Air Pollution Control Innovations

Andy Bartocci

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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.

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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

HCl Scrubbers for Regenerative Thermal Oxidizers (RTO's)

Posted by Andy Bartocci on Wed, Mar 24, 2021 @ 11:05 AM

Regenerative thermal oxidizer’s (RTO’s) are thermally efficient devices used to destroy low concentrations of volatile organic compounds (VOC’s). Chlorinated compounds, if present, oxidize into hydrochloric acid (HCl) which must beIllumina HCl Scrubber removed after the RTO.

Two examples are Carestream Health in Rochester, NY, a health care products supplier, and Illumina in San Diego, CA, a biotechnology provider.  Facilities at both companies generate low concentrations of chlorinated VOC’s.  Control devices are needed to remove HCl emissions downstream of RTO’s used to meet VOC emissions.

Envitech packed bed absorbers were selected to treat the RTO exhaust gases.  The first step in the scrubbing process is an evaporative quencher to cool the gas to saturation.  A horizontal quencher simplifies ductwork and installation cost.  Al6XN construction provides corrosion resistance.es are Carestream Health in Rochester, NY, a health care products supplier, and Illumina in San Diego, CA, a biotechnology provider.  Facilities at both companies generate low concentrations of chlorinated VOC’s.  Control devices are needed to remove HCl emissions downstream of RTO’s used to meet VOC emissions.Envitech packed bed absorbers were selected to treat the RTO exhaust gases.  The first step in the scrubbing process is an evaporative quencher to cool the gas to saturation.  A horizontal quencher simplifies ductwork and installation cost.  Al6XN construction provides corrosion resistance.  

The quencher is followed by a fiber reinforced plastic (FRP) vertical packed bed absorber with gas flowing vertically upward, counter current to downward flowing water.  Excess water from the quencher and packed bed collects in the absorber sump and recirculates to the quencher and packed bed.  A dilute caustic solution (NaOH) is injected into the discharge side of the recirculation pump to neutralize HCl.  A blowdown stream purges the system of reaction products.   Caustic injection and blowdown are controlled by pH and oxidation reduction potential (ORP).

Gaseous HCl readily absorbs into the scrubber recirculation liquid.  A fraction of the HCl forms a submicron aerosol as gas contacts water in the quencher to cool the gas.  The aerosol is removed by a properly designed mist eliminator.  Gas calculations are used to estimate the fraction of acid aerosol based on gas dew point and partial pressures of water and acid.  The mist eliminator must be capable of removing aerosol at the expected concentration and droplet size distribution. This  impacts the mist eliminator selection, vessel size, and pressure drop of the system.

The scrubbers were put into service and effectively operate on a continuous basis with minimal operator management. Operating parameters and performances are summarized below.

Design Carestream, NY Illumina, CA
Flow, acfm 6,000 4,000
Inlet Temp, oF 585 230
Inlet HCl, lb/hr 92 10
HCl Removal Efficiency, % 99 99

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

Download Literature

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

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.

Download Literature

 

 

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.

Download Literature

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.

Download Literature

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

International Confernce on Thermal Treatment Technologies

Posted by Andy Bartocci on Tue, May 19, 2020 @ 10:16 AM

IT3 2021 Logo

The Air and Waste Management Association (AWMA) has announced details for this years International Conference on Thermal Treatment Technologies and Hazardous Waste Combustors ( IT3/HWC). The Conference will be held January 27-28, 2021 in West Palm Beach, FL. New topics added for 2021 include PFAS sampling, methods, and laboratory analysis, waste/compliance impacts of health pandemics and natural disasters, plastics to energy/closed loop processing, and comprehensive performance testing (CPT). There is a call for abstracts (CFA) due July 27, 2020. Envitech will host a booth in the exhibit hall and will be presenting a paper. We look forward to seeing friends and colleagues at the conference. If you haven’t already, please put it in your calendars.  Hope to see you there.

Topics: Announcements

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 PARAMETERS

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.

Download Literature

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

BP Amoco Purified Terephthalic Acid (PTA) Plant Quencher

Posted by Andy Bartocci on Wed, Jan 29, 2020 @ 09:00 AM

Venturi_Quencher_BP_AmocoBP Amoco was engaged in expanding production capacity for purified terephthalic acid (PTA) at the CAPCO 6 and Zhuhai 1 petrochemical plants in China. PTA is used in the manufacture of polyester resin and polyethylene terephthalate (PET) plastic bottles. It is also widely used in the pharmaceutical, food, textile and packaging industries. The expansion projects were part of efforts to achieve process simplifications and lower capital costs. Project goals were to reduce plot area and the number of equipment pieces by 40%

The process includes up to 530,000 acfm of corrosive exhaust gases that are cooled to the adiabatic saturation temperature. Cooling large flow rate gases is challenging due to potential void spaces in the water spray system. Splitting flows into smaller exhaust trains is a common method to overcome this challenge. However, this adds ductwork and installation cost. For capital cost reductions, the customer wanted to saturate the gas in a single train in a horizontal arrangement to conserve space and to minimize ductwork.

BP Amoco PTA Venturi QuencherThe customer selected a custom engineered Envitech horizonal quencher. The material of construction is Hastelloy C276 to provide corrosion resistance at high inlet temperatures. A proprietary internal water injection and throat design splits the stream inside the vessel to ensure turbulence for mixing gases and water. Gases accelerate through the throat areas in combination with a recirculated water spray system. A small pressure drop cools gases over a wide flow rate operating range and minimizes the number of nozzles. The water spray header is removable to facilitate nozzle replacement and maintenance. The vessel is 13 feet in diameter in a horizontal arrangement. This allows the quencher to be shop fabricated so that inspection and quality assurance are done in a controlled environment. The unit is shipped as one piece.

The Envitech quenchers were installed in 2001 and operate to the design parameters summarized below. The proprietary design contributed to BP Amoco’s goals to reduce footprint area, process equipment pieces, and capital cost.

DESIGN PARAMETER

  • Max flow rate: 530,000 acfm
  • Inlet temperature: 560oF
  • Inlet pressure: 518 In. W.C. 
  • Guarantee: Cooling to +/- 40oF of the saturation temperature

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

Download Literature

Topics: Venturi scrubbers, Scrubbers, quenchers, Wet Scrubbers