Optimization Studies for Integrated Solar Combined Cycle Systems

Author(s):  
Bruce Kelly ◽  
Ulf Herrmann ◽  
Mary Jane Hale

Abstract The integrated solar plant concept was initially proposed by Luz Solar International [1] as a means of integrating a parabolic trough solar plant with modern combined cycle power plants. An integrated plant consists of a conventional combined cycle plant, a solar collector field, and a solar steam generator. During sunny periods, feedwater is withdrawn from the combined cycle plant heat recovery steam generator, and converted to saturated steam in the solar steam generator. The saturated steam is returned to the heat recovery steam generator, and the combined fossil and solar steam flows are superheated in the heat recovery steam generator. The increased steam flow rate provides an increase in the output of the Rankine cycle. During cloudy periods and at night, the integrated plant operates as a conventional combined cycle facility. Two studies on integrated plant designs using a General Electric Frame 7(FA) gas turbine and a three pressure heat recovery steam generator are currently being conducted by the authors. Preliminary results include the following items: 1) the most efficient use of solar thermal energy is the production of high pressure saturated steam for addition to the heat recovery steam generator; 2) the quantity of high pressure steam generation duty which can be transferred from the heat recovery steam generator to the solar steam generator is limited; thus, the maximum practical solar contribution is also reasonably well defined; 3) small annual solar thermal contributions to an integrated plant can be converted to electric energy at a higher efficiency than a solar-only parabolic trough plant, and can also raise the overall thermal-to-electric conversion efficiency in the Rankine cycle; and 4) annual solar contributions up to 12 percent in an integrated plant should offer economic advantages over a conventional solar-only parabolic trough power plant.

Author(s):  
P. J. Dechamps

The last decade has seen remarkable improvement in gas turbine based power generation technologies, with the increasing use of natural gas-fuelled combined cycle units in various regions of the world. The struggle for efficiency has produced highly complex combined cycle schemes based on heat recovery steam generators with multiple pressure levels and possibly reheat. As ever, the evolution of these schemes is the result of a technico-economic balance between the improvement in performance and the increased costs resulting from a more complex system. This paper looks from the thermodynamic point of view at some simplified combined cycle schemes based on the concept of water flashing. In such systems, high pressure saturated water is taken off the high pressure drum and flashed into a tank. The vapour phase is expanded as low pressure saturated steam or returned to the heat recovery steam generator for superheating, whilst the liquid phase is recirculated through the economizer. With only one drum and three or four heat exchangers in the boiler as in single pressure level systems, the plant might have a performance similar to that of a more complex dual pressure level system. Various configurations with flash tanks are studied based on commercially available 150 MW-class E-technology gas turbines and compared with classical multiple pressure level combined cycles. Reheat units are covered, both with flash tanks and as genuine combined cycles for comparison purposes. The design implications for the heat recovery steam generator in terms of heat transfer surfaces are emphasized. Off-design considerations are also covered for the flash based schemes, as well as transient performances of these schemes, because the simplicity of the flash systems compared to normal combined cycles significantly affects the dynamic behaviour of the plant.


2021 ◽  
Vol 65 (1) ◽  
pp. 93-104
Author(s):  
Onkar Singh ◽  
Gaitry Arora ◽  
Vinod Kumar Sharma

Heliostat-based solar thermal power system consisting of a combination of the Brayton cycle, Rankine cycle, and organic Rankine cycle is a potential option for harnessing solar energy for power generation. Among different options for improving the performance of solarized triple combined cycle the option of introducing intercooling and reheating in the gas turbine cycle and utilizing the waste heat for augmenting the power output needs investigation. Present study considers a solarized triple combined cycle with intercooling and reheating in gas turbines while using the heat rejected in intercooling in heat recovery vapour generator and heat recovery steam generator separately in two different arrangements. A comparison of two distinct cycle arrangements has been carried out based on Ist law and IInd law of thermodynamics with the help of thermodynamic parameters. Results show that triple combined cycle having intercooling heat used in heat recovery vapour generator offers maximum energy efficiency of 63.54% at 8 CPR & 300K ambient temperature and maximum exergetic efficiency of 38.37% at 14 CPR & 300 K. While the use of intercooling heat in heat recovery steam generator offers maximum energy and exergetic efficiency of 64.15% and 39.72% respectively at 16 CPR & 300 K ambient temperature.


Author(s):  
Mohammad R. Shahnazari ◽  
Abbas Abbassi

A common repowering option is converting a fossil-fired steam unit to a gas-fired combined-cycle plant by addition of a combustion turbine and a Heat Recovery Steam Generator. In this approach the existing steam turbine and related auxiliaries are typically retained and some plant modification is applied. This paper intends to study this option for two old power plants. In this study the HRSGs are modeled, designed and their costs are estimated. Total generating cost for both plants are calculated in order to show whether or not the final cost is competitive with the cost of a new combined cycle unit.


