Air Pollution Control Innovations

Secondary Lead Smelter Wet Electrostatic Precipitator Case Study

Posted by Andy Bartocci on Mon, Dec 03, 2012 @ 09:30 AM

A secondary lead smelter in Southern California recovers leadlead scrubber, lead smelter scrubber from used automobile batteries. The process uses a combination of combustion processes including kilns and furnaces. Despite extensive control equipment including bag-houses, HEPA filters, and wet scrubbers, low concentrations of heavy metals were being emitted from various stack sources.  Cancer risk index standards were being exceeded due to the close proximity of residents to the plant.  To be compliant with state regulations a solution was needed to reduce these emissions. The special circumstances of nearby residents and a stringent cancer risk index required the facility to meet emission limits well below any other secondary lead smelter in the country.

A case study is now available to describe how an Envitech high performance Wet Electrostatic Precipitator was used to solve this problem.

Please click on the icon below to download the case study.

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Topics: particulate control, Scrubbers, SO2 Scrubber, wet electrostatic precipitators

Sulfite Pulp Mill Scrubber / WESP Case Study

Posted by Andy Bartocci on Mon, Nov 26, 2012 @ 08:43 AM

A specialty cellulose provider, Tembec,Sulfite Pulp Mill Scrubber is upgrading a sulfite pulping mill in Eastern Canada to incorporate a new red liquor recovery boiler for power generation.  The boiler system increases annual green energy production by up to 40-megawatts, reduces sulfur dioxide emissions by 70%, and increases annual production capacity of specialty cellulose by 5,000 metric tonnes.  The off-gas from the recovery boiler contains a high concentration of SO2 which needs to be recovered for re-use in the production process. 

A cost effective solution was needed to recover sulfur and clean the stack gases to meet stringent particulate and SO2 emission limits.  The plant is located in a high labor rate area, which makes a field erected system very expensive due to lengthy installation time.

A case study is now available to describe how an Envitech scrubber/wet electrostatic precipitator (WESP) system solves this problem.

Please click on the icon below to download the case study.

Download  Case Study

Topics: particulate control, Venturi scrubbers, Scrubbers, SO2 Scrubber, wet electrostatic precipitators

Wet Electrostatic Precipitator Case Study for Lead Removal

Posted by Andy Bartocci on Wed, Nov 21, 2012 @ 08:58 AM

lead removal, lead scrubber

I previously posted a blog post about a new project for lead removal using a wet electrostatic precipitator (WESP). A Midwestern manufacturer heat treats metal materials in a furnace that generates low concentrations of lead fumes.  The fumes are sub-micron in size, making them difficult to remove.  The facility is compliant with their existing permit, but wants to be pro-active to control emissions further. They investigated several technologies including HEPA and cartridge filters, Venturi scrubbers, and wet electrostatic precipitators (WESPs). Because of the small particle size, low concentration, and high removal efficiency, they had difficulty finding technologies or vendors willing to guarantee the requested performance limit.

A case study is now available to describe how an Envitech high performance Wet Electrostatic Precipitator solves this problem.

Please click on the icon below to download the case study.

Download Case Study

Topics: particulate control, wet electrostatic precipitators

Sulfite Pulping Mill Recovery Boiler Scrubber System

Posted by Andy Bartocci on Tue, Oct 30, 2012 @ 08:55 AM

Envitech has received an order from Tembec to supply an ammonia based red liquor recovery boiler scrubber for the Temiscaming sulfite pulping mill in Québec, Canada.   The scrubber system will treat the off-gas from an upstream sulfite power boiler supplied by Andritz and will meet stringent emission standards for particulate and SO2.sulfit pulp mill scrubber, recovery boiler scrubber, red liquor boilerr

This system is part of a $190-million power generation project that will upgrade Tembec’s existing specialty cellulose manufacturing facility.  The upgrade will increase annual green energy production by up to 40-megawatts, reduce sulfur dioxide emissions by 70%, and increase annual production capacity of specialty cellulose by 5,000 metric tonnes.  The upgrade will make Temiscaming one of the lowest-cost specialty cellulose manufacturing facilities in the world.

