Gas Turbine Exhaust Research Articles

Performance of sCO2 Cycles for Waste Heat Recovery and Techno-Economic Perspective As Gas Turbine Bottoming Cycle

Abstract Supercritical carbon dioxide (sCO2) cycles are compact and widely adaptable to various heat sources, including the waste heat from gas turbine (GT) exhaust gases. While the addition of a steam cycle enhances the typical 40%-efficiency of GTs up to 60%, their substantial investments render them less appealing for smaller GTs. This creates an opportunity for sCO2 cycles, but a comprehensive comparison of their performance with that of steam across a range of applications remains lacking. Moreover, their applicability to various industrial scenarios based on existing installations is missing from a techno-economic standpoint. To address these needs, four promising sCO2 cycles are optimized and compared with the simple steam cycle. Their techno-economic performances are then investigated for 20 industrial GTs of different size. The analysis yielded performance maps demonstrating comparable performances for sCO2 and steam cycles, as well as significant techno-economic advantages for sCO2 bottoming cycles for smaller GTs. However, when it comes to larger GTs combined with reheats and expansions steam cycles, sCO2 cannot outperform them in current technological standards. Nevertheless sCO2 cycles offers an attractive alternative, facilitating cogeneration. Among the different approaches designed to integrate the heat requirements of amine-based capture, steam cycles have always proved more suitable because of the thermal stability of amines. In conclusion, the research underscores the cost-effectiveness and adaptability of sCO2 cycles for heat recovery applications, particularly as bottoming cycles for smaller GTs, while larger GTs present a challenge.

Numerical study of film cooling at the outlet of gas turbine exhaust

Abstract In order to mitigate the potential operational damage risk caused by traditional cooling methods in engineering applications of heavy-duty gas turbine component testing, the film cooling unit and realizable K-epsilon turbulence model were employed. Numerical simulations were conducted for multiple exhaust film holes with varying curvature and pitch-row under different operating conditions. The heat transfer distribution along the flow direction and radial direction of the high temperature wall was analyzed, as well as the influence of heat transfer under different geometrical parameters. The results indicate that for the integrated configuration of large-diameter cooling units, a blowing ratio of 0.3 yields the most comprehensive cooling effect, primarily due to the extensive spatial coverage by the gas film and the weakening of eddy dissipation mechanisms. Additionally, it was observed that with an increase in hole distance ratio for multiple exhaust film holes, cold air could more stably participate in heat exchange with high-temperature flue gas wake at the outlet of the gas film hole; thus, a hole distance ratio of 3.0 provides optimal comprehensive cooling effects.

Collaborative disposal of exhaust gas and waste wind turbine blades: Mechanical properties of recycled glass fibres and economic analysis

The accumulation of waste wind turbine blades poses significant environmental challenges. Pyrolysis offers an industrially viable solution for both disposal and the recycling of valuable glass fibers from these blades. Exhaust gas from industrials with waste heat can be utilized to reduce the process cost. However, for mixed atmosphere of exhaust gas containing both CO2 and O2, its influence on resin matrix decomposition characteristics and fiber mechanical properties are currently unclear. This work provided a solution collaborated with exhaust gas to disposal of waste wind turbine blades, in which operating parameters (atmosphere composition and process procedure) were optimized. Results showed that the early invention at pyrolysis with low concentration of O2 in exhaust gas played a major role in facilitating the formation of surface protection. Atmosphere during oxidation of pyrolytic residual carbon was crucial in maintaining fiber strength. At this stage, the interaction between CO2 (especially at 15% concentration) and O2 could mitigating fiber degradation through promoting the re-oxidization of Si dangling bonds and reducing water corrosion. However, stepwise processing of pyrolysis first and then oxidation under exhaust gas with O2 containing was not recommended due to its little cost-effectiveness. The single step disposal of wind turbine blades collaborated with coal-fired flue gas could increase the strength of recycled glass fiber by over 50% and reduced process costs by 34%.

