Air Pollution Control Innovations

Peat Dryer Horizontal Venturi Scrubber

Posted by Andy Bartocci on Thu, Jan 09, 2020 @ 05:30 AM

An agricultural solutions company, American Peat Technology, transforms locally harvested unprocessed peatPeat Dryer Horizontal Venturi into a consistent granular media. The media is used as a natural microbial carrier to inoculate millions of acres of food crops each year. The transformation process relies on drying harvested material in industrial rotary dryers. A fraction of the material becomes entrained in the flue gas as particulate emissions. The facility is expanding operations to double the capacity. A scrubber solution is needed to reduce total plant particulate emissions.

The customer selected two identical Envitech horizontal Venturi scrubbPeat Dryer Horizontal Venturi_long viewers. The scrubbers are comprised of a variable throat Venturi scrubber and a chevron style entrainment separator mounted on an equipment skid. The scope of supply for each scrubber includes a control system, re-circulation pump with pre-assembled piping, valves and fittings. Instruments are pre-mounted in the piping where possible and pre-wired to a junction box on the skid. The horizontal configuration provides a compact design to fit inside the building with easy maintenance access to valves and instruments.

The skid arrangement allows the scrubbers to be shop assembled and tested prior to shipment.  The combination of a variable throat Venturi with a chevron style mist eliminator allows a wide turn-down ratio while maintaining high performance. The use of a wet scrubber instead of a bag-house eliminates the potential for bag fires that could be caused by occasional hot embers entrained in the gas.  The facility is also able to make use of the latent heat absorbed by the scrubber, making use of hot recirculated scrubber water to thaw out frozen peat in the winter before it is fed to the dryers. 

The scrubbers were commissioned in December 2019 and are now operational. Both scrubbers are used for two dryers providing a wide operating range. The scrubbers meet the design parameters listed below:

DESIGN PARAMETERS

  • Inlet flow rate: 25,000 acfm
  • Inlet temperature: 185oF
  • Inlet Particulate: 15 lbs/hr 
  • Particulate Removal: > 99%

Click on the link below to download a case study and other Venturi scrubbing literature.

Download Literature

Topics: particulate control, Venturi scrubbers, Scrubbers, Wet Scrubbers

Mineral Processing Venturi Scrubber

Posted by Andy Bartocci on Wed, Dec 04, 2019 @ 08:04 AM

US Magnesium is implementing an electrolytic expansion project located in Rowley, UT. A scrubbing system isUS Mag Venturi Scrubber needed to remove particulate from a chlorine gas stream that originates in the anode compartments of electrolytic cells that produce magnesium metal. A significant portion of the particulate is less than 1 micron in size, making it difficult to remove.

Chlorine is an important by-product of the electrolytic process. Scrubbed chlorine flows to a chlorine plant for further processing and liquefaction. The scrubbing equipment must be designed and constructed in a manner to minimize air in-leakage and chlorine emissions. Materials of construction must be selected to withstand severe corrosive characteristics of > 90% chlorine (Cl2) gas.

Particulates in the gas leads to maintenance associated with downstream filters in the chlorine plant. It is therefore necessary to maximize removal efficiency to minimize filter maintenance costs.

The customer selected an Envitech high efficiency Venturi Scrubber. The equipment includes a fixed throat fiber reinforced plasUS Mag Venturi Scrubber Fanstic (FRP) Venturi scrubber and horizontal chevron style entrainment separator. Additional scope of supply includes instruments, pre-assembled pump skid with redundant titanium pumps (1 operating and 1 spare), pre-assembled CPVC piping, redundant fans with titanium wheel and housing, interconnect FRP ductwork, dampers, and equipment skid and platforms.

Because a large fraction of particulate is submicron in size and difficult to remove, the fans and vessels are designed to operate at -70” water column pressure drop.

An Envitech Venturi scrubber was installed on the original process in 1999. The new scrubber for the expansion project was installed in 2011. Both systems continue to operate with high reliability and uptime. The table below summarizes key design parameters for the new Venturi scrubber.

