Air Pollution Control Innovations

Particulate Removal Using a Venturi Scrubber

Posted by Andy Bartocci on Mon, Apr 11, 2016 @ 11:52 AM

Venturi_Westlake.jpgA Venturi scrubber is a common air pollution control device that is used to remove particulate. Because it is a wet scrubber, collected particulate is purged in a liquid discharge stream called the blowdown.

Venturi scrubbers are commonly used for industrial dryer applications (see photo). They have a relatively low inlet temperature or might have sticky particulate which prevent the use of a bag-house. Typical dryer applications include coal dryers, pot ash mining, CPVC plastics manufacturing, bio-solids sludge drying, or salt production. Venturi scrubbers are also used in insulation or glass manufacturing, magnesium mining, and hazardous and medical waste incineration.

It is important to saturate or pre-cool the gas before entering the Venturi throat to minimize evaporation. That is because during evaporation, water molecules leave the water droplet surfaces which push particles away from the droplets and reduce collection efficiency. It is also important to keep the inlet walls of the Venturi wetted to avoid fouling from wet-dry line interface.


In accordance with Bernoulli's equation, inlet gas accelerates at the converging section of the Venturi throat, increasing gas-liquid contact. As water is injected perpendicular to the gas flow in the throat, the accelerated gas particles are captured by water droplets upon collision. Three mechanisms account for collection in a Venturi which is summarized below. The adjacent graphic scrubber illustrates the three mechanisms.


  • Diffusion – Particle is so small its path is erratic due to Brownian motion.
  • Interception – Particle follows streamline around droplet, makes contact if within a particle radius.
  • Impaction – Particle’s inertia cause it to leave stream line and impact the droplet.

Impaction is the dominant collection mechanism for large particles, greater than 15 microns. They can be collected with efficiency greater than 99%. Diffusion and interception are more prevalent for smaller particles. Collection efficiency is lower for these particles because their small size increases the probability they will flow around the water droplets and avoid collection.

The graph below illustrates the impact of particle size on collection efficiency. The vertical axis is collection efficiency and the horizontal axis is pressure drop. The curves represent different particle sizes ranging from 0.2 to 5 microns. It can be seen that collection efficiency increases for larger particles and higher pressure drops. The net result is overall collection efficiency is dependent on the aerodynamic particle size distribution (PSD).













After particle collection in the Venturi throat, the resulting droplets aggregate through the diverging section and are separated from the process gas by the mist eliminator (ME) in the entrainment separator (ES). The ability of the mist eliminator to remove water droplets from the gas stream can have a significant impact on the scrubber performance. Any water droplets that "escape" the ME will carry entrained particulate and increase the measured outlet emissions. A more detailed discussion on mist elimination can be found in the previous blog post on “Improving Entrainment Separator Design”.

To download a free case study on a Venturi scrubber used to remove particulate from a CPVC dryer.

Download Case Study 


Topics: particulate control, Venturi scrubbers, Scrubbers

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

Medical Waste Incinerator Scrubber Used to Process Ebola Waste

Posted by Andy Bartocci on Wed, Nov 05, 2014 @ 05:43 PM

Envitech recently got noticed in a local news story by Michael Chen of Channel 10 News, “Local Company Helps Dispose of Ebola-tainted Waste”.  The story talks about the challenges of processing Ebola waste and how Envitech’s Medical Waste Incinerator Scrubber at the University of Texas Medical Branch (UTMB) was used to dispose of waste generated by an Ebola patient in Texas.

UTMB operates the only permitted medical waste incinerator in the state of Texas.  Since 1991 the facility has operated an incinerator which uses an Envitech wet scrubber system to clean the exhaust gases of harmful pollutants.  A new incinerator system was recently installed to meet the new EPA rules promulgated for the hospital, medical, and infectious waste incinerator (HMIWI) maximum achievable control technology (MACT) standard.  The impact of these rules is discussed in a previous blog post.

