Purified Terephthalic Acid Plant

Purified Terephthalic Acid Plant

The Challenge

A major chemical manufacturer required a pollution control system to destroy the halogenated Volatile Organic Compounds (VOCs) emitted during the formulation of Purified Terephthalic Acid (PTA). During the production process, methyl bromide is converted to hydrogen bromide. The pollution control system had to be designed to withstand the corrosive nature of the hydrogen bromide as well as the varying organic loading, which alter the temperature of the abatement system.

The Solution

After a thorough supplier evaluation, the plant selected and contracted Anguil Environmental Systems to solve their VOC emission problem. Because of the high loading of CO and the presence of methyl bromide, Anguil recommended a Catalytic Recuperative Oxidation System. It would utilize a specialized metallic catalyst specifically designed for PTA plant exhausts. Anguil’s success with catalytic oxidation of halogenated compounds and experience integrating control devices into existing processes were crucial factors in the plant’s decision.

The Result

An Anguil catalytic oxidation system designed for 90,000 SCFM (144,450 Nm3/hr) was used to process the airflow. The presence of methyl bromide in the emission stream presented additional design considerations. The catalyst oxidizes the methyl bromide to hydrogen bromide (HBr). If hydrogen bromide drops below its dew point it becomes corrosive to the equipment. The equipment downstream of the catalyst must be engineered to avoid any “cool spots” where the hydrogen bromide can condense.

The heat exchanger is one potential “cool spot.” Without proper design, the heat exchanger could lower the temperature of the air exiting the catalytic oxidizer to below the dew point of hydrogen bromide. To avoid the potential condensation of hydrogen bromide and subsequent corrosion to the system, Anguil incorporated a steam pre-heater on the incoming process stream before the catalytic oxidizer. The exhaust from the PTA plant is heated with a 316L stainless steel plate and frame steam pre-heater. The preheated process air then enters the tube side of the shell and tube heat exchanger. The increased temperature of the process air entering the tube side of the heat exchanger prevents the condensation of HBr on the shell side of the heat exchanger, a critical issue in the overall design of the system.

The process exhaust from the PTA plant varies in organic loading; therefore, the catalytic oxidizer design must accommodate these varying levels with minimal use of auxiliary fuel. This is accomplished by utilizing a bypass on the 316L stainless steel shell and tube heat exchanger. Under low organic loading conditions, the heat exchanger bypass is closed so that the full effectiveness of the heat exchanger is available to preheat the incoming stream. At high organic loading, the outlet temperature of the catalyst is raised, resulting in a high preheat temperature from the heat exchanger. This high preheat temperature could cause overheating and shutdown of the system. The “hot side” heat exchanger bypass supplied by Anguil controls the preheat temperature from the heat exchanger, preventing any high-temperature conditions.

The selection of the proper catalyst that would oxidize both the carbon monoxide and the methyl bromide at low temperatures was critical to the project. Historically, halogenated compounds, which include chlorine, bromine, iodine and fluorine, have had damaging effects on both noble metal and base metal oxidation catalysts. Several significant advances in catalyst technology have occurred in recent years, resulting in the development of catalysts suitable for the air stream under consideration. A platinum/palladium-based catalyst deposited on a ceramic substrate was utilized in this design. Anguil’s proprietary catalyst rack design, including specialty gaskets, eliminated the risk of gas bypassing the catalyst which would result in incomplete destruction.

This Anguil Catalytic Recuperative Oxidation System is currently operating and achieving the regulatory compliance demanded of the PTA plant. With the success of this system, the customer purchased an identical 90,000 SCFM (144,450 Nm3/hr) unit and additional systems were installed for PTA manufacturers in the Middle East and Southeastern United States.

Kiln Emission Control Technologies

The Challenge

A specialty ceramic material manufacturer in the United States operates several custom-built furnaces in their manufacturing process. Sometimes referred to as kilns, these high-temperature process devices are generally a major source of air pollutants and require an abatement technology to meet environmental regulations with the state or federal agencies. As is the case with many industrial manufacturing operations, emissions are best destroyed through the use of oxidation technologies.  Thermal and catalytic oxidizers utilize temperature, time and turbulence to destroy emissions. This particular manufacturer was operating direct-fired thermal oxidizers, as well as Regenerative Thermal Oxidizers (RTOs) for abatement of the various emission streams at this one facility.  

