Air Pollution Control Innovations

Oxygen Strippers Using Natural Gas

Posted by Andy Bartocci on Tue, Jun 09, 2020 @ 08:30 AM

Oxy Petroleum Stripper TowersVintage Petroleum, LLC, a subsidiary of Occidental Petroleum Corporation operates oil and gas fields in Lost Hills, California, northwest of Bakersfield. The fields operate steam boilers that use nearby canal water. High concentrations of dissolved oxygen in the canal water caused excessive corrosion in the boilers.

Vintage was looking for an effective means to reduce oxygen content in the canal water to prolong boiler life and reduce maintenance costs.

The customer selected Envitech to design and build two stripper towers. The towers use high pressure natural gas to strip oxygen from the canal water. The water is pumped 1,000 feet from the canal to the tower locations. After stripping to remove oxygen, the water is pumped to an existing fresh water tank.

The vessels are constructed of carbon steel with a 3/16 inch corrosion allowance and painted internally and externally. The
vessels are fabricated in accordance with ASME Code Section VIII Division I requirements and stamped. The maximum vessel design working pressure is 100 psig at a maximum design temperature of 300 °F and also designed for half vacuum.

The lower vessels are 6 feet in diameter. The upper packed bed sections are 4 feet in diameter. The overall vessel height is 27 feet.

The first system was installed in 2013. The second system was installed in 2014. Both systems are operational and the facility reports success in prolonging boiler life. Designed to the parameters summarized in the adjacent table, the stripping towers resulted in an innovative process solution to solve a unique operational problem.

  • Gas flow rate, mscfd: 328
  • Water flow rate, gpm: 450
  • Operating temperature, oF: 60 to 120
  • Operating pressure, psig: 40
  • Oxygen content of in stripping gas, ppm: 70
  • Dissolved oxygen content in canal water, mg/L: 9
  • Dissolved oxygen removal: > 90%

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

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Topics: particulate control, Scrubbers, Incinerator Scrubber, quenchers, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

Auto Shredder RTO and Acid Gas Scrubber

Posted by Andy Bartocci on Tue, Jun 02, 2020 @ 08:30 AM

The metal recycling industry provides tremendous societal benefit by preserving natural resources and reducing greenhouse gases. Metal recycling entails pulverizing and shredding vehicles and appliances into smaller pieces to facilitate melting processes. Large mega shredders are often eAuto Shredder RTO Scrubber_Browsenclosed to capture process emissions. Volatile organic compounds (VOCs) and other hazardous air pollutants (HAPs) are released during shredding, including small amounts of halogenated compounds.

In recent years, some state and regional regulatory agencies have begun requiring Best Available Control Technology (BACT) to treat shredder exhaust gases for VOCs and other HAPs. One facility had a need to treat a large volumetric flow rate from their shredder enclosure. The equipment must meet stringent performance limits, be reliable, and capable of 24/7 operation.

Envitech partnered with Process Combustion Corporation (PCC) to provide a comprehensive BACT solution. The partnership leverages PCC’s 50 years of experience engineering thermal systems for air pollution control with Envitech’s wet scrubber expertise. PCC provided a regenerative thermal oxidizer (RTO) for VOC control and interconnect ductwork and incorporated an Envitech packed bed acid gas scrubber system. The scrubber scope of supply includes two (2) equal trains consisting of a horizontal Hastelloy C276 quencher, 13 foot diameter fiberglass packed bed absorber, instruments, pre-assembled recirculation pump skid with redundant pumps, and stack.

The horizontal quenchers ensure the gas is fully saturated across all operating conditions and simplifies ductwork between the RTO and scrubber.

CFD modeling minimizes pressure drop and prevents re-entrainment.

The system will be installed and operational in 2021. Guarantees are provided to meet the below design conditions. The combined PCC/Envitech process provides a reliable, comprehensive solution to meet the demands of a more stringent regulatory environment.

  • Gas flow rate: 140,000 acfm
  • VOC destruction: > 98%
  • Acid gas removal (HF and HCl): > 99.5%
Click on the link below to download literature about this application.

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Topics: particulate control, Scrubbers, Incinerator Scrubber, quenchers, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

Thermal Oxidizer Quencher Treating Silicon Dioxide (SiO2) Particulate and HCl

Posted by Andy Bartocci on Wed, May 27, 2020 @ 07:26 AM

A pharmaceutical company, Roche Carolina, operates a thermal oxidizerThermal oxidizer SiO2 Quencher (TO) that treats a rich stream of chlorinated compounds and an organic silicon compound. HCl and silicon dioxide (SiO2) particulate are formed during combustion. The exhaust is treated by a Hastelloy evaporative quencher followed by a caustic scrubber.