DESIGN PARAMETER

  • Inlet flow rate: 8,200 acfm
  • Inlet temperature: 130oF
  • Gas Composition:  > 90% Cl2 gas
  • Pressure drop: 60" W.C.
  • PM Removal: > 75%

Click on the link below to download a case study and other Venturi scrubbing literature.

Download Literature

Topics: particulate control, Venturi scrubbers, Scrubbers, Wet Scrubbers

Hot Mix Asphalt Dryer Emissions Control

Posted by Andy Olds on Wed, Dec 04, 2019 @ 06:30 AM

Hot mix asphalt (HMA) plants combine aggregate and petroleum byproducts to form paving material.  HMA plants can be permanent, transportable (skid-mounted), or portable.  For large asphalt projects, it is economical to use transportable or portable HMA plants so as to set up near the project and reduce the delivery time of asphalt to the site.  Large HMA manufacturers thus transport their manufacturing equipment from site to site.Env Horz VS scrub

The most common HMA plant is a batch mix plant.  A batch plant consists of an aggregate dryer to dewater the aggregate, a mixer to combine the aggregate with asphalt cement, and a load-out bay for transferring the final product to trucks for transport.  Auxiliary equipment includes a cyclone for aggregate collection after the dryer, a secondary collection device for particulate emissions, a blue haze control device to curb VOC emissions.  Reclaimed asphalt pavement (RAP) is typically used to reduce costs and promote sustainability within the industry.  The stage at which RAP is introduced depends on the qualities of the RAP and the desired properties of the final asphalt product.

According to the EPA, there are two primary techologies for the secondary collection devices: Venturi scrubbers and baghouses.  Venturi scrubbers are wet devices that capture particulate through inertial impaction.  Venturis are fractional efficiency devices capable of efficiently capturing particulate as small as 1 micron.  Venturis are inherently self cleaning: water sprays continuously from the Venturi throat and the accelerated gas shears any wall buildup.  Thus, Venturis are excellent in the removal of sticky particulate that would foul other forms of particulate control. Also, as a wet process, Venturis have the ability of capturing condensables and water soluble vapors.  The alternative technology for secondary particulate capture is a baghouse.  A baghouse achieves particle collection by filtering the gas through a physical barrier. Baghouses can efficiently remove submicron particulate, provided that the particulate is filterable.  Baghouses are not able to capture condensibles, but can capture some acid gases if an appropriate dry chemical is added to the dryer flue gas.

Recently, Envitech has developed an economical Venturi scrubber that can be either built on a skid for easy transport, or built on a truck bed for portability.  Envitech's Venturi scrubber is capable of meeting even the most stringent PM-10 requirements for particulate control, and works well with downstream blue haze control devices. Our Venturi scrubber is also anti-fouling and capable of consistently meeting control targets even with difficult RAP and exotic formulations with minimal maintenance.   

Topics: particulate control, Venturi scrubbers, Scrubbers

Wet Scrubber Basics

Posted by Andy Bartocci on Tue, Sep 10, 2019 @ 09:02 AM

 

As an equipment supplier of custom engineered wet scrubber equipment, Envitech frequently provides lunch and learns (L&L’s) to engineering companies to help educate engineers about the basics of available technology.

Figure 1 below is a summary chart of predominant wet scrubber technology options. The main product categories include packed bed absorbers, Venturi scrubbers, and wet electrostatic precipitators (WESPs). Each wet scrubber type serves a different purpose and is used in different circumstances. For instance, packed bed absorbers are primarily used to remove gaseous emissions like SO2, HCl, or HF. We often receive packed bed absorber inquiries for particulate removal, however, this would be a misuse of technology. Packed bed absorbers remove some particulate but they are not nearly as efficient as other options.

Figure 1: Wet scrubber technology summaryEnv wet scrubber technologies

Venturi scrubbers are used for particulate removal. Just like we sometimes receive packed bed absorber inquiries for particulate removal, we’ll occasionally get Venturi scrubber inquiries for acid gas removal. This would also be a misuse of technology. Venturi scrubbers achieve some acid gas removal, but they have poor mass transfer compared to a packed bed absorbers.  

