Volume 95 Issue 14 | pp. 34-35
Issue Date: April 3, 2017

New hazardous waste incinerator comes online

Clean Harbors unit is first built in the U.S. in two decades
Department: Science & Technology
Keywords: safety, Safety, Business, Environment, Pollution, hazardous waste, incineration

At the end of 2016, for the first time in two decades, a new commercial hazardous waste incinerator built in the U.S. came on-line. The $120 million incinerator, operated by Clean Harbors in El Dorado, Ark., can handle industrial and laboratory chemicals, manufacturing by-products, medical waste, and other solid and liquid materials.

“As all chemists know, you can’t destroy or create matter,” says Scot Shoemaker, the company’s vice president for engineering and operations. “But you can change its form into something less toxic, and that’s something that incinerators do very effectively.”

After the U.S. passed the Resource Conservation & Recovery Act—the primary law governing disposal of hazardous waste—in 1976, commercial waste handlers spent 20 years building hazardous waste incinerators to the point of overcapacity. Demand is only now catching up to capacity, leading to the need for a new incinerator, says Shoemaker, who has a bachelor’s degree in chemistry and a master’s in chemical engineering. The U.S. market for hazardous waste management is expected to reach $13.6 billion in 2020, according to a 2016 report by the market research firm Freedonia Group.

Clean Harbors already had two incinerators at its El Dorado site, and the additional unit will increase the site’s capacity from roughly 73,000 metric tons to approximately 140,000 metric tons of material annually. The company has no plans to take any of its other incinerators off-line, Shoemaker says. The Arkansas Economic Development Commission and the El Dorado-Union County Chamber of Commerce supported the expansion.

Besides being the first U.S. hazardous waste incinerator built in the 21st century, the new facility is also the only one required to meet current air emissions standards under the Clean Air Act; older incinerators are grandfathered in under less stringent limits. “It meets air pollution control requirements that I thought were not really achievable,” says David Case, executive director of the Environmental Technology Council, a trade association of commercial environmental firms involved in waste management. For example, the new incinerator may not release more than 8.1 µg mercury/m3 dry gas from its stack, compared to 130 µg for older incinerators. The new incinerator also must limit emissions of nitrogen oxides to 40 tons/year; restrictions on older incinerators vary by state.

 

 

Emissions standards

Clean Harbors’ new incinerator must meet more stringent requirements than older units.

UNITS EXISTING INCINERATOR AS OF 2008 INCINERATOR NEWLY BUILT OR RECONSTRUCTED AFTER 2008
Dioxins and furans ng of toxic equivalents/m3 dry gas 0.40 0.11
Carbon monoxide ppm dry volume 100 100
Total hydrocarbons ppm dry volume 10 10
Hydrochloric acid and chlorine ppm dry volume 32 21
Semivolatile metals (cadmium, lead) μg/m3 dry gas 230 10
Low-volatility metals (arsenic, beryllium, chromium) μg/m3 dry gas 92 23
Mercury μg/m3 dry gas 130 8.1
Particulate matter grains/m3 dry gas 0.459 0.053

Source: 40 CFR Parts 9, 63, 260, 264, 265, 266, 270, and 271, “National Emission Standards for Hazardous Air Pollutants: Final Standards for Hazardous Air Pollutants for Hazardous Waste Combustors (Phase I Final Replace- ment Standards and Phase II),” Federal Register, 2005

 

 

To meet those standards, “we used proven, reliable technologies that have been used for a number of years,” Shoemaker says. “We looked at alternatives, but to meet those very stringent emissions limits, we decided that we needed to run with what we knew.” The key instead was in how Clean Harbors designed and configured the various components of the system. In addition to controlling emissions, Clean Harbors also wanted to engineer the incinerator to stay running more than 90% of the time.

The first step to meeting both goals happens before any waste enters the incinerator. Clean Harbors staff carefully manage incoming waste to ensure that they know exactly what they’re dealing with. Customers document what is in the waste, but Clean Harbors follows up with its own analysis to ensure the documentation is accurate—whether the waste arrives “in a pail or a tanker truck,” Shoemaker says. Tests include pH measurements, various forms of chromatography for halogens and organic compounds, spectrometry for metals, and bomb calorimetry for determining heat of combustion.

“If we can’t safely handle something, then we’ll reject it and send it back to the customer,” Shoemaker says. “It doesn’t happen very often. Most customers are very responsible with their waste streams.”

Once the contents of the waste are verified, the waste is stored until the incinerator can accept it. The incinerator can accept waste in multiple forms, including bulk solid, shredded material, and liquid. Computer programs analyze the inventory of stored waste to determine what combinations to feed into the incinerator and when. “The programs take into account things like the physical characteristics and the energy, halogen, or metal content of the waste, and create a mix such that we can run our incinerator in a steady-state fashion and meet emissions compliance,” Shoemaker says.

When waste enters the incineration unit, it is burned at about 1,000 °C in a rotary kiln followed by a secondary chamber to ensure the material is completely combusted. Ash and noncombustible solids get removed and gases and airborne particulates pass through various cleanup steps: spray drying to remove particulate matter, salts, and some metals; wet scrubbing to remove sulfur dioxide, acids, and halogenated species; activated carbon treatment for dioxins, furans, and mercury; and catalytic reduction of nitrogen oxides.

