Expander Inlet Temperature Research Articles

Effects of evaporation parameters on recuperative transcritical organic Rankine cycle using binary mixture fluids

Abstract In this study, thermodynamic analysis was performed on basic and recuperative transcritical organic Rankine cycles by using five pure and six mixed fluids. The effects of evaporation parameters on the first- and second-law efficiencies (ηI and ηII) as well as power output were investigated. The results indicate that a recuperator had a positive effect on the ηI and ηII and negative effects on the specific power. The total irreversibility of the system was improved by the recuperator. However, the total irreversibility considerably increased with an increase in the expander inlet temperature (Texp,in) due to the significant increase in irreversibility in the condenser, particularly for working fluids with low critical temperatures, namely R134a, R1234yf and R290, and low proportions of R245fa and R600a in mixed fluids. For both the pure and mixed fluids, the specific power linearly increased with an increase in the expander inlet pressure (Pexp,in) and Texp,in. However, with an increase in Pexp,in, the ηI and ηII first increased and then decreased. Finally, for ηI and ηII, the effect of the recuperator increased with an increase in Texp,in even though the recuperator had a relatively small effect on the working fluids with high critical temperature, especially when Pexp,in was high.

Experimental study of Organic Rankine cycle system by using R141b as working fluid

Organic Rankine cycle (ORC) is one of the renewable energy to generate power at low temperatures; however, the thermal and physical properties data of the working fluid in this system are limited. In this regards, the experimental study by using R-141b as the working fluid and hot water (i.e. 50°C and 90°C) on the ORC system was conducted in order to evaluate the ORC performance via changing temperatures. Further, the air compressor was modified to act as a multi-vane expander in the ORC system. Energy and exergy analysis of ORC system was done by using Engineering Equation Solver (EES) program.
 It was found that the performance of the expander is acceptable and suitable for operating conditions. In addition, the heat source temperature has a direct effect on expander performance. The higher temperatures of the heat source led to an increase the expander inlet temperature. This system satisfied maximum thermal and exergy efficiency and they found equal to 1.8 % and 21%, respectively. Moreover, the rotation speed and power of expander are equal to 1200 RPM and 2.331 kW respectively. It was concluded that the working fluid R-141b is suitable for ORC system due to consider the working fluid that do not need high temperatures to evaporate.

Optimization of Small-Scale Natural Gas Liquefaction using Nitrogen Expander with Precooled Cycle

Nitrogen expander is the liquefaction process which suitable for small scale liquefied natural gas plant because its characteristic. However, the major issue of technology is low energy efficiency. In this study, optimization of small-scale natural gas liquefaction process using nitrogen expander with precooled cycles were conducted. The specific energy consumption is chosen as an objective function with decision variables are natural gas pressure after compression, nitrogen pressure after compression, inlet temperature of high pressure expander, evaporation temperature in precooling cycle, and type of precooling refrigerant. The refrigerant used for precooling cycle are propane, cyclopropane, isobutane, butane, and neopentane. The simulation and optimization processes are are performed by UniSim and GAMS software. The results show that integrating precooling cycle to the nitrogen expander system can reduce specific energy consumption up to 25, 24% and propane is the most effective precooling refrigerant.

Optimizations and comparison of three two-stage Rankine cycles under different heat source temperatures and NG distribution pressures

