Air Pollution Control Innovations

Catalyst Calciner Particulate SO2 Scrubber

Posted by Andy Bartocci on Tue, Jan 18, 2022 @ 08:00 AM

Catalyst Calciner ScrubberA catalyst production facility operates a calciner that generates a small stream of hot dirty gas. The exhaust is cleaned using a particulate/SO2 scrubber followed by a vertical entrainment separator.  The configuration is problematic for operation.  The scrubber requires a long duct run from near grade to the scrubber inlet flange.  There is a U-shaped bend to the inlet flange.   Particulate condenses in the duct and plugs over time.  The process is routinely shut down to clean out accumulated material. This limits production capacity.  The customer sought to redesign the scrubber to increase production while maintaining as much of the original equipment as possible.

The customer selected Envitech to redesign and supply a scrubber to be retrofit into the existing system.  The scrubber inlet was replaced with a high efficiency Hastelloy Venturi scrubber for particulate removal.  The Venturi length was significantly decreased and oriented at an angle to the entrainment separator inlet.  The shorter distance and angled orientation significantly reduced the duct run from the calciner outlet to the scrubber inlet, minimizing fouling potential.

The top of the entrainment separator was replaced with a packed bed absorber to neutralize and remove SO2.  Structural modifications to the existing vessel ensures the  new packed bed is well supported.

After the Venturi, the gas enters the bottom of the packed bed and travels vertically upward, counter current to downward flowing water.  Excess water from the Venturi and the packed bed collects in a common sump.  Caustic solution injected into the recirculation line neutralizes acid gases.  Liquid recirculates back to the Venturi throat and top of the packed bed.  The gas passes through a vertical entrainment separator above the packing to remove water droplets before exiting the system.

The scrubber was put into service in early 2021.  A continuous emissions monitoring system (CEMS)  confirms emission limits are met. The duct clean out time has been reduced from 24 to 36 hours to < 1 hour.  System uptime has improved from < 60% to > 80%, enabling higher production capacity. The Venturi scrubber is significantly smaller in size, making replacement cost less expensive.   The scrubber is designed to meet the process conditions below:

  • Flow rate: < 1,000 acfm
  • Inlet Temp, 400 oF
  • Particulate removal: > 99.8%
  • SO2 removal: > 99.9%

Click on the link below to download literature about the catalyst Calciner scrubber.

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Topics: Venturi scrubbers, Scrubbers, SO2 Scrubber, Acid Gas, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

Lithium Extraction Chlorine/HCl Scrubber

Posted by Andy Bartocci on Tue, Jan 04, 2022 @ 08:30 AM

1144 Lithium Extraction ScrubberA dual purpose, low flow scrubber is needed for a facility that extracts lithium from geothermal brine. The scrubber treats a chlorine (Cl2) rich stream from a chlor-alkali process and HCl from a caustic storage tank vent line.  The scrubber is installed outdoors in a desert environment with significant seismic and wind requirements.  Temperatures reach 113oF in the summer.  The furthest emission source is 70 ft away. The scrubber will use and induced draft (ID) fan to pull exhaust gas from the upstream sources. The fan must be corrosion resistant and capable of pulling a low flow rate draft  across the pressure drop of the inlet ductwork and scrubber.

The customer selected an Envitech packed bed scrubber.  The scope of supply includes a fiber reinforced plastic (FRP) packed bed absorber, instruments, control system with HMI display, pre-assembled recirculation pump, piping, valves, and fittings, interconnect duct, and an FRP ID fan.  Instruments are pre-mounted in the piping and pre-wired to the control system.

The Cl2 scrubbing reaction is exothermic.  A dilution air damper on the HCl tank vent line dilutes pollutant concentrations to a range that keeps the scrubber from getting too hot.  It also provides enough flow for the minimum cross-sectional area needed to house the packing.  The packed bed vessel and ductwork are self-supporting for wind and seismic.  A high-performance mesh pad at the top of the scrubber removes acid aerosol droplets formed in the scrubber.  The recirculation liquid operates at a high pH. The scrubber needs to achieve 99.98% removal for the worst-case loading conditions.  The scrubber height and mesh pad  work together to achieve performance guarantees.

