Compressor Inlet Research Articles

A comprehensive study of simple and recuperative gas turbine cycles with inlet fogging and overspray

Ambient temperature has an adverse effect on gas turbine performance. This problem could be overcome through air cooling technologies such as evaporative cooling, fogging, mechanical cooling, absorption chillers, and thermal energy storage. Therefore, this article aims to evaluate the performance of simple and regenerative gas turbine cycles at dry and wet compression cases. A numerical model was constructed for this purpose then the model was validated for dry cycle conditions with an existing turbine SULZER S3 performance data. An inlet fogging was used to full saturate the inlet air and overspray was used for decreasing the compressor inlet temperature at various ambient temperatures. The results showed that the inlet fogging and overspray reduce the compressor work up to 12%. The results also showed that the thermal efficiency was improved with using the inlet fogging and by increasing the overspray rate. The highest thermal efficiency of 44% was achieved when overspray 3% with recuperation was applied. It can be concluded from this work that the specific fuel consumption is reduced significantly and the output power increases, increasing the thermal efficiency when using the recuperator combined with the wet compression and the overspray.

Surge prevention for gas turbines connected with large volume size: Experimental demonstration with a microturbine

The aim of this work is the demonstration of a surge prevention technique for advanced gas turbine cycles. There is significant surge risk in dynamic operation for turbines connected with large volume size additional components, such as a fuel cell stack, a saturator, a solar receiver or a heat exchanger for external combustion. In comparison with standard gas turbines, the volume size generates different behaviour during dynamic operations (with significant surge risk), especially considering that such additional components are including important dynamic constraints.In order to prevent the surge events, a vibration analysis was carried out to develop precursors which are able to highlight the approach of this unstable operative zone. Since the sub-synchronous content of the measured vibrations is significantly increasing approaching the surge line, special attention was devoted to this parameter.The demonstration of a surge prevention system based on the sub-synchronous vibration content was carried out at the Innovative Energy Systems Laboratory of the University of Genoa. In this laboratory, a recuperated microturbine connected with a large size vessel was used. Starting from the stable operation, closing a valve in the main air line or increasing the compressor inlet temperature produced operative conditions with significant surge risk. The increase in sub-synchronous vibration content detected by the control system was used to perform an active operation (bleed valve opening) to avoid the approaching surge event.

Flow in a High-Velocity Mixed Compression Inlet Studied by the RANS/ILES Method in Different Operation Modes

The separated flows taking place in different-geometry diffusers and in a high velocity inlet have been studied by the Reynolds Averaged Navier-Stokes–Implicit Large Eddy Simulation (RANS/ILES) method. The presented modified method makes it possible to increase the computation accuracy of separated areas and attached boundary layers. The flows in a model inlet of mixed compression with a rectangle cross section are calculated for incoming flow Mach number of 5.9 on a grid with 4.13 × 106 cells, beginning with a mode without throttling and finishing with buzz mode. The boundary where the inlet becomes unstable, if throttling is increased, is determined. The relationship of the pressure on time at the upper wall of the inlet isolator channel for all modes, including the buzz mode, is compared with the experimental one. The correlation between inlet throttling and buzz frequency is revealed. The performance curve is determined. The experimental and calculated results are in good agreement for all available experimental parameters for the examined inlet. The presented method demonstrates higher accuracy with respect to the calculations performed by the LES method on the fine grid of the examined inlet.

Energy, Exergy, Economic, and Environmental analysis for various inlet air cooling methods on Shahid Hashemi-Nezhad gas turbines refinery

In this paper, the effects of various compressor inlet air cooling methods to increase the performance of Shahid Hashemi-Nezhad gas turbines refinery were investigated. These methods included media, fogging, and absorption chillers as common inlet air cooling methods and pressure drop station as novel cooling method. By using the exergy, environmental, and economic analysis, the best method for compressor inlet air cooling was selected. Based on the results, the absorption chiller system had the highest compressor inlet air temperature drop and increased the thermal and exergy efficiencies of cycle by about 2.5 and 3%, respectively, in hot season. Using absorption chiller, pressure drop station, fogging, and media had further reduction in CO2 and CO than simple gas turbine, respectively. Finally based on the net present value and internal rate of return coefficients, the pressure drop station method is the most economically feasible option.