Studi Numerik Pengaruh Penambahan Turning Vane Terhadap Bentuk Aliran dan Distribusi Temperatur di Heat Recovery Steam Genertor (HRSG)

Tanjung Uncang Power Plant is one of the facilities in Indonesia that utilizes CCGT (Combined Cycle Gas Turbine). This cycle uses an HRSG (Heat Recovery Steam Generator) to heat steam using the exhaust gases from the gas turbine. At Tanjung Uncang's HRSG, the SOP requires that the gas turbine exhaust during cold start conditions must be below 400°C. Meanwhile, the gas turbine at Tanjung Uncang has a base load of 5 MW with a temperature range of 560°C - 580°C. Therefore, an asynchronous process is necessary to reach the FSNL (Full Speed No Load) condition for the gas turbine, with the damper angles set at 51°, 68°, and 90° for 45 minutes. Additionally, to achieve optimal conditions with the gas turbine running at 45 MW, a time span of 8 hours is required, which results in losses of up to 700 million. The extended time required can be due to uneven flue gas distribution, necessitating time for the HRSG to reach optimal conditions. This underscores the need to analyze the effects of adding turning vanes with angles of 35°, 53°, and 71°, and inlet temperatures of 400°C and 580°C on the characteristics of flue gas distribution. The analysis was conducted using CFD with ANSYS Fluent 2021 software. The simulation outputs include velocity vectors, velocity contours, and temperature distribution contours.

Studi Numerik Pengaruh Sudut Bukaan Damper dan Flue Gas Temperatur Terhadap Distribusi Temperatur Pada Heat Recovery Steam Generator (HRSG)

The Combined Cycle Gas Turbine Power Plant (PLTGU) utilizes the waste heat from the gas turbine to produce steam in a Heat Recovery Steam Generator (HRSG). The steam from the HRSG is then used to generate electricity in a steam turbine. In HRSG operation, several variables significantly impact its performance, including the damper angle and inlet temperature. At the Tanjung Uncang Power Plant in Batam, the manufacturer's standard operating procedure (SOP) requires that the exhaust gas temperature when the damper is open must be below 400°C. However, the gas turbine with an initial load of 5 MW has an exhaust gas temperature of 560°C - 580°C. Therefore, it is necessary to perform a gas turbine load release or FSNL (Full Speed No Load) to reduce the inlet temperature of the gas turbine. During FSNL, there are SOPs for diverter damper angles of 51°, 68°, and 90°. This leads to the need for analyzing the impact of diverter damper angles and inlet temperature on the flow pattern and temperature distribution. The analysis was conducted using CFD (Computational Fluid Dynamics) with ANSYS Fluent 2020 software. The variations used are diverter damper angles of 51°, 68°, and 90°, combined with inlet temperatures of 400°C and 580°C. The simulation outputs include velocity contours, temperature contours, and equivalent stress on the superheater tubes. The HRSG simulation results show that the flue gas is not distributed uniformly. The turbine exhaust gas only spreads along 4 – 11 meters, leading to slower steam production from the superheater. Additionally, when the superheater tubes are empty, the steady-state thermal and structural simulation results indicate that an inlet temperature of 580°C, whether at damper angles of 51°, 68°, or 90°, can cause a larger temperature difference between the inner and outer walls, ranging from 117.04°C to 125.5°C. This temperature difference can lead to thermal stress on the superheater tubes. This is shown in the S-N Curve for SA 213 T22 material, with a convection coefficient of 5 W/m² K (no steam), where the equivalent stress exceeds the endurance limit (infinite zone).

Cryogenic carbon capture design through [formula omitted] anti-sublimation for a gas turbine exhaust: Environmental, economic, energy, and exergy analysis

To achieve a net zero-emission society, current industries must transition to become less carbon-intensive while fulfilling the rising power demand. In this study, we present a novel multigeneration system that produces power, cooling, and solid carbon dioxide by applying cryogenic carbon capture to a gas turbine flue gas. The energy recovery concept is efficiently employed to avoid energy and exergy losses in the system. The system is simulated in Aspen Plus with the mathematical models of the exergy streams and solid-vapor equilibrium written in Matlab. The performance of the plant is assessed based on energy, exergy, economic, and environmental evaluations. Thermodynamic analysis indicates that 1.2 MJ of electricity is required to capture 1 kg of CO2 from the gas turbine exhaust gas (which is lower compared to conventional systems) with 100 % CO2 purity. The net generated power, energy efficiency, exergy efficiency, m˙CO2,captured, and m˙CO2,emitted for the proposed system are 179.4 MW, 41.2 %, 59.3 %, 500,000 tons annually, and 255,000 tons a year, respectively. Sensitivity analysis shows that reducing the flue gas temperature positively impacts the CO2 content in the flue gas while having a negative effect on energy and exergy efficiency. The economic investigation shows that the system is economically profitable.

