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Waste Heat Generates Steam and Savings

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The Challenge

A coil coating facility purchased a new 15,000 SCFM (24,075 Nm3/hr) Regenerative Thermal Oxidizer (RTO), which had a nominal heat transfer efficiency rate of 90% thermal energy recovery. It was designed with supplemental fuel injection (SFI), which is used during low VOC loading conditions to help save fuel cost. The facility was looking for additional ways to decrease their exhaust air temperature and reduce operating costs. 

The Solution

The high exhaust temperature (above 650°F) and large airflow (12,650 SCFM, 20,303 Nm3/hr) in the oxidizer exhaust stack provided the customer an opportunity to add energy recovery measures to further optimize their process and decrease their operating expenses. Because their process required a significant amount of steam, it would likely provide the quickest payback for an energy recovery project.

The Result

Anguil Environmental installed an air-to-steam waste heat recovery boiler to recover exhaust waste heat from the natural gas fired thermal oxidizer and produce 25 psig of steam. The boilers use X-ID tubing for enhanced heat transfer through the helical ribs on the inside of the tubes.  

The waste heat boiler package is a skid-mounted unit, with forced circulation, fire tube, and heat recovery steam generator. The unit has automatic, modulating, exhaust gas bypass that is controlled by steam pressure. A boiler feedwater and blowdown separator was included as part of the package.   

Installing the waste heat boiler system recovered about 2.58 MM BTU/hr of energy, lowering the  stack temperature to 338°F. The addition of the waste heat boiler on this application saved the facility $216,770 per year. The total payback period for this project was less than six (6) months. 


Oxidizer Energy Recovery Options

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The Challenge

The mainstream media today is full of allusions to energy awareness and conservation. Just as visible these days are media references to astronomical dollar figures that can boggle the mind. This article does not seek to break out of that mold, but rather to conform to it, as Oxidizer Stack Heat Recovery offers a tremendous opportunity for both energy conservation and energy cost reduction.

The Solution

Consider the following: at any hour of the day there are likely to be more than 10,000 oxidizer systems in service, using a high temperature reaction chamber (with or without catalyst) to treat the exhaust gases from a wide range of industrial processes. The final component of nearly all of these oxidizer systems is an exhaust stack, where the treated exhaust gases are released to the atmosphere at elevated temperatures.

Historically, oxidizer systems have been sized to treat exhaust air flows from 100 SCFM (Standard Cubic Feet per Minute) (160.5 Nm3/hr) up to several hundred thousand SCFM. But conservatively, the average oxidizer system airflow processing capability (i.e. “size”) can be estimated to be between 15,000 and 20,000 SCFM (24,075-32,100 Nm3/hr).

Now, considering these 10,000 stacks emitting hot, treated gases to the atmosphere around the clock; if heat recovery equipment capable of dropping the exhaust stack temperature by 100 ˚F could be installed into each one of them, this would lead to an overall value of over 18 billion BTUs (British Thermal Unit) per hour of energy conservation!

Assuming $10/MM BTU and year round operation – this equates to recovering over $1.5 billion (US Dollars) worth of energy per year!

Taking this into account, it is no surprise that a wide range of stack energy recovery options have been developed and marketed to end-users of oxidizer systems. This article will discuss three important aspects of energy reclamation from hot oxidizer stacks:

  • Energy reclamation from oxidizer stacks is one of three potential areas of optimization for oxidizer systems.
  • There are distinct challenges that must be addressed in the process of evaluating potential energy savings options.
  • There are multiple potential equipment options for this application, each with its own benefits and limitations.

The Result

The ABC’s of Oxidizer Stack Energy Recovery

Oxidizer Energy Recovery Options

Using ABC’s in the title of this section is actually a misnomer. Truthfully, the letters A and B should be set aside and the caption should read – The CDE’s of Oxidizer Stack Energy Recovery. The reason for this is twofold:

First of all, any plan for recovering waste heat in the exhaust stack of an oxidizer system is already a Plan C. For anyone taking a hard look at optimizing the energy efficiency of an oxidizer system as a whole, Plan A should consider ‘upstream’ opportunities. For example, retrofits that reduce overall airflow to the oxidizer system and/or increase the concentration of solvents to be treated. Plan B should focus on the internal TER (Thermal Energy Recovery) of the oxidizer system itself. After airflow reduction, maximizing the internal energy recovery of an oxidizer system will almost always lead to the best project payback.

Hence, it follows that energy recovery in the exhaust stack of the oxidizer is Plan C. Now calling it Plan C is by no means meant to downplay the opportunities associated with oxidizer stack energy recovery. The only intent is to fit the concept into the greater framework of energy usage in the oxidizer system as a whole. There are many reasons why Plan A and/or Plan B as defined above may not be attractive or even feasible, making Plan C: Energy Recovery in the Oxidizer Exhaust Stack, the best overall choice for energy conservation efforts.

The second reason that the letters C, D and E are a better fit for the title of this section is that those three letters represent the challenges associated with energy recovery efforts in oxidizer exhaust stacks, namely:

  • CAPTURING the energy from the stack itself
  • DELIVERING the energy back into the plant cost-effectively
  • EMPLOYING the recovered energy effectively inside the plant

Following is a brief discussion of each of these challenges along with the different options for recovering oxidizer stack heat.

Challenge #1: Capturing the Energy

Of the three challenges, the first – Capturing the Energy – is usually the easiest to evaluate and estimate. By simply knowing the airflow and temperature of the exhaust gases in the oxidizer stack, suppliers of energy recovery equipment can quickly begin to model an appropriate device for reclaiming energy effectively. It is often during this first challenge that the overall opportunity for yearly savings is also quantified.

