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[Introduction] Compressed air energy storage (CAES), as a long-term energy storage, has the advantages of large-scale energy storage capacity, higher safety, longer service life, economic and environmental protection, and shorter construction cycle, making it a future energy storage technology comparable to pumped storage and becoming a key direction for future energy storage layout. By summarizing the current status of CAES technology, the working principles, challenges, and solutions of different CAES technologies are analyzed, which is provided for the development of CAES technology through research. [Method] Firstly, the principle of CAES was introduced, the key equipment, such as compressors, turbo-expanders, and heat exchangers, was analyzed, and the key equipment suitable for the CAES was proposed. Then, the commonly used key technologies, development trends, and engineering cases of large-scale CAES were introduced from the perspective of ground key process technologies and underground gas storage facilities. Finally, the future development trend of CAES technology was analyzed. [Result] The results show that regenerative CAES is currently the mainstream technology in China, and high-temperature heat storage has become the future development direction of CAES, and is also an important way to improve the efficiency of CAES. At the same time, there is still room for improvement in key equipment and technology optimization, cost reduction, and application scenario development of the system. [Conclusions] CAES, as a long-term energy storage method, plays an important supporting role in the construction of future new power systems.

A novel mechanism is proposed to simultaneous recovery and storage of energy for use in the natural gas depressurization process. The main idea of this proposal is to use a compressor and a pump coupled with the turbo-expander to directly store the mechanical power produced by the expansion turbine in the energy storage system based on the pumped hydro combined with compressed gas. The compressor is used to create preset pressure in the vessel of the energy storage system, and the pump is used to inject water into the vessel. In this way, the density of energy storage in the system increases. In the discharge stage, electricity is produced by passing water through the turbo-generator during peak consumption hours or when energy prices are higher. The capability of the presented new method has been tested in a natural gas pressure reducing station with a nominal capacity of 50,000 Nm3/h, and the effect of different factors within the energy storage system on its performance, including the preset pressure and the volumetric ratio of water to gas in the pressurized tank, has been studied. By using the proposed plan, due to the elimination of unnecessary energy conversions the efficiency of recovery, storage and release of energy enhances. The results showed that by employing the proposed system, about 1.3 (GWh) of energy can be harvested annually; while this amount of energy is currently wasted. Also, the overall energy conversion efficiency of 48.64 %.

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The turbo-expander is the crucial equipment for obtaining refrigeration capacity and power in the system, and the aerodynamic performance is vital for the system. Spontaneous condensation of moist air in a high-speed turbo expander has a significant effect on the efficiency and output power. Based on the model of non-equilibrium spontaneous condensation, the flow of moist air in a high-speed turbo expander was studied, which is verified by the experiments. The meridional surface shape affects the variation of the flow passage cross-sectional area. The impeller with a uniform variation in cross-sectional area has the highest efficiency. Based on the optimal meridional surface shape, the condensation flow of moist air with different impeller blade diversion curvature was compared. The optimal curvature can increase the efficiency of the moist air turbo-expander by 2.83 %, and the optimized impeller has 3.53 % higher output power. The largest curvature of the blade leads to an efficiency reduction by 3.06 %, but it has little droplet condensation in the impeller, which can help to avoid damage of high-speed blades.

[Introduction] As a long-term energy storage form, compressed air energy storage (CAES) has broad application space in peak shaving and valley filling, grid peak regulation, new energy consumption, auxiliary services, and other aspects, which is of great significance for accelerating the construction of a new power system with new energy as the main body in the context of "carbon peak & carbon neutrality". [Method] Firstly, current status of CAES were analyzed and summarized from the principles and technical classifications. Then, based on the current technological development, a creative solution of CAES was proposed by China Energy Engineering Corporation Limited, which includes the "medium temperature adiabatic compression" technology route for 180 ℃ high-pressure hot water heat storage and the "high temperature adiabatic compression" technology route for 340 ℃ low melting point molten salt and 180 ℃ hot water combined heat storage. The key technical points, such as system integration and optimization, equipment selection, heat storage medium, gas storage equipment, and digital network storage coordination, have been introduced. Finally, engineering cases were introduced around the two technical routes. [Result] The results indicate that, in order to improve the conversion efficiency of power plants, it is necessary to comprehensively consider the material flow and energy flow coupling characteristics of various systems, such as compressor system, turbo-expander system, heat storage system, and gas storage system, and then develop the key equipment such as compressors, turbo-expanders, heat exchangers suitable for compressed air energy storage, as well as key technologies such as underground gas storage and grid storage coordination. [Conclusions] The research can provide scientific reference for the subsequent development of CAES.

Abstract Over the years, people paid more attention to using renewable energy such as geothermal energy to decrease the dependency on fossil fuel energy. Organic Rankine cycle (ORC) can generate electricity by using low‐temperature heat sources, and geothermal energy is an ideal pollution‐free heat source that can provide continuous and stable energy. Meanwhile, the turbo expander, one of the essential components in ORC, has the advantages of high speed and single‐stage expansion ratio. In this work, we simulated and analyzed the flow field characteristics of the turbo expander under the assigned working conditions using CFX software. The results showed that the working fluid distributed uniformly in the volute, and there was no apparent whirlpool flow or secondary flow. The pressure near the leading edge of the impeller blade was sparse but became dense at the vicinity of the trailing edge. When the speed of the expander was 15000rad min−1 and the inlet pressure was 0.59 MPa, the isentropic efficiency reached the maximum value, and the change of the inlet temperature had little effect on the isentropic efficiency, which can be ignored in actual operation. The results guide in improving the practical application of geothermal energy.