Economic and operational assessment of solar-assisted hybrid carbon capture system for combined cycle power plants

The paper presents a post-combustion CO2 capture process which involves two configurations for enhancing the CO2 separation driving force in the conventional amine-based Carbon Capture System (CCS): a multi-stage membrane module for selective exhaust gas recirculation (SEGR case) and the combination of turbine exhaust gas recirculation with SEGR (EGR + SEGR case). Furthermore, the stripper reboiler in both configurations is integrated with a parabolic trough solar collector field with a 4-h thermal energy storage to provide the required thermal duty for solvent regeneration. Various system components are designed, simulated, and integrated with an economic model to evaluate the system's techno-economic performance across a wide range of loads. The results show that the proposed designs have efficient part-load performance although efficiency degradation is inevitable during partial-loads. A stable supply of solar thermal energy results during the partial operation of NGCC even during night. The EGR + SEGR case represents the case with the lowest levelized cost of electricity and CO2 avoided cost, 81.43 $/MWh and 101.66 $/tonneCO2, among the CCS-equipped designs, which highlight the advantages of this design over baseline and SEGR case. The proposed hybrid system shows promise for significantly decarbonizing fossil-fuel power plants and increasing power sector flexibility.

Power Augmentation of Gas Turbine Using Exhaust Flue Gas Operated Vapor Absorption Machine

Industrial gas turbines (GT) that operate at constant speed are constant-volume-flow combustion machines. As the specific volume of air is directly proportional to the temperature, an increase in air density results in a higher air mass flow rate at low air ambient temperatures. This results more mass of air is now passes through same volume gas turbine space. Consequently, the gas turbine power output increases proportionally with the increase in air mass flow rate. For geographic regions where warm and humid months are predominant throughout the year, significant power loss occurs during these months, and a higher rate of expensive fuel is fired at reduced power output. A gas turbine inlet air cooling technique is a useful option to enhance GT output. One of the innovative options for power augmentation of gas turbine is inlet air conditioning using a vapor absorption machine (VAM). Using VAM for GT intake air conditioning has the advantage over other systems in that it can be operated from waste heat. Many gas turbine machines, particularly natural gas pumping stations, are operated without heat recovery steam generator (HRSG) or heat recovery option. Valuable heat energy is escaped with exhaust flue gas in these systems. This paper demonstrates how GT exhaust waste heat can be utilized for its own power generation enhancement. In this study, a flue gas-based vapor absorption machine is selected for cooling the inlet air of a 26 MW gas turbine, which is used to drive the booster compressor of a natural gas pumping station. The capacity of the VAM for the required cooling effect has been calculated. The expected GT power enhancement from intake air gas conditioning has also been estimated in this paper.

A novel biogas-driven CCHP system based on chemical reinjection

In the process of vaporizing water within the biogas-driven CCHP system based on chemical recuperation, a significant temperature disparity in heat transfer exists, leading to increased irreversible loss, and the methane conversion rate is low because the gas turbine exhaust gas is difficult to drive efficient methane conversion. This paper proposed a novel biogas-driven CCHP system based on chemical reinjection. Through the reinjection of a portion of the exhaust gas into the reactor, a self-thermal reforming reaction process is engineered, leading to a substantial enhancement in methane conversion rate. The heat matching of the heat exchange unit is optimized by the reheat air, and the power generation and cooling capacity of the system are improved. Notably, the electricity and cooling generation of the new system increased by 55.52 kW (6.20 %) and 542.49 kW (101.49 %), respectively, while the exergy efficiency increased by 8.31 %. The study delves into the influence of key parameters on the system thermal performance. During the reforming process, the exhaust gas split ratio has a significant impact on carbon deposition and methane conversion. When the methane is nearly completely converted, there is no significant change in electricity generation of the system. Excessive turbine inlet temperature is found to be unfavorable for improving the exergy efficiency of the new system from a holistic system perspective. Finally, a comprehensive comparison of the thermal performance between the new system and the reference system is conducted under various ambient temperatures. This study offer a new design scheme for the efficient utilization of biogas.

