Wet Scrubber Buyer's Guide

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Contents

Wet Scrubber Buyer's Guide

Wet Scrubber Market Overview .........................................................................................................................................3

Wet Scrubber Types .................................................................................................................................................................4

When Should You Use a Wet Scrubber Rather Than a Dry Dust Collector? .....................................................5

Questions to Ask Potential Wet Scrubber Suppliers .................................................................................................6

Pricing Considerations ...........................................................................................................................................................8

How Sly Wet Scrubbers Are Different ..............................................................................................................................9

Sly Impinjet® Scrubbers ...................................................................................................................................................... 10

Sly Venturi Scrubbers .......................................................................................................................................................... 11

Sly Eductor Scrubbers ......................................................................................................................................................... 12

Sly Packed Tower Scrubbers ............................................................................................................................................. 13

The Sly Difference in Dust Collection ........................................................................................................................... 14

Why Sly? .................................................................................................................................................................................... 14

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Wet Scrubber Market Overview Market research predicts that the value of the global dust control systems market for both wet scrubbers and dry collectors is poised to rise at a compound annual growth rate of 6.77% from 2018 through 2022. The wet scrubber segment accounted for a larger share of the global dust control systems market in 2017. Demand for these systems is being fueled by growing awareness of the impact of air pollution on health and the environment among consumers, combined with rapid urbanization and industrialization.

What is a wet scrubber?

A wet scrubber is a mechanical system that removes pollutants from an air stream by bringing it in contact with a scrubbing liquid, most often water. Wet scrubbers are generally the only single air pollution control device that can remove both particulates and gases/vapors. They are highly efficient at capturing the smallest dust particles and can eliminate more than 99% of airborne particulate matter by capturing it in liquid droplets. Wet scrubbers that remove gaseous pollutants are also referred to as absorbers.

Wet scrubbers are used in a wide range of industries to control emissions, from acid, fertilizer and asphalt plants to steel mills and power plants. They offer an alternative to baghouses and other dry dust collection approaches; they’re often used for controlling exhaust from process equipment or they can be located downstream from baghouses/cartridge filter systems, furnaces, dryers, mixers, bucket elevators, bagging stations, and other emission points.

Impinjet® Scrubber

Eductor Venturi Scrubber

Venturi Scrubber

Packed Tower Scrubber

Three Stage Unit

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Wet Scrubber TypesFour different types of wet scrubbers are commonly used in industry:

Impinjet® Wet Scrubbers collect particulates and clean, cool and absorb vapors and gases. They offer high collection efficiencies (99% for particles 5 microns or larger) with low water recirculation and minimum pressure drop. Impinjet scrubbers are highly resistant to fouling and available with capacities as high as 200,000+ CFM. Impingement plate (or tray) scrubbers use a flowing bed of water across a perforated surface. The airflow is drawn into the scrubber and passes through the plate water. The water traps the contaminants, removing them from the airstream. Impingement plate systems typically use lower energy/lower pressure drop to scrub the gas.

Impingement scrubbers are suitable for particulate scrubbing and applications where both particulate and gaseous contaminants must be collected.

Venturi Scrubbers with cyclonic separators are often the best choice for high-efficiency collection of fine particulates. They use the differential between high-velocity gases and free-flowing water to create droplets that entrap contaminants and deliver them as a suspended solids solution. The venturi scrubber design requires more water and higher pressure drop to remove particulate than impingement plate scrubbers. The converging section of the venturi throat (where the water and airstream merge) creates atomized water droplets to provide

efficiencies of 99 percent on particles 1 micron in size and larger. The efficiency can increase to 99.8 percent for particles 5 microns and larger. For more details on venturi scrubbers, download a copy of "Venturi Scrubbers, Physics & The Big Bang Theory.”

Eductor Venturi Scrubbers remove both soluble gases and particulates by inducing a gas flow using high-pressure liquid focused into a venturi throat. This eliminates the need for a separate exhaust fan or blower to transport the contaminant-laden airstream to the scrubber. Eductor venturi scrubbers can also be used for direct-contact condensation. A high liquid flow rate makes this type of scrubber particularly well-suited for collecting sticky and/or gummy particulate,

as well as gases that decompose on contact with water. Eductor scrubbers are often used in combination with other collection devices such as packed tower scrubbers.

