Air Pollution Control Innovations

Rectangular Acid Gas Scrubber Lowers Installation Cost and Improves Maintenance

Posted by Andy Bartocci on Thu, Jul 09, 2015 @ 03:29 PM

Acid gas scrubbers are one of the most common types of air pollution control systems found in industry.  They are often used to treat exhaust gases from combustion sources such as incinerators, hazardous waste combustors, thermal oxidizers, regenerative thermal oxidizers (RTO), furnaces, and direct fired heaters.   Acid gas scrubbers are found on a wide range of facilities including, geothermal plants, secondary lead smelters, waste oil re-refiners, refineries, chemical and pharmaceutical plants, and mineral and metal processing facilities.  The most common types of acid gas emissions are HCl and SO2, but can also include Cl2, HBr, HF, and NOx.

Most acid gas scrubbers are wet scrubbers using vertical packed bed absorbers.   In the case of combustion sources, the scrubber is coupled to an evaporative quencher to cool the gas to saturation before it passes to the packed bed. This arrangement is shown in the adjacent figure for a medical waste WSU_Vertical_Scrubberincinerator.  The incinerator exhaust is ducted to a metal quencher (shown in the foreground). The hot gas enters the top of the quencher and flows vertically downward. The gas then elbows into the bottom of a vertical packed bed scrubber (shown in the background). The gas passes upward through the packed bed as re-circulated water flows downward, counter-current to the gas from the top of the packed bed.  Water from the quencher and packed bed is collected in the sump and re-circulated back to the quencher and packed bed.  An entrainment separator at the top of the scrubber removes entrained water droplets.  After exiting the scrubber vessel, an interconnect duct transports the gas to a induced draft fan located at grade.

The scrubber above is one of the earliest Envitech medical waste incinerator scrubbers.  These types of scrubbers are often installed in hospitals where critical design considerations include limited space, low ceilings, and difficult to reach locations through elevators and narrow corridors.  To help minimize installation costs Envitech developed a rectangular scrubber which is shown in the figure below. 













This configuration provides several advantages over a vertical scrubber, including:

Greater integration and pre-assembly of ancillary equipment and pumps, piping, valves, and fittings.

  • Ground level access manways for safer, easier maintenance.
  • Simplified ductwork connection to the fan and stack.
  • Elimination of caged ladders and platforms for nozzle and mist eliminator access.
  • Ability to fit in locations with low head space.
  • Simplified requirements for setting and integrating equipment which lowers installation costs.

The rectangular scrubber has been used on over 60 installations.  Envitech has found that facilities tend to prefer a rectangular design over a vertical scrubber for the advantages noted above.  In some cases, total installed cost is reduced by 40% to  50%.  Weather a scrubber is purchased from an EPC contractor, upstream equipment supplier, or architectural & engineering firm, it is recommended that facility preferences be taken into consideration in the final selection process.

The video link below shows a few recently installed rectangular scrubbers at waste oil re-refiners as well as several examples of other rectangular scrubber installations.


Click the link below for a free case study on  a rectangular acid gas scrubber for a direct fired heater at a waste oil re-refiner.


Click the link below for a free case study on a rectangular medical waste incinerator scrubber for the control of acid gases, particulate, and heavy metals.


Topics: Scrubbers, SO2 Scrubber, Acid Gas, HMIWI Scrubber

Refinery Sulfur Recovery Unit (SRU) SO2 Scrubber for Startup, Shutdown, and Malfunction

Posted by Andy Bartocci on Wed, Jun 24, 2015 @ 05:55 PM

For years, many states have exempted industrial facilities from rules prohibiting the release of toxic pollution during startup, shutdown, and malfunctions. That could all soon change.  On May 22, 2015, the U.S. Environmental Protection Agency (EPA) finalized a rule which will force state regulators to limit industrial upset emissions. The EPA issued a state implementation plan (SIP) call action to 36 states directing them to correct specific startup, shutdown, and malfunction provisions in their SIPs to ensure they are fully consistent with the Clean Air Act (CAA).  The ruling will affect a wide range of facilities including refineries, chemical manufacturers, and natural gas producers.  This will create challenges for state regulators and industrial facilities and opportunities for technology providers and environmental consulting and engineering firms.