The more information that an oxidizer end-user can provide at this juncture, the more realistic the opportunity analysis can be. At a minimum, those considering stack energy recovery should gather the following before beginning this process:

  • Expected airflow and average temperature in the oxidizer stack
  • Expected hours of operation per year
  • Current energy rates for the plant (gas or oil and electric)

The first two items are often monitored already on a continuous basis in oxidizer data recorders. If that is not the case for a particular system, the most recent EPA (Environmental Protection Agency) stack testing data can be an excellent source for this information.

Two other issues for consideration during this phase of an evaluation are:

Constituents in the exhaust gases (and especially their dew points): Any effort to reclaim energy in the exhaust stack of an oxidizer will lower the oxidizer exhaust gas temperature, bringing with it the potential for condensation of acids. Suppliers of energy recovery equipment will typically take care to ensure that final stack temperature is above any acid dew points. Given the typical solvent laden exhaust from printing presses, this is rarely an issue of concern for oxidizer systems in the flexographic printing industry.

Adding energy recovery equipment to an oxidizer exhaust stack will also come with a system back-pressure penalty. The existing oxidizer fan will usually be tasked with pushing or pulling air through the ‘hot side’ of the added heat recovery component. To keep overall project payback attractive, the goal is usually to choose energy recovery equipment that will limit the added system back-pressure to an amount that the existing oxidizer system fan can handle without major modification. Therefore, knowing the additional capacity available in the oxidizer system fan will help narrow down which cost-effective options for energy recovery are feasible.

Challenge #1 for a typical application may look like this:

Consider a flexographic printer with a ten year old 20,000 SCFM (32,100 Nm3/hr) Regenerative Thermal Oxidizer (RTO). The combined exhaust from all dryers and capture hoods routed to the RTO is 20,000 SCFM (32,100 Nm3/hr) at approximately 150˚F (65.5˚C). The average exhaust temperature from the RTO is 275˚F (135˚C).

Plan C – A 50% effective heat exchanger installed in the oxidizer exhaust stack to transfer the waste heat to air or fluid would drop the stack temperature by approximately 125˚F (51.7˚C) – capturing approximately 2.7 MM BTU/hr. If this energy was 100% useful inside the plant and the plant operated around the clock, this could lead to a yearly savings of up to $225,000.00. A payback of one to two years is certainly possible for a project of this nature.

By comparison:

Plan A – reducing airflow to the RTO by 10% could save approximately 0.3 MM BTU/hr or up to $25,200.00/year. This could likely be accomplished with very little capital investment at all. A payback of less than six months is possible for this option.

Plan B – for the data presented, this RTO is operating with an internal thermal energy recovery (TER) of approximately 92%. Installing additional ceramic heat recovery media to raise the TER to 95% could save approximately 1.0 MM BTU/hr or up to $84,000.00/year. A payback of less than one year is possible for this option.

Challenge #2:  Delivering the Energy Back into the Plant Facility Cost Effectively

As seen in Challenge #1, sizing energy recovery equipment and estimating the overall savings opportunity with oxidizer stack energy recovery are not difficult tasks. To take an opportunity analysis and turn it into an actual payback period however, one has to determine the cost of installing the equipment and providing the infrastructure for delivering captured energy back to the plant.

For a cursory analysis, some will take the cost of the energy recovery equipment and double it, calling that the estimated cost of installation. (i.e. Total Estimated Cost = One Part Equipment Cost + Two Parts Installation Cost) This can provide for a quick check of whether a particular idea merits additional investigation. To obtain true payback numbers then a site visit by different tradespeople to estimate the overall cost of energy recovery system installation will be necessary. Fans and/or pumps, control valves, thermocouples, etc. will all need to be both mechanically installed and electrically wired to an existing or new control system. This is often the challenge where the overall project feasibility hangs in the balance.

Challenge #3:  Employing the Recovered Energy Effectively inside the Plant Facility

The final challenge is also extremely important for optimizing energy recovery project payback. Ideally, the oxidizer end-user should look for ways in which recovered stack energy can be used in the same process that the oxidizer is connected to. This typically provides the best payback because there are energy demands by that process at nearly all times that oxidizer waste heat is available. In contrast, projects focused on recovering oxidizer exhaust stack energy to help heat a facility, for example, may only be useful for part of the year.

Oxidizer Stack Energy Recovery Options

Oxidizer stack heat has been recovered to perform a wide variety of functions in the plant environment.

Air-to-air heat exchangers have been used to provide pre-warmed fresh air back to process ovens, dryers and/or plant make up air units.

Air-to-fluid heat exchangers have been used to transfer oxidizer stack heat to boiler feed water, plant makeup water, process water, glycol and other thermal fluid loops.

In extreme cases, waste heat boilers have been used with oxidizer stack heat to create steam.

And on the horizon, heat-to-power systems are in development for reclaiming oxidizer stack heat and creating electricity.

One additional option that has been used sparingly is taking hot oxidizer stack air directly back for use in production processes. This is sometimes referred to as Direct Heat Recovery, while the options mentioned above would be termed Indirect Heat Recovery. Direct Heat Recovery from oxidizer stacks is generally shied away from due to the risks of introducing products of incomplete combustion back into a plant environment or the risk of oxidizer “oven dirt” contaminating product, but there are limited cases where this form of oxidizer stack energy recovery has been used effectively.

Each of these options for recovering heat from oxidizer exhaust stacks can be considered within the framework of the three challenges discussed previously.