Over the years, people paid more attention to using renewable energy such as geothermal energy to decrease the dependency on fossil fuel energy. Organic Rankine cycle (ORC) can generate electricity by using low‐temperature heat sources, and geothermal energy is an ideal pollution‐free heat source that can provide continuous and stable energy. Meanwhile, the turbo expander, one of the essential components in ORC, has the advantages of high speed and single‐stage expansion ratio. In this work, we simulated and analyzed the flow field characteristics of the turbo expander under the assigned working conditions using CFX software. The results showed that the working fluid distributed uniformly in the volute, and there was no apparent whirlpool flow or secondary flow. The pressure near the leading edge of the impeller blade was sparse but became dense at the vicinity of the trailing edge. When the speed of the expander was 15000rad min−1 and the inlet pressure was 0.59 MPa, the isentropic efficiency reached the maximum value, and the change of the inlet temperature had little effect on the isentropic efficiency, which can be ignored in actual operation. The results guide in improving the practical application of geothermal energy. [ABSTRACT FROM AUTHOR]

One of the most rational methods of energy utilization of compressed gas in pipelines is to use turbo-expander installations. In particular, these are autonomous turbo-expander power stations. A fundamentally new concept has been devised to improve the technical and economic performance of this type of machines. This concept is not focused on a separate aspect of the plant's operation but on their entire set. In particular, physical principles, structures, and technologies were considered as an object of research. First, effective parameters of gas-dynamic flows and heat-mass transfer were determined based on the modeling of work processes. Secondly, progressive designs of turbo-expander units have been created. Thirdly, technologies for the production of parts and assemblies of turbo-expander units have been developed, which combine, unlike the traditional ones, different types of strengthening for contacting parts in their pair. A method of parametric modeling was used to substantiate the technical solutions of the elements of turbo-expander power plants. This makes it possible to determine the technical characteristics of these installations under a certain set of parameters. By purposeful variation, a recommended set of their parameters was determined, which ensure the improvement of the most important technical characteristics. A specialized database was built, which contains an array of information about the regularities of the influence of variation of significant parameters on various characteristics of turbo-expander power plants. Already on this basis, the problems of synthesis of successful technical solutions of turbo-expander power plants are solved. As a result, their high energy efficiency is ensured. Thus, the efficiency of the expander was achieved at the level of 86 % while the resource increased by 20–25 %. All these solutions were implemented in a number of unique turbo-expander units. Their effectiveness has been demonstrated during operation [ABSTRACT FROM AUTHOR]

This paper discusses the numerical modeling of an automobile fuel cell system using a two-stage turbo-compressor for air supply. The numerical model incorporates essential input parameters for air and hydrogen flow. The model also performed mass and energy balances across different components such as pump, fan, heat-exchanger, air compressor and keeps in consideration the pressure losses across flow pipes and various mechanical parts. The compressor design process initiates with numerical analysis of the preliminary design of a highly efficient two-stage turbo compressor with an expander, as a single-stage compressor has several limitations in terms of efficiency and pressure ratio. The compressor’s design parameters were carefully studied and analyzed with respect to the highly efficient fuel cell stack (FCS) used in modern hydrogen vehicles. The model is solved to evaluate the overall performance of PEM FCS. The final compressor has a total pressure and temperature of 4.2 bar and 149.3°C, whereas the required power is 20.08kW with 3.18kW power losses and having a combined efficiency of 70.8%. According to the FC model with and without expander, the net-power outputs are 98.15kW and 88.27kW, respectively, and the maximum efficiencies are 65.1% and 59.1%, respectively. Therefore, it can be concluded that a two-stage turbo compressor with a turbo-expander can have significant effects on overall system power and efficiency. The model can be used to predict and optimize system performance for PEM FCS at different operating conditions.

Natural gas is a mixture that is widely used in the industries. Knowledge of its thermodynamic properties is essential for evaluating the process and equipment performance. This paper quantifies the energy that can be extracted from natural gas using a turbo expander. Natural gases of wide-ranging compositions collected from 6 different gas fields in Egypt were investigated based on energy and exergy analysis. The study was conducted using MATLAB. Numerous simulation runs were made by taking various typical feed compositions classified as lean and rich. The effects of increasing the amount of C1, C5 in the feed stream on the efficiency of energy utilization are presented. A validation analysis was performed. The results show similar trends and good agreements. It was concluded from the results that when the concentration of methane in the gas mixture increase, the exergetic efficiency decreases. The results also show that the values of thermodynamic properties depend on the relative amount of heavy components in the feed stream.

