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Water: reduce, reuse and recycle

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Water: reduce, reuse and recycle

July 17, 2011 - 16:00
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BRUSSELS, July 18, 2011 (RISI) -If the US pulp and paper industry would implement water reuse and recycle to reduce water consumption by 1 m3/ton of paper produced, the industry would reduce its water consumption by nearly 23 billion gallons/yr and reduce energy costs by approximately $50 million dollars (1 m3is equal to 265 gallons). That's enough to supply Spain's entire population with a full day's worth of drinking water (based on the recommended daily intake of water (8 cups/day).

It's possible to reduce by even more. Net water use for the manufacture of pulp and paper varies significantly not only depending on the grade, but also within the same type of paper by ton of product. For example, tissue has a process that consumes an average of 8,000 gal/ton (30 m³/ton) of water at the minimum and 50,000 gal/ton (190 m³/ton) at the maximum.

Figure 1 shows water consumption by type of product. As can be seen, water within the same grade varies significantly. Fine paper, for example, has a range of water use between 9,000 and 45,000 gal/ton. At the lower limit the manufacturer can produce one ton of product with a process that requires 9,000 gallons of water compared with another fine paper manufacturer with a process that requires 45,000 gallons/ton of product produced. The question then becomes how can these two producers remain competitive when one uses five times the amount of water as compared with the other? The difference in North American water consumption is even higher when compared with the European benchmark. In most modern mills that have a tighter process, producers are able to reduce water requirements.

Figure 1 - Net water use for pulp and paper manufacturing

Why does North America use so much?

Why is water consumption so much higher in North America? The pulp and paper industry has much older equipment that was built when water consumption and environmental concerns were not critical priorities for mills. Energy costs were not high enough to play a significant role in the overall manufacturing cost structure. Figure 2 shows the average age of paper machines across the world. It presents the average capacity of paper machines versus the average technical age of operating paper machines. As can be seen, North America has the oldest average technical age of paper machines (at 35+ years) and is currently producing 25% of the global paper, followed by Europe at 29 years, Asia at 20 years and China at 15 years. The installations were driven by environmental regulations and represent the available water and wastewater technology at that time. During this period, neither energy nor chemical costs impacted the total manufacturing cost structure.

Figure 2 - Average paper machine capacity compared with average technical age

When cost savings are a top priority and there is market pressure to reduce costs, the aging equipment makes this challenging. Paper producers may not have the capabilities to cut water consumption without making significant, and oftentimes expensive, modernizations to the process. Figure 3 shows the age of existing water and wastewater treatment plants in the pulp and paper industry in North America.

Figure 3 - Average age of water and wastewater treatment plants in North America

Seventy percent of the existing water and wastewater treatment plants are approximately 30-35 years old. Given the technology progression in the industry, in addition to increased competition between equipment suppliers, we have seen a substantial reduction in manufacturing costs due to reductions in energy, water and chemical consumption as well as improved fiber recovery systems in the paper machine process area. In the early 1990s, a plant that generates zero effluence was built in Albuquerque, NM.

Environmental regulations are the main drivers that help push pulp and paper producers to install newer, more efficient technology. The equipment reduces water consumption, thus translating into a reduction in manufacturing costs. Today's paper machines are already equipped with water loop capability consisting of systems to reuse and recycle. Bleach plants and brownstock washing within pulping facilities are now using technology that provides substantial water reduction as well.

The pulp and paper industry continues to adopt a myriad of technological changes that require less water consumption in process equipment. The savings can be quantified by reductions in water use through energy reductions due to less pumping and heating, reductions in chemicals and increased fiber recovery.

Benefits of recycle reuse modification could result in a few dollars per ton of product, or substantially more. Given a reduction in water consumption by 1 m³/ton, the savings in energy costs for heating, for example, will result in a savings of $0.60/ton of product produced. Upon reviewing the statistical data of water usage, it becomes clear that reduction of water can be much more than 1 m³ or 265 gallons/ton of product, which would equate to an even bigger savings. For example, a producer would obtain approximately $12/ton of energy cost savings simply by making reuse and recycle modernizations to achieve a 6,000-gallon/ton water reduction. This does not include other cost savings benefits such as fiber recovered, chemical reduction water intake and effluent treatment costs.

Many options available

Companies that supply water reuse and recycle equipment and wastewater treatment have developed new systems that can be installed within the pulp and paper technological process without changing process equipment. These systems allow producers to reduce, reuse and recycle. Siemens has developed several technological advancements for water reuse which include multi-barrier filtration systems, low pressure membrane filtration systems, membrane bio reactors (MBR), nanofiltration (NF)/reverse osmosis (RO) and rapid sand filtration. The treatment method will depend on the intended use and process conditions. For lower water quality, conventional systems like pressure-filters and flow-bed-filters can be applied. If high water quality is required, ultra filtration (UF) in combination with a biological system such as MBR can be utilized. For highest water quality, a mill can use membrane systems such as micro-filtration, nano-filtration, UF and RO technology. There is also technology for process and treatment water, as well as sludge, intake water, advanced boiler feed water and effluent treatment.

Figure 4 - Cost savings can be achieved by reusing and recycling within the manufacturing process

Siemens case study

Siemens has developed equipment that can be supplied across the entire mill. The Albert Kohler mill, located in Gengenbach, Germany, produces roughly 40,000 tons/yr of high-quality paperboard. When the local government instituted a large increase in wastewater surcharges, on-site wastewater treatment and reuse and recycle became necessary. The mill chose an integrated system of MBR and RO process. As a result, the mill now sends treated water back to production and reduces well water use by 75%, thus translating to energy, fiber, chemical and treatment cost savings.

Cost savings can be achieved by reusing and recycling within manufacturing process without touching the waste water treatment plant. Modifications of recycle reuse of water with process loops are possible with a reasonable investment that can provide a return on investment in less than a year. Such modifications would require proper review of present processes and proper evaluation of water use in the mill. Water is becoming an increasingly important component of every mill process, not only for its quality but also for its quantity.

Energy cost savings calculations: (Efficiency at 75% and natural gas at price of $5.45/1,000 ft3. Inlet temperature of 15°C and effluent temperature 35°C).