On-Line Calculation On Thermoeconomic Indicators For A Large Fire Power Generating Unit

For fire power generating units, realizing energy conversation has become an urgent problem solved at present, as a result of the 11^th five-year energy-saving layout and the competitive power market. Actual energy consumption is much higher than the planned value, due to the low operating level, showed in a survey. To increase operating level, by on-line monitoring performance and guiding operation, has been proved to be an effective way to save energy.So as to evaluate their operating performance, ascertain main factors caused unnecessary energy losses, increase thermoeconomic indicators, it is necessary to study the methods of quantitatively evaluating operating performance. So based on a 300MW unit, several aspects were studied as follows:1. Mathematic models and calculation methods of thermoeconomic indicators were analyzed respectively, and calculations under variable loads were carried out. It showed that, under the rated load, thermal efficiency of the boiler and the turbine was respectively 91.68% and 43.0%, and that of the unit was 38.2%.2. The theory of off-design calculations for governing stage was deeply studied. Based on the control of sequence valve, calculation models were founded according to the nozzle governing. Characteristic parameters for the governing stage were calculated and characteristic curves were drawn. The curves were described as follows:η_u=-1.223ε²+2.345ε-0.321,μ=-3.424ε+3.716.η_u,εandμrespectively represent the circumference of wheel efficiency, the pressure ratio and the flow coefficient.3. On-line calculation methods of steam turbine exhaust enthalpy were studied. For exhaust steam is wet steam, its enthalpy is related to pressure and moisture, but the moisture cannot be obtained in field measurement. On-line calculation models were founded according to energy balance of the unit for avoiding iterative calculation. Under the rated load, the calculated exhaust enthalpy is 2482.4kJ/kg. Compared to the designed value 2447.5kJ/kg, relative error is only 1.4%.4. The Principle and method of off-desigen calculation for the unit were studied, and determining of the target values for operating parameters was analyzed. Parameters were divided into 3 kinds, and their target values were determined respectively by the design data, the performance test data and the data obtained from off-design calculation.5. Energy consumption deviations related to key operating parameters and their relationships with loads were studied. Under the rated load, the deviation of turbine efficiency leaded to a 6.19g increase for standard coal consumption, and several key parameters leaded to 5.93g, relative error was 4.38%. The loss was mainly caused by pressure deviations of the new steam and the exhaust, showed analysis results.6. Based on founded models, software of on-line performance monitoring for a coal-fired power generating unit was developed by using VB language and Access database. It can monitor present operating conditions, calculate thermoeconomic indicators and analyze energy consumption deviations.