Using a turbo-expander instead of a regulator, the output temperature will be reduced. Reducing the gas temperature to the freezing temperature of the water within gas can damage the station equipment. In the present work, the gas flow is simulated in a turbo-expander under the real conditions of natural gas pressure reduction stations and the amount of gas temperature reduction during this process is predicted. The equations of continuity, Navier-Stokes, energy, and k−ε turbulence model are solved with the help of CFD. Simulation results for twelve real cases, including three different input pressures, two different output pressures, and two different input temperatures are obtained. Results show that almost for every 9 psi pressure reduction, the temperature decreases by 1 °C. Also, the highest temperature drop occurs in the middle part of the outlet. Results show that due to a very low temperature of outlet gas, using a turbo-expander in the case of high-pressure stations is not recommended. In the case of medium pressure stations, a turbo-expander may be used with a heater. In the case of low-pressure stations, as the temperature at the center of outlet is lower than at the other points, installing a flow mixer can solve the freezing problem. [ABSTRACT FROM AUTHOR]

Natural gas is one of the most reliable and general energy sources globally, which their reservoirs always have high pressures. Nowadays, due to the production and supply of a variety of turbine expansions, it is possible to generate power from natural gas extraction. In this research, by considering the operational conditions and exploitation data, the possibility and advantage of using turbo-expander in gas extraction process are explored. Based on the results, 0.26-1.1 MW of power can be generated from each production well using the pressure drop in the turbo-expander with the flow ranges between 0.5-2.0 million STD_m3/d. The power generation capacity due to natural gas conditions may be associated with the production of gas condensates which has also been studied in this research.

Natural gas liquids production from natural gas streams is essential for energy diversification, economic development, environmental sustainability, and ensuring a stable and reliable energy supply. However, the NGL recovery process is associated with high energy consumption and significant environmental impact. This study compares three common NGL recovery processes based on turbo expander, Joule-Thomson, and combined processes through a 4E analysis approach. The 4E analysis framework includes four key aspects: environmental impact, energy consumption, exergy efficiency, and economic feasibility. By simultaneously considering these factors, a comprehensive assessment can be achieved. The specific energy consumption is optimized, and the results show that the specific energy consumption of the turbo-expander process is 164.4 % and 181.7% lower than the Joule-Thomson and combined processes, respectively. Also, the exergy efficiency for the turbo-expander, Joule-Thomson, and combined processes is 75, 71, and 60%, respectively. In addition, the ethane recovery rates for the turbo-expander, Joule-Thomson, and combined processes are 74.85%, 31%, and 69.87%, respectively. Economic analysis also indicated that the turbo-expander is more cost-effective than the other two processes, and the production cost in the turbo-expander process is lower by 45.45 and 54.54%, respectively. In addition, the turbo-expander process emits less carbon dioxide during NGL production. • A comparison is made between three conventional refrigeration methods for NGL production. • NGL production is enhanced by optimizing specific energy consumption. • Utilizing a turbo-expander has lower production costs and more ethane recovery. • Turbo-expander is superior to two other processes in terms of exergy efficiency. • Using a turbo-expander for NGL production reduces CO 2 emissions. [ABSTRACT FROM AUTHOR]

In this research, a direct energy harvesting and storage strategy was proposed for the recovered energy from the natural gas pressure reduction station. For this purpose, a novel turbo-pump system is proposed, which consists of a turbo-expander and a water pump. The proposed plan was integrated into a gas pressure reduction station with a capacity of 300,000 Nm3/hr. In gas pressure reduction stations, a regulator reduces gas pressure, which wastes natural gas energy in the depressurization process. To recover this wasted energy, a turbo-expander has been used instead of the regulator. The designed turbo-expander shaft is connected to the pump shaft. By receiving mechanical energy from the turbo-expander, the pump transfers the water into the water towers and thus stores the energy. For this purpose, water towers with different sizes were designed and their energy storage capacity and efficiency was calculated. The obtained results showed that 15.3 GWh energy can be recovered annually, which this amount of energy is currently wasted. While harvesting this significant amount of energy from a gas pressure reduction station, emissions are also prevented. The analysis results of the designed energy storage system also showed that the total energy conversion efficiency of recovered energy from natural gas in the pressure reduction process to electrical energy in the discharge stage of the energy storage system is about 52%. Also, the average daily electrical power generated during peak consumption hours is between 0.7 and 17.9 MW. By recovering and storing wasted energy from just one gas pressure reduction station, in addition to generating electrical energy during peak hours, the emission of 4620 tons of carbon dioxide can be prevented annually. The designed energy storage system can be installed as discrete packs of energy storage in different capacities, which have high installation and flexibility. [Display omitted] • A novel approach is proposed for energy recovery and direct storage for natural gas pressure reduction station. • Using innovative turbo-pump system energy conversion efficiency enhances. • Using the proposed methodology, recovered wasted energy could be converted to valuable electricity during peak hours. • The average electrical power generated from the designed energy storage system during peak consumption hours is 0.7–17.9 MW. [ABSTRACT FROM AUTHOR]

This report details the testing of an ACT turbo-expander on a high-speed Diesel engine to explore if NOX reduction can be achieved by turbo-expansion cooling. NOX reduction in Diesels is needed due to the detrimental environmental and health impacts it has across the globe. Testing was completed using a Ford 1.5 DuraTorq engine and a custom test cycle. The test cycle was developed to test the most used section of the engines rev range, whilst also overcoming oil cooling and low intake temperature issues. A NOX analyser failure meant that NOX emissions result could not be gathered. Exhaust temperatures were compared between the standard engine and turbo-expander equipped engine, as a decrease in exhaust temperatures would indicate a reduction in combustion temperature and therefore NOX emissions. 3 tests were carried out under each condition; the results were then analysed using a two-tailed T-test with a significance level of 0.05. The results showed that at an engine speed of 2500rpm or greater the reduction in exhaust temperature was statistically significant, with the largest reduction in exhaust temperature being 34.51°C at 2750rpm at 70% throttle. At low engine speeds the turbo-expander was showed to increase the exhaust temperature with the largest increase being 52.28°C at 2000rpm at 70% throttle. The turbo-expander was also proven to reduce engine power by an average of 1kW due the reduced intake pressure resulting from the frictional loses in the turbo-expander rotating assembly. If testing is repeated changes to the test setup must be made to make it more repeatable and to capture more data.