The scrubber system is engineered to Tembec’s requirements and is the result of close collaboration with the customer over several months and their engineering firm Pöyry.   The design leverages experience from several other large volumetric flow rate applications including a coal dryer scrubber, secondary lead smelter wet electrostatic precipitator (WESP) system, and a hazardous waste incinerator scrubber.  The scope of supply includes an inlet duct from the boiler exhaust fan, quencher, ammonia scrubber, condenser, WESP, caustic scrubber, heat exchangers, structural steel, access platforms, and stack.  Primary vessels will be shop fabricated and shipped to the site for assembly and installation.  This provides a lower total installed cost, greater quality control over manufacturing, and shorter delivery and installation time.  System start-up will occur in the fall of 2013.

To read more about this system, download the case study below.

Download  Case Study

Topics: particulate control, Scrubbers, SO2 Scrubber, wet electrostatic precipitators, quenchers

Lead Removal using wet electrostatic precipitator (WESP) Technology

Posted by Andy Bartocci on Sat, Jun 23, 2012 @ 07:50 AM

I’ve made several blog posts regarding the removal of hazardous air pollutant (HAPs), including lead, from a secondary lead smelter in CA using a Wet Electrostatic Precipitator (WESP). There is also an article published in the August 2010 issue of Pollution Engineering on this system.  My last blog post references a letter to the EPA reporting metals reductions aswet electrostatic precipitator high as 98% and 99% and reductions of lead from 615 lb/yr to 1.22 lb/hr.  The facility is now achieving emissions that are several orders of magnitude lower than other secondary lead smelters.

Envitech is in the design phase for a new project that will apply the WESP technology to an industrial facility that has lead emissions similar to stack emissions from a controlled secondary lead facility.  The WESP system guarantees 95% lead removal from inlet concentrations of 0.003 gr/dscf.

The system was selected after the facility performed a thorough evaluation of different technologies including HEPA and cartridge filters as well as other WESP suppliers.   The system will be operational in Q1 2013 with stack test results due by the middle of 2013.

Envitech is implementing cost reductions that will enable reduced capital expenditure for future installations and make the technology more economically feasible to be considered best available control technology (BACT) by the EPA.   This new system will be a good surrogate to further demonstrate the performance of the Envitech WESP system to get the lead out!

Click on the link below to download a white paper from the International Conference on Thermal Treatment Technologies and Hazardous Waste Combustions (IT3/HWC) on a WESP system for a secondary lead smelter.

Download Free White Paper

Topics: particulate control, wet electrostatic precipitators

Secondary Lead Smelter WESP Performance

Posted by Andy Bartocci on Tue, Oct 04, 2011 @ 01:56 PM

In 2009 I gave a paper at International Conference on Thermal Treatment Technologies (IT3) on a wet electrostatic precipitator (WESP) system for the Quemetco secondary lead smelting facility in Southern California.  It was explained that the system was an add-on control to help the plant meet a cancer risk index by removing low concentrations of metals.  The facility was meeting stack emission limits and had similar control technology used by other facilities in the industry including bag-houses,Wet Electrostatic Precipitator HEPA filters, and wet scrubbers. Because residential neighborhoods had moved closer to the boundaries of the plant over the years, the stack emission limits were insufficient to meet the cancer risk index.  In other words, the facility had to achieve lower emission levels than other similar plants. The WESP system was installed in 2007 and provided a performance guarantee for arsenic, lead, and nickel which were the larger contributors to the cancer risk index.


In May 2011, the EPA released the new National Emissions Standards for Hazardous Air Pollutants (NESHAP) for secondary lead smelting facilities.  The report sites in section III.B.2 that two of the 14 secondary lead smelting facilities have estimated actual lead emission only moderately lower than the allowable emission level (about 2-3 time lower).  The majority of the other facilities have estimated actual emissions in the range of 10 to 100 times lower than allowable.  However, one facility with highly advanced controls has an estimated actual emission of about 1,500 times below allowable emission levels. This facility is the Quemetco facility operating with a WESP system.  It can be surmised the plant is achieving emission levels 15 to 150 times lower than the other lead smelting facilities.


In June of 2010 a public letter on behalf of RSR Corporation (Quemetco) was presented to Mr. Charles French, Metals and Minerals Group, of the EPA. The letter states that the WESP system yielded dramatic reductions in air emissions from its operations.  The cancer risk was reduced by 87% to 2.88 cancer cases in one million exposed individuals over a 70-year evaluation period.  Prior to installation of the WESP, Quemetco emitted 615 pound of lead annually.  The letter reports that lead emissions plummeted to 1.22 pounds per year – a 99.8 percent reduction.  A table is provided in the letter that summarizes significant reductions of other hazardous air pollutants. Some of the reported metals reductions include the following: 


Pre-WESP Emissions (lb/yr)

Post-WESP Emissions (lb/yr)

Percent Reduction (%)

















Chromium (VI)






3.83 x 10-7


The data presented in the letter is consistent with the initial stack test data that was shared with Envitech following the installation.  Although the system provided a guarantee for only three metal compounds, we expected similar removal for any condensed metal at the inlet of the WESP.  The data demonstrates this was the case.

