Abstract:

In order to study the influence of structure parameters and operating parameters of evaporator on the thermal economy of waste heat recovery in Organic Rankine Cycle (ORC) system, from the perspective of exergy recovery, combined with the thermo-economic theory, which considered the initial investment of equipment, the time-value of fund and the costs of the evaporator in whole life cycle, an thermo-economic evaluation model with the annual net profit CNPV as an important criterion, was established for the evaporator. Based on the model, an example was calculated and analyzed. It is found that the annual net income of ORC waste heat recovery project may be negative when the net recycling exergy of ORC system is positive, which shows that a single evaluation method considering net recycling exergy as the only indicator is not accurate for the evaporator. There is an optimum condition in ORC system, in which the max annual net profit value can be reached. The highest annual net profit value (about 14 650 yuan per year) can be achieved when the heat transfer area of the evaporator, the flow of organic working fluid and the mass flow ratio of flue gas and organic working fluid are 28 m2, 0.06 kg/s and 7.8, respectively. When the operational parameters deviate from the optimum condition, it will lead to the greatly decrease or even loss of the annual net profit of waste heat recovery project.

Key words: Organic Rankine Cycle, evaporator, exergy recovery, waste heat recovery, energy economy