The permanent magnet synchronous generator (PMSG) has been widely employed in high-speed direct-drive turbo-expander for distributed energy generation. However, for conventional PMSG based turbo-expander system, expensive mechanical balance devices should be installed on the rotor to restrain the axial force of turbine impeller under high-speed flow, which may cause both complex system structure and higher manufacturing cost. Thus, in this paper, a direct-drive conical-rotor PMSG (CR-PMSG) for turbo-expander is developed, which can generate an axial magnetic force as equilibrant to counteract the axial force of turbine impeller without mechanical balance device, so as to reduce the system complexity, improve the operating performance and extend the operating cycle. First, the structural features of the CR-PMSG are introduced and the basic principle of axial force balance is analyzed. Then, a 1.5 kW, 6000 rpm CR-PMSG with cone angle of 6° is designed. Using 3-D finite element analysis, the axial force of turbine impeller, the axial magnetic force of the rotor, and the electromagnetic performance are simulated. Also, the control strategy of d, q-axis currents is obtained to achieve the adaptive equilibrium of axial force. Finally, a CR-PMSG prototype is fabricated and tested to validate the theory.

Incentives to increase efficiency and reduce CO2 emissions have led to the development of many plant process designs incorporating turbo-expanders. Turbo-expanders provide the most efficient solution when it is required to reduce the pressure of a fluid stream. By expanding high pressure fluid, energy in the high-pressure fluid entering the turbo-expander can be efficiently used for electrical power generation. The energy recovered from the expansion is supplementary, thereby improving the thermal efficiency of the plant without leaving any noticeable trace of greenhouse gas emissions. This article focuses on both mechanical and electrical considerations for the implementation of turbo-expander generators. In an example of LNG liquefaction plant, the article discusses the plant thermal efficiency, turbo-expander performance curve, generator sizing, and the choice between the induction and the synchronous generator. The impact on the plant real and reactive power balance and the system stability is shown in an example. Furthermore, this article evaluates the options for the turbo-expander generator tie-in points within the electrical system. [ABSTRACT FROM AUTHOR]

An increase in fossil fuel consumption has significantly increased the concentration of greenhouse gases (GHGs). Waste energy recovery can reduce GHGs by reducing fossil fuel consumption. In the FCC unit in refineries, the catalyst is continuously regenerated by burning off the deposited coke with air and a large flux of waste gas with high temperature is generated which is vented into the atmosphere. The purpose of this study was to investigate the effect of waste heat/pressure recovery of the waste gas on the reduction of GHGs and air pollutant emissions. Based on this objective, exergy and economic analysis were carried out for two scenarios (S-1 and S-2). The S-1 scenario involved the installation of a Heat Recovery Steam Generator (HRSG), while S-2 applied the simultaneous usage of HRSG and a turbo-expander to evaluate electricity production using waste gas pressure. The exergy of waste gas was formulated and an in-house code was developed for solving the equations via a trial and error method. The results showed that exergy loss of the waste gas was higher than 660 MW and it was possible to recover about 64 MW and 75 MW in the S-1 and S-2, respectively. The amount of steam and the electrical energy produced were found to be about 88 ton/h and 8323 MWh/month, respectively. The results also showed that S-1 can reduce 72227 tCO2e of GHGs and 327 ton of air pollutant and S-2 can reduce 143464 tCO2e of GHGs and 649 ton of air pollutant annually. The economic indexes were evaluated and the results indicated that the internal rates of return (IRR) were found to be 33.18% and 36.76% for S-1 and S-2, respectively. This showed that the two scenarios were economically feasible, but from an environmental, economic and energy recovery standpoint, S-2 was the best scenario and the economic analysis on S-2 certified that there was no economic risk.

• CFD technique was used to investigate the NGL recovery. • The cooling performance was improved by replacing supersonic separator instead of J–T valve. • Compared to the J–T valve, this new method derives about 2.85 time higher of C 3 +. In this study, we employed the computational fluid dynamic (CFD) technique in conjunction with a thermodynamic EOS package to investigate the liquid hydrocarbon recovery of dehydration/NGL recovery unit. The effect of modification in dehydration/NGL recovery unit using the supersonic separator was studied. The Peng–Robinson equation of state in conjunction with the thermodynamic process modeling package were used to simulate the heavy hydrocarbon separation in the supersonic separator. The κ–ε turbulence model was used to simulate the natural gas flow in supersonic separator and the behavior of gas pressure reduction on refrigeration performance was studied under the conditions of specified boundary layers. The CFD modeling results revealed a satisfactory agreement with the measured data reported in literature. The results showed that cooling performance was improved for this system compared to J–T valve and turbo-expander. The performance of this system can be further intensified by comparing the refrigeration effect in the same pressure difference. Furthermore, the condensation process of natural gas stream was investigated with the modification of design of dehydration/NGL recovery unit. Compared to the Joule–Thomson valve, this new method derives about 2.85 time higher of C 3 +. The results showed that, when the pressure reduction of this device is equal to that of Joule–Thomson valve, the supersonic separator has a better cooling and separation performance. [ABSTRACT FROM AUTHOR]

