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Manufacturers are trying to increase ramp rates to improve the operational flexibility of gas turbines. However, higher ramp rates lead to rapid variation in the combustion gas temperature and shorten the life of the turbine. To increase the rate without reducing the life, this study considers the use of a compressed air energy storage (CAES). Injecting pressurized air that is stored in CAES into the combustor of a gas turbine increases the power output of the gas turbine without increasing fuel supply. Therefore, the ramp rate of the turbine can be increased while suppressing the temperature change of the combustion gas. The injection schedule was optimized through a dynamic simulation to increase the ramp rate. A genetic algorithm was used in the optimization of the schedule. The optimized schedule turned out to be a simple form consisting of a linear increase and decrease in the injection flow rate. Furthermore, despite the increased ramp rate, the fluctuation of turbine inlet temperature could be maintained under a safe level due to the optimized compressed air injection.

The major cause of the performance degradation of industrial gas turbines is compressor fouling due to airborne contaminants. Performance diagnostics is required to evaluate degradation precisely. In general, the measured performance in the fully opened inlet guide vane (IGV) condition is regarded as full-load performance and used for diagnostics. A new diagnostic method is proposed in this study. A scheme to determine whether the measured performance is at full-load operation is suggested. If operation is not at full-load, a virtual gas turbine state corresponding to the measured data is modeled using adaptive modeling. Then, the virtual full-load performance and the corrected performance are predicted using a reference firing temperature. This calculation methodology is applied to almost two-years of data of a 150 MW class gas turbine. The analysis revealed that the maximum reduction of power output and efficiency are 14.8 MW and 0.8 percentage points compared with the rated performance. In addition, it was shown that if the measured performance is used directly, the maximum deviation in the predicted power degradation was as much as 4.9 MW (2.8%) compared with the rated performance. This paper demonstrates the necessity of a model-based analysis for enhancing the accuracy of performance diagnostics.

Micro gas turbines are manufactured to have a compact structure and small volume, which makes them more vulnerable to internal leakages compared to heavy-duty gas turbines. Accordingly, precise diagnosis of the performance degradation in a micro gas turbine is important. This study investigates the characteristics of degradation. Performance maps were used for the compressor and turbine, and a multi-segment counter-flow heat exchanger model was used for the recuperator. The component models were refined using actual operation data, resulting in precise simulation of the reference operation without leakage. A performance analysis was carried out, and the results were analyzed for three types of leakage with the following paths: from the compressor outlet to the recuperator’s cold-side outlet, from the compressor outlet to the combustor outlet, and from the combustor inlet to the turbine outlet. The third path produced the largest reduction in engine efficiency. The degradations were also compared with those related to compressor fouling and turbine erosion, which are the most common causes of degradation in a gas turbine. Even when qualitatively similar performance changes were observed, the root cause could be determined by analyzing differences in performance parameters such as the fuel flow.

One of the major research areas in combined heat and power (CHP) systems is optimal dispatch, which involves the minimization of the operating cost. In economic dispatch, it is important to use a model that accurately simulates the performance of the power and heat generation equipment. However, physics-based characteristic models require considerable time for the analysis, so it is hard to apply them to the optimization of dispatch schedules. This study introduced a neural network model, which was built based upon the simulation results of a physics-based model, to optimize a CHP system. The novel method was used to optimize the operation schedule of a system consisting of a gas turbine, steam turbine bottoming cycle, compressed air energy storage, and a boiler. The schedule was optimized to minimize the operation cost per day and according to the power and heating demand of users. The results showed that the introduction of the neural network reduced the time required for the system analysis by more than 7000 times. Furthermore, the optimization results confirmed the importance of accurately predicting the performance of each device using the physics-based model. This study contributes to the reduction in computation time and improvement of optimization accuracy.

We investigated the influence of firing biogas on the performance and operating characteristics of gas turbines. Combined heat and power systems based on two different gas turbines (simple and recuperative cycle engines) in a similar power class were simulated. A full off-design analysis was performed to predict the variations in operations due to firing biogas instead of natural gas. A wide range of biogas compositions differing in CH4 content was simulated. Without consideration of operating restrictions on the compressor and turbine, using biogas was predicted to augment the power output in both engines. Power output increased as CH4 content decreased. The main reason is the increase in turbine power due to increased fuel flow. Gas turbine efficiency increased with decreasing CH4 content in the simple cycle engine, but decreased in the recuperative cycle engine. Net efficiency including the fuel compression power consumption decreased with decreasing CH4 content even in the simple cycle engine. The heat recovery also increased by firing biogas. However, the increased turbine flow was accompanied by a surge margin reduction of the compressor and overheating of the turbine blade. These two problems were more severe in simple cycle gas turbines and as the ambient temperature increased. The turbine blade temperature and the compressor surge margin could be recovered to the reference values by either under-firing or compressor air bleeding, which are effective for blade temperature control and surge margin control, respectively. However, satisfaction of both restrictions by a single modulation caused excessive power and efficiency losses. An optimal combination between under-firing and air bleeding would minimize the performance penalty.

