Our planet is getting warmer. At what rate it is occurring or how much human activity has to do with the increasing temperatures is a heated debate. One thing we do know for sure is that Carbon Dioxide (CO2) is a contributing factor in global warming and humans are responsible for a large portion of these emissions. These days, many individuals and businesses alike are trying to reduce their environmental impact and GHG (Green House Gas) emissions. What the average person does not realize is that they have two types of footprints, a primary and secondary. The primary footprint is a measure of our direct emissions of CO2 from the burning of fossil fuels including domestic energy consumption and transportation, e.g. car and plane. The secondary footprint is a measure of indirect CO2 emissions from the whole lifecycle of products we use, those associated with their manufacturing and eventual breakdown. To put it simply: the more we buy, the more emissions will be caused on our behalf.
Thankfully companies like Corus, a subsidiary of Tata Steel, are doing their part to reduce the world’s secondary footprint by improving the energy efficiency of their manufacturing processes. Corus is Europe’s second largest steel producer and comprises three operating divisions: Strip Products, Long Products, and Distribution and Building Systems. Corus Colors as part of the Strip Products Division is an international business manufacturing pre-finished steel for the building envelope, domestic appliances and manufactured goods markets.
Corus Colors Shotton Works, located at Deeside, North Wales, produces organic paint coated prefinished steel principally for cladding, composite walling and roofing applications within the building and construction sector both in the UK and overseas. There are two manufacturing processes at Shotton Works for coating steel strips with paint. They use a series of driven roller coaters and industrial curing ovens, controlled within a continuous process line, that are capable of applying protective and decorative high quality finishes to the galvanized flat steel strip substrate. The No1 Colorcoat Line process is capable of coating strip widths up to 1400mm with a thickness up to 1.6mm, giving a weekly throughput capability of up to 4000 tonnes subject to product type and dimensions.
This manufacturing process requires large amounts of natural gas to ensure proper application and fast curing time in the ovens, which, in turn generates a substantial amount of CO2 and NOX (Nitrous Oxides). In addition to these emissions, the solvent-based coatings release HAPs (Hazardous Air Pollutants) and VOCs (Volatile Organic Compounds) during the drying process that need to be treated by an air pollution control device such as an oxidiser. New oxidiser systems are capable of destroying over 99% of the HAPs and VOCs through the process of high temperature destruction with very little fuel consumption. However older technologies can be a source of CO2 and NOX as well as the requirement for high maintenance and large operating expenditures.
Pollution control initiatives are nothing new to Corus, the company has been monitoring and controlling their oven emissions at the Shotton Works, North Wales facility, since the 1970’s. Their first oxidiser/incinerator was installed on the paint coating processes for abating exhaust gases and solvents. Even then, the company was thinking green by utilizing waste heat from these older oxidisers/incinerators to preheat the ovens and to supply their manufacturing facility with additional process steam. However, as environmental regulations tightened, energy prices increased and new technologies emerged, the company decided to re-evaluate their entire system as part of their manufacturing efficiency improvements as well as the wider Corporate Responsibility Program for energy usage reduction. The objective was to reduce the gas consumption by at least 45% and increase processing speeds on certain products but they quickly realised another benefit to their sustainable energy plans…a much smaller carbon footprint.
Looking for a sustainable energy solution, they turned to Spooner Industries in the United Kingdom who have worked closely with Corus on a number of projects over the past 30 years. Oven technology and safety regulations had changed dramatically since the line was first installed, but Spooner was able to successfully complete several upgrades that brought the system up to current standards and increased its flexibility.
- Each zone was retrofitted with a special low NOX burner to reduce emissions.
- Variable frequency drives or inverters on every oven fan were incorporated into the control system to make each section more efficient and reduce electrical consumption.
- The ductwork was changed to bring hot air into the system quickly, reducing maintenance issues.
- New thermocouples (temperature measurement), pressure transmitters, pressure switches and flow measurement systems were installed in the ovens to bring the equipment up to today’s technology standards, allowing for remote monitoring and fine-tuning.
- A new computer controlled system was integrated with the SCADA (System Control and Data Acquisition) program. The proper PLC (Programmable Logic Controller) allows the central Corus system to communicate with the ovens so they can be set up for different production runs, eliminating errors and decreasing setup time.