The quencher utilizes spray pig tailed nozzles, some of which are orientated upward into the gas to prevent fouling from SiO2 accumulation on the spray headers. The pigtails gradually plug both inside and outside as SiO2 particulate collect outside the nozzles.

The stainless inlet duct flange connection frequently springs leaks, causing shutdowns for repairs. It was thought that the upward pointed nozzles wetted the welded flange surfaces resulting in acid gas corrosion from HCl and possible stress from thermal expansion differences between the two metals.

An improved design was sought to increase reliability and eliminate operational and maintenance problems. The design needed to address the potential for:

    • Spray nozzle plugging from SiO2 particulate.
    • SiO2 accumulation on the quencher walls.
    • Acid gas corrosion.
    • Weld leakage and failure.
The customer selected a custom engineered Envitech quencher.

Tangential pipes with large orifices at the top of the quencher keeps the walls fully wetted and prevents SiO2 particulate build-up.

A barrel at the inlet flange extends into the quencher with the same diameter as the inlet duct. The tangential nozzles are placed behind the barrel wall to protect injected water from traveling up into the duct.

Elimination of the pigtail nozzles prevents associated gradual nozzle plugging.

Because water is not put into the quencher-inlet duct interface, the possibility of leaking from this connection is eliminated. Risk of corrosion attack is also minimized.
Weld leakage and failure.

The bottom section is the same as the original design to facilitate integration.

The quencher has been operational since 2008 to the below design conditions. The facility reports good results and significantly improved reliability and lower maintenance costs.

  • Max flow rate, acfm: 6,700 acfm
  • Nominal flow rate: acfm 3,000 acfm
  • Max inlet temperature, oF: 850
  • SiO2 particulate, gr/dscf: up to 0.1
  • HCl, ppmv: 31
  • Saturation temperature, oF: 145

Click on the link below to download a case study and related quencher and wet scrubber literature.

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Topics: particulate control, Scrubbers, Incinerator Scrubber, quenchers, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

Refinery Thermal Oxidizer SO2 scrubber and Sulfuric Acid Mist Candle Filter

Posted by Andy Bartocci on Wed, Apr 08, 2020 @ 10:00 AM

Sulfuric acid mist arrangementWaste oil is recycled and refined into low sulfur marine diesel and other industrial fuels at West Coast refineries. Waste gas is sent to thermal oxidizers for volatile organic compound (VOC) destruction. Sulfur compounds in the waste gas are oxidized to SO2 and removed by a packed bed scrubber. A fraction of SO2 converts to sulfur trioxide (SO3) before entering the scrubber. SO3 further converts to sulfuric acid (H2SO4) and generates a submicron liquid mist upon quenching the gas. New ground level pollutant regulations require removal of sulfuric acid mist before exhausting the flue gas to atmosphere. A multi-pollutant solution is needed to remove both SO2 and sulfuric acid mist. 

The customer selected an Envitech SO2 scrubber, candle filter system. The arrangement includes a quencher to cool the gas to saturation, a caustic packed bed absorber to remove SO2, and a candle filter to capture sulfuric acid mist. Internal ducts with outlets near grade simplifies ductwork between the caustic scrubber and candle filter and between the candle filter and ID fan. The scrubber comes with pre-assembled pump skids. Instruments are pre-mounted in pre-assembled piping and pre-wired to a junction box to reduce installation time and cost.

Both scrubbers have been shipped to the sites. The smaller system was put into service in early 2020. The scrubbers meet the design conditions summarized below.

candle filter


Design Plant 1 Plant 2
Flow rate, acfm 10,000 4,500
Inlet temp, oF 1,600 376
SO2 removal > 90% > 95%
H2SO4 removal > 99% > 99%







Click on the link below to download a case study and related wet scrubber literature.

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Topics: Scrubbers, SO2 Scrubber, Acid Gas, SO3 Aerosol, Packed Bed Absorbers, Packed Bed Scrubbers, Wet Scrubbers

Pharmaceutical Fermentation H2S Scrubber

Posted by Andy Bartocci on Tue, Jan 21, 2020 @ 06:00 AM

A major pharmaceutical company is implementing an expansion project in their Midwest facility. It includes two production Fermentors,Fermentation H2S Scrubber a secondary feed tank and secondary make-up tank. Combined vent gases contain up to 1,500 ppmv (24 lb/hr) of Hydrogen Sulfide (H2S) in air.