Abstract In this paper, a novel configuration of microgrid with incorporation of turbo-expander (TE) has been presented. The cooling and electrical energy recovered by TE are used to supply the microgrid demand. The purification and preheating processes are imbedded on the inlet gas, which, according to the need, provide and control the recovery of electrical energy and cooling. Due to the unique features and limitations of TE, determination of type and optimal size of energy resources in this microgrid is special; so an innovative optimal capacity sizing (OCS) method was presented. For determination of optimal size of TE, the constraints and needs of the local natural gas (NG) network should also be considered, which, differentiates it from other energy sources. Another key feature of the proposed OCS method is optimization of inlet NG temperature passing through TE. Performance and economic evaluation of the TE-based microgrid was compared with the traditional microgrid without TE. Analysis showed that O&M and emission costs of the TE-based microgrid were reduced significantly (about 27% and 30%, respectively) culminating in low prices for the generated energies. In addition, net present value and internal rate of return of the TE-based microgrid were higher (38.5% and 6%, respectively). Highlights • Proposing a new configuration for Turbo-expander based microgrid. • Adjusting the cooling and electrical energy recovered by TE. • Proposing an algorithm for optimal capacity sizing of TE-based microgrid. • Developing a method for determining the optimal capacity of Turbo-expander. [ABSTRACT FROM AUTHOR]

Highlights • High speed rotor-foil bearing system of cryogenic turboexpander was modeled using finite element method. • Static structural stiffness and damping coefficients of the foil bearings are obtained from static tests. • Rotordynamic analysis on the rotor-foil bearing system was conducted for further comprehensive design. • Transient numerical results from the cryogenic turboexpander with foil bearings are validated with experimental results. Abstract High speed turbo-expander is an essential refrigerating component in cryogenic systems. In addition to thermodynamic performance, its stability in transient high speed operation is also of great concern for its comprehensive performance. Oil free foil bearing has a great application potential in high speed turbomachinery by virtue of its high stability with no extra external supplying gas. In this paper, finite element model of a 150 Nm3/h cryogenic turbo-expander using foil bearing for air separation is configured for a case study. Influence of bearing structural stiffness and damping characteristics on the rotor-foil bearing system are evaluated for stable operation. Static structural stiffness and damping coefficients of the protuberant foil journal bearing and thrust bearings are obtained from the static loading and deflection tests. With the tested coefficients, rotordynamic performances of the rotor-bearing system is analyzed numerically and compared with the transient experimental results. [ABSTRACT FROM AUTHOR]

Turbo-expanders are widely used as power generators in the field of energy conversion such as organic Rankine cycle (ORC) systems. When the available thermal energy is not sufficient to operate the turbo-expander in full admission, it is much better to operate in partial admission instead of stand-down. However, the performance of the turbo-expander greatly depends on the operating conditions. Among many operating conditions, the flow angle at the nozzle and solidity can be major factors affecting the performance of the expander. In order to investigate the optimal operation conditions, experiments were conducted in a linear cascade apparatus simulating the operation of turbo-expander in partial admission. Three different nozzle flow angles of 58°, 65°, and 72° were adopted, and the experiments were conducted with respective solidities of 1.25, 1.38, and 1.67 at each nozzle flow angle. The cross section of the nozzle was rectangular and the chord of the tested blade was 200 mm. The blades moved in a rotational direction, and the forces on the blades were measured with the surface pressure at steady state. The experimental results showed that the rotational force increased for a larger solidity or for a smaller nozzle flow angle.

Abstract: recovery is considered as a case study in a conventional turbo-expander process. Some practical problems occurred in the multi-stream heat exchanger lead to plant shot down. In order to conquer the problem and avoid expensive cost of multi-line heat exchanger replacement, simulation carried out using Aspen HYSYS to investigate the design variables and effective parameter on the plant performance. Some modifications are suggested and applied to the simulation. Hydrocarbon recovery is measured in the original plant and the modified plant. Methane recovery is not affected significantly by the modifications, but ethane recovery in the modified plant decreased to the half of the original one. Simulation showed that proposed modification is satisfying enough to be applied to the real plant. After modification, hydrocarbon recovery, turbo-expander performance and heat exchanger conditions are compared for the original design and the modified plant. Using the simulation results and recommended modifications, the plant could survive. [ABSTRACT FROM AUTHOR]

This paper aims to make possible the operation of a turbo-expander (TE) as a renewable resource at the Neka power plant in fault condition in the auxiliary service system (ASS), which is considered one of the fundamental problems in network operation. In this paper, the effect of the failure on the performance of the TE is analyzed whilst the performance of a dynamic voltage restorer (DVR) and static synchronous compensator (STATCOM) to compensate the fault in the ASS network is investigated. To improve the performance of DVR, a novel topology is developed; additionally, the compensatory strategies are assessed, simulated, and validated. In order to optimize the performance of the compensators, their possible presence situations on the ASS in various scenarios under the conditions of severe disturbance, synchronization of fault conditions, and starting of TE are tested. The results of PSCAD/EMTDC software simulation demonstrate that by applying the improved topology and selected compensation strategy of DVR, severe voltage sags are compensated, and the fault ride-through (FRT) capability for the TE is provided. Eventually, it is evident that the proposed solution is technically and economically feasible and the TE can supply the total ASS power consumption in all disturbances.

