Air Pollution Control Innovations

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

Wet Scrubber Basics

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


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

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

Figure 1: Wet scrubber technology summaryEnv wet scrubber technologies

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

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

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

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

Envitech WESP Venturi Performance

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

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

Figure 3: Incinerator wet scrubber arrangement

Env wet scrubber arrangement

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

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

Click on the icon below to download an Envitech brochure.

Download Literature



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

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

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

IT3 Logo

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

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

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

Papers presented in technical sessions cover:

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

Envitech will present papers on the following two topics.

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

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

Sewage Sludge Incinerator (SSI) Mercury Control Technologies

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

Click on the icon below to download an Envitech brochure.

Download Brochure



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

Technology Solutions for Sulfuric Acid Formation and Removal in Thermal Oxidizers

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

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

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

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

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

SO2 + 1/2O2 => SO3

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

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

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

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

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

Download Literature

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

IT3/HWC 2015 Conference October 20-22, 2015 – Wet Electrostatic Precipitator for Medical Waste Incinerators

Posted by Andy Bartocci on Tue, Sep 22, 2015 @ 10:47 AM

Envitech will attend the International Conference on Thermal Treatment Technologies (IT3/HWC), October 20-22, 2015 at the Crowne Plaza Hotel in downtown, Houston, Texas.  The preliminary technical program can be downloaded from the conference website.   The conference features key note speakers from Veolia, Clean Harbors, Essroc, TCEQ, and B3 Systems.

Envitech will have an exhibit booth and present a paper, “Meeting the New Hospital, Medical, and Infectious Waste Incinerator (HMIWI) MACT with a Wet Electrostatic Precipitator (WESP)”.  The paper will provide an overview of a new medical waste incinerator scrubber system with a wet electrostatic precipitator to treat the off gas from two existing medical waste incinerators. The new system was required to achieve a 20% reduction in particulate (PM) emissions, and a 93% reduction in lead (Pb) emissions from the previous gas cleaning system.  The new system has been operational since October 2014.  The table below compares the performance of the emission limits to the new compliance standards. The results demonstrate the system comfortably meets the new EPA MACT standards.







Test Result

% of limit

Particulates, EPA Method 5 gr/dscf 0.020 15%
Pb EPA Method 29 mg/dscm 0.018 6%
Cd, EPA Method 29 mg/dscm 0.013 10%
Hg mg/dscm 0.025 1.0%
Dioxins/furans, EPA Method 23 Total (ng/dscm) 0.85 5%
  TEQ (ng/dscm) 0.020 15%
HCl, EPA Method 26 ppmv 7.7 1.6%
SO2 ppmv 4.2 35%

Click on the icon below to download a copy of the paper.


Topics: particulate control, Venturi scrubbers, wet electrostatic precipitators, MACT Standards, Medical Waste Incinerator Scrubber, Incinerator Scrubber, HMIWI Scrubber

Arsenic Scrubber for Copper Mine Roaster

Posted by Andy Bartocci on Thu, Jan 09, 2014 @ 01:00 PM

With an expanding global population, demand for minerals continues to grow.   Development of non-traditional resources is expected to increase to meet this growing demand. This includesCopper Mine copper resources challenged by high levels of arsenic.  Mining operations may incur penalties for arsenic in concentrates that exceed a certain amount.  As ore with low levels of arsenic is depleted, these penalties will continue to rise.

One facility seeking to reduce the impact of penalties is the Aranzazu project in Zacatecas Mexico by Aura Minerals.  The facility will use a partial roasting technology by Technip to achieve arsenic reduction in the concentrate.  After treatment, the concentrate is expected to contain less than 0.3% arsenic.  This will decrease expected arsenic related penalties by up to $1.00 per payable pound of copper produced.

wet electrostatic precipitator


The roaster off-gas will be treated by an Envitech wet scrubber system to remove arsenic with a 99.9% performance guarantee. The inlet gas to the scrubber will be at an elevated temperature well above 1,000oF and will have a high concentration of particulate, sulfur, and arsenic. The scrubber system combines Envitech’s wet scrubber technology which has been used to remove hazardous air pollutants from medical and hazardous waste incinerators with Envitech’s wet electrostatic precipitator technology (WESP) for final collection and removal of arsenic.  Envitech’s WESP technology has demonstrated high performance for arsenic removal on other furnace applications at secondary lead smelting facilities.

 For more information on the removal of heavy metals using wet electrostatic precipatators, please download our white paper on the capture of emissions from a smelter.

Download Free White Paper


Topics: Venturi scrubbers, wet electrostatic precipitators

Wet Scrubber Technology for Reducing China’s Air Pollution

Posted by Andy Bartocci on Wed, Jun 26, 2013 @ 12:01 PM

Envitech recently got noticed in a local news story by Michael Chen of KGTV Channel 10 News, “San Diego Companies Could Help Clean China’s Air”.  The story is about how California’s Governor Jerry Brown’s diplomatic trip to China could lead to opportunities for local San Diego companies like Envitech.  During his visit, Gov. Brown signed a pact that will pave the way for California companies to help China measure and improve its air quality.   As a leader in industrial air pollution control equipment, Envitech has process technology that can be used in China for reducing hazardous air pollutants (HAPs) and pollutants that contribute to regional haze like sulfur dioxide (SO2). These technologies have been applied to many processes in North America including a coal gasification plant, hazardous waste incinerators, lead smelters, sulfite pulping mills, waste oil re-refiners, geothermal plants, and mining and mineral processing to name a few.  Envitech has pursued several opportunities in China through 3rd party customers and will have one installation starting up later this year.

For more information on Envitech's capabilities, please download our product brochure.