The oven alterations brought this production line from the least efficient in the Corus group to the most, meeting one of the two objectives for the company. While some of these improvements reduced the company’s environmental footprint and gas consumption, the increased throughput would further complicate their environmental responsibilities. Two existing, inefficient oxidisers for the Prime and Finish Ovens were being used to control VOC and HAP emissions at the North Wales facility. To achieve proper destruction the systems required large amounts of natural gas which affected operating expenses and contributed to CO2 and NOX emissions. Furthermore, breakdowns and maintenance problems were not only costing the company money to repair but also revenue in lost production. Because the oven and oxidiser are so vital to each other, Corus wanted a solution provider with experience and knowledge on both. In addition, they were looking for a system with low operating costs and heat recovery capabilities that could achieve 99.5% DRE (Destruction Removal Efficiency) which was well above their permit requirements.
Spooner, having recently partnered with Anguil Environmental Systems in The United States to fabricate and install their oxidiser designs on applications throughout Europe, was confident that it could be done. After consulting with the engineers at both Spooner Industries and Anguil Environmental Systems, Corus made the decision to replace their multiple air pollution control systems with one, RTO (Regenerative Thermal Oxidiser) from Spooner Anguil. It would give them the desired efficiency and single-source solution they were looking for. The system has the following features and benefits:
- The oxidiser is a 3-chamber design that processes 83,000 Nm3/hr (55,000 SCFM) of air, achieving 99%+ DRE without visible emissions and 85%+ heat recovery for energy-efficient operation.
- The RTO self-sustains at low solvent-loading conditions, meaning that once the oxidiser is at operating temperature and receiving process airflow it requires no additional fuel for emission destruction, releasing very little CO2 and NOX.
- A secondary heat exchanger sends waste heat directly back to the ovens, reducing the amount of natural gas required for product curing.
- Stainless-steel components throughout the system prevent corrosion and allow for high temperature process streams.
- A hot-gas bypass on the RTO is used during high loading situations to avoid overheating the oxidiser.
- An intelligent bake-out feature cleans the RTO of condensable organics without internal fires or safety concerns.
- The control panel has a large operator screen with a built-in maintenance manual and troubleshooting guide which makes for ease of use.
- Corus has made a significant investment for the new equipment, upgrades and implementation of this energy reduction project. It has dropped their cost, per ton of steel produced, considerably and they estimate the payback will be less than one year.
The reduction in carbon emissions and energy consumption from this facility is dramatic. Their gas usage has dropped by more than 60%, an average reduction of 522 m³/hr (or 5742 kW) per hour – saving over £1million a year. At 181 grams of CO2 produced per KWH used, Corus is preventing 1 tonne of carbon from reaching our atmosphere each hour, nearly 8,000 tonnes per year.
With innovation and continuous improvement at the heart of its business, the company is already planning for similar modifications at other Corus plants. A spokesperson from Corus commented: “We are committed to minimizing the environmental impact of our operations and our products through the adoption of sustainable practices and continuous improvement in environmental performance.”
Tekra Corporation has always had an eye on their energy conservation. They are a custom coater of plastic films in Wisconsin where state regulations require over 98% of the Volatile Organic Compounds (VOCs) emitted from their process be destroyed in an oxidizer system. While considering their first oxidizer system, Tekra’s Engineers did their homework and invested in an early model Regenerative Thermal Oxidizer (RTO). While at the time RTOs were not the cheapest oxidizer option capital-wise, Tekra knew that long-term, an RTO was their best choice for reliable air pollution control, lower operating costs, and a smaller carbon footprint. “We have always tried to be a green company,” said Zachary Gernetz, Project Engineer for Tekra.
In 2003, it was time for Tekra to replace their aging RTO system, and they turned to Anguil Environmental Systems out of Milwaukee, WI. The equipment of choice was again an RTO, although Anguil’s RTO had significant advantages over the previous model including: 95% TER (Thermal Energy Recovery), lower horsepower, lower operating temperatures, and better options for turndown and idle modes.
“Tekra went so far as to have us install a small odometer-style meter right on the front of the control panel for the Anguil RTO, showing exactly how many BTUs they were saving over their previous unit,” says Greg Blando, Service Manager for Anguil.
CERAMIC MEDIA RETROFIT
Tekra’s focus on achieving better energy efficiency did not end there. With a new nationwide focus on green business practices and energy costs on the rise, they again challenged Anguil to perform even better in 2009. Anguil studied the temperature charts of the RTO system and took air samples during peak VOC loading production runs and determined that the 95% TER of the system could be pushed closer to 97% without creating any adverse high-temperature conditions in the RTO. Thermal Efficiency of an RTO relates to the ceramic media inside of this type of oxidizer which captures and then utilizes energy from combustion to pre-heat the incoming, untreated airstream.