The scrubber will be delivered in the first quarter of 2022 and is designed to meet the following design conditions:

  • Inlet flow rate – 400 acfm
  • Inlet temperature – Ambient
  • Max HCl and Cl2 discharge limit < 5 ppmv
  • Removal efficiency > 99.98%
Click on the link below to download literature on this application and other literature..

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Topics: Scrubbers, Acid Gas, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

Wet Electrostatic Precipitator (WESP) for submicron lead particulate

Posted by Andy Bartocci on Mon, Sep 27, 2021 @ 11:02 AM

WESP Mag 2

In 2012 Envitech supplied a wet electrostatic precipitator (WESP) to remove submicron particulate and lead particles from a metal processing coating device. Envitech recently completed the start-up of a 2nd WESP for a different coating device at the same facility. Both systems are designed to remove greater than 95% of lead from low inlet concentrations. The inlet lead concentration is similar to that of a secondary lead smelter reverb furnace. Click on the link to read about the secondary lead smelter WESP.

The scope of supply for the new system includes a WESP, instruments, control system, pre-assembled pump skids, interconnect ductwork, dampers, stack, access platforms, and make-up water treatment system. The WESP is a hexagonal tube, upflow design. The gas enters the bottom of the WESP and passes through the conditioning section to ensure the gas is fully saturated and evenly distributed to maximize collection efficiency.

After the conditioning section, the gas enters the collection section. Electrostatic forces remove particles contained in the gas stream (see graphic below). The collector consists of grounded collector tubes and high voltage discharge electrodes. A voltage is applied to the discharge electrodes to both charge the particles and create a powerful electric field. The voltage on the discharge electrodes instigates a corona discharge of electrons from disks on the electrodes. The electrons move from the discharge disk to the collector tubes. Some of the electrons intercept particles in the gas stream which charges the particles. Once charged, particles migrate across the gas stream towards the grounded collector tubes. The particles are intermittently flushed with water from a spray header above the collector. Collected particulate containing lead fall by gravity from the tube walls into the WESP sump.

WESP Collection MechanismThe outlet section is the last section and contains an entrainment separator to collect water drops that were entrained in the gas stream during the collector wash cycle. It also houses a support structure for the high voltage electrodes and wash water spray header.

The system has a unique water and wastewater treatment system that mitigates the need for a hazardous liquid blowdown. An upstream water treatment system conditions the city water used to makeup losses associated with evaporation. The recirculation water to the system is filtered to remove hazardous particulate as a solid, greatly reducing the operating cost of disposal. The collection of the hazardous waste as a solid substantially reduced the facility hazardous disposal costs.

The facility reports high reliability and uptime with little intervention required to maintain operation and performance. The electrodes are rigid mast and firmly held in placed after alignment during start-up. Less than 2% of the electrodes have been replaced in seven years of operation. The WESP is designed to meet the below parameters:

  • Inlet flow rate - 35,000 acfm
  • Inlet temperature – 140°F
  • Lead particulate performance guarantee – greater than 95% removal

Click on the link below to download a case study on this application.

Download Case Study

Topics: particulate control, wet electrostatic precipitators

Air Scrubbers for Chrome Plating

Posted by Andy Bartocci on Thu, Sep 23, 2021 @ 06:05 AM

Envitech chrome plating scrubberThe California Air Resource Board (CARB) is considering new rules in California affecting chrome plating processes for metal finishers. An estimated 100,000 people participate in the chrome plating supply chain. A hundred and fifty chrome plating operations are in California. Eighty to ninety of those are for defense and aerospace applications.

Chrome plating is a process where an electrical charge is applied to a plating bath containing an electrolytic salt (chromium anhydride) solution. The electrical charge causes the chromium metal in the bath to fall out of solution and deposit onto a metallic surface placed into the bath. During the process, hexavalent chromium is emitted as an aerosol and can adversely impact public health.

Decorative chrome plating is utilized in the consumer marketplace. Functional plating is utilized by the aerospace and defense industries and includes hard plating and chromic acid anodizing. Hard plating provides extremely hard, corrosion resistant coatings with exceptional wear, abrasion, and corrosion resistance. Chromic acid anodizing creates a thin aluminum oxide film used for flight-critical aluminum components subjected to high stresses, such as landing gear. Functional plating processes must meet strict OEM and MIL-SPEC defense requirements.