Two-stage Rankine cycles draw more and more attention with the increasing trade of LNG (liquefied natural gas) and the recovery of both the cold exergy of LNG and the thermal exergy of low temperature heat source. To figure out the best configuration of two-stage Rankine cycles, three mostly studied configuration, cascade two-stage ORC (organic Rankine cycle), parallel two-stage ORC and two-condensation ORC are optimized and compared under different heat source temperatures and different NG distribution pressures. Ten substances are selected as the working fluids. The evaporation, condensation and expander inlet temperatures of both ORCs and the LNG regasification pressure are optimized to obtain the maximum exergy efficiency. The results show that both the increase of heat source temperature and the decrease of NG distribution pressure can improve the exergy efficiencies greatly. The increase of heat source temperature not only increases the optimal key parameters but also affects the ranking of optimal fluids, while the increase of NG distribution pressure only affects the optimal parameters. Different from conventional Rankine cycles, there is also an optimal condensation temperature to match the heat absorption line of LNG and it increases with increase of the NG distribution pressure. The LNG regasification pressure is a key parameter which determines the proportion of power outputs between ORCs and direct expansion cycles. The thermodynamic performances of parallel two-stage ORC and two-condensation ORC are almost the same, which are obviously better than that of cascade two-stage ORC. Both parallel two-stage ORC and two-condensation ORC with ammonia as the working fluid achieve the maximum efficiency of 30.54% under the heat source temperature of 200 ℃ and the NG distribution pressure of 3 MPa. Two-condensation ORC is the optimum configuration with both good thermodynamic and economic performances. The lowest electricity production cost of two-condensation ORC achieved in this paper is 0.033$/kW·h. The environmental side effect caused by working fluid leakage is negligible compared with the saved CO2 emission via the electricity generation.

Dynamic performance and control strategy of CO2-mixture transcritical power cycle for heavy-duty diesel engine waste-heat recovery

Carbon dioxide mixture transcritical power cycle (CMTPC) is considered as a new promising technology for waste heat recovery (WHR), while there are still critical challenges arising from the transient fluctuations of heat sources when it comes to the heavy-duty diesel engines (HDDEs) applications. This paper presents a dynamic model of CMTPC systems, which is carefully validated against experimental data. Constant temperature, constant pressure and optimal control strategies are proposed to realize stable and optimal operation. The dynamic performance of the system with different control strategies is predicted under slow step change and transient change conditions. The results demonstrate that under slow step change conditions, the stability of optimal control system and constant pressure control system is better than that of constant temperature control system. In addition, the net power output keeps maximum under the optimal control because of the compromise between operating pressure and temperature. However, under transient conditions the control performance of optimal control is not as obvious as under slow step change conditions. Compared with open loop system, the improvement of system power by optimal control under slow step change is 2.31%, while that is only 0.07% under transient change condition. By contrast, it is found that the constant pressure control achieves the best power improvement of 0.58% under transient conditions because of the satisfactory control effect on operating pressure and relatively small fluctuations of expander inlet temperature. In a word, different control strategies behave obviously different performance under various conditions.

PARAMETRIC INVESTIGATION OF ORGANIC RANKINE CYCLE EVAPORATOR FOR LOW TEMPERATURE APPLICATIONS

The present work deals with the development of thermodynamic model of low temperature basic Organic Rankine Cycle (ORC) system and a chevron plate heat exchanger evaporator sub-model using Engineering Equation Solver (EES). Work output is evaluated using the ORC thermodynamic model, while the evaporator sub-model calculates the total surface area of the heat exchanger. Using these mathematical models, the effect of evaporation pressure, expander inlet temperature and pinch point temperature difference (PPTD) on the network output and evaporator cost are studied. In addition to this, the effect of plate spacing and plate width of chevron plate heat exchanger on pressure drop and evaporator cost are analyzed in detail. Finally, thermodynamic and geometric optimization is carried out using genetic algorithm to identify the optimum parameters at which the network output is maximized and pressure drop in the evaporator is minimized. Sensitivity analysis showed that optimum evaporator pressure existed at which network output is maximum. Thermodynamic optimization showed that work output was maximum (5.03 kW) at evaporator pressure of 5.77 bar. No improvement in the work output was seen with increase in PPTD and expander inlet temperature. Increase in plate width and plate spacing led to increase in evaporator cost and decrease in pressure drop.