“A two percent improvement in TER may not sound all that impressive,” says Mike Scholz, Project Engineer for Anguil. “But most RTOs out there today were designed to achieve about 95% TER. The natural gas required by those systems is directly tied to that five percent of energy lost. Getting back two of the ‘lost five percent’ is actually a 40% reduction in energy lost. In practical terms, that two percent improvement in TER can translate into 40% less on your RTO natural gas bill.” In addition, the enhanced performance at Tekra put their oxidizer into a self-sustaining mode more often, meaning the fuel value in the VOC-laden exhaust gases are enough to operate the RTO and no auxiliary fuel is needed, hence fewer greenhouse gases emitted.
Because of advances in RTO ceramic heat recovery media, Anguil is routinely able to provide RTO operators like Tekra with a performance upgrade by either adding to the top of existing media beds or at times, replacing the top several layers of existing beds with new extruded ceramic media blocks. “With this type of project, payback is king,” comments Lee Kottke, a manufacturer’s rep for Anguil closely involved in the Tekra relationship. “That’s why it is exciting that Anguil can achieve this level of success with only partial media change-outs. That keeps the project cost down and payback periods very reasonable.”
There are other possible effects on project payback to consider. Deeper media beds may require the relocation of chamber instrumentation – like thermocouples. Also, higher efficiency media styles can come with increased back pressure and electrical horsepower cost. Often, however, as in the case of Tekra’s RTO, the electrical penalty is minor compared to the natural gas savings.
Gernetz said that with two coaters running a variety of coating weights and line speeds, it is difficult to get an exact dollar savings. However, prior to the media replacement their RTO often required natural gas to maintain temperature when only treating the exhausts from one coating line. Post retrofit, “the RTO rarely requires natural gas even when only one coater is operating and never when both are on,” says Gernetz. Zach added, “Jobs that were never self-sustaining before are now, so I know that the media retrofit is saving us money.” He estimates a two year payback for this retrofit.
Considering some enhancements to your RTO? Think about this:
- Up until recently, most RTOs were designed with 95% Thermal Energy Recovery (TER%) or less.
- Rule of Thumb for a self-check: If the average RTO outlet temperature is more than 100°F higher than the RTO inlet temperature, your actual TER% is probably less than 95%.
- Even a small increase in TER% can have a dramatic effect on RTO fuel usage. In some cases, a bump in TER% could eliminate RTO fuel use entirely.
- Advances in ceramic media have allowed Anguil to improve TER% in RTOs by only replacing a portion of the existing ceramic media beds, improving payback periods.
- Anguil has performed this retrofit on numerous RTOs, regardless of original manufacturer, and we offer free savings analysis for those interested.
According to Chris Anguil, President of Anguil Environmental Systems, Inc, “When I reflect on the relationship between Anguil and Tekra, it strikes me how RTOs, while such a huge leap forward in energy efficiency over previous oxidizer styles, are continuing to evolve. Advances in media and controls mean there is still room for efficiency improvements on any RTO system out there, regardless of age. Anyone owning an RTO should follow Tekra’s lead and continue to ask if they can do even better energy efficiency-wise. We applaud Tekra’s commitment to environmental compliance and energy efficiency and thank them for challenging us with this opportunity.”
Control of air emissions has become an important issue that flexible packaging converters must consider when changing or upgrading equipment. A producer of printed shrink films, bags and pouches for a diverse range of applications addressed its emissions in 1991 and 1996 by investing in two Anguil catalytic oxidizers to control the EPA-regulated air emissions generated in their various processes.
But when the company decided to purchase a new 10-color gearless press to increase capacity and capability years later, management knew they also needed to determine if an alternate technology would reduce their operational costs compared to their two catalytic oxidizers.
Having supplied the original catalytic oxidizers, the customer contacted Anguil Environmental to analyze the most cost-effective and compliant way to replace the two aged systems. After an analysis, Anguil recommended replacement of the existing equipment with a single 25,000 Regenerative Thermal Oxidizer (RTO).
RTOs Replace Catalytic Oxidizers
Though the catalytic units were a logical choice at the time of purchase, technological advances in the ensuing years had caused the RTO to become a much more viable abatement strategy.
