chemical Recovery Process Optimization

Objectives

  • Produce high quality and consistent white liquor
  • Reduce pressure filter maintenance
  • Minimize energy consumption
  • Minimize chemical use and losses
  • Increase downstream digester efficiency

Process Summary

The Causticizing Control System developed by Automation Applications Inc, LLC (AAI) utilizes the latest concepts in control strategy for the causticizing process using the tools available in modern computer based control systems and instrumentation typical of the causticizing process. By incorporating functionality which has traditionally been under manual control, and moving to a control strategy with a predictive model, the system improves caustic efficiency, maximizes white liquor quality and throughput, and improves digester, evaporator and recovery boiler efficiency.

The recausticizing process, is an essential element of the chemical recovery process in pulp manufacturing facilities. The process includes mixing clarified green liquor with lime, causing a chemical reaction to produce sodium hydroxide, sodium sulphite and calcium carbonate. The calcium carbonate, an insoluble mud, is filtered out. The calcium carbonate mud is then washed, filtered and calcined in the lime kiln where it is converted back to lime suitable for slaking more green liquor. The sodium hydroxide and sodium sulphite or ‘white’ liquor is then introduced with wood chips into the digester.

A general philosophy of control systems design used by AAI is to provide the highest level of control functionality and flexibility at the lowest level (regulatory level) of a system. This not only allows the mill to change operating priorities as conditions change, but provides the greatest opportunity for cost reductions and operational efficiency gain. In addition, AAI places heavy emphasis on user interface and system functionality which leads to quick operations acceptance of the control implementation.

Benefits

AAI furnishes guarantees of performance with installations of Causticizing Optimization Systems based on a survey of existing operation. Guarantees typically involve measurable system and process parameters such as percentage of time on full automatic, process throughput, or percent variations. AAI is confident that installation of a system will result tangible benefit for the end user and is willing to back installations with a firm warranty. However, for the benefit of the client as well as AAI, it is important that a set of precisely measurable parameters make up the boundaries for determining process performance before and after system installation.

Some typical areas of system performance include:

  • Caustic efficiency is maintained at a determined level with ±%
  • TTA variation is maintained at defined %
  • Automatic control will be provided by the system 95% of the time

Conclusion

AAI believes that competitive advantage can be gained by pulp and paper industry manufacturers through the proper application and use of today’s computer and control equipment. This is proved every day by AAI engineers who leverage their technical systems knowledge with process experience to provide clients with significant dollar savings through higher process throughputs and efficiencies. The AAI causticizing system is a specific example of this.

With this installation a mill can expect reduced energy costs through improved efficiency, reduced downtime and improved chemical recovery performance in lime kilns, digesters and recovery boilers.