Many chrome plating operations started out in remote locations. Communities have built up around these facilities over time. Close proximity between communities and plating facilities increase public health risk. CARB had proposed new rules to mitigate these risks by requiring facilities to transition from the use of hexavalent chromium for decorative and functional plating to alternative technologies, largely based on trivalent chromium technologies. Processes affected by the proposed transition timeline are strictly controlled and require extensive qualification. Because industry viewed the timeline as extremely aggressive CARB has withdrawn the proposed rules and will propose new rules in the months ahead.

Existing hexavalent hard and decorative chromium electroplating and chromic acid anodizing facilities need to meet a hexavalent chromium limit of 0.0015 milligrams/ampere-hour as measured after an add-on air pollution control device. The size of the air pollution control (APC) system depends on the ventilation gas flow rate. A typical large plating operation may be comprised of several plating tanks with a ventilation flow rate of 40,000 to 50,000 acfm. The APC technology is comprised of a multi-stage mist elimination followed by HEPA filters for final polishing. The above figure provides an isometric view of a system. The footprint is 45 ft by 30 ft with a height of 31 ft to the top of the vessel. The vessel and ductwork are constructed from fiber reinforced plastic (FRP) to provide structural integrity to meet wind and seismic requirements as well as long life. FRP doubles the life of equipment compared to lower cost polyvinyl chloride (PVC) material which has also been used for material of construction.

Vent gases enter the bottom of the mist eliminator vessel and passes vertically upward through mesh pad stages in series. A recirculation pump recirculates dilute chromic effluent from the vessel sump to provide a continuous wash on some of the mesh pad stages. A periodic fresh-water wash is applied to the other stages. Wash water falls by gravity and is collected in the vessel sump. A blowdown stream from the discharge side of the pump purges the system of collected contaminants into a separate storage tank.

After the final mesh pad stage, the gas passes through an internal duct to exit the mist eliminator vessel near grade into an induced draft fan. For additional performance, the gas then splits into two separate lines into a re-heater duct to heat the gas above the dew point before entering a HEPA filter for final contaminant removal. Reheat minimizes condensation fouling in the HEPA filters. After the HEPA filters the gases enter a common stack before exhausting to atmosphere.

The challenge for meeting the emission limits is the mesh pad performance is dependent on the aerosol droplet size formed by the bath solution. Mesh pad suppliers provide performance characteristics down to a specific droplet size. Multi-stage mesh pads may be sufficient to meet the 0.0015 milligrams/ampere-hour limit. Downstream HEPA filters provide additional assurance performance guarantees are met under all conditions.

Click on the link below to download Envitech brochures.

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Topics: Scrubbers, Vent

Medical Waste Incinerator Scrubber MACT Standard Compliance

Posted by Andy Bartocci on Wed, Sep 01, 2021 @ 07:50 AM

Medical waste scrubber DHSThere are several different waste incinerator source categories controlled by EPA standards under the Clean Air Act (CAA). These include hazardous waste combustors (HWC), sewage sludge incinerators (SSI), municipal solid waste (MSW) incinerators, commercial and industrial solid waste (CISWI) incinerators, and Hospital, Medical, and Infectious Waste Incinerators (HMIWI). Each incinerator type has its own Maximum Achievable Control Technology (MACT) standard which establishes technology based limits for emitted HAPs. MACT standards are part of the National Emission Standards for 

Medical Waste Venturi DHS

Hazardous Air Pollutants (NESHAP) and are applied to source categories that pose adverse risk to human health by the emission of hazardous air pollutants (HAPs).  The HMIWI MACT standard for medical waste incinerators is the most challenging of the incinerator source categories. This standard controls particulate (PM), hydrogen chloride (HCl), sulfur dioxide (SO2), lead (Pb), cadmium (Cd), mercury (Hg), dioxins/furans (D/F), nitrous oxide (NOx), and carbon monoxide (CO). Emission limits depend on the incinerator size and weather it is a new or existing source. Small incinerators are less than 200 lb/hr of waste throughput, medium incinerators are between 200 lb/hr and 500 lb/hr, and large incinerators are greater than 500 lb/hr.

