A recuperative thermal oxidizer showcasing the system’s electrical control panel and blower fan that regulates the process airflows
Thermal Cleaning Technology: The Sustainable Alternative
Fig. 1. To gain earlier access to kilns and to increase safety and productivity, some facilities employ heavy-duty, remote-controlled demolition robots for descaling and debricking applications.
A recuperative thermal oxidizer showcasing the system’s electrical control panel and blower fan that regulates the process airflows
Tasha Jamaluddin – Epcon Industrial Systems; Conroe, Texas
Thermal cleaning solutions can be a more cost-effective and environmentally sound alternative to traditional industrial cleaning methods. Countless manufactured goods require parts cleaning at some stage in the production process. Beyond this, there are all kinds of scientific, governmental or unseen applications where materials are exposed to hazardous materials and must be sanitized.
While the overall principal of thermal cleaning is a constant, technologies and custom equipment designs vary greatly based on the application and requirements. This article explores three different industrial thermal cleaning applications: deoiling, decontamination and decommissioning. Case studies are presented to demonstrate the benefits of each system.
Thermal Cleaning Systems Explained
Thermal cleaning systems are a secure and effective means of sanitizing products using heat alone. They essentially remove a variety of hazardous and volatile materials without the use of water, solvents or other chemicals. These systems use extremely high heat to break the chemical bonds and properties of volatile organic compounds (VOCs), hazardous air pollutants (HAPs), irritants, explosive materials and other dangerous compounds.
The most common thermal cleaning application is thermal deoiling, a process that uses indirectly heated dry air to clean parts contaminated with oils or lubricants. The basic thermal process is well known and extensively used in industrial operations that require clean, dry parts such as brazing, coating, soldering and plating. Replacing a traditional wash line with a thermal deoiler is a sustainable solution that saves facilities from generating wastewater and the use of toxic chemicals for parts cleanings. Thermal deoilers not only divert these pollutants from entering clean watersheds but also save the operation from paying costly disposal fees.
However, there are many other lesser-known types of thermal cleaning applications outside of thermal deoiling. For example, garments and tools that are contaminated cannot just easily be disposed of and are best processed immediately in a decontamination system and repurposed. A similar, but more extreme, application is the decommissioning of old ammunitions, which can be volatile and dangerous to store and need a safe method for permanent disposal.
Regardless of the application, it is critical that thermal cleaning systems are custom-designed to manage the unique challenges of the specific materials being processed as well as the toxic or dangerous pollutants to be destroyed. Engineers need to calculate the precise temperature range and exposure time necessary to break down the hazardous chemical compounds present.
Depending on the hazardous pollutants being treated, an air-pollution control system is usually developed in tandem to ensure environmental compliance in the process. Furthermore, integrating the thermal cleaning technology with the air-pollution control and even processes heating equipment via heat-recovery methods can greatly increase overall operational efficiencies. By designing a comprehensive system, it is possible to recover and recycle thermal energy, which is then reused across the production process for functions such as providing hot air for ovens, heated water for washers or steam for indirect heating, generating substantial fuel savings.
Case Study 1: Thermal Deoiler Replaces Liquid-Based Degreaser for Automotive Parts Supplier
A major manufacturer of automobile air conditioners had been deoiling metal parts in a conveyorized solvent-based vapor degreasing line, but the state environmental agency mandated that the line be shut down due to the excessive water and air pollution it generated.
For the fabrication of air-conditioner evaporators, the facility created aluminum parts of various geometry and weight with stamping machines that used oil as a drawing lubricant. The final brazing of these parts was accomplished in a vacuum furnace that required fully clean and dry surfaces to prevent failures or irregularities from the brazing process.
In order to keep producing, the manufacturer desperately needed to find an alternate cleaning technology for aluminum evaporator fins that did not use tetrachloroethene solvent but would still remove all the oil residue in the same amount of time or less.