Now 15-20 years following the original catalytic oxidizer installations, the customer and Anguil’s objectives were to:
- Achieve destruction of 98 percent of the Volatile Organic Compounds (VOCs) in the press exhaust
- Fit the system into limited space
- Complete the tear-out and subsequent installation in just six days
The operation of the RTO is considerably different from the existing catalytic units. The oxidizer consists of two reinforced, insulated chambers filled with high temperature structured ceramic energy recovery media. The oxidizer utilizes a burner to maintain the oxidation temperature. Located beside the energy recovery chambers are diverter valves and air duct plenum passages, which allow the press exhaust to be diverted into and out of the oxidizer in either a clockwise or counterclockwise mode. The directional mode is controlled by a PLC, which changes the direction of airflow at regular intervals to optimize system efficiency.
The RTO in Action
In operation, solvent laden air (SLA) enters the oxidizer via an energy recovery chamber where the high temperature ceramic heat transfer media preheats the SLA prior to introduction into the oxidation chamber. As the SLA passes up through the bed, its temperature rapidly increases. After the chemical oxidation purification reaction occurs, the hot, clean, outgoing gas heats the exit energy recovery bed. In order to maintain optimum heat recovery efficiency, the SLA flow direction is switched at regular intervals by the automatic diverter valves on demand from the PLC control system. This periodic flow direction shift provided a high thermal efficiency to minimize customer operational cost.
With sufficient concentration of hydrocarbons in the process air stream, the heat energy content of the VOCs will result in self-sustained operation with no auxiliary fuel usage.
Features that are specific to the RTO include:
- High volumetric turn-down capability, enabling the control of multiple presses and the reduction of operating cost.
- Thermal energy recovery of 95 percent or higher, allowing self-sustaining operation with no auxiliary fuel usage at levels as low VOC exhaust concentrations..
- Customized thermal energy recovery media, providing low-pressure drop and low electrical cost.
Anguil’s vast experience, gained after supplying more than 2,000 successful systems around the world, provided the confidence necessary for this customer to choose Anguil as their continued VOC control supplier for three decades and counting. Anguil was able to modify its standard RTO design to fit into the space provided and to execute tear-out and new installation within a short timeline. The result was a system that exceeded the 98 percent destruction efficiency objective while lowering operating cost by more than 60 percent.
It’s not just about increasing production for Fredman Bag’s president, Tim Fredman Jr., it’s also about being an environmentally conscious neighbor. A converter’s decision to expand their capacity is often made more complicated by a corresponding need to invest in air pollution control equipment. Recent expansions had Fredman Bag making major investments in their air pollution control equipment not only to meet EPA (Environment Protection Agency) regulations but also keep their reputation as a good neighbor.
Fredman Bag, a Milwaukee-based flexible packaging converter purchased a new, eight-color, gearless CI-flexo press from Uteco Converting to adapt to their customer’s growing needs, enhancing their product offering and delivery capabilities. The gearless-press runs at faster speeds with a higher resolution, printing a superior-quality product and increasing production for Fredman Bag by nearly 40%.
The VOCs (Volatile Organic Compounds) and HAPs (Hazardous Air Pollutants) emitted by a printing press are not only harmful to the environment but also people who breathe them. Fredman Bag had been using an Anguil 6,000 SCFM (9,630 Nm3/hr) catalytic oxidizer as an effective means of air pollution control before their expansion but the increase in emissions and flow from the new press was beyond the capacity of the existing 10-year old oxidizer. After serious consideration, Fredman again turned to Anguil Environmental Systems, also a Milwaukee based firm, to address their pollution control needs.
Anguil’s application-specific engineering, stressing air volume reduction, energy-efficiency and improved emissions capture provides an affordable and flexible solution. Taking into consideration future growth, a 12,000 SCFM (19,260 Nm3/hr) Regenerative Thermal Oxidizer (RTO) was selected to ensure regulatory compliance. The Anguil RTO technology provides significant operating cost savings.
The Anguil two-chamber RTO heats exhaust air from the printing presses as it passes through beds of ceramic media located in an energy recovery chamber. The process air moves from the recovery chamber toward the combustion chamber, where the VOCs are oxidized, releasing energy into the second energy recovery chamber. A diverter valve switches the airflow direction so both energy recovery beds alternately store and release energy to minimize operating costs by reducing any auxiliary fuel requirement. This system is designed for heat recovery of over 95% and is self-sustaining, requiring little if any auxiliary fuel even with low VOC loadings. This energy-efficient recovery means the Anguil RTO offers lower operating costs over other emission treatment methods. As a result of Fredman’s decision to use the energy-efficient Anguil oxidizer, the company was eligible for Wisconsin Energy’s, Focus on Energy program. The incentives they received allowed them to go ahead with the project sooner than they had initially hoped.
