Turboexpander Research Articles

Turbo-Expander Units on Low Boiling Working Fluids

The article examines the possibility of increasing the efficiency of the turbo-expander cycles on low-boiling working fluids using those methods that are used for steam turbines, viz. increasing the parameters of the working fluid before the turbo-expander and using secondary overheating. Thus, four schemes of the turbo-expander cycle are considered: the one without overheating of the low-boiling working fluid, the one with single overheating of low-boiling fluid, the one with double overheating and the one with double overheating at supercritical parameters. All the studied cycles were considered with a heat exchanger at the outlet of the turbo expander, designed to heat the condensate of a low-boiling working fluid formed in the condenser of the turbo expander unit. Cycles inP–hcoordinates were built for the studied schemes. The method of thermodynamic analysis of the studied cycles based on the exergetic efficiency has been developed. The results of the research are presented in the form of Grassman-Shargut diagrams, which show exergy losses in the elements of the studied cycles on a scale, and also show the positive effect of the operation of the turbo-expander cycle in the form of electrical power. The analysis of the obtained results showed that the main losses that have a significant impact on the exergy efficiency are the losses of exergy in the recovery boiler. The increase of parameters of low-boiling working body, and the use of intermediate superheating reduce losses in the waste heat boiler and, consequently, increases exergetic efficiency of turbo-expander cycle. The turbo-expander cycle with double overheating at supercritical parameters of the low-boiling fluid is of the largest exergetic efficiency out of the schemes that have been examined.

Identification of Protein Direct Interactome with Genetic Code Expansion and Search Engine OpenUaa

Protein crosslinks occur endogenously such as modifications by ubiquitin-like proteins for signaling, or exogenously through genetically encoded chemical crosslinkers (GECX) for studying elusive protein-protein interactions. However, it remains challenging to identify these protein crosslinks efficiently at the proteomic scale. Herein, software OpenUaa is developed for identifying protein crosslinks generated by genetically encoded unnatural amino acids and endogenous protein conjugation. OpenUaa features inclusive and open search capability, dramatically improving identification sensitivity and coverage. Integrating GECX with OpenUaa, the direct interactome of thioredoxin is identified in Escherichia coli cells, yielding 289 crosslinked peptides and corresponding to 205 direct binding protein of thioredoxin. These identified direct binders provide evidence for thioredoxin's regulation of redox state and mitochondria energy metabolism. When identifying endogenous conjugation of small ubiquitin-like modifier (SUMO), OpenUaa also markedly improves coverage of SUMOylated peptides by ≈92%, revealing new SUMO targets. GECX-OpenUaa will enable efficient identification of direct interactomes of various proteins in live cells.

Thermodynamic analysis with energy recovery comparison of transcritical CO2 heat pump system using various expansion devices.

The high irreversibility caused by the expansion valve in the conventional transcritical CO2 heat pump cycle has been reported as the major drawback on the overall system performance. To overcome this problem and recover some of the energy lost, different isentropic expansion devices such as turbine expander and two phase ejector have been proposed. This study aims to numerically compare the performance of the transcrtical CO2 heat pump in terms of first and second law of thermodynamics. In addition, the energy recovered by the two phase ejector and the turbine expander cycles have been evaluated. The pressure recovery and entrainment ratio in the ejector device were investigated comprehensively. Two numerical models using MATLAB and ASPEN PLUS software have been developed, and REFPROP database was used to estimate the refrigerant thermophysical properties. The results showed that the heating coefficient of performance (COPh) of the ejector cycle is higher than that of the turbine and valve cycles by 10.15 % and 20.84 % respectively. In addition, the ejector cycle has the highest second law efficiency (0.1) and the recovered energy is (0.63 kW) compared to (0.107 kW) gained by the turbine cycle. The ejector device has the least exergy destruction (0.2 kW) and can recover 0.7 Mpa of the pressure losses.

Research on structure characteristics of the helium-lubricated spiral grooved thrust bearing for helium turbine expander

The helium-lubricated spiral grooved thrust bearing of helium turbo expander was studied by numerically simulating the steady-state non-linear Reynolds equation, the Reynolds equation of the pressure was solved by finite difference method (FDM), the film pressure distribution is calculated iteratively by MATLAB program, the structural parameters including the spiral angle, the groove length ratio, the groove width ratio influenced on the static characteristics were analyzed. The results show that: The bearing loading capacity of helium lubricated spiral grooved thrust gas bearing is lower than that of air lubricated bearing under the same conditions; The viscosity of the lubricant only affects the gas carrying capacity of the thrust disc when the spiral groove is on the bearing, while the density of the lubricant has a greater influence on the bearing loading capacity; When the spiral groove is designed on the rotor thrust disc, the bearing loading capacity of the spiral grooved thrust bearing increases by 6% on average compared with that of the spiral groove on the bearing.

