OPTIMIZATION OF RETENTION IN WET END OF PAPER MAKING

Abstract

Paper making is a process involving removal of water from very low consistency furnish at wire. Paper making furnish is hetrogenous in nature, consisting of fibers, fiber fines, inorganic fines and chemical additives, in the form of solution, suspension or emulsion. Removal of water from furnish suspension is carried out at wire part under certain differential pressure created by various drainage elements. The removal of water at the wire part of Fourdrinier cause the drainage of almost all the furnish components. The proportion of fiber retained in web is relatively more (95%) , although some of these pass through forming fabric open area till first fiber is retained. The fines start retaining there-after. More and more fines are retained as web consolidates and water tends to filter out through the porous mat of web. The amount of fines retained is basically related to open area of forming fabric and shape of drainage channel of forming fabric. However, the retention of the smaller fraction can be enhanced by creating favourable physio-chemical conditions for absorption of chemical additives and finer constituents on bigger size fiber. The physio-chemical conditions responsible for retention phenomenon are CSF, Temperature, quantity of additives and charge level of system. The reported investigations on a Fourdrinier commercial writing printing grade paper machine were designed to study the effect of few papermaking variables on First-Pass Retention. The papermaking variables studied were CSF of machine chest stock, paper machine speed, inorganic filler loading level, pH of back water, temperature of head box stock, dilution of head box stock, dosage of guargum, dosage of cationic starch, Zeta potential of. head box stock, basis weight of paper and type of forming fabric used. The investigations were carried over a period of 8-9 months where-in the data have been collected and statistically analysed to states of one variable and others being constant. The conditions were observed and recorded during normal production schedule and later analysed for constants and variables to interpret the factors affecting First-Pass Retention. First-Pass Retention of paper machine was calculated by determining consistencies of head box stock and back water of paper machine.