H2S is a highly toxic gas that can kill or seriously harm human health when exposed to it. For general industry the OSHA permissible exposure limit (PEL) is 20 ppm for an 8 hour period. The specification requires 99.9% removal which achieves less than 1.5 ppmv, well below the PEL.

Installation is on the first floor with a limited footprint area of 18 ft L x 8 ft W. Redundancy is required for pumps and ID fans. The customer desires maximum integration and pre-assembly to limit installation work on site.

The customer selected an Envitech H2S packed bed scrubber. The scope includes a fiber reinforced plastic (FRP) packed bed absorber, instruments, recirculation pumps (1 operating, 1 spare), pre-assembled CPVC piping, valves, and fittings with pre-mounted instruments, metering pumps, ID fans (1 operating, 1 spare), interconnect duct, and stack.
The stack passes through a second floor before breeching the roof.  Fans are located near the outlet on a mezzanine. A custom arrangement accounts for obstacles and interferences in the installation space.

H2SFermentation scrubber vesselVent gases enter the bottom of the absorber and travels vertically upward. A removable spray nozzle in the quench zone pre-scrubs and cools the process vent stream. Recirculated water sprayed over the packed bed mixes with counter current upward flowing gas. A dilute solution of sodium hydroxide (NaOH) and sodium hypochlorite (NaOCl) metered into the recirculation line neutralizes and oxidizes acid gases. Chemical addition is controlled by pH and ORP.

An entrainment separator at the top of the absorber removes water droplets before exiting the scrubber.

The equipment has been delivered and will be installed in early 2020.  Design and performance parameters are summarized below.


  • Inlet flow rate: 3,000 acfm
  • Inlet temperature: 102oF to 212oF
  • H2S inlet concentration: 1,500 ppmv 
  • H2S Removal: > 99.9%

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

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

Renewable Energy Food Digester Ammonia Scrubber

Posted by Andy Bartocci on Tue, Jan 14, 2020 @ 07:00 AM

The University of California, Davis (UCD) operates an anaerobic biodigester that converts 50 metric tons of Env Lab Scrub Sketchfood waste per day into 100 MMBtu/d of renewable energy biogas. The digester is sited near campus at a decommissioned landfill.

The biodigester produces a digestate liquid waste stream. It’s odor and high ammonia concentration render it unsuitable for composting or direct land-applied fertilizer. To avoid expensive hauling costs, a distillation column strips ammonia out of the digestate into the vapor phase so that the digestate can be treated in an existing Wastewater Treatment Plant (WWTP). An Ammonia Scrubber Package is needed to meet air emission limits and to recover a saleable liquid fertilizer product from the vapor phase ammonia.

Ammonia is an odorless gas that is harmful to human health with a permissible exposure limit (PEL) of 50 ppm. The scrubber must have high removal efficiency and be capable of treating a low flow rate exhaust and be robust and reliable.

The customer selected an Envitech ammonia lab scrubber. The scope of supply includes a fiber reinforced plastic (FRP) packed bed absorber, instruments pre-wired to a control system wLab Scrub Mktg 1ith HMI, pre-assembled pump, piping, valves and fittings, ID fan with VFD, and free-standing interconnect duct and stack.

Ammonia laden stripped gas enters the scrubber and travels vertically upward through the packed bed, counter-current to downward flowing recirculation liquid. Scrubbing liquid is collected in the sump and is re-circulated to the top of the packed bed. Sulfuric acid (H2SO4) is metered into the recirculation line to neutralize ammonia and is controlled by pH. A blowdown stream purges ammonia sulfate (NH4)2SO4 reaction products which can be sold as fertilizer. A mist eliminator at the top of the scrubber removes entrained water droplets before exiting through an induced draft fan and stack.

The ammonia scrubber will be commissioned in the 1st half of 2020 and will meet the design parameters and performances below.



  • Inlet flow rate: 1,000 acfm (capable of up to 2,000 acfm)
  • Inlet temperature: 160oF
  • Gas Composition:  Air with 1.4% mole ammonia
  • Ammonia Removal: > 97.5% permitted (capable of > 99% removal).