Author(s):  
T S Kim ◽  
S T Ro

For combined cycle plants that consist of heavy-duty gas turbine and single-pressure heat recovery steam generator, the effect of gas turbine coolant modulation on plant performance is analysed. Two distinct schemes for gas turbine load control are adopted (the fuel-only control and the variable compressor geometry control), based on the gas turbine calculation in Part 1 of this series of papers. Models for heat recovery steam generator and steam turbine are combined with the gas turbine models of Part 1 to result in a complete analysis routine for combined cycles. The purpose of gas turbine coolant modulation is to minimize coolant consumption by maintaining the turbine blade temperatures as high as possible. It is found that the coolant modulation leads to reduction in heat recovery capacity, which decreases steam cycle power. However, since the benefit of coolant modulation for the gas turbine cycle is large enough, the combine cycle efficiency is improved.


Author(s):  
Dietmar Schmidt ◽  
Terrence Sullivan

Turnkey and thermal island supply scopes present turbine manufacturers with a perfect way to sell their rotating products. The popularity of these plant configurations, along with the recent availability of more holistic test codes, has led to the need for an accurate and reasonable method of determining the thermal performance of the externally-purchased HRSG component. To assess a multiple pressure HRSG, it is advantageous and convenient to have one single criterion for the evaluation of performance, especially when this criterion provides for the compensation of the different outlet energy streams. The so-called Model Steam Turbine method of HRSG evaluation was developed for these reasons. The result of the calculation, a lone performance criterion, is the shaft power of the fictitious Model Steam Turbine. In this paper we will detail the components of the Model Steam Turbine calculation and explore the merits of this method. Some thoughts on performance corrections are also presented.


2019 ◽  
Vol 66 (5) ◽  
pp. 331-339
Author(s):  
M. N. Maidanik ◽  
A. N. Tugov ◽  
N. I. Mishustin ◽  
A. E. Zelinskii

Author(s):  
Ravin G. Naik ◽  
Chirayu M. Shah ◽  
Arvind S. Mohite

To produce the power with higher overall efficiency and reasonable cost is ultimate aim for the power industries in the power deficient scenario. Though combined cycle power plant is most efficient way to produce the power in today’s world, rapidly increasing fuel prices motivates to define a strategy for cost-effective optimization of this system. The heat recovery steam generator is one of the equipment which is custom made for combined cycle power plant. So, here the particular interest is to optimize the combined power cycle performance through optimum design of heat recovery steam generator. The case of combined cycle power plant re-powered from the existing Rankine cycle based power plant is considered to be simulated and optimized. Various possible configuration and arrangements for heat recovery steam generator has been examined to produce the steam for steam turbine. Arrangement of heat exchangers of heat recovery steam generator is optimized for bottoming cycle’s power through what-if analysis. Steady state model has been developed using heat and mass balance equations for various subsystems to simulate the performance of combined power cycles. To evaluate the performance of combined power cycles and its subsystems in the view of second law of thermodynamics, exergy analysis has been performed and exergetic efficiency has been determined. Exergy concepts provide the deep insight into the losses through subsystems and actual performance. If the sole objective of optimization of heat recovery steam generator is to increase the exergetic efficiency or minimizing the exergy losses then it leads to the very high cost of power which is not acceptable. The exergo-economic analysis has been carried to find the cost flow from each subsystem involved to the combined power cycles. Thus the second law of thermodynamics combined with economics represents a very powerful tool for the systematic study and optimization of combined power cycles. Optimization studies have been carried out to evaluate the values of decision parameters of heat recovery steam generator for optimum exergetic efficiency and product cost. Genetic algorithm has been utilized for multi-objective optimization of this complex and nonlinear system. Pareto fronts generated by this study represent the set of best solutions and thus providing a support to the decision-making.


Author(s):  
Akber Pasha

In recent years the combined cycle has become a very attractive power plant arrangement because of its high cycle efficiency, short order-to-on-line time and flexibility in the sizing when compared to conventional steam power plants. However, optimization of the cycle and selection of combined cycle equipment has become more complex because the three major components, Gas Turbine, Heat Recovery Steam Generator and Steam Turbine, are often designed and built by different manufacturers. Heat Recovery Steam Generators are classified into two major categories — 1) Natural Circulation and 2) Forced Circulation. Both circulation designs have certain advantages, disadvantages and limitations. This paper analyzes various factors including; availability, start-up, gas turbine exhaust conditions, reliability, space requirements, etc., which are affected by the type of circulation and which in turn affect the design, price and performance of the Heat Recovery Steam Generator. Modern trends around the world are discussed and conclusions are drawn as to the best type of circulation for a Heat Recovery Steam Generator for combined cycle application.


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