Thermoeconomic analysis of a gas turbine and cascaded CO2 combined cycle using thermal oil as an intermediate heat-transfer fluid

This paper reports an investigation of a gas turbine (GT) and two-stage cascaded supercritical and transcritical CO2 (s-CO2/t-CO2) combined power cycle using liquefied natural gas (LNG) as a low-temperature heat sink. This cycle may be well-suited for installation near LNG import terminals. GT exhaust supplies input heat to an intermediate s-CO2 cycle through a thermal oil loop. Waste heat from the s-CO2 cycle and residual heat from the GT cycle drives a lower temperature t-CO2 cycle. The t-CO2 cycle is LNG-cooled. A solution procedure is performed to perform a coupled analysis of the thermodynamic and economic performance of this combined cycle. Results show that the GT-cascade CO2 combined cycle has an optimal operating point determined by the s-CO2 compressor inlet conditions. Genetic algorithm (GA) optimization indicates that a Taurus 60 GT-cascaded CO2 combined cycle could reach 51.44% efficiency. For 20-year lifetime and 5% rate of interest, thermoeconomic optimization (after-tax profit, ATP as objective) results show ATP, levelized cost of electricity (LCOE) and net power are $2.935 × 106, $0.0420 kWh−1 and 8.886 MW, respectively. Findings suggest that the GT-cascaded CO2 combined cycle is an efficient and commercially viable technology for power generation.

The performance assessment of a combined organic Rankine-vapor compression refrigeration cycle aided hydrogen liquefaction

In this study, the performance of the combined cooling cycle with the Organic Rankine power cycle, which provides cooling of the hydrogen at the compressor inlet which compresses the constant temperature in the Claude cycle used for hydrogen liquefaction, on the system is examined. The Organic Rankine combined cooling cycle was considered to be using a geothermal source with a flow rate of 120 kg/s at a temperature of 200 °C. The first and second law performance evaluations of the whole system were made depending on the heat energy at different levels taken from the geothermal source. The thermodynamic analysis of the equipment making up the system has been done in detail. The temperature values at which the hydrogen can be effectively cooled were determined in the presented combined system. The efficiency coefficient of the total system was calculated based on varying pre-cooling values. As a result of the study, it was determined that cold entry of hydrogen into the Claude cycle reduced the energy consumption required for liquefaction. Amount of hydrogen cooled to specified temperature increase by increase in mass flow of geothermal water and its temperature. Liquefaction cost is calculated to be 0.995 $/kg H2 and electricity produced by itself is calculated to be 0.025 $/kWh by the new model of liquefaction system. Cost of the liquefaction in the proposed system is about 39.7% lower than direct value of hydrogen liquefaction of 1.650 $/kg given in the literature.

Optimization of wet compression effect on the performance of V94.2 gas turbine

Wet compression has been widely used in recent years for power augmentation and gas turbine efficiency improvement. In order to explore this issue, the paper first focuses on the effects of wet compression, an analytical method based on droplet evaporation. Matching compressor-turbine or typically matching component has been added to this model for the compatibility of mass flow, rotational speed and power. Since this essay advances the idea of optimization, one of the metaheuristic algorithms Cuckoo Search (CS) has been considered. Three variables including droplet diameter, amount of overspray and droplet size have been taken into account. The objective function is turbine output work where compressor will work out of surge and choke domain. The numerical results indicate degradation in compressor inlet air temperature and noticeable power increments.

Measuring turbocharger compressor inlet backflow through particle image velocimetry

An experimental measurement campaign is presented where particle image velocimetry (PIV) was used in an effort to characterize the velocity field in a turbocharger compressor when unstable operating conditions lead to flow reversing from the diffuser into the inlet pipe. Previous studies have successfully used this and similar techniques, but the most relevant results have been obtained in an open compressor where the backflow can diffuse into the ambient. In this work a glass pipe long enough to confine the full extent of the backflow has been used. Advantage was taken from the fact that this backflow is at higher temperature due to the compression process, enabling a preliminary work where a thermocouple array was used to estimate its maximum length across the compressor map. Using these results as a reference both axial and transversal velocity fields were measured. Issues associated with each one are described, along with relevant results that show how the technique correctly identifies the reversed flow, a conclusion that is supported by the comparison of the velocity average and standard deviation profiles with those of measured temperature.