Venturi scrubbers use mechanical forces to remove particulate. Particles are captured through a process of impaction between particles in the gas and water droplets in the Venturi throat. A high differential velocity is created between particles and droplets by accelerating the gas in the throat. A pressure drop in the throat provides energy to capture the particles. Smaller particles less than 1 micron in size avoid capture by behaving like gas molecules and finding slip streams around the water droplets. Venturi scrubber performance drops offs exponentially for submicron particulate. Overall removal efficiency may be limited for a gas stream with a high concentration of submicron particulate. Venturi scrubbers are a good choice for industrial dryers or other applications with large size particulate.

Wet electrostatic precipitator (WESP) are the third type of wet scrubber summarized in the table. Like Venturi scrubbers, they are also particulate removal devices. They differ from Venturi scrubbers in a couple of ways, 1.) electrical, not mechanical forces are used to capture particulate, and 2,) they are efficient at capturing submicron particulate. Figure 2 shows a performance comparison between a WESP and Venturi scrubber. It can be seen that performance drops off dramatically for Venturi scrubbers for particles less than 1 micron in size. WESP’s on the other hand remove particles regardless of particle size.

Figure 2: WESP, Venturi scrubber performance comparison versus particle size.

Envitech WESP Venturi Performance

The summary in Figure 1 also shows how each wet scrubber technology differs in regulatory control. A packed bed absorber is typically controlled for recirculation flow rate and liquid pH. A Venturi scrubber is controlled by recirculation rate and pressure drop. A WESP is controlled by voltage. Control limits are typically spelled out in the operating permit.

Finally, some examples of applications are given for each type of wet scrubber. It should be noted that there are many applications that have multiple types of pollutants. A hazardous waste incinerator, for instance, contains particulate, acid gases, and specific heavy metals like cadmium and lead. A fraction of particulate is submicron in size and difficult for a Venturi scrubber to remove. It is common for different types of wet scrubbers to be combined into a multi-pollutant device. Figure 3 shows a common arrangement for an incinerator scrubber. The gas is first cooled in a quencher. A packed bed absorber removes acid gases. A Venturi scrubber removes particulate and a WESP removes the submicron particulate and heavy metals.

Figure 3: Incinerator wet scrubber arrangement

Env wet scrubber arrangement

Wet scrubbers can also be combined with dry scrubbers in certain circumstances. An upstream bag-house can remove particulate followed by a packed bed absorber for acid gas removal. A cyclone can be used to knock out large particulate before using a Venturi scrubber for the remaining particulate. A cyclone helps to minimize blowdown and water consumption. In some cases, a dry filter or carbon bed absorber can be integrated downstream of a wet scrubber for mercury and/or dioxin/furan. Click here to read a blog piece about an example of a wet scrubber combined with a carbon bed.

This about covers wet scrubber basics. If you’re with an engineering company and want to discuss scheduling a lunch an learn, please give Envitech a call. You can click on the icon below for a set of Envitech brochures.

Click on the icon below to download an Envitech brochure.

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Topics: particulate control, Venturi scrubbers, Scrubbers, SO2 Scrubber, wet electrostatic precipitators, Acid Gas, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

International Conference on Thermal Treatment Technologies and Hazardous Waste Combustors (IT3/HWC)

Posted by Andy Bartocci on Mon, Aug 26, 2019 @ 10:55 AM

IT3 Logo

Envitech will be attending and exhibiting at the 37th International Conference on Thermal Treatment Technologies and Hazardous Waste Combustors (IT3/HWC) in League City, TX on October 2nd and 3rd, 2019. If you happen to be attending the conference, please stop by the Envitech booth or find me at the conference to say hello.

Three keynote panels will include high level experts and cover hot topics in the industry:

  • PFAS Overview, Regulatory Approach, Testing and Destruction
  • Emerging Air Quality Monitoring
  • Lessons Learned from the United Kingdom's 2018 Novichok Nerve Agent Incident

Papers presented in technical sessions cover:

  • Technologies and Trends in Incineration
  • Plastics Recycle and Reuse
  • Emission Monitoring
  • Waste-to-energy, Emission Monitoring, Pyrolysis 

Envitech will present papers on the following two topics.

