Fuzzy Nonlinear Dynamic Evaporator Model in Supercritical Organic Rankine Cycle Waste Heat Recovery Systems

A Control-Oriented ANFIS Model of Evaporator in a 1-kWe Organic Rankine Cycle Prototype

This paper presents a control-oriented neuro-fuzzy model of brazed-plate evaporators for use in organic Rankine cycle (ORC) engines for waste heat recovery from exhaust-gas streams of diesel engines, amongst other applications. Careful modelling of the evaporator is both crucial to assess the dynamic performance of the ORC system and challenging due to the high nonlinearity of its governing equations. The proposed adaptive neuro-fuzzy inference system (ANFIS) model consists of two separate neuro-fuzzy sub-models for predicting the evaporator output temperature and evaporating pressure. Experimental data are collected from a 1-kWe ORC prototype to train, and verify the accuracy of the ANFIS model, which benefits from the feed-forward output calculation and backpropagation capability of the neural network, while keeping the interpretability of fuzzy systems. The effect of training the models using gradient-descent least-square estimate (GD-LSE) and particle swarm optimisation (PSO) techniques is investigated, and the performance of both techniques are compared in terms of RMSEs and correlation coefficients. The simulation results indicate strong learning ability and high generalisation performance for both. Training the ANFIS models using the PSO algorithm improved the obtained test data RMSE values by 29% for the evaporator outlet temperature and by 18% for the evaporator outlet pressure. The accuracy and speed of the model illustrate its potential for real-time control purposes.

Thermodynamic Investigation of an Integrated Solar Combined Cycle with an ORC System

An integrated solar combined cycle (ISCC) with a low temperature waste heat recovery system is proposed in this paper. The combined system consists of a conventional natural gas combined cycle, organic Rankine cycle and solar fields. The performance of an organic Rankine cycle subsystem as well as the overall proposed ISCC system are analyzed using organic working fluids. Besides, parameters including the pump discharge pressure, exhaust gas temperature, thermal and exergy efficiencies, unit cost of exergy for product and annual CO₂-savings were considered. Results indicate that Rc318 contributes the highest exhaust gas temperature of 71.2℃, while R113 showed the lowest exhaust gas temperature of 65.89 at 800 W/m², in the proposed ISCC system. The overall plant thermal efficiency increases rapidly with solar radiation, while the exergy efficiency appears to have a downward trend. R227ea had both the largest thermal efficiency of 58.33% and exergy efficiency of 48.09% at 800W/m². In addition, for the organic Rankine cycle, the exergy destructions of the evaporator, turbine and condenser decreased with increasing solar radiation. The evaporator contributed the largest exergy destruction followed by the turbine, condenser and pump. Besides, according to the economic analysis, R227ea had the lowest production cost of 19.3 $/GJ.

Exergy Analysis and Performance Improvement of a Subcritical/Supercritical Organic Rankine Cycle (ORC) for Exhaust Gas Waste Heat Recovery in a Biogas Fuelled Combined Heat and Power (CHP) Engine Through the Use of Regeneration

In the present study, a subcritical and supercritical regenerative organic Rankine cycle (rORC) was designed. The designed rORCs assist a combined heat and power (CHP) engine, the fuel of which is biogas produced from anaerobic digestion of domestic wastes in Belgium. R245fa was selected as the working fluid for both the subcritical and supercritical rORC. During the parametric optimisation, the net power production, mass flow rate, exchanged heat in the regenerator, total pump power consumption, thermal and exergetic efficiencies of rORC were calculated for varying turbine inlet temperatures and pressures. After parametric optimisation of the rORC, the results were compared with the results of the previous study, in which only a simple ORC is analysed and parametrically optimised. Moreover, the effect of the regenerator was revealed by examining all results together. Finally, the exergetic analysis of the best performing subcritical and supercritical rORC was performed. Furthermore, the results of the present and previous studies were considered together and it is clearly seen that the subcritical rORC shows the best performance. Consequently, by using the subcritical rORC, the disadvantages of the using simple ORC (low performance) and supercritical cycle (safety, investment) can be eliminated and system performance can be improved.