Systems for Fiber Stock Preparation

The target of fiber preparation systems is to modify the raw materials for paper production so that the stock suits the requirements of the paper machine as well as those of the finished paper or board. Raw materials are virgin fibers from different sources such as chemical pulps from hard- or softwood or mechanical fibers like SGW, PGW, TMP or CTMP. The largest portion of raw materials today is recovered paper which is processed into secondary or recycled fibers. The recovered paper grades differ a lot as regards fiber compostion and cleanliness levels (see Vol.l). Therefore the processing systems have to take into account these differences as well as the various quality requirements of the finished stock. 

The systems for primary fiber preparation are less complex than a recovered paper processing system due to the much lower level of impurities and contamination in virgin fiber pulps. Depending on the paper type produced and the availability of the various fiber types, a paper machine, or especially a multi-layer board machine, may be fed by several different fiber qualities, each of them treated in separate lines with different process steps. 

---

Systems for Fiber Stock Preparation l97 4.3.2.1.1 System for Wood-containing Graphic Papers... 

Systems for Fiber Stock Preparation l99 Table 4.3 Effect of the process stages on quality parameters of wood-containing DIP. 

The objective of fiber stock preparation systems is to modify the different ingoing raw materials in such a way that the finished stock finally supplied to the paper machine suits the requirements of the paper machine and of the quality demands put on the produced paper or board. The raw stocks used are the various types of virgin pulps as well as recovered paper grades. They are available in the form of bales, loose material or, in the case of integrated mills, as suspensions. The finished stock is a suspension of defined quality as far as the mixture and characteristics of the fibers, additives, and impurities are concerned. This quality essentially determines paper machine runnability and is the basis for the final paper and board quality. 

The main unit processes, their principles and the machinery appHed will be described in the next sections followed by a description of fiber stock preparation systems for different kinds of fiber raw material and final application of the finished stock. 

The main field of automation in a fiber stock preparation system Hes in the control of those operational parameters which are important for every stage in the process e.g. consistency, flow, pressure, level, power consumption and tempera-... 

The purpose of repulping or slushing is to break down the dried primary fiber pulp or recovered paper into individual fibers or, at least, to form a suspension which can be pumped. In the latter case the remaining flakes have to be broken down in subsequent deflaking machinery. Repulping is needed not only at the beginning of the stock preparation system but also for the wet or dry broke from the paper machine. 

Again, the fresh water is added only at the paper machine. White water 11 is used for redilution after thickening in the stock preparation plant. The save-all clear filtrate is used for make-up in the fiber preparation system. Filtrate from the thickening stage in the fiber preparation system is the main source of water for slushing and dilution. Waste water is sent as filtrate from reject handling to the end-of-pipe effluent treatment. 

A substituted fatty anide condensate wax concentrate, designed for use in the preparation of stock softener solution or suitable softener products at 20%-27% solids. This material requires the use of acetic acid in order to produce a cationic softener system. This wax softener is recommended for cotton synthetics, and blends of these fibers. 

---