Improved energy recovery from the condensed steam as part of HEN retrofit

The conventional approach to heat exchanger network (HEN) retrofit involving design techniques based on Pinch Technology (PT) is extended to include minimization of energy losses resulting from steam-condensate expansion. The authors proposed a new approach to minimize energy losses in utility system, thermally coupled with the combined heat and power (CHP) plant, using condensate subcooling phenomena. Moreover, applying condensate subcooling can counteract the drawbacks of commonly used multi-stage condensate expansion which increase operability and reduces investment and maintenance costs. A case study illustrates the suitability of improved condensate management as a HEN retrofit measure. The study object is a Methyl-Tert-Butyl Ether (MTBE) plant processing 18 t/h isobutylene and consuming 4386 kW of hot utility (steam) in the HEN. A study of the maximum possible heat recovery using PT indicates that the combined heat recovery from hot process streams and condensate can be increased by 510 kW compared to the existing state. At the same time, it is possible to generate additional power of 120 kW in the CHP plant that supplies energy to the MTBE plant. The locations of heat exchangers are accounted for in HEN reconfiguring. A new scheme of steam and condensate system is presented. •Heat exchanger network (HEN) is essential for the process plant's energy efficiency.•HEN retrofit may include introducing rational energy recovery from steam condensate.•Condensate subcooling in the retrofitted HEN may enhance the energy recovery.•Case study illustrates the effect of condensate subcooling as HEN retrofit measure.•Condensate subcooling enhance electricity production in combined heat and power plant.