Psce 2011 Article final
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PSCE 2011 Article final
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Value Unit Gross Electric Power 105 MW Sugarcane milling 17000 T/day Ethanol production 1800 m³/day High Pressure (abs) 101 Bar Medium Pressure – extraction (abs) 17 Bar Low Pressure – process (abs) 2,5 Bar Electricity production 80 MWe Electricity aux. consumption 10 MWe MP turbine consumption 4 MW Escape Steam flow from BPSTGs 383 T/h Escape Steam flow from TPs 36.4 T/h Steam flow from Conditioning Valve 0.6 T/h Escape Steam Loss 10.7 T/h Escape Steam Temperature 126.8 ºC Escape Steam Pressure (abs) 2.4 Bar Escape Steam Enthalpy 2715.7 kJ/kg Escape Condensate Temperature 123 ºC Escape Condensate Pressure 2.18 bar Escape Condensate Enthalpy 516.564 kJ/kg Bagasse LHV 7578.5 kJ/kg Boiler bagasse consumption 181681 kg/h Useful Mechanical/Electrical Work 74000 kWh/h Useful Heat 250029.5 kWh/h Fuel Energy 382463 kWh/h FUE t 84.72 % Premise 2 – for temperature, pressure and flow measurements, it is assumed the average parameter value integrated in a one second time base. It means that for each one second there is a heat calculation for each stream. Thus, the one second time based calculated operational heat values are integrated for the average one hour time based heat in each flow. This premise is important to obtain a better accuracy