The performance of a transcritical organic Rankine cycle (TRC) system is affected by the heat source conditions of the exhaust gases resulting from a turbo-expander under off-design conditions. In the present study, the axial-turbo-expander of the TRC system under the design point was designed through 1-D aerodynamic theory and validated using a computational fluid dynamics (CFD) solver. The CFD solver was also used to simulate and analyze the thermal-fluid field of the turbine under various heat source conditions to determine the turbine efficiency under off-design point. The axial-turbo-expander in the TRC system, with R134a serving as the working fluid, was numerically examined to investigate the turbine performance at expander inlet temperatures of 140–115 °C and circulated loop mass flow rates of 15–12.5 kg/s. The results revealed that the isentropic efficiency of the turbine sharply dropped as the circulated loop mass flow rate increased at m w > 14.5 kg/s. However, the isentropic efficiency was only slightly affected by T in_exp at T in_exp > 130°C. In conclusion, the temperature of the circulated loop was increased to fix the mass flow rate of the circulated loop at the increasing thermal power of the exhaust gases due to the isentropic of the turbine slightly affected by the increasing temperature of the heat source. In contrast to the increasing thermal power of the exhaust gases, the mass flow rate of the circulated loop was decreased at the decreasing thermal power of the heat source. [ABSTRACT FROM AUTHOR]

The performance of a transcritical organic Rankine cycle (TRC) system is affected by the heat source conditions of the exhaust gases resulting from a turbo-expander under off-design conditions. In the present study, the axial-turbo-expander of the TRC system under the design point was designed through 1-D aerodynamic theory and validated using a computational fluid dynamics (CFD) solver. The CFD solver was also used to simulate and analyze the thermal-fluid field of the turbine under various heat source conditions to determine the turbine efficiency under off-design point. The axial-turbo-expander in the TRC system, with R134a serving as the working fluid, was numerically examined to investigate the turbine performance at expander inlet temperatures of 140–115 °C and circulated loop mass flow rates of 15–12.5 kg/s. The results revealed that the isentropic efficiency of the turbine sharply dropped as the circulated loop mass flow rate increased at mw > 14.5 kg/s. However, the isentropic efficiency was only slightly affected by Tin_exp at Tin_exp > 130°C. In conclusion, the temperature of the circulated loop was increased to fix the mass flow rate of the circulated loop at the increasing thermal power of the exhaust gases due to the isentropic of the turbine slightly affected by the increasing temperature of the heat source. In contrast to the increasing thermal power of the exhaust gases, the mass flow rate of the circulated loop was decreased at the decreasing thermal power of the heat source. [ABSTRACT FROM AUTHOR]

This paper dedicates on the multi-faults decoupling of turbo-expander rotor system using Differential-based Ensemble Empirical Mode Decomposition (DEEMD). DEEMD is an improved version of DEMD to resolve the imperfection of mode mixing. The nonlinear behaviors of the turbo-expander considering temperature gradient with crack, rub-impact and pedestal looseness faults are investigated respectively, so that the baseline for the multi-faults decoupling can be established. DEEMD is then utilized on the vibration signals of the rotor system with coupling faults acquired by numerical simulation, and the results indicate that DEEMD can successfully decouple the coupling faults, which is more efficient than EEMD. DEEMD is also applied on the vibration signal of the misalignment coupling with rub-impact fault obtained during the adjustment of the experimental system. The conclusion shows that DEEMD can decompose the practical multi-faults signal and the industrial prospect of DEEMD is verified as well. [ABSTRACT FROM AUTHOR]

The feasibility of employing combined heat and power (CHP) systems for providing the required heat in power productive gas expansion stations (PPGES) has been studied. However, there is no study in the literature indicating which PPGES is an economically efficient host for the CHP technology. In this work, comprehensive energetic and economic analyses are accomplished on several gas expansion stations (GES) in Iran. The corresponding power generation units and CHP systems of each of these stations are sized and designed. Net present value (NPV) is the economic method of used for the sizing and design procedure. The novel technical criterion of relative heating demand (RHD) which makes the economic index of relative NPV (RNPV) equal to zero determined the eligible PPGESs for being equipped with a CHP unit. The results show that a PPGES might be an appropriate host for a properly sized and designed CHP system if its RHD value is greater than 0.35. This value for the simple GESs was found as 0.23. [ABSTRACT FROM AUTHOR]

Turbo-expanders have been used for energy conversion in many fields. They are sometimes operated in partial admission mode, depending on the stability of the energy source, such as solar energy or waste thermal energy, which can fluctuate depending on environmental or process condition. The ability to operate in partial admission can be advantageous because it allows continuous operation without interchanging components. However, this method also leads to lower turbo-expander efficiency. This experimental study was conducted to investigate losses at various partial admission rates. In addition, the effect of tip clearance was studied since it is another important parameter affecting turbo-expander performance. A linear cascade was fabricated with a nozzle that was set to 65° based on the axial direction. A blade row was designed to be movable along the pitchwise direction in order to investigate flow characteristics as a function of blade movement. Flow structures and pressure losses were measured for various partial admission rates and tip clearances. The experiment was conducted at a Reynolds number of 3 × 10 5 based on the chord. The experimental results showed that losses in the passages depended not only on partial admission rate but also location relative to the nozzle. [ABSTRACT FROM AUTHOR]