Envitech recently completed a project for two medical waste incinerators at a Midwest research facility. These are the first new medical waste incinerators installed in the United States since Envitech installed a 525 lb/hr medical waste incinerator at a research facility in Galveston, TX in 2013.

The scope of supply includes two medical waste incinerator scrubbers and a water treatment system to treat the blowdown from both incinerators. The incinerators are permitted as new, medium size incinerators. Ozone injection is integrated into the system to meet a NOx limit of 67 ppmv. The systems include pre-assembled pumps, piping, valves, and fittings to minimize installation time and cost. The pre-assembly provides long term rigidity, consolidation of space, longer up-time, and improved safety for operators. A description of the process arrangement can be found in this link to an earlier blog post.

Stack testing was performed in June 2021 for both incinerators. Test results confirm the Envitech system reduced emissions well below MACT standard limits, providing a comfortable margin for compliance over the range of operating conditions and waste feed. Below is a summary of stack test performance.

Parameter Emission Limit Result, %Limit
PM < 0.0095 gr/dscf 17.9
Pb < 0.018 mg/dscfm 8.9
Cd < 0.0098 mg/dscfm 4.6
Hg < 0.0035 mg/dscfm 25.7
D/F < 0.014 ng/dscm TEQ < 1
HCl < 7.7 ppmv dry < 1
SO2 < 1.4 ppmv < 1
NOx < 67 ppmv dry 24

Click on the link below to download literature on medical waste incinerator scrubbers.

Download Literature

Topics: Scrubbers, MACT Standards, Medical Waste Incinerator Scrubber, Incinerator Scrubber, HMIWI Scrubber, Stack Testing, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

SO2 Scrubber for Refinery and Petrochemical Applications

Posted by Andy Bartocci on Mon, May 03, 2021 @ 10:20 AM

A common wet scrubber air pollution control application is the removal of sulfur dioxide (SO2) and related compounds from combustion processes. This class of compounds is often referred to as SOx. The formation of SOx and SO2 occurs from sulfur bearing fuels or materials oxidizing to SO2 upon combustion. SO2 has negative health effects and can contribute to respiratory illness, especially in children, the elderly, and individuals with pre-existing conditions.   In addition to health effects, SO2 contributes to acid rain which can harm plants, trees, rivers, streams, and lakes. SO2 also reacts with other compounds in the atmosphere to form small particles that contribute to particulate matter (PM) pollution and regional haze otherwise known as smog. Regulatory agencies often control SO2 not only to minimize harmful health affects but to reduce regional haze.

Packed bed scrubbers are often considered the best available control technology (BACT) for SO2 removal. Below is a summary of SO2 exhaust streams Envitech has treated using packed bed scrubbers.

  • Waste oil refinery waste gas thermal oxidizer and direct fired heater
  • Refinery sulfur recovery unit (SRU) thermal oxidizer
  • Geothermal power generation regenerative thermal oxidizer
  • Secondary lead smelter furnace
  • Mineral processing furnace
  • Catalyst regeneration kiln
  • Ceramic tile kiln
  • Hazardous waste combustor
  • Medical waste incinerator
  • Marine diesel engine

In these applications Envitech has treated SO2 loads as high as 48 tons per day and achieved efficiencies exceeding 99.9% removal. Gas flow rates can vary from < 500 cfm to more than several hundred thousand cfm.


An example of a large refinery/petrochemical thermal oxidizer SO2 scrubber application illustrates the technology. Below is a summary of design conditions. Liquid discharge limits for chemical oxygen demand (COD) and biochemical oxygen demand (BOD) require oxidation of the blow

Petronas PFD


Design Conditions

  • Flow rate: 300,000 acfm
  • Temperature: 1560oF
  • SO2: 300 lb/hr
  • Chemical oxygen demand (COD): < 200 mg/l
  • Biochemical oxygen demand (BOD: < 50 mg/l
  • SO2 removal > 99%

The above figure shows the scrubber equipment arrangement. Waste gas, fuel, and air are fed into the thermal oxidizer. Combustion in the thermal oxidizer generates exhaust gas of 300,000 acfm @ 1,560oF with 300 lb/hr of SO2. The first step of the scrubbing process cools the gas to saturation using adiabatic cooling through evaporation of water. Excess water flows into the packed bed absorber sump.