Technology Solutions for Sulfuric Acid Formation and Removal in Liquid Waste and Waste Gas Thermal Oxidizers

Petrochemical plants, refineries, and waste-oil re-refiners operate liquid waste or waste gas thermal oxidizers.Candle filter The thermal oxidizers need a wet scrubber to neutralize and remove SO2. Flue gas entering the scrubber contain some sulfur trioxide (SO3) which is converted to sulfuric acid (H2SO4) in the quencher. Sulfuric acid is a submicron liquid aerosol that passes through the downstream packed bed absorber. Some facilities are now being regulated for H2SO4. This paper evaluates and compares candle filters versus wet electrostatic precipitators (WESP’s) for H2SO4 removal in these applications.

Sewage Sludge Incinerator (SSI) Mercury Control Technologies

Mercury Control ScrubberWaste water treatment facilities operating sewage sludge incinerators (SSI) can reduce sludge volume and disposal costs by combusting dewatered sewage sludge. Emissions are regulated by the US EPA Maximum Available Control Technology (MACT) standard 40 CFR Part 60 and 62 to control particulate, lead (Pb), cadmium (Cd), SO2, HCl, dioxins/furans, and mercury (Hg). Many SSI’s need a control device specifically for mercury. This paper evaluates two mercury control technologies: sulfur‐impregnated activated carbon and Gore sorbent polymer catalyst (SPC) modules. Several facilities have used sulfur-impregnated activated carbon but safety issues have arisen due to fires which have shut down some systems. The Gore SPC modules are a relatively new technology with at least seven installations. A comparison is made of capital cost, operating cost, mercury removal efficiency, fire and performance risks based on incineration of 3,000 lbs/hr of sewage sludge. Finally, an overview is provided for an Envitech SPC mercury control scrubber operating at one facility.

Click on the icon below to download an Envitech brochure.

Download Brochure

 

 

Topics: particulate control, Scrubbers, SO2 Scrubber, wet electrostatic precipitators, Acid Gas, Incinerator Scrubber, SO3 Aerosol

Technology Solutions for Sulfuric Acid Formation and Removal in Thermal Oxidizers

Posted by Andy Bartocci on Fri, Aug 23, 2019 @ 02:56 PM

Enivtech will be attending the 2019 International Conference on Thermal Treatment Technologies andCandle filter Hazardous Waste Combustors  (IT3/HWC)  October 2-3 in Houston, TX. A paper will be given on “Technology Solutions for Sulfuric Acid Formation and Removal in Liquid Waste and Waste Gas Thermal Oxidizers”. The paper is available for download by clicking the button at the bottom of this blog piece.

Petrochemical plants, refineries, and waste-oil re-refiners operate liquid waste or waste gas thermal oxidizers. The thermal oxidizers need a wet scrubber to neutralize and remove SO2. Flue gas entering the scrubber contains some sulfur trioxide (SO3) which is converted to sulfuric acid (H2SO4) in the presence of water vapor. Sulfuric acid is a submicron liquid aerosol that can pass through downstream equipment, such as a packed bed absorber or a baghouse. Some facilities are now being regulated for H2SO4.

WESPOver the last decade, Envitech has supplied SO2 scrubbers for thermal oxidizers burning sulfur containing compounds in refining applications. Most of these do not have add-on controls for capturing sulfuric acid mist. More recently, however, Envitech has supplied two systems with candle filters for the capture of sulfuric acid mist. Another known system used a wet electrostatic precipitator for the capture of sulfuric acid mist. A potential fourth system with a large gas flow rate with expected SO3 emissions was evaluated for a wet electrostatic precipitator.

A thermal oxidizer converts sulfur containing liquid or gaseous waste in the presence of excess oxygen to sulfur dioxide (SO2). A fraction of SO2 is further converted to SO3. The reaction is:

SO2 + 1/2O2 => SO3

The conversion amount is influenced by many factors including the thermal oxidizer operating temperature, residence time, sulfur concentration, amount of excess air, and the presence of catalytic oxides and metal catalysts in the fuel. Literature suggests that even a well-performing thermal oxidizer still converts 1 to 5% of SO2 into SO3. Given the numerous factors influencing the formation of SO3¬, most designers select a conservative estimate of SO3 conversion, even when actual SO3 emissions have been measured, as variations in operation can generate substantially higher conversion.

