Conventional Rankine Cycle Research Articles

A numerical model for the CO2–sodium chemical interactions in Sodium Fast nuclear Reactors

Supercritical CO2 (sCO2) Brayton cycles have gained interest in the frame of Sodium-cooled nuclear Fast Reactors (SFRs), as an alternative to the conventional water Rankine cycles. If CO2 leaks inside the CO2–Na heat exchanger, an underexpanded CO2-into-liquid-sodium jet is formed. CO2 chemically reacts with sodium, following an exothermic reaction which forms mainly solid products. In order to develop a model to numerically reproduce the jet development, a detailed description of the CO2–Na chemical reaction mechanism must be investigated. In this paper, a chemical reaction model at the dispersed phase scale between CO2–sodium, inside an underexpanded CO2-into-sodium jet, is presented. The model considers the reaction between a sodium droplet with the surrounding CO2 environment for the region close to the leakage, where mist flow is supposed to exist, and between a CO2 bubble with the surrounding liquid sodium environment for the region further downstream the leakage, where bubbly flow takes place. The depletion rate for a single particle (droplet or bubble) is determined, as a function of the main influencing parameters, such as temperature, droplet slip velocity, bulk mass fractions, and the chemical kinetics.

Thermodynamic optimisation and analysis of four Kalina cycle layouts for high temperature applications

The Kalina cycle has seen increased interest in the last few years as an efficient alternative to the conventional steam Rankine cycle. However, the available literature gives little information on the algorithms to solve or optimise this inherently complex cycle. This paper presents a detailed approach to solve and optimise a Kalina cycle for high temperature (a turbine inlet temperature of 500 °C) and high pressure (over 100 bar) applications using a computationally efficient solution algorithm. A central receiver solar thermal power plant with direct steam generation was considered as a case study. Four different layouts for the Kalina cycle based on the number and/or placement of the recuperators in the cycle were optimised and compared based on performance parameters such as the cycle efficiency and the cooling water requirement. The cycles were modelled in steady state and optimised with the maximisation of the cycle efficiency as the objective function. It is observed that the different cycle layouts result in different regions for the optimal value of the turbine inlet ammonia mass fraction. Out of the four compared layouts, the most complex layout KC1234 gives the highest efficiency. The cooling water requirement is closely related to the cycle efficiency, i.e., the better the efficiency, the lower is the cooling water requirement.

Preliminary Design and Simulation of a Turbo Expander for Small Rated Power Organic Rankine Cycle (ORC)

Nowadays, the Organic Rankine Cycle (ORC) system, which operates with organic fluids, is one of the leading technologies for “waste energy recovery”. It works as a conventional Rankine Cycle but, as mentioned, instead of steam/water, an organic fluid is used. This change allows it to convert low temperature heat into electric energy where required. Large numbers of studies have been carried out to identify the most suitable fluids, system parameters and the various configurations. In the present market, most ORC systems are designed and manufactured for the recovery of thermal energy from various sources operating at “large power rating” (exhaust gas turbines, internal combustion engines, geothermal sources, large melting furnaces, biomass, solar, etc.); from which it is possible to produce a large amount of electric energy (30 kW ÷ 300 kW). Such applications for small nominal power sources, as well as the exhaust gases of internal combustion engines (car sedan or town, ships, etc.) or small heat exchangers, are very limited. The few systems that have been designed and built for small scale applications, have, on the other hand, different types of expander (screw, scroll, etc.). These devices are not adapted for placement in small and restricted places like the interior of a conventional car. The aim of this work is to perform the preliminary design of a turbo-expander that meets diverse system requirements such as low pressure, small size and low mass flow rates. The expander must be adaptable to a small ORC system utilizing gas of a diesel engine or small gas turbine as thermal source to produce 2–10 kW of electricity. The temperature and pressure of the exhaust gases, in this case study (400–600 °C and a pressure of 2 bar), imposes a limit on the use of an organic fluid and on the net power that can be produced. In addition to water, fluids such as CO2, R134a and R245fa have been considered. Once the operating fluids has been chosen, the turbine characteristics (dimensions, input and output temperature, pressure ratio, etc.) have been calculated and an attempt to find the “nearly-optimal” combination has been carried out. The detailed design of a radial expander is presented and discussed. A thermo-mechanical performance study was carry out to verify structural tension and possible displacement. On the other hand, preliminary CFD analyses have been performed to verify the effectiveness of the design procedure.