Utilization of Turbo-Expander to Generate Power in Natural Gas Extraction Process

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.

Investigating supercritical carbon dioxide power cycles and the potential of improvement of turbine leakage characteristics via a barrier gas

The supercritical carbon dioxide power cycle has recently received tremendous interest owing to its compactness and enhanced efficiency. However, the inherent characteristics of supercritical carbon dioxide and high rotational speeds pose unique challenges in designing cycle turbomachinery sealing. Conventional sealing technology can result in an efficiency penalty as high as 0.55–0.65%. This drives the need for designing a more efficient sealing system to enable a supercritical carbon dioxide power cycle.In this study, leakage characteristics of a 500 °C class supercritical carbon dioxide turbine with labyrinth seals are modeled and investigated. The labyrinth seal model was validated against experimental results. In contrast to previous studies, a new leakage management scheme using a barrier gas was proposed and simulated. The carbon dioxide from the main cycle is utilized as the barrier gas; hence, no additional cost is incurred to produce the high-pressure barrier gas. The comprehensive parametric study revealed that the performance of the labyrinth seal with barrier gas is mainly influenced by leakage inlet pressure, barrier gas injection pressure, the differential pressure between the barrier gas and exit pressure, and the length of the seals. Subsequently, the performance of the proposed design is optimized using a pattern search algorithm in the MATLAB environment. The electric power required to reinject the leaked flow into the main cycle is taken as the objective function. The leakage flowrates for the benchmark and proposed cases are 0.0071 kg/s and 0.0108 kg/s, respectively. The proposed design reduced the reinjection power by collecting the leakage at a higher pressure of 832.28 kPa, compared to 101.325 kPa for the benchmark case. The optimization results show that, via the proposed scheme, the leakage recovery power demand is 2.897 kW whereas it is 3.725 kW for the benchmark case. Thus, the proposed scheme results in a 22.24% saving in electric power, compared to the benchmark case. Furthermore, it is reported for the proposed case that the amount of leakage avoiding turbine expansion is 0.0086 kg/s while for the benchmark case it was 0.0071. For the simulation conditions considered in this study, the extra leakage results in a 0.15% power penalty from the turbine, which is insignificant compared to the power saving in the leakage compression power.

Improvement potential of Cryogenic Energy Storage systems by process modifications and heat integration

Cryogenic Energy Storage (CES) system is currently gaining significant attention in the field of large-scale energy storage systems. This is because this system can provide high energy-density during storage and uses air or nitrogen that are available at no or a low cost. Moreover, the technology has matured and can be used on-site in a decoupled manner. The CES system has three sub-processes, namely, charging or liquefaction, storage, discharging or power cycle. To investigate the improvement potential of such systems, state-of-the-art configurations for each sub-processes have been analyzed in this paper. A configuration consisting of a multi-stage turbine expansion, a turbine and a JT-valve connected in series at the liquefaction stage, Organic Rankine cycle for utilization of heat of compression, and a four-stage reheat Rankine cycle with thermal energy storage at cryogenic temperature has been proposed. The study suggests that a high turnaround efficiency (about 90%) of the process may be achieved by an appropriate external source of thermal energy.

Investigating density-dependent patterns of population growth in Southern Italy, 1861–2019

Density-dependent population growth is a powerful engine of metropolitan expansion. However, spatial heterogeneity in demographic dynamics of advanced economies makes identification of density-dependent mechanisms of population growth a particularly hard task. The intrinsic linkage between long-term population increase, settlement expansion, and economic growth was investigated in Southern Italy, a peripheral European region, with use of Geographically Weighted Regressions verifying (global and local) mechanisms of density-dependent population growth in 2500 municipalities between 1861 and 2019. At the global scale, results demonstrate that population growth rates increased with population density since 1951. At the local scale, this relationship was particularly evident in the largest metropolitan regions (Naples, Bari, Palermo, Cagliari) between 1951 and 1981, becoming more intense in coastal, rural districts between 1991 and 2019. These findings delineate the predominance of density-independent mechanisms of population growth up to World War II, in a context of high fertility and accelerated emigration rates from Southern Italy. A density-dependent population growth was observed since 1951, enlarging socioeconomic disparities and consolidating the urban hierarchy centred on few large cities. Taken together, these results evidence the intrinsic nexus between demographic dynamics and agglomeration/scale factors fuelling urban expansion and state-driven industrialization in Italy.

