Industrial Scrubbers 101: What Are the Key Components of a Scrubber
Summary
An industrial wet scrubber has six components: the inlet, mass transfer section, spray headers, mist eliminator, sump, and outlet transition. Contaminants leave the air in the mass transfer section, where packing wetted by recirculating solution creates gas-liquid contact; the spray headers distribute that solution, and the mist eliminator catches droplets before discharge. The sump holds the pumps and chemistry controls, while the inlet and outlet connect the scrubber to the ductwork and fan.
When you’re evaluating an industrial wet scrubber, you need to know whether it can meet your removal target, how hard the fan will have to work, and how easily your crew can service it. For the packed bed designs covered here, understanding six main components helps you assess all three.
The process starts at the inlet, where contaminated air enters the scrubber and moves into the mass transfer section. There, packing wetted by a recirculating scrubbing solution creates the contact needed to transfer contaminants from the air into the liquid. Spray headers distribute that solution across the packing, while the sump holds the liquid that feeds the recirculation loop.
Before the air leaves through the outlet transition, the mist eliminator catches droplets of scrubbing solution carried out of the packing. Each component has a distinct job, and its design affects how the system performs. Packing depth, liquid distribution, and maintenance access all deserve a closer look when you’re specifying a scrubber.
Key Takeaways
- The packed bed industrial wet scrubbers covered here have six main components: the inlet, mass transfer section, spray headers, mist eliminator, sump, and outlet transition. Their design and operating conditions affect removal performance.
- The mass transfer section does the cleaning. Packing type, packing depth, and air velocity through the bed (400 to 600 FPM in Viron's standard designs) set both removal and pressure drop.
- Packing only works where it's wet. Viron's standard design point is 4 GPM of recirculation per square foot of open packing area.
- Droplet-capture requirements help guide mist eliminator selection. Viron’s composite mesh pads capture 99% of 3-micron droplets, while its horizontal and vertical blade designs target larger droplets.
- The sump holds the pumps, chemistry controls, and most of the plumbing. Viron plumbs and water-tests that system at the factory before the scrubber ships.
1. The Inlet
The inlet is where your exhaust duct meets the scrubber body. Mechanically, not much happens here.
But the conditions at the inlet are the numbers every other component gets sized against: airflow in ACFM, the loading rate of each contaminant, air temperature, and the removal efficiency you need. They top the list of what we ask for before designing a wet scrubber. We also offer inlet and outlet expansion joints that absorb vibration and small misalignments between the duct run and the scrubber.
2. The Mass Transfer Section
Where the Cleaning Happens
This is where contaminants move out of the air and into the scrubbing liquid. Everything else in a packed bed scrubber exists to feed it or clean up after it.
The section is a housing filled with packing media. We build housings in PVC, polypropylene, FRP, or a PVC/FRP overlay. The FRP version uses a chemical-resistant vinyl ester resin (VER 9300, or as specified) with an inner corrosion barrier reinforced by surface veil.
Inside, the packing multiplies the surface area where gas meets liquid without choking off the airflow. Our standard packing is loose-fill polypropylene, such as Jaeger Tri-Packs® or Lantec Lanpac®: hollow spheres built from a network of ribs, struts, and drip rods. The geometry is the point. Uniform shapes resist nesting, so liquid wets every surface instead of channeling down a few paths and leaving dry zones that contaminants slip straight through. For hotter or harsher chemistries, packing also comes in CPVC, Kynar, ECTFE, ceramic, and stainless steel.
Two numbers define this section. Air velocity through the packing runs 400 to 600 FPM in Viron's standard designs. Packing depth ranges from 12 to 180 inches, and a deeper bed buys more removal at the cost of higher pressure drop.
That pressure drop doubles as an early warning. When scrubber packing fouls or channels, static pressure across the bed climbs, and the fan burns more energy moving the same air.
More on the mechanics: How Packed Bed Scrubbers Work
3. Spray Headers and Liquid Distribution
Packing only removes contaminants where it's wet.
The spray headers take scrubbing solution from the recirculation pumps and spread it across the top of the bed. On Viron units, the headers are PVC Schedule 80 pipe fitted with true union ball valves, so a header can come out for cleaning without shutting down recirculation. Each PVC or polypropylene nozzle sprays roughly 7 to 50 GPM at 10 psi of pump pressure.
Recirculation rate is the governing spec. Most Viron horizontal and vertical scrubbers run between 2 and 15 GPM per square foot of open packing area, with 4 GPM as the standard design point. Weir troughs are an alternative to nozzles and distribute liquid using less energy. The choice turns on recirculation rate, pump horsepower, droplet size, the mist eliminator downstream, and energy consumption.
A change in pressure drop can prompt a check of the liquid distribution system, including spray headers that may need cleaning or replacement. Access matters when that work is needed. On fully enclosed units, we bring the scrubber body inward at the header level and add an access door there, so your maintenance crew doesn’t have to reach through about a foot and a half of empty space to get to the headers.