Operation matching model and analysis between an air inlet and a compressor in an Air Turbo Rocket

Operation matching between an air inlet and a compressor in an Air Turbo Rocket (ATR) is crucial to the full development of the advantages of engines. In this study, operation characteristic models of an air inlet and a compressor were established and verified through numerical simulation to gain the matched operation characteristics of the air inlet and the compressor in an ATR. The air inlet–compressor matching model was constructed on the basis of coupling relations, such as “flow equilibrium,” “interface parameter equilibrium,” and “pressure ratio equilibrium,” between the air inlet and the compressor in the ATR. Finally, the integrated 3D numerical simulation of the air inlet–compressor was verified. Results demonstrate that (1) the operation characteristic model of the air inlet can accurately calculate the effects of backpressure in the air inlet (Pb) on the total pressure recovery coefficients of the throat, the supersonic diffuser, and the whole air inlet in the ATR. Model prediction results are highly accurate as confirmed by 3D numerical simulation results in the following ranges: 2.75 < Ma < 3.75 and 0.5 atm <Pb < 3 atm. The maximum absolute error is less than 0.05. (2) The centrifugal compressor model can indicate the airflow and performance parameters of different characteristic sectors of impeller entrance, compressor exit, and axial diffuser entrance and exit. The 3D numerical simulation reports that the maximum relative errors of static pressure, total pressure, and total temperature predictions are 13.25%, 11.30%, and 5.65%, respectively. (3) The constructed air inlet–compressor matching model can rapidly predict the airflow parameters and performance parameters of their characteristic sections under specific operation conditions. The “most stable operation curve” introduced in the pressure ratio characteristic curve of the compressor can quickly and accurately accomplish the initialization of matching iterative computations, thereby solving aerodynamic coupling problems on an air inlet–compressor interface. (4) The integrated 3D numerical simulation of the air inlet/compressor reveals that the relative errors of 17 in 18 airflow parameters of two components are lower than 8%, and the relative error of the other parameters is 10.91%. The model exhibits high accuracy and can satisfy the requirements for the performance prediction of air inlet systems in ATR.

Effect of Impurities on Compressor and Cooler in Supercritical CO2 Cycles

With the increasing demand for electric power, the development of new power generation technologies is gaining increased attention. The supercritical carbon dioxide (S-CO2) cycle is one such technology, which has relatively high efficiency, compactness, and potentially could provide complete carbon capture. The S-CO2 cycle technology is adaptable for almost all of the existing heat sources such as solar, geothermal, fossil, nuclear power plants, and waste heat recovery systems. However, it is known that optimal combinations of operating conditions, equipment, working fluid, and cycle layout determine the maximum achievable efficiency of a cycle. Within an S-CO2 cycle, the compression device is of critical importance as it is operating near the critical point of CO2. However, near the critical point, the thermo-physical properties of CO2 are highly sensitive to changes of pressure and temperature. Therefore, the conditions of CO2 at the compressor inlet are critical in the design of such cycles. Also, the impurity species diluted within the S-CO2 will cause deviation from an ideal S-CO2 cycle as these impurities will change the thermodynamic properties of the working fluid. Accordingly, the current work examines the effects of different impurity compositions, considering binary mixtures of CO2 and He, CO, O2, N2, H2, CH4, or H2S on various S-CO2 cycle components. The second part of the study focuses on the calculation of the basic cycles and component efficiencies. The results of this study will provide guidance and define the optimal composition of mixtures for compressors and coolers.

Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors—Additional Findings

This study presents additional important findings to the results of the research paper; “Optimization of the efficiency of stall control using air injection for centrifugal compressors” published in the Journal of Engineering for Gas Turbines and Power in 2015 (Halawa, T., Gadala, M. S., Alqaradawi, M., and Badr, O., 2015, “Optimization of the Efficiency of Stall Control Using Air Injection for Centrifugal Compressors,” ASME J. Eng. Gas Turbines Power, 137(7), p. 072604). The aim of this study is to make a fine determination of the injection angle, which provides the best stable condition when the compressor operates close to stall condition. A relatively narrower range of injection angles with smaller intervals was selected comparing to the results of the referred published paper, which clarified that the best injection angle is 30 deg. External air was injected close to the diffuser entrance at the shroud surface. Injection was applied with mass flow rate equals 1.5% of the design compressor inlet mass flow rate with injection angles ranged from 16 deg to 34 deg measured from the tangential direction at the vaneless region. It was found that both of injection angles of 28 deg and 30 deg achieved the best results in terms of compressor stabilization but each one of them has a specific advantage comparing to the other one. Using injection angle of 28 deg provided the lowest kinetic energy losses while the best orientation of the fluid through diffuser resulted when using an injection angle of 30 deg.