Working Fluid Dependence on Source Temperature for Organic Rankine Cycles

Abstract This paper presents the results of numerical simulations of organic Rankine cycles (ORCs) for low-grade heat source temperature in the range of 373–653 K for 20 working fluids. The goal of the study is to determine the importance of the level of the source temperature in the selection of working fluids and operation conditions. As a performance indicator, a function of the net power, the internal and external exergy efficiencies, and the exergy efficiency of the evaporator is used. The results show that there is a strong correlation between the level of the source temperature and the critical temperature, between the expander inlet temperature and the source temperature, and between the expander inlet pressure and the critical pressure of the working fluids tested. The study shows that once the source temperature level is known, it is possible to select the working fluid and the conditions at the expander entrance.

Investigation of exergy efficiency of organic Rankine cycle

Organic Rankine cycle (ORC) which recovers waste heat in the temperature range of 80°C-140°C was investigated. Exergy efficiencies of various components and ORC system were paid great attention. The working fluids of R245fa and R600a are used. It is found that, for saturated ORCs, the expander inlet temperature has the optimum value, so the system exergy efficiency is maximum. With the increase of heat source temperature, the optimal inlet temperature of the expander is also increased. And also for saturated ORCs, the exergy efficiencies of evaporator and expander are highest efficiency, when evaporator exergy efficiency is increased with increase of heat source temperatures, the expander exergy efficiency is unchanged. The condenser decreased exergy efficiencies by increasing the heat source temperatures.

Enhancing refrigeration capacity of turbo expander by means of multipoint design optimization

Turbo expander produces cold energy in cryogenic Air Separation Unit (ASU) to meet the requirement of liquefied air fractional distillation. The study is initiated by recent commissioning operation of a single-point designed turbo expander in the 1600 Nm3/h oxygen yield ASU, where the online measured cold energy at an off-design operation point is under the requirement. To enhance the expander refrigeration capacity over a wide-spread condition and support the ASU flexible operations, a novel multipoint design optimization method is proposed. Characterization of the ASU expander condition point is done by allowing for the expander real status in the operational ASU; a 3-factors and 5-levels’ uniform design experimentation scheme is proposed and used to identify the multiple design points in the 3D space (formed by the expander inlet pressure and temperature, and shaft speed) and they are used to establish the multipoint objective function; adaptive surrogate model-based optimization algorithms are incorporated to enable the aim-oriented global optimal searching with considerably reduced CFD computations. The multipoint optimized expander impeller is manufactured and used to replace the original. In the restarted ASU, the expander operates at a new condition point but produces high-level overall performance and sufficient cold energy for liquefied air fractional distillation.

Exergoeconomic analysis of a novel trigeneration system based on organic quadrilateral cycle integrated with cascade absorption-compression system for waste heat recovery

The present research proposes a novel trigeneration system for cooling, heating, and power generation which is consisted of organic quadrilateral cycle (QLC) and cascade absorption – compression system. The system is simulated and studied from energy, exergy, and exergoeconomic viewpoints. Cyclohexane, LiBr-H2O, and R410a are respectively used as working fluids for QLC, Absorption refrigeration system (ARS), and Compression refrigeration system (CRS) in the combined system. Using QLC instead of simple organic Rankine cycle (ORC) in the combined system makes it possible to generate electricity besides improvement of total system performance from energy and exergy viewpoints for the same input values. According to the base case results, the unit cost of electricity is 36.9 $/GJ and it has much less value compared with unit cost of heating and cooling which are equal to 101 $/GJ and 84.7 $/GJ, respectively. Therefore, more electricity production by employing QLC instead of ORC is economical. The results of system parametric analysis show that by variation of QLC expander inlet temperature and QLC condensation temperature while cooling rate decreases, the other output parameters such as output electricity, heating rate, exergy efficiency, and total cost rate improve. Selection of these two input parameters depends on demands. On the other hand, less ARS evaporation temperature and higher CRS evaporation temperature in the allowed range lead to better performance of the system.

