Software for the Performance Evaluation of Combined Cycles

This paper describes a software package developed under the auspices of the Electric Power Research Institute to monitor combined cycle power plant performance. By monitoring plant performance a usefull data base can be created. When trended and compared against a performance model this database can be used to schedule performance maintenance and repairs, and to evaluate the benefits of maintenance and/or upgrade options. The software is named EMAP, an acronym for “Efficiency Maintenance Analysis Program”, and is available through EPRI.

Comparison Method for Complex Cycle Analysis

A new methodology is developed for the performance estimation of complex cycles such as conventional combined cycle, steam injected gas turbine cycle, AFBC coal burned exhaust heated combined cycle, alternative fuel heat recovery cycle and so on. The basic idea of this method is to compare the performance of the complex cycles with the well-known performance of the main sub-cycle (for example, the gas turbine cycle) in some way and then add simple correction factors if necessary. With such approach, the thermodynamic performance of complex cycles can be estimated and expressed very simply, directly and conveniently. The abovementioned complex cycles have been analyzed successfully by this method; the obtained results are brief and concise, and compared well with practical data and other detailed theoretical analysis results.

Preliminary Engineering for a 50 MW Compressed Air Energy Storage Plant for Alabama Electric Cooperative, Inc.

This paper presents preliminary engineering results for a 50 MW Compressed Air Energy Storage (CAES) plant for the Alabama Electric Cooperative, Inc. (AEC). The CAES plant would improve AEC’s power generation mix in two ways: (a) it would provide needed peaking/intermediate power (otherwise purchased) and (b) it would increase the load factor of economical baseload units. The paper presents the following: a. Comparative trade-off analysis of various conceptual arrangements with underground storage depths ranging between 1000 feet and 4000 feet. (The most economical concept is selected based on the consideration of economics of the overall plant including underground storage). b. Engineering and cost data, performance data, construction schedule and environmental data for the selected CAES plant concept. The results of this preliminary engineering effort prove that a CAES plant is a cost effective addition to AEC’s installed power generation plants.

Circulating Fluidized Bed Combustor Utilization With Compressed Air Energy Storage Plants

This paper presents results of engineering of a Circulating Fluidized Bed Combustor (CFBC) for Compressed Air Energy Storage (CAES) application. This development allows eliminating the use of premium fuels thus resolving economic as well as institutional issues. The paper summarizes the engineering, performance and cost data for a CFBC and presents comparative technical and economic analyses of a CAES plant with CFBC (burning coal) versus a conventional CAES plant (burning premium fuel).

Exergy Analysis of Combined Cycles: Part 2 — Analysis and Optimization of Two-Pressure Steam Bottoming Cycles

Results of a study for selecting the optimum parameters of a dual-pressure bottoming cycle as a function of the gas turbine exhaust temperature are presented. Realistic constraints reflecting current technological practice are assumed. Exergy analysis is applied to quantify all loss sources in each cycle. Compared to a single pressure at typical exhaust gas temperatures the optimized dual-pressure configuration is found to increase steam cycle work output on the order of 3%, principally through the reduction of the heat transfer irreversibility from about 15% to 8% of the exhaust gas energy. Measures to further reduce the heat transfer irreversibility such as three-pressure systems or use of multi-component mixtures can therefore only result in modest additional gains. The results for the efficiency of optimized dual pressure bottoming cycles are correlated against turbine exit temperature by simple polynomial fits. Sensitivity of the results to variations in the constraint envelope are presented.

Exergy Analysis of Combined Cycles: Part 1 — Air-Cooled Brayton-Cycle Gas Turbines

Quantitative analytical tools based upon the second law of thermodynamics provide insight into the complex optimization tradeoffs encountered in the design of a combined cycle. Those tools are especially valuable when considering approaches beyond the existing body of experience, whether in cycle configuration or in gas turbine cooling technology. A framework for such analysis was provided by the author in references [1]-[3] using simplified, constant-property models. In this paper, this theme is developed to include actual chemical and thermodynamic properties as well as relevant practical design details reflecting current engineering practice. The second law model is applied to calculate and provide a detailed breakdown of the sources of inefficiency of a combined cycle. Stage-by-stage turbine cooling flow and loss analysis calculations are performed using the GASCAN program and examples of the resulting loss-breakdowns presented. It is shown that the dominant interaction governing the variation of cycle efficiency with turbine inlet temperature is that between combustion irreversibility and turbine cooling losses. Compressor and pressure-drop losses are shown to be relatively small. A detailed analysis and loss-breakdown of the steam bottoming cycle is presented in Part 2 of this paper.

Benefits of Converting Utility Gas Turbines to Combined-Cycle Plants

A large number of simple cycle gas turbines (about 8% of the total current electric generating capacity) had been installed by utilities by the late 1970s. Because of the low efficiency of these, older simple cycle gas turbines (about 25% at full load, much worse at part load) and the reduced demand for electricity, little use is now made of these machines by most utilities. The paper considers the specific and broader benefits of converting these older gas turbines to combined-cycle plants. The benefits include dramatic efficiency improvement at all loads, improved operating reliability, low cost additions to utility generating capacity, and the potential availability of significant new capacity in many regions of the country in a short time. The combined cycles can also be operated instead of oil-fired and coal-fired cycling steam plants — at significantly lower startup-up costs in fuel and operating personnel, and with considerable reduction in the wear and tear of the steam plants from cycling thermal stresses. When additional, new peaking capacity is needed, these older, converted gas turbines can be replaced with new, more efficient machines.

Advanced Recuperator for Compressed Air Energy Storage Plants

This paper presents solutions to the extensive corrosion problems affecting recuperators in Compressed Air Energy Storage (CAES) applications. Two advanced designs for a 50 MW CAES plant were engineered: (a) a two-section counterflow arrangement with a replaceable cold end section which operates with tube wall temperatures below the exhaust gas dew point temperature, (b) a three-section design with a flow arrangement which eliminates tube wall temperatures below the exhaust gas dew point temperature. Presented in this paper are a general description, design specifics, performance and cost data for these two conceptual designs. Technical and economic analyses were performed to determine the most practical and economic design.

Advanced Compressed Air Energy Storage Plants With Utilization of Thermal Energy Storage Systems

This paper presents results of engineering development for utilization of thermal energy storage (TES) for Compressed Air Energy Storage (CAES) plant applications. Presented results include the following: - Turbomachinery cycle optimization for TES application - TES systems engineering and optimization - Comparative technical and economic analysis of various CAES plant concepts with TES versus a conventional CAES plant concept The paper concludes that utilization of TES is feasible, practical and economically attractive.

Waste Energy Utilization in Regenerative Gas Turbine Cycles

One of the ways that can be used to increase the efficiency of a shaft gas turbine engine is by installing a regenerative heat exchanger in one of the following two configurations: 1. after the low pressure turbine (usual case). 2. after the high pressure turbine (suggested). Analysis of ideal cycles as well as real cycle for both configurations is done by using a computer program, where the following parameters were studied: heat exchanger effectiveness, turbine efficiency, compressor efficiency, ratio of turbine inlet pressure to compressor delivery pressure (P3/P2), and maximum temperature ratio (T3/T1). From the sensitivity analysis for both configurations the usual configuration is inferior to the suggested in terms of the relative effects of compressor and turbine efficiencies on the overall efficiency and turbine inlet pressure on overall thermal efficiency and power output. However, the usual method is superior with respect to the relative effects of the compressor and turbine efficiencies on power output and flow path design and manufacture.