Clean Harbors used fluid dynamics modeling and other approaches to design the process and determine how to configure specific components, Shoemaker says. In some cases, the company turned to special materials to get the desired performance. For example, the company used specialized stainless steel alloys to resist corrosion in the baghouse where trace acidic material collects after the wet scrubbing steps. All material that doesn’t waft out of the stack gets sent to contained landfills.

“When customers send us their waste, they expect us to ensure that we are safely and compliantly managing the stream through complete destruction and proper disposal,” Shoemaker says, noting that the U.S. now has clearer skies and cleaner water than it has in the past. “Incineration is needed technology and is a key component of proper waste management and disposal today.” 

 

 

Incinerate

But that’s just the first part—a modern incinerator mostly involves equipment to control emissions.

 
 

1 - Rotary kiln and secondary combustion chamber.
Harbors first feeds material into the rotary kiln (horizontal, foreground), where the waste is incinerated at about 1,000 °C. Depending on the material, it might be dropped in as a bulk solid, shredded, or dispersed into droplets. After incineration in the kiln, ash and noncombustible solids are removed. Gases and airborne particulates feed into the secondary combustion chamber (vertical, background), which completes gas-phase combustion.

 

 

2 - Spray dryer.
After the secondary combustion chamber (left), the hot stream moves into the spray dryer (right). The gas stream rapidly cools to about 200 °C as it is sprayed through a nozzle. The quick cooling minimizes formation of dioxins and furans. Particulate matter, salts, and some metals condense out.

 

 

3 - First baghouse and wet scrubbers.
The first baghouse (left, behind truck) collects material de- posited from the spray dryer. Then the gas stream passes into two wet scrubber treatments: satura- tion and condensation (vertical columns on right). The saturator sprays water into the gas stream to reduce the temperature to about 80 °C and cap- ture sulfur dioxide, hydrochloric acid, hydrofluoric acid, and halogenated species. The condenser takes the remaining stream through another spray of water along with a neutralization agent such as sodium hydroxide to remove any remaining acidic species.

 

 

4 - Second baghouse.
The second baghouse incorporates filters for final removal of particulate matter and metals. Activated carbon adsorbs dioxins, furans, and mercury. Lime removes residual sulfur trioxide mist.

 

 

5 - DeNOx and stack.
None of the previous steps removes nitrogen oxides. Ammonia and a vanadium pentoxide catalyst in the DeNOx unit (rectangular structure in back) reduce these species to nitrogen gas and water. Finally, the processed gas is released to the atmosphere through the stack.

 

Incinerate

But that’s just the first part—a modern incinerator mostly involves equipment to control emissions.

 
 

1 - Rotary kiln and secondary combustion chamber.
Harbors first feeds material into the rotary kiln (horizontal, foreground), where the waste is incinerated at about 1,000 °C. Depending on the material, it might be dropped in as a bulk solid, shredded, or dispersed into droplets. After incineration in the kiln, ash and noncombustible solids are removed. Gases and airborne particulates feed into the secondary combustion chamber (vertical, background), which completes gas-phase combustion.

 

 

2 - Spray dryer.
After the secondary combustion chamber (left), the hot stream moves into the spray dryer (right). The gas stream rapidly cools to about 200 °C as it is sprayed through a nozzle. The quick cooling minimizes formation of dioxins and furans. Particulate matter, salts, and some metals condense out.

 

 

3 - First baghouse and wet scrubbers.
The first baghouse (left, behind truck) collects material de- posited from the spray dryer. Then the gas stream passes into two wet scrubber treatments: satura- tion and condensation (vertical columns on right). The saturator sprays water into the gas stream to reduce the temperature to about 80 °C and cap- ture sulfur dioxide, hydrochloric acid, hydrofluoric acid, and halogenated species. The condenser takes the remaining stream through another spray of water along with a neutralization agent such as sodium hydroxide to remove any remaining acidic species.

 

 

4 - Second baghouse.
The second baghouse incorporates filters for final removal of particulate matter and metals. Activated carbon adsorbs dioxins, furans, and mercury. Lime removes residual sulfur trioxide mist.

 

 

5 - DeNOx and stack.
None of the previous steps removes nitrogen oxides. Ammonia and a vanadium pentoxide catalyst in the DeNOx unit (rectangular structure in back) reduce these species to nitrogen gas and water. Finally, the processed gas is released to the atmosphere through the stack.

 
Credit: Clean Harbors (All)
 

 
 
Chemical & Engineering News
ISSN 0009-2347
Copyright © American Chemical Society
Comments
Dennis Shilling (Fri Jun 23 11:35:21 EDT 2017)
A far greater improvement compared to the old incinerators of the 70's and 80's, I say Kudos to Cleanharbors for this improved version for haz waste disposal.
John Chan (Wed Oct 04 21:07:18 EDT 2017)
Are Clean Harbor hazardous waste incinerators regulated and permitted by EPA regulations set forth in Chapter 40 of the Code of Federal Regulations (CFR), Part 264, and are supplemented by the EPA technical and permit guidance?
JB (Sat Oct 21 20:55:32 EDT 2017)
Is it possible to make these incinerators to zero-emissions standard?

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