Retention and drainage systems

Once a system has been adopted by the papermaker, the supplier has also to provide or ensure reliable product supply, reliable make-up equipment, reliable product dosing, ongoing technical support and troubleshooting services. Failure in any of these key areas will compromise the retention and drainage system chosen. 

Regular reviews and reappraisals of the retention and drainage system are essential to maintain the high level of performance required by the papermaker, as changes to the pulps, fillers, effect chemicals, water usage and machinery can all have a significant effect on the system efficiency and may require an alternative product/ system to be implemented. 

The following products form part of the considerations for the retention and drainage systan which will eventually be used and should therefore be looked upon as components of the retention and drainage system - as any change in the product used or the dosage, application point, etc. can have a significant effect on the retention and drainage aid efficiency on the machine ... 

Machine production rate Bigger, faster machines generally require a more robust retention and drainage system due to the higher shear forces in the headbox and on the wire. 

Retention and drainage aids are chemicals which are added to the fibre and filler suspension to assist the efficiency of the filtration process. Growth in recent years in the use of retention aids has been greater than that of almost any other paper chemical additive. It has been caused by a combination of factors increased machine speeds, the increased use of filler in alkaline systems, the increased use of recycled paper and the growing tendency to use fillers in newsprint. Retention aids are water-soluble polymers which may be cationic,... 

Increased water system closure and iuCTcased water temperatures are also altering the environment within which the retention and drainage aid has to function, requiring an alternative approach in many cases. 

There is a large range of retention and drainage products available from many suppliers, which can be used alone or in combination as retention systems. These products and systems are identified chemically, their use explained and guidance given on the application, testing and suitability of the various systems. 

The paper machine and system chemistry factors which can affect the retention and drainage aid performance are discussed along with some troubleshooting guidelines and examples. 

For the supplier, having a wide range of retention and drainage aid products and systems is essential as everything starts with the needs of the papermaker, the products made and the papermaking machinery used. 

As machine speeds have increased and wet-end system chemistry has become more complex, the demands on the retention and drainage aid have increased considerably. This has led to the development of an increasing number of retention and drainage aid systems which incorporate two, three or even four components selected from the above list. A very general representation of the time frame for this development is shown in Fig. 3.3. 

All of the above retention and drainage aid products and systems are in use currently. The system used depends on machine type, machine speed, paper/ board type, production rate, requirements, etc. 

The basic criteria used for selection of the most suitable retention and drainage aid product or system, include the following ... 

Stock approach flow This can be a limiting factor in application of the most efficient products. The papermaking systems need to be able to cope with the changes necessary for implementation of an efficient retention and drainage aid system. Restrictions on pulper capacity, fan pump capacity etc. can reduce the suitability of the most effective system, requiring a less powerful system to be used, as can limited machine speed, water removal capacity and drying capacity. 

Paper/board quality All retention and drainage aids products and systems affect the sheet formation. The need to maintain acceptable formation can limit the type of system that can be applied and also the level of retention and drainage performance which can be sustained. As many trials fail due to an over-performing retention aid as fail due to an under-performing retention aid. 

As the retention and drainage aid is the last chemical addition to the papermaking system, it generally comes under snspicion whenever retention or drainage effect is... 

Additives - all additives have the potential to affect the system response to retention and drainage aids - the main considerations are the additive charge... 

Optical whiteners (OBA, FWA) are anionically charged and can have significant impact on the system charge and effectiveness of the retention and drainage aid. 

All aspects of the stock flow system and the paper or board machine equipment will have an effect on the retention and drainage aid. 

Initial choice of the retention aid/system which can be used may depend on the capability of the fan pump flow or machine speed to increase it may require adjustments to the foil drainage elements or vacuum boxes. Any changes to the system need to be evaluated for impact on retention and drainage aid - machine wires in particular. Changing a wire can inaease or decrease first-pass retention on the machine by as much as 10% in extreme cases. Where drainage is readily achievable, using a more closed wire can be one route to increased retention. 

Table 7.1 shows the trade-offs that can be made with different methods of achieving increased dry strength. The papermaker must assess his needs versus the disadvantages of alternative approaches. The use of a chemical system can offer other collateral benefits as well as disadvantages. Examples are improved retention and drainage, increased porosity, promotion or interference with other chemical additives, and increased BOD and COD in the water system. 

The solution proposed in the paper uses experience of approved rainwater and flood management of developed countries, mainly from stormwater management of SUDS and rest from LID and BMPs, with consideration of Fujian s actual conditions, to design rain adap-tative landscape system for city. Based on linear landscape of retention and drainage which leads water into dotted water landscape of reservoirs, combined permeable paving, it forms primary, intermediate and advanced stormwater reducer made by rain adaptative landscape to perform source, midway and end controls. 

Normal physiological functioning of the sinuses depends on ostial patency, mucociliary function, and the quantity and quality of secretions. Retention of sinus secretions may result if ostial diameter is compromised if cilia are damaged, impairing mucociliary clearance of secretions or if increased viscosity or volume of secretions exceeds the clearing capacity of the sinus mucociliary drainage system. 

The passive targeting of polymeric micelles to solid tumors can be achieved by the enhanced permeability and retention effect (EPR effect). Maeda and his coworkers presented this new drug targeting strategy in 1986 (31,32). As illustrated in Fig. 3, the vascular permeability of tumor tissues is enhanced by the actions of secreted factors such as kinin. As a result of this increased vascular permeability, macromolecules selectively increase their transport from blood vessels to tumor tissues. Furthermore, the lymphatic drainage system does not operate effectively in tumor tissues. 

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