Рекуперация тепла с использованием органического цикла Ренкина

Heat losses in industrial processes can be divided into three sections (high-, medium-, and low-temperature heat), depending on the temperature of the exhaust gases. This heat is usually recovered either by heat exchangers or by a closed Rankine cycle. However, about 60% of low-temperature heat losses remain irreplaceable. Currently, the organic Rankine cycle has become a promising method of low-temperature energy recovery, and several theoretical studies on this topic have appeared, but a small number of experimental studies have been performed. In our work, we have built a 2 kW heat recovery laboratory test bench using tube-type heat exchangers, a gear pump and a turbo expander on the working fluid R141b. As a result, we found that the efficiency of the cycle increases as the boiling point and pressure increase, but an increase in overheating at the inlet of the expander leads to a decrease in efficiency due to the use of the working fluid R141b. At the inlet of the evaporator and the outlet of the condenser, respectively, overheating and supercooling of the working fluid occurs, which negatively affects the efficiency of the cycle. The amount of useful heat obtained was 45.4 W with an efficiency of 2.24%. as a result of low efficiency of the expander and pump, as well as leaks during the test. The development of an experimental test bench with working on organic Rankin cycle requires long-term research work and great scientific potential. In the future, it will be necessary to create a new test bench based on a deeper study, so that we can get a higher efficiency of the expander and pump, which would affect the efficiency of this cycle. Also, we need to replace the working fluid in the cycle with a more efficient one.

Investigation on the performance of ‘Fino’ materials to stabilize expansive soil: A case study in Yeka Sub City, Addis Ababa, Ethiopia

Expansive soil swells when it is wet, and it will shrink when it dries. Due to this behavior of the soil, the strength and other properties of soil are inferior. To improve its properties, it is necessary to stabilize the soil with different stabilizers. Soil stabilization is a process to treat the soil to maintain, alter, or improve expansive soil performance. In this study, the potential of 'Fino' as stabilizing additive to expansive soil was investigated for the improving engineering properties of expansive soil to be used as subgrade material. The evaluation involved the determination of the Free Swell test, CBR test, Atterberg's limits, and the Proctor test of expansive soil in its natural state as well as when mixed with varying proportions of 'Fino.' The practices were performed on six proportions 5%, 10%, 15%, 20%, 25% and 30 % with expansive soil. The research result indicated a considerable reduction in Swelling, and the Maximum dry Density of soil was improved. Optimum moisture content decreased in increasing 'Fino.' At 30% of 'Fino,' the CBR values of expansive soil increased from 1.06% to 5.94%, Liquid Limit decreased from 95.2% to 29.4%, plasticity index decreased from 57.24% to 17.82% and the degree of expansion of the natural subgrade soil has reduced from very high to medium. Hence, it is concluded that the 'Fino' at 30% has shown significant improvement in the expansive soil's engineering properties meeting the ERA and AASHTO Standard specifications requirements for road subgrade material.

Design of 10 kW Low Temperature Power Cycle Using Amine— CO2 Fluid

Our thermodynamic study indicated that low temperature power cycle using amine-CO2 fluid can obtain the performance equal to or higher than that of the current organic Rankine cycle. We designed a 10 kW test equipment. We set high temperature heat source is hot water at the temperature of 90°C and the flow rate of 8,200kg/h, which is a coolant from a gas engine. The heat and mass balance of the equipment was calculated thermodynamically. The result showed the power of 10.5kW and the system efficiency of 7.3 per cent at the the amine – CO2 fluid flow rate of 1,000kg/h, and the turbine expansion ratio of 4.8. The preliminary estimation shows as follows. The diameter and rotational speed of the turbine blade are 0.115m and 54,400min-1, respectively. The number, width, and length of the recuperator plates are 20, 117mm, and 835mm, respectively. The height and cross sectional area of the absorption bed are 0.35m and 0.027m2, respectively.

The Application of an Expansion Turbine in the Production of Expanded Aggregates

The research into the expansion of Cypris clay from the overburden rocks of the Družba brown coal open-pit mine in North Bohemia has proven that targeted expansion enables good use of the thermal energy of hot aggregates, which has not yet been fully exploited. The integration of an electricity production expansion turbine into the production line and the use of residual gas heat in the turbine cycle can reduce production costs. The article assesses two possible solutions for the integration of the expansion turbine into the technological line, namely with an open and closed working cycle using various gaseous media. In both cases, the proportion of the energy usable for electricity generation in the expansion turbine cycle has been calculated along with the possible fuel savings in the rotary kiln by using combustion air preheated to a high temperature by the residual heat of the gas from the turbine gas cycle.