The consistent performance since the installation in 2007 demonstrates the tremendous capability of the WESP system to achieve dramatic reductions of condensed metals in a robust fashion for a process that must operate 24/7/365 days per year.

For a copy of the full paper, please download the white paper below.

Download Free White Paper

Topics: particulate control, wet electrostatic precipitators, MACT Standards

Wet Electrostatic Precipitator (WESP) Control of Heavy Metals

Posted by Andy Bartocci on Tue, Apr 06, 2010 @ 04:11 PM

Last November I made a blog post describing the use of a wet electrostatic precipitator (WESP) for meeting metals emisssions.  This topic will be discussed in greater detail in an Envitech paper being presented at the 2010 A&WMA 103rd annual conference in Calgary, Canada.   wet electrostatic precipitator

The metals of concern can include mercury, arsenic, lead, cadmium, nickel and others, depending on the process.  A control strategy using a wet electrostatic precipitator (WESP) in conjunction with sub-cooling was used on a secondary lead smelter to meet more stringent emission standards.  This approach achieved > 98% removal of arsenic and > 92% removal of lead and other condensed metals downstream of a bag-house.  This substantially reduced the plant's cancer risk index and helped to meet reduced fence line lead emission limits.   

The table below provides a summary of other processes facing similar challenges including the additional removal efficiencies that can be required downstream of existing air pollution controls.  Most of the processes are from combustion sources and use a range of air pollution controls including bag-houses, packed bed absorbers, and Venturi scrubbers.  In some cases a combination of controls are used. Despite existing controls, very low concentrations of heavy metals can be emitted.  In the case of bag-houses for instance, the operating temperature may be in a range that some of the metals are in a gas phase.  In such case they will not be collected by particulate control devices. In other cases, the concentrations of submicron, condensed phase heavy metals may exceed the removal capability of controls like packed bed absorbers or Venturi scrubbers.

Process Upstream Controls Compounds Requiring Polishing  Add-On Removal Efficiency* 
Secondary Lead Smelters


Packed Bed Absorbers 

 Lead (Pb)

Arsenic (As)

 92% - 98%

Primary Lead Smelters


 Arsenic (As)  > 85%
Hazardous Waste Incinerators

Venturi Scrubbers

Packed Bed Absorbers

 Lead (Pd)

Cadmium (Cd)

Mercury (Hg)

 80% - 90%
Refinery Sludge Incinerators

Venturi Scrubbers

Packed Bed Absorbers

 Cadmium (Cd)  98%-99%
Geothermal Plants Packed Bed Absorbers

 Arsenic (As)

Mercury (Hg)

 > 90%

*Refers to additional removal efficiency after the upstream controls. 

The performances achieved on a secondary lead smelter using a WESP, suggest the approach can be used on these other processes to remove residual concentrations of condensed metals.  In the case of mercury, the ability to remove it with a WESP depends on whether it is in a condensed form. This requires reliable speciation data to make that determination.  More specifically, the mercury must be in a particulate or oxidized form for it to be removed by a WESP.

Please click on the below icon to download a white paper on this topic from the 2010 A&WMA's 103 Annual Converence in Calgary, Canada: "Wet Electrostatic Precipitator (WESP) Control for Meeting Metals Emission Standards".

Download Paper

Topics: particulate control, wet electrostatic precipitators

Wet Electrostatic Precipitator Control for Meeting Metals Emissions

Posted by Andy Bartocci on Thu, Nov 12, 2009 @ 09:10 AM

There are several industrial processes that face the challenge of meeting increasingly aggressive metals emission standards.  In many cases these standards exceed the capability of existing air pollution control equipment which can include bag-houses and packed bed absorbers. Some of these processes include:Refinery

  • Secondary lead smelters
  • Lead refining
  • Refinery sludge incinerators
  • Geothermal energy plants

Some of the metals of concern can include mercury, arsenic, lead, cadmium, nickel and others, depending on the process.  To achieve more stringent metals emission standards, three features should be designed into the air pollution control system. 