Once formed in the thermal oxidizer, SO3 reacts with water in the downstream quencher to form sulfuric acid (H2SO4) by the reaction:

SO3(g) + H2O(l) => H2SO4(l)

At temperatures below 350°F, H2SO4 condenses into submicron liquid droplets which are difficult to remove because of their small size. Aerosol droplets pass through a quencher and packed bed absorber. A separate control device is needed for sulfuric acid removal that is suitable for submicron droplets.

Click on the link below to download the IT3/HWC conference paper to learn about “Technology Solutions for Sulfuric Acid Formation and Removal in Liquid Waste and Waste Gas Thermal Oxidizers”. The paper evaluates and compares candle filters versus wet electrostatic precipitators (WESPs) for H2SO4 removal in these types of applications.

Download Literature

Topics: particulate control, Scrubbers, SO2 Scrubber, wet electrostatic precipitators, Acid Gas, Incinerator Scrubber, SO3 Aerosol

Horizontal Venturi Scrubber for Particulate Control

Posted by Andy Bartocci on Mon, Oct 22, 2018 @ 12:21 PM

Venturi scrubbers are mechanical impaction devices that are used to control particulate on a wide range of applications. These include medical and hazardous waste incineration, potash drying, sewage sludge incineration and processing, coal drying, mineral wool manufacturing, and copper roasting to name a few.  In one of my last blog posts I discussed a Venturi collision scrubber used to treat exhaust fumes of a Banbury mixer for rubber compounding.  The Envitech collision scrubber is used in several Goodyear Tire manufacturing facilities around the world.   


Venturi scrubber

A recent new application is a horizontal Venturi scrubber for an aggregate asphalt drum dyer.  The asphalt process is semi-stationary operating at fixed locations for several months at a time. The process is periodically broken down and moved to new locations for operation.  The horizontal arrangement makes the horizontal Venturi scrubber an ideal solution for mobile applications.  The equipment package is transportable on a single flatbed with only minor disassembly required for shipment and installation.  The equipment is mounted onto a skid with pre-assembled piping and wiring to facilitate equipment mobility. 

Particles are captured in the horizontal Venturi scrubber through a process of impaction by water droplets injected into the Venturi throat.  A fraction of particulate laden water becomes entrained in the gas which has a droplet size distribution.  The droplets are removed from the gas by a mist eliminator.   There are two pathways for particles to escape capture by the scrubber. The first is penetration.  Smaller particles lacking the mass for impaction penetrate through the scrubber.  The second is through carry over of particulate laden water droplets.  Droplet capture efficiency, or mist elimination, therefore impacts scrubber efficiency and overall plant emissions.

The horizontal Venturi scrubber uses a damper blade and actuator to maintain constant pressure drop across a wide range of gas flows.  A high efficiency chevron mist eliminator removes particulate laden droplets before the gas exits the scrubber.  A chevron mist eliminator removes greater than 99.9% of water droplets down to 27 microns with less than 0.25 inches W.C. of pressure drop.  By comparison, a cyclonic separator requires several inches W.C. of pressure drop to remove 98% of 27 microns droplets.   The advantages of a chevron mist eliminator are higher performance, larger turn down ratio, and lower pressure drop.

Envitech is currently building two new horizontal Venturi scrubbers sized for 45,000 acfm each for a peat drying operation. The compact design allows the scrubber to be easily installed inside a building. The high level of pre-assembly and lower profile reduces installation time and improves maintenance access for plant personnel.  The horizontal Venturi scrubber can be a cost effective alternative to many processes that use a typical vertical arrangement.

Click on the link below to download Venturi scrubber literature.

 Download Literature

Topics: particulate control, Venturi scrubbers, Scrubbers

Envitech Lab Scrubbers for Gaseous Emissions and/or Particulate Control

Posted by Andy Bartocci on Tue, May 22, 2018 @ 11:31 AM

Packed bed absorbers are often used to treat gaseous emissions for reasonably large gas flow rates ranging from a few thousand cfm to greater than 70,000 cfm. Common emissions include SOx, HCl, HF, and NOx. The absorbers are often custom engineered for a specific plants and have been used for secondary lead smelters, geothermal power plants, waste oil-re-refiners, ceramic tile manufacturing, waste incinerators, and ethanol plants. The types of emission sources range from thermal oxidizers, regenerative thermal oxidizers (RTO’s), furnaces, kilns, direct fired heaters, incinerators, fermenters, vent tanks, and batch mixers.

