SUSPENDED SOLIDS IN GREEN LIQUOR
APPLICATION NOTE 4.004.A0
INDUSTRY-PULP & PAPER
INTRODUCTION
The pulping process within a mill has always been a concern for operations and maintenance. It is the area in which chemical reactions are very critical to the overall process including the efficiency of the causticizing area.
APPLICATION
Our main concern in this application is to monitor for suspended solids in the clarified green liquor. By monitoring the solids, the operators are able to divert a potentially high suspended solids level from continuing downstream into the causticizers and white liquor clarifier. This is a key measurement since the suspended solids level can dramatically affect the efficiency of the process.
SOLUTION
The Monitek acoustic suspended solids monitor will continuously check the clear green liquor and immediately detect the presence of solids (dregs). The carryover of dregs in green liquor is a major problem in the operation of the recausticizing process. A good target is for dregs (TSS) in the green liquor to be 50 mg/l or less. A high level of dregs carryover (>200) will cause problems in lime mud filtration and reduce lime availability (%CaO). (In processes where polymer is used, the monitor allows for feed forward control for polymer addition due to high dregs content into the clarifier and feedback for high dregs content in the clarified green liquor.)
The ultimate goal is to reduce the level of downstream contaminants from entering into the causticizers, white liquor clarifiers and white liquor digesters.
In-line monitoring has been a problem in the past, due to the nature of the process liquid. The green liquor is harsh and has a propensity for fouling, however Monitek offers an alternative to traditional optical methods of detection. Monitek’s patented acoustical system allows maintenance free operation in the harshest environments.
ADDITIONAL COMMENTS
The current monitoring method in most plants is by lab sampling, but large amounts of contaminated material can travel through the process before being detected. Therefore, continuous in-line monitoring is preferred for immediate action. Note: Similar monitoring can be done for suspended solids in white liquor. (For more information see Application Note 4.003.AO.)
