Seal Water Filtration Upgrade for Pulp and Paper Mill

Project Overview

A Tennessee paper mill operating several 200 HP liquid-ring vacuum pumps was experiencing rapid fouling of its plate-and-frame heat exchanger.
The pumps use recirculated seal water as part of the vacuum-generating process, and over time the returning seal water became heavily contaminated with paper fiber, fines, and machine clothing debris.

This contamination was being pushed directly through the plate-and-frame cooler, clogging passages and forcing operators into a constant cycle of shutdown, disassembly, cleaning, and recommissioning.
The mill requested a reliable inline filtration system that could remove fiber before the heat exchanger and operate continuously at ~3,300 GPM.

Project Requirements

From the mill’s initial request, several critical requirements were defined:

• Protect the Plate-and-Frame Heat Exchanger
  Remove fiber and fabric debris from the seal-water return prior to cooling.

• Continuous Operation at 3,300 GPM
  The process cannot tolerate extended downtime.

• Minimal Water Loss
  A backwashing strainer was not desirable due to high seal-water consumption.

• Mechanical, Non-Backwash Cleaning
  The customer specifically required a scraper-type system to avoid the operational complexity and water usage associated with backwash systems.

• Controls to Match Plant Standards
  The mill requested Allen-Bradley PLC and HMI for seamless integration with their facility.

Fil-Trek Solution

Fil-Trek engineered a duplex 98 Series Automatic Self-Cleaning Strainer system, skid-mounted with a common manifold.
This configuration divides the total 3,300 GPM between two housings while preserving short-term single-unit capability.

Duplex Skid Architecture

Although not a full redundant (“N+1”) design, each 98 Series unit was sized to handle the entire flow for limited periods. This gives the mill operational flexibility during service intervals or upset conditions.

Key advantages of the duplex configuration:

• Reduced downtime: One unit can maintain flow while the other is isolated.
• Compact footprint: Skid and manifold arrangement simplified installation.
• Efficient debris handling: Mechanical scraping eliminates backwash water loss.
• Operational stability: Consistent differential pressure and steady flow to the heat exchanger.

Mechanical Cleaning — No Backwash Line Required

Unlike traditional backwash strainers that require a dedicated discharge line and consume significant water during cleaning cycles, Fil-Trek’s 98 Series uses a rotating scraper and purge chamber to remove debris mechanically.

Benefits include:

• Minimal seal-water loss
• Consistent cleaning effectiveness on fibrous contaminants
• No dependency on plant backwash pressure

This feature was particularly important for the mill’s water-constrained seal loop.

Controls and Integration

The entire system, including scraper drive, purge sequence, and alarms, was built around an Allen-Bradley PLC and PanelView HMI, matching mill standards for:

• Programming conventions
• Network architecture
• Maintenance familiarity

This allowed the customer’s electrical group to integrate the system with zero retraining.

Materials and Construction

The strainers were supplied in stainless steel with heavy-duty scraper assemblies suitable for fibrous pulp debris.
Instrumentation, gearmotor drives, and enclosures were specified for industrial wet-service environments commonly found around vacuum pump pits and seal-water systems.

Commissioning and Expected Results

The new automatic strainer system is designed to deliver:

• Significant reduction in heat exchanger fouling
• Reduced labor from eliminating manual cleaning cycles
• More stable vacuum pump operation
• Lower seal-water consumption compared to backwash technologies

By removing paper fiber prior to the cooler, the mill expects substantial savings in both maintenance hours and process interruptions.

Related Products

• 98 Series Automatic Strainer