The Solution

For one of these processes, this manufacturer needed an RTO to be installed onto a mezzanine inside the building. A special design was required to fit within the height restrictions, yet tall enough for the RTO to operate. Anguil Environmental designed and built the RTO with high-cell density ceramic media to still get 95% thermal energy recovery, but with a much shorter bed elevation. This, along with other design changes, allowed the equipment to be installed inside the building on the mezzanine with a very short vertical dimension.  

Having successfully worked with the company before, they again turned to Anguil for a destruction device for another process within their facility. The preferred location for the installation was equally challenging as the last, also on a mezzanine. In this application, the process exhaust was already quite warm, within the temperature range normally associated with catalytic oxidation temperatures (600°F or higher). Rather than design a heavy RTO to fit into this area, Anguil designed and built a catalytic oxidizer to remove the Volatile Organic Compounds (VOCs) and Hazardous Air Pollutants (HAPs) from their exhaust. Since the process exhaust temperature was already hot enough to sustain high levels of oxidation with the catalyst, the oxidizer was supplied without a heater or a heat exchanger. This allowed for a very simple method of controlling the emissions from the process with reduced capital and installation costs.  

On the discharge of a third process line, they were operating an older (non-Anguil) RTO to treat the VOCs and HAPs. This specific process required the use of nitrogen to keep the internal kiln chamber starved of oxygen. The inert gas stream allows their end products to cure properly. 

Nearing the end of its life cycle, the aging RTO utilized poppet valves to direct airflow within the destruction device and maximize energy recovery within the oxidizer. This process continues to alternate and repeat during normal operation of the RTO, approximately every three to five minutes. The RTO diverter valves were designed without a pressure relief system, meaning that pulses of pressure were traveling back up the ductwork into the process equipment each time the RTO poppets switched. Internal pressure within the kilns affected the control and usage of nitrogen and negatively impacted the process operation and operating costs. 

The RTO technology is generally considered to be the most efficient oxidation device and is therefore the most commonly used. However, this manufacturer was successfully utilizing catalytic oxidizers for emission control on another process and felt one should be applied here as well. They wanted a technology that would not only keep them in compliance, but do it without the pressure pulses that had been negatively impacting the process equipment.

Having supplied both thermal and catalytic oxidizers to this facility before, Anguil was called in once again to evaluate the situation and make equipment recommendations. Anguil, along with engineers at this customer, selected a catalytic oxidizer for this unique process. The Products of Combustion (POC) from any oxidizer are Carbon Dioxide (CO2), water vapor and heat. Anguil designed and manufactured this catalytic system with multiple heat exchangers to utilize the heat generated during combustion. The added benefit of this third Anguil control system is that it re-circulates inert oxidizer POC back into their process. 

A secondary heat exchanger downstream of the oxidizer cools the treated air so that it can supply the process with tempered supply gas. To enable reentry into the kiln, oxygen concentrations leaving the catalytic oxidizer are maintained at very low levels with custom designed electronic control systems, supply fans and ductwork. Maintaining low oxygen levels and recirculating this offgas reduces the amount of nitrogen required by the process and therefore lowers operating costs for this production line. In addition, a primary heat exchanger within the oxidizer was designed to minimize fuel consumption of the abatement device itself, using heat from the exothermic reaction to preheat incoming pollutants. 

The Result

The 20,000 SCFM (32,100 Nm3/hr), Anguil thermal oxidizer was installed indoors, near the process equipment. To keep it under negative pressure at all times, Anguil manufactured the oxidizer in an induced draft fan configuration. Pulling gases through the system with the main fan ensures that no oxygen depleted gases are emitted into the building where personnel were present.

Anguil differentiates itself from the competition by offering all of the different oxidizer technologies used for the destruction of pollutants. This ensures an unbiased equipment selection for each application based on the destruction requirements, efficiency needs and process parameters. They not only design, manufacture, service and install Regenerative Thermal Oxidizers (RTOs), but also direct-fired, catalytic and thermal recuperative systems. Each one of these oxidizer types uses high temperature combustion in a unique manner to best suit each application.  

Formaldehyde Production

The Challenge

A major chemical manufacturer required a pollution control system with minimal operational cost to destroy the Hazardous Air Pollutant (HAP) by-products of a formaldehyde production process. A key issue was system reliability; the plant operates 24 hours a day and only shuts down once per year for plant-wide preventive maintenance.

The Solution

After thorough technical evaluation, the company selected Anguil Environmental Systems, Inc. to solve their HAPs emission problem and put them in compliance. Anguil installed a catalytic oxidation system that meets all applicable regulatory requirements. The system uses a 65% effective shell and tube heat exchanger that allows self-sufficient operation under normal process loadings.

