Air Pollution Control Innovations

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.

A 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.

Envitech has joined the paperless revolution by launching Interactive O&M manuals on electronic tablets (Apple iPads). Traditional paper based-manuals present several problems – they may be easily lost or damaged; large three-ring binders that are difficult to search and cumbersome to carry; and lastly, red-lined changes and as-builts often are not captured in the final revision.

Starting with 2015 projects, Envitech created web-based O&M manuals for its customers. Due to the positive feedback received to date, Envitech decided to phase out paper copies and fully implement interactive O&M manuals through the use of customized electronic tablets. Each tablet is equipped with 16GB of memory, Wi-Fi capabilities, video and audio calling, personalized e-mail account, video recording, camera, and text messaging. Our customers can access their online manuals and its features with the click of a button. Specific advantages of the Envitech interactive O&M manual are:

1. Portability - Tablets are thin, light and you can store more information than in 3-ring binders. Information is secure and readily accessible while you are out in the field. 
2. Updates - Online manuals allows us to make updates with ease. You have immediate access to the material rather than waiting for the manual to be re-printed and delivered. 
3. Troubleshooting - Our tablets allow you to contact our service team via text, e-mail or facetime.    

Portability

•  Compact tablet design eliminates the need for large storage capacity - 16GB of memory can store up to 4,096 photos, 3 hours of video, or +10,000 PDF files.
• Always available - Access your online manual 24-7 when and where you need it through the use of a tablet, phone or computer.
• Print select documents - Airprint is an Apple technology that allows you to print documents from your tablet.  
• Improved file management - Search and find files more efficiently.

 Figure 1. Click to navigate: simply click or swipe to access your files.

Always Up To Date

•  O&M Manual Updates - Red-lined changes and updates via online eliminates the need to re-print +500 page manuals.
• Offline capabilities - Access your manual without Wi-Fi connectivity.
• Revision management - Track changes made to your manual with online revision tables. 

Figure 2. Revision table

Interactive Troubleshooting

• Contact us - Each project has a unique username that allows you to reach our service team via text, e-mail, and facetime from your tablet.         
• Photo and video capturing - Send us photos/videos from your tablet to assess the situation.    
• Instruction videos - Access training videos and learn how to maintain/calibrate your equipment.   

Figure 3: Texting Support	Figure 4: Email Support	Figure 5: Facetime Support

To learn more about Envitech's service capabilities, please download our brochure.

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.

Compliance testing often brings anxiety to environmental managers.  Testing is expensive and can comprise a significant fraction of the environmental operating budget.  Planning takes several months, often culminating in a tight testing window with long days and unforeseen delays.  And always looming is a dreaded phone call of a failed test.  What three things should environmental managers do to ensure a successful compliance test?

1. Calibrate your control instruments

Manufacturers use complex instruments to ensure that their equipment meets its performance objectives.  These instruments must remain calibrated for the control equipment to perform properly. pH sensors, ORP probes, flow transmitters and conductivity sensors ensure optimal acid gas removal.  RTDs and thermocouples are vital to reliable operation for thermal oxidizers, condensers and reheaters.  Pressure transmitters provide important information for the performance of Venturis, and the condition of baghouse, carbon beds and packed beds.

The most common deficiency reported in our service call database is an out-of-calibration instrument.  Make sure that your instruments calibration is up to date, and check its performance a month prior to compliance testing to ensure you have the time to order a replacement instrument if required.

2. Inspect and clean your equipment

Environmental control equipment typically faces an array of upset conditions.  Waste streams change or cycle through daily, weekly or seasonal disruptions.  Auxiliary equipment fails leading to changes in the quality of makeup water, instrument air, or power.  Repeated startups and shutdowns lead to transient states of substandard performance.  The struggle to keep environmental compliance equipment operational at all times leads to an "emergency-only" attitude towards preventive maintenance.  All of these factors lead to degradation of equipment and instruments.

Ahead of compliance testing, it is important to challenge the operations staff to inspect and clean the equipment.  Ensure instruments do not have buildup that dampens response time.  Confirm pressure drops across filters, strainers, spray nozzles are at design conditions; high pressures may be indicative of fouling.  Make sure consumables such as pH probes and filter bags are new and up to date.  Check for air ingress; most compliance tests measure the oxygen content of the gas to ensure that emissions are not artificially lowered by dilution air.  Clean sumps, separators and nozzles during regular shutdowns.  Ensure that your emissions are limited to that which occurs during steady state operation, and not from old emissions that have built up on the internal surfaces of your equipment.

3. Interview your stack tester

The EPA has well-developed procedures for every type of emission test.  However, with ever lowering standards, stack testers are forced to push their instruments and apparatuses to their technological limit in order to accurately measure emissions.  Stack testers have found ways to extend these limits, but the difference between emissions and noise is narrowing.  Minimizing the noise, and understanding the methodology of the stack test, will ensure you and your equipment are well-prepared.

For all stack tests, ask the following:

• What EPA procedures will you be using?
• Are there any known interferences for the procedures?
• What is the experience level of the stack test operators with each procedure?
• Are you prepared for lower than expected gas flow rates, greater than expected dilution, or other flue gas variances?

For initial testing:

• What is your expectation of the non-detectable limit with the procedure provided?
• Is the expected non-detectable limit sufficiently low to provide accuracy below my emission limit?
• How do you intend to reliably rig and stabilize your instruments?
• What can I do to give the stack testers the best opportunity to provide reliable data?

If your permit has changed since your last stack compliance test:

• Have you accounted for my new permit requirements, and how has that changed your testing protocol?

Getting ready to perform a stack compliance test?  Contact Envitech Service for a site visit to calibrate your instruments and inspect your equipment.

