Organic Rankine cycle (ORC) is a novice technology for the conversion of waste heat to electricity. Although many energy intensive industries could benefit significantly from the integration of ORC technology, its current adoption rate is limited. ORC use organic working fluids. An essential advantage of ORC systems is however, the utilization of organic working fluids that can simply employ a single stage expander hence offering advantages of simple design, low capital cost and maintenance. A thermo-economic modelling has been carried out in this literature for waste heat recovery and power generation calculation from the data collected from low temperature flue gases of Numaligarh Refinery limited furnace exhausts (1st stage crude oil heater of hydrocracker unit), based on Organic Rankine Cycle (ORC) with an organic fluid as the working media and exhaust heat flue gases as source of energy. In the system designed, the working fluid considered is “R245fa” based on the parametric analysis which includes GWP (Global Warming Potential), ODP (Ozone Depletion Potential), Safety factor, Critical temperature and pressure, Molecular mass, Atmospheric lifetime., a reciprocating piston type expander selected to produce work, heat exchanger designed as evaporator. The alternator coupled to the expander shaft convert the mechanical power into electricity. Simulation of the process is done using DWSIM process simulator and also a exergy analysis has been carried out to validate the model. Based on the simulation results , the values of the Wnet at different input conditions were computed and efficiencies are calculated accordingly. The net work done (Wnet), 1st law efficiency (ηI) and 2nd law efficiency (ηII) were computed. The expander output is calculated around 2.475 Kw with 75% efficiency and with a alternator with similar efficiency coupled, net power will be 1.8 to 2 kW. Results indicate that proposed system model can generate electricity in the range of 2kW to enable lighting of the industry street lights and result in cost savings. The 1st law and 2nd law efficiencies of the cycle varies from 5 to 7%.The payback period for the system is estimated to be around 7-8 years. Economic cost calculator software based on industrial factors and parameters is developed as a part of the project which will calculate the total capital to be invested (TCI) for any project .The Fixed capital costing calculated are revalidated using market survey methods.

Thermo-economic modeling and system simulation with DWSim analyzer for an organic Rankine cycle with heat from waste heat flue gases and development of an economic cost calculator

ACS Fall 2021

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