Fig. 1. A large-scale thermal deoiling system for thermal cleaning of metal parts, featuring integrated air-pollution control technology along the top of the unit
Epcon proposed a waterless and solventless deoiling system (Fig. 1). The new system was to be a one-on-one replacement for the existing cleaning line in terms of production rate, configuration and parts carriers, measuring approximately 100 feet in overall length.
In order to eliminate the VOCs from the vaporized oil, a thermal oxidizer was added to the system. Operating at 1500°F with a combustion-chamber residence time of 1.0 second, a destruction removal efficiency (DRE) of greater than 95% was achieved.
The integrated system was designed so the oil vapor was burned off, or oxidized, in the thermal oxidizer, which provided clean, dry heat for the deoiling chamber. The natural-gas-fired burner within the thermal oxidizer provided the balance of the heat needed for complete destruction of the oil and other surface contaminants while simultaneously providing indirect heating to avoid condensation of water or oil vapor in the deoiling chamber or on the parts. In effect, the oil itself is helping to clean the parts while it is being oxidized to carbon dioxide and water.
Low-pressure and high-pressure recirculation fans with variable-frequency drives were installed at critical points to provide temperature balancing within the deoiler chamber. Additionally, air curtains and carefully placed return-air plenums were installed to prevent vaporized oil fumes from escaping the entry and exit vestibules. An advanced control system design was critical to allow the operator to monitor and make real-time changes to temperatures, fan speeds and motor-actuated damper positions.
Fig. 2. A recuperative thermal oxidizer with air-pollution control technology featuring internal heat recovery with a shell-and-tube-type heat exchanger
Fig. 3. A specialty decommissioning system for sensitive ammunitions for the U.S. government
In addition, two stainless steel shell-and-tube heat exchangers were installed (Fig. 2) at the oxidizer’s exhaust. The primary exchanger heated up the ambient air, which supplied heat to the deoiler chamber, and a secondary exchanger saved fuel by elevating the temperature of the exhausted oil vapor prior to its destruction in the combustion chamber.
In general, there are several benefits of thermal deoiling when compared to steam or liquid deoiling. The associated industrial health, safety and environmental issues – including fugitive emissions and air pollution – are reduced to a minimum, while the transport, storage and handling of chemicals, waste treatment and disposal cost are completely eliminated.
However, this deoiling system in particular resulted in substantial reduction of operating costs compared to the old vapor degreasing line. On chemical cost and disposal alone, the company was spending about $20 million a year. After they installed the thermal cleaning system, their chemicals’ cost and pollution disposal fees went to zero, leaving natural gas for the burners as the only operating expense.
The combustion of the oil itself provided up to 1,000,000 BTUs per hour of thermal energy, which was captured by the addition of the heat exchanger and utilized in the thermal deoiler. This thermal recovery greatly reduced the operating fuel cost, bringing the annual natural gas bill to under $150,000. The company’s final operating savings was at approximately $19,850,000 per year.
Case Study 2: Decontamination System for Exposed Military Garments
A major government contractor was seeking a solution to thermally decontaminate demilitarization protective ensemble (DPE) suits. These DPE suits were developed to protect the wearer against highly dangerous liquid and vapor chemical agents such as HD (hydrogen deuteride), GB (sarin nerve gas) and VX (nerve agent). They consisted of detachable 20- to 30-mm-thick outer garments made of chlorinated polyethylene. Each suit weighed 15 pounds and had an optical polyvinyl chloride visor and flat dimensions of 3 feet wide x 7 feet tall.
To handle these specialized DPE suits of varying materials and destroy their potential life-threatening contaminants, Epcon developed a custom high-air-velocity thermal decontamination system with a temperature range of 190-400°F (Fig. 3). The system was capable of reaching the desired temperature at 15-20 minutes using electric heating elements.
The extremely hot air inside the decontamination unit was used to vaporize and subsequently burn off gases and chemical residuals on the DPE suits. A high-velocity and high-pressure airflow was carefully engineered to produce not only uniform airflow and heat recirculation but also facilitate DPE suit movement to ensure complete decontamination throughout the chamber and prevent the surfaces of the suits from sticking together.
