Power plants operating in combined cycle present higher thermal efficiency (over 60%) and increased power generation when compared to traditional simple cycles, such as gas or steam turbines operating alone. Considering that the power plant evaluated in this paper is already operational, a further development concerning to the power plant control system is required in order to evaluate disturbances and frequency variations, generated by the electrical grid during normal operation, as the loads applied to the turbines are intrinsically associated to the grid frequency. A computer program able to simulate the control system was developed to cope with these instabilities and to guarantee the necessary protection to the power plant operation. The develop program was made using MATLAB Simulink®. The main components of the power plant consists of 2 gas turbines of 90 MW each and a steam turbine of 320 MW, totalizing 500 MW. Firstly, the power plant main components were constructed separately. Once obtained stable models, the exhaust from the gas turbine was connected to the water-steam cycle through the heat recovery steam generator. The main parameters necessary to adjust the model such as gains, limits and constants were obtained from the power plant operational data. The simulation results allowed the evaluation of some key parameters; others are possible but not shown, such as power, exhaust gas temperature, fuel flow and variable stator angles during grid instabilities. The studies were conducted by testing the robustness, response time, transient analysis, steady state analysis and reliability of the proposed model.
Current energy conversion machines such as the micro gas turbine can be improved by harvesting the low-grade energy of the exhaust. A prominent option for such is the organic Rankine cycle due to its relatively efficient and reliable design. This manuscript presents a review on the subject and is the first step toward the design of an organic Rankine cycle bottoming a 100 kWe recuperated gas turbine. After introducing and covering the historical development of the technology, appropriate guidelines for defining the cycle arrangement and selecting the fluid are presented. At last, the viability of the cycle is assessed by assuming an appropriate efficiency value and general cost functions. The organic Rankine is expected to generate an additional 16.6 kWe of power, increasing the electrical efficiency from 30 to 35%. However, the capital cost increase was estimated in 48%.
The increasing fuel prices and stringent environmental legislation compel industries worldwide to pursue means to increase their processes efficiency. A higher efficiency relates to a reduction in fuel consumption, which results in a lower operational cost and emissions. When considering a steel mill, processes encountered in the blast furnace and in the coke oven, for example, generate gases that can be availed as low-grade fuels to return some sort of energy back to the process. This practice reduces the amount of high-grade fuel required and increases the global efficiency of the industrial site; however, demands higher investments and increase the management complexity. A thorough evaluation of such power cycles is important to assess their application.
This paper is based on a currently operational combined-cycle power plant composed by two gas turbines that are adapted to use blast furnace gas as main fuel and one steam turbine with a total power rating of 490 MWe. This power plant configuration is compared to another one in which the topping cycle — composed by two gas turbines — is eliminated, and the same amount of blast furnace gas is burnt in a conventional steam generator, operating as a Rankine-cycle. The software Gate Cycle™ was used to model and simulate both cycles and provide the main parameters to analyze their performance. Parameters such as power rating, efficiency, emissions, and expected capital expenditure provided means to assess both options and evaluate their application.
The combined-cycle provided higher efficiency and power rating when compared with the Rankine-cycle. However, the expected values for capital expenditure showed to be also higher. A major difference between both cycles is the higher flexibility of the combined-cycle power plant, which is essential to guarantee an electric energy source within the industrial site. As a counterpart, the operational complexity is significantly higher when compared with the Rankine-cycle. Overall, the present work provides valuable information to assess both solutions.
The association of turbochargers with piston engines is widespread since both the efficiency and the power output of an engine could be improved. However, a piston engine operational range is wide and highly variable. This characteristic imposes challenges for the project and application of a turbocharger that should perform properly within the operational range. An important tool used to evaluate the performance of both turbine and compressor, which compose a turbocharger, is the characteristic map. The map condenses the main performance parameters into a single graphic that allow the evaluation of the machine characteristics, such as the operational width. A typical characteristic map relates the pressure ratio, mass flow rate, rotation and efficiency for each operational condition. The present work provides a technique to obtain the characteristic map of a turbocharger centrifugal compressor with reduced time consumption through steady state simulation using a fully unstructured mesh. Evaluation of the results indicated good accuracy for the predicted mass flow rate and pressure ratio. However, the resulting efficiency presented considerable discrepancy, which was aggravated when simulating extreme operational conditions or when the mass flow was used as a boundary condition. At last, the porter shroud and volute were evaluated within the entire range to provide an insight into the compressor operation.
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