Aerodynamic noise and its reduction of the marine gas turbine air exhaust system.

The aerodynamic noise of pipelines is an important part of the noise of a ship's system. This paper conducted numerical investigations on the flow and acoustic characteristics of the marine gas turbine exhaust system. The near-field and far-field acoustic characteristics of the internal flow noise of the exhaust system are calculated by employing the Möhring's sound analogy method. In addition, the far-field acoustic characteristics of the external jet flow noise of the exhaust system are calculated by employing the stochastic noise generation and radiation (SNGR) method. Two kinds of protrusions are added to the main nozzle outlet to achieve noise reduction. The internal sound field of the marine exhaust system is dominated by low frequency sound sources, which are more obvious as the exhaust mass flow rate decreases. As for the external sound field of the marine exhaust system, the peak frequency of the far-field noise spectrum decreases with the decrease in the exhaust mass flow rate. The eight periodic protrusions perform better in reducing the internal aerodynamic noise of the exhaust system, while the five aperiodic protrusions perform better in reducing the external jet noise of the exhaust system.

Effect Analysis of Boiler Feed Water and Exhaust Gas Turbine Generator against Steam Products

Effect Analysis of Boiler Feed Water and Exhaust Gas Turbine Generator against Steam Products

Vectorial generative adversarial surrogate modeling reliability evaluation framework for engineering structural systems

To effectively evaluate the multi-objective reliability of engineering structural systems, the vectorial generative adversarial surrogate modeling (VGASM) reliability evaluation concept is proposed by integrating the surrogate model, matrix theory, generate adversarial strategy, Copula thought, and linkage sampling technology. In this concept, the surrogate model is employed as a basis function; the matrix theory is applied to establish the vectors and cell arrays of variables and hyperparameters; the generate adversarial strategy is adopted to determine the hyperparameters; the Copula thought and linkage sampling technology are utilized to simultaneously implement multi-objective correlated reliability analysis. Under this concept, the vectorial generative adversarial Kriging (VGAK) reliability evaluation method is developed by combining the Kriging model with VGASM reliability evaluation concept. In addition, a mathematical example and two engineering cases (i.e., aeroengine exhaust gas temperature and turbine blisk multi-failures) are employed to validate the proposed method. The reliability devel of aeroengine exhaust gas temperature and turbine blisk are 0.9989 and 0.9984, when the allowable values of EGT, deformation, and strain are 950 °C, 1.9253 × 10−3 m, and 5.2898 × 10−3 m. Besides, the presented method holds excellent modeling and simulation properties by comparing multiple methods. The study can provide theoretical references for the multi-objective reliability evaluation of engineering structural systems.

Energy, exergy and economic analysis of a poly-generation system combining sludge pyrolysis and medical waste plasma gasification

To optimize the processes of treating medical waste and pyrolyzing sludge, we propose a new integrated system that combines plasma gasification for medical waste treatment, combined cycle power generation, and sludge pyrolysis. The medical waste is first incinerated, and then the synthesis gas from plasma gasification powers a gas turbine to generate electricity in this integrated system. The gas turbine's exhaust gas heats steam and feedwater from the HRSG to achieve a combined gas-steam cycle. Simultaneously, turbine exhaust steam energizes sludge pyrolysis, allowing for efficient conversion of medical waste into electricity in an eco-friendly manner. A hybrid design study was conducted using different methods, including energy, exergy, and economic analysis. The study revealed that the medical waste-to-energy system integration has the potential to attain 66.31% energy efficiency and 66.70% exergy efficiency. Moreover, the medical waste-electricity project has a dynamic payback period of 2.46 years and a relative net present value of 38,949.91k$. These outcomes suggest that this innovative concept is practical, advantageous, and has excellent potential for further development in the field of waste-to-energy conversion.

