Air Pollution Control Innovations

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.

PROBLEM:

A Midwestern ceramic tile manufacturer needed an acid gas scrubber to treat the off gas from 3 kilns being installed at a new manufacturing plant. Each kiln was equal in size and emits HF, HCl, and SO₂. The scrubber needed to remove > 98.5% of acid gases. The scope of supply included an ID Fan, interconnect duct, stack, control system, and pump skid. The facility was faced with the additional challenge of less than 22 ft of overhead space inside the building. A tight schedule required receipt of equipment in 16 weeks, including engineering. The customer operated other scrubbers at different facilities and reported difficulty in controlling the spray quenchers to cool and saturate the gas.

SOLUTION:

The customer selected an Envitech quencher/packed bed scrubber to meet their requirements. To eliminate difficulty in controlling gas cooling the scrubber used a proprietary, low pressure drop Venturi quencher. This provided a means to saturate the gas over a wide range of operating conditions and flow rates. The scrubber used a proprietary internal duct design with an outlet and entrainment separator at the bottom of the scrubber. This allowed the scrubber to fit in the low overhead space with no roof penetrations to minimize installation cost and time. Other equipment features included:

•  Quencher design to capture > 90% of particulate > 3 microns.
• Skid mounted dual pumps (1 opr/1 spare) with pre-piped and valved instruments.
• Hydro-testing of piping assemblies.
• Instruments pre-wired to a junction box.
• Control System Factory Acceptance Test (FAT).
• High efficiency, low pressure drop packing with high void spaces to prevent material accumulation and fouling.

 RESULTS:

The customer placed the order in June, 2015. The equipment shipped on time in October 2015 and arrived on site one week early, 15 weeks from order placement. The system will be operational in early 2016. Stack testing will confirm compliance with the performance guarantee summarized in the table below.

 To download a Free Case Study, please click on the icon below.

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.

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 incinerator 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 500^oF to 600^oF.  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 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.

To read more about the use of Envitech's scrubbers in difficult refinery applications, please download the white paper below on the topic of meeting ultra-low SO₂ emissions.