Air-to-Air Heat Recovery

Probably the most common energy recovery product applied to oxidizer stacks is an air-to-air heat exchanger. Be it a shell-and-tube or plate type heat exchanger, there is a cold side air stream (typically fresh air) and a hot side air stream (typically the oxidizer exhaust) that are used for heat transfer.

Air-to-air heat exchangers have been integral to oxidizers themselves for decades so it is a well-known technology for oxidizer manufacturers to incorporate into an overall system. The programs for sizing air-to-air heat exchangers are quick and easy to use. There are a wide variety of footprints and physical layouts for ease of installation. There are also many low back pressure models that work well with existing oxidizer system fans.

The limiting factor for air-to-air heat recovery in oxidizer exhaust stacks is Challenge #2: Delivering the Energy Back into the Plant Facility Cost Effectively. With air-to-air heat recovery, insulated ductwork is required to transport captured heat back into the facility. Costs for running ductwork in a plant vary widely and can also add up very quickly. The best applications are those with short duct runs for returning heated air.

Air-to-Fluid Heat Recovery

Air-to-fluid heat exchangers are the second most common energy recovery product for oxidizer stacks. As the name implies, heat is transferred from the hot oxidizer exhaust air (again the hot side air stream) to a circulating fluid (the cold side stream). This is typically accomplished by passing the hot air over a coil containing the fluid to be heated. As with air-to-air heat recovery there are a variety of low back pressure designs that can allow installation into an oxidizer exhaust stack without adversely affecting the oxidizer system.

Because piping is less expensive than ducting, air-to-fluid heat recovery has a definite advantage over air-to-air heat recovery when considering Challenge #2: Delivering the Energy Back into the Plant Facility Cost Effectively. However, unless the heated fluid is used directly back in the process that the oxidizer is connected to, Challenge #3: Employing the Recovered Energy Effectively inside the Plant Facility, can be more difficult to address with air-to-fluid heat recovery. Meeting this challenge requires a detailed analysis of the demands for energy in the fluid system versus the availability of waste heat in the oxidizer stack. For example, in some plants the biggest hot water demands come in shutdown situations when the oxidizer is not running.

Air-to-Steam Heat Recovery (Waste Heat Recovery Boilers)

When the solvent laden air sent to an oxidizer system is sufficiently rich, the oxidizer’s internal heat recovery component may need to be partially bypassed or forgone completely. This leads to higher than normal oxidizer stack temperatures and allows for additional options in heat recovery equipment. One such option is a waste heat recovery boiler to recover oxidizer exhaust stack heat and produce steam. Waste heat recovery boilers are custom sized for a particular exhaust gas capacity as well as required steam pressure. A variety of systems are available in vertical, horizontal, single or multi pass configurations. Oxidizers on most applications rarely have the necessary solvent loading and corresponding exhaust stack temperatures to sustain this option.


Sometimes referred to as cogeneration, heat-to-power is an emerging technology that is capable of sending kilowatts directly back into a facility for electrical power. The concept has been implemented on different applications throughout the world but is only now being integrated with combustion devices such as oxidizers. Heat-to-power systems can currently generate up to 100kw per hour from a modest heat source. However, the payback is normally greater than three years, the value most companies use for acceptable capital investment. As electricity costs increase and greater efficiencies are achieved with the technology it will be a very attractive option in the near future. Today, heat-to-power is not necessarily a cost reduction strategy but rather a green initiative that could be used to promote a company as a leader in energy conservation.

Oxidizer stacks represent a significant opportunity for the reclamation of energy. This applies to all oxidizer systems – including both the aging catalytic oxidizers popular in the industry years ago as well as the newer, high efficiency regenerative thermal oxidizers (RTOs) being supplied today. Achieving a cost-effective installation of energy recovery equipment with an attractive payback is not without challenges, but those challenges are being met today in a variety of ways.

Air-to-Water Heat Exchanger Reduces Operating Costs by $120,000 per year

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The Challenge

This pharmaceutical company had a 5,000 SCFM (8,025 Nm3/hr) oxidizer that they were looking to relocate to another facility across the United States. The destruction rate efficiency and heat recovery expectation at the new location differed from the original design conditions at the current facility.

The Solution

An Anguil field service engineer went to site to inspect the unit. A report detailing the current condition of the oxidizer at its current location was generated as well as a written procedure for the proper dis-assembly and reassembly of the equipment. The service engineer evaluated the unit and made recommendations outlining the modifications necessary to make the unit run at the new facility’s desired destruction efficiency rate and the energy requirements.

The Result

Anguil worked closely with the customer to modify and upgrade the system based on the detailed site inspection report. The work included a control package upgrade and a new hot gas bypass damper. 

To address the energy recovery requirements at the new facility, a new economizer was installed between the oxidizer and exhaust stack to transfer heat to water. The exhaust heat from the stack was transferred to the Anguil economizer which in turn created hot water. This otherwise lost energy is captured and can be used in various applications such as boiler feedwater, cold makeup water, process water, glycol, and thermal fluids.

The stainless steel system is a tube and fin style heat exchanger with access doors for inspecting and cleaning of the tubes. The exhaust flow from the catalytic oxidizer is 5,400 SCFM (8,667 Nm3/hr) and the temperature is 450°F (232°C). Roughly 160 GPM of water is heated to 140°F (60°C) with the economizer. The total energy recovered is 1.43 MM BTU/hr or an estimated total savings of $120,512 per year. 

