Scrubbing a PPC Tank: An Introduction to Fume Scrubbers

Poly Processing Company engineers and manufacturers chemical storage systems that address not just containment but safe management of vapors emitted from stored chemicals. Chemicals stored in polyethylene tanks require venting. Depending on the chemical you’re storing, the harmful fumes emitted from the storage tank can’t be directly released into the atmosphere. To reduce the harmful fumes before they evacuate the system and to control air pollution, you need a properly designed chemical fume scrubber.

Chemical fume scrubbers are engineered to capture, neutralize, and safely exhaust vapors that present health, safety, or environmental risks. These devices serve a specific function in chemical storage systems by preventing hazardous fumes from freely entering the air while allowing necessary venting pressure control of the tank.

The PolyScrub™ Wet Scrubber

Poly Processing Company (PPC) offers a polyethylene chemical storage tank scrubber solution called PolyScrub. PolyScrub is an ideal solution for facilities in search of a cost-effective chemical  fume scrubber. 

The scrubber is engineered to process vapor that is discharged from chemical tanks during operation and filling. Each PolyScrub is designed by our application engineers to accommodate proper ACFM (Actual Cubic Feet Per Minute) for your specific system.

Types of Chemicals That Require a Chemical Fume Scrubber

Certain chemicals release vapors that are corrosive, irritant, or hazardous when vented directly to the atmosphere. Chemicals commonly stored in polyethylene tanks that typically require a chemical fume scrubber include hydrochloric acid, ammonia, acetic acid, and other corrosive or volatile fluids.

The chemical composition influences scrubber design. For example, acidic vapors may require alkaline solutions in the scrubber media, while basic vapors may require acidic media. High volatility chemicals with greater vapor pressure demand larger contact surfaces and media volumes to ensure neutralization. Tailoring the scrubber’s internal media and liquid chemistry to the specific stored chemical ensures safe and efficient operation.

How The PolyScrub™ Wet Scrubber Works

The PolyScrub functions by contacting the target compounds with a scrubbing solution. Often, the solution is simply water, but it can also be a specific reagent to address particular chemicals.

Some of the chemicals that are stored in Poly Processing Company tanks that require scrubbers are hydrochloric acid, ammonia, and acetic acid. When storing these types of chemicals you need to construct a system that addresses venting needs by installing a compatible scrubber.

As with typical wet scrubbers, the PolyScrub system introduces a water or reagent solution through a submerged plenum. The fumes percolate up and through the scrubbing solution. Neutralization and absorption reduce the concentration of hazardous constituents in the gas stream, then the treated air vents out of the top of the scrubber system.

Sizing a Chemical Fume Scrubber for Your System

Scrubbers are typically sized for the particular bulk storage tank being used and the specific chemical that needs to be scrubbed. Essential factors include the vapor generation rate of the chemical, the maximum fill and off-load rates of the tank, and the desired contact time between the vapor and scrubbing media. Proper sizing ensures that pressure relief and emission control are both achieved without imposing excessive back-pressure on the tank vent.

A well-sized system prevents saturation of the scrubbing media too quickly and extends service life while offering consistent performance.

Custom Designing and Building Your Wet Scrubber

Let's take a look at how the PolyScrub fume scrubber is built for your chemical storage tank application. We start with a crosslinked polyethylene open-top tank. We then manufacture an Ultra High Molecular Weight lid with the necessary size fitting package for your specific application. 

Once the lid is constructed, we build a plenum (also known as a diffuser), which goes inside the tank. This plenum is used to distribute the fumes from the bulk tank into the liquid media of the wet scrubber. 

When fitting a PolyScrub™ system, normally a 6" vent pipe is installed in the bulk tank. The pipe elbows over and down and connects to a flange attached to the top of the scrubber. This allows the bulk storage tank to vent into the scrubber and not into the atmosphere.

Inspection and Maintenance of Scrubbers

A chemical fume scrubber’s performance depends on regular inspection and maintenance. Operators should routinely check:

• Liquid level and pH of the scrubbing solution.
• Signs of corrosion or scaling on plenum and wetted surfaces.
• Proper vent pipe connections and flange integrity.
• Pressure drop across the scrubber as an indicator of media saturation.

Routine maintenance extends scrubber life and prevents breakthrough of untreated fumes.

Basic Rules for Scrubber Design/Build

Poly Processing recommends purchasing one of our scrubbers for use with a PPC tank. We have years of experience building scrubbers for our tanks and we know what designs work safely and effectively.

PPC does not build scrubbers for other manufacturers’ tanks. Some customers want to build their own chemical scrubbers, but these designs often fail to meet the safety guidelines of a professionally designed PPC scrubber. The safety and longevity of a tank system rely on both a properly designed bulk tank and scrubber.

A few of the basic safety rules for scrubber design include:

• PPC scrubber systems have a built-in overflow so that the submersion depth of the plenum cannot exceed 10 inches water column which is the absolute maximum pressure for polyethylene tanks.
• The submersion depth of the plenum is set to operate between 6 and 8 inches water column to maintain a margin of safety.
  
• The plenum should be a slotted pipe with .010” slots and the slots should be every .125”. The slotted openings in the plenum must exceed the cross-sectional area of the connecting vent pipe by 120% for a margin of safety. See PPC PolyScrub Basic Drawing.
• The liquid media in the scrubber should be 1.1 spg or less. Specific gravity affects the back pressure of the scrubber system.

Signs Scrubber Media is Approaching Exhaustion

Indicators the scrubber media is nearing exhaustion include:

• Increased venting odors near the scrubber exhaust.
• Faster pH drift requiring more frequent adjustment.
• Increased pressure differential across the scrubber indicating reduced flow.
• Visible carryover of liquid droplets.

Recognizing these signs early allows replacement or regeneration of media before untreated fumes escape.

Effects of Ambient Temperature and Humidity

Ambient conditions influence scrubber performance. Higher temperatures increase vapor pressure of stored chemicals leading to greater off-gassing rates. High humidity can affect absorption and neutralization efficiency by diluting scrubbing solutions. Operators should monitor conditions and adjust scrubbing solution strength or media volume as needed to maintain performance.

Ensuring Proper Scrubber Installation

Proper installation prevents tank pressurization issues and ensures effective venting. The vent piping must be sized to match fill cycles and vapor generation rates. Connections should be rigid and leak-free. Back-pressure at the vent point must be minimized so the tank can breathe without undue resistance during both filling and normal operation. Careful placement of the scrubber and appropriate vent termination location also protects surrounding equipment and personnel.

Closing Thoughts on Chemical Fume Scrubbers

Choosing, sizing, installing, and maintaining a chemical fume scrubber are essential parts of protecting your personnel and complying with environmental expectations. A properly designed system ensures harmful vapors are neutralized, minimizes tank pressure concerns, and helps sustain long-term operational performance.

For more information about wet scrubbers for your polyethylene storage tank contact one of our tank engineers.

CHECK OUT OUR FUME SCRUBBER RESOURCE PAGE.