Lime slaking is a pivotal operating step in the recausticizing plant. This is where dry meets wet and not only is the cooking liquor reformed, but also where the lime mud slurry is created. The Slaker is responsible for ensuring proper lime and green liquor contact time and mixing and should take about 20 minutes. The slaker can be divided into two major sections; the bowl and the classifier. Green liquor, a solution of sodium carbonate and sodium sulfide, is often introduced to the bowl via a cyclone type feeder. The lime addition is added through the centre of this device. It is very important that the green liquor be of the best quality possible, i.e. low dregs load. Combining the liquor and lime requires a balance of stoichiometry, temperature control, agitation, and vapour and dust removal. Proper slaking introduces to hot green liquor, 90-95C (195-204F), to cooled lime nodules. An exothermic reaction begins when the lime contacts the solution and can bring the temperature up by 12-14C (22-25F). A key operating parameter of lime slaking is temperature control. Being able to operate the slaker just below boiling point without boiling is essential to creating large lime mud particles while avoiding grit carry over. Grit carryover may lead to a number of unwanted operation and equipment issues that will be discussed later.
Over the next four/five months McFarlen Engineering will detail and review Slaker operating conditions, design considerations and upset conditions. Please contact McFarlen Engineering at Office@recaust.comfor more information.