A Competitive Advantage

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Semiconductor FabricationAt Anguil, we are experts in environmental efficiency through the design and manufacturing of air pollution, water treatment, and energy recovery systems. Our customers know they can trust our team to develop and deliver quality solutions to their unique environmental challenges. In one case, a large semiconductor chip fabricator wanted to reduce their environmental impact, maintain their productivity, and save on operational costs.

Project Highlights:
  • Client needed an abatement system with  over 100,000 SCFM (160,500 Nm3/hr) volume processing capacity and over 98% VOC removal efficiency
  • Anguil compiled a system of a rotor concentrator wheel, custom-designed thermal oxidizer with a destruction efficiency rate (DRE) of >99.5%, and a specialized heat exchanger
  • Each system was able to meet and exceed the processing capacity and destruction efficiency requested, with the processing capacity double that of the two previous systems combined

The Challenge

As a large semiconductor chip fabricator, this customer realized the environmental effects of their operation. The fabrication of semiconductor chips generates significant amounts of wastewater and waste gases, both of which require treatment prior to their release into the sewer system or atmosphere, respectively. As fabrication operations have grown, so too has the amount of waste produced and, consequently, the need for abatement technology.

The customer approached our team with a request for a new abatement system for their plants. They came to us to stay ahead of their competition by tackling the challenge of reducing their environmental impact without sacrificing their facilities’ productivity and output. While they were currently employing the use of two systems, each with capacities for less than 50,000 SCFM (80,250 Nm3/hr), they were looking for a more efficient and effective solution. Ultimately, they were seeking a system that doubled their SCFM volume processing capacity with a 98% VOC removal level.

Their exact system requirements were as follows:

  • >100,000 SCFM (160,500 Nm3/hr) volume processing capacity in a single system with the same footprint as the two existing pollution control devices
  • >98% VOC removal efficiency
  • No upstream pressure fluctuations

The Solution

SemiconductorAfter reviewing the customer’s requirements and discussing the project objectives with the customer, our team decided that rotor concentrator thermal oxidizers (RCTO) would be the ideal air pollution control solution. The solution that was designed and constructed featured a zeolite rotor concentrator wheel sized to handle more than 100,000 SCFM (160,500 Nm3/hr) of process air and a custom-designed thermal recuperative oxidizer (TO) with a destruction efficiency rate (DRE) of >99.5% and specialized heat exchanger constructed to minimize silica build-up and facilitate maintenance operations.

Once fully assembled, all three systems were installed on mezzanine levels of the existing plants. After installation, our technicians completed final commissioning and provided comprehensive operator training. Ultimately, the customer was left with a system that met their needs and a team trained to properly use that equipment.

The Result

At the end of the project, the customer was fully satisfied with the performance of all three systems. Each system was able to meet and exceed the processing capacity and destruction efficiency requested, with the processing capacity double that of the two previous systems combined and the destruction efficiency surpassing that of the one required.

Additionally, by replacing their old air pollution systems with our more effective and efficient system, the customer was able to save on floor space and operational costs.


Wind Turbine Manufacturer Implements Clean Air Initiative

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The Challenge

When you think about generating electricity from wind, clean energy comes to mind. However, the wind turbine production process can be a major source of air pollution without the proper controls in place. Manufacturing and painting the blades, towers, and nacelles requires composite construction material and solvent-based coatings. The potential to emit Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) such as xylene, ethyl benzene, styrene, and phenol into the atmosphere is a major concern for communities and regulatory agencies.

The Solution

One of the world’s largest turbine manufacturers is doing their part to keep wind power a truly clean source of energy. With the expansion of several new production lines, the company enlisted help from Anguil Environmental Systems to ensure proper air pollution control from their component painting processes in The United States.

The Result

Approximately 40,000 SCFM (64,200 Nm3/hr) of solvent-laden air is diverted from multiple paint booths to an Anguil Regenerative Thermal Oxidizer (RTO), which destroys over 99% of the air pollutants. Similar to the RTO shown here, this system incorporates pre-filters to stop overspray from plugging the oxidizer ceramic media. Designed for 95% thermal efficiency, the Anguil RTO can self-sustain at low concentration levels, which reduces the need for auxiliary fuel.

Demand for renewable energy is on the rise, and experts predict that 70 to 80 new wind turbine blade factories could come online throughout the world in the next decade. With multiple systems on applications such as this, Anguil’s experience makes them the preferred vendor for emission control systems in the wind turbine market.

Styrene Emissions: Catalytic Oxidizer with Concentrator

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The Challenge

The world’s largest button manufacturer needed a pollution control system that would destroy styrene emissions and odors from a variety of plant processes. The plant was proactively seeking a cost-effective air pollution control solution to preempt future regulatory action. The main concern of the customer was the high operating cost of an emission control system.

The Solution

After thorough evaluation of several possible technology solutions, the company selected an Anguil abatement device to treat their styrene emissions. Anguil recommended a uniquely efficient solution in an  Emissions Concentrator coupled with a Catalytic Oxidizer.  A key factor in this decision was the emission concentrator’s ability to lower the volume of air that needed treatment by achieving a 10 to 1 flow rate reduction. Anguil provided the customer with a static pilot test to prove the effectiveness of the concentrator rotor on styrene. The successful results from the static test ensured the customer’s confidence in the new application of the concentrator technology to control styrene emissions.

Three main considerations guided the design of this solution: the need for an emission control system with low operating costs, the control of the high volume, low volatile organic compound (VOC) concentration of the process air stream, and the unique characteristics of styrene.