A common industrial application which may be impacted by the new rule is found in refineries for sulfur recovery units (SRU).  Most SRU’s are based on a multi-step Claus process which recovers sulfur from gaseous hydrogen sulfide. The hydrogen sulfide is found in by-product gases from refining crude oil and other industrial processes.  A Tail Gas Treatment Unit (TGTU) follows the SRU to recover sulfur and return it to the SRU.  A TGTU can yield 99.9% sulfur recovery for a typical oil refining plant.  An in1110_-_Sinclair2cinerator and waste heat boiler treats the TGTU off-gas before it is exhausted to atmosphere. 

During normal operations, there is very little SO2 emissions due to the high sulfur recovery. However, TGTU upsets can occur several times per year which sends unrecovered sulfur to the incinerator.  During these upsets, SO2 emissions can be as high as 1 tph  or more for a period of 8 to 12 hours.

Envtech is designing a refinery standby SRU tail gas caustic scrubber which will eliminate SO2 emissions during upset conditions.  The scrubber uses Envitech’s proprietary quencher which acts as a low pressure drop Venturi. The quencher is  followed by a packed bed absorber for SO2 removal.  The overall pressure drop is less than 10 inches and has lower power consumption than other types of SRU scrubbers installed in refineries.   Special design considerations enable the exhaust gas to pass through the scrubber at both elevated and cool temperatures.  During normal operation, hot gas from the TGTU passes through the scrubber in standby mode with the re-circulation pumps turned off.  In this mode, the gas is at elevated temperatures of 500oF to 600oF.  During a trip event, the TGTU is bypassed and the recirculation pumps turn on automatically.  The gases are then cooled to saturation and SO2 is absorbed and removed in the packed bed.  Implementation will enable to the facility to reduce SO2 emission by 40 to 80 tpy and to meet the new EPA compliance standards for start-up, shutdown, & malfunction.    The scrubber is a good example of how an innovative solution can help a facility meet the new emission requirements during upset conditions with significant benefit to the environment.

Topics: Scrubbers, SO2 Scrubber, Acid Gas

Medical Waste Incinerator Scrubber Used to Process Ebola Waste

Posted by Andy Bartocci on Wed, Nov 05, 2014 @ 08:43 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.

Topics: Venturi scrubbers, MACT Standards, Ebola Waste, Medical Waste Incinerator Scrubber, Incinerator Scrubber, HMIWI Scrubber

Marine Diesel Scrubber Passes CARB Testing

Posted by Andy Bartocci on Mon, Jan 13, 2014 @ 07:04 PM

Marine ScrubberIn 2012 Envitech designed and built a marine diesel scrubber to remove SO2 from the engine exhaust of ocean going vessels.  The scrubber was integrated into the Advanced Maritime Emissions Control System (AMECS) used at the Port of Long Beach.  AMECS is a stationary system that uses a bonnet to capture the exhaust gas from the ships stack while at port. The exhaust gases are conveyed to AMECS to clean the gases of particulate (PM), NOx and SOx before exhausting to atmosphere. This allows the ship to operate its auxiliary engines and boiler system while at port to provide power to the ship.  AMECS provides a cost effective way for ships and port operators to reduce emissions and to meet tougher regulatory standards. 

