South East Paper Mill Realizes True Water Savings

It’s a known fact that we all use too much seal water. It doesn’t matter whether the pumps are equipped with Mechanical Seals or Mechanical Packing. The volume of Seal Water consumed has long reached economic impact.

Every excess gallon or litre of flush water that is fed into the process streams is just one more gallon that needs to be removed later in the process. Removing it is expensive, whether it is removed by evaporation or through effluent treatment.

The question becomes how much seal water is required to adequately lubricate the sealing device while reducing the inherent temperature rise caused by the process and the dynamic sealing assembly. In most applications we default to “better too much than not enough”. But the actual flowrate is seldom if ever measured. We just know it is in excess, or not.

North America is facing increased demands for water. The continent wide drought continues to create concerns for all of us. Recently one pulp mill in British Columbia, Canada shut down a major part of its production because of water shortages. Reducing the ongoing demand for flush water is a major opportunity for pulp mills.

A Pulp and Paper mill in the southern USA has addressed this issue. One section of the plant measured the flowrates in 40 Goulds Pumps .The pumps ranged in size from 3196MTi’s ANSI Pumps to 3175 Stock Pumps. The total flow for the 40 pumps was 154 USGPM . Not much you may think, except that flowrate translates to 80,942,000 USG per Year.

 

To reduce the water use, the Mill Maintenance team decided to install SealRyt Corporation’s patented close-clearance stuffing box bearing known by many in the industry as the PackRyt BLR. The mechanical packing incorporated with the BLR was sized and selected to suit the application. This is in contrast to many packing installations where the packing is selected based on the actual cross-section rather than cross-section coupled with proper process application. (Packing selection is critical to greater MTBF and contributes greatly to the life of the shaft and/or shaft sleeve.)

Figure 1 – Installation of PackRyt BLR and Packing Rings

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The PackRyt BLR’s and the 3 die-formed packing rings were installed following the recommended procedure. Furthermore, care was taken to adjust the packing over time, as is required to create effective process sealing.

The pumps were started and the resulting Seal Water flowrates were measured. The overall flow rate declined from 154 USGPM to just 18.5 USGPM. As a result, the demand for seal water was reduced to just 9,723,000 USG/year. This represents an 88% reduction in water use, with consumption down over 71,000,000 USG/year. This was in just 40 pumps. The following table shows the improvements at three of the pumps.westcan2

 

Accurate measurements of seal water consumption have helped the mill make better ongoing decisions about its packing. They were able to calculate the costs related to water supply, related to the cost of removing the excess flush water from the process stream, and related to the post-process treatment of the water waste stream. This particular mill uses steam to remove excess water from the process. Since evaporation typically requires 1,000 pounds of steam per pound of water, it doesn’t take a lot of extra water remaining in the process to drive up steam costs very quickly. Accurate measurements have let the mill team reach the conclusion that the cost of using the SealRyt solution is easily paid for by the savings related to water use and disposal.

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A  significant challenge is the  actual measurement of seal water  flow. Figure 2 illustrates a minimum piping arrangement to accurately determine seal water flow and pressure.

This flush water is typically re-introduced to the process stream in pulp mills, and the water is removed later in the process using steam. Evaporation typically requires 1,000 pounds of steam per pound of water.

 

Doing your own measurements of flush water usage, and using the savings at this south east mill as an example will let you do your own math!

For more information about how to assess the benefits for your plant, please contact us at watersavings@westcan.com.

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