Many of the processes that emit styrene, such as boat building and FRP production, have high air flows with low VOC and styrene concentrations. Button manufacturing presents a similar problem but on a slightly smaller scale. The plant’s airflows were approximately 15,000 SCFM (24,075 Nm3/hr) with styrene concentrations ranging from 50-200 ppmv. The customer considered a Regenerative Thermal Oxidizer (RTO) and a bio-filtration system as other possible solutions. While effective in destroying styrene, both of these would have been very expensive solutions because higher air flows result in higher costs for treatment technologies. The operating costs of the RTO and the biofilter were much higher than the chosen solution because these systems had to treat the entire 15,000 SCFM (24,075 Nm3/hr) of process air.

The Result

An emissions concentrator coupled with a catalytic oxidizer reduced the process air that needed to be treated by a factor of 10. The high volume airstream, approximately 15,000 SCFM (24,075 Nm3/hr) with 50-200 ppmv of VOC, is passed through the emissions concentrator rotor where the VOCs and styrene are adsorbed in the bed, purifying the high volume air. This high volume air is then exhausted to atmosphere. The concentrator rotor rotates continuously, transporting adsorbed VOCs into a desorption section where they are desorbed from the media with a low volume heated airstream. After being desorbed from the wheel, the air volume has been reduced from 15,000 SCFM (24,075 Nm3/hr) to about 1,500 SCFM (2,407.5 Nm3/hr) and the VOC concentration of the air stream is increased to about 500- 2000 ppmv. This low volume, high pollutant-laden air is then processed by the oxidizer. By isolating and treating the lower air volume, Anguil is able to provide a system with far lower operating costs than other emission control systems.

Anguil was able to further reduce the operating cost of the system by utilizing a catalytic oxidizer to destroy the concentrated, contaminated air stream. Anguil’s experience with styrene emissions has demonstrated the easily oxidizable nature of styrene in the presence of catalyst. Catalytic oxidation systems typically achieve greater than 99% destruction of styrene with relatively low temperature requirements. An Anguil Catalytic Recuperative Oxidizer designed for 1,500 SCFM (2,407.5 Nm3/hr) was installed to process the pollutant-laden airstream with minimal auxiliary fuel consumption.

The final design consideration was to address the unique characteristics of the styrene emissions. The customer was concerned with the possibility of styrene polymerization on the rotor and subsequent system failure. Anguil had performed extensive tests to establish that certain zeolite formulations function better than others in the presence of styrene and eliminate the possibility of polymerization. However, Anguil went to the next step in order to relieve the customer’s concerns. Working closely with one of their technology partners, Anguil ran several static (live) pilot tests to prove the effectiveness and reliability of the concentrator/oxidizer technology. This testing process convinced the customer to move ahead with the Anguil solution.

Another benefit to the customer of the concentrator/oxidizer system was low maintenance cost. The zeolite material has an expected life of 10 years under continuous operation. The easy regeneration and durability of zeolite provides considerable savings over the constant maintenance and replacement required of carbon beds. Additional maintenance savings come from the durable design of the emissions concentrator. The absorbent wheel is rotated with a simple motor and belt drive, reliable components that last at least five years and require minimal maintenance.

In order to expedite installation, Anguil assembled the entire system in its manufacturing facility, allowing for customer review and inspection prior to shipment. The system was then re-erected in the field and integrated into the customer’s process. Anguil’s combination of proven experience and technologically advanced air pollution control products have led to another satisfied customer.

Fiberglass Polymer Emissions: RTO Control Technology

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The Challenge

A producer and supplier of corrosion resistant piping systems was looking to improve the reliability and lower operating expenses of an existing air pollution control system at their facility. During their manufacturing process, centrifugally cast mortar pipe systems are reinforced with a fiberglass polymer. This makes the pipe ideally suited for most corrosive piping applications but also produces a significant amount of styrene emissions that need to be destroyed. Plant personnel knew that their existing 40,000 SCFM (64,200 Nm3/hr) fixed-bed concentrator and catalytic oxidizer could not handle future expansion plans and the decision was made to look for a replacement.

The Solution

After speaking with several vendors, the Regenerative Thermal Oxidizer (RTO) was selected as the best available control technology. It not only far exceeded the 95% destruction efficiency required in their permit but also dramatically reduced operating costs. The pipe manufacturer then identified what qualifications they were looking for in a solution provider:

  • Styrene Experience
  • Proven Performance
  • Stable Supplier
  • Cost-Effective Equipment
  • Turnkey Capabilities

Anguil was selected based on their ability to meet these equipment and supplier requirements.

The Result

Anguil’s engineering staff worked closely with the customer throughout the design and manufacturing processes to ensure that the system precisely met their requirements and expectations. An Anguil Model 500 RTO (50,000 SCFM, 80,250 Nm3/hr) was selected based on the process airflow concentrations, destruction rate requirements, and for its overall energy-efficient operation.

Special considerations were taken to deal with the particulate in the process stream. A 48-cartridge collector was put upstream of the oxidizer to collect fiberglass pieces that could clog the RTO. Once filtered, process gases with Volatile Organic Compound (VOC) contaminants enter the oxidizer through an inlet manifold. Dual disk poppet valves direct this gas into energy recovery chambers where the process gas is preheated, then progressively heated in the ceramic beds as they move toward the combustion chamber.

The VOCs are oxidized in the combustion chamber, releasing thermal energy in the structured ceramic media beds that are in the outlet flow direction from the combustion chamber. These outlet beds are heated and the gas is cooled so that the outlet gas temperature is only slightly higher than the process inlet temperature. Fasting acting, vertical poppet valves alternate the airflow direction into the ceramic beds to maximize energy recovery within the oxidizer. The VOC oxidation and high energy recovery within the oxidizer reduces the auxiliary fuel demands and operating costs. For example, at 95% thermal energy recovery, the outlet temperature may be only 70`F (40`C) higher than the inlet process gas temperature with an RTO. The oxidizer can reach self-sustaining operation with no auxiliary fuel usage at low concentrations.