  • Removal of the bulk particulate load
  • Sub-cooling the gas
  • Wet Electrostatic Precipitator (WESP) for polishing

Geothermal EnergyRemoval of the bulk particulate load - Removal of the bulk particulate load may be required if there is a high particulate concentration from the upstream process.  This will be the case for secondary lead smelters, lead refining, and refinery sludge incinerators.   Geothermal energy plants will not have this requirement.  A bag-house will be used for secondary lead smelters and lead refining.  A wet Venturi scrubber system can be used for refinery sludge incinerators   Removal of the bulk particulate minimizes space-charge effects inside the WESP. Space-charge effects occur when particles interact and repel each other. This reduces WESP performance because it interferes with the migration of charged particle to the tube wall for collection.

Sub-cooling the gas - Some of the volatile metals may be in the vapor phase when they pass through a bag-house at higher temperature.  In this case they will pass right through the bag-house and will not be collected.   Sub-cooling the gas is done after the bag-house and uses a condenser/absorber to cool the gas below the saturation temperature.  Sub-cooling is beneficial because it condenses as much of the volatile metals as possible so they can later be removed as particulate.  In the case where a Venturi is used to remove bulk particulate, like for a refinery sludge incinerator, it has the added benefit of condensing water onto the particulate and condensed metals.  This increases their diameter making them easier to remove in a Venturi scrubber.  Sub-cooling also reduces the gas volume, which helps to reduce the size and cost of a downstream WESP.

Wet Electrostatic Precipitator (WESP) for polishing - A wet electrostatic precipitator is used as a final particulate polishing stage.  The performance is relatively independent of the particle size so it is highly effective at sub-micron particulate control.  In some cases, a condenser/absorber (C/A) for sub-cooling can be integrated into the conditioning section of an upflow WESP.  This was successfully done at a secondary lead smelter downstream of bag-house.  The C/A was also used to neutralize SO2 in the gas stream. The integrated C/A and WESP achieved > 98% removal of arsenic and > 92% removal of lead and other condensed metals after the bag-house.  This substantially reduced the plants cancer risk index and helped to meet more stringent fence line lead emission standards. 

To download a free white paper on wet electrostatic precipitator for a secondary lead smelter, click the link below.

wet electrostatic precipitator

Download Free White Paper


To view a free wet electrostatic precipitator video, click on the link below. 

wet electrostatic precipitator
Free Video

Geothermal by Louis Falcon

Refinery by Szeke

Topics: Venturi scrubbers, Scrubbers, wet electrostatic precipitators

CFD in Air Pollution Control Systems

Posted by Andy Olds on Tue, Oct 27, 2009 @ 06:00 AM

By Mike Simon
Director of Simulation Products, Digital Dimensions

Understanding how simple design changes affect the airflow inside of Envitech's products is critical in designing efficient industrial gas cleaning systems.  Engineers who design this equipment need to analyze and understand the behavior of the components if they want to improve performance.  Computational Fluid Dynamics (CFD) is a good tool for studying the effects of different design changes on these systems.  CFD provides a way to save time and money in obtaining the necessary information, and assists engineers in designing better quality air pollution control systems.    The use of CFD makes it possible to minimize the use of physical prototypes and find serious flaws much earlier in the design process. 

SolidWorks is the 3D CAD system used by Envitech to design their industrial gas cleaning systems.  SolidWorks has a number of complementary features to its mechanical CAD system including CFD capabilities that are fully integrated within the main CAD interface.  SolidWorks Flow Simulation is the name of the CFD program inside of SolidWorks that allows engineers to take their 3D CAD models and perform virtual prototyping on their designs without having to fabricate any parts.  To perform a simulation, the following steps are needed:

  • 1. Create solid model in the SolidWorks CAD system
  • 2. Specify the working fluid ( air was used in this case)
  • 3. Specify the flow rate at the duct inlet
  • 4. Specify the outlet opening of the duct
  • 5. Specify the pressure drop or resistance properties of the filter material (properties taken from filter manufacturer specifications)
  • 6. Run the simulation inside of the SolidWorks interface

Flow Simulation


Envitech's products were particularly challenging since Envitech's products utilized very thin fins and packing materials within a large ducting area.  Thin fins are used to direct the airflow and also to collect water from entering the system.  SolidWorks Flow Simulation was able to capture the geometry of these thin fins and create a corresponding CFD model for the simulations.  Packing material is used to help distribute airflow and trap particulates from being released into the environment.  The porous media feature inside of SolidWorks Flow Simulation was used to simulate the packing material and create the additional resistance to the airflow.  After performing the simulations, the Envitech engineers had the ability see the effectiveness of the scrubber fins in directing the airflow and to understand the pressure drops caused by the packing material.  The simulations helped the Envitech engineers validate their designs and gave them additional insight into how to improve future product performance.