Download Brochure

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

Medical Waste Incinerator Scrubbers for the new HMIWI MACT Standard

Posted by Andy Bartocci on Fri, May 24, 2013 @ 01:00 PM

In 2009 I wrote a blog piece about the new EPA rules promulgated for the hospital, medical, and infectious waste incinerator (HMIWI) maximum achievable control technology (MACT)describe the image standard.  The compliance dates for these rules are fast approaching.  Facilities with existing equipment must demonstrate compliance to the new standards by October 2014.  Envitech is already under contract with several facilities to retro-fit existing medical waste incinerator scrubbers with add-on control equipment to meet the new standards. 

The emissions reduction challenge with the new rules can be seen in the adjacent graph which compares the difference between the 2007 MACT standard to the new MACT standard.   Medical Waste ScrubbersStack emissions must meet substantially lower limits for Cd, Pb, and Hg. In many cases, this requires add-on controls capable of greater than 90% removal of sub-micron condensed metals.  Most facilities are putting on a re-heat and filter package to remove the condensed metals.  A few will use wet electrostatic precipitators (WESP) which are more expensive.   The ability to meet the new rules using a re-heat and filter package has been demonstrated for lead and cadmium on a commercial and industrial waste incinerator (CISWI).  The WESP capability has been demonstrated for reduction of lead emission achieved at a secondary lead smelter in California.

Another emissions reductions challenge is dioxins/furans (D/F).  Emission limits for D/F have been reduced from 125 ng/dscm Total and 2.3 ng/dscm TEQ (corrected to 7% O2) to 25 and 0.6 ng/dscm, respectively.  These emission limits are too low to be met with carbon injection.  An add-on control package of re-heat and carbon bed absorber is required to meet the new limits.

Solutions to these challenges exist and facilities are taking steps to meet them.  Click on the link below to download the HMIWI MACT Rule paper from the 2010 International Conference of Thermal Treatment Technologies and Hazardous Waste Combustors (IT3/HWC).

Download Free Paper 


Topics: particulate control, Venturi scrubbers, Scrubbers, wet electrostatic precipitators, cleaning systems, MACT Standards

Wet Electrostatic Precipitator Insulator Design

Posted by Liliana Chen on Mon, Mar 18, 2013 @ 06:00 AM

The purpose of a wet electrostatic precipitator (WESP) is to remove particulates that are smaller than one micron from a gas stream.  One of the common industrial applications is downstream of standard pollution control equipment on power plants or pulp mill facilities. Power plants typically use wet electrostatic precipitators after all other pollution control equipment for polishing.  Pellet mill facilities use wet electrostatic precipitators upstream of RTOs to prevent buildup on the RTO media. Particulate removal is achieved by sending process gas through an array of high voltage electrodes and grounded collectors.  Particles in the gas are charged and then attracted to the collector surface;  clean gas continues up the WESP.

The outlet section of a WESP houses the insulator compartments.  Insulator compartments support a high voltage grid which holds the discharge electrodes in place. This arrangement separates the high voltage grid from the grounded section. The introduction of purge air through the insulator compartment reduces dust and moisture buildup on the walls of the compartments. This not only keeps the insulator bushing clean but also maintains a positive air pressure to prevent process gases from entering the compartment. 


The diagram above shows how the WESP is connected to the insultator compartment with a shroud. Operating the system at minimum purge air flow helps reduce operating cost as less energy will be required to heat up the purge air. The caveat here is that inadequate flow will result in wet process gases swirling into the insulator compartment through the shroud from the WESP. In an attempt to optimize our operating conditions, flow simulation was performed to analyze the flow pattern of purge air through the shroud at varying inlet flow rates.

The close-up view of the shroud shown on the bottom was taken facing the insulator compartment with WESP at the back. The green/blue color indicates air flow towards the WESP (into the page), while the red/yellow represents flow towards the insulator (out of the page). This illustrates a positive air flow into the WESP achieved at minimal flow rate. Under this operating condition, energy savings will be maximized while ensuring no swirling of wet process gas into the insulator compartment. 



To see how this modeling is applied, download our case study on treating a lead fume using a wet electrostatic precipitator.

Download Paper

Topics: wet electrostatic precipitators

Wet Electrostatic Precipitators for Pellet Mills

Posted by Andy Bartocci on Thu, Mar 07, 2013 @ 03:42 PM

Envitech will be attending the International Biomass Conference & Expo in Minneapolis, MNWESP April 8-10, 2013.  We will exhibit at Booth 807.  During the conference I will be presenting in the Pellets & Densified Biomass track between 8:30 am and 10:00 on Wednesday, April 10th. The topic will be "High Performance Wet Electrostatic Precipitator (WESP) for Pellet Mills".   


A large portion of wood pellets produced in North America are exported to Europe to support aggressive low-carbon fuel incentives.  Growth of the export market has lead to large scale pellet mills with production capacities ranging from 500,000 to 750,000 tons of pellets per year.

Pellet MillThese mills use wood dryers to remove moisture from incoming feed material.  A wet electrostatic precipitator (WESP) collects particulate (PM) and condensed volatile organic compounds (VOC) from the dryer exhaust. This is required to protect a downstream regenerative thermal oxidizer (RTO) from fouling. The RTO destroys volatile organic compounds (VOCs) before exhausting to the atmosphere.  The process flow conditions are large and typically several hundred thousand cubic feet per minute.

This presentation will discuss a high performance WESP design to treat the pellet mill dryer exhaust.   The design leverages experience from several large flow rate applications including a coal dryer scrubber, secondary lead smelter WESP, and sulfite pulp mill recovery boiler WESP.  The presentation will focus on how the design achieves high performance.

A copy of the presentation is available by clicking the link below.

Download Free Presentation


Topics: wet electrostatic precipitators