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

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

Pigment Manufacturing Ammonia Recovery System

Posted by Andy Bartocci on Tue, Jan 07, 2020 @ 07:00 AM

A pigment manufacturer operates batch reactors that emit very low volumes of highly concentrated ammoniaAmmonia Recovery Scrubber. Batches occur over a 20-hour period and ammonia concentrations varies from <1 to 96%.

Ammonia is an odorless gas with a permissible exposure limit (PEL) of 50 ppm. Ammonia can also form explosive mixtures in air with a lower explosive limit (LEL) of 15% and upper explosive limit (UEL) of 28%.

The customer needs to recover a 25-28% (w/w) aqueous solution of ammonia for re-use as a raw material while meeting air emission limits. The recovered ammonia can have no potential silicone due to sensitivity of the end-product. The system must be robust and safe to operate.

The customer selected a custom designed Envitech ammonia recovery system based on Envitech’s proprietary design for low flow rate applications. The scope of supply includes a compressor, a packed bed concentrator, a packed bed absorber, instruments, PLC and HMI control system, and an equipment skid containing pre-assembled vessels, instruments, control system, pumps, piping, valves, fitting, and instruments with pre-wiring. Panel and components are explosion proof. Vessels are 316SS fabricated to pressure vessel ASME code for 90 PSI. All components are specially selected to ensure no possible silicone contamination.

The gas is drawn out of the reactor using a specially selected compressor ideally suited to handle corrosive, low flow rate gases and to generate high pressures while generating an upstream vacuum.

The concentrator uses recirculated water to absorb and concentrate ammonia. A 2nd stage absorber recovers residual ammonia to meet air emission limits.
Blowdown from both stages purge concentrated ammonia for re-use as raw material.

The recovery system will be commissioned in early 2020 and will meet the design parameters and performances below.


  • Inlet flow rate: 50 acfm
  • Inlet temperature: 68oF
  • Carrier gas composition:  N2
  • Peak ammonia concentration: 96%
  • Concentration of recovered ammonia: > 25%
  • Ammonia removal: > 98% 

Click on the link below to download an ammonia recovery system case study and other scrubbing literature.

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

Refinery Catalyst Regeneration SO2 Scrubber

Posted by Andy Bartocci on Mon, Dec 16, 2019 @ 06:59 AM

A Saudi petrochemical plant operates a hydrogenation reactor to Refinery Catalyst Regen SO2 Scrubber renderingreduce organic compounds using a catalyst. In-situ regeneration is desired to restore the catalyst for additional processing. This improves operational efficiency and safety. The facility is evaluating technology options to achieve this goal. One approach is to
contact the catalyst with a carrier gas at elevated temperature to promote oxidation, resulting in SO2 emissions.

A wet scrubber is needed with this approach to remove SO2 before exhausting to atmosphere. The scrubber will be installed outdoors in a harsh coastal environment with summer temperatures exceeding 114oF. It will operate 3 to 5 days every 18 months and needs to be stored properly to maintain operational condition between uses.

The scrubber is to be built in conformance with over 12,000 pages of detailed refinery specifications with extensive quality assurance requirements.  Because of a tight schedule, a scrubber engineering order is initiated in parallel to evaluating other technology options. This reduces scrubber delivery time if the carrier gas oxidation approach is selected.

The customer selected an Envitech scrubber for the engineering order after extensive evaluation. The equipment scope includes a quencher, packed bed absorber, instruments, recirculation pump, pre-assembled piping, valves, and fittings with pre-mounted instruments. Pre-mounted instruments are pre-wired to control boxes. Components meet Class I, Div 2 area classification.

The quencher and vessel are designed using T316SS with internal and external coating. Piping Saudi refineryis T316SS conforming to ASME B31.1. Welds are specified to be magnetically and X-ray tested using certified welders.

The design submittal includes more than 90% of final engineering deliverables. The design order was complete and meets the design conditions outlined in the table below.

Although designed as stationary equipment, this type of scrubber can also be designed for mobility for use in other applications or acid gases. Alternate materials of construction are available such as FRP or alloy steels.


  • Inlet flow rate: 3,200 acfm
  • Inlet temperature: 510oF
  • Carrier gas composition:  N2
  •  Inlet SO2: 64 lb/hr
  • Outlet SO2:  < 50 ppmv
Click on the link below to download a case study for a refinery catalyst regeneration SO2 scrubber and other scrubbing literature.

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Topics: Scrubbers, Packed Bed Absorbers, Packed Bed Scrubbers, Wet 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.

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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