Heat-transfer equipment, condensers exchangers

If the optimum size heat exchanger for the initial plant is installed, an additional exchanger either in parallel or in series will be required when the plant is expanded. This may be the best option when the heat transfer involves condensation and subcooling. The exchanger can be designed to perform both functions initially, and then when the plant is expanded an aftercooler can be installed and the initial equipment can act only as a condenser. 

David Johnsori/ P E / M S C E Heat Exchanger Specialist, AAmerican Institute of Chemical Engineers American Society of Mechanical Engineers API Subcommittee on Heat Transfer Equipment API 660/1SO 16812, API 661/lSO 13706, API 662/lSO 15547 (Thermal Design of Heat Exchangers, Condensers, Reboilers)... 

Heat-transfer equipment in the form of heat exchangers and condensers is a vital part of the chemical process industries. Heat exchangers are used for the cooling or heating of all sorts of process materials, while condensers are used largely for the condensation of vapors from evaporators and consequent production of vacuum, and for the recovery of materials volatilized from stills. 

Today we switch from heat-transfer operations (heat exchange, evaporation, condensation) to mass-transfer operations (distillation, extraction, absorption, humidification). Instead of sizing equipment to exchange heat between two phases we will size equipment to exchange mass between two phases. 

Evaporative-cooled condensers in many applications give greater heat transfer than air-cooled or water-cooled condensers. The evaporative equipment can do this by offering a lower temperature sink. Evaporative-cooled condensers are frequently called wet-surfece air-coolers. Perhaps the best description for this type of equipment is a combination shell-and-tube exchanger and cooling tower built into a single package. The tube surfaces are cooled by evaporation of water into air. 

For energy exchange equipment Supply sufficient excess of heat transfer area in reboilers, condensers, cooling jackets, and heat removal systems for reactors to be able to handle the anticipated upsets and dynamic changes. Sometimes extra area is needed in overhead condensers to subcool the condensate to prevent flashing in the downstream control valves. Too frequently, overzealous engineers size the optimum heat exchangers based on an economic minimum based on steady-state conditions and produce uncontrollable systems. 

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