Lab Scrub Mktg 1-1Envitech developed a lab scrubber to provide an economic solution for smaller gas flow rate applications.  The lab scrubber is a packaged unit designed for high efficiency of water soluble contaminants and can handle up to 2,000 cfm of gas at a maximum temperature of 180°F. The system is engineered for reduced footprint at 4 ft x 4 ft and includes a pre-wired control panel and pre-piped service utility connections requiring minimal installation and maintenance costs. Scrubber units are configurable to different levels of automation and treatment applications.  

A recent lab scrubber is for a manufacturer of pharmaceutical products in Southern, California. The scrubber is designed to remove HCl from the exhaust of several small laboratory process vent streams. The vent streams includes low organic concentrations which are incompatible with many common plastic materials. Special resin was selected for the fiber reinforced plastic (FRP) vessel and ductwork.  Piping and valves were assembled using PVDF.  The scrubber is designed for a classified area with explosion proof motors and instruments and is provided as a turn-key installation.

 

 

Lab Scrub Mktg 3Another example  is a process vent scrubber for a blending facility in South Carolina that produces crop protection products for agricultural markets.  The vent stream is 1,500 cfm and includes HCl and water soluble particulate greater than 3 micron in size. The Envitech lab scrubber was configured to include a low pressure drop Venturi for particulate control combined with a packed bed absorber for HCl control.  The system includes instruments, control system, recirculation pump, pre-assembled piping, valves, and fittings, interconnect duct, ID fan, and stack. 

Vent ScrubberA different use for a lab scrubber includes an ethylenediamine (EDA) scrubber installed in the South Eastern United States.  The storage of this precursor chemical requires extra handling than is typical with other common industrial chemicals.  With a relatively low exposure limit of 10 ppm, storage tanks must be properly engineered and scrubbed to remove excess vapors.  The Envitech lab scrubber is an ideal, low cost solution for this type of storage system.

Please click on the link below to download a brochure and case studies for the lab scrubber.

 Download Literature

Topics: particulate control, Scrubbers, SO2 Scrubber, Acid Gas, NOx, Vent

Venturi Fume Scrubber for Tire Manufacturing Banbury Mixers

Posted by Andy Bartocci on Wed, Jun 15, 2016 @ 10:53 AM

Venturi Scrubbers are used to control particulate on a wide range of applications including medical and hazardous waste incineration, pot ash mining, sewage sludge processing and incineration, coal drying, textile and mineral wool insulation manufacturing and copper roasting. A previous blog post in April discusses the mechanisms for particulate removal by a Venturi scrubber. One application for Venturi scrubbers is removal of fumes generated by a Banbury mixer. A Banbury mixer is an industrial mixer used in a wide range of applications including food, chemical, pharmaceutical, plastic, mineral, and rubber processing. Venturi fume scrubberBanbury mixers are used, for instance, to compound rubber material for manufacturing automobile tires. Uncontrolled fumes from the mixers can create a nuisance by settling around the facility. Envitech’s Venturi collision scrubber has been used to control these fumes. The figure on the right shows a typical Venturi collision scrubber for a 25,000 cfm mixer exhaust. The scrubber separates the exhaust into two streams internal to the scrubber. The streams are then directed to two opposing Venturi throats. Recirculated water injected into each throat is atomized into fine droplets as the gas is accelerated. Fume particles and droplets collide and are captured by the atomized water as the steams are recombined into a third Venturi throat. A diffusion section redistributes the gas to a horizontal chevron style mist eliminator to remove entrained water droplets. Water is collected and drained into a common sump and recirculated back to the Venturi throats. A blowdown stream purges the collected material.

The scrubber is designed for 24/7, semi-automatic operation and is skid mounted with redundant pumps, one operating and one spare. Instruments are pre-mounted into the piping assembly and pre-wired to a junction box. The systems are often provided with an ID fan which can be mounted on the roof of the building. Typical design conditions and performance are indicated in the table below.