Exergy Analysis of Coal-Fired Power Plants in Two Cooling Condition

The distribution of exergy destruction is different in power plant systems with water cooled condenser and air cooled condenser. A detailed comparison based on a conventional Rankine cycle with two different cooling configurations is carried out in this paper in an exergy perspective. The inefficiency of the overall systems is analyzed in the same amount of heat transfer capacity condition, it shows that the distribution of exergy destruction among components is similar in both conditions. And this study of energy consumption is benefit for realization of auto-efficient-working power plants in future.

A new technology for the combined production of charcoal and electricity through cogeneration

This paper presents an historical approach on the development of the existing biomass carbonization technologies in industrial operation in Brazil, the biggest charcoal producing country in the world. The gravimetric yield of charcoal from wood does not usually surpass 25%; the time of each operation cycle is more than seven days; and less than 50% of the energy contained in the feedstock is transformed into charcoal – the rest is discharged into the environment. The electricity generation associated with charcoal production is nowadays inexistent in Brazil. This paper presents the development of an industrial technology of semi-continuous pyrolysis process, characterized by using metallic kilns with forced exhaust system: the Rima Container Kiln (RCK). The results of the test runs are related to 5 m3 and 40 m3 kilns, with a thermal power of 200 kW (pilot scale: 5 m3) and 3000 kW (industrial scale: 40 m3). The low heating value of the pyrolysis gases is 670 and 1470 kJ/m³, respectively.The main results are: a 3 h carbonization time; an average productivity per kiln of 1 ton of charcoal per hour; and a gravimetric yield of 35%. In this paper, four scenarios for the conversion of exhaust gases and tar into electricity were evaluated: the Conventional Rankine Cycle (CRC) and the Organic Rankine Cycle (ORC), each one with and without forest residues utilization. It is shown that the best economic indicators correspond to the scenario where ORC technology is used. The electricity generation cost is around U$30/MWhe for ORC and US$40/MWhe for CRC.

Design and modeling of an advanced marine machinery system including waste heat recovery and removal of sulphur oxides

Stricter legislation on sulphur oxide emissions from ships will apply as of 2015 in emission control areas. Consequently, prices on low sulphur fuels are expected to increase drastically, providing a strong incentive to find alternative ways of complying with the legislation and improving the efficiency of machinery systems. The wet sulphuric acid process is an effective way of removing flue gas sulphur oxides from land-based coal-fired power plants. Moreover, organic Rankine cycles (ORC) are suitable for heat to power conversion for low temperature heat sources. This paper describes the design and modeling of a highly efficient machinery system which includes the removal of exhaust gas sulphur oxides. The system consists of a two-stroke diesel engine, the wet sulphuric process for sulphur removal, a conventional steam Rankine cycle and an ORC. Results of numerical modeling efforts suggest that an ORC placed after the conventional waste heat recovery system is able to extract the sulphuric acid from the exhaust gas, while at the same time increase the combined cycle thermal efficiency by 2.6%. The findings indicate that the technology has potential in marine applications regarding both energy and the environment; however, further research and development efforts are needed.

The CHEST (Compressed Heat Energy STorage) concept for facility scale thermo mechanical energy storage

Electric energy storage is considered to become a key element of the future electricity infrastructure. PTES (Pumped thermal electricity storage) represents an emerging thermo mechanical storage technology based on the transformation of low temperature heat by surplus electricity. After transformation, the high enthalpy heat is stored. During the discharge process, this heat is used to drive a thermodynamic cycle generating electricity. This concept allows storage of energy in the multi-MW range for several hours without any specific geographical requirements. Various combinations of thermodynamic cycles and storage types have been suggested for implementation using either low temperature storage (<200 °C) or high temperature storage (>500 °C). In contrast to these PTES concepts, the Compressed Heat Energy STorage (CHEST) concept presented in this paper is based on a medium temperature conventional Rankine cycle combined with a latent heat storage unit according to the current state of the art. This concept attains an efficiency of 70% while the maximum temperature is below 400 °C. The integration of heat provided by low temperature sources during the charging process represents an additional option of the CHEST concept; losses can be compensated, the electric work delivered during the discharge process might even outweigh the work needed during the charging process.

Performance of a 5 kWe Solar-only Organic Rankine Unit Coupled to a Reverse Osmosis Plant

Organic Rankine Cycle (ORC) systems are one of the most promising energy conversion technologies available for remote areas and low temperature energy sources. An ORC system works like a conventional Rankine cycle but it uses an organic compound as working fluid, instead of water. A small ORC unit coupled with a solar thermal energy system could be used to convert solar thermal energy into electricity in remote areas, offering an alternative to Photovoltaic (PV) systems to provide the energy required by desalination applications like reverse osmosis (RO). In this work an analysis of the performance of a specific solar desalination ORC system at part load operation is presented, in order to understand its behavior from a thermodynamic perspective and be able to predict the total water production with changing operation conditions. The results showed that water production is around 1.2 m3/h, and it is stable during day and night thanks to the thermal storage and only under bad irradiance circumstances the production would stop.

