By Mark Rushton, Editor, PPI magazine, RISI
BRUSSELS,
July 31, 2008
(Viewpoint) -
Members of the International Environmental Council, stated at the World Recycling Convention held Monte Carlo in early June, that recycling activity across all industries, including pulp and paper is responsible for saving well over 500 million tonnes of carbon dioxide emissions each year. But Hendrik Harjula, from the Environment Directorate, Organization for Economic Co-operation and Development, warned the assembled delegates that it must become even more efficient: “We are experiencing a paradigm shift from cradle-to-grave to cradle-to-cradle, and recycling is becoming more and more important all the time and as population growth (and growing affluence in emerging countries) places a greater strain on the environment and natural resources. Your role will be key in trying to provide for this increase in consumption”.
But papermakers don’t need lecturing about all this. Paper recovery and recycling has been going on for centuries and efficiency and technology is improving all the time - and it has to. One of the biggest dilemmas facing pulp and paper, at least in the northern hemisphere, is the lack of fiber, and this will only get worse as other industries start fighting for virgin fiber and the land it is planted on. This will result in further demand for recovered paper which of course in turn drives up prices. This means that paper manufacturers have to maximize their efficiencies. Fortunately there are suppliers out there whose life’s work is to develop technologies that identify and isolate every area in the process where improvements can be made.
The shape of things to come
The latest technology in deinking from Metso comes quite literally in the shape of its OptiCell floatation cell which is a new linear and elliptical design which, it says, is proven to provide excellent characteristics for smooth flow velocities allowing for maximized bubble rise and efficient froth removal, attributes which are central to the deinking process. Other new features of the cell include a new up-flow feed injector that enables better flow patterns which improve on the conventional injectors by 20% resulting in maximum air generation, and energy saving which can be better used in creating turbulence to break down the size of air bubbles.
From a practical sense, the designers have concentrated on maximum user friendliness and minimum maintenance downtime. In the case of the injector – which is now accessible from the top – and allows maintenance without having to empty the whole cell. Metso also says that because the headbox feeds the flow to the injectors there is now no need for individual pipes which leads to good space savings.
One of the first Opticell floatation units has been ordered by Stora Enso for its Maxau mill near Karlsruhe, Germany. The deinking facility at the mill has a capacity of 380,000 tonnes/yr and its three machines produce around 700,000 tonnes/yr of magazine paper and newsprint.
Less maintenance
Andritz is also concentrating on the maintenance aspects of deinking and recycling. Michael Rošker, in charge of the company’s DIP product group says: “The main focus of both areas of deinking and recycling is reducing operating and maintenance costs for either an entire system or single process stage. Therefore, developments for our applications are centered on utilizing cleaner designs for low pressure drops, reducing the number of pumps and chests to optimize pulp and water flows, employing frequency converters for drives and increasing consistencies in pulping”.
In pulping, Andritz supplies its FibreFlow drum pulper which is built around the concept of treating fibers gently to obtain minimum fiber loss. There are currently 160 of the drum units employed worldwide. Rošker explains: “With gentle pulping, we achieve lower flake content, fewer stickies, and less dirt. We aim for maximum removal of coarse contaminants with the minimum of fiber loss. This is becoming increasingly important; getting the maximum grade quality out of what fiber is available.
In terms of floatation, the company supplies its SelectaFlot unit. Rošker continues: “ We use the optimized machine concept for floatation, and the cell is designed for smooth symmetric flow conditions with modular cells and injectors which are tailor made for efficient ink removal. But the emphasis is on a stable control scheme, safe and constant operation and fast startup. Short maintenance and downtimes are achieved by making the machine accessible from all sides of the cell.” The SelectaFlot uses multi injectors which Andritz says produce more bubbles in the most important size leading to maximum dirt speck removal and optimum brightness with low fiber loss.
Focus on energy
Voith Paper’s EcoProcess is gaining some attention due to one of the most important areas of concern for today’s papermaker, energy savings. Lee & Man Paper has recently ordered a complete stock preparation system from the company, including an Intensa Pulper IP for its new PM 17 machine in Hongmei, China. The machine is to produce 444,000 tonnes/yr of 100% recycled paper starting in 2009.
The central theme of the concept is the lowering of operating costs at the same time as producing high stock quality at maximum efficiency. This is achieved says Voith due to the Intensa Pulper IP and its associated disposal system which represents a “quantum leap” in terms of energy savings when compared to a conventional pulper. It also saves energy in other sections of the machine because the requirements are much lower than for a conventional design.
The cost savings are achieved in the EcoProcess by the elimination of several vats which results in fewer pipes and pumps, and less electrical equipment. Energy savings are also achieved by improved quality in the stock preparation section since dispersion of short fibers is eliminated.
Ink splitting
Kadant is also tackling challenges related to deinking, including handling lower quality raw materials and higher levels of contaminants, increasing operational costs, and optimisation of energy utilisation. In addition, DIP lines must be capable of reducing micro-stickies content in stock and process water while optimising yield and controlling ash content. The company says that its MAC Cell deinking line and its latest ink splitter for compact DIP installations address these challenges.
The MAC Cell deinking system pumps stock tangentially to the top of the cell after being aerated by a set of small auto-clean injectors. Once in the cell, air bubbles collect ink particles and rise up to the top of the cell to create a thick foam mat that is then removed. The partially de-inked stock goes to a de-aeration chamber and is pumped full flow to the next stage. This operation is repeated up to five times, thus giving the best possible ink removal under industrial conditions. Re-mixing of the air coming from the downstream stages aids the upper stages significantly improving the overall cell efficiency. The limited footprint, low power consumption, and high foam consistency make the MAC cell a highly efficient solution. Kadant’s fiberline division’s latest concept to simplify the deinking line design with a more compact one that incorporates increased ash control, fines ink fiber, and increased yield is expected to further enhance DIP line efficiency and effectiveness.
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Kadant Johnson recently completed a multi-year optimization project to develop a high-efficiency thermocompressor. The advances made to the geometry of the thermocompressor minimize the consumption of high-pressure motive steam while optimizing flow characteristics. The high-efficiency thermocompressor is used to recompress low-pressure steam and discharge steam at a higher pressure.
According to Gerald Timm, vice president of research and development at Kadant Johnson, "The major breakthroughs we made with the new line of high-efficiency thermocompressors has allowed our customers to decrease motive steam consumption by up to 25% while increasing the recompression of low pressure steam. This can help save a lot of motive steam for a quick payback and reduced energy consumption."
Kadant customizes each thermocompressor to match the unique characteristics of the steam system. When applied to paper dryers, the syphons and thermocompressors are matched to ensure the most efficient operation. Kadant says the new systems are available in custom sizes and can be used in new installations as well as replacements for existing thermocompressors. |
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