Hybrid-Electric Turbocharger and High-Speed SiC Variable-Frequency Drive Using Sensorless Control Algorithm

Electrically assisted engine boosting systems lend themselves to better throttle response, wider effective operating ranges, and can provide the ability to extract excess energy during deceleration and high-load events (and store it in a vehicle's onboard batteries). This can lead to better overall vehicle performance, emissions, and efficiency while allowing for further engine downsizing and increased power density. In this research effort, a hybrid-electric turbocharger, variable-frequency drive (VFD), and novel sensorless control algorithm were developed. An 11 kW permanent-magnet (PM) machine was coupled to a commercial turbocharger via an in-line, bolt-on housing attached to the compressor inlet. A high-efficiency, high-temperature VFD, consisting of custom control and power electronics, was also developed. The VFD uses SiC MOSFETS to achieve high-switching frequency and can be cooled using an existing engine coolant loop operating at up to 105 °C at an efficiency greater than 98%. A digital sliding mode-observer sensorless speed control algorithm was created to command and regulate speed and achieved ramp rates of over 68,000 rpm/s. A two-machine benchtop motor/generator test stand was constructed for initial testing and tuning of the VFD and sensorless control algorithm. A gas blow-down test stand was constructed to test the mechanical operation of the hybrid-electric turbocharger and speed control using the VFD. In addition, a liquid-pump cart was assembled for high-temperature testing of the VFD. Initial on-engine testing is planned for later this year. This paper intends to present a design overview of the in-line, hybrid-electric device, VFD, and performance characterization of the electronics and sensorless control algorithm.

Inverted Brayton Cycle With Exhaust Gas Condensation

Approximately 30% of the energy from an internal combustion engine is rejected as heat in the exhaust gases. An inverted Brayton cycle (IBC) is one potential means of recovering some of this energy. When a fuel is burnt, water and CO2 are produced and expelled as part of the exhaust gases. In an IBC, in order to reduce compression work, the exhaust gases are cooled before compression up to ambient pressure. If coolant with a low enough temperature is available, it is possible to condense some of the water out of the exhaust gases, further reducing compressor work. In this study, the condensation of exhaust gas water is studied. The results show that the IBC installed in series on a turbocharged engine can produce an improvement of approximately 5% in brake-specific fuel consumption at the baseline conditions chosen and for a compressor inlet temperature of 310 K. The main factors that influence the work output are heat exchanger pressure drop, turbine expansion ratio, coolant temperature, and turbine inlet temperature. For conditions when condensation is possible, the water content of the exhaust gas has a significant influence on work output. The hydrogen to carbon ratio of the fuel has the most potential to vary the water content and hence the work generated by the system. Finally, a number of uses for the water generated have been presented such as to reduce the additional heat rejection required by the cycle. It can also potentially be used for engine water injection to reduce emissions.

Techno-economic analysis of waste heat recovery systems for wet-cooled combined cycle power plants

Increasing ambient temperature negatively impacts the performance of natural gas combined cycle (NGCC) power plants. There have been multiple approaches to mitigate this performance reduction by chilling the compressor inlet air of the gas turbine, as well as by recovering the waste heat emanating from the power plant to generate additional power. In the present study, a detailed techno-economic assessment on the application of different types of waste heat recovery systems used to chill the compressor inlet air has been assessed. A simplified thermodynamic and heat transfer model is developed to predict the performance of an evaporatively cooled NGCC at varying ambient conditions. By taking typical meteorological year (TMY3) hourly weather data for two different locations – Los Angeles, California and Houston, Texas – the yearly output for a 565 MW plant is predicted at a 100% capacity factor. The feasibilities of different waste heat recovery (WHR) systems including a flue gas driven absorption chiller, a steam driven absorption chiller, and an electrically driven vapor compression chiller are assessed by calculating the levelized cost of electricity (LCOE) for each scenario. The results of the analysis showed that, for a fixed WHR system costs (i.e., $ per kWth), the system powered by flue gas generated the smallest LCOE, followed by the mechanically-driven vapor compression, steam-heated chiller, and, finally, the gas turbine exhaust chiller for both the locations at all COP combinations. The analysis also investigated the impact of fixed investments cost, and the flue gas system again yielded the smallest LCOE, while still yielding a lower LCOE than at baseline case over a wide range of COP and tolerable cooling costs for both locations.