Oxy-fuel combustion of natural gas: A review

The article compares newly developed methods of natural gas combustion through oxy-fuel technologies. It describes in detail the basic technological differences and ordering of technological parts for five different cycles using carbon dioxide and steam as a working medium in expansion turbines in electricity production. Among the procedures using steam as the working medium, attention is focused on GRAZ and CES cycles. In oxy-fuel procedures utilising carbon dioxide produced by natural gas combustion, the focus is on COOLCEP, MATIANS and COOPERATE cycles. For each cycle described, the respective operating conditions and principles are given. Additionally, detailed process diagrams are also provided. Important advantages of all of these cycles include the possibility of the combustion of not only liquefied natural gas but also other gaseous fossil fuels, whose introduction into production is not very time-consuming, and the possibility of connection to power distribution network within a relatively short period of time.

A novel volatile organic compound cryogenic recovery system with cold energy storage

For recovery of volatile organic compounds (VOCs) from exhaust gas, the traditional condensation method cannot meet existing emission standards because the refrigeration is insufficient, and the operating cost is high when dealing with exhaust gas discharged intermittently or under variable conditions. To overcome these problems, a novel VOC cryogenic recovery system with cold energy storage has been designed by combining turbine expansion refrigeration technology with cold energy storage technology. Intermittently discharged oil gas was selected as the treatment object, and steady-state and dynamic simulation of the system was carried out by HYSYS. The steady-state simulation results show that the non-methane total hydrocarbon emission concentration (NMHC) after treatment is 57.54 mg/Nm3 and the comprehensive recovery rate of oil gas is as high as 99.99%, which can meet the current emission standards. In addition, due to the application of cold energy storage technology, the system can use valley power for large-scale cold storage, providing cooling capacity for system operation at peak power consumption, which can reduce the operating cost. Finally, the dynamic simulation results show that the system has good dynamic characteristics. When the feed condition of the system is disturbed, the system can recover stability, and the overall performance parameters are less disturbed, which proves that the system can deal effectively with off-design VOC exhaust gas. The conclusions of this paper are of great significance to industrial applications involving VOC exhaust gas with variable conditions and intermittent emission.

A Study on the Performance and Policy Evaluation of Turbo Expander Generation Interconnected to Distribution Systems

In the face of environmental problems, the energy industry needs to convert energy sources into clean energy, but the technological maturity of renewable energy such as solar and wind power is not high enough, so each country is implementing expansion and dissemination policies based on various systems. The most representative energy policy, renewable energy certificate (REC) transaction system, based on the renewable portfolio standard (RPS), is a policy to supplement the economic feasibility of renewable generations until the technological maturity of them is completed, and is characterized by giving proper weights to each sources. TEG, a power generation source that utilizes waste pressure in the process of decompressing high-pressure gas, is one of the new renewable power candidates in the spotlight in terms of high eco-friendliness and energy recovery. In this paper, the economic and policy factors are evaluated to calculate the REC multipliers for new types of power sources. In particular, it is estimated based on the power generation and electricity sales performance data collected through the operation of the 300 kW TEG operating at the Gimhae decompression facility in Korea.

Down-speeding diesel engines with two-stage turbochargers: Analysis and control considerations

Diesel engines continue to be used in truck applications, so reducing fuel use and hence CO2emissions, is a priority. Single-stage turbocharged diesel engines are known to be fuel efficient under steady load at low speeds. However, the engine’s ability to track load transients becomes limited by emission constraints due to the rate of production values for smoke and the resulting higher nitrogen oxides (NOx). Modern air-path solutions including a variable geometry turbine (VGT) and high pressure exhaust gas recirculation (EGR) can be used to improve dynamic response without increasing NOxemissions, but lead to complex interactions that can be difficult to control. This paper develops a two-stage, in-series, air-path configuration, which improves the typical part-load performance at low engine-speeds through adjustments to the turbine expansion ratios. Better EGR rates (for NOxreduction) at low engine speeds can be achieved whilst the engine transient response is maintained. The air-path system is simulated using Ricardo Wave software and analysed for steady-state and transient behaviour in order to identify the relationships, constraints and performance measures for different operating regions that specify the controller requirements.