4. The Mist Eliminator
Air leaving the packing carries droplets of scrubbing solution. Those droplets then carry the contaminants you just captured.
The mist eliminator keeps them inside. Our chevron blades force the air through a zig-zag path. The droplets can't follow the turns, so they hit the blade walls and grow into larger drops that drain back to the bottom of the scrubber.
Your outlet micron target drives the choice. Horizontal cross-flow blades remove 99% of 20-micron droplets, and vertical counter-current blades handle 99% at 32 microns. If you need finer capture, composite mesh pads get down to 99% of 3 microns.
Finer capture costs you headroom, though. A specialized mist eliminator for a tight micron target can also add height to the unit.
5. The Sump and Recirculation System
The sump is the reservoir at the base of the scrubber and, in practice, the unit's operating center. The pumps mount here or on a remote tank. The chemistry gets managed here.
We build two arrangements. A self-contained unit mounts the recirculation pump on a sump attached to the scrubber housing, with the motor bolted above the highest liquid level. It fits indoor installations and climates where freezing is rare. A remote unit puts the pump on a separate tank inside the building, which takes weight off the roof and reduces the need for scrubber heaters, since the tank stays indoors where it won't freeze.
Standard pumps are sealless CPVC sump pumps that can run dry for a short period without damage. FRP, SSTeelcoat coated stainless steel, and polypropylene pumps are options. Specify a backup pump and the system can keep running while the primary is serviced.
The sump is also where a wet chemical scrubber's chemistry gets managed. pH and conductivity sensors track the scrubbing solution, a level sensor protects the pumps, a flow meter confirms the headers are getting liquid, and makeup and blowdown loops keep dissolved solids from building up. Our controls engineer programs that logic in-house.
Two Viron practices center on this section. As standard practice, we plumb each scrubber at our facility and run water through it to check valves, pumps, sensors, and joints before it ships. For facilities that want more than a containment pan, we also offer a fiberglass shell around the plumbing, so a leak drains to secondary containment instead of the floor. Access doors cover routine work. When a pump or motor has to come out, a wall section unbolts for a forklift or jib crane.
6. The Outlet Transition
The outlet transition carries treated air from the scrubber body to the fan or stack duct. The fan must overcome the scrubber’s pressure drop, including resistance from the packing and mist eliminator, along with the rest of the connected exhaust system. We build AMCA-certified fans and account for those requirements when sizing them.
More on that: Centrifugal Industrial Fan Performance Requirements.
Inside an Industrial Scrubber:
6 Components, One Airstream
Follow the exhaust from duct to fan.
Specifying a scrubber?
Where the Six Components Meet the Job Site
One thing no component list shows is how the unit arrives. On larger scrubbers, Viron splits the body into sections with gasketed, flanged plumbing connections. The contractor sets the base, sets the middle, bolts the seams and piping, then sets the top.
Installing contractors are welcome at our facility before shipment to walk the connection points, and Wet Scrubber Installation Best Practices covers the rest.
If you're specifying an industrial wet scrubber, send our engineers your ACFM, contaminant loading, temperature, and removal target. We'll tell you what each of these six components should look like for your wet scrubber application, and whether a vertical or horizontal layout fits your site better.
Request a quote or contact us today to talk through your scrubber spec with a Viron engineer.
Frequently Asked Questions About Industrial Scrubbers
Does a vertical or horizontal scrubber change these components?
The six components stay the same; their arrangement changes. In a vertical unit, the air makes a 90-degree turn into the packing, which saturates more easily, so it can usually run a smaller pump and motor. A horizontal unit has a lower profile for rooftops and height-limited spaces, and its spray headers can be reached without tall ladders, a convenience you don’t want to underestimate.
Does a higher removal target mean a bigger scrubber?
Often, yes. Airflow sets the baseline size, but pushing removal of a specific chemical to 98% or 99% can call for a larger unit or deeper packing. Size for the process you'll have in a few years, too: a scrubber spec'd for five tools gets undersized fast when four more are added to the same exhaust.
How do I choose between PVC, polypropylene, and FRP for the housing?
Chemistry and temperature decide it, so start with Viron's chemical resistance chart. PVC is the lower-cost option where its chemical and temperature limits fit. Material also affects shipping: Viron will move a PVC scrubber in a heated or refrigerated truck when the route could warp it or make it brittle.
What instrumentation belongs on a scrubber control panel?
A typical Viron package can include a NEMA 4X enclosure for corrosive outdoor duty, a PLC for alarms and data logging, an HMI for setpoints, and VFDs on the pumps. A differential pressure transmitter across the packing is worth specifying, because it gives operators a live read on fouling.
Who handles startup on a new scrubber?
Viron's controls engineer programs our scrubbers in-house, and our team can be on site during startup to commission the system and troubleshoot with your operators.