Mapping scroll expander performance for organic working fluids using dimensionless parameters in Ns-Ds diagram

This paper presents an analysis of single-stage scroll expander performance for pure fluids and their zeotropic mixtures in supercritical conditions using dimensionless parameters, namely specific speed (Ns) and specific diameter (Ds). Scroll geometries with different aspect ratios were modeled for a range of expander inlet temperatures. The expander efficiency was modeled accounting for losses due to leakage, friction, and over- and under-expansion. The expander efficiency was plotted as a function of two dimensionless parameters to analyze the applicability domain of scroll expanders. For a particular expander inlet temperature (Tin), zeotropic mixtures result in more compact scroll geometries than pure fluids, leading to reduced losses and better expander efficiency. Any increase in Tin results in larger scrolls leading to higher leakage and thereby lower efficiency. At suitable operating conditions, an optimized scroll expander design can achieve expansion efficiency as high as 75%. Sub-optimal scroll designs for a given application lead to lower expansion efficiency due to over- or under-expansion losses.

Analysis and assessment of partial re-liquefaction system for liquefied hydrogen tankers using liquefied natural gas (LNG) and H2 hybrid propulsion

Boil-off gas (BOG) is inevitable on board liquefied hydrogen tankers and must be managed effectively, by using it as fuel, re-liquefying it or burning it, to avoid cargo tank pressure issues. This study aims to develop a BOG re-liquefaction system optimized for l60,000 m3 liquefied hydrogen tankers with an LNG and hydrogen hybrid propulsion system. The proposed system comprises hydrogen compression and helium refrigerant sections with 2 J–Brayton cascade cycles. Cold energy recovery from the fuels and feed BOG exiting the cargo tanks was used. The system exhibits a coefficient of performance (COP) of 0.07, a specific energy consumption (SEC) of 3.30 kWh/kgLH2, and exergy efficiency of 74.9%, with the hydrogen BOG entering the re-liquefaction system at a feed temperature of −220 °C. The theoretical COP and SEC values at ideal conditions were 0.09 and 2.47 kWh/kgLH2, respectively. The effects of varying the hydrogen compression pressure, inlet temperature of the hydrogen expander, feed hydrogen temperature and helium compression pressure were investigated. Additionally, the LNG-to-hydrogen fuel ratio was adjusted to satisfy the Energy Efficiency Design Index (EEDI) Phase 2 and 3 emission requirements.

Investigation on performance improvement of small scale compressed-air energy storage system based on efficient radial-inflow expander configuration

Distributed power generation systems powered by compressed air energy storage can be considered as one of the effective solutions for high energy demand. In this regard, the key component for such systems is the expander where the overall system efficiency has been affected by the expander performance. Therefore, this work outlines a novel integrated methodology to predict the performance characteristics of the radial-inflow expander for small scale compressed air energy storage CAES system for low mass flow rate applications. The integrated methodology combines the mean-line design and 3D CFD simulations for the expander with thermodynamics analysis for CAES system. The expander mean-line design is verified against the data available in open literature and compared with the delivered results from the CFD simulations using ANSYS-CFX. Moreover, comprehensive parametric studies are carried out based on the CFD analyses under design and off-design conditions in terms of rotational speed, expander inlet temperature and expansion ratio in order to investigate the effect of those conditions beside the geometric parameters on the expander and system performance. The delivered results from CFD simulations and CAES system analyses highlighted that radial-inflow expander with CAES can be used for distributed power generation. The expander performance maps based on CFD analyses exhibited that the maximum power and efficiency were 3.282 kW and 76.70% respectively with CASE system efficiency of 12.46% and the system round trip efficiency of 59.08%.

