Modeling And Performance Analysis For Coal Gas Fired Gas Turbine

Integrated Gasification Combined Cycle (IGCC) is an important development direction for clean coal power generation technologies. As one of the key parts of IGCC, the design fuel for gas turbine is usually natural gas and light diesel. When converted to burn fuel gas from coal with much lower heat value compared with natural gas, gas turbine will confront problems including performance prediction, throughflow match between compressor and turbine, as well as working lifetime of the high-temperature parts decrease, etc. This paper proposed methods for compressor map prediction as well as turbine cooling information prediction, and then built a performance model for coal fuel gas fired gas turbine, analyzed and compared the impacts on gas turbine performance, throughflow capacity, working lifetime of high-temperature parts, as well as the overall IGCC performance by several methods for throughflow adjustment. The contents include:1. Methods for compressor map predictionThree methods to predict compressor map are proposed:polynomial fitting method based on parameter estimation; equivalent value reverse-deduction method based on the operational data of the whole IGCC system. The results show that, the polynomial fitting method is fit for the cases in which 8 groups of experimental data for each single rotation speed, and the original data can well reflect the shape of the whole characteristic curve. The modulization method takes the designed working point as the center, and introduces liner modeling method. This method has high prediction accuracy around the designed working point, while the error will increase as moving away from the designed working point. The modulization method is fit for gas turbine simulation if the operational points of the gas turbine are always around the designed working point. The equivalent value reverse-deduction method, which is based on the overall operational data of the gas turbine, can be used to estimate the overall performance of the gas turbine when combined with reasonable assumptions.2. Turbine cooling modelThree turbine cooling methods with different simplification degrees to estimate the cooling air amount are analyzed:the simple thermal-dynamics estimation method which combines the overall gas turbine efficiency, the combustor outlet temperature and turbine outlet temperature into consideration to reverse deduce the information for turbine cooling air; The method that consider the metal temperature of the cooled turbine, specific heat ratio, etc., and estimate the cooling air amount with empirical formula; The method that consider the heat exchange parameters, including heat exchange parameter, heat exchange area, specific heat, etc., and also the parameters that can represent the cooling effect, including the cooling efficiency, as well as the effective cooling parameter, etc., and then estimate the cooling air amount with semi-empirical formulas. Then the selection principles for the parameters of these three methods as well as the fitted application conditions are analyzed. Then, the accuracies of the three methods are analyzed based on the results from the literatures. In the end, the cooling air amount of the GE PG9351FA gas turbine is estimated.3. Thermal model for gas turbineThree different gas turbine thermal models are developed for PG 9351FA gas turbine:equivalent turbine inlet temperature model, the non-graded turbine model and the graded turbine model. The performance of the gas turbine at designed working condition and off-design working conditions are simulated with these three models. The results show that, although the detailed degree for consideration of the expanding process of the turbine by these three models are far different, and the turbine efficiencies gained for each turbine also vary, the results gained by each model, including the power output, heat consumption, and off gas flow, etc., are basically agree with each other, with the biggest error compared with the results from literatures no more than 3%.4. Gas turbine performance when firing low heat value coal gasThe performance of GE PG9351FA gas turbine when applied for coal fuel gas with mid-low heat value are calculated. Impacts on the throughflow matching, surface metal temperature of the first grade static blade, and also the average working lifetime of the high-temperature blade when the gas turbine is used for coal fuel gas is applied are analyzed. Impacts on the overall performance of the gas turbine by the three throughflow matching methods, including adjusting the inlet guiding vane (IGV) angle, increase the throughflow are, as well as reduce the T3 temperature, are analyzed. Then the paper analyzed the performance of the GE 9FA gas turbine when using coal fuel gases of different heat values and compositions. The results show that, when the gas turbine is converted to use coal fuel gas with mid-low heat value, the power output increases, the surge margin decreases, the working lifetime of the high-temperature parts decreases, and throughflow adjustment is required. Each method for throughflow adjustment has its own advantages and disadvantages for restrict the gas turbine power output, increase the surge margin, as well as increase the average working lifetime of the high temperature parts.5. IGCC performance when several adjustments are made to gas turbineTransport air gasifier based IGCC is selected as the studies object, and several throughflow adjustment methods are evaluated from the viewpoint of overall thermal dynamical performance of the whole IGCC system. The effect to mitigate the problem of throughflow by integration of gas turbine as well as gasifier, as well as the impact on the overall performance of the whole IGCC system are analyzed. The results show that, when no adjustments are made to the gas turbine, the integration degree between the gas turbine and the gafier needs to be as high as 70%, to satisfy the requirement for throughflow. From the viewpoint of the overall performance of the total IGCC system, the total power output as well as efficiency are high when integration is applied. When the integration degree is 70%, the power output of the IGCC system is 50-160MW higher than the case when throughflow is adjusted for the gas turbine, with the power generation efficiency 0.7-3.6 percentages higher than the later case.