By Tony Johnson, Barbara Johnson and Peter Gleadow
BRUSSELS,
March 31, 2009
(Viewpoint) -
The design of a modern 21st Century pulping complex is dramatically different to mills of the past. Pressures to maximize energy efficiency, improve product quality, reduce environmental impact, and optimize capital and operating costs have significantly shaped 21st Century pulping and bleaching processes.
New mills have responded to these demands by adopting efficient, low impact designs on economies of scale that far surpass most existing mills. New fiberlines have been built mainly in Asia and South America where access to fast growing raw material and other production advantages give favourable levels of cost and return.
Market pulp capacity and trends
The world market for bleached kraft pulp has experienced steady expansion. In 2005 global market pulp capacity was approximately 54 million tonnes. Bleached kraft pulp (BKP) accounted for 85% of capacity, equally divided between bleached softwood kraft pulp (BSKP) and bleached hardwood kraft pulp (BHKP) (Figure 1). North America, at approximately 37%, has the majority share by region, followed by Western Europe (25%) and Latin America (18%).
Over the period 1990-2005, all market BKP capacity has increased from 29 to 45 million tonnes. BHKP capacity has grown at a faster rate than BSKP, almost doubling to 22 million tonnes compared with a 40% increase in BSKP to around 23 million tonnes (Figure 2). Fifty percent of this new capacity has come from large greenfield mills and new fiberlines on existing sites. Incremental debottlenecking and expansion of existing brownfield fiberlines account for the balance.
In terms of geographic region, two thirds of the increase in global market pulp capacity has been in Latin America and Asia (excluding Japan) with lesser growth in Western Europe and Canada (Figure 2). The growth in market pulp capacity in Latin America and Asia is a direct result of access to wood supply and other production advantages.
Important considerations
In establishing billion dollar BKP mills, there are many drivers and demands that influence the business decisions. Companies today must not only consider the traditional forces of economic efficiency and environmental protection but also address the concept of social responsibility for a new development. Key factors considered for 21st Century mills are:
• Wood supply
• Economy of scale
• Environmental impact
• Energy efficiency
• Operating and capital cost
• Product quality and markets.
Wood supply: Tree selection and breeding programs have driven forest yields to more than 40 m³ per hectare per year (m³/ha/yr) for hardwood. Coupled with short rotations for eucalyptus and acacia of 6-9 years, the relative area required to support large pulp mills has been reduced. For eucalyptus this represents a dramatic competitive advantage over northern hardwood species like birch. Therefore, proximity to plantation forests is a key consideration. For the Hainan Jinhai mill in China, the planning and development of the mill was accompanied by a 233,000-ha plantation forestry project as part of the objective to become self-sufficient in fiber. A follow on from this for a modern mill is optimized wood handling in the mill with wood storage, seasoning period, dry debarking, chipping, chip storage and chip dimensions all warranting close attention.
Economy of scale: The selling price of pulp has traditionally been volatile, with prices cycling between supply and demand side extremes in about a 7-9 year cycle. Underlying this cyclical volatility, there has been a long-term decline in market pulp prices, in constant dollar terms, making it paramount to be a low cost producer. The trend for new mills is towards large single fiberlines that take advantage of technology advances in equipment design and function. Economies to be gained from increasing the scale of an operation is perhaps the most critical factor driving the evolution of increasing single-line capacity. Not only is there a lower investment cost per tonne of pulp, but fixed costs are also lower. The capacity of vessels such as the digester and bleach towers has increased significantly. For example, the Hainan Jinhai mill has one of the world’s largest digesters with a bottom diameter of 12.5 m and a recovery boiler with a design capacity of 5,000 tonnes/day of dry solids. Figure 3 illustrates the chronological development of capacity for kraft fiberlines [1]. This trend towards larger single fiberlines is continuing with mills currently planned with a design capacity of 5,000 tonnes/day.
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Environmental impact: BKP mills embodying the latest technologies and management practices aim to minimize the environmental effect of pollutants released from the production processes. Rigid environmental standards are in place in most jurisdictions to ensure this is the case.
Technologies allowing maximum system closure such as low water consumption and reduced environmental impact compared with earlier BKP mills are implemented in new mills: technologies such as modified cooking and 2-stage oxygen delignification, and practices such as integrated warm and hot water systems, effective spill recovery and evaporator condensate segregation and treatment systems. Dissolved organic material is increasingly recycled by highly efficient washers and, in some unique circumstances, via bleach plant filtrate recycle. Although these features are not new, they can be combined in new mills and take advantage of improved equipment now available.
One common criterion is that the technology should achieve the desired emissions in a cost-effective manner. There are various terms for this including Accepted Modern Technology (AMT) [1], Best Management Practice (BMP), or Best Available Techniques (BAT), but the crux is being technically effective and economically viable on an industrial scale in minimizing the discharge of pollutants.
