Cycle Based Waste Heat Recovery Research Articles

Organic Rankine Cycle based waste heat recovery modeling and control of the low pressure side using direct condensation and dedicated fans

Organic Rankine cycle based waste heat recovery has been studied over the past decade as a potential solution to reduce fuel consumption and fulfill the requirements of upcoming regulations on CO2 emissions for heavy-duty trucks. This study, focusing on a particular configuration of the system, using direct condensation and dedicated fans, presents the models of all the components in the system and validation of the evaporator and fan model according to experimental results. A special attention has been paid to the effectiveness of the fan speed and condensation pressure control to increase the net power output of the direct condensed ORC. Road cycle simulations are run over an internal Volvo cycle that is suitable for the present application, using a "base" control strategy; afterwards a sensitivity analysis and optimization, involving the low pressure loop of the system, are performed, leading to better performance in terms of net power produced by the Rankine system.

Control of Supercritical Organic Rankine Cycle based Waste Heat Recovery System Using Conventional and Fuzzy Self-tuned PID Controllers

This research develops a supercritical organic Rankine cycle (ORC) based waste heat recovery (WHR) system for control system simulation. In supercritical ORC-WHR systems, the evaporator is a main contributor to the thermal inertia of the system, which is greatly affected by transient heat sources during operation. In order to capture the thermal inertia of the system and reduce the computation time in the simulation process, a fuzzy-based dynamic evaporator model was developed and integrated with other component models to provide a complete dynamic ORC-WHR model. This paper presents two control strategies for the ORC-WHR system: evaporator temperature control and expander output control, and two control algorithms: a conventional PID controller and a fuzzy-based self-tuning PID controller. The performances of the proposed controllers are tested for set point tracking and disturbance rejection ability in the presence of steady and transient thermal input conditions. The robustness of the proposed controllers is investigated with respect to various operating conditions. The results show that the fuzzy self-tuning PID controller outperformed the conventional PID controller in terms of set point tracking and disturbance rejection ability at all conditions encountered in the paper.

Model predictive control of an automotive waste heat recovery system

This paper proposes a model predictive control strategy for an Organic Rankine Cycle based waste heat recovery system. The control strategy uses a prediction model based on gain scheduling of local models, which results in a quadratic program to efficiently calculate the optimal control inputs. To ensure an optimal system operation, the reference values are obtained from a steady-state optimization. To capture a model-plant mismatch, the control concept features an EKF-based estimator of the model uncertainties. Simulations on a validated simulation model show that this control strategy can track the optimal reference very well, even for a large model-plant mismatch.

Towards working fluid properties and selection of Rankine cycle based waste heat recovery (WHR) systems for internal combustion engines – A fundamental analysis

Working fluid selection is one of the most important procedures in the design of Rankine cycle based waste heat recovery systems for internal combustion engines. The system’s performance, cost, and environmental impacts can be greatly influenced by the properties of its working fluid. In this work, we present an original formulation of a theoretical thermal efficiency model to fundamentally understand how the working fluid properties affect the thermal performance of the Rankine cycle based waste heat recovery systems for internal combustion engines. The derived theoretical thermal efficiency formula is validated under several different operating conditions. Overall very good agreements are achieved between the actual and theoretical approximated solutions. The results show that when the evaporation and condensation temperatures of the waste heat recovery system are fixed, the system’s thermal efficiency is simply governed by a non-dimensionalized parameter Jakob number. A working fluid with a smaller Jakob number is preferable in terms of system thermal efficiency. The observation is also further understood from a more fundamental physical perspective. Finally, a preliminary working fluid selection approach with a solid physics is proposed to screen the fluid candidates from the perspective of system performance.

An investigation of marine waste heat recovery system based on organic Rankine cycle under various engine operating conditions

Energy-saving, stricter regulations on pollution prevention, increasing energy efficiency and reducing operational costs have become common and primary issues for maritime industry, recently. One of the methods to improve these requirements onboard is to use a waste heat recovery system based on organic Rankine cycle. In this article, organic Rankine cycle–based waste heat recovery system for a chemical/oil tanker is investigated at different engine operating conditions by thermodynamic, environmental and economic analyses. The jacket cooling water, scavenge air, exhaust gas and combination of these three sources are used as the waste heat sources. R245fa is selected as the working fluid. The performance parameters of four different organic Rankine cycle–based waste heat recovery systems integrated with the main engine of the tanker are calculated and presented. The results show that by using the organic Rankine cycle–based waste heat recovery system onboard, it is possible to increase the overall thermal efficiency of the ship’s power plant by more than 6% and the combined organic Rankine cycle–based waste heat recovery system can meet all navigation electricity demand when the engine is operated at 82% maximum continuous rating or higher engine loads. In comparison with other organic Rankine cycle–based waste heat recovery systems, the combined organic Rankine cycle–based waste heat recovery system has the highest capital cost, but it has the shortest payback time. Furthermore, this system can reduce the ship emissions by about 6.9%.

Minimum variance control of organic Rankine cycle based waste heat recovery

Abstract In this paper, an online self-tuning generalized minimum variance (GMV) controller is proposed for a 100 KW waste heat recovery system with organic Rankine cycle (ORC). The ORC process model is formulated by the controlled autoregressive moving average (CARMA) model whose parameters are identified using the recursive least squares (RLS) algorithm with forgetting factor. The generalized minimum variance algorithm is applied to regulate ORC based waste heat recovery system. The contributions of this work are twofold: (1) the proposed control strategy is formulated under the data-driven framework, which does not need the precise mathematic model; (2) this proposed method is applied to handle tracking set-point variations and process disturbances by improved minimum objective GMV function. The performance of GMV controller is compared with the PID controller. The simulation results show that the proposed strategy can achieve satisfactory set-point tracking and disturbance rejection performance.