Air Pollution Control Innovations

There are several different waste incinerator source categories controlled by EPA standards under the Clean Air Act (CAA). These include hazardous waste combustors (HWC), sewage sludge incinerators (SSI), municipal solid waste (MSW) incinerators, commercial and industrial solid waste (CISWI) incinerators, and Hospital, Medical, and Infectious Waste Incinerators (HMIWI). Each incinerator type has its own Maximum Achievable Control Technology (MACT) standard which establishes technology based limits for emitted HAPs. MACT standards are part of the National Emission Standards for 

Hazardous Air Pollutants (NESHAP) and are applied to source categories that pose adverse risk to human health by the emission of hazardous air pollutants (HAPs).  The HMIWI MACT standard for medical waste incinerators is the most challenging of the incinerator source categories. This standard controls particulate (PM), hydrogen chloride (HCl), sulfur dioxide (SO2), lead (Pb), cadmium (Cd), mercury (Hg), dioxins/furans (D/F), nitrous oxide (NOx), and carbon monoxide (CO). Emission limits depend on the incinerator size and weather it is a new or existing source. Small incinerators are less than 200 lb/hr of waste throughput, medium incinerators are between 200 lb/hr and 500 lb/hr, and large incinerators are greater than 500 lb/hr.

Envitech recently completed a project for two medical waste incinerators at a Midwest research facility. These are the first new medical waste incinerators installed in the United States since Envitech installed a 525 lb/hr medical waste incinerator at a research facility in Galveston, TX in 2013.

The scope of supply includes two medical waste incinerator scrubbers and a water treatment system to treat the blowdown from both incinerators. The incinerators are permitted as new, medium size incinerators. Ozone injection is integrated into the system to meet a NOx limit of 67 ppmv. The systems include pre-assembled pumps, piping, valves, and fittings to minimize installation time and cost. The pre-assembly provides long term rigidity, consolidation of space, longer up-time, and improved safety for operators. A description of the process arrangement can be found in this link to an earlier blog post.

Stack testing was performed in June 2021 for both incinerators. Test results confirm the Envitech system reduced emissions well below MACT standard limits, providing a comfortable margin for compliance over the range of operating conditions and waste feed. Below is a summary of stack test performance.

Click on the link below to download literature on medical waste incinerator scrubbers.

Last March I gave a paper and presentation at the International Conference on Thermal Treatment Technologies and Hazardous Waste Combustors (IT3/HWC) in Houston, TX.  The paper discusses the challenges for meeting ultra-low emission limits for medical waste incinerators.  Wet scrubbers are used to control hazardous air pollutants (HAPs) on many hospital, medical, and infectious waste incinerators (HMIWI).   The Maximum Available Control Technology (MACT) standard for these incinerators was revised and became final in 2009.  The new standard has the lowest emission limits for incinerators today. The limits exceeded the capability of systems designed to the previous standard with respect to particulate matter (PM), lead (Pd), cadmium (Cd), mercury (Hg), and dioxin/furans (D/F).  By 2014 all existing medical waste incinerators were either shut down or upgraded to comply with the new standard.  Envitech successfully upgraded four existing medical waste incinerators.  A paper presented at the 2012 IT3/HWC conference describes one of these systems which was installed at the National Institute of Health (NIH), Rocky Mountain Labs.

The challenge moving forward will be new medical waste incinerators which have even more stringent, ultra-low emission limits.  Building a new incinerator requires critical decisions on control technologies and permitting.  The IT3/HWC paper reviews these issues for specific HAPs and discuss trade-offs between permitting a new medium size incinerator versus a large incinerator.   An example is provided of an air pollution control system meeting the emission requirements for a new large medical waste incinerator at the University of Texas Medical Branch (UTMB) in Galveston, TX.  Envitech is also building gas cleaning systems for two new medium size medical waste incinerators for a research facility which integrate NOx control using ozone injection.

Please click on the links below download the presentation and paper.

In 2009, the US EPA revised the emission limits for the Hospital, Medical, and Infectious Waste Incinerator (HMIWI) MACT standard. You can follow the link to the blog piece published in May 2013 on the new standard. It dramatically reduced the emission limits for several pollutants including particulate (PM), lead (Pb), and dioxins and furans (D/F). Several existing medical waste incinerators in operation at the time were not capable of meeting the new limits, especially for lead (Pb) and/or dioxin and furans (D/F). Cost effective add-on controls were needed to bring existing system into compliance with the new rules and to allow them to continue to operate.

