Review of Experimental Research on Supercritical and Transcritical Thermodynamic Cycles Designed for Heat Recovery Application

Abstract

Supercritical operation is considered a main technique to achieve higher cycle efficiency in various thermodynamic systems. The present paper is a review of experimental investigations on supercritical operation considering both heat-to-upgraded heat and heat-to-power systems. Experimental works are reported and subsequently analyzed. Main findings can be summarized as: steam Rankine cycles does not show much studies in the literature, transcritical organic Rankine cycles are intensely investigated and few plants are already online, carbon dioxide is considered as a promising fluid for closed Brayton and Rankine cycles but its unique properties call for a new thinking in designing cycle components. Transcritical heat pumps are extensively used in domestic and industrial applications, but supercritical heat pumps with a working fluid other than CO2 are scarce. To increase the adoption rate of supercritical thermodynamic systems further research is needed on the heat transfer behavior and the optimal design of compressors and expanders with special attention to the mechanical integrity.

Integrated Geothermal Energy Systems for Small-Scale Combined Heat and Power Production: Energy and Economic Investigation

“…Specifically, several factors affect the performance of ORC units: the thermal level of the external source, the working fluid, as well as the type of expander and operating conditions; therefore, the system architecture can vary significantly with the specific application and a standard setup is not completely established [11,32]. Moreover, the electric power of current geothermal systems is usually larger than 200 kW el with values also higher than 50 MW el [14,15,33,34]. On the other hand, few examples on small-scale ORCs are present, owing to higher specific costs and lower electric production [16,35].…”

“…The novelty of this work consists in the adoption of a transcritical ORC configuration with superheated conditions at the expander inlet. Transcritical systems show, in fact, higher performance compared to subcritical configurations [33,58] and provide a more efficient thermal exchange between the geofluid and organic fluid and lower irreversibility and exergy destruction [59]. Another benefit is the component downsizing due to the higher density of fluid.…”

“…The internal regeneration has been considered to maximise the electric power and achieve higher efficiency with respect to the mean value of typical geothermal plants (close to 12%) and isobutane has been selected as working fluid owing to its good performance and low specific costs, according to the literature [64][65][66][67]. In particular, isobutane is considered one of the organic fluids with zero ODP (ozone depletion potential), suitable for supercritical ORC applications [33]. Even though the relatively high pressures lead to higher operating costs, the integrated system reaches higher global efficiency for high thermal level geothermal sources.…”

Deep neural network approach to estimation of power production for an organic Rankine cycle system

“…In these literature studies, the main objective is one of improving ORC performance is by the use of different working fluids, changing turbine inlet parameters, and using different ORC design configurations (simple, regenerative, dual loop, etc.) [18,19]. In spite of the various experimental and theoretical studies, it is still not possible to precisely predict how much energy might be recovered and ORC performance due to the presence of various heat sources and dynamic variation of the heat source parameters.…”

Development of a Novel Shaft Dryer for Coal-Based Green Needle Coke Drying Process

“…It is indicated that the dryers widely used in other industries are not suitable for green coke drying. Given the advantageous material flow and heat transfer of shaft facilities [28][29][30], this work aims at designing a novel efficient drying system with a shaft dryer that is suitable for green coke drying, with sound energy usage [31] and low environmental impact [32,33]. In addition, key characteristics of the green coke, including particle size distribution [34], initial moisture content, vertex angle, pressure drop scheme [35], and the discharge characteristics, are essential to determine the parameters of the designed dryer [36].…”