Industrial Refractometers and Green Liquor Scale Mitigation

Industrial Refractometers and Green Liquor Scale Mitigation

Green liquor, a by-product of the kraft process, is the dissolved concentration of sodium sulfide, sodium carbonate, and other compounds in solution. Keeping track of its component concentration is important to the pulp processing cycle. Green liquor scaling, which includes calcite, sodium aluminosilicates, and pirssonite,  is a problem in most kraft process mills and can cause huge maintenance problems and slow production. Understanding the formation of, and potential ways to control, these formations scale is critical for optimal safety and performance.

Industrial inline process refractometers, such as Electron Machine's MPR E-Scan, are used to measure the green liquor dissolved density, or TTA, at two stages in the process: after the green liquor dissolving tank and after the green liquor clarifier. The inline measurement, with the refractometer sensing head mounted directly in the main process lines, allows real-time control of green liquor dilution to meet target TTA set-points. The measurement is also used to indicate (and prevent) excessive green liquor density and the resulting dangerous impending crystallization within the dissolving tank, and lower the potential for scaling.

Refractometer operating conditions must be optimized for close monitoring and control of green liquor density. Consideration of scale and coating build-up on the optical sensor on the refractometer sensing head is a primary area of concern. A clean sensing head will allow maximum accuracy of the refractometer,  maintaining tight density control, minimize scaling, and increasing kraft process quality.

With overall quality and safety in mind, the use of a refractometer sensing head cleaning system is compulsory. The use of ancillary inline cleaning systems, such as Electron Machine's HPC-2 High Pressure Cleaner, that use pressurized water heated to the process temperature, will clean the refractometer optical components and therefore mitigate scaling issues and the related quality, safety, and production problems in the kraft process.