The outlet emission requirements of the new standards are a significant reduction from the previous 1997 standards.  The allowable outlet emissions for many of the metals, i.e. lead (Pd), Cadmium (Cd) are less than 1% of the previous emission limits. For example, the allowable concentrations for Pb,and Cd are measured in 10-7 and 10-8 gr/dscf, respectively.  These are some of the lowest HAPs emission limits for industrial sources in the United States. Medical Waste Scrubber Below is a summary performance guarantee for the new scrubber system based on the new HMIWI standard:

  • PM < 18.3 mg/dscm (0.008 gr/dscf)
  • Lead < 0.00069 mg/dscm (3.0 x 10-7 gr/dscf)
  • Cd < 0.00013 mg/dscm (5.7 x 10-8 gr/dscf)
  • HCl < 5.1 ppmv dry
  • SO2 < 8.1 ppmv dry
  • Dioxins/Furans < 0.035 ng/dscm on TEQ basis

Recent episodes of processing highly infectious waste from Ebola patients may re-ignite a policy debate on medical waste disposal. In the early 1990, many hospitals were going to a model of owning and operating a relatively small medical waste incinerator to process and destroy medical waste generated in-house. These systems typically have a capacity of 500 to 1,500 lb/hr. As air emission standards became stricter, many hospitals decided to shut down their incinerators and ship their waste to larger, centralized medical waste incinerators. These systems are much larger in capacity. For example, the largest medical waste incinerator facility is in Baltimore, MD with a permitted capacity of 150 ton/hr. The trade-off of a centralized waste incinerator is the risk and liability of transporting the waste on public roads and highways. The recent Ebola outbreaks bring to light that some of this waste can be highly infectious and pose a significantly greater risk to public health. It also came to light that a single Ebola patient generates a substantial amount of infectious waste. In this scenario, it may make more sense for facilities to have the capacity to destroy their own waste and avoid the risk of transporting it over great distances on public roads.

The advancement of scrubber technology and compliance with the new, more stringent EPA MACT standards, confirm the ability to operate medical waste incinerators with virtually no harmful emissions into the air.  In addition to the UTMB medical waste scrubber system, Envitech has upgraded several other medical waste incinerators for meeting the new standards.  Based on the extreme low emission limits, the results are truly groundbreaking and may encourage states and facilities to permit new systems.

For more information on HMIWI regulations, please read our white paper.

Download Free Paper

Topics: Venturi scrubbers, MACT Standards, Ebola Waste, 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

Improving Entrainment Separator Design

Posted by Liliana Chen on Tue, Mar 26, 2013 @ 08:38 AM


Venturi scrubbers are used to remove particulate from the exhaust gas of industrial sources.  They are highly efficient at removing particulate 1-micron in size and larger. Venturi scrubbers are used in solid waste incineration, waste-to-energy production, mining, biosolids sludge processing, plastics production and coal gasification.  In many of these applications, the Venturi is used on the back end of a dryer or thermal destruction device.
describe the image
In accordance with Bernoulli's equation, inlet gas accelerates at the converging section, increasing gas-liquid contact. As water is injected perpendicular to the gas flow, the accelerated gas particles are captured by water droplets upon collision. The resulting droplets aggregate through the diverging section and are separated from the process gas by the mist eliminator (ME) in the entrainment separator (ES). 

The ability of the mist eliminator to remove water droplets from the gas stream can have a significant impact on the scrubber performance. Any water droplets that "escape" the ME will carry entrained particulate which can foul a stack test and increase the measured outlet emissions. The amount of pressure drop consumed by the ME can impact scrubber performance.   Minimizing ME pressure drop allows a higher pressure drop across the Venturi  which increases the particulate capture efficiency in the Venturi throat.

The mist eliminator efficiency is heavily impacted by velocity.  Therefore, it is critical to achieve even flow distribution before reaching the ME. The ability to distribute the flow uniformly will allow the system to operate more effectively under a wider range of inlet gas flow rates.

Flow studies were performed to evaluate the capability of three different designs:

  • Envitech design
  • Design from an ES supplier (referred to as Config. 1)
  • Design from a customer based on past experience (referred to as Config. 2).