Predicting the Performance of Turbine Exhaust Diffuser-Collector Systems Across the Operating Range: Comparison of Lattice-Boltzmann Method Simulations With Experiments

Abstract The predictive capability of the lattice-Boltzmann very large eddy simulation (LBM-VLES) methodology was evaluated for industrial gas turbine exhaust diffuser-collector applications. The effort focused on evaluating the accuracy of performance predictions against experimental rig data gathered at engine representative conditions including the Reynolds number, Mach number, and inlet flow conditions. The performance prediction capability of LBM-VLES simulations was also compared against Reynolds-averaged Navier–Stokes (RANS) simulations. Evaluations were completed for two distinct exhaust rig geometries at conditions indicative of their respective design points, and the performance prediction capability was also evaluated at conditions depicting two off-design cases. The off-design conditions were represented by an increase in inlet swirl angle and associated incidence on the diffuser struts. Overall, the authors found that LBM-VLES simulations were a suitable approach for predicting the performance of gas turbine exhaust diffuser-collector systems at both on- and off-design conditions. The LBM-VLES simulation accuracy was substantially better than that achieved by RANS simulations, with 66% lower RMS pressure recovery error between computational fluid dynamics (CFD) and experiments for the four cases studied, and an 89% reduction in error for the furthest off-design case. The computational cost of the transient LBM-VLES simulations was roughly the same as the RANS simulations performed using best practices for that solver.

A general class of improved population variance estimators under non-sampling errors using calibrated weights in stratified sampling.

This paper proposes a new calibration estimator for population variance within a stratified two-phase sampling design. It takes into account random non-response and measurement errors, specifically applying this method to estimate the variance in Gas turbine exhaust pressure data. The study integrates additional information from two highly positively correlated auxiliary variables to develop a general class of estimators tailored for the stratified two-phase sampling scheme. The properties of these estimators, in terms of their biases and mean square errors, have been thoroughly examined and extensively analyzed through numerical and simulation studies. Furthermore, the calibrated weights of the strata are derived. The proposed estimators outperform the natural estimator of population variance. Finally, suitable recommendations have been made for survey statisticians intending to apply these findings to real-life problems.

NOx formation processes in rotating detonation engines

High-fidelity simulations of RDEs with H2-Air-NOx chemistry are employed to study NOx emissions in such devices. Discrete injection of gaseous hydrogen fuel and continuous injection of air oxidizer is used at various mass flow rate conditions in several 3D RDE simulations to understand resulting NOx production behaviors. Simulations are also performed for two different injector configurations, one in which air is injected axially into the detonation chamber [Axial Air Inlet (AAI)] and one in which air is injected radially [Radial Air Inlet (RAI)]. It is seen that the AAI RDE produces much less NOx than the RAI RDE, mainly due to the weaker waves seen in this system as a result of parasitic combustion losses from product gas recirculation. Parasitic combustion does lead to NOx formation in its own right, but the emissions levels from this process are negligible compared to emissions stemming directly from detonation processes. In regards to detonation strength in particular, it is generally seen that detonation strength increases with increasing mass flow rate, in turn increasing peak pressure, peak heat release and NOx emissions levels. Nevertheless, even the highest recorded NOx levels at the combustor exit in this study remain on the same order of magnitude as compared to gas turbine exhaust emissions levels, supporting the claim that significant differences between detonative and deflagrative combustion do not necessarily lead to significant differences in NOx levels. Overall, this study provides greater understanding into the behaviors of NOx formation in RDEs and how these behaviors are affected by changes in operating parameters.

Operation and control of compact offshore combined cycles for power generation

Gas turbines are the main means for generating power in offshore installations. To increase energy efficiency, and thus reduce CO2 emissions, a steam bottoming cycle can be added to produce additional power by recovering surplus heat from the gas turbine exhaust. Due to space constraints, this solution is not widespread for offshore power generation. To enable deployment, the system must be compact and be able to provide varying power demands. In this paper, we analyze the operation and control problem for such compact combined cycles, consisting of two gas turbines and one steam bottoming cycle. We analyze the steady-state performance of the combined cycle with respect to efficiency and CO2 emissions for two control strategies for coordinating the power setpoint of the two gas turbines. Equal load allocation of the gas turbines showed a higher thermal efficiency and lower emissions compared to keeping one gas turbine close to nominal and letting the second one handle load variations. The main controlled variables for the steam bottoming cycle are the superheated steam pressure and temperature. We implement decentralized control strategies based on standard PID-controllers and nonlinear feedforward. Due to reduced throttle losses, sliding pressure shows higher efficiency and lower CO2 emissions compared to keeping a constant steam pressure, which conversely provides a better temperature dynamic response and may be necessary with highly varying power demand.