With all the DPE suits 100% free of all toxic agents upon exiting, the new decontamination line proved to be a success. Thermal cleaning systems like this one allow facilities to safely reuse specialized materials, tools and garments, diverting them from costly disposal processes or long-term hazard storage.
Case Study 3: Specialty System Designed for Decommissioning Old Bombs
The U.S. Department of Defense approached Epcon to develop a decontamination system to decommission old bombs. To be successful, the furnace had to operate between 1200-1400°F and withstand continual batch loads of 150,000 pounds. Because of the residual explosive charge in the bomb shells, it was imperative that the heating system was very safe, utilizing steam or indirect heat as the source, and located far away from the decontamination chamber to prevent potential fires or explosive flashbacks. There were many risks associated with this unique project. The engineers had to calculate a variety of peak temperatures, residence times, pressures and airflows to ensure complete decommissioning, while managing the explosive volatility of materials.
Epcon proposed a decontamination chamber and thermal oxidizer with two sets of heat exchangers. A solution that “killed 3 birds with one stone:” thermal decontamination, multistage heat recovery and pollution control. The final system consisted of a car-bottom-type thermal decontamination chamber for batch loading located inside the building (Fig. 4); a high-temperature furnace similar to a spheroidizing furnace in heating principal and design; and a thermal oxidizer for air-pollution control located outdoors.
An indirect heating system was required to ensure the flame was nowhere near the proximity of the volatile munitions. Therefore, the heat was supplied by the oxidizer located outdoors approximately 75-100 feet away. The exhaust from the decontamination chamber was ducted back to the thermal oxidizer via the heat exchangers. In addition, the safety design features and the operating controls were highly sophisticated due to the unpredictability of the explosives.
The final project complied with all governmental requirements for the critical nature of the work while ensuring maximum operational safety. The multistage heat recovery (Fig. 5) saved millions of BTUs of fuel consumption by harnessing the heat generated in the process. The greatest success of the new system, however, was the relief of social and fiscal burden of the long-term storage of such dangerous weapons of destruction.
Fig. 4. A batch oven with guillotine doors and car-bottom design installed for the decontamination of hazardous materials
Fig. 5. Process flow diagram of a regenerative thermal oxidizer, highlighting the heat recovery between the three alternating combustion chambers
The regulatory compliance governing industrial health, safety and the environment has made outdated aqueous and solvent-based cleaning methods and their associated operational costs and risk management a much less sustainable choice. This has pushed many facilities across industries to seek out alternatives to their traditional wash lines or steam cleaning system and turn toward thermal cleaning solutions.
Whether it’s a system for highly sensitive decommissioning of old munitions or garments exposed to hazardous materials, all of these systems promote safer solutions to hazardous products that could pose dangers for generations to come. Likewise, thermal deoiling systems have successfully removed the need for toxic cleaning chemicals and diverted wastewater from leaving industrial processes. Beyond being the most sustainable solution, thermal cleaning systems also save operators on chemical purchasing cost, handling hazards and disposal fees.
While these case studies highlight the overall safety, environmental and cost benefits of thermal cleaning systems, it is critical to also consider any additional opportunities to increase operational efficiencies. Comprehensive systems, where the thermal cleaning is integrated with the process heating and/or the air-pollution control equipment via heat exchangers, is one of the best ways to capitalize on thermal recycling and reduce operating cost.
Whether a facility is upgrading an existing system or has a new challenging industrial cleaning need, it is critical to seek an experienced engineering team and manufacturing partner that can develop a robust custom solution to meet the material and project demands.
For more information: Tasha Jamaluddin is managing director of Epcon Industrial Systems. A graduate of Harvard Business School with a master’s degree from NYU, she has technical expertise across a range of industrial applications. She can be reached at email@example.com or at 936-273-3300.
All graphics supplied by the author.