A type of foil journal bearings with double-layer protuberant foils as elastic support was studied by numerical analysis and experiments. Two kinds of material (beryllium bronze and stainless steel) with different elasticity were used for the protuberant foils of the bearings. The analyzing model couples the hydrodynamics pressure of the gas film to the elastic deflection of the top foil and the underlying protuberant foils. The hydrodynamics of gas film is described by the Reynolds equation. The top foil and the protuberant foils are modeled as thin plates and the protuberances are treated as rigid support. For calculating the deflection of the top foil, the deflection of the protuberant layer beneath the top foil is taken into account. With a given load, the gas film thickness and pressure are obtained by using finite element method and finite difference method. The key static and dynamic parameters are presented. In experiments, both of the two foil bearings run well in a turbo-expander. The new takeoff and shutoff pressure and speed are proposed for practical operation of the hydrodynamic lubricated high speed turbo-expander. In addition, the synchronous and subsynchronous rotor motions have been tested and analyzed. The experimental tests of the two bearings in a high-speed turbo-expander suggest that the bearing using stainless steel as the foil material shows higher stiffness, which agrees well with the numerical predictions.

Spontaneous condensation processes are common in the industry and have a significant impact on the aerodynamic characteristics of turbines. The spontaneous condensation process of moist air in a high-speed turbo-expander was investigated experimentally and numerically. Temperature and humidity of the moist air into the turbo-expander were controlled independently in a psychrometric chamber. A liquid fraction of 0.8% was achieved at the turbo-expander outlet which was corresponding to a relative humidity of 76.9% at 303.2 K. The non-equilibrium condensation model was validated against the experimental results, and the maximum relative deviations of outlet temperature, absolute humidity, and moist efficiency were 0.16%, 3.23%, and 2.15%, respectively. Based on numerical simulations, the nucleation process and droplet distribution in the turbo-expander were studied. Compared with the suction surface, the nucleation region near the pressure surface was more extensive. The effect of inlet temperature, humidity, and pressure was compared. The inlet pressure had the most significant impact on the nucleation initial position, and the inlet temperature mainly determined the nucleation rate and droplet number. The wetness loss due to the vapor condensation mainly occurred in the impeller, and the efficiency drop could reach 2.17% when the pressure ratio was 2.1. • Spontaneous condensation processes of moist air in the turboexpander are studied. • The aerodynamic parameters distribution with condensation process is analyzed. • Effect of inlet temperature, humidity, and pressure on the condensation process. • Inlet relative humidity of 76.9% at 303.2 K leads to a liquid fraction of 0.8%. [ABSTRACT FROM AUTHOR]

Desublimation-based cryogenic carbon capture has drawn particular attention to mitigate the climate issue of global warming. Turbo-expander based refrigeration system is a potential option to provide cooling at 150 K for CO 2 desublimation, while the CO 2 spontaneous desublimation in turbo-expander complicates the expansion process and leads to wetness losses. In this paper, the non-equilibrium desublimation process is included in the one-dimensional mean streamline model of a cryogenic turbo-expander, and the expansion process with CO 2 desublimation in air is investigated. The distribution of CO 2 desublimation parameters in the flow passage of turbo-expander is obtained, and the two-phase expansion processes are classified into two types including desublimation expansion and subcooled expansion. A parametric study shows that a decrease in inlet temperature, an increase in pressure ratio and inlet CO 2 concentration lead to a larger wetness loss, where inlet temperature is the most important parameter, followed by pressure ratio and inlet CO 2 concentration. For a turbo-expander with inlet pressure of 300 kPa and CO 2 concentration of 0.64%, the significant desublimation occurs at a subcooling degree of 23.7 K, leading to a wetness loss of 1.2%. To avoid desublimation as well as wetness loss in passage of a turbo-expander, the designed maximum subcooling degree is supposed to be smaller than 15 K for the turbo-expander of a cryogenic carbon capture system. [Display omitted] [ABSTRACT FROM AUTHOR]

This paper dedicates on the rotor dynamics behaviour research on the turbo-expander rotor system involving droplet impact. A stochastic model based on Beta distribution and Bernoulli distribution of droplet generation is established and the formulations of droplet impact forces are deduced, which is applied on the rotor dynamics equations of the tilting pad bearing supported turbo-expander considering the temperature gradient for a further analysis. A time domain research is carried out and a conclusion that continuously droplet impact will perturb the steady vibration of the turbo-expander rotor system is obtained. Monte Carlo method is implemented for a statistics dynamics research and the results suggests that in the design of expander impellers, in order to decrease the uncertainty brought by droplet impact, the number of channels should be as few as possible, the droplet impact should be controlled to occur uniformly, and the collision, entrainment of the primary droplets and the stripping of the liquid film on the blade should be strictly restrained. [ABSTRACT FROM AUTHOR]