Allen Bradley Programmable Logic Controllers (PLCs) control the automatic operation of the oxidizer from startup to shutdown, so minimal operator interface is required. These controls also provide for remote telemetry to enable the system’s operation to be viewed and altered via a modem connection to reduce maintenance costs.

The customer is achieving 98% destruction rate efficiency and the oxidizer is operating extremely efficiently at 95% thermal rate efficiency. Low operating costs and equipment reliability have resulted in another satisfied Anguil customer.

Carbon Fiber: Oven Emission Control Strategies

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The Challenge

Carbon fiber machineryCarbon fiber (fibre) and composites are materials that are revolutionizing the products we use everyday by making them stronger, lighter, and more durable. However, the manufacturing process can have serious environmental ramifications and immediate danger to human health if careful consideration is not given to emission control at the production phase of these materials.

A carbon fiber company in the People’s Republic of China was faced with this challenge while designing a new facility and process line for their specialty fiber products. Company officials knew they would need a pollution control device that not only met the local regulations but also protected their employees and heavily populated neighborhood. The new line would include a furnace and oven with the potential to discharge significant levels of Carbon Monoxide (CO), Ammonia (NH3) and lethal amounts of Hydrogen Cyanide (HCN).

The Solution

There are two primary pollution control technologies applied downstream of the ovens and furnaces at carbon fiber processing plants. The industry has historically used dual stage, Direct-Fired Thermal Oxidizers (DFTOs) for emission control on the furnaces and Regenerative Thermal Oxidizers (RTOs) for oven exhaust treatment. Both technologies are capable of destruction removal efficiencies (DRE) over 99%, but the RTO has the advantage of very low operating costs.  

When searching for an air pollution control partner, the carbon fiber processor looked for a vendor that not only had the necessary experience but also a local presence. Each producer’s fiber differs from those of its competitors, and the processing details that give each brand its signature characteristics should be considered when selecting the emission control device. The Anguil Asia teams located in both Taiwan and China demonstrated their understanding of the capture, control, and compliance hurdles that the processing plants face. Prior to equipment selection, Anguil ran an energy analysis at the facility which helped in selecting the proper technology based on destruction requirements, efficiency needs, and process parameters. 

Anguil recommended a model 25,000 SCFM (40,125 Nm3/hr) RTO with several features that improved reliability, performance, and efficiency. 

  • The proprietary design has oversized valves, a fan, and a stack to handle the elevated temperatures coming from the process and to allow for future expansion. 
  • On most applications, airflow is generally pushed through an RTO, but this application was designed for an induced draft configuration. This ensures that all of the hydrogen cyanide emissions would be drawn into the oxidizer for destruction, protecting the company’s employees and neighborhood from a potentially lethal situation. 
  • A Supplemental Fuel Injection (SFI) system was included on the RTO for increased fuel efficiency and ultra low NOx emissions. 
  • The poppet valve design on the RTO operates without process interference at the oven.

The Result

Once fabricated, the Anguil RTO was installed and running in less than four weeks. It is currently achieving greater than 98% destruction removal efficiency with over 95% thermal heat recovery. The system is extremely efficient, self-sustaining at low emission loading, and requires very little supplemental fuel for destruction.

Anguil’s involvement didn’t stop at the oxidizer; they saw this emission control project as an opportunity to reduce operating costs for their customer. Ovens on a carbon fiber process can require a significant amount of natural gas to maintain temperatures from 392°F to 572°F (200°C to 300°C). A secondary heat exchanger made of 304 stainless steel was installed after the oxidizer to preheat the oxidation oven. The plate-type heat exchanger recovers 75% of the RTO exhaust, using that preheated air in lieu of ambient air for the oven. Initial estimates indicated a one year payback on the added capital equipment cost, but it actually took only 5 months.

The project resulted in an overall reduction of emissions and operating expenses for the carbon fiber company, and they are currently considering future green initiatives with Anguil.

Carbon Fiber: Furnace & Oven Emission Control

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The Challenge

A carbon fiber company in China was faced with the challenge of selecting an emission control system for a new pilot line at their specialty fiber products facility. The line would include furnaces and three ovens, both of which would emit Carbon Monoxide (CO), Ammonia (NH3), and lethal amounts of Hydrogen Cyanide (HCN).  

The Solution

The carbon fiber processor selected Anguil Asia because of their local presence in the region and specific design for this application. Before beginning the project, the Anguil team in Asia ran an energy analysis at the facility, which ensured that the proper technology would be applied based on the destruction requirements, efficiency needs and process parameters. A Direct Fired Thermal Oxidizer (DFTO) was selected to process the furnace exhausts while a Regenerative Thermal Oxidizer (RTO) was chosen to process the oven exhausts.

The Result

To treat the higher concentration exhaust stream coming from the carbon fiber furnaces, Anguil designed a specialized multi-zone DFTO whereby the nitrogen compounds are disassociated at high temperatures in an oxygen depleted chamber. The remaining gases are quenched before moving into a secondary zone where total emission destruction efficiency is over 99% with minimal NOX generation.