Energy and Exergy Analysis of the Kalina Cycle for Use in Concentrated Solar Power Plants with Direct Steam Generation

In concentrated solar power plants using direct steam generation, the usage of a thermal storage unit based only on sensible heat may lead to large exergetic losses during charging and discharging, due to a poor matching of the temperature profiles. By the use of the Kalina cycle, in which evaporation and condensation takes place over a temperature range, the efficiency of the heat exchange processes can be improved, possibly resulting also in improved overall performance of the system. This paper is aimed at evaluating the prospect of using the Kalina cycle for concentrated solar power plants with direct steam generation. The following two scenarios were addressed using energy and exergy analysis: generating power using heat from only the receiver and using only stored heat. For each of these scenarios comparisons were made for mixture concentrations ranging from 0.1 mole fraction of ammonia to 0.9, and compared to the conventional Rankine cycle. This comparison was then also carried out for various turbine inlet pressures (100bar to critical pressures). The results suggest that there would be no benefit from using a Kalina cycle instead of a Rankine cycle when generating power from heat taken directly from the solar receiver. Compared to a baseline Rankine cycle, the efficiency of the Kalina cycle was about around 5% lower for this scenario. When using heat from the storage unit, however, the Kalina cycle achieved efficiencies up to 20% higher than what was achieved using the Rankine cycle. Overall, when based on an average assumed 18hours cycle, consisting of 12hours using heat from the receiver and 6hours using heat from the storage, the Kalina cycle and Rankine cycle achieved almost equal efficiencies. A Kalina cycle operating with an ammonia mole fraction of about 0.7 returned an averaged efficiency of about 30.7% compared to 30.3% for the Rankine cycle.

Technical Assessment of a Renewable Aided Power Plant for Different Operational Load

Renewable aided power generation (RAPG) is capable of integrating low to medium temperature renewable resources in the case of 90-260°C into a conventional Rankine cycle power plant to replace the extraction steam of power plant. In a RAPG plant, renewable fluid is used to preheat the feed water of power plant, instead of the extraction steam, thus the replaced extraction steam expand further in steam turbine to generate electricity. The renewable fluid can be used to replace the extraction steam of power plant at different extraction points and replace different percentage of extraction steam. In the current study, a model of RAPG plant has been developed in order to calculate the technical and economic assessment of RAPG plant for different operational conditions. The overall efficiency of the RAPG plant and the renewable thermal share of power generation with different replacement of extraction steam at different operational load have been studied in this paper. A 1000 MW ultra supercritical power plant has been used as case study, the power plant at 100%, 75%, 50%load have been studied in this paper.

VHTR-based power plants' performance enhancement using Rankine cycles

When very high temperature reactors operate as power plants where helium is being considered as cooling fluid for the primary loop, cost effective performance enhancement can be achieved under safety operating conditions by means of alternative thermal cycles to the conventional steam Rankine and combined cycles. The proposed improvements require the implementation of some Rankine cycle structures operating with carbon dioxide condensed at quasi-critical conditions combined with Rankine cycles coupled in series where carbon dioxide or water are used in order to achieve cooling capacity. Under this structure several cycles are proposed and studied so that according to the chosen performance criteria, a cycle structure is available. The results of the study show that plant structures composed by a high temperature topping Rankine cycle operating with carbon dioxide followed by a low temperature bottoming Rankine coupled in series allow the choice of a plant structure capable of advantageously rendering at least one of the following characteristics without violating safety standards: High net efficiency (from actual 48% to more than 56%) by sacrificing cooling capacity and specific power or high cooling capacity and specific power by sacrificing efficiency.

Converting energy from fusion into useful forms

If fusion power reactors are to be feasible, it will still be necessary to convert the energy of the nuclear reaction into usable form. The heat produced will be removed from the reactor core by a primary coolant, which might be water, helium, molten lithium-lead, molten lithium-containing salt, or CO2. The heat could then be transferred to a conventional Rankine cycle or Brayton (gas turbine) cycle. Alternatively, it could be used for thermochemical processes such as producing hydrogen or other transport fuels. Fusion presents new problems because of the high energy neutrons released. These affect the selection of materials and the operating temperature, ultimately determining the choice of coolant and working cycle. The limited temperature ranges allowed by present day irradiated structural materials, combined with the large internal power demand of the plant, will limit the overall thermal efficiency. The operating conditions of the fusion power source, the materials, coolant, and energy conversion system will all need to be closely integrated.