Packed Towers are designed for chemical scrubbing of gaseous contaminants and are often used to remove sulfur dioxide, hydrogen chloride, ammonia, hydrogen sulfide, and other gases. In vertical scrubbers, the gas flows upward through the bed, while the liquid trickles downward by gravity through the packing, which is typically made up of small plastic or metal objects. The liquid wets the surfaces of the packing materials, which are designed to provide a large amount of surface area for contact between gas and liquid. A liquid distribution

header located above the packing evenly distributes the scrubbing solution across the top of the packing. Recirculated scrubbing liquid typically contains alkaline, acid, or oxidizing scrubbing agents to achieve the desired outlet emissions. Prior to leaving the scrubber, the scrubbed air passes through a mesh or chevron style mist eliminator to remove entrained droplets.

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When Should You Use a Wet Scrubber Rather Than a Dry Dust Collector?Wet scrubbers can be used in many of the same types of applications as dry dust collectors (baghouses and cartridge collectors). However, certain applications all but demand the use of a wet scrubber:

• Combustible/hazardous dusts. Wet scrubbers are often the best option for handling combustible dust because they can effectively minimize the risk factors for a dust explosion. Combustible dusts include a wide range of food products, agricultural products, carbonaceous dusts, chemicals, and metal and plastic dusts. For more details on common types of combustible dust and tips on assessing the likelihood of dust explosions, request the Sly white paper titled “Using Wet Scrubbers for Combustible Dust Control” or download OSHA’s free “Combustible Dust” poster from OSHA.

However, wet scrubbers are not appropriate for handling all dust types; some dusts (such as alkali metals like lithium, sodium and potassium and alkaline earth metals like beryllium, magnesium and calcium) are actually water reactive, which means they’re more hazardous when they come in contact with water.

• High-temperature applications. Wet scrubbers also offer a good solution for dealing with high process temperatures. Unlike dry collectors, which require special high-temperature design and construction methods and expensive high-temperature filter bags, standard wet scrubbers can handle high process temperatures without these added costs. Because adding water into the system does not affect scrubber operation, quench systems can be employed prior to the inlet to the scrubber. A scrubber that includes a pre-quench section can handle temperatures higher than 2,000°F.

• Moisture in the gas stream. Humidity in the gas stream will foul or plug a dry dust collector and cause caking on the filter bags, but a wet scrubber can handle it without problems. Given that the scrubber uses water or another scrubbing liquid to saturate the gas stream for particulate removal, moist process gas is no problem.

• A combination of particulate and gaseous contaminants. A combined dust and gas stream is particularly problematic for dry collectors because they can only address the solid particulates; a secondary piece of equipment, such as a scrubber, would also be needed to remove the gases. In contrast, many types of wet scrubbers can collect both solid and gaseous components from the waste stream with just one piece of equipment.

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Questions to Ask Potential Wet Scrubber SuppliersFinding and implementing the right wet scrubber system takes much more than just reviewing a data sheet and issuing a purchase order. Take the time necessary to find the answers to the following questions for any scrubber supplier under consideration.

• How long has the supplier been in the pollution control business? Lots of companies sell air pollution control equipment, but none have been doing it as long as Sly. We bring close to a century-and-a-half of experience in helping industrial customers find and implement the most cost-effective solutions for their dust collection requirements.

• Does the supplier manufacture their own wet scrubber equipment or do they outsource it? Wet scrubbers require in-depth knowledge to design and install correctly and cost-effectively. At Sly, unlike many of our competitors, we don’t outsource fabrication; our systems are built in our own plant in Mathiston, Mississippi. We control every step of the process, so we can produce designs that can accommodate your unique application and environment.

• Does the supplier maintain an inventory of parts for repair/maintenance? When your scrubber shuts down, so can your production. In addition to maintaining an in-house supply of replacements, you need a national supplier who keeps a full range of OEM-quality parts in stock, so they can ship them promptly.

• What types of scrubbers do they offer? Look for a company capable of designing, building and supporting a variety of solutions. Let’s face it, a supplier that can only offer one kind of scrubber will try to make it fit all its customers’ applications. At Sly, we believe in fitting the equipment to the customer’s needs, not the customer to the equipment’s capabilities.

• Do they have experience in designing scrubbers for my industry/application? Different industries and applications present different challenges. Before you start your vendor selection process, take the time needed to talk to others with similar applications and ask about their experiences, both before and after the sale.