The next step is SO2 absorption via mass transfer promoted by high efficiency packing media. The gas flows vertically upward, counter-current to downward flowing recirculation water. Neutralization via caustic addition improves the SO2 absorption rate. An entrainment separator at the top of the packed bed absorber removes water droplets in the gas before exiting the system. Water from the absorber sump is recirculated to the quencher and to the top of the packed bed. Make-up water replaces evaporation and blowdown losses.Petronas GA

The SO2 load is low enough that the scrubber absorber sump can serve as an oxidation tank. Air is sparged into the sump to oxidize sulfites (SO-23) to sulfates (SO-24) in order to meet COD and BOD limits. Caustic addition ensures sulfate formation and minimizes sulfur dioxide off-gassing. Larger SO2 loads may require external oxidation tanks.

The adjacent figure shows a typical arrangement to handle 300,000 acfm of gas flow. The system is modularized with 12 feet diameter shop fabricated vessels. Recirculation pump skids and aeration pump skids are pre-assembled in the shop. Instruments are pre-mounted in the piping assembly where possible and pre-wired to a junction box on board the skid. Shop fabrication and assembly minimizes installation time and cost.

Advantages of a packed bed scrubber includes:

  • High removal efficiency
  • Proven technology
  • Low capital cost
  • Automatic operation
  • High reliability, low maintenance

Click on the link below to download literature about SO2 scrubbing.

Download Literature

Topics: Scrubbers, SO2 Scrubber, Acid Gas, quenchers, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

Refinery SRU SO2 Scrubber

Posted by Andy Bartocci on Mon, Apr 26, 2021 @ 08:30 AM

SO2 Scrubber ModelA refinery is upgrading an SO2 quencher-scrubber treating incinerator exhaust from a thermal oxidizer of a sulfur recovery unit (SRU).   The quencher is a re-purposed eductor type Venturi that is at end of life and will be replaced.  Scrubber recirculation water passes through a heat exchanger to subcool the gas, eliminating make-up water.  Upstream heat recovery is removed which increases the gas flow rate to the scrubber.

Duct design to the new quencher must ensure flange connections properly mate and will withstand stresses and loads.  A 180o ductwork bend makes the final connection to the quencher.  Of particular concern is the heat load thermally transmitted from the duct flange to the mating quencher flange. 

Refinery VS SO2 ScrubberThe customer selected Envitech to provide a replacement quencher and to make scrubber modifications to accommodate higher gas flow.  The new quencher is an Envitech design sized to fit into existing footprint, platforms, and flange connections.  Water injection through open ports in the quencher throat eliminates a spray nozzle to improve reliability and maintenance.  Recirculated water to the quencher is significantly reduced. Existing pumps are oversized but reused by recirculating excess water from the discharge to the pump return.  Scrubber packing and mist eliminator are redesigned using high performance components for larger gas flow and reduced pressure drop.

Envitech performed a thermal study using SolidworksTM modeling on the flange connection between the ductwork and mating quencher inlet flange.  Study results were used to ensure proper material selection.  Scope of supply includes two 90o refractory lined duct elbows connecting to the quencher.

The elbows are insulated with a rain shield. The connecting 90o elbow to the quencher is mitered with a flange and transition section using high temperature alloy.  All supplied equipment is compliant with refinery quality and design specifications.  Coordination with the end-user and 3rd party engineering firm ensures fit-up and proper mechanical design for interconnecting ductwork and connections.

The scrubber upgrade meets the below design parameters and allows the plant to safely to operate with higher flow while re-using a substantial amount of existing equipment.

Design Value
Flow rate, acfm 10,400
Inlet temp, oF 1,500
SO2 load, lb/hr 223
SO2 removal > 99.9%

Click on the link below to download literature about this application.

Download Literature

Topics: Scrubbers, SO2 Scrubber, Acid Gas, quenchers, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

Wet Electrostatic Precipitators for Submicron Particulate Removal

Posted by Andy Bartocci on Mon, Apr 19, 2021 @ 08:30 AM

Industrial facilities are increasingly called upon to consider the use of wet electrostatic precipitators (WESPs) for emissions control as regulations for PM 2.5 and specific heavy metals become more stringent. Facility and Environmental, Health, and Safety (EHS) Managers may need to become familiar with WESP technology and how they can be applied to their facilities.