In the formaldehyde production process, methanol reacts with air in the presence of catalyst to produce formaldehyde. Process yields are normally quite high, with over 95% to 98% of methanol ending up as formaldehyde. Some ancillary compounds are generated in the oxidation process due to catalyst inefficiencies. The emission by-products that require control are carbon monoxide, dimethyl ether, methanol and formaldehyde. Both formaldehyde and methanol are classified as Hazardous Air Pollutants (HAPs) and require stringent emission reduction.

Anguil’s extensive experience with formaldehyde manufacturers helped the company in examining possible pollution control solutions. On this application conditions were favorable to use a catalyst for VOC control.  Since the customer uses catalyst in their process, they were comfortable using catalyst for VOC and CO oxidation. In addition, there is a relatively high CO and VOC concentration exhausted from the process which would allow the catalytic oxidizer to function without any auxiliary energy requirement.  

A precious metal catalyst was selected as the core of the catalytic system due to its ability to provide 99+% DRE of the formaldehyde, methanol, dimethyl ether, and carbon monoxide at a catalyst bed inlet temperature as low as 525° F (275° C). The catalyst is deposited on a monolithic, honeycomb, stainless steel substrate. The catalyst design minimizes the pressure drop through the oxidizer.

Another cost-effective design feature was the integral 65% effective shell and tube heat exchanger that was selected to preheat the incoming process stream prior to the catalyst bed. The exhaust air from the catalyst outlet  is hot sufficient to keep the oxidizer operating at temperature with no auxiliary energy requirements. 

Oxidizer warm-up following a plant shut-down was also a crucial design consideration. Neither natural gas nor propane is readily available at many of the company’s formaldehyde plants. For this reason an electric heating system was selected to bring the oxidizer up to the 525° F operational temperature prior to the processing of the plant off-gases. A small pre-heat fan and an electric heater were designed to bring the system up to initial operating conditions. Once at setpoint  temperature, the oxidizer process inlet valve is incrementally opened to allow the process exhaust gases. As sufficient CO/HAP/VOC loading enters the oxidizer releasing heat from the exothermic reaction, the electric preheat elements shut off completely. No additional energy is added to the system. In fact, the oxidizer doesn’t even use fan energy since it takes advantage of the process pressure to push through the oxidizer.

The Result

The system is operating and providing well over the 99+% destruction efficiency required. The success of this system resulted in this chemical company purchasing another 25 and counting additional Anguil systems for formaldehyde plants around the world. Anguil’s experience, innovative design and quality manufacturing resulted in another satisfied Anguil customer and a long-term partner with  air pollution control.

Cumene Plant

The Challenge

An East coast chemical plant that manufactures phenol, acetone and alphametyl styrene from cumene planned to install an air pollution control system to control the Volatile Organic Compounds (VOCs) emitted during their chemical production process. Phenol is consumed internally as an intermediate chemical while the acetone and alphametyl styrene are sold off. Once the chemicals are produced, they are shipped to another plant to make carpet fibers. This plant already had a carbon recovery system in place, but needed a system to control the low concentration residual process stream from the carbon recovery system.

The Solution

After thorough vendor evaluation, the plant selected and contracted Anguil Environmental Systems to solve their emission problem. The combination of VOCs in the stream and their low concentration made catalytic oxidation the ideal technical choice. Plant engineers had concerns that an oxidation system might have an adverse effect on the precise pressure and volume control required in their production process. Anguil’s experience and success with chemical process applications provided the plant personnel with the confidence that catalytic oxidation was a viable solution.

The Result

An Anguil Model 400 forced draft catalytic oxidizer, rated for 65,000 SCFM (102,512 Nm3/Hr) was selected to process the flow from twenty-five sources of production emissions. As always, Anguil’s engineering staff worked closely with the customer throughout the design and manufacturing processes to ensure that the system precisely met their requirements. The system was sized to provide 99% destruction removal efficiency and 70% thermal energy recovery. The reactor section contains a catalyst bed to oxidize the incoming airflow. The catalyst converts VOCs into carbon dioxide, water vapor and thermal energy. 

In order to address the concern of the precise pressure and volume control required for the customer’s production process, Anguil manufactured a four-module, fully welded shell and tube heat exchanger. By using a greater plate thickness, as well as fabricating “ribs” and “dimples” on the plates, a pressure differential of 87.5 w.c. was sustained.