Thermodynamic analysis and optimization of organic Rankine cycles based on radial-inflow turbine design

In recent years, high-temperature organic Rankine cycle (ORC) with a heat source temperature over 300 °C has attracted interests, which has wide range of applications from industrial point of view. However, few researchers have focused on the coupled design and optimization of the high-temperature ORC system and radial-inflow turbine (RIT). In this work, a coupled design of the ORC system and RIT with the heat source inlet temperatures of 300, 350 and 400 °C is developed using non-dominated sorting genetic algorithm. The ORC thermal efficiency and turbine performance factor (PF) are introduced as optimization objectives. Two mixtures of siloxanes, seven pure siloxanes and nine pure hydrocarbons are considered as working fluid candidates. In addition, the thermodynamic comparison between mixtures of siloxanes and pure working fluids is presented. Moreover, the influences of the turbine inlet total temperature, total-to-static expansion ratio, and specific speed on the ORC thermal efficiency, turbine performance, and turbine size are investigated. The results show that the turbine power output and cycle thermal efficiency are more sensitive to the expansion ratio while turbine size is more sensitive to the turbine inlet total temperature and specific speed. In addition, PF increases with the rise of the turbine inlet total temperature, expansion ratio and specific speed. Moreover, compared with pure working fluids, mixtures of siloxanes have higher efficiencies, but larger turbine and heat exchanger size. Cyclohexane, toluene, m-xylene and hexane with higher PF and smaller size of turbine and heat exchanger are promising working fluids in applications where the compact turbine and heat exchanger is preferred, such as vehicle waste heat recovery.

Preliminary plant design of thermochemical conversion for rice straw-based second-generation bioethanol production in West Java

Thermochemical conversion is selected in the design of a rice straw-based bioethanol production plant. This study examines the gasification and catalytic synthetic process technologies of rice straw into ethanol. The size of rice straw was reduced and dried before entering the gasification reactor to convert into syngas. The clean gas goes to the mixed alcohol synthesis process in a plug flow reactor with CuO/ZnO as a catalyst. The product is then purified through several separation methods, i.e., column distillation, stripping, and absorption. The controlled parameters for this plant are temperature, flow rate, pressure, level, and concentration. The paper describes the piping instrumentation diagram with a graphical representation of the equipment, piping, and instrumentation. A Heat Exchanger Network analysis achieves an efficiency of 34.4%. The electricity required is fulfilled by turbine expander for about 1,493 kW, and the rest of it is provided by PLN, besides an emergency generator sets. The capacity of this plant is 100,000 kL/year.

Influence of Pre-Turbine Small-Sized Oxidation Catalyst on Engine Performance and Emissions under Driving Conditions

The earlier activation of the catalytic converters in internal combustion engines is becoming highly challenging due to the reduction in exhaust gas temperature caused by the application of CO2 reduction technologies. In this context, the use of pre-turbine catalysts arises as a potential way to increase the conversion efficiency of the exhaust aftertreatment system. In this work, a small-sized oxidation catalyst consisting of a honeycomb thin-wall metallic substrate was placed upstream of the turbine to benefit from the higher temperature and pressure prior to the turbine expansion. The change in engine performance and emissions in comparison to the baseline configuration are analyzed under driving conditions. As an individual element, the pre-turbine catalyst contributed positively with a relevant increase in the overall CO and HC conversion efficiency. However, its placement produced secondary effects on the engine and baseline aftertreatment response. Although small-sized monoliths are advantageous to minimize the thermal inertia impact on the turbocharger lag, the catalyst cross-section is in trade-off with the additional pressure drop that the monolith causes. As a result, the higher exhaust manifold pressure in pre-turbine pre-catalyst configuration caused a fuel consumption increase higher than 3% while the engine-out CO and HC emissions did around 50%. These increments were not completely offset despite the high pre-turbine pre-catalyst conversion efficiency (>40%) because the partial abatement of the emissions in this device conditioned the performance of the close-coupled oxidation catalyst.

The Current State of the Engineering Method for the Optimal Gas-Dynamic Design and Calculation of Centrifugal Compressor

In the practice of centrifugal compressor designing, different engineering techniques are widely used because flow motion differential equations cannot be integrated, and Computational fluid dynamics cannot resolve the problem as a whole. Engineering personal computers’ programs are based on experimental data and the gas dynamics theory. The universal modeling method’s (UMM) mathematical model is a set of equations that determine the pressure loss in the elements of the centrifugal compressor flow path. By the earlier versions of the UMM, dozens of process compressors were designed. Several sets of empirical coefficients for stages of different specific speeds were applied. The paper presents the current state of the universal modeling method that was recently improved. The models of the centrifugal compressor characteristic calculation are described. A new model of the loading factor characteristic, an improved version of the compressor efficiency, and being based on a CFD-calculation vaneless diffuser model are samples of the improvements. Careful identification and verification demonstrate effective characteristic simulation with a single set of empirical coefficients. Centrifugal compressor new design examples of a turbo expander unit and a turbocharger are presented. The calculated characteristics are compared with the test results. For both objects, the experiments confirmed the calculated gas-dynamic characteristics with sufficient accuracy for engineering methods.