The feed bottom exchanger is normally applied to improve the heat recovery, thereby reducing the external heat addition by means of live steam, re-boiler duty, or fired heater duty. A typical approach to heat integration to maximize the heat recovery using feed bottom exchangers would require overcoming the temperature cross in the exchangers. Thermodynamically, heat exchange beyond the cross temperature in a heat exchanger which is not truly countercurrent, is actually not possible. Hence penalty by means of excess area (extra shell) is required to overcome the cross temperature. Conventionally E-shells in series are applied to facilitate the heat exchange beyond the temperature cross. The F-shell exchanger, which is truly countercurrent, can also be used to achieve the same, but constrains such as physical and thermal leakage limit the usage. Recent advancement by the use of twisted tubes in F shell, avoids the physical leakage, because twisted tube bundle is a baffle free design. For the case under study, the heat exchange beyond the temperature cross is not likely to benefit. Hence the use of F shell exchanger will not be attractive. To overcome the temperature cross, the exchanger design is tuned by increasing number of passes or by increasing the number of exchangers in series, enabling more area requirement. An alternative proposal of heat exchange up to the temperature cross is delineated. The parameters that affect/impact the scenario are discussed. The feed bottom exchanger commonly used in units is hydro-treater reactor, amine regenerator and sour water stripper. In the present investigation Sour Water Stripper (SWS) is considered for the case studies.

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