WESPs date back to the 1970’s and are a tried-and-true method for removing submicron particulates, aerosols, SO3, opacity, and condensed heavy metals. They are generally robust and suitable for 24/7 continuous operations. Their use is found in steel melting furnaces, secondary lead smelters, hazardous waste combustors (HWC), medical waste and sewage sludge incinerators, wood products and pellet manufacturing, mineral wool and glass manufacturing, silicon monomer manufacturing, semiconductor manufacturing, and even industrial fryers.

Particle Removal EfficiencyThe adjacent figure illustrates WESP’s primary use. The graph shows removal efficiency on the vertical axis and particle size on the horizontal axis. The red curve shows typical WESP performance.   The dotted blue curve shows typical Venturi scrubber performance. A comparison shows that a Venturi scrubber is highly effective at removing particles greater than 1 micron in size. However, performance drops off rapidly for particles below 1 micron. WESP performance is relatively immune to particle size and maintains high performance for particles below 1 micron. This capability is derived from the use of electrical forces for particle removal compared to a Venturi scrubber which uses mechanical forces. WESP’s are generally higher capital cost than Venturi scrubbers but lower operating cost. They are used in cases where performance cannot be achieved with a Venturi scrubber or other, lower cost control device.

Env wet scrubber arrangementWESPs are often integrated with other control technologies and used as a polishing device at the end of a process. This is shown in the adjacent illustration for a typical waste incinerator. Perhaps the most important aspect to understand about WESP technology is the relationship between performance, size, and cost. Higher performance requires more collection area, larger footprint, and more cost. This is different than other control technologies like a Venturi scrubber or packed bed scrubber. For these devices, size and cost is primarily determined by the gas flow rate while operating cost is determined by performance. Size and cost for a WESP on the other hand is determined not only by gas flow rate but also removal efficiency. It is therefore important to have a good understanding of the range of inlet particulate concentrations and outlet emission limits. Specifying performance of 90%, 95%, or 99% removal will make a substantial difference on size and cost.

WESP technologies can vary greatly between vendors which can have an impact on footprint, maintenance, and long-term performance. Some of these differences include:

  • Tube geometry (square, round, or hexagonal)WESP
  • Tube size
  • Tube length
  • Operating voltage
  • Electrode construction
  • Electrode alignment mechanism
  • Bottom support grid requirement
  • Gas distribution mechanism

It’s recommended that facilities evaluating WESP technologies dedicate time to understand differences in WESP designs and potential impacts on operations. Evaluation may also include how the WESP is integrated with other upstream equipment needed to meet multipollutant emissions criteria.

WESP technology is a substantial investment for any facility but may be the best available control technology for a submicron particulate application.

Click on the link below to download WESP scrubber literature.

Download Literature

Topics: particulate control, Scrubbers, wet electrostatic precipitators, SO3 Aerosol

Thermal Oxidizer HCl Scrubbers for Vinyl Chloride Facilities

Posted by Andy Bartocci on Mon, Apr 12, 2021 @ 08:30 AM

Illumina HCl ScrubberHCl emissions are encountered in a wide range of applications including hazardous waste combustors (HWC), medical waste incinerators, pharmaceutical production, and ceramic tile manufacturing. There is a wide range of performance requirements depending on the application and applicable state or US EPA standard. Below is a summary of performance requirements for some of these applications.

  • Hospital, medical, and infectious waste incinerator (HMIWI) MACT standard: 5.1 to 15 ppmv depending on the size of the incinerator and whether it is an existing or new incinerator.
  • Hazardous waste combustor (HWC) MACT standard: 32 ppmv for existing incinerators and 21 ppmv for new incinerators; adjusted to 7% O2.
  • Ceramic tile kiln scrubber: > 97% removal
  • Pharmaceutical manufacturing RTO scrubber: > 99% removal
A specific HCl application is the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Polyvinyl Chloride and Copolymers (PVC) Production. The US EPA has granted petitions for reconsideration of the emission limits in the 2012 final rules for process vents, process wastewater, and stripped resin for major and area sources. A typical exhaust source from these facilities is treated by a thermal oxidizer followed by a quencher and a packed bed scrubber.  HCl loads are high and can range from 10,000 ppmv to peak loads of 25,000 ppmv. The proposed new NESHAP rule reduces HCl limits from 78 ppmv to 0.64 ppmv for existing sources. New sources must meet an emission limit of 0.17 ppmv. These are challenging limits and require greater than 99.998% removal efficiency.

