Abstract
Organic Rankine cycle systems are suitable technologies for utilization of low/medium-temperature heat sources, especially for small-scale systems. Waste heat from engines in the transportation sector, solar energy, and intermittent industrial waste heat are by nature transient heat sources, making it a challenging task to design and operate the organic Rankine cycle system safely and efficiently for these heat sources. Therefore, it is of crucial importance to investigate the dynamic behavior of the organic Rankine cycle system and develop suitable control strategies. This paper provides a comprehensive review of the previous studies in the area of dynamic modeling and control of the organic Rankine cycle system. The most common dynamic modeling approaches, typical issues during dynamic simulations, and different control strategies are discussed in detail. The most suitable dynamic modeling approaches of each component, solutions to common problems, and optimal control approaches are identified. Directions for future research are provided. The review indicates that the dynamics of the organic Rankine cycle system is mainly governed by the heat exchangers. Depending on the level of accuracy and computational effort, a moving boundary approach, a finite volume method or a two-volume simplification can be used for the modeling of the heat exchangers. From the control perspective, the model predictive controllers, especially improved model predictive controllers (e.g. the multiple model predictive control, switching model predictive control, and non-linear model predictive control approach), provide excellent control performance compared to conventional control strategies (e.g. proportional–integral controller, proportional–derivative controller, and proportional–integral–derivative controllers). We recommend that future research focuses on the integrated design and optimization, especially considering the design of the heat exchangers, the dynamic response of the system and its controllability.
Highlights
The future energy demand of the ever-increasing global population requires efficient utilization of current energy resources as well as the development of sustainable energy solutions
We provide a detailed description of the methodology and state-of-the-art approach used for the dynamic modeling of the organic Rankine cycle (ORC) components, namely, the heat exchangers, expander, pump, control valves, and storage tank
The dynamic response of the organic Rankine cycle system depends on the heat source, system size, operating conditions, type of equipment and working fluid to some extent
Summary
The future energy demand of the ever-increasing global population requires efficient utilization of current energy resources as well as the development of sustainable energy solutions. The low-grade thermal energy cannot be converted efficiently to electrical power by conventional energy conversion technologies (Steam Rankine or Brayton cycle), and a large amount of low-temperature heat sources remain untapped. Design/Modeling/Analysis Optimization Expander/Turbine Working fluid Dynamics Control Pump Heat exchanger Cycle configuration. The expertise and guidelines concerning the dynamic modeling of ORC systems can be obtained from the fields of steam power plants, gas turbine engines, and combined cycle power plants [19,20] These power plants typically operate close to the design point, whereas ORC systems utilizing fluctuating heat sources often operate far from the design point depending on the heat source, cold sink and loading conditions.
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