With the world’s population expected to balloon by one billion people by 2030, conservation of critical resources such as water is an important societal goal. The United Nations estimates that water scarcity currently affects 40 percent of the population, already making it a significant concern.
Processes that use high volumes of water in pulp and paper production plants, among other industrial processing, are under scrutiny due to high levels of water consumption. One of the most important and common liquids to be pumped in a paper mill during the papermaking process is paper stock in all of its forms—black liquor, white liquor, green liquor, etc. With water scarcity issues facing communities around the world, and taking increasingly stringent environmental regulations into account, the pulp and paper industry is examining how paper stocks are handled as a way to reduce water waste and increase sustainability.
At the center of paper stock processing, mechanical seals are used in heavy-duty centrifugal process pumps throughout a pulp and paper mill to seal the rotating shaft against a stationary pump housing. These pumps move liquids including black liquors, water, chemicals, or sludge from one place to another during the manufacturing process. This makes seal selection vital to plant production and any pump reliability plan. Underscoring the importance of mechanical seal selection, reliability records show that up to 60 percent of all problems with centrifugal pumps originate with mechanical seal failures.
If you want to minimize water waste to reduce your mill’s environmental footprint while boosting pump reliability at the same time, the right mechanical seal can help you overcome many challenges:
• Limiting leakage from rotating equipment
• Minimizing water usage that is required to support the seal
• Reducing the power consumption at the seal
• Lowering heat generation and friction at the seal, which can increase energy efficiency
Consider these seven key water waste reduction strategies in your pulp and paper mill to achieve dramatically improved results:
1. Convert compression packing to single mechanical seals to reduce water consumption and eliminate leakage. The decision to move from packing to mechanical seals can be driven by the impact of constant leakage from packing on the shaft and bearings, which can have a negative impact on your equipment maintenance.
2. If you are using an external water source as a flush for a single mechanical seal, the flush should be at a higher pressure than the seal chamber to perform correctly. If the external water source is uncontrolled, water consumption increases, creating more water waste. Therefore, the best practice is to install flow meters used for single seals or packing. This allows you to regulate the external water supply to reduce water consumption.
3. Further optimize your pumps by selecting dual mechanical seals with enhanced seal face technology to reduce water consumption and overcome harsh conditions including low lubricity, high heat and friction. This seal face treatment upgrade can address poor mill water quality and low water pressure challenges in pulp and paper mills, while improving pump reliability and reducing maintenance costs.
4. Use dual mechanical seals paired with a seal support system, such as API Plan 53A, to further optimize your pumps and extend the life of the mechanical seal as it is running in its own clean environment. This approach reduces water consumption in the case of a seal failure where only the water in the seal support system is lost, which typically equates to only eight liters (two gallons).
5. Install control valves that operate mechanically like a household water tap. For optimal seal water reduction, be sure to monitor and open the values only when necessary to flush the system. Do not keep the valves open continuously or it will defeat the purpose.
6. Install flow meters to reduce seal water by controlling seal water flow and pressure. Used in conjunction with mechanical control values, flow meters can reduce seal water use while improving mechanical seal reliability.
7. Use smart water control systems that reduce up to 97 percent of water consumption compared to the water savings produced by flow meters. These control systems regulate water consumption based on seal temperature, only allowing seal water to flow through the system when needed to cool the seal. Unlike flow meters, where the seal water runs through the system once and drains, smart water control systems reuse the same water multiple times, further reducing water consumption.
The world’s water scarcity will continue to impact all types of industry. Processes that use high volumes of water—like pulp and paper production, mining, and others—will face important decisions about how to decrease water use and increase energy savings. These issues, along with a need to increase mean time between repairs (MTBR), will continue to drive operators to do more.
Selecting the best equipment for the application can make a difference in each of these areas of interest. Seals, including packing and single or dual mechanical seals, are crucial components in any pulp and paper operation. Choosing the right seals can mean saving millions of gallons of water, plus the associated costs and environmental impact.
Jussi Sorvoja, P.E., is market director, Pulp and Paper, for John Crane, www.johncrane.com.