Causticizing Analyzer

The Causticizing Liquor Analyzer Solution: This solution is a turnkey application for carrying out white and green liquor analysis at strategic locations throughout the causticizing process. The standard configuration supports four sample lines. These include sample points from the green liquor to the slaker, 1st causticizing tank, last  causticizing tank and from the white liquor clarifier. Utilizing a series of industrial spectrometers white and green liquor analysis provides measurements for Total Titrateable Alkali(TTA), Active Alkali(AA) and Effective Alkali (EA), of which all individual chemicals are calculated and displayed.

The analyzer package consists of an industrial spectrometer configured for white & green liquor analysis, an acid cleaning system to remove any scale buildup from the sampling optics and all the necessary sampling hardware to collect white and green liquor from the process. Samples are brought into the system with ½” Teflon tubing or equivalent and ¾” EPDM hose. Sampling and cleaning is completely automated and is controlled by the spectrometer and sampling system microcontroller.

Application Technology
Reliable and accurate green liquor analysis is important for optimizing lime usage in the slaking process. The green liquor sodium carbonate (Na2CO3) level is needed to be accurately known to ensure the addition of the correct amount of lime. The two primary sources of variation that interfere with control are lime quality and green liquor variations. Knowing the green liquor composition, one source of variation is eliminated.

With the online analyzer, the green liquor is trimmed in real time to meet target total titrateable alkali (TTA) or Na2CO3 levels. The lime feed rate then only depends on green liquor throughput leading to reduced variations in lime screw speed. Alternatively, variations in green liquor composition and green liquor flow can be used to determine the required lime addition rate. Either approach requires an accurate online analysis of the green liquor entering the slaker.

The DURALYZER-NIR green liquor analyzer provides the Active Alkali (AA) and TTA measurements in a timely, accurate and reliable manner. Additionally, green liquor effective alkali (EA), total Dissolved solids (TDS) and total Dissolved dead-load (TDD) levels are also available from the same analyzer.

Manufacturer: R.E. Hodges; Auburn, Alabama

Causticizing Control Application:

The first step of the Causticizing Advanced Control is the stabilization of the green liquor TTA going to the Slaker. A ratio control takes into account both the flow and TTA measurements of the weak wash trim and green liquor main stream. This drastically improves the stabilization of the EA out of the final Causticizer.

With all of the GL components known from the Liquor Analyzer, the CE% control is a feed forward function, controlled by the calculated optimum set point from Goodwin's curve. Feedbacks from the first and last Causticizers compensate for changes in the lime quality. Feed back control is performed by a Model Predictive Controller (MPC) due the long lag times in the process that can be several hours.

Measurements for MPC are mainly coming from the DURALYZER-NIR. This Advanced Control will stabilize the white liquor EA and can result in the savings of hundreds of thousands of dollars. Payback can be counted in months versus years.

• Stabilized Effective Alkaline
• Maximized white liquor production
• Less dead loads- energy savings
• Reduction in soda losses
• Reduction in make-up chemicals
• Reduction in Fresh Lime Make-Up
• Reduction in Fuel Consumption in the Kiln
• Energy Savings in Digester
• Steam Savings in the Evaporator
• Energy Savings in Recovery Boiler