Performance enhancement of two-stage condensation combined cycle for LNG cold energy recovery using zeotropic mixtures

The isothermal phase transition process of pure working fluids cannot effectively match the liquefied natural gas (LNG) gasification process, resulting in low efficiency of LNG cold energy power generation systems. In order to improve the temperature matching characteristics, mixed working fluids with a temperature glide during the phase change process can be adopted. In our previous study, the two-stage condensing process also effectively improved the temperature matching characteristics; thus, this paper presents a two-stage condensation combined cycle using zeotropic mixtures, and the effects of the type and number of components for mixed refrigerants on the two-stage condensing combined cycle system performance are studied. With the net power output as the objective function, the evaporation temperature, condensing temperatures, LNG expander inlet temperature, and working fluid mole fractions are optimised by the genetic algorithm. The results demonstrate that the net power output of n-C5H12 is the largest among the studied pure fluids. The net power output of the binary mixed working fluid at the optimum mole fractions is obviously superior to that of pure working fluids. The system performance is improved when the hydrocarbon mixture is selected as a working fluid, and the optimum number of components is three.

Payback period investigation of the organic Rankine cycle with mixed working fluids to recover waste heat from the exhaust gas of a large marine diesel engine

The aim of this study is to investigate the payback period and the payback-period reduction of the organic Rankine cycle (ORC) with mixtures for waste heat recovery from the exhaust gas of a large marine diesel engine. Working fluids with zero-ozone-depletion potential, such as R236fa, R245fa, R600, R1234ze, and their mixtures, are selected to analyze the economic and thermodynamic performances in the conversion cycle. The optimal mass fractions of the mixed working fluids R236fa/R245fa, R236fa/R1234ze, and R600/R1234ze for the lowest payback period with the corresponding optimal expander inlet temperature and condenser outlet temperature of the ORC have been obtained. R600/R1234ze possesses the best performance in terms of payback period. Under optimal conditions, the payback period of the ORC with R600/R1234ze is the lowest and is shorter than that with R236fa, R245fa, R600, R1234ze, R236fa/R245fa, and R236fa/R1234ze by 7.55%, 6.47%, 9%, 9.17%, 0.9%, and 2.88%, respectively. To evaluate the economic potential of mixed working fluids using different types of expander such as turbine, scroll, and screw expanders properly, the relationships between the isentropic efficiencies of the expander and their corresponding optimal expander inlet temperature and optimal mass fraction are obtained. Optimal correlations are proposed to conveniently predict the optimal mass fractions of the mixtures R236fa/R245fa, R236fa/R1234ze, and R600/R1234ze in the ORC and to assess the reduction of their payback periods for the waste heat recovery of a large marine diesel engine. The results highlight the significant potential of the mixtures used in the ORC for performance improvement and demonstrate the importance of mixture assessment for reducing the payback period in further work.

Deep Water Cooled ORC for Offshore Floating Oil Platform Applications

Normal 0 21 false false false ES X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Normal Tablo; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:Times New Roman,serif; mso-ansi-language:EN-US; mso-fareast-language:EN-US;} Due to global warming, environmental pollution and cost reduction, increasing efficiency of electricity conversion has become a key issue for the offshore market. This paper proposes an Organic Rankine Cycle (ORC), which uses heat waste from exhaust gases of an FPSO (Floating, Production, Storage and Offloading unit) as heating source, and deep ocean water as cooling source. A genetic algorithm optimization was conducted targeting maximization of net power output, by taking in to consideration of 23 working fluids. Expander inlet temperature and pressure were set as independent variables. The analysis encompasses subcritical or supercritical conditions and recuperation was included in a second version of the system as an option. The first configuration presented ethanol as optimal fluid, followed by toluene and the second configuration indicated cyclohexane followed by ethanol. Use of recuperation, when feasible, increased power output specially for cycles operating with dry and isentropic fluids, presenting an average contribution of 22.7%. Net power and efficiency results from ORC using deep sea water in condenser were presented and compared with ORC using shallow ocean water as cooling source and with Carnot efficiency operating under the same temperatures. Use of deep water raised net power output by 23.3% (cyclohexane recuperative ORC) and 12.5% (ethanol non-recuperative ORC) for the optimal configurations.

