Process Thermodynamic

Process Thermodynamic

Profile of a Process Application — Gravity Drainage, Shell and Tube Heat Exchanger
Tubes, coils or jackets are used with heat exchangers, tanks or vats for heating liquids in either batch or continuous operation, typical of shell and tube heaters. Equipment is generally protected from the weather and typically features a single coil. Heavy startup loads, followed by smaller running loads are to be expected, but without the extreme swings of weather-exposed equipment. Adequate air venting is most important as the equipment is often run on daily or weekly schedules. Tendency is for total shutdown of equipment following completion of run or batch. Air in a heating system significantly reduces its efficiency. Air is a very poor conductor of heat and air filming on pipes and heat exchanger tubes reduces the heat transfer rate through their metal walls. Also, steam mixed with air contains fewer BTUs at a given pressure than steam alone. It is the function of a steam trap to aid in venting air from a steam system, but auxiliary thermostatic air vents are often required. Open to cooler air and closed to hotter steam they greatly speed up the air purging process. When frequent startups and shutdowns are the rule, rapid air purging is a significant factor. Yarway lever style thermodynamic traps are often favored for their excellent air handling characteristics on startup.

Profile of a Process Application — Syphon/Lift Drainage Rotary Drier (using lever traps)
In this application, continuous drying of materials is being performed by exposure to the heated surfaces of rotating cylinders or drums. Commonly used in the manufacture of felt, rubber, textiles, paper and other sheet or fibrous materials, including foods and slurries of chemicals. Higher startup loads and moderate running loads are typical. When several dryers are in series, the first will have the highest load while those toward the end have progressively smaller loads. Each dryer should be trapped individually to prevent flooding. Syphon drainage is standard practice. CAUTION! Condensate moving up the syphon from the outer rim to the center of the drum is subject to reheating and flashing. Flashed condensate can break the siphon (steam binding). Therefore, steam traps must have hot discharge and fast response with the ability to handle flash steam by means of a small bleed passage. Air venting capability is an important requirement during startup when drums or cylinders contain large amounts of air.

Why Choose a Thermodynamic Steam Trap?
Thermodynamic traps are phase detectors in that they can discriminate between condensate and steam. The working principle is simple and, with only one moving part, these devices are small and rugged. There are three basic types of thermodynamic traps which differ from one another by the configuration of the valve they use to open and close a port. Each is well-adapted to a particular set of service conditions. The main thermodynamic feature that is desirable in process applications is the hot-running design and responsiveness to load changes. Thermodynamic traps also handle air very well, which is essential to an efficient heat transfer rate. This requires an understanding that steam mixed with air contains fewer BTUs at a given pressure than pure steam.

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