Dal_Tile_installIt is well known that gaseous HCl readily absorbs into water and can be removed with high efficiency with caustic addition. The challenge however is that a fraction of the inlet HCl condenses into acid aerosol when hot gas from the thermal oxidizer contacts water in the quencher. The aerosol quantity formed and the particle size distribution (PSD) of the acid droplets vary from process to process. Predictive models to accurately estimate these values are limited and imprecise. In some cases as much as 20% of the HCl can form an acid aerosol fog. Aerosol carry-over exhausting from the scrubber will show up in stack tests and contribute to plant emissions.

It is common for HCl scrubbers to utilize mesh pads above the packed bed to remove aerosol droplets before exiting the scrubber. As noted above, many applications require 97% to 99% removal efficiency. This arrangement is generally adequate for these removal efficiencies. The proposed NESHAP standards for vinyl chloride facilities, however, requires higher efficiency. This increased efficiency demand requires additional consideration in the scrubber design and mist eliminator to guarantee performance. Facilities should rely on experienced scrubber suppliers that understand HCl aerosol and account for it in the scrubber design to guarantee emission limits.

Click on the link below to download HCl scrubber literature.

Download Literature

Topics: Scrubbers, Incinerator Scrubber, quenchers, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers, HCl Scrubbers

Secondary Lead Smelter SO2 Scrubber

Posted by Andy Bartocci on Tue, Mar 30, 2021 @ 08:00 AM

Secondary lead smelters recycle lead bearing scrap metal, primarily lead acid car batteries, into elemental lead or lead alloys.  Metal from the batteries are remelted in blast or reverb furnaces and then refined in secondary smelters. The batteries contain high amounts of sulfur which oxidizes to SO2 in the furnaces.SO2_Scrubber_Lead_Smelter

An unutilized secondary lead smelting facility was retrofitted with new process equipment to restart operations. Air pollution control equipment was needed to achieve greater than 96% removal of peak loads of up to 4,500 lb/hr of SO2 from the furnace exhaust. 

The customer selected an Envitech packed bed scrubber to meet emission requirements.  Three combustion sources are combined in a duct header into a forced draft fan. The fan provides motive force through the scrubber.

The first scrubber step  is an evaporative quencher to cool the gas to saturation. The quencher is constructed from T316SS and is a low pressure drop Venturi to provide turbulence for rapid quenching with a wide turn-down ratio. A fiber reinforced plastic (FRP) elbow connects the quencher to a 10 foot diameter FRP absorber vessel.

Gas from the quencher passes vertically upward through a packed bed, counter-current to downward flowing recirculated water.  Scrubbing water and excess quench water are collected in a common sump and is recirculated to the top of the packed bed and quencher. 

A pre-assembled recirculation pump skid with redundant pumps was supplied with the scrubber.  Instruments were pre-mounted and pre-wired to a control box on the skid.

A dilute solution of plant-supplied sodium hydroxide is metered into the scrubber recirculation line to neutralize acid gases and is controlled by the recirculation liquid pH.  A blowdown stream purges the system of reaction products and is controlled by conductivity.  Blowdown liquid is treated by separate oxidation tanks to convert sulfite reaction products to sulfates.

After the packed bed, the gas passes through a chevron style mist eliminator above the packing material to remove water droplets.  A wash header below the mist eliminator provides a periodic wash to keep the chevrons clean.  Finally, the gas exits the system and is exhausted through a stack.

The scrubber has been operational since 2010 with good result.  Below is a summary of design and performance results.

Design Value
Flow rate, acfm 60,000
Inlet temp, oF 400
Peak SO2 load, lb/hr 4,500
SO2 removal > 98%

Click on the link below to download literature about this application.

Download Literature

Topics: Scrubbers, SO2 Scrubber, Acid Gas, quenchers, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers