FRP for Pulp and Paper Mills: Bleach Plant Tanks, Ducts and Grating

In short: The bleach plant is one of the most corrosive places in any industry. Chlorine dioxide, hot acidic filtrates, caustic and wet chlorinated vapors attack carbon steel and many stainless grades. That is why mills use FRP for chlorine dioxide handling, filtrate tanks, D-stage equipment, scrubbers, ducts and stock lines. Performance depends on the resin and a well-built corrosion barrier. Published vinyl ester data show how narrow some limits are: about 20°C (70°F) for saturated chlorine dioxide solution storage, against 80–95°C for chlorine dioxide bleaching solutions, depending on the grade. FIBROVX makes tanks, scrubbers, pipes, fans and grating to order for each mill's chemistry and temperature, and confirms the resin and design in writing for every quotation.

Why the bleach plant is so hard on materials

Kraft pulp is brown. To make it white, mills bleach it in a sequence of stages. Most modern sequences are elemental chlorine free (ECF) and use chlorine dioxide (ClO₂) stages, often written "D" stages, between alkaline extraction stages that use caustic soda, oxygen and hydrogen peroxide.

That mix creates a tough environment:

• Chlorine dioxide is a strong oxidizer. In solution it attacks many metals and degrades many polymers, especially when warm.
• Filtrates from washers are hot, acidic and carry chlorides.
• Alkaline stages use caustic and peroxide, which attack glass fibers if they reach them.
• Vapors and vents are wet, warm and chlorinated, and condense on cool surfaces.
• Cycling between stages and during washouts adds thermal and chemical swings.

Corrosion engineers in the industry have used FRP for decades in this area. A US composites inspection firm summarizes typical FRP uses in the bleach plant as carrying bleach filtrates, filtrate tanks, chlorine dioxide handling, D-stage pre-tubes and stock lines. Chlorine dioxide storage tanks are typically large-diameter FRP tanks, according to a TAPPI case history on relining one.

Where FRP is used in a mill

Tanks and process vessels

Chemical storage and process tanks are the core use. FIBROVX builds FRP chemical tanks, vertical or horizontal, with the resin and laminate chosen for the medium. For general water, process water and fire water, modular FRP water tanks are assembled from panels on site. Our FRP storage tanks guide and FRP tank standards guide explain the design basics.

Scrubbers, ducts and fans

Bleach plant vents, ClO₂ generator vents and tank vents are often routed to a scrubber. FRP acid fume scrubbers and FRP fans handle wet, corrosive gas without the coatings steel would need. Our packed-bed scrubber sizing guide covers the basics.

Pipes

Filtrate, stock, effluent and chemical lines are a natural fit for FRP pipes. Diameter, pressure class, stiffness, resin and joint type are agreed per project. See FRP pipe basics.

Grating, handrail and access

Bleach plant floors see spills and constant washdown. FRP molded grating does not rust, and with a gritted top it gives good grip on wet floors. Add FRP handrail systems and FRP ladders for complete corrosion-resistant access.

What the resin data show

Resin makers publish maximum service temperatures for each chemical. The resin manufacturer's chemical resistance guide includes several pulp and paper entries. For its standard bisphenol-A epoxy vinyl ester, it lists:

For the chlorine dioxide bleaching solution, the same table lists 95°C (200°F) for the novolac vinyl ester grade.

Two lessons follow. First, the limit depends on the exact service: saturated ClO₂ storage is rated far lower than bleaching solution. Second, resin grade matters, so the resin choice has to follow the chemistry. A resin manufacturer notes that its table gives the highest temperatures at which equipment has given good service or passed testing, and that this is not necessarily the maximum service temperature. These are published resin data, not FIBROVX ratings. See our guide to FRP temperature limits by resin type and the FRP chemical resistance guide.

The corrosion barrier is the critical layer

In corrosion-resistant FRP, the inner surface does the chemical work. The resin manufacturer's chemical resistance guide describes a typical corrosion barrier as 2.5 to 6.3 mm (100 to 250 mil) thick. The first layer is resin-rich (about 95% resin) and reinforced with one or two surfacing veils. It is backed by chopped strand mat at about 75% resin, and then by the structural laminate that carries the loads.

The guide's footnotes show how specific the barrier details are. For saturated chlorine dioxide storage it calls for a double C-veil in the barrier; for sodium hydroxide and black liquor it calls for a double synthetic veil; and for chlorine dioxide bleaching solutions it asks users to check with the resin maker for a specific recommendation. The guide also notes that barrier thickness is proportional to service life. A well-made barrier is the difference between decades of service and an early reline.