All three systems have their respective "plate" design to help improve the flow distribution.

describe the image

Differential pressure (∆P) across the mist eliminator is a direct indicator of how well distributed the flow is; the lower the ∆P, the more evenly the flow is distributed. The graph below compares the ∆P across the mist eliminator and the plate respectively for the three designs. The ideal ∆P across ME was obtained at uniform inlet gas flow through the ES. Envitech's design has the lowest ∆Ps, reflecting that the plate distributes the flow most effectively and as a result the ∆P across ME is the closest to ideal.

To provide a visual illustration, the cut plots below were obtained from flow studies showing the velocity(y) distribution prior to the plate, before and after mist eliminator. A zone with high velocity (red) was observed in all designs before entering the plate. The plate breaks up the hot spot and re-distributes the flow. The flow pattern before and after the ME for the Envitech design is the most homogenous among the three which is consistent with the pressure drop results.

describe the image


The flow studies enabled the Envitech Venturi Scrubber to be optimized three ways as follows:

  • Reduced the material cost wiwthout compromising scrubber ability to agglomerate and remove particles.
  • Refined the flow distribution to expand the process window in the entrainment separator.
  • Reduced the pressure drop across the ES which allows a higher pressure drop across the Venturi throat.

To read more about this particular application, please download the case study below.

Download Case Study

Topics: particulate control, Venturi scrubbers, Scrubbers

Wet Scrubber – Coal Gasification Project Update

Posted by Andy Bartocci on Tue, Jan 22, 2013 @ 04:51 PM

Mississippi Power Company recently released a Youtube video providing an update on theCoal Gasification scrubber Kemper County Coal Gasificaton Integrated Combined Cycle (IGCC) Project.  The project is a 582-megawatt power plant currently under construction.  The facility will convert locally mined lignite coal into energy using a state of the art coal gasification process call Transport Integrated Gasification, or TRIGTM.  The process enables a 65% CO2 reduction making green house gas emissions equivalent to similar size natural gas combined cycle power plant

wet scrubber



The lignite coal is very wet and needs to be dried before it is gasified.  An Envitech wet scrubber-condenser system is used in the material handling/drying train.  The system is comprised of a Venturi scrubber and packed bed condenserThe wet scrubber equipment treats 2.1 MM cfm of dryer exhaust and can be seen in the lower left corner of the screen 28 seconds into the video.

Part of the CO2 reduction comes from CO2 capture using 200 ft solvent absorbers.  The CO2 will be piped to another location in MS and used for enhanced oil recovery. This will allow an increase in oil production of approximately 2M barrels per year. Some milestones/features of the plant include:

  • Installation is 70% complete
  • Start-up planned during the summer of 2013
  • The plant will be a zero liquid discharge facility
  • Approximately 2,500 workers are currently on site
  • Over 12,000 construction jobs will be created during the course of onstruction
  • About 1,000 permanent positions will be created once the facility is open.

Click on the icon below to download a free presentation from the 2012 Coal-Gen conference on the coal dryer wet scrubber system.

Download Free Presentation



Topics: Venturi scrubbers, gasification, Scrubbers, cleaning systems

Coal Dryer Venturi Scrubber Case Study for a 582 MW Power Plant

Posted by Andy Bartocci on Tue, Nov 27, 2012 @ 08:44 AM

A 582-megawatt (MW) electric generating plantVenturi Scrubber, coal dryer scrubber in Kemper County Mississippi is being built. The process uses locally mined lignite coal for fuel which contains 40% moisture.  The coal must be dried before it is converted to syngas in the gasifier.

Six (6) fluidized bed dryers dry the coal with a combined exhaust gas flow rate of 2.1 MM cfm.  A cost effective means was needed to remove particulate and moisture from the exhaust gas before it is recycled back to the dryers.

A case study is now available to describe how an Envitech Venturi scrubber-condenser solves this problem.

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

Download  Case Study 


Follow the link to a previous blog post to download a presentation on this project from the 2012 Coal-Gen Conference.

Topics: Venturi scrubbers, gasification, Scrubbers

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