The application of the turbo-expander in the auxiliary service system of Neka power plant in Iran causes considerable voltage sag, which is very dangerous to the auxiliary service system. To reduce the voltage sag, the dynamic voltage restorer (DVR) is proposed. The auxiliary service system and main substation of the power plant with compensators are simulated by Power System Computer Aided Design (PSCAD/EMTDC) software. The application of the static synchronous compensator in different scenarios is discussed, and the results are compared with the results of the application of the DVR, which has a new topology and minimum injection power control strategy. It is shown that the results of the DVR application are better in all tested scenarios. Also, the economic assessment shows that the payback period is reduced to half in case of using DVR instead of static synchronous compensator. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The difficulty of data measurement in cryogenic environments and the complicated mechanism of nucleation process have restricted the design of wet type turbo-expander for cryogenic liquid plants. In this paper, equilibrium and non-equilibrium models are used to model the spontaneous condensation flow in a cryogenic turbo-expander along the main stream passage including nozzle, impeller and diffuser. The comparison shows a distinct difference of the predicted wetness fraction distribution along the streamline between the equilibrium model and the non-equilibrium model. In non-equilibrium model, the distributions of supercooling and nucleation rate along the length of turbo-expander are given for the analysis of flow characteristics. The comparison of outlet wetness fraction with the experimental data is also provided for verification and discussion. Both the effects of the rotation on nucleation and the effects of the nucleation on flow along suction side of the impeller are investigated. [ABSTRACT FROM AUTHOR]

Compressor inlet air cooling is one of the most well-known methods to improve gas turbine power plant performance. In this study, pressure reduction valve in natural gas pressure reduction station is replaced by a turbo-expander to use the potential energy of the compressed gas. The turbo-expander shaft is connected to a mechanical chiller to produce refrigeration; the produced refrigeration is used to decrease the compressor inlet air temperature. Moreover, thermodynamic and exergetic analyses are carried out and the effect of compressor air cooling on the performance of the plant is studied. To do so, Montazer Ghaem power plant is considered as the case study. Results showed that using cooling system causes 3.2% temperature drop which leads to 1.138% increment in both thermal efficiency and net output power in the warmest month. Exergetic analysis reveals that using the cooling system leads to a higher exergy efficiency and hence lower exergy destruction. Also combustion chamber with 81.26 MW has the highest amount of exergy destruction which decreases to 77.36 MW after implementation of the cooling system. In January, exergetic efficiency of total plant has 1.86% enhancement and exergy destruction reduces about 3.8 MW. [ABSTRACT FROM AUTHOR]

In the present paper, a vertical ground-coupled heat pump system is proposed for energy saving in a natural gas expansion plant. Such plant is a modern type of conventional natural gas pressure drop station. Unlike the conventional type, which waste the natural gas pressure exergy in throttling process, the modern one uses the pressure exergy of the natural gas for producing electrical power. A remarkable feature of the proposed system is the type of energy resource used for preheating aim. In previous studies, natural gas was used for the preheating process, however; the proposed system employs geothermal energy as a renewable energy resource for providing part of heating demand. Initially, the vertical ground-coupled heat pump system preheats the natural gas stream up to medium temperatures, then, gas stream passes through station heater and reaches the desired temperature. For studying the economic and thermal performance of the proposed system, first of all, a system with a high net present value is selected, and then the performance of the selected system is studied in detail. The analysis revealed that the fuel saving potential of the system is 45.80% annually. Economically, the discounted payback period was also calculated about 6 years. [ABSTRACT FROM AUTHOR]

Turbo-expanders are relatively new sources of dispersed generation which are used to drive the electrical generators. The conventional pressure regulating valves are replaced by these devices in the gas pressure reduction station. Connecting the dispersed generation to the distribution networks especially for squirrel cage induction generators, may result in some power quality problems. These problems can be obviated using special devices in electrical networks or modifying the control system of the prime mover system in mechanical parts. In this paper, it is focused on the Point of Common Coupling (PCC) voltage where a turbo-expander driven induction generator is connected. A new control strategy based on fuzzy controlled PID is considered for the mechanical part of the turbo-expander nozzle system. The results show a better control of turbo-expander output power in a linear form over the full range of operating points. The other purpose of the control system modification is to improve the power quality and stabilize the PCC voltage in different operating point conditions. [ABSTRACT FROM AUTHOR]

C2+ recovery in a conventional turbo-expander process is considered a case study. Some practical problems occur in the multi-stream heat exchanger, which lead to the plant shut down. In order to solve the problem and avoid the expensive cost connected with the multi-line heat exchanger replacement, simulation is carried out using Aspen HYSYS aiming to investigate the effect of the design variables and the effective parameters on the plant performance. Some modifications are suggested and applied to the simulation procedure. The hydrocarbon recovery as well as the performance of the turbo-expander and the heat exchanger observed after the modification is compared to those provided by the original design. The simulation shows that the modification proposed is adequate to be applied to the actual plant process. [ABSTRACT FROM AUTHOR]

Abstract: The organic Rankine cycle is widely used to obtain electric power from renewable energy sources, such as solar energy, geothermal energy, and waste thermal energy. In a typical ORC, a turbo-expander or volumetric expander is applied to convert the thermal energy to mechanical energy. The turbo-expander is widely used for large-scale output power because it has merits when used with large mass flowrates; the scroll expander is used for small-scale output power. In ORCs that produce small-scale output power, the available thermal energy as a renewable heat source usually cannot be supplied continuously. For fluctuating levels of available thermal energy, positive displacement machine has difficulty in adjusting the mass flowrate. In order to regulate the mass flowrate for varying thermal energies, a small-scale radial-type turbine and supersonic nozzles were designed specifically for this study. R245fa was used as the working fluid, and the thermodynamic properties of the working fluid in the cycle were predicted on the basis of the designed turbine blade and nozzle shape even though the mass flowrates were varied. The output powers at the off-design operations were predicted for the full range of 30 kW according to the number of nozzles used. [Copyright &y& Elsevier]