Envitech recently launched a new Service Program to provide scrubber operators with a knowledgeable and responsive resource to keep their air pollution control equipment functioning properly.  One of the service program options is true 24-7 remote plant coverage that connects operators directly with our service staff.  To be able to offer this service as a small business requires both dedication from our service team and implementation of the latest service technology.  In this post, we discuss the technologies we rely upon to offer this service. 

FaceTime

In the last year, Envitech has stepped up its use of FaceTime to remotely communicate with service technicians.  For those unfamiliar with the technology, FaceTime is an Apple application that connects users by video through their mobile phone.  Below are screen shots of a FaceTime connection using WiFi.

Envitech has found that the quality of this technology has improved such that engineers can remotely direct technicians through troubleshooting, calibration, or simple repairs.

For scrubber operators equipped with an Apple product, FaceTime provides an immediate and direct method to connect to our service technicians.  FaceTime's realtime video technology lets Envitech technicians see the issue, direct the repair, and confirm a successful outcome, all without the cost and downtime of a site visit.

GoToAssist

Envitech has invested heavily in PLC and HMI training for its engineers.  All of our engineers are capable of minor modifications of PLC logic, online changes to HMI screens, and trending data through PLC software.  Until recently, this level of assistance was not available remotely.  Older peer to peer technologies were not sufficiently reliable to allow logic interface.  HMI screens were typically built remotely and uploaded onsite by a qualified operator.  Trending was often not available "live" and had to be downloaded and transmitted by a trained software specialist.

Envitech purchased GoToAssist in 2014 to connect our engineers to our startup teams.  GoToAssist is a Citrix product that connects the user to a remote computer by invitation.  Upon acceptance of a connection, the remote engineer can manipulate the local computer.  Below is a photo of the GoToAssist software from the engineer's perspective.

Envitech has found the software to be tremendously useful, reducing our startup team sizes, shaving days off the startup schedule, and increasing the accessibility of our variety of engineering talent.  Customers have caught on, seeing how quickly and effectively we can make programming changes remotely to improve their process, and have requested this as an add-on service.  To date, we have logged over 125 support session with customers totaling more than 400 hours of remote troubleshooting using GoToAssist.

Some of the tasks our customers have enjoyed using remote troubleshooting via GoToAssist include:

• Rescaling ranges within the logic for replacement instruments
• Trending process and control variables to tune control loops
• Revising HMI screens live with operator feedback
• Downloading operational data for analysis
• Adjusting stoking frequencies for incinerators and cleaning frequencies for WESPs

Web-Based O&M Manual

Historically, the use of O&M manuals has been the first option for maintenance and troubleshooting for the operator.  In the past ten years, component manufacturers with standard products have begun to offer their manuals via web access.  Our engineers and service technicians made use of this offering by frequently downloading a specific manual online for troubleshooting an equipment issue.

Still, most system integrators or custom manufacturers like Envitech have only delivered "binder" manuals or large PDF electronic files.  The problem with this approach is that the "binder" manuals are not very portable or sortable and often get lost or damaged.  Large PDF electronic files are often electronically misplaced and forgotten.  The result is that operators are scraping ID tags for model numbers or replacing equipment without a thought to troubleshooting or repair.

Seeing the ease of use online manuals from component manufacturers has provided, Envitech challenged itself to produce an online manual for its custom manufacturered equipment.  Starting with projects ordered in 2015, Envitech has produced an online manual for its customers.  The feedback to date has been positive, and we intend to extend this benefit to all customers via our service plan.

If you are interested in learning more about our Service Program and other features and benefits of using Envitech for your scrubber maintenance, press the buttom below.

Envitech is proud to launch a new scrubber service and maintenance program for all users of air pollution control equipment.  Envitech offers the program to provide plant managers, environmental departments, plant engineering and operations and maintenance staffs access to our trained, experienced group of engineers and technicians.  Our goal is to improve your uptime, reduce your operating costs, ensure you meet compliance and offer you an on-demand technical resource for troubleshooting your equipment.  Additionally, we want to help you organize your maintenance programs and provide training to keep your operators up to date.

Over the past year we have strengthened our service department with technicians, tools, and training. In so doing, we have provided new and varied service to our existing customers.  For example we have:

• Tuned a medical waste incinerator remotely to minimize CO emissions and to reduce fuel usage
• Calibrated pH and conductivity probes prior to a successful stack test
• Rescaled a replacement transmitter after the existing model was discontinued
• Added HMI screens to permit trending of critical instruments
• Upgraded VFD, PLC and HMI software to improve security of Ethernet controlled equipment
• Precoated new cartridge filters and used Visolite to detect for filter breaches

As part of the program we offer the following services:

• Regular visits for onsite training and inspection
• O&M manual conversion to web-based access
• Instrument (pH, conductivity) calibration training including how-to videos
• Control loop tuning, logic modification and HMI screen changes
• Remote servicing using Apple's FaceTime and Citrix GoToAssist
• Secure website with access to all your site specific services
• Accurate recordkeeping of services performed on your equipment

Our service program is built for the following equipment:

• Quenchers
• Packed Bed Absorbers (Scrubbers)
• Condensers
• Venturi Scrubbers
• Collision Scrubbers
• Entrainment Separators
• Wet Electrostatic Precipitators
• Fans
• Cartridge Filters
• Carbon Beds

Additionally, we maintain key relationships with other pollution control suppliers to help you service equipment such as:

• Regenerative Thermal Oxidizers (RTO)
• Medical Waste Incinerators
• Hazardous Waste Incinerators
• Afterburners
• Thermal Oxidizers
• Baghouses
• Dryers
• Cooling Towers
• Oxidations Systems
• Wastewater Treatment

If you are interested call or email Envitech today.

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.

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.