Lost production was another concern for Tim Fredman, Jr. Air pollution control equipment doesn’t increase a manufacturer’s bottom dollar like other capital equipment does but it can often cost them significantly in downtime. Anguil took careful measures to assure that there were no disruptions in Fredman’s process. By utilizing existing ductwork, preparing accordingly and coordinating with the customer, Anguil was able to install the complete system in under three days. The oxidizer was delivered to Fredman Bag on a Thursday during a scheduled maintenance shutdown, installation was complete by Saturday and start-up was done that same day, saving the converter any lost production.
The Anguil system can be monitored and controlled 24/7 from remote locations for ease of troubleshooting and adjustments, eliminating unnecessary service calls. It has a high volumetric turndown capacity to minimize operating costs during process idle, downtime or on weekends. The Anguil oxidizer has been operating, maintenance free at 99% destruction rate efficiency since start-up. A trouble free air pollution control system allows Tim Fredman Jr. to concentrate on production and sales, knowing his company is in compliance.
Originally published in Tablets & Capsules Magazine
Capturing and destroying harmful emissions from pharmaceutical processes can be challenging. It’s not because the volatile organic compounds (VOCs) are difficult to destroy using catalytic or thermal techniques. It’s because their concentrations can be so high. These process streams raise safety concerns, both when they’re collected in vents and when they reach the final combustion equipment. This article discusses the options.
Catalytic and thermal oxidation are the two best technologies for destroying VOCs in emissions from pharmaceutical and other operations. Both use high-temperature combustion to break down pollutants, leaving only carbon dioxide (CO2), heat, and water vapor. Pharmaceutical operations, however, typically require customized emission control systems to handle the high VOC concentrations that emanate from tablet coating, fluid-bed processing, and tray drying. Often the concentrations reach the explosive range, which means the emissions must be diluted before they’re introduced to an oxidizer to ensure a safe operation that protects employees and property.
Today, most tablet coatings are aqueous, but many pharmaceutical manufacturing operations still use VOCs such as ethanol and isopropyl alcohol (IPA). This includes the manufacture of active pharmaceutical ingredients (APIs) that are dissolved in VOCs and then spray-dried to create an amorphous solid or granules. Most of these processes are batch operations, and that leads to significant and nonlinear VOC concentrations in their exhaust. In fact, the VOC concentration often exceeds the lower explosive limit (LEL) by 100 percent. In the presence of an ignition source and sufficient oxygen, these process exhausts—if not mitigated—will lead to an explosion.
Figure 1 below tracks the emissions and LEL concentration of the exhaust from a fully loaded tray dryer that was measured after heat was applied to drive off the VOCs. Approximately 30 seconds after heat was applied, the IPA concentration peaked at approximately 250 percent of LEL. If this stream was delivered straight to an oxidizer operating at high temperature, there would be an explosion. About 8 minutes after spiking, the VOC concentration decreased to approximately 25 percent of LEL, which is the acceptance limit of most standard equipment that treat VOCs using catalytic or thermal oxidation.
Fluid-bed processors can generate the same peaks, as Figure 2 shows. In this case, the processor’s inlet air temperature is 40°C for 20 minutes and then remains at 45°C until the end of the production run. Following the initial product transfer into the fluid-bed dryer, the exhaust concentration reached an initial peak concentration of approximately 370 percent of LEL. Approximately 6 minutes later, a second VOC spike occurred after the process bowl was scraped. This second spike resulted in a peak concentration of about 200 percent of LEL. These exhaust concentrations, with an ignition source and sufficient oxygen, would result in an explosion.
Vent collection and oxidizer control software
In short, the data tell us that you should expect high VOC concentrations in emissions from coating, fluid-bed, and tray drying operations. There are two common ways to manage the peaks, mitigate the risks, and operate safely. The first is vent control software that recognizes when processes or batches are ready to start. It then “reserves space” for them in the vent collection system. The second method uses software in the oxidizer’s control system to identify how many processes are running. It then allows only one new process to come online to the oxidizer and only during a specific period.