• Do they offer dust analysis capabilities? Before a supplier can make an informed recommendation on a scrubber, they need to understand the dust and gases that a process produces. That starts with measuring its bulk density—information that can be used to diagnose re-entrainment or to aid in scrubber design. The analysis should also cover particle size distribution, which is useful for predicting scrubber performance in applications where similar dusts are involved. Sly offers both analyses.

• Will the scrubber being proposed comply with emission requirements for my industry/application? Ask potential suppliers if they have experience in designing systems that meet both the needs of the application and the local emissions standards.

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• Do they have in-house system design and customization capabilities? At Sly, we do our own engineering, metal fabrication, painting, assembly and quality control. That lets us control every step of the process, allowing us greater flexibility to customize your scrubber for the needs of your specific application.

• Who will be your point of contact during design, installation and operation? With a system as complex as a wet scrubber, you probably don’t have the time or the patience to play phone tag with lots of different vendor employees, each handling a different aspect of the sale, installation, startup, etc. At Sly, you have one point of contact who can answer all your questions.

• Does the supplier have in-house staff experienced in troubleshooting? How many engineers are on staff? At some suppliers, once the invoice is paid, you may have trouble finding anyone who can help you keep your scrubber running efficiently over the long term. Some may not even have engineers on staff who can understand your questions and recommend solutions. Sly’s commitment to total customer support and experienced engineering staff help guarantee the ongoing value of your investment.

• Will they take all the time necessary to understand the application’s requirements before quoting a price? Scrubber systems can’t be quoted by someone looking up prices in a catalog; it takes expert understanding of the specific application and the environment in which it will be operated. When you are narrowing down your list of vendor options, ask each about the procedures they use to evaluate your needs. At Sly, the specification process starts with answering these questions: - Gas volume?

- Process description?

- Temperature?

• Are replacement parts for the system they recommend widely available or only available through that supplier? A system that requires a proprietary replacement part can keep you tied to a vendor for many years or can present obsolescence problems if the vendor goes out of business. Choose a vendor that provides systems that have parts designed to stand up to the harsh environment inside a scrubber and readily available replacements.

• What level of support can your scrubber supplier provide after the sale and installation? Sly’s engineering staff can help you troubleshoot your scrubber or assist with any other field service problems that might occur at your facility.

• Will the supplier work with you to establish a maintenance program to ensure the ongoing performance and efficiency of your system? A wet scrubber represents a major capital investment that needs to be regularly maintained. Ask potential suppliers about kinds of support they provide for developing your in-house maintenance program.

- Particle size?

- Moisture content?

- Type of contaminant?

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Pricing ConsiderationsEvery combination of scrubber application and environment is unique, with a variety of factors that will contribute to the final cost. Here are some of the considerations that must be taken into account when specifying a system:

• Size of scrubber the application requires. Once the scrubber type best suited for the application has been determined, the next step is sizing it. The factors affecting sizing are gas flow rate, temperature, pressure, gas composition, humidity, contaminant loading and desired outlet conditions. The availability of an appropriate scrubbing liquid is an important consideration. Although gas streams entering a wet scrubber might not be fully saturated, they will exit the scrubber fully saturated, which results in a change in volume, temperature and density. The overall scrubber size (diameter) is a function of velocity of saturated gas through the scrubber shell. By knowing the moisture content of a gas stream (generally expressed as pounds of water per pound of dry gas) and the inlet temperature, the saturation temperature and saturated volume content can be calculated. For more details on calculating scrubber size, consult Sly’s Wet Scrubber Application Guide.

• Cost of non-standard design or modifications. Not surprisingly, highly customized designs will generally cost more than standard ones, so factor the added expense into your budget.

• Ductwork. Don’t forget to include the cost of ductwork required to connect your dust pickup points to the scrubber.

• Optional equipment and features. The use of corrosion-resistant materials, recirculation pumps and piping, instrumentation and controls, etc. can all add to the final system cost.

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How Sly Wet Scrubbers are Different

A wider range of options. Suppliers that can only offer one kind of solution will try to make it fit all their customers’ applications. At Sly, we design and build multiple types of both dry collectors and wet scrubbers. Our philosophy is to fit the equipment to the customer’s needs, not the customer to the equipment’s capabilities.

Higher-quality welding. Our shop can fabricate welded structures from carbon steel, abrasion resistant steel, stainless steel, and other high alloy materials like Inconel, Hastelloy, and AL6XN. All welders are certified to the AWS Structural Welding Code for D1.1 (structural steel); D1.3 (sheet metal); and D1.6 (stainless steel). We also have certified welding inspectors on staff.

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Sly Impinjet® Scrubbers

Sly's unique perforated plate with impingement baffle strips allows the Impinjet scrubber to collect fine particulates and absorb gases. Its simple but rugged design offers efficiencies higher than 99% for many types of dust or gas.

To improve efficiency to handle new requirements, the flexible architecture of Impinjet scrubbers makes it simple to incorporate additional stages to existing installations, rather than buying new units.

The outlet gas can be cooled to less than 5°F more than the temperature of the incoming liquid. Chilled liquid is used as direct contact condensing liquid and removes the heat from the gas stream as it gains heat. Scrubbers also recover waste heat. Heat from dryers and other processes that would normally be exhausted can be used to heat water being fed to the scrubber almost to the wet bulb temperature of the inlet gas. For cooling and condensing and for heat recovery, our designs can accommodate high hydraulic loadings.

Features• Handles combustible dusts safely, without modifications

• High condensing and cooling efficiency for gases

• Efficiencies exceeding 99% for particles 5 microns or larger

• Multiple stages can be added to improve efficiency

• Capacities from 500 to over 100,000 CFM

• Water recirculation as low as 3 GPM per 1000 ACFM

• Emissions warranties available

• Low maintenance

• No moving parts

• Oversized access doors to service plates and sprays

Standard Equipment• Conditioning sprays

• Stainless steel impingement baffle plates

• Fixed blade mist eliminator

• Self-draining design

• Bolted access doors

• Carbon steel/stainless steel construction

Optional Equipment and Features• Stainless steel, high alloy, fiberglass-reinforced plastic (FRP) or plastic construction

• Mesh or chevron mist eliminators

• Quick opening access door

• Integral sumps

• Recirculation tanks

• Pumps

• Exhaust fans

• Instruments

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Sly Venturi Scrubbers

The Sly Venturi Scrubber removes a variety of pollutants, including hazardous and nuisance dust, fumes and mists from stack gases. It uses the differential between high velocity gases and free-flowing water to create droplets that entrap contaminants and deliver them as a slurry. Its simple, yet highly efficient design offers a non-plugging, trouble-free way to introduce scrubbing liquid and an easily adjustable throat. A flooded elbow arrangement collects agglomerated particulates and provides an abrasion-resistant barrier that reduces scrubber wear. The Sly Venturi Scrubber incorporates features proven to maximize collection efficiency while minimizing operating and maintenance costs.

Features• Handles combustible dusts safely, without modifications

• Collects fine particles and mists

• Adjustable throat permits fine-tuning to maximize efficiency

• High collection efficiency for sub-micron particulates

• Water recirculation typically 8 GPM per 1000 CFM

• Capacities from 1500 to 150,000 CFM

• Pressure drops from 12" w.g. to 40" w.g.

• Emission warranties available

Standard Equipment• Wetted approach inlet

• Removable liquid distributors (no spray nozzles used)

• Manually adjustable throat

• Flooded elbow

• Adjustable cyclonic spin damper

• Access doors (bolted)

• Carbon steel/stainless steel construction

Optional Equipment and Features• Stainless steel, high alloy, fiberglass-reinforced plastic (FRP) or plastic construction

• Combination units (Venturi/packed tower) available

• Auto adjustable throat positioner

• Quick opening doors

• Recirculation tanks

• Pumps

• Exhaust fans

• Instruments

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Sly Eductor Scrubbers

Eductor Venturi Scrubbers are designed to remove soluble gases and particulates by inducing a gas flow using high pressure liquid focused into a venturi throat. Additionally, eductor scrubbers can be used for direct-contact condensation. A high liquid flow rate makes the Sly eductor particularly appropriate for collecting sticky and/or gummy particulates, as well as gases that decompose on contact with water.

Standard Features• Access door in tank

• Flanged inlet and outlet

• Integral recirculation reservoir

• Anchor lugs

• Lifting lugs

Optional Accessories/Features• Pressure differential gauge

• Internal sloped bottom

• Cone bottom

• Recirculation pump

• Recirculation piping

• Instrumentation package

• Exhaust fan

• Skid mounting (6' diameter and smaller)

• Control panel

• Sump heaters (freeze protection)

• Chemical feed systems

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Sly Packed Tower ScrubbersPacked tower scrubbers (also known as packed bed or packed column absorbers) are designed for chemical scrubbing of gaseous contaminants from air streams. Internal packing in the scrubber vessel provides a large wetted surface area to induce close contact between the contaminated air and the scrubbing liquid. The contaminant absorbs into or reacts with the scrubbing liquid. Recirculated scrubbing liquid typically contains alkaline, acid, or oxidizing scrubbing agents to achieve the desired outlet emissions.

Sly’s custom designed and fabricated packed tower scrubbers are engineered for specific applications for optimum tower diameter, packing depth, recirculation flow rate, and the appropriate mist eliminator style. Packed tower scrubbers can be designed to handle a wide range of airflows and can be

constructed from a variety of metallic and non-metallic materials. Packed tower systems, when designed correctly, can successfully absorb and neutralize harmful, toxic gas streams and exhaust clean air into the atmosphere. Applications range from product recovery to air pollution and odor control.

In vertical, countercurrent scrubber operation, the gas flows upward through the bed, while the liquid travels downward by gravity through the bed. A liquid distribution header evenly distributes the scrubbing solution across the top of the packing. Traveling a complex route through the packing extends the contact time between the air and the liquid and increases the closeness of gas and liquid contact. The type of gas and the desired removal efficiency will determine the bed depth, packing size, irrigation rate, and chemical requirement. Prior to leaving the scrubber, the scrubbed air passes through a mesh or chevron-style mist eliminator to remove entrained droplets. Liquid can often be discharged to the sanitary sewer without further treatment.

Packed towers are commonly used to remove SO2, HCI, NH3, H2S, and other gases. Some applications may require the use of two or more chemical additives. The most commonly used chemical additives are:

• Sodium hydroxide (alkali) or sulfuric acid (acid) for pH control

• Sodium hypochlorite or hydrogen peroxide for ORP (oxidation reduction potential) control

Standard Equipment• Packing to promote mass transfer

• Packing support

• Liquid distributor

• Mist eliminator

• Recirculation tank

Optional Accessories/Features• Stainless steel, FRP, or high alloy construction

• Instrumentation and controls

• Exhaust fan

• Recirculation pump

• Chemical feed system

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We’ve been in the business longer than anyone else: Sly, Inc. was founded almost a century-and-a-half ago in 1874 and we haven’t lost sight of the importance of serving our customers’ needs.

We believe in delivering responsive, personal, hassle-free customer service: When you become a Sly customer, you won’t have to waste time playing “telephone tag,” trying to track down someone to answer your questions about an order.

We employ engineers, not order takers: Other companies often don’t have trained engineers on staff who can understand your questions and recommend solutions.

Why Sly? No other dust collector company provides a better customer experience throughout the entire sale lifecycle: pre-sale advice, design customization, fabrication, product performance and post-sale support.

About Sly, Inc. With nearly 150 years of pollution control expertise, Sly is a trusted advisor to leading manufacturers in designing industrial dust collector and wet scrubber systems. We manufacture our own dust collectors and scrubbers and can customize our solutions for a wide range of applications. Long-term customer relationships are a hallmark of our business because we work closely with customers to develop the right solutions and deliver quotes and finished systems on time. Learn more by visiting www.slyinc.com.

The Sly Difference in Dust CollectionAt Sly, what makes us different from other wet scrubber vendors is what makes us better:

We have the flexibility to meet your schedule: All Sly scrubbers are designed and built to your specifications, so we don’t keep finished units in stock. Our typical delivery times for larger units are typically from 12 to 14 weeks from the receipt of the order. However, because we build our systems in our own shop, we can often arrange for expedited delivery.

We provide responsive, detailed proposals: Before you buy a Sly scrubber, you’ll understand what you’re getting and what it can do for you.

We deliver meaningful emissions guarantees: We don’t believe in making empty performance promises.

We bring an in-depth understanding of the relevant regulations and standards to the design and construction of your system. Sly has been in the scrubber business for as long as there have been scrubbers.