Investigation of air cooler fan start-up delay in liquid refrigerant defrosting system

To prevent problems concerning rapid rise in cold-storage temperature and severe frosting of the compressor inlet in liquid refrigerant defrosting systems (LRDS), a shutter has been installed upstream of the air cooler as well as the motor damper installed downstream. It is also proposed that the air-cooler fan is switched into operation delay after defrosting. Experimental results demonstrate that the best time to switch the fan into operation post defrosting is when the enclosed-space temperature of the air cooler falls in line with the cold-storage temperature. Time delays for the fan were set as 8.6 min, 8.8 min, and 8.9 min corresponding to frost-mass values of 1 kg, 2 kg, and 3 kg, respectively. Through use of the proposed technique, the observed increase in cold-storage temperature was controlled within 5 °C. In addition, gas return temperature of the compressor was observed to be greater compared to that of the air cooler; the compressor, therefore, utilized the available superheat to prevent the occurrence of wet compression.

Thermodynamic Analysis of Supercritical CO2 Power Cycle with Fluidized Bed Coal Combustion

Closed supercritical carbon dioxide (S-CO2) Brayton cycle is a promising alternative to steam Rankine cycle due to higher cycle efficiency at equivalent turbine inlet conditions, which has been explored to apply to nuclear, solar power, waste heat recovery, and coal-fired power plant. This study establishes 300MW S-CO2 power system based on modified recompression Brayton cycle integrated with coal-fired circulating fluidized bed (CFB) boiler. The influences of two stages split flow on system performance have been investigated in detail. In addition, thermodynamic analysis of critical operating parameters has been carried out, including terminal temperature difference, turbine inlet pressure/temperature, reheat stages, and parameters as well as compressor inlet pressure/temperature. The results show that rational distribution of split ratio to the recompressor (SR1) achieves maximal cycle efficiency where heat capacities of both sides in the low temperature recuperator (LTR) realize an excellent matching. The optimal SR1 decreases in the approximately linear proportion to high pressure turbine (HPT) inlet pressure due to gradually narrowing specific heat differences in the LTR. Secondary split ratio to the economizer of CFB boiler (SR2) can recover moderate flue gas heat caused by narrow temperature range and improve boiler efficiency. Smaller terminal temperature difference corresponds to higher efficiency and brings about larger cost and pressure drops of the recuperators, which probably decrease efficiency conversely. Single reheat improves cycle efficiency by 1.5% under the condition of 600°C/600°C/25Mpa while efficiency improvement for double reheat is less obvious compared to steam Rankine cycle largely due to much lower pressure ratio. Reheat pressure and main compressor (MC) inlet pressure have corresponding optimal values. HPT and low pressure turbine (LPT) inlet temperature both have positive influences on system performance.

4E modeling and multi-criteria optimization of CCHPW gas turbine plant with inlet air cooling and steam injection

An integrated plant for production of combined cooling, heating, power and water (CCHPW) has been investigated here. The plant included a gas turbine (with steam injection in combustion chamber), an HRSG producing steam (with reheat and dual drum pressures) and absorption refrigeration system (for both space and inlet air cooling). Four E (Energy, Exergy, Environmental, and Economic) modeling and optimization of an integrated CCHPW plant was performed to evaluate the optimum values of nine design parameters. Multi-objective optimization of CCHPW plant using genetic algorithm method with exergy efficiency and total annual cost (TAC) of system as two objective functions was applied. Results showed that at the optimum design point, compressor inlet air temperature was 18.5 °C and steam injection into combustion chamber of gas turbine was 1.8%. The exergetic efficiency and TAC of integrated CCHPW plant at the selected optimum point was 30.7% and 28.545 million dollars, respectively. The payback period of about 4.38 years was estimated for the analyzed plant at the optimum design point. Finally, the sensitivity analysis of change in capital investment and fuel costs on the optimal values of design parameters was also performed and presented.