The vent collection software puts you in communication with operators or links to automatic controls at each stage of production, signaling when it’s safe to come online and when to wait. If multiple demands to vent arrive at the same time, the software delays new batches and processing until it learns that exhausts from earlier batches are well beyond peak VOC concentration.
This control method uses the dilution capacity of existing process exhaust points—beyond their peak concentrations—to verify safe status and allow a new batch. If no processes are online to the oxidizer and a batch start is requested, then the software must verify that enough fresh dilution air is available. This software can also verify that sufficient fresh air is available to process several batches in quick succession, maximizing production.
The oxidizer control software works in the system’s PLC-based controls to communicate with operators or equipment to signal when more processes can come online. It could require, for example, a minimum number of processes to be online to the oxidizer for a certain period. That would indicate that the VOC concentrations are beyond the peak and a new source can come online. The software can also verify that a minimum amount of fresh air is sent to a new production source to dilute the exhaust before it reaches the oxidizer.
Even with this software installed, additional safety provisions for emission control would likely be incorporated following a plant-wide process hazard analysis (PHA). They would likely include LEL high-limit switches to prevent a dangerous concentration from entering the oxidizer or abatement device. Ideally, these LEL devices would be self-calibrating to minimize expenses and respond very quickly. A PHA would also show where to install LEL controls in relation to the process-exhaust and oxidizer-isolation dampers. Often, flame or detonation arrestors are placed in each process-exhaust line to mitigate damage to the processes if all other safety measures fail.
Emission control methods
VOC emissions from many pharmaceutical coating and drying processes have historically been controlled with catalytic oxidation. The process is similar to how automotive catalytic converters treat exhaust. Process emissions pass through a catalyst that allows lower oxidation temperature to destroy the VOCs. Because the process emissions—often alcohols and/or acetone—are very catalyst-friendly, catalytic oxidation can remove VOCs at high rates. However, in contrast to automobile exhaust, these industrial emissions are at a low temperature and must be heated to activate the catalyst so it can oxidize the VOCs. Typically, this is done using the oxidizers gas-fired burner, often in conjunction with integral heat recovery to reduce fuel consumption. Recovering this thermal energy—typically at rates of 65 to 70 percent—also reduces the amount of CO2 emitted into the atmosphere because the system is more energy efficient and depends less on auxiliary fuel-fired burners.
The photo below shows an integrated catalytic oxidation system that incorporates the catalyst, integral heat exchanger, gas-fired auxiliary heat system, system fan, and a PLC-based control panel. This equipment controls the emissions from 12 pharmaceutical coating pans and tray dryers, as well as VOCs from an air stripper’s exhaust.
Although catalytic oxidizers have been used successfully in the pharmaceutical industry for many years, other control technologies have gained appeal because they can treat larger exhaust volumes more efficiently. Abatement equipment is also being used to control VOCs from more sources, which increases emission volume and the need to dilute emissions to safe LEL levels. The abatement equipment thus grows in size. In order to reduce costs, companies are opting for fewer but larger abatement devices.
Regenerative thermal oxidation
Like other industries where abatement equipment volumes have increased over time, the pharmaceutical industry is witnessing a shift from catalytic oxidation to regenerative thermal oxidation (RTO). RTO uses high-temperature combustion (with little supplemental fuel) to break down pollutants, converting them into small amounts of CO2, heat, and water vapor. Specifically, the process gas and contaminants are progressively heated as they move through insulated chambers filled with ceramic media. Once oxidized in the combustion chamber, the hot, purified air releases thermal energy as it passes through a second media bed in the outlet flow direction. Valves alternate the airflow direction into the media beds to maximize energy recovery within the oxidizer. The outlet bed is heated and the gas is cooled so that its temperature at the outlet is only slightly higher than it is at the process inlet. This greatly reduces the need for auxiliary fuel, which lowers operating costs.
RTOs can also provide very high VOC oxidation efficiency but do so at higher combustion chamber temperature without the need for catalyst to maintain that temperature. Even at RTO’s higher operating temperatures, auxiliary fuel usage can be lower compared with catalytic oxidation because RTOs energy recovery and thermal efficiency are generally 95 percent but can reach values as high as 97 percent. Thus, auxiliary fuel consumption and the resulting CO2 emissions to atmosphere are lower with an RTO device than they are with a catalytic oxidizer.