Optimization of organic Rankine cycle used for waste heat recovery of construction equipment engine with additional waste heat of hydraulic oil cooler

The aim of this study is to provide an optimal organic Rankine cycle (ORC) system for waste heat recovery (WHR) from a construction equipment engine. Construction equipment machines have very high annual fuel consumption, and most of the engine power is used to drive a hydraulic oil pump, thus producing additional waste heat from the hydraulic oil cooler. In order to compare the WHR of the construction equipment engine with that of a conventional engine without the heat of the hydraulic oil, four different single-loop ORC cases were considered and optimized for maximum net power. The results of this study showed that at the half-load condition as the primary operating condition, the use of additional waste heat from the hydraulic oil can increase the net power output of the ORC in the construction equipment engine by 11% despite at a low expander inlet temperature without a recuperator as compared to the system without the heat of hydraulic oil. However, the use of waste heat from the hydraulic oil increased the cost of the system owing to the preheater used by hydraulic oil and the increased condenser size.

Thermodynamic and multi-objective optimisation of solar-driven Organic Rankine Cycle using zeotropic mixtures

ABSTRACTThis paper communicates the performance of low-grade solar heat source powered Organic Rankine Cycle (ORC). To investigate the system performance, first law and exergetic efficiencies, power output are evaluated and compared for zeotropic mixtures of (iso)butane/(iso)pentane and cyclohexane/R123. The results indicate that there exists an optimal mass fraction for which energy and exergetic efficiencies, and power output are maximum corresponding to a given value of expander inlet temperature compared with pure fluids. However, the specific volume flow ratio of the expander is higher for zeotropic mixtures; which results in a lower economy of mixtures than pure fluids. The use of an internal heat exchanger in the system improves cycle performance. Moreover, the multi-objective genetic algorithm further improves the performance of ORC and exhibits better exergetic efficiency 51–57% and 0–14.09% reduction in lower expander-specific volume flow ratio (v6/v5) than thermodynamically optimised ORC.

Thermo-economic analysis of the transcritical organic Rankine cycle using R1234yf/R32 mixtures as the working fluids for lower-grade waste heat recovery

The aim of this study is to investigate the thermo-economic performance of the transcritical organic Rankine cycle (TORC) system using R1234yf/R32 mixtures as the working fluids for the lower-grade waste heat recovery (WHR). The components of R32 and R1234yf are selected due to their zero ozone depletion potential, lower global warming potential and complementary thermodynamic properties. The influences of the mass fractions of R1234yf/R32 mixtures, isentropic efficiencies of the expander, condensation temperature, turbine inlet pressure and temperature on performances have been investigated. The results show that R1234yf/R32 at optimal mass fraction is superior to pure R1234yf and pure R32 by 1.46% and 4.88% in thermo-economic performance, respectively. The optimal compositions of mixtures and the optimal temperature entropy diagrams are obtained to fit the various isentropic efficiencies possessed by the different types of expanders. In thermo-economic evaluation, the lower the condensation temperature is, the larger the optimal mass fraction of R32 in the mixtures will be. The increase of optimal expander inlet pressure and temperature are proportional to that of mass fraction of R32 in mixtures. The relationships among mass fraction, optimal expander inlet pressure and temperature and performance are expressed as the correlations for convenient design in lower-grade WHR.

Development of air-cooled compact Organic Rankine Cycle power generation technology utilizing waste heat

As the effective utilization method of unused heat energy between 100 and 300 degree-C in the industrial sector, Organic Rankine Cycle (ORC) was selected from the viewpoint of high efficiency. The prototype of air-cooled compact ORC electric power generation system for 1kW class was evaluated in variation of the ambient temperature of condenser and the inlet temperature of expander. In the experimental results, at the expander inlet temperature of 175 degree-C and the ambient temperature of 20 degree-C for condenser, the generated power by the expander is 1,027W and the gross power generation efficiency is 10.3%. The net power generation efficiency, considering the input power of auxiliary equipment such as pumps and fans, is 9.0%. In the result of energy balance analysis, power consumptions of the pump and the fan are small and almost of the generated power is effectively available.