Green liquor sludge

Our own method for analysis of green liquor containing green liquor sludge, lime gravel and lime

The chemical pulp processes' kidney - that is the separation of green liquor sludge from green liquor. As pulp processes are getting increasingly closed, the importance to see how and if the sludge composition changes also increases in order to make sure that the separation works 100 percent. MoRe has a special method to analyse metal content in green liquor as well as green liquor sludge.

Many metal compositions disappear from the recycling process together with the green liquor sludge sedimented or filtered during sludge separation. Otherwise these metal compositions cause quite a few problems in the lime cycle. The green liquor must be clean enough and without green liquor sludge during causticising.

When analysing metals in green liquor containing green liquor sludge it is important to know how the customer wants the samples to be analysed. Before analysis we need to know if the sample should be analysed after shaking (containing green liquor sludge) or if the metal content in the green liquor is interesting (sedimented sample). The green liquor sample is treated with peroxide and analysed using the standard addition technique with ICP-OES. When analysing green liquor samples containing green liquor sludge we use a method developed by MoDo R&D.

We first separate the sludge from the green liquor and than treat the two fractions separately. The treated fractions are then added together and analysed with ICP-OES. The result shows the different metals and their content.

It is important to keep track of especially aluminium and magnesium in the liquor cycle. That is why it is necessary that the sludge separation works properly, not releasing sludge together with the green liquor. Our green liquor and sludge analyses make it easy to keep track of the metals disturbing the process and thus solve problems arising later in the process but caused during green liquor sludge separation.

With increased closing of the pulp process, the process disturbing metal content increases and thus also the risk for problems. Scaling may for instance be formed in pipes and heat exchangers which decrease their efficiency. Also filtrations may be negatively influenced.

Lars Sundvall Manager Process Technology. +46 70 526 52 21 E-mail