Larger air volumes also argue in favor of RTO devices because they are generally built of carbon steel. That reduces their cost compared to catalytic oxidizers, which not only incorporate precious metal catalysts, but are also primarily built of stainless steel. (RTO devices that handle halogenated VOCs are built using higher-cost alloys to resist acidic gases.) While RTO devices are replacing catalytic oxidizers in many cases, the selection depends on the application. One drawback of RTO is that the equipment is much heavier, which reduces installation options.
The photo below shows an RTO system Installed at a pharmaceutical plant. It controls emissions from four tray dryers, 13 fluid-bed dryers, and three coating pans. Much like the catalytic oxidizer shown above, the system incorporates LEL controls to verify a safe operating system. Because it’s located in a cold-weather area, any dilution air that’s added is heated to minimize the chance that water or VOCs will condense within the abatement system.
When processes emit extremely high VOC concentrations and exhaust flows are very large, dilution becomes more difficult, and the abatement system can grow quite large and expensive. In those cases, emissions that are soluble in water, such as alcohols, can be treated using a wet scrubber. The VOCs, however, will likely be transferred to a water stream for disposal, which may be an additional burden on the facility. In addition, the vapor pressure of the alcohols can be relatively high, which means that the wet scrubbers often use “once-through” water. That raises concerns about the volume of water used and how to dispose of it. Even so, this method has been used on occasion to control high concentrations of VOC (alcohol) emissions. In some instances, wet scrubbers are used in conjunction with oxidation equipment such as RTOs.
When designing abatement systems for pharmaceutical processes that involve coaters or dryers, understand the emission types, what the VOC concentrations are, and how they fluctuate during processing. Next, conduct a PHA to identify the design requirements for the abatement system to operate safely and effectively.
Once you have determined the flow and total VOC emission rate from the facility, consider all the technology options for removing the VOCs. Catalytic oxidation remains a viable technology for relatively small exhaust flow rates. RTO offers lower capital and operating costs at process exhaust flows of 5,000 SCFM (8,025 Nm3/hr) or larger. Wet scrubbers also warrant consideration, even though their high consumption of water and the need to dispose of the wastewater make it unattractive in many applications.
Emission control and the operating costs associated with meeting environmental regulations were nothing new for the Coated Products Division of Brady Corp. The company has been manufacturing coated films for nearly 60 years, demonstrating over that time a commitment to pollution prevention and emission reduction programs. But these considerations were magnified when the Milwaukee coating facility chose to implement a new, energy-efficient emission control system. The division maintains 200 different coating formulas on three main continuously operating process lines. Two of the company’s three coaters are operated as so-called “white rooms” to allow the manufacturing of exceptionally clean products. Applying adhesives, topcoats, cast films and other coatings onto a range of substrates requires solvent-based coatings with mixtures of chemicals. Some of the many solvents used in the process are: toluene, MEK, MIBK, heptane, hexane, ethyl acetate, IPA, nitroethane, nMP, cyclohexanone, and 1,3-dioxolane. The dynamic process stream poses many challenges to the company, particularly in that it eliminates the option of solvent recovery.
The capital cost of emission control equipment can be negligible compared to the operating costs if careful consideration is not given to proper equipment selection. With natural gas prices continuing to rise, the company has focused on getting the most efficiency from its incineration equipment. Since the early 1990s, the facility has spent millions of dollars on air pollution control equipment to meet a variety of EPA regulations imposed on coating companies. Including thermal recuperative and regenerative thermal oxidizers (RTOs), as well as concentrator systems, the company has purchased a total of 12 units with a 13th on order for the Milwaukee location alone. The oxidizers have been used to treat everything from coating emissions to low-point floor sweeps located throughout the facility. As natural gas prices started rising in the late 1990s, and with associated costs for emission control equipment steadily increasing, the company looked for ways to reduce their yearly operating and maintenance costs.
The operating and maintenance costs were overwhelming. When one of the old electric RTOs would fail, it generally took over a week to replace the cold face support grid and electric heating elements, and then bring the unit back up to temperature. It occurred so frequently that the maintenance department constructed a special tent so the repairs could be done in the rain or snow. The thermal recuperative oxidizers on site had so many problems with internal heat exchanger failure that a roller system was installed just to move the large duct transition, allowing access to weld the tube sheet without bringing in a crane.
The decision was made to begin replacing the oldest and least efficient oxidizers; the type of systems would be determined by the maintenance team. The first phase of what plant personnel started referring to as its “efficient emission control plan” would replace one of the thermal recuperative oxidizers with a 35,000 SCFM (56,175 Nm3/hr) RTO from Anguil Environmental Systems Inc.
