| 摘要 |
A system and method of exchanging heat are disclosed. Three heat exchange sections are used: a dry indirect contact heat exchange section, a second indirect contact heat exchange section that is operable in either a wet or dry mode, and a direct contact heat exchange section. The three sections are next to each other in an apparatus to reduce the overall height of the apparatus. The dry and second indirect contact heat exchange sections receive a process fluid in series or in parallel. Separate ambient air streams pass through the second indirect and direct contact heat exchange sections before mixing and entering the dry indirect contact heat exchange section. Another ambient air stream is mixed in upstream of the dry indirect contact heat exchange section when the system is operated in the dry mode. Two independent evaporative liquid distribution systems are included. One selectively distributes evaporative liquid over the second indirect contact heat exchange section. The other selectively distributes evaporative liquid over the direct contact heat exchange section. Separate sumps, pumps and conduits are provided for the second indirect and direct contact heat exchange sections. The system is operable in different modes to extract heat from the process fluid in the most efficient way with respect to annual water consumption. At low temperatures, the system operates dry with primary heat extraction performed by the dry indirect contact heat exchange section. At higher temperatures, evaporative liquid is distributed over the second indirect contact heat exchange section but not over the direct contact heat exchange section. At still higher temperatures, evaporative liquid is distributed over both the second indirect and direct contact heat exchange sections. A temperature or pressure sensor may be provided so that operation of the apparatus may be based upon the process fluid temperature or pressure. Alternatively, operation may be based upon ambient air temperature.
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