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Where will mechanical pulping be in 2020? The date may be a long way off, but predicting trends does not necessarily take 20-20 vision
By Erkki Huusari
Moving ahead with mechanical pulping
Looking ahead to 2020 may be jumping the gun in most industries, but in terms of mechanical pulping developments the predictions are not that premature. For example, what has happened to mechanical pulp production for printing papers since 1980? Not that much really. The main processes - thermomechanical pulping (TMP) and pressurized groundwood pulping (PGW) - are basically the same today as they were 20 years ago. There have, of course, been vast improvements in pulp processing after the defibration stages and developments in screening have greatly enhanced the properties of mechanical pulp for high quality printing papers. But in the broadest sense, dramatic shifts in the technology have been few and far between.
Continuous operation holds the key to grinding
As a result, it should be reasonable to try and make some very long term predictions about the future of mechanical pulping. Going forward, the main driving forces behind developments will be:
• developing paper grades to improve the competitiveness of the printing industry
• developments in the properties of available wood raw materials
• the availability and cost of electricity.
Taking the first point, tough competition within printed media, as well from electronic media, will force the printing industry to reduce costs and improve productivity in the future. The need to lower costs will boost the trend toward less expensive paper and lighter paper grades. Printers will improve productivity by installing wider and faster printing presses and good paper runnability will be a must. In addition to lower costs and improved productivity, high brightness papers with the best possible printability will be used to boost the competitiveness of printed media.
Secondly, the variation in fiber characteristics between different species, and even between individual trees of the same species, has a great impact on pulp properties. Going forward, wood properties will determine the selection and development of the pulping process. For example, mechanical pulping of pine will require a system that can handle problems caused by the large amount of resin in the wood. The successful use of aspen groundwood and aspen chemi-thermomechanical pulp (CTMP) in traditional woodfree papers will enlarge the future applications of mechanical pulp. The paper industry will also pay more attention to the selection of wood raw materials for mechanical pulping. Tree breeding, forest management, and in the longer term, genetic engineering of wood fibers, will be used to select the most suitable wood for future mechanical pulps.
Finally, developments in mechanical pulping will also depend on the availability and cost of electricity. It is unlikely that there will be a general shortage of electricity, but prices may increase due to taxes set on energy production and usage. Higher energy prices will undoubtedly improve the competitiveness of low energy mechanical pulping such as pressurized groundwood. But they will also favor the use and development of low energy TMP systems.
Technical edge
Taking all the above factors into account, suppliers will be focusing their attention on several areas when they look into future technological developments. These include:
• low energy refining
• large capacity production units
• continuous pressure grinding
• advanced fractionation technology
• online control of pulp quality
• management of mill water systems.
In the 1990s improved screening technology and effective refining of screen rejects made the production of paper with improved properties possible. This increased the use of mechanical pulp for higher quality printing papers. Production capacities of future refiner lines will continue to increase. Figure 1 shows that the motor size and production capacity of refiner lines producing TMP for newsprint has increased rapidly over the years. The industry is likely to see similar developments in the production of low freeness pulps.
Figure 1 - Installed Refiner Power
In the future, a single, high capacity TMP line will be able to produce all the mechanical pulp needed on a modern, high speed paper machine in most cases. New high strength and corrosion resistant materials will also enable suppliers to construct more accurate and rigid machines with less maintenance needs. Going forward, new materials are likely to extend plate change intervals as well.
In the stone groundwood process, modern water jet pulp stone conditioning technology has greatly reduced the quality variations after individual grinders. On top of that, continuously operating PGW grinders of the future will eliminate the pulp quality variations caused by the batch-wise operating principle of today's grinders. Not only will this have an impact on quality, but it will also allow a noticeable increase in production.
Recently the PGW process has shown its excellent potential to cope with the most demanding printability properties of the highest printing paper grades.
Figure 2 - Screening Technology Development
Fine tuning
Separation of fines and other developed material after the defibering stage makes it possible to give an extra-intensified treatment to coarse undeveloped fibers in the later process stages. For example, trials with enzymatic treatment of coarse TMP rejects have considerably reduced the need for refining energy without the deterioration of pulp properties. In future, further improvements in the functional properties of paper will be reached by adjusting the amount and properties of different fiber fractions. In fractionation technology, there is also further room for improvement as most of the existing systems with successive dilutions and thickening are complicated and expensive.
In addition to variations in wood properties, poor control of refiner throughput and refining consistency are the main reasons behind pulp quality variations. Improved technology to control the refining conditions and measure the properties of pulp and raw materials will make a reliable online control of pulp quality possible.
Refining intensity could be adjusted during the normal operation. In this way, it would be possible to reduce quality variations caused by changes in the wood raw material. The new "constant operating point" control strategy of the grinding process will maintain grinders in an operating point that provides the desired quality at maximum production rate at all times.
Finally, improved management of mill water systems will boost the efficiency of pulp and paper production. Separating pulp and paper mill water systems will result in reduced use of chemical fixatives and will increase paper machine runnability as well.
When precipitated on fibers, different components released into process waters in pulping and bleaching will have an influence on the bonding ability of the fiber surface. Pulp properties could be improved by enzymatic modification of dissolved and colloidal material, as well as by enzymatic treatment of different fiber fractions. Improved understanding and control of the fiber surface chemistry will greatly improve the overall operation of future pulp and papermaking systems.
Figure 3 - Suppliers of Mechanical Pulping Systems
Gathering supplies
The picture of the supplier industry has changed considerably since the early 1970s. Apart from one local manufacturer of grinders, there are only two main suppliers left today in the field of mechanical pulping. Higher levels of technical know-how, research and development, tough competition and shrinking markets have led to today's consolidation.
At the same time, these factors will enable the remaining suppliers to become more competent producers of complete pulp and papermaking systems. They will also be able to provide better services, not only to meet the paper industry's operating demands, but also to respond to its development needs in the future.
Erkki Huusari is general manager for technology at Valmet Mechanical Pulping in Finland
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