The furnace exhausts typically contain tar which often causes plugging in a standard emission control device. Special design considerations were taken to reduce these maintenance concerns and improve reliability. The Anguil system introduces furnace exhaust into the DFTO with a unique inlet manifold that eliminates tar build up and plugging concerns. Anguil also provided an induced draft system for increased safety. This ensures that all of the Hydrogen Cyanide emissions would be drawn into the oxidizer for destruction, protecting the company’s employees and neighborhood from the potentially lethal gas leaking out of flanges, instruments, etc.   

Because the customer’s three oxidation ovens were electrically heated, reducing the electrical consumption was a critical objective on this project. As part of the complete energy analysis done at this facility, Anguil understood that the oxidation ovens can require a significant amount of supplemental energy to maintain temperatures from 392°F to 572°F (200°C to 300°C). The customer wanted to recover as much energy as possible from the oxidizer systems to save on the electrical power used in the ovens.  Keeping this in mind Anguil proposed several secondary heat exchangers to provide the necessary preheated makeup air back to the electrically heated ovens.   

The DFTO would be exhausting at 1600°F (870°C) so Anguil incorporated three shell and tube heat recovery bundles in series, following the oxidizer. The first two stainless steel heat exchangers would be providing preheated makeup air back to Oven #2 and Oven #3. The process exhaust downstream of that system still contained usable heat, so a third shell and tube heat exchanger was incorporated to preheat the combustion air used in the DFTO. Preheating the DFTO combustion air made the destruction device itself more energy efficient and reduced the amount of supplemental natural gas required. 

A summary of this energy recovery project is listed below:

  • The shell and tube heat exchangers recover approximately 1.0 MMBTU/h (293 kW/h) to be returned as preheated air back to Oven #2 and Oven #3
  • The estimated payback on the heat exchangers is less than 3 months
  • The shell and tube heat exchanger to preheat combustion air to the DFTO will recover approximately 0.18 MMBTU/h (53 kW/h)
  • The estimated payback on the combustion air heat exchanger is less than 7 months (based on a natural gas cost of $10.00/MMBTU and assuming 24 hour/day operation)

To treat the higher flow, lower concentration exhaust from the ovens, Anguil selected an RTO. This type of oxidizer is capable of 98-99%+ destruction efficiency with very low operating costs compared to other emission abatement technologies. With achievable thermal efficiency over 96% the RTO is capable of operating with little to no supplemental fuel use.

During operation the emission laden process gas enters the RTO through an inlet manifold to flow control poppet valves that direct this gas into energy recovery chambers to be preheated. The process gas and contaminants are progressively heated in the ceramic media beds as they move toward the combustion chamber.

Once oxidized in the combustion chamber, the hot purified air releases thermal energy as it passes through the media bed in the outlet flow direction. The outlet bed is heated and the gas is cooled so that the stack temperature is only slightly higher than the process inlet temperature. Poppet valves alternate the airflow direction into the media beds to maximize energy recovery within the oxidizer.

In keeping with the overall goal of the oxidation system to provide all of the required preheated makeup air back to the ovens, Anguil installed a secondary heat exchanger following the RTO.  The plate-type heat exchanger recovers 70+% of the RTO exhaust energy.  That preheated air is used in lieu of ambient air for the oven.   

  • The plate heat exchanger will recover approximately 0.42 MMBTU/h (123 kw/h)
  • The estimated payback on the heat recovery system is less than 3 months

The project resulted in an overall reduction of emissions and operating expenses for the carbon fiber company. Even on this small pilot line operation, Anguil was able to show a substantial reduction in the overall energy requirement. Due to the success of this project, Anguil will be installing air pollution control equipment on the customer’s full scale production line. The new system will also be energy efficient, keeping with Anguil’s goal of providing air pollution control equipment today to keep our customers profitable tomorrow.

RTO Handles High VOC Loading at Silgan Containers

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The Challenge

Regeneration Game – Originally printed in The Canmaker Magazine – Sayers Publishing Group

As the first generation of oxidizer systems in the industry nears the end of their service life, many canmaking plants face repair or replacement of their existing air pollution control systems. Like many others in the industry, a Silgan canmaking plant in the Midwest had been using a thermal recuperative oxidizer with direct heat recovery for control of emissions from its sheet coating lines. After more than a decade of service, the oxidizer was reaching a point that repairs would be needed in order to continue to meet strict compliance limits so Silgan began looking for an effective, efficient solution.

The Solution

Historically, thermal recuperative oxidizers with direct heat recovery have been a popular choice in canmaking facilities – especially those with oven zones operating above 350 deg F (177 deg C).

In the past, thermal recuperative oxidizers had a capital cost advantage over regenerative thermal oxidizers (RTOs) and boasted much more flexible Volatile Organic Compounds (VOC) loading limitations. Their one drawback has always been in supplemental fuel usage. Thermal recuperative oxidizers top out at 70 percent internal heat recovery, whereas RTOs are able to achieve more than 95 percent.

For canmakers, this drawback was minimized with the use of additional heat recovery. Hot, purified air from the oxidizer is routed directly back to the oven zones and not lost to the atmosphere. This has reduced the operating cost ‘penalty’ of the thermal recuperative oxidizer and – in the past – has swung the balance toward specifying that system for VOC loads above ten percent Lower Explosive Limit (LEL) almost exclusively.

So exclusively that, when hearing that Anguil Environmental Systems had recommended an RTO for its Midwest coating facility, Silgan responded almost incredulously: “They recommended what? This is clearly not an RTO application.”

