Using Low Pressure Excess Steam as Heat Source in an Organic Rankine Cycle for Power Generation

In many refineries and petrochemical complexes, low-pressure excess steam is discharged into the atmosphere or with energy consumption condensate and returns to the system. In this case, high volumes of mass and low vapor energy are wasted without any use. In this research, the purpose is the optimal use of the surplus low-pressure steam in Kharbiran gas refinery. The Organic Rankine Cycle (ORC) is an interesting heat recovery alternative for low grade heat at the present time. The paper presents the idea of using organic rankine cycle with pure and zeotropic mixtures as working fluids, in order to convert the low temperature thermal energy sources into electrical energy. The types of fluid, the composition and the operating conditions that achieved the maximum network output were determined through Aspen Hysys software and Matlab. The results show that the Organic Rankin Cycle with Isobutane pure working fluid has the best performance and the corresponding power output of the system is 116.4 kW. While the optimal binary mixture is Isopentane/cyclohexane (0.68-0.32, by mole fraction) and the corresponding power output of system is 129.9kW. Compared with the pure working fluid, there is a 11.5% increase in net power output of system. The use of mixtures as working fluids leads to an efficiency increase compared to pure fluids, due to a glide match of temperature profiles in the condenser and evaporator ORC is one of the effective methods to recover low-grade heat, which makes use of environment-friendly organics as working fluids, and low temperature thermal energy as the driving energy.

Keywords:

Low grade heat , Organic Rankine Cycle , Zeotropic working fluid , low pressure excess steam