Effect of inlet conditions on the thermal insulation performance of marine gas turbine exhaust systems

A marine gas turbine insulation solution was designed to reduce exhaust system temperatures. The effects of cooling gas temperature (45?C, 55?C, 65?C), cooling air velocity (2 m/s - 10 m/s), and a range of classic aerodynamic conditions ranging on the thermal insulation performance of the gas turbine exhaust system were investigated using numerical simulations. The results indicate that the use of aerogel insulation material effectively reduces the average temperature of the exterior volute casing to 71?C from 315?C under rated turbine conditions. The exterior volute casing temperature increases with higher cooling gas inlet temperatures but decreases with increasing cooling gas inlet velocities. Additionally, alterations in the aerodynamic conditions at the gas inlet will induce changes in the thermal insulation performance of the exhaust system, and excessive circumferential flow velocities can cause localized overheating in the exhaust volute casing.

Study on MCFC-integrated GSCC systems with SEGR in parallel or series and CO2 capture

In this paper, two new molten carbonate fuel cell (MCFC)-integrated gas–steam combined cycle (GSCC) systems with selective exhaust gas recirculation (SEGR) and CO2 capture are proposed and analyzed. The CO2 concentration in the gas turbine emission is increased because CO2 is selectively recycled with the help of SEGR. Molten carbonate fuel cells (MCFCs) are another way to increase CO2 concentration in the gas turbine flue gas by translating only CO2 from the cathode to the anode. In these two new gas–steam combined cycle systems, SEGR connected with MCFC, either in parallel or series, increases CO2 concentration beyond 11%. A gas–steam combined cycle system combined with MCFC and CO2 capture without SEGR is used as the reference system. Aspen Plus software is adopted to build the system models, and the performances of different systems are discussed and compared. The research results reveal that for the MCFC-integrated gas–steam combined cycle system with SEGR in series and CO2 capture, the CO2 concentration of gas turbine exhaust increases to 11.72% and the thermal efficiency is 56.29% when the overall CO2 capture rate is 88.16%, which is 1.13% higher than that of the reference system; for the MCFC-integrated gas–steam combined cycle system with SEGR in parallel and CO2 capture, the CO2 concentration of gas turbine exhaust increases to 14.15% and the thermal efficiency is 56.62%, which is 1.46% higher than that of the reference system. Furthermore, the economic analysis results show that the economic performances of new systems are mainly influenced by MCFC cost and will be gradually improved with the decrease in the MCFC cost.

Optimum design of bivariate operation strategy for a supercritical/ transcritical CO2 hybrid waste heat recovery system driven by gas turbine exhaust

Gas turbines are always operated under part-load conditions to participate in the frequency regulation of power grids; therefore, the exhaust gas has fluctuating temperature and mass flow rate parameters. For better utilization of the waste heat in gas turbine exhaust under part-load conditions, a supercritical/transcritical carbon dioxide (CO2) hybrid waste heat recovery system with different operation strategies was studied. The turbine inlet pressure and mass flow rate were considered as the dominant factors affecting the system part-load performance, which formed a bivariate operation strategy. A solution procedure was proposed to optimize the bivariate operation strategy for a hybrid waste heat recovery system. The results indicate that the mass flow rate of the transcritical CO2 cycle has a greater effect on its net power than the turbine inlet pressure whereas these two regulation variables should be controlled cooperatively. The net power of the hybrid waste heat recovery system increased with an increase in the inlet valve opening of the supercritical CO2 turbine under a specific gas turbine load. Generally, the optimal bivariate operation strategy has the advantage of enhancing the part-load performance of a hybrid waste heat recovery system driven by gas turbine exhaust.