Given the technologies offered when Silgan made its initial selection of a thermal recuperative oxidizer, this was an understandable response. It also served as an ideal framework to study what has changed in oxidizer design over the past decade to reverse such a drastic initial response:

  • Thermal recuperative oxidizers no longer have capital cost advantage
  • With hot gas bypass and feed forward technology, RTOs are now specified in situations up to 25 percent LEL
  • With fuel costs being unstable and still on the rise, every heat recovery percentage points counts
  • New requirements for VOC capture plus destruction have marginalized direct heat recovery and increased the operating cost gap between thermal recups and RTOs.

Silgan’s existing thermal recuperative oxidizer was designed based on volume of airflow, organic vapor concentrations and desired destruction efficiency. During operation, VOC-laden air is drawn into the system fan and is discharged into a heat exchanger. The air is preheated through the tube side of the heat exchanger and then passes the burner, where the contaminated air is raised to the thermal oxidation temperature (1,200-1,800 deg F / 650-1,000 deg C). When the VOC-laden air is raised to the thermal oxidation temperature for the specified residence time (0.5-2.0 seconds), an exothermic reaction takes place. The VOCs in the air stream are converted to carbon dioxide and water vapor. The hot, purified air then passes on the shell side of the heat exchanger where the energy released by the reaction is used to preheat the incoming solvent laden air reducing the system’s fuel consumption. Finally, the contaminant-free air is exhausted into the atmosphere.

A weakness in all thermal recuperative oxidizer designs is that the steel in the heat exchanger is exposed to high burner chamber temperatures (typically up to 1600 deg F / 871 deg C). The system at Silgan had a history of requiring ongoing maintenance in this area, which had been driving up cost and impacting throughput. The engineering team at Silgan needed to fix the aging system, replace it with an equivalent, or look for alternative equipment.

After evaluating several options, the RTO selection was based on the capital cost advantage and operating cost savings. It would be a custom-built abatement system designed specifically for this application with high loadings and concentrations. Anguil would design, manufacture and install a 40,000 SCFM (64,200 Nm3/hr) RTO with heat recovery, hot gas bypass and oven purge system. 

The Result

Silgan’s new RTO operates as follows:
The solvent laden process gas enters the oxidizer through an inlet manifold. Flow control, poppet valves direct this gas into one of two energy recovery chambers where the process gas is preheated. The process gas and contaminants are progressively heated in the inlet ceramic bed as they move toward the combustion chamber.

The VOCs are oxidized in the combustion chamber, releasing thermal energy in the ceramic bed that is in the outlet flow direction from the combustion chamber. The outlet ceramic bed is heated and the gas is cooled so that the outlet gas temperature is only slightly higher than the process inlet temperature. Flow control, poppet valves routinely alternate the airflow direction into the ceramic beds to maximize energy recovery within the oxidizer.  The VOC oxidation and high energy recovery within these oxidizers reduces the auxiliary fuel requirement and saves operating cost.  For example, at 95 percent thermal energy recovery, the outlet temperature may be only 70 deg F (40 deg F) higher than the inlet process gas temperature with an RTO. The oxidizer can reach self-sustaining operation with no auxiliary fuel usage at typical operating concentrations.  The process emissions at the Silgan facility as well as the temperature of the oven zones presented some challenges, as well as opportunities. 

With process LEL levels as high as 14 percent there was a concern over high temperature in the RTO. A hot side bypass valve was provided to allow excess RTO reaction chamber heat to be vented directly into the exhaust or the back to the oven inlet manifold during periods when the inlet VOC loading provides more heat than is necessary to maintain the set point temperature. This primary heat recovery saves thousands of dollars in operating costs because the ovens require much less fuel to reach the desired temperature. With the Anguil design there is no loss of residence time at temperature, ensuring destruction and eliminating the concern of overheating the unit. VOC destruction efficiency is guaranteed whether the bypass is open or not.   
Silgan is also investigating another energy reduction strategy by using a secondary heat exchanger to recover additional heat from the RTO exhaust stack.  Initial estimates show that an extra 6.5 million btu/hr can be recovered by utilizing a heat exchanger in the oxidizer stack.  Fresh air (at an average outdoor temperature of 46 deg F / 8 deg C) passes through a single pass 50 percent effective heat exchanger and is heated up to approximately 350 deg F (177 deg C). This recovered heat can be used for processes or comfort heat during the winter months, which could translate into significant savings.

The RTO is also equipped with a high temperature bake-out system, very similar to the self-cleaning option in an oven. This feature removes organic build-up on the cold face of the heat exchange media. In the bake-out mode, the RTO is taken off-line from the process. At a reduced airflow, the outlet temperature is allowed to reach an elevated temperature before the flow direction is switched. This hot air vaporizes organic particulate, essentially clearing the media bed of any obstruction. The flow direction is then switched and the opposite cold face is cleaned. Standard bake-out occurs at 650 deg F (343 deg C), stainless steel media supports and poppet valves were used on the Silgan system that allowed bake-out temperatures to reach 800 deg F (427 deg C), ensuring a more complete cleaning. Scheduled RTO bake-outs reduce the pressure drop across the heat recovery beds. Therefore, Anguil included the transmitters necessary to monitor media bed pressure drop and provide both continuous recording of this data as well as an indication to the operators when a bake-out is recommended.

Dan Gallo, Silgan’s area manager of manufacturing, was pleased with the outcome. “We selected Anguil because of its technical excellence and commitment to service,” he said. “Not only has the company been able to troubleshoot its own equipment, but Anguil has also provided operating solutions for oxidizers made by other manufacturers. We are pleased with their dedication to excellence and are happy to have Anguil as a business partner.”

* Mike Scholz is a senior application engineer at Anguil Environmental Systems.