Failure Analysis of a Low-Temperature Energy Conversion System Using Organic Rankine Cycles

It is widely believed that Rankine cycle power plant using organic fluids as the working medium has advantages over conventional Rankine cycle with water steam as the working medium in low-to-medium temperature heat conversion. It is also testified in the market. However, besides the integration of the cycle and the characteristic of the working fluid, the design and debugging of the energy conversion unit are also important part in acquiring good performance. In this research some phenomenon of failure is investigated. Accordingly, the theoretical and practical reasons and solutions are obtained. It provides good guideline on the design and optimization of the energy conversion unit.

Experimental Study and Numerical Simulation of a Regenerative ORC Utilizing Low-Grade Heat Source

In this paper, the performance of the regenerative organic rankine cycle (ORC) working with R123 is experimentally analyzed at different heat source temperatures of approximately 85, 95, 110, and 130°C. The higher heat source temperature leads to higher turbine inlet temperature, turbine inlet pressure, and turbine rotation speed. The regenerator and the increment of turbine inlet temperature can both increase the efficiency of the system. The experimental data of ORC are compared with that of the conventional Rankine cycle (CRC), which employs water as the working fluid. The results indicate that the thermal efficiency and the turbine isentropic efficiency of the ORC are higher than that of the CRC by approximately 5.9 and 24%, respectively. A numerical model is built by interconnecting different submodels: a turbine model, a volumetric pump model, and the heat exchanger models. The numerical results show a good agreement with the experimental data in terms of system efficiency. The model is finally used to calculate the pressure drop and pump power of the system.

Thermodynamic comparison of organic Rankine cycles employing liquid-flooded expansion or a solution circuit

Two modifications to a conventional Organic Rankine Cycle (ORC) are investigated: an Organic Rankine Cycle with Liquid-Flooded Expansion (ORCLFE), and an Organic Rankine Cycle with Solution Circuit (ORCSC). The ORCLFE involves “flooding” the expansion device with a liquid that is in thermal equilibrium with the primary working fluid, while simultaneously expanding the primary working fluid through the same device. The ORCSC employs a zeotropic mixture consisting of two components with a large boiling point difference. The more volatile component in the vapor phase is separated from the absorbent in the liquid phase; the vapor then flows through the expansion device, whereas the liquid absorbent gives rise to a regenerative solution circuit.A thermodynamic model is used to compare these modified ORCs with conventional ORC technology for a range of working fluids including ammonia, water, CO2, acetone, pentane, R134a and R245fa. The working fluid pairs considered for the ORCSC are ammonia–water and CO2–acetone. Based purely on thermodynamic considerations, the conventional ORC using water as the working fluid is found to be more efficient than ORCs that use other working fluids. It yields almost 65% of the Carnot efficiency for a source and sink temperature of 200 °C and 20 °C, respectively. However, the use of water requires low expander exhaust quality, large pressure ratios, and a large expander due to its low density at the expander exhaust. Thus, the practical challenges of using water as a working fluid at typical ORC input temperatures may make its use prohibitive. The ORCLFE always leads to improved cycle efficiency when compared to an ORC for a given working fluid, but it requires the use of a positive displacement expander. The ORCSC shows the lowest efficiencies for the working fluid pairs studied. There are significant practical advantages intrinsic to both the ORCLFE and the ORCSC. For example, the more isothermal expansion of the ORCLFE eliminates the concern of low expander exhaust quality for wet working fluids. The ORCSC provides the ability to use the two-phase temperature glide to match source and sink temperature profiles, facilitates intrinsic capacity control, and can have significantly lower working pressures than an ORC. Ultimately, the overall best choice of cycle and working fluid is highly application-specific and should balance the tradeoffs between efficiency and practical concerns. The thermodynamic analysis presented in this work represents a step toward identifying an optimal ORC solution for an application where the temperature glides of the source and sink fluids are sufficiently small to approximate a thermal energy reservoir.