One-dimensional univariate work simulation of turbocharged engine with restrictor before compressor inlet

All over the world, and in Russia, especially, the engineering sports competitions "Formula Student" are gaining popularity. Formula Student - is an international competition held among students of technical universities, in order to get practical knowledge in the process of developing and building a Formula student class racecar. When creating a car, you must adhere to strict technical regulations. So, one of the limitations is the maximum engine capacity - 710 cubic meters, which, in itself, implies the use of a motorcycle engine. A mandatory condition is the presence of a restrictive nozzle (restrictor) which have 20 mm diameter and placing in the inlet system. This causes many problems when designing engine intake systems. However, it allowed using various systems of pressurization of engines. The most common and effective is the installation of the turbocharger. This helps to solve the problem of insufficient amount of air that entering to the engine. Moreover, with the correct configuration of all components of the intake system in combination with the turbocharger, it is possible to achieve power and torque exceeding the standard engine without a restrictive nozzle. The article presents the data obtained in the course of a one-dimensional simulation of the KTM LC4 engine with a turbocharger and a restrictor in the intake manifold. The purpose of the work is to reduce the negative influence of the restrictor on the power and torque parameters of the KTM LC4 engine by using a turbocharger. In the course of the work, an analysis was made of gas-dynamic processes occurring in various parts of the engine intake system that affect its output values based on numerical studies. Because of the research, the dependences of the output parameters of the engine (maximum power and maximum torque) on the parameters, shapes and sizes of various components of the intake system with a turbocharger.

Deep seawater intake for primary cooling in tropical offshore processing of natural gas with high carbon dioxide content: Energy, emissions and economic assessments

In deepwaters offshore oil-gas rigs, centrifugal compressor trains are major power consumers, requiring intercoolers conventionally designed assuming surface seawater for primary cooling, limiting compressor inlet gas temperatures to 40 °C at tropical sites. On the other hand, at tropical deepwaters the available deep seawater at 4 °C can be exploited to reduce compression power – nearly proportional to inlet gas absolute temperature – entailing energy, economic and environmental benefits. This work considers a new primary cooling for deepwaters offshore platforms based on deep seawater (DSW) intake at 4 °C from depths around 900 m, reducing the outlet temperature of intercoolers to 12 °C. DSW intake alternative is assessed in terms of power consumption, CO2 emissions and economy employing detailed equipment sizing and cost estimation. Depending on gas flow rate, it is shown that DSW intake lowers compressors power up to 9.2%, besides several indirect benefits: elimination of one CO2 compressor; 30% less heat transfer areas; 4.5% less fuel gas consumption; 4% less gas turbines power; 9.5% (15 MMUS$) less investment; 14.4% (226 t) less topside weight, while making refrigeration unnecessary for dew point adjustment. DSW intake also entails 5% more efficient energy usage and 9327 tCO2/y less emissions, boosting economic performance under carbon taxation.

Design of a Wide-Range Centrifugal Compressor Stage for Supercritical CO2 Power Cycles

Supercritical carbon dioxide (sCO2) power cycles require high compressor efficiency at both the design point and over a wide operating range. Increasing the compressor efficiency and range helps maximize the power output of the cycle and allows operation over a broader range of transient and part-load operating conditions. For sCO2 cycles operating with compressor inlets near the critical point, large variations in fluid properties are possible with small changes in temperature or pressure. This leads to particular challenges for air-cooled cycles where compressor inlet temperature and associated fluid density are subject to daily and seasonal variations as well as transient events. Design and off-design operating requirements for a wide-range compressor impeller are presented where the impeller is implemented on an integrally geared compressor–expander concept for a high temperature sCO2 recompression cycle. In order to satisfy the range and efficiency requirements of the cycle, a novel compressor stage design incorporating a semi-open impeller concept with a passive recirculating casing treatment is presented that mitigates inducer stall and extends the low flow operating range. The stage design also incorporates splitter blades and a vaneless diffuser to maximize efficiency and operating range. These advanced impeller design features are enabled through the use of direct metal laser sintering (DMLS) manufacturing. The resulting design increases the range from 45% to 73% relative to a conventional closed impeller design while maintaining high design point efficiency.