In this study, system layouts for integrated gasification solid oxide fuel cell/gas turbine (IG-SOFC/GT) systems were proposed and their performance was comparatively evaluated. A baseline IGCC was simulated, and the calculation models were validated. Based on the IGCC system, two IG-SOFC/GT system layouts with different SOFC thermal management methods were established, and their performance was analyzed. The IG-SOFC/GT systems were found to produce much higher power and better efficiency than the IGCC. With regard to SOFC thermal management, the exit gas recirculation scheme showed better performance than the cathode heat exchange scheme. The impact of CO2 capture was investigated in both the IGCC and IG-SOFC/GT systems, and the penalties in power output and efficiency due to pre-combustion CO2 capture were found to be milder in the IG-SOFC/GT systems than in the IGCC. An IG-SOFC/GT system adopting oxy-combustion-based CO2 capture was proposed, and its thermal efficiency was predicted to be sensibly higher than the system with pre-combustion CO2 capture. Its net power output was predicted to be less than that of the system with pre-combustion technology, but was still much larger than that of the IGCC with pre-combustion CO2 capture.

An integrated power generation system combining solid oxide fuel cell (SOFC) and oxy-fuel combustion technology is proposed. The system is revised from a pressurized SOFC-gas turbine hybrid system to capture CO2 almost completely while maintaining high efficiency. The system consists of SOFC, gas turbine, oxy-combustion bottoming cycle, and CO2 capture and compression process. An ion transport membrane (ITM) is used to separate oxygen from the cathode exit air. The fuel cell operates at an elevated pressure to facilitate the use of the ITM, which requires high pressure and temperature. The remaining fuel at the SOFC anode exit is completely burned with oxygen at the oxy-combustor. Almost all of the CO2 generated during the reforming process of the SOFC and at the oxy-fuel combustor is extracted from the condenser of the oxy-combustion cycle. The oxygen-depleted high pressure air from the SOFC cathode expands at the gas turbine. Therefore, the expander of the oxy-combustion cycle and the gas turbine provides additional power output. The two major design variables (steam expander inlet temperature and condenser pressure) of the oxy-fuel combustion system are determined through parametric analysis. There exists an optimal condenser pressure (below atmospheric pressure) in terms of global energy efficiency considering both the system power output and CO2 compression power consumption. It was shown that the integrated system can be designed to have almost equivalent system efficiency as the simple SOFC-gas turbine hybrid system. With the voltage of 0.752 V at the SOFC operating at 900 °C and 8 bar, system efficiency over 69.2% is predicted. Efficiency penalty due to the CO2 capture and compression up to 150 bar is around 6.1%.

As the need for clean coal technology grows, research and development efforts for integrated gasification combined cycle (IGCC) plants have increased worldwide. An IGCC plant couples a gas turbine with a gasification block. Various technical issues exist in designing the entire system. Among these issues, the matching between the gas turbine and the air separation unit is especially important. In particular, the operating condition of a gas turbine in an IGCC plant may be very different from that of its original design. In this study, we analyzed the impact of the use of syngas on operating conditions of the gas turbine in an IGCC plant. We evaluated the performance of a gas turbine under operating limitations in terms of compressor surge and turbine metal temperature. Although a lower degree of integration may theoretically allow higher gas turbine power output and efficiency, it causes a reduction in compressor surge margin and overheating of the turbine metal. The turbine overheating problem may be solved using several methods, such as a reduction in the firing temperature or an increase in the turbine cooling air. The latter yields a much smaller performance penalty. To achieve an acceptable margin for the compressor surge, either further reduction in the firing temperature or further increase in the coolant is required. Ventilation of some of the nitrogen generated by the air separation unit, i.e., a reduction of the nitrogen supply to the combustor, is another option. Coolant modulation yields the lowest performance penalty. Reduction of the nitrogen supply provides much greater system power output than control of the firing temperature. For nitrogen flow and firing temperature controls, there are optimal levels of integration degrees in terms of net system power output and efficiency.

Microturbines are promising power sources for small scale combined heat and power (CHP) systems. However, the power output and efficiency of microturbines decreases much as the ambient temperature increases. As a remedy to minimize the performance penalty at hot ambient conditions, the injection of water or steam into a microturbine CHP system was analyzed in this work. An analysis program to simulate the operation of a microturbine CHP system was set up and validated by using measured test data. The injection of hot water, which is generated at the heat recovery unit, at two different locations inside the microturbine was predicted. The generation of steam through the same heat recovery unit and its injection at the two locations was predicted as well. All the four cases provide sufficiently enhanced power output. Injection at the recuperator inlet exhibits a higher efficiency than injection at the combustor in both water and steam injections. Steam injection provides a higher power generation efficiency than water injection on the average. The injection of steam at the recuperator inlet is most promising in terms of power generation efficiency. However, water injection at the recuperator also enhances power generation efficiency while still providing thermal energy to some extent.

An IGCC (integrated gasification combined cycle) plant consists of a power block and a gasifier block, and a smooth integration of these two parts is important. This work has analyzed the influences of the major design options on the performance of an IGCC plant. These options include the method of integrating a gas turbine with an air separation unit and the degree of nitrogen supply from the ASU to the gas turbine combustor. Research focus was given to the effect of each option on the gas turbine operating condition along with plant performance. Initially, an analysis adopting an existing gas turbine without any modifications of its components was performed to examine the influence of two design options on the operability of the gas turbine and performance of the entire IGCC plant. It is shown that a high integration degree, where much of the air required at the air separation unit is supplied by the gas turbine compressor, can be a better option considering both the system performance and operation limitation of the gas turbine. The nitrogen supply enhances system performance, but a high supply ratio can only be acceptable in high integration degree designs. Secondly, the modifications of gas turbine components to resume the operating surge margin, such as increasing the maximum compressor pressure ratio by adding a couple of stages and increasing turbine swallowing capacity, were simulated and their effects on system performance were examined. Modification can be a good option when a low integration degree is to be adopted, as it provides a considerable power increase.