Thermoeconomic optimization of heat recovery steam generators operating parameters for combined plants (original) (raw)
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Optimization of heat recovery steam generators for combined cycle gas turbine power plants
Applied Thermal Engineering, 2001
The heat recovery steam generator (HRSG) is one of the few components of combined cycle gas turbine power plants tailored for each speci®c application. Any change in its design would directly aect all the variables of the cycle and therefore the availability of tools for its optimization is of the greatest relevance. This paper presents a method for the optimization of the HRSG based on the application of in¯uence coecients. The in¯uence coecients are a useful mathematical tool in design optimization problems. They are obtained after solving the equations of the system through the Newton±Raphson method. The main advantage of the proposed method is that it permits a better understanding of the in¯uence of the design parameters on the cycle performance. The study of the optimization of the distribution of the boiler area between its dierent components is presented as an example of the proposed technique. Ó
THEMOECONOMIC OPTIMIZATION OF TRIPLE PRESSURE HRSG OPERATING PARAMETERS FOR COMBINED CYCLE PLANTS
The aim of this work is to develop a method for optimization of operating parameters of a triple pressure heat recovery steam generator. Two types of optimization: (a) thermodynamic and (b) thermoeconomic were preformed. The purpose of the thermodynamic optimization is to maximize the efficiency of the plant. The selected objective for this purpose is minimization of the exergy destruction in the heat recovery steam generator (HRSG). The purpose of the thermoeconomic optimization is to decrease the production cost of electricity. Here, the total annual cost of HRSG, defined as a sum of annual values of the capital costs and the cost of the exergy destruction, is selected as the objective function. The optimal values of the most influencing variables are obtained by minimizing the objective function while satisfying a group of constraints. The optimization algorithm is developed and tested on a case of CCGT plant with complex configuration. Six operating parameters were subject of optimization: pressures and pinch point temperatures of every three (high, intermediate and low pressure) steam stream in the HRSG. The influence of these variables on the objective function and production cost are investigated in detail. The differences between results of thermodynamic and the thermoeconomic optimization are discussed.
Optimum gas turbine cycle for combined cycle power plant
Energy Conversion and Management, 2008
The gas turbine based power plant is characterized by its relatively low capital cost compared with the steam power plant. It has environmental advantages and short construction lead time. However, conventional industrial engines have lower efficiencies, especially at part load. One of the technologies adopted nowadays for efficiency improvement is the ''combined cycle''. The combined cycle technology is now well established and offers superior efficiency to any of the competing gas turbine based systems that are likely to be available in the medium term for large scale power generation applications. This paper has as objective the optimization of a combined cycle power plant describing and comparing four different gas turbine cycles: simple cycle, intercooled cycle, reheated cycle and intercooled and reheated cycle. The proposed combined cycle plant would produce 300 MW of power (200 MW from the gas turbine and 100 MW from the steam turbine). The results showed that the reheated gas turbine is the most desirable overall, mainly because of its high turbine exhaust gas temperature and resulting high thermal efficiency of the bottoming steam cycle. The optimal gas turbine (GT) cycle will lead to a more efficient combined cycle power plant (CCPP), and this will result in great savings. The initial approach adopted is to investigate independently the four theoretically possible configurations of the gas plant. On the basis of combining these with a single pressure Rankine cycle, the optimum gas scheme is found. Once the gas turbine is selected, the next step is to investigate the impact of the steam cycle design and parameters on the overall performance of the plant, in order to choose the combined cycle offering the best fit with the objectives of the work as depicted above.
HRSGs for Next Generation Combined Cycle Plants
The relative ease of manufacturing and erecting a combined cycle power plant (CCPP) and the considerable shortening of time required to achieve commercial operation has made the CCPP the plant of choice for utilities as well as independent power producers. This popularity has led to many innovations for increasing the power output and the efficiency. Of the three main components of the CCPP—gas turbine (GT), heat recovery steam generator (HRSG) and steam turbine (ST)—the GT has gone through numerous innovations and improvements. The ST traditionally has the capacity to accept higher amounts of steam at higher pressures, so very little improvements to the ST were needed. However, the HRSG, which is sandwiched between the GT and ST, has to undergo many changes due to the impact of higher amounts of gas at higher temperatures from the GT and the requirement of higher-pressure steam at a higher temperature to boost the ST efficiency. HRSGs for the new generation of CCPPs have to be designed with the proper material to accept the higher temperatures and pressures. The new plants are also required to be on line faster and are subjected to cycling operations. These additional constraints require design innovations using advanced analysis techniques. New Combined Cycle Plants The combined cycle units using advanced class of gas turbines from various manufacturers have certain common aspects. These can be listed as: • Higher efficiency at about 60 percent or beyond. However, 60 percent seems to be the limit for conventional Brayton and Rankine cycles. Generally, the size of GT makes it improbable to have higher than 40 percent efficiency for the GT by itself. The steam turbine efficiency adds about another 20 percent. • Higher gas turbine exhaust mass flows and temperatures. Higher GT firing temperatures result in increasing the GT efficiency, however, these also mandate that the exhaust temperature to the HRSG be high so the GT can have an economical size. • Higher GT exhaust temperature can allow for higher steam temperatures. Higher steam temperatures for superheated and reheated steam can deliver better steam turbine efficiency. These requirements pose design challenges for the mechanical integrity of the HRSG. Critical among these are: • Material to withstand higher metal temperatures due to higher gas and steam temperatures • Mechanical stability for higher gas velocity and turbulent nature of the flow • Larger and thicker steam drums and steam piping due to higher steam flows and pressures
The aim of this work is to develop a method for optimization of operating parameters of a triple pressure heat recovery steam generator. Two types of optimization: (a) thermodynamic and (b) thermoeconomic were performed. The purpose of the thermodynamic optimization is to maximize the efficiency of the plant. The selected objective for this purpose is minimization of the exergy destruction in the heat recovery steam generator. The purpose of the thermoeconomic optimization is to decrease the production cost of electricity. Here, the total annual cost of heat recovery steam generator, defined as a sum of annual values of the capital costs and the cost of the exergy destruction, is selected as the objective function. The optimal values of the most influencing variables are obtained by minimizing the objective function while satisfying a group of constraints. The optimization algorithm is developed and tested on a case of combined cycle gas turbine plant with complex configuration. Six operating parameters were subject of optimization: pressures and pinch point temperatures of every three (high, intermediate, and low pressure) steam stream. The influence of these variables on the objective function and production cost are investigated in detail. The differences between results of thermodynamic and the thermoeconomic optimization are discussed.
A narrow path exists to a sustainable solution which passes through careful steps of efficiency improvement (resource management) and provides environmental friendly energies. Thermal power plants are more common in many power production sites around the world. Therefore, in this current research study a comprehensive thermodynamic modeling of a combined cycle power plant with dual pressure heat recovery steam generator is presented. Since the steam turbine outlet quality is a restrictive parameter, optimization of three cases with different steam quality are conducted and discussed. In other hand, energy and exergy analysis of each components for these three different cases estimated and compared. Obtained results show that it is really important to keep the quality of the vapor at turbine outlet constant in 88% for the results to be more realistic and also optimization and data are more technically feasible and applicable.