The plant’s process operates 24 hours a day, seven days a week. The oxidation unit is required to run continuously, with 100% up-time to accommodate the aggressive chemical production process. 

The Programmable Logic Control (PLC) system was integrated into the customer’s control system and redundancy was designed into the most critical items. A difficult pollution control issue was solved by Anguil, resulting in another satisfied customer.

Engine Test Cell Exhaust: RTO

The Challenge

A Midwestern outboard engine manufacturer bought a three-year-old plant to produce its marine engines. When finished, the engines are removed from the assembly line and run for quality control. The 25,000 SCFM (40,125 Nm3/hr) of exhaust from testing contains volatile organic compounds (VOCs) that require regulatory compliance. Also within this exhaust is a great deal of water vapor and carbon monoxide (CO).

Anguil had already planned to equip this plant with pollution control equipment for its paint processing operation using a new Anguil Emissions Concentrator coupled with an existing 17,000 SCFM (27,285 Nm3/hr) Regenerative Thermal Oxidizer (RTO) that the company inherited with the plant. However, the engine test cell emission control issue was complicated by the water vapor emitted with the VOCs. Control of the CO emissions was not an objective for this application because its release was not a concern to any local regulatory authority.

The Solution

After a thorough technical evaluation, Anguil engineers chose a new 25,000 SCFM (40,125 Nm3/hr) RTO as the most cost-effective solution for the existing conditions.

The Result

Several factors affected this decision. The presence of a large percentage of water vapor in the process exhaust caused concern regarding the effectiveness of the concentrator type adsorption system. Vapor-liquid separators could be used to minimize the water introduced to the concentrator but the low winter temperatures would require the additional cost of heat tracing and insulation to prevent freezing, increasing the overall cost of the system.

Another potential problem regarding the concentrator system was the presence of small amounts of high-boiling oils that may not adequately be desorbed off a concentrator system. The boiling point temperatures of these oils was high enough that even the high temperature desorption that was offered on this concentrator was determined to be insufficient to obtain complete desorption. This problem could have been addressed by installing a “sacrificial” guard bed of carbon in front of the concentrator to capture the high-boiling VOCs, but at additional cost and inconvenience. There would be added process equipment to purchase and maintain, replenishment of carbon in the beds on a routine basis, and proper disposal of the used material, an unattractive option.

A more suitable technology choice emerged in the RTO. Emissions from the test cells were still low and this technology is extremely cost-effective at low concentrations with 95% thermal energy recovery typically achieved and options for up to 97% thermal energy recovery available. However, the existing RTO coupled to the concentrator controlling the paint processing did not offer the needed capacity or the upgraded materials of construction to provide resistance to corrosion.

Anguil engineers presented their analysis to the customer with all the control options available and the optimal technology chosen for treating the engine test cell emission was a new RTO. The engineering study, which considered the high quantity of water vapor and CO emissions, determined that all ductwork between the test cells and the RTO must be constructed of stainless steel to prevent corrosion. The ductwork was also sloped back to the process entry stream to minimize carryover of excessive amounts of water to the RTO. The oxidizer’s internal insulation and inlet ductwork were also designed to process the high amount of water vapor to minimize erosion of the RTO insulation and corrosion potential of the steel.

The system operation is very energy efficient with thermal energy recovery of 95% or higher. The process air containing VOCs passes through vertical beds of ceramic media that alternately stores and releases heat to elevate the process air temperature before it enters the combustion chamber. Since RTOs have such high heat recovery, the process air can be heated to a value very close to the combustion chamber set-point temperature. Heat released from VOC destruction during oxidation further elevates the process air temperature to the point where the RTO is often self-sustaining with no auxiliary fuel usage.

With this system, they elected to use supplemental fuel injection (SFI) that reduces the point of self-sustained operation to a lower process VOC concentration. Burners are shut off during operation with SFI which minimizes the introduction of combustion air into the chamber, and further reduces operating fuel usage with a flameless design that eliminates NOx emissions from the burner, problematic in some RTOs.

The manufacturing plant is now able to meet compliance on multiple emission sources while saving capitol expense. First, by utilizing equipment inherited with their plant purchase, plus the operational cost savings on the newer more efficient RTO. An additional benefit with selection of an RTO was to the environment. Although not required, RTOs control the CO emissions along with VOCs from the test cells. This facility can accommodate future expansion and stay in compliance for many years to come.