For additional information on SolidWorks CAD or SolidWorks Flow Simulation software, go to or contact Mike Simon, Director of Simulation Products, at

For a case study on the impact of CFD analysis, click on the link below.

Download  Case Study

Topics: Venturi scrubbers, Scrubbers, wet electrostatic precipitators, Guests

Acid Gas Dewpoint

Posted by Andy Olds on Mon, Aug 31, 2009 @ 09:00 AM

acid gas scrubberAcid gases can be found in the exhaust of a large number of combustion processes.  As a gas, the acid compounds usually are not particularly corrosive and are relatively easy to remove.  However, when the temperature of the gas drops below the acid gas dewpoint, an acid mist can form.  The acid mist can turn into a fine aerosol or it can condense on a cold surface.  Acid mist poses a number of design problems, due to the small size of the mist particles and the corrosivity of the liquid form of the acid.

Aerosol Formation

Aerosol formation occurs when the bulk temperature of the gas drops below the acid dewpoint of the gas.  Much like the formation of fog, the acid gas condenses into tiny liquid droplets.  The size of these droplets can vary widely depending on the acid, the amount of condensation nuclei present in the gas, and degree of supersaturation.

The most common problem that occurs with acid aerosol formation is the inability to capture the aerosol.  Many acid gas exhaust treatment systems utilize a packed bed scrubber to remove the acid.  Packed bed scrubbers are extremely efficient at removing acid in the gas, but unfortunately are ineffective at removing acid aerosol.

The solution to removing acidic aerosol mist is to use a high efficiency entrainment separator or Venturi scrubber, which can effectively capture particles to 1-micron or 0.5-micron, respectively.  If the acidic aerosol mist is primarily sub-micron in nature, a wet electrostatic precipitator also provides a useful solution.

Wall Condensation

Wall condensation occurs when a cold surface is in contact with a hot gas.  If the wall is cooler than the acid dewpoint, acid can condense onto the surface of the wall.  There are several dangers with wall condensation.

First, the material selection for an acid is dependent on its form.  Many acids are not corrosive as a gas, but are very corrosive as acids.  Engineers selecting materials under the assumption that the acid remains a gas often choose materials that are not compatible with the acid in its liquid form.

Second, when condensed, the acid is much more concentrated than it is in the bulk medium.  Instead of selecting a material for a gas containing 10 ppm of SO3 gas, the engineer now has to worry about a nearly pure sulfuric acid droplet.

Finally, the acid can condense in non-ideal locations, leading to pooling and further corrosion concerns.

The solution to preventing the effects of wall condensation is to insulate walls to prevent cold surfaces and select materials for the concentrated, liquid form of the acid in locations where wall condensation is unavoidable.

Acid Dew Point

All gases have a dew point that is dependent on the temperature, pressure, and concentration of the acid in the gas.  This article provides acid gas dewpoint equations for a number of acids.  Below are the formulae for a few of the more common acids in exhaust gases.

Tdp = Dewpoint Temperature, K

Pw = Partial Pressure of water, mmHg

Pa = Partial Pressure of acid, mmHg

Hydrochloric acid (HCl)

1000/Tdp = 3.7368 - 0.1591 * ln (Pw) - 0.0326 ln (Pa) + 0.00269 * ln (Pa) * ln (Pw)

Sulfur Dioxide (SO2)

1000/Tdp = 3.9526 - 0.1863 * ln (Pw) + 0.000867 ln (Pa) - 0.000913 * ln (Pa) * ln (Pw)

Sulfuric Acid (H2SO4)

1000/Tdp = 2.276 - 0.0294 * ln (Pw) - 0.0858 ln (Pa) + 0.0062 * ln (Pa) * ln (Pw)


Click on the button below to down load an Envitech packed bed absorber cut sheet for acid gas removal.

Download Cut Sheet

Packed bed absorber cut sheet

Photo Credit: tinyfroglet

Topics: Venturi scrubbers, Scrubbers, wet electrostatic precipitators, Acid Gas