Proceeding Articles

The design of more responsive control systems for papermachine dryer sections requires a knowledge of the coupling between web moisture content and changes in basis weight and machine speed. The interactive effect of changes in basis weight and machine speed on the measured moisture content must be known to allow proper compensation.

An estimate of the steady state coupling coefficients was made by forming an approximate mathematical model and calculating the steady state response surfaces for average web moisture content versus machine speed and basis weight. The model was a realistic representation of the partial differential equations relating heat conduction and vapour diffusion within the web. Approximate, constant values of web properties and transport coefficients and the alternating boundary conditions characteristic of conventional cylinder drying were used . Basis weight of 26-90 lb/1 000 ft2 and speeds of 800-1800 ft/min were studied.

The calculated coefficients showed that, for typical production conditions of 421b board at 1 400 ft/min, a 1 lb change in basis weight would be expected to produce a 2 percent change in web moisture content; a speed change of 100 ft/min would produce a 5 percent change in moisture content. The dependence of the coupling coefficients on the level of basis weight and speed was also demonstrated. The coupling coefficients for basis weight and for speed both increased approximately linearly with the operating speed, whereas the increases in both coefficients through basis weight changes were less significant. These results are of use in the design of non-interactive control systems for papermachine dryer sections.

Although the calculated results were restricted to the steady state gains for this system, an indication is given of the possible use of a more complex model in studying the dynamic behaviour of the drying system.

Control systems, whereby a final customer may obtain a satisfactory product after it has passed through several stages of manufacturing, are characterised by considerable time delays in both feedforward and feedback paths. These systems are examples of the industrial dynamics problems investigated by Forrester and others. The matter under discussion in this paper is concerned with the establishment of sensible control systems and the maintenance of their reliability and accuracy. It specifically considers paper products used in data processing as punched cards and forms for optical character recognition.

Models of the behaviour of national economies have been developed and popularised for some time. The economic behaviour of whole industries has also been examined and statistical analysis has uncovered at least the main features of the working of a number of industries. There is no difficulty in principle in carrying this process of analysis on to the examination of individual products . The paper  discusses these topics and illustrations are provided of national and industrial economic models and the behaviour of several product groups in the U.K. paper industry are examined. The results show that statistical analysis can reveal important economic influences at work, but that it is necessary to beware of special factors, technical, political and social, which can be of overriding importance for particular products at particular times.

Control of a complex organisation requires that its response to decision inputs be predictable . Traditionally, this has been made possible by almost breaking down the organisation into very simply coupled subsystems. This allows decision-makers to use a relatively simple and usually informal model.

Size and environmental rate of change are now tending to make the decoupling hard to make effective. Industrial dynamics provides both a theoretical structure and a computer simulation technique designed to provide decision-makers with a richer model of the dynamic feedback processes generally involved in industrial operations. The structure defines a system in terms of a closed boundary containing feedback loops, which in turn are formed by the relation between level and rate variables . The DYNAMO compiler allows models of systems conceived on these lines to be programmed in a straightforward way so as to allow experimental investigation of the system variables. The paper discusses case studies and concludes with notes on model validity and the problem of data.

Up to a few years ago, all industrial processes were either batch processes or were operated on a steady state basis, although some (like papermills, automatic looms and steel-rolling mills) operated in steady state only for a limited period until the specification or grade of the output had to be changed. Thus, industrial processes can be divided into three classes:

1. Batch processes.
2. Continuous processes.
3. Quasi-batch processes.

History and philosophy of control systems

The past decade has witnessed a major advance in the use of process control systems by the paper industry. Before that time, very few variables were controlled automatically, many instruments were either indicating or else, if controlling, were operated in the manual mode much of the time and the degree of instrument reliability and accuracy in the average mill did not promote operator confidence or use . Pneumatic controllers performing simple control loop strategies were the norm. Making paper was an art and frequently different papermakers would operate a machine in quite different ways to make the same given grade of paper. Fairly broad tolerances in paper specifications were accepted in the trade, since few machines could achieve or maintain very stable operations.

There is no difference, at least in principle, between control of administrative systems and control of other systems. The purpose of a control procedure is to specify the way in which the behaviour of a system can be affected. The controller of the system scrutinises information about the performance

of the system and every so often he has to make a decision, namely, to choose between several courses of action open to him. This decision is transmitted to the system with the expectation that it will react in a certain way. This cycle of events monitoring and evaluation of the system’s behaviour, followed by a decision for corrective action is the essence of the control process, irrespective of whether it is control of inanimate systems or managerial control of industrial enterprises.

Optimizing the fibre property distribution could increase the pulp properties as well as the process efficiency of chemimechanical pulps (CMP/CTMP). This can only be achieved with a better understanding of how evenly distributed sulphonate concentrations are between the individual CTMP fibres. Given that the quality of wood chips varies with the chipping methods used in pulpwood processing and sawmill processing, as well as with the chip screening system, it is a challenge to develop an impregnation process that ensures even distribution of sodium sulphite (Na2SO3) in the liquid used to impregnate the Chemimechanical pulp (CMP/CTMP). Therefore, the distribution of sulphonate groups within wood chips and individual fibres must be measured at the microscale level. On a micro level, the degree of unevenness, i.e., the amount of fibre sulphonation and softening before defibration, cannot be determined due to the use of excessively robust or complex processing methods. By having it, we could better understand how sulphonation occurs before defibration, so we could improve impregnation. Developing a laboratory scale miniaturized energy dispersive X-ray fluorescence (ED-XRF) method that measures sulphur distribution at the fibre level can enable us to study the influence of impregnation improving processes.

The export of market kraft pulp is a significant part of the Canadian forest products industry. Although northern softwood kraft pulps are premium products in the international pulp marketplace, there is interest in producing truly specialty pulps whose properties extend beyond the physical and chemical property boundaries of current pulping and bleaching operations. Whereas the pulping and bleaching literature has for decades focused on improving pulp properties, we know of only a few examples of post-bleaching fiber modification in pulp mills. Instead, the pulp producers leave it to papermakers to tune paper properties with chemical additives in the papermaking processes. Most papermill fiber chemical treatments including sizing additives, dry strength resins, and wet strength resins, involve interactions with the exterior surfaces of pulp fibers. We propose that market pulp mills producing dry, or nearly dry, pulp offer a unique opportunity to influence fiber surface properties by fixing reactive polymers onto fiber surfaces when the pulp is heated on pulp drying machines. The objective of the work described herein was to develop new approaches to modify pulp fiber surfaces at the end of the pulp mill bleaching processes through polymer grafting. This contribution covers the highlights of recent publications [1-4].

Cellulose nanofibril (CNF) foam, which has advantages of sustainability and biodegradability, has a potential to apply to diverse fields including packaging, thermal insulation, and absorbent. In recent days, the oven drying of Pickering-stabilized CNF wet foam was proposed as an alternate approach to manufacture CNF-based porous foams. To produce CNF foam with uniform structure, the properties of wet foam are very important. In this study, carboxymethylated cellulose nanofibril (CMCNF) was used to prepare CNF foam. The effects of wet foaming conditions such as CMCNF consistency, surfactant amount, and shear rate on the properties of the wet and dry foams were investigated. A low addition level of surfactant led to insufficient generation of bubbles, whereas high levels of surfactant generated unstable wet foam. A proper amount of the surfactant and CMCNF consistency yielded wet foams with excellent stability. CNF wet foam with high stability resulted in CNF foam with uniform pore structure and high compressive strength. The shear rate during wet foam generation also had a significant impact on the foamability of wet foam, which determined the density and the pore size of the oven-dried CNF foam.