White Paper: Optimizing Black Liquor Sealing in Pulp and Paper Mills

Executive Summary:
A Southeastern-based paper mill faced challenges with the black liquor circulation pumps A and B, experiencing frequent mechanical seal failures and high maintenance costs. Seeking a cost-effective and reliable solution, they turned to SEPCO for assistance. This white paper presents the comprehensive analysis and cost-saving benefits of converting the pumps from mechanical seals to braided packing.

Pumps A and B Facts:

PUMP A: Total Cost of Ownership

Subject Equipment:  Goulds 3180 XL Liquor Circulation Pump A

Product: Black Liquor

Issue: This pump was replaced 27 times due to mechanical seal failures from 2012 to 2023. Its average life has been 74 days.

Observations:
This piece of equipment is on a spring base, which causes alignment difficulties. SEPCO engineering has reviewed this service several times over the years and, barring a change in the base mounting, has recommended sealing it with packing.

Maintenance and Operating Cost History:

Assuming the Inboard Seal life was only about 22 days before failure and probably experienced a catastrophic mechanical event due to alignment issues. Based on the water supply line size, this service saw 20,160 gallons of liquor dilution daily.  This resulted in 52 days of product dilution totaling 1,048,320 gallons of additional evaporation cost.

PUMP B
Subject Equipment: Goulds 3180 XL Liquor Circulation Pumps B

Product: Black Liquor

Issue: This pump was replaced 11 times due to mechanical seal failures from 2012 to 2023. Its average life has been 365 days.

Observations:
This piece of equipment is on a spring base, which causes alignment difficulties. SEPCO engineering has reviewed this service several times over the years and, barring a change in the base mounting, has recommended sealing it with packing.

Maintenance and Operating Cost History:

Assuming the Inboard Seal life was only about 109 days before failure and probably experienced a catastrophic mechanical event due to alignment issues. Based on the water supply line size, this service saw 20,160 gallons of liquor dilution daily. This resulted in 256 days of product dilution totaling 5,160,960 gallons of additional evaporation cost.

Introduction to Black Liquor:

Black liquor circulation pumps are critical equipment in pulp and paper mills. They are tasked with efficiently transporting black liquor, a byproduct of the pulp-making process. However, mechanical seal failures and associated maintenance costs posed significant challenges for this mill. To address these issues, SEPCO proposed converting the pumps from mechanical seals to braided packing to improve reliability and reduce operational expenses.

USGS Wastage Analysis:
Black liquor dilution from flushing was calculated using the USGS drip calculator. One drip per minute per this calculator is 347 gallons per year.  The recommended external leakage rate is ten drips per minute per inch of shaft.   A 5-inch shaft will leak externally 1735 gallons per year. This external leakage is operating at a pressure differential of about 50 psi. The internal dilution rate is roughly ½ the external leak rate due to the fact the pressure differential is only 15 psi. The annual dilution to the process is about 868 gallons annually. The evaporation cost annually for this water dilution is $78.12

Conversion to Braided Packing:
SEPCO replaced the mechanical seals on circulation pumps A and B with braided packing. The packing sets were changed annually during scheduled outages, ensuring no production downtime. The average packing life was one year, providing consistent performance and reliability.

SEPCO packing set cost: $118.00

Cost Analysis:
SEPCO conducted a comprehensive cost analysis comparing the expenses associated with running mechanical seals versus braided packing on both circulation pumps. The results revealed substantial cost savings for this mill after switching to braided packing.

Financial Benefits:

• Circulation Pump A:
• Mechanical Seals: $1,814,140.00 per year
• Braided Packing: $196.12 per year
• Circulation Pump B:
• Mechanical Seal: $732,966.00 per year
• Braided Packing: $196.12 per year

Total Cost of Ownership Study:
SEPCO further analyzed the total cost of ownership for both circulation pumps A and B, considering factors such as mechanical seal costs, installation labor, paper machine downtime, and black liquor dilution evaporation costs. The results demonstrated significant cost savings and improved reliability after converting to braided packing. 

Conclusion:
The conversion of black liquor circulation pumps A and B from mechanical seals to braided packing proved to be a successful solution for this particular mill. SEPCO’s expertise and cost-effective sealing products not only improved pump reliability but also resulted in substantial cost savings for the company. By partnering with SEPCO, this mill achieved enhanced operational efficiency and reduced maintenance expenses, contributing to its overall success in the industry.