Inorganic scale buildup in a bleach plant- : a mill case study

When a particular mill modified its bleaching process, the changes led to the buildup of calcium carbonate scale Scale built up in the chute and in the thick stock pump leading from the discharge of the washer for the alkaline extraction stage to the inlet of the up-flow tube of the D 1 chlorine dioxide stage. The buildup of scale restricts the stock flow and ultimately the production. The mill was shutting down to clean the bleach plant every seven weeks, but there were some times when the mill had to shut down prematurely because of excessive scalling. The lest occurrence of unscheduled downtime pmmpted the mill personnel to try an antiscalant in the bleaching process. The rate of antiscalant addition was varied to optimize it, and the discharge pressure of the thick stock pump was monitored along with the daily production rate. Adding the antiscalant at the upper pond flow on the alkaline extraction washer controlled the excessive buildup of scale and resulted in a daily production increase of 10-50 tons/day.