To meet this new challenge, Envitech designed a carbon bed adsorber and filter package to be installed downstream of existing wet scrubbers. The package is comprised of a new fan to overcome additional system pressure drop. Heat of compression from the fan and a re-heater duct heats the wet gas above the dew point to prevent condensation fouling in downstream filter and/or carbon bed adsorber. The system is delivered pre-assembled on a skid to reduce installation time and cost. A cartridge filter removes low concentrations of condensed Pb particulate. The carbon bed adsorber removes dioxins, furans and mercury (Hg). Envitech has upgraded four medical waste incinerators to meet the new MACT standards. All four are operational and compliant with the new standards.

In one case for Wyoming Medical Center (WMC), space was limited for add-on controls. The system had to be installed outdoors and capable of withstanding below freezing temperatures. The existing system did not meet the new limits for lead (Pb) and dioxins/furnace (D/F).The add-on controls included a cartridge filter and a carbon bed adsorber. The equipment was insulated and heat traced to maintain temperature above the dew point after re-heat. System features include:

•  Shop and skid mounted assembly for ease of installation.
• Insulation and heat tracing for outdoor operation in a cold climate.
• Silicon controlled rectifier (SCR) controller to control the heater duct.
• Compressed air pulse cleaning for automatic particulate removal from the cartridge filters.
• Pre-wired instrumentation to a control box located on the skid.
• Manways to facilitate maintenance access.

The system has been operational since 2014 and has been used on a routine basis during cold winter months.   The system comfortably passed a stack test in 2015. Compliance for lead (Pd) is 20 times below the limit and Dioxins/Furans (D/F) is 5 times below the limit. The re-heat and filter package has been used on several other medical waste incinerators and provide a cost effective solution for meeting stringent emission limits. 

Download a free case study to find out how Wymoming Medical Center met the new EPA HMIWI emission limits for their existing medical waste incinerator.

Download a free white paper from the 2010 Internationa Conference on Thermal Treatment Technologies and Hazardous Waste Combustors (IT3/HWC) on the 2009 HMIWI MACT standard for medicl waste incinerators.

In October 2014, existing medical waste incinerators had to be compliant with the US EPA’s new Hospital, Medical, and Infectious Waste Incinerator (HMIWI) MACT standards. Nearly all of the systems that planned to continue incineratrion had to be upgraded with add-on controls to meet particulate (PM), lead (Pb), mercury (Hg), Cadmium (Cd), dioxins/furans (D/F), or a combination of the pollutants. Pb was the most common of those pollutants requiring additional capture.

Envitech upgraded scrubbers for three existing medical waste incinerators. In October 2015, I presented a paper at the International Conference of Thermal Treatment Technologies and Hazardous Waste Combustors (IT3/HWC) about using a wet electrostatic precipitator (WESP) on the National Institute of Health’s (NIH’s) Rocky Mountain Lab (RML) existing medical waste incinerator. Envitech also designed and built a fourth scrubber system which was permitted as a large (> 500 llb/hr of waste) new medical waste incinerator. The table below compares the previous 1997 standard for lead (Pb) for a large incinerator to the current (2009) standard for an existing incinerator and a new incinerator.

As shown, the current emission limit for an existing incinerator is just 3% of the limit for the 1997 standard. Add-on controls need to achieve 97% reduction in Pb for medical waste incinerators just meeting the previous limit. This is a significant reduction.

Lead (Pb) Emission Limits for Large Incinerators, mg/dscm

• 1997 standard                   1.2
• 2009 standard existing       0.036
• 2009 standard new            0.00069

Pb reduction for a new large medical waste incinerator is even more dramatic. The emission limit is a mere 0.06% of the 1997 standard. Compared to an existing system permitted to the new standard, a large new medical waste incinerator must emit 2 orders of magnitude less Pb.

Envitech’s scrubber for a permitted new medical waste incinerator recently passed the stack test and demonstrated compliance with Pb emission less than 0.00069 mg/dscm. We believe it’s the only systems in operation today that is compliant with the HMIWI MACT standard for a large, new medical waste incinerator.

It is interesting that despite the ultra low emission standards required by the HMIWI MACT standard, there is still significant public resistance to new permitted systems. It’s clear the public doesn’t understand the impact of these rules and how far technology has come to enable environmentally friendly and safe operation of these systems. The role of these captive systems (treating waste from the facility where it is generated) may become more important in emergency response plans of state and local governments. This was evident during the recent Ebola episode where large amounts of waste needed to be treated and disposed. Some would claim that treating the waste at the facility where it is generated poses less public risk than transporting the waste on public roads and highways to a centralized hazardous waste facility. More work needs to be done to educate the public on the capability of these advanced emission control technologies.

For more information on this topic, please read our paper at the IT3 conference.

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.

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 incinerator.  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.