Energy efficiency: Emphasis on conservation and environmental stewardship extends to energy policy. New mills should be energy self-sufficient and ideally be capable of supplying power to the external grid. The power balance of a new facility should target maximum power-to-heat ratio. New mills have a recovery boiler, may have a bark fired power boiler and either may have the ability to burn effluent sludge, turbine generators (with both back pressure extraction and condensing turbines) and steam and power distribution systems. Considerations include selection of processes with low heat (10-11 GJ/adt) and power (550 kWh/adt) demand and efficient use of secondary heat. An integral part of energy policy is the sustainable plantation forest. For short rotation forestry, wood is debarked in the forest to leave the biomass, nutrients and trace elements in the forest. If more energy is required, extra plantation area is allocated.
Operating and capital costs: The long-term viability of a BKP mill depends on its position on the manufacturing cost curve. Strategic plans longer than 15-20 years should include all inputs (wood, chemicals, labor, capital, energy) and outputs (pulp, market data, price projections, etc) and be evaluated against normal financial criteria (ROI, NPV, IRR, etc). Constant focus on efficiency and mill optimization ensures a long-term future.
Capital cost is a major factor in the development of a project. Capital investment in mills can be compared on the basis of US dollars per annual ton. Figure 4 illustrates that capital cost is directly related to scale hence driving up the size of new mills.
Product quality and markets: Uniform high quality products are imperative to secure a position in the commodity market pulp business. Supply and demand fluctuations mean the low cost producer can gain market share only if its products meet market standards. Quality starts in the forest with segregation of wood by species, age or density and flows through the entire process. For process and product uniformity well-tuned monitoring and control systems are essential.
New fiberlines
There are many new and developing technologies available to mills to respond to these pressures. New fiberlines have been built in Asia and South America where access to fast growing raw material and other production advantages give favorable levels of cost and return. This trend is likely to continue.
Veracel Celulose, the bleached high brightness eucalyptus mill located in the north-eastern state of Bahia in Brazil, is representative of an efficient modern, low-impact fiberline. The mill has a design capacity of 900,000 air dried tonnes/yr and includes 2-vessel vapor-phase Lo-Solids® continuous cooking, two stages of oxygen delignification and a 4-stage, hot chlorine dioxide ECF bleaching sequence EEopDP (Figure 5). Cooking utilizes lower cooking temperatures and optimized alkali profiles resulting in thorough impregnation and pulp yield. High efficiency multi-stage Drum Displacement (DD) washers achieve high displacement ratios. A hot chlorine dioxide stage is used for hexenuronic acid removal.
Hainan Jinhai is the world’s largest single-line pulp mill producing in excess of one million tonnes/yr of bleached hardwood kraft pulp. Hainan Jinhai utilises Compact CookingTM technology, two-stage DualoxTM oxygen delignification and DualdTM hot chlorine dioxide bleaching. Acacia and E. grandis are pulped in a digester of massive scale (12.5 m diameter) at relatively low cooking temperatures and alkali demand. Compact wash presses are used throughout the fiberline. The Dhot(Eop)DD bleaching sequence is similar to that used at Veracel (Figure 6). Emphasis is on optimal chemical consumption, retention of pulp strength, and minimal brightness reversion.
Emission and effluent control technologies have also developed to make this new generation of kraft pulp mills truly of minimal impact. A combination of in-mill systems for spill control, low water use equipment, excellent filtrate management systems, comprehensive odour collection systems, minimal solids discharges and improved energy efficiency result in a mill footprint that is greatly reduced compared with mills of the 1990s.
The detailed design, operation and performance of the Veracel and Hainan Jinhai pulp mills are reviewed elsewhere [2].
Tony Johnson is general manager, New Zealand Forest Industries, Beca AMEC, and Barbara Johnson is senior process engineer, Beca AMEC, Tauranga, New Zealand; Peter Gleadow is process specialist, AMEC Power and Process, Vancouver, BC, Canada
REFERENCES
1. Beca AMEC, Study report: Independent Advice on the Development of Environmental Guidelines for any new Bleached Eucalypt Kraft Pulp Mill in Tasmania, prepared for the Resource Planning and Development Commission, Tasmania, Australia, at http://www.rpdc.tas.gov.au/__data/assets/pdf_file/0005/66335/Study_Report.pdf (2004).
2. JOHNSON, T., JOHNSON, B., GLEADOW, P., SILVA, F.A., AQULIAR, R.M., HSIANG, C.J., ARANEDA, H. 21st Century Fibrelines, In 2008 Proceedings of International Pulp Bleaching Conference, Quebec City, Canada, p 1 (2008).
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