The world’s population is expected to reach 8.5 billion by 2030, and the conservation of critical resources, such as water is a crucial societal goal. The United Nations estimates that water scarcity currently affects 40% of the population, making it a significant concern.
Processes in pulp and paper production plants, among other industrial processing, rely on slurry movement that uses high volumes of water. Regions, where pulp and paper mills operate, are under increasing scrutiny for water use, effluent and wastewater disposal. With expectations for tighter legislation on water consumption targets, and many companies making public declarations of their water and energy savings targets, water conservation in the pulp and paper processing industry has never been more important than it is today.
Water is used in almost every paper production process, from moving slurries and paper stock to steam creation for heat transfer in cooking and dehydrating pulp by-products and creating concentrated liquors and waste products. Mechanical seals are used in heavy-duty centrifugal process pumps that move liquids, including black liquors, water, chemicals or sludge, to support manufacturing. The variations encountered with process water and waste liquids make pump and seal selection vital to plant productivity and process reliability.
Today, virtually all paper mills face challenges in reducing water consumption and increasing water reuse and recycling to reduce the mill’s environmental footprint. Specifying the correct mechanical sealing technology can dramatically improve system reliability, greatly reduce water consumption and significantly impact the parasitic losses of sealed shafts.
Modern, well-designed mechanical seals will:
- Limit leakage from rotation shafts
- Reduce power losses associated with compression packing
- Lower the frictional heat associated with packing
- Minimize water consumption
- Reduce maintenance hours associated with rotating equipment
- Recycle process water and eliminate harmful solids using self-clearing filtration technology
Consider these four water-waste reduction strategies to achieve dramatically improved results in your pulp and paper mill:
- Convert compression packing to single mechanical seals to reduce water consumption and eliminate leakage. The proper operation of mechanical shaft packing requires a constant water flow to cool and lubricate the sealed shaft. More than a century old, this technology amounts to a balancing act of radial compression exerted by the packing, a constant flow of pressurized water used to cool the pump sleeve and process leakage required to lubricate the packing rings. Replacing packing with a mechanical seal will reduce water consumption by at least half and eliminate the need for daily or weekly maintenance activities to tighten packing.
- Where mechanical packing cannot be easily upgraded to a mechanical seal, consider using a CPR bushing. This device meters and distributes flush water while excluding solids from spoiling the inboard packing ring.
- If you use an external water source as a flush for a single or dual mechanical seal, the flush should be set to a higher pressure than the stuffing box to effectively flush the seal or packing. When the external water source is uncontrolled, water consumption increases, leading to more water waste. Where flush water is used, the standard practice should include, at a minimum, a simple manual control valve to avoid full-flow flush consumption where it may not be necessary.
- The installation of a water metering instrument will ensure the desired pressure and ultimately reduce flush water consumption to a known and planned amount. Flow meters are used in conjunction with mechanical control values and reduce seal water use while improving mechanical seal reliability. The John Crane Safeunit™ is a combined metering and control device that allows for fixing the flow to only the value required for optimal seal performance, and by measuring the flow, enables monitoring of the consumption at the seal. John Crane Safeunit™ should be used to control single seal flush and dual seal water flow.
The world’s water scarcity will continue to impact all types of industries in the coming years. Processes that use high volumes of water—like pulp and paper production, mining, and others—will face important decisions about decreasing water usage and increasing energy savings. These issues and a need to increase mean time between repairs will continue to drive operators to do more.
Partner with Experts
Selecting the best equipment for the application can make a difference in each of these areas. Seals, including packing and single or dual mechanical seals, are crucial components in any pulp and paper operation. John Crane has the expertise to help you select the right seals to save millions of gallons of water and its associated costs and environmental impact.
Links to further resources:
- Water savings webinar
- Blog on upgrading from packing to a mechanical seal
- Safeunit case studies: John Crane Mechanical Seal Flow Control, John Crane Safeunit Water Control and Monitoring System Upgrade
- Safeunit Brochure
Note: This content was featured in the PITA journal Paper Technology International®