The new system tested out at a destruction efficiency rate of 99.2 percent, and was equipped with a hot-gas bypass that allowed it to process VOCs at rates up to 850 lbs/hour. This high-capacity VOC processing allowed some of the other less efficient oxidizers to shift their load over to the new RTO through a unique common manifold collection system. With the concentration of hydrocarbons in the process air stream, the heat energy content of the VOCs was self-sustained and the oxidation process required no additional fuel for destruction.
RTO technology utilizes ceramic media in two or more beds as a high-efficiency heat exchanger. Process gas with VOC contaminants enters the RTO through an inlet manifold. A flow diverter valve diverts the gas into an energy recovery chamber, which preheats the process stream. The process gas and contaminants are progressively heated by the ceramic bed as they move toward the combustion chamber.
The VOCs are then oxidized, releasing energy that is transferred to the second ceramic bed, thereby reducing any auxiliary fuel requirement. Heat is transferred from the gas to the ceramic bed so that the outlet gas temperature is only slightly higher than the inlet temperature. A flow diverter valve switches, alternating the ceramic beds so each is in inlet and outlet modes over time. If the process gas contains sufficient VOCs, the energy released from their combustion promotes self-sustained operations. For example, at 95-percent thermal energy recovery, the outlet temperature may be only 77°F higher than the inlet process gas temperature.
The maintenance team investigated several types of RTO systems, including a new rotary valve system. The rotary valves seemed to be a viable option, but they were a close-tolerance proprietary item that could only come from the specific vendor. The rotary valve location underneath the RTO also presented major maintenance concerns. The company went with Anguil’s poppet valve design, believing the maintenance levels were more satisfactory.
The company also was pleased that the RTO manufacturer was willing to share its complete computer operating program, something other vendors were not willing to do. Some of the other items on the system included:
- A stairway for access to platforms rather than the usual vertical ladders – a feature especially appreciated in Wisconsin winters
- Replaceable valve seats on the poppet valves and large access doors.
- Heavier gauge access doors with fewer bolts to be removed.
- Block-off plates after the system fan as required for confined space entry.
The second stage of the plan would prove to be a little more challenging, but even more effective in reducing the company’s operating costs. The EPA’s requirement of a permanent total enclosure, or PTE, required coaters to create a negative pressure in all areas of the facility that process any volume of solvents. Due to the layout of the coaters, this became a large volume of exhaust air with very low VOC levels.
Two of the old electric RTOs were treating this high-volume, low-concentration stream from pump rooms, wash-up areas, compounding areas and floor sweeps located throughout the facility. Large volumes of natural gas were consumed to burn a very small amount of pollutants. In addition, the unit could not be turned off during plant shutdowns because of time-consuming reheat procedure, which could take up to four days.
After evaluating the solvent vapors and various concentrations, an Anguil Model 350 (35,000 SCFM, 56,175 Nm3/hr) rotor concentrator and Model 50 (5,000 SCFM, 8,025 Nm3/hr) RTO were selected to handle this portion of the process. By absorbing and concentrating the VOCs they were able to achieve a 10-to-one concentration ratio, requiring an oxidizer only a tenth the size to handle the concentrated process stream. The energy contained in the concentrated stream entering the RTO proved sufficient to allow self-sustaining operation, requiring little to no auxiliary fuel.
The third but not final stage of the company’s plan is still in motion. They have placed an order for another 35,000 SCFM (56,175 Nm3/hr) RTO to replace the last thermal recuperative system on site. When this system has been installed, heat from the RTO will be used to preheat the facility’s ovens, further reducing energy consumption. The system will have enough capacity to eliminate the final thermal recuperative unit and another aging electric RTO.
In addition to replacing old oxidation technologies at the facility, careful consideration has been given to all the oxidizers as a single system. The company has implemented a dual collection and distribution manifold that allows operators to divert process streams from one oxidizer to another for maintenance or equipment shutdowns.
The impact of these efforts has exceeded expectations for reliability and efficiency. Gas usage on the company’s three coating lines have continued to drop at a steady rate. At a time when gas prices continue to trend high, coupled with increases in production, the reduction in energy consumption drops straight to the bottom line.
The company is continuing to investigate energy reduction strategies, and is currently investigating the option of placing secondary heat exchangers on all of its oxidizers. The process would return waste heat to preheat the air streams on all of its other coating lines.