Design of a Steady-State Adjustment Method and Sensitivity Analysis for an ORC System with Plate Heat Exchangers

Abstract

Because of its low concentration and low energy in an organic Rankine cycle (ORC) system, more than 50% of low-grade thermal energy with a temperature below 300 °C is not taken seriously. The relationship between changeable working condition parameters and operating parameters is typically not taken into account in a model while studying ORC systems. It is insufficient to analyze the system performance changes solely on changes in the performance parameters of the heat exchangers. Furthermore, a model perspective of the system control solution is absent from the steady-state control of the system when the heat source varies. In this paper, we created a system model for the application scenario of a 100–200 kW ORC system with brazed plate heat exchangers in order to address the aforementioned issues using MATLAB R2016b. Additionally, a sensitivity analysis of the system was conducted based on heat exchangers of performance variations. In addition, a modeling computation and adjustment scheme were put forth to guarantee that the system could continue to produce steady power production even when the temperature of the heat source fluctuated. Preliminary results showed that the system’s internal parameters included its evaporation pressure and condensation temperature. An increase in evaporation pressure will reduce the mass flow rate and heat flux of an evaporator, thus reducing the heat transfer coefficient. The two-phase region of the evaporator accounted for the highest proportion, of 70.22%, and continued to increase to 75.83%, followed by the supercooling region, and gradually decreasing. The utilization rate of the evaporator decreased from 74.85% to 38.32%. The system output power increased first and then decreased, with a maximum value of 153.11 kW. The system efficiency increased from 5.74% to 11.04%. The increase in condensation temperature increased the proportion of the two-phase region and the superheating region, and the mass flow rate did not change much. The increase in heat flux increased the heat transfer coefficient from 1721.31 W/(m2·K) to 2374.77 W/(m2·K), and the utilization rate of the evaporator decreased from 70.56% to 51.91%. The aforementioned change rules were used in the building of the steady-state regulation model to balance out the changes in the generating power as the heat source temperature increased. The model output was cross-checked and validated against pertinent experimental test literature data. The results of this research can serve as a valid and useful guide for ORC system design and practical applications.