Thermodynamic performance of Kalina cycle system 11 (KCS11): feasibility of using alternative zeotropic mixtures

With the ever increasing demand for energy, exploiting low-temperature heat sources has seen significant interest recently. The conventional organic Rankine cycle (ORC) is a typical approach used to exploit low-temperature heat sources but suffers from low efficiency. The Kalina cycle is a reversed absorption cooling system that normally utilizes an ammonia-water binary mixture as the working fluid. This paper investigates, using thermodynamic modelling, the performance of Kalina cycle system 11 (KCS11) used for low-temperature heat sources below 2008C compared with the ORC based on pure ammonia and R134a. The cycle performance was investigated at various operating conditions including the evaporator pressure of 10-50 bars, heat source temperature of 333-473 K, heat sink temperature of 283 K and in the case of KCS11 various ammonia mass fractions at the evaporator outlet. Results show that the KCS11 can produce up to 40% increase in the efficiency compared with the ORC when using ammonia and up to 20% increase when using R134a. Although the ammonia-water working pair has zero ozone depletion potential (ODP) and very low global warming potential (GWP), it is toxic and needs special safety procedures against leak as ammonia is part of this binary mixture. Therefore, further investigation was carried out to explore the feasibility of using alternative working pairs that are non-toxic and outperform the ammonia-water pair for the Kalina cycle. Nineteen working pairs were investigated and results showed that propane and propylene-based mixtures have the potential to replace the ammonia-water pair in the KCS11.

Energy and exergy analysis of an absorption power cycle

The thermal efficiency of a power cycle is drastically reduced when the temperatures of the heating and cooling fluids approach, which is the case of cycles run by waste heat streams and low temperature solar or geothermal systems. In this work, an absorption LiBr–H2O power cycle is analysed and compared to a conventional Rankine cycle operating between two heat sources at similar temperatures. The absorption power cycle is found to improve the thermal efficiency, and this improvement in efficiency is higher for lower temperature differences between the heating and the cooling external fluids. The relative efficiency improvement of the absorption cycle is as high as 40% operating with a similar turbine to that of the conventional Rankine cycle.The exergy destruction of both the absorption and the conventional cycle was also analysed. In a conventional Rankine cycle, the constant temperature at which phase change occurs leads to higher temperature differences between the operating fluid and the heating and cooling external fluids, producing high exergy destruction. The absorption cycle permits a better temperature match, reducing the exergy destruction. Therefore, the exergetic efficiency of the absorption power cycle is around 10% higher than that of the conventional Rankine cycle.

A review of combined power and cooling cycles

Combined power and refrigeration cycles have been explored for improving their overall energy conversion efficiency and decreasing the cost of energy produced. Bottoming cycles can be used to recover the waste heat or exhaust heat of gas turbines and conventional steam Rankine cycles and convert it to work and/or refrigeration. In most applications, refrigeration is the more expensive product than power because it requires refrigeration equipment as well as power to produce conventional refrigeration. Therefore, the additional output of refrigeration by the combined cycle provides greater benefit than conventional power systems. This paper presents a review of combined power and cooling cycles for effective utilization of heat sources.This article is categorized under: Concentrating Solar Power &gt; Science and Materials Energy Efficiency &gt; Science and Materials Energy Systems Economics &gt; Science and Materials

Experiment on pumpless Rankine-type cycle with scroll expander

The first experiment on a pumpless Rankine-type cycle (PRC) with a practical expander was performed to verify the feasibility of the PRC in power generation from low-grade heat sources. The PRC is an alternative to a Rankine cycle (RC) for lower output power and lower- and/or unstable temperature heat sources, where the conventional RC is rarely economically efficient owing to the low efficiency of the working fluid pump. The PRC mainly consists of a scroll expander, two heat exchangers, and switching valves for the expander and heat exchangers. A switching valves method that does not require the use of a working fluid pump is employed to control the PRC, hence avoiding problems such as cavitation caused by the working fluid pump. A mini-PRC experimental system showed that the PRC could successfully function with a scroll expander and produce actual power of 20 W. In addition, the PRC generated relatively larger net power than the conventional organic Rankine cycle in a very small output range.

Solar Hybrid Combined Cycle Performance Prediction Influence of Gas Turbine Model and Spool Arrangements

A modeling procedure was developed to simulate design and off-design operation of hybrid solar gas turbines in a combined cycle (CC) configuration. The system includes a heliostat field, a receiver, and a commercial gas turbine (GT) interfaced with a conventional steam Rankine cycle. Solar power input is integrated in the GT combustor by natural gas. Advanced commercial software tools were combined together to get design and off-design performance prediction: TRNSYS® was used to model the solar field and the receiver while the gas turbine and steam cycle simulations were performed by means of Thermoflex®. Three GT models were considered, in the 35–45 MW range: a single shaft engine (Siemens SGT-800) and two two-shaft engines (the heavy-duty GT Siemens SGT-750 and the aero derivative GE LM6000 PF). This was in order to assess the influence of different GT spool arrangements and control strategies on GT solarization. The simulation method provided an accurate modeling of the daily solar hybrid CC behavior to be compared against the standard CC. The effects of solarization were estimated in terms of electric power and efficiency reduction, fossil fuel savings, and solar energy-to-electricity conversion efficiency.