The AMECS team recently announced that the California Air Resource Board (CARB) has approved AMECS as an alternative technology for the At-Berth Regulation.  This approval follows more than 1500 hours of validation testing on 40+ vessels during 2012 and 2013.  The most recent testing occurred in October of 2013 and was attended by representative of CARB and SCAQMD as well as representatives from the Ports of Long Beach and Los Angeles.  The test yielded impressive results, including:

    • PM                                                                  94.5%
    • NOx (@1.6ppm ammonia slip)                       99+%
    • SO2                                                                 98.5%
    • VOCs                                                              99.5%

In a parallel track, the maritime industry is looking for ways to meet tougher standards not only at port but while operating at sea based on the IMO Annex VI MARIPOL Tier III requirements. Envitech continues to develop De-SOx technology options for ship based marine diesel engines.  The recent CARB approval is a milestone achievement for demonstrating the Envitech scrubbers ability to achieve high SO2 removal efficiency over a wide range of diesel exhaust and operating conditions.

Click on the link below to download a case study on the marine scrubber.

describe the image




Topics: Scrubbers, SO2 Scrubber, Marine Scrubber

Arsenic Scrubber for Copper Mine Roaster

Posted by Andy Bartocci on Thu, Jan 09, 2014 @ 04:00 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.



Topics: Venturi scrubbers, wet electrostatic precipitators

Geothermal Plant SO2 Scrubber

Posted by Andy Bartocci on Fri, Sep 13, 2013 @ 11:56 AM

A geothermal plant produces a sustainable source of energy by converting super heated fluidsCal Energy Geothermal Plant from the earth’s geothermal resources into electrical energy.  The fluids are recovered in the
process and re-injected back into the earth. The following YouTube video from CalEnergy provides a good overview of how a typical geothermal plant works.  California currently obtains about 4.5% of its electricity from geothermal plants. Most of these plants are sized at 50 MW but some plants can be larger in the 150MW range.  There is an estimated 2,300 megawatts of undeveloped energy in an area in Imperial County California near the Salton Sea just outside of San Diego.

Ormat Scrubber


The geothermal energy conversion process generates a sulfur containing off-gas which passes through a thermal oxidizer to destroy volatile organic compounds (VOC’s).   The sulfur compounds are oxidized to sulfur dioxide (SO2) and must be removed before exhausting to atmosphere.  A packed bed absorber treats the thermal oxidizer exhaust to remove SO2.  Often times geothermal plants are located in an extreme desert environment with summer  temperatures reaching > 120oF.  The scrubber equipment must be designed to achieve high removal efficiency, continuous operation and withstand the extreme environment.    


Click the link below to download a case study for an SO2 scrubber installed at an ORMAT geothermal plant near the Salton Sea in Southern California.





Topics: Scrubbers, SO2 Scrubber, Acid Gas

Sulfite Pulp Mill SO2 Scrubber and Wet Electrostatic Precipitator

Posted by Andy Bartocci on Mon, Jul 15, 2013 @ 06:57 PM

 A previous blog post made a case study available for wet electrostatic precipitator (WESP), SO2 scrubber system that will treat the off-gas of a red liquor recoverywesp boiler for a sulfite pulp mill in Quebec, Canada.  The scrubber system is part of a larger green energy project that will produce 40-megawatts of power and increase annual production capacity of specialty cellulose by 5,000 metric tonnes.   The new production capacity is slated to be complete by September 2014.

The system is comprised of a sulfur recovery island that cools the boiler exhaust gases and recovers sulfur using ammonia as a scrubbing reagent.  SO2 ScrubberThe sulfur containing effluent is re-used in the cellulose producton process. The sulfur recovery island is followed by a gas cleaning island comprised of an packed bed SO2 scrubber integrated with an Envitech wet electrostatic precipitator (WESP).  The gas cleaning island removes SO2 and particulate before exhausting to the atmosphere.

Envitech has completed the system design and released major equipment orders. Some major components will be complete as early as this month.  Delivery will take place before the end of 2013. The adjacent and  above images show a recent rendering of the system.







Wet Scrubber Technology for Reducing China’s Air Pollution

Posted by Andy Bartocci on Wed, Jun 26, 2013 @ 03:01 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.



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 @ 04:00 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).

describe the image




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 @ 11:38 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.

Topics: particulate control, Venturi scrubbers, Scrubbers

    Subscribe to our blog

    Ask an Expert