Thermal Deoiling Replaces Liquid Based Degreasing

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 on a certain date due to the excessive water and air pollution it generated. 

The facility uses aluminum parts of various geometry and weight in the fabrication of automobile air conditioner evaporators. The parts are formed in stamping machines in which oil is used as a drawing lubricant. Brazing of the parts is accomplished in a vacuum furnace that requires clean and dry parts to prevent failures of the brazed surfaces. The need for clean, dry parts in manufacturing processes is increasing because of increased emphases on quality and reliability. 

At the same time, the costs of compliance with rules and regulations governing industrial hygiene, safety and the environment are forcing manufacturers to reevaluate cleaning methods. In aqueous cleaning and solvent based cleaning there are not only costs associated with purchasing chemicals, but also disposal costs, high operation and maintenance costs and risk management costs. Thermal deoiling eliminates most of these costs.

The Process

Thermal deoiling is a process that uses indirectly heated dry air to clean parts contaminated with oils or lubricants. No water, solvents or other chemicals are used. The basic thermal process is well known, having been used for many years in industrial operations that require clean, dry parts such as brazing, coating, soldering and plating. The difference between an oven and a thermal deoiler is that the deoiler burns the oil vapor in a thermal oxidizer to provide clean, dry heat for the deoiling chamber. In effect, the oil itself is helping to clean the parts while it is being oxidized to carbon dioxide and water.

A natural gas fired burner in the thermal oxidizer provides the balance of the heat needed for complete destruction of the oil. Indirect heating avoids condensation of water or oil vapor in the deoiling chamber or on the parts. 

The Solution

Epcon Industrial Systems LP.of The Woodlands, Texas was contracted by the manufacturer to design and construct a waterless and solventless deoiling system to replace the solvent line in time to meet the deadline. Epcon is a manufacturer of thermal oxidizers, industrial ovens, heat exchangers, wash lines and coating lines. 

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. After evaluating the existing line, a U-shaped configuration was selected which was approximately one hundred feet in overall length and had an eight feet wide working space. Low pressure and high pressure recirculation fans with variable frequency drives were installed at critical points to provide temperature balancing within the deoiler chamber. 

The installation of air curtains and careful placement of the return air plenums prevents vaporized oil from escaping the entry and exit vestibules. A programmable logic controller (PLC) serves as the operator interface. The operator is able to monitor and make changes to temperatures, fan speeds, motor actuated damper positions and alarms. The PLC also keeps running records of the data, which can be charted in graph form at any time.

In order to eliminate the vaporized oil (volatile organic compounds) a thermal oxidizer was added to the system. Operating at 1,500°F with a combustion chamber residence time of 1.0 second, vapor destruction removal efficiencies (DREs) of greater than 95% were demonstrated. Two stainless steel shell and tube heat exchangers were installed at the oxidizer’s exhaust. The primary exchanger heats ambient air, which supplies the heat to the deoiler chamber, and a secondary exchanger saves fuel by elevating the temperature of the exhausted oil vapor prior to its destruction in the combustion chamber.  The combustion of the oil provides up to 1,000,000 Btu per hour of heat for the deoiler. No heat source other than the natural gas fired burner and the oil’s heat of combustion are needed for maintaining the required temperature for deoiling.

The Benefits

 There are several benefits of thermal deoiling when compared to liquid deoiling. The transport, storage and handling of chemicals are eliminated. Industrial hygiene, safety and environmental issues are reduced to a minimum. Fugitive emissions are eliminated and air pollution is reduced to a minimum. Waste treatment and disposal are eliminated. Maintenance and operating costs are reduced. There is no contact of the parts with the products of combustion – they exit the deoiler clean and dry.

 In the case of the automobile equipment manufacturer, the deoiling system, which has been operating since December, 1998, has resulted in the substantial reduction of costs compared to the cost-intensive vapor degreasing line. The reduction of intangibles such as safety and industrial hygiene management costs is unknown, but probably significant.

Quality products require quality cleaning. Thermal deoiling has been shown to be a viable, money saving technology when compared to other cleaning methods. Deoiler, oxidizer and heat exchanger configurations can be designed for almost any part size, production rate, VOC loading and operating temperature. Conveyorized and batch systems are available.

For more information contact Epcon Industrial Systems LP. at(936) 273-3300; Fax (936) 273-4600; email: epcon@epconlp.com.