Heat tracing systems costs

Based on dryer cost alone, indirect-heat dryers are more expensive to build and install than direct-heat dryers designed for the same duty. As environmental concerns and resulting restrictions on process emissions increase, however, indirect-heat dryers are more attractive because they employ purge gas only to remove vapor and not to transport heat as well. Dust and vapor recovery systems for indirect-heat dryers are smaller and less cosdy to supply heat for drying, gas throughput in direct-heat dryers is 3—10 kg/kg of water evaporated indirect-heat dryers require only 1—1.5 kg/kg of vapor removed. System costs vary directly with size, so whereas more money may be spent for the dryer, much more is saved in recovery costs. Wet scmbbers ate employed for dust recovery on indirect-heat dryers because dryer exit gas usually is close to saturation. Where dry systems are employed, all external surfaces must be insulated and traced to prevent vapor condensation inside. 

Fuel handling system. The transfer piping is heat traced to maintain the fuel at the elevated temperature to reduce pumping costs. Further, fuel recirculation lines are provided to establish and maintain the desired operating temperatures. The plant layout considerations and need for hydraxdic transient analysis bsted in the section on naphtha are also appUcable here. 

Designers of evaporation systems strive to achieve high heat transfer rates. This can be justified by a cost/benefit analysis. High rates of heat transfer in theory must often be proved in practice. Evaporators designed for high rates of heat transfer are generally more affected by traces of scale or non-condensable gases. 

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