Inspection and relining

Even well-built FRP equipment ages in ClO₂ service. The usual signs are surface softening, loss of gloss, exposed fibers, blistering and cracking of the inner surface. Mills inspect FRP on a schedule, often during shutdowns, and reline the corrosion barrier before the structural layer is reached. The TAPPI case history on a ClO₂ storage tank covers inspection findings and best practice for relining. Our FRP tank inspection and maintenance guide covers what to look for, and a confined-space permit is needed before anyone enters a tank.

Safety notes

Chlorine dioxide is toxic and hazardous to handle. ClO₂ systems are designed by specialist engineers and the chemical supplier. FRP equipment for this service should be designed to a recognized tank or pipe standard chosen by the engineer, with resin and laminate agreed with the fabricator. FIBROVX does not design ClO₂ generation systems; we build the FRP equipment to the specification provided.

Designing custom FRP equipment for a mill

1. Define the chemistry. Every chemical, concentration, temperature range and upset, including washouts and steam-outs.
2. Choose the resin and corrosion barrier. Resin grade, veil type and barrier thickness to suit the exact service.
3. Set the design basis. Design standard named by your engineer, plus pressure, vacuum, wind, seismic and agitator loads.
4. Agree the details. Nozzles, manways, lifting lugs, hold-downs, ladders and platforms.
5. Plan inspection. Access for future inspection and relining.

Every FIBROVX item is custom: size, resin, barrier, color, nozzles and accessories are set by your project. Product pages include reference properties and load examples. Resin, laminate, design data and any required compliance evidence must be confirmed for the quoted item. See also custom FRP manufacturing and the tank data sheet checklist.

Beyond the bleach plant

FRP is also used across the rest of the mill: effluent treatment (see FRP in wastewater treatment plants), cooling towers, odor control and chemical unloading. For other sectors we serve, see Industries We Serve.

Common mistakes

• One resin for the whole mill. ClO₂ storage, bleaching solution and caustic stages need different checks.
• Ignoring upsets. Steam-outs and hot washes can exceed the resin's limit.
• Thin corrosion barriers. Bleach service needs a proper resin-rich barrier.
• No inspection plan. Plan access for inspection and relining from day one.
• Wrong veil. Follow the resin maker's veil notes, for example synthetic veil in caustic service.

Key terms

• ECF: Elemental chlorine free bleaching, using chlorine dioxide instead of chlorine gas.
• D stage: A chlorine dioxide bleaching stage.
• Filtrate: Liquid recovered from pulp washers.
• Corrosion barrier: Resin-rich inner layers that resist the chemical.
• Reline: Replacing a worn corrosion barrier.

FAQ

Is FRP suitable for chlorine dioxide? Corrosion-grade vinyl ester FRP is widely used in ClO₂ service, but limits are narrow and depend on the exact service. Saturated solution storage is rated much lower than bleaching solution in published resin data.

Which resin is used in bleach plants? Epoxy vinyl esters, including novolac grades for hotter service, are common. The resin is chosen from the maker's chemical resistance data for each service.

How long does FRP last in a bleach plant? It depends on the resin, the barrier, the temperature and maintenance. Inspect regularly and reline before the structural laminate is attacked.

Can you build to our mill's specification? Yes. Send your data sheet, drawings and design standard, and we will confirm the resin, laminate and design in the quotation.

Do you supply grating for bleach plant floors? Yes. FRP molded grating with a gritted surface, plus handrail and ladders, made to your layout.

Related guides

• FRP Chemical Resistance Guide
• FRP Temperature Limits by Resin Type
• FRP Tank Inspection and Maintenance
• FRP Scrubbers Guide

Sources

• A resin manufacturer, Resin Selection Guide for Chemical Resistance (chlorine dioxide, liquor and caustic entries; corrosion barrier description)
• An FRP pole manufacturer, Fiberglass reinforced plastic assets: corrosion barrier condition and remaining service life (typical FRP uses in pulp bleaching)
• TAPPI PEERS 2022, Relining of a Chlorine Dioxide Storage Tank: A Case History (abstract): https://imisrise.tappi.org/TAPPI/Products/22/22PEE/22PEE12.aspx
• TAPPI PEERS 2018, Corrosion Resistant FRP Equipment for Pulp and Paper (abstract): https://imisrise.tappi.org/TAPPI/Products/18/PEE/18PEE70.aspx