DESIGN VALUE
Flow Rate, acfm Up to 25,000 cfm
Temp, oF 90
Particulate, gr/dscf 0.015
Particle Removal > 99.5%*

*particles > 2.5 microns

Envitech Venturi collision scrubbers have been in operation at several tire manufacturing facilities since the early 80’s. Over 17 systems have been installed including several in recent years.

Click on the icon below to download a case study for Envitech Venturi Collision scrubbers learn how the scrubber solved the emission problems for Goodyear Tire & Rubber Company.

Download Case Study

Topics: particulate control, Venturi scrubbers, Scrubbers

Venturi Scrubber for Glass Furnace

Posted by Andy Bartocci on Tue, Jun 14, 2016 @ 02:14 PM

Venturi Scrubbers are used to control particulate on a wide range of applications including medical and hazardous waste incineration, pot ash mining, sewage sludge processing and incineration, coal drying, tire manufacturing, and copper roasting. One particular application is glass fiber manufacturing which can include both textile fiber and wool fiber insulation. Both types of fibers are manufactured by similar processes which use high-temperature to convert raw materials (predominantly borosilicates) into glass fibers. Emissions control is needed for both glass melting and fiber forming and finishing processes. A survey of stack test data from 10 manufacturing lines at different glass furnace operations demonstrate typical particulate emissions in the range of 0.0035 gr/dscf to 0.015 gr/dscf for volumetric gas flow rates ranging from 20,000 dscfm to 50,000 dscm. Most of these lines use a 10 in. W.C. pressure drop Venturi scrubbers. A few use wet electrostatic precipitators (WESP’s). Stack test data and particle size distribution (PSD) data indicate there can be significant differences in particle size distribution between different glass furnace manufacturing lines which account for the range in outlet concentrations. The figure on the right shows removal efficiency by particle size for a 10” pressure dropEnvitech_10_in_Venturi_curve.jpg Venturi. It indicates that nearly all particles > 2 micron in size are removed by the Venturi. Performance drops off dramatically, however, for smaller particles. Mechanisms for particulate removal by a Venturi scrubber are discussed in more detail in an earlier blog post, dated April 14, 2016.

The image below shows a typical Venturi scrubber used for glass fiber manufacturing facility. The process exhaust gas passes through the Venturi scrubber throat for particulate removal. The Venturi has a variable throat damper that is pneumatically actuated for maintaining the Venturi scrubber Venturi_Scrubber_Flat.jpgpressure drop over a minimum and maximum gas flow rate.  The damper position is governed by proportional-integral-derivative control based on the differential pressure across the throat. 

After the Venturi scrubber throat the gas passes through a flooded elbow and enters a vertical entrainment separator through a tangential inlet. Large water droplets are removed by centrifugal forces by the spin induced by the tangential entry. After passing through internals to smooth the gas flow distribution, the gas passes through a vertical chevron style mist eliminator to remove remaining water droplets from the gas. A spray header provides a periodic wash to keep the chevrons clean from particulate and debris.   Liquid from the Venturi is collected in the entrainment separator sump and re-circulated to the Venturi throat. A blowdown stream is taken from the recirculation line to purge the collected particulate.

Venturi scrubbers have proven to be highly reliable on a wide range of applications, including several collecting fibrous material. Several considerations should be taken into account to design reliability into the system.  A well designed Venturi scrubber can operate continuously with just one or two shifts of maintenance per year. Although Venturi scrubbers are quite common on glass fiber manufacturing lines some sites have relied on wet electrostatic precipitators (WESP) to meet emission limits. This may be driven by a combination of the particle size distribution (PSD) of the process and site specific permit limits. In general, a WESP is used when there is a large fraction of submicron particulate that exceeds the capability of the Venturi scrubber to meet the permit limit. A WESP has higher capital cost, but will have lower operating cost from lower energy consumption.

 

Click on the icon below to view a video of a variable throat Venturi scrubber damper blade.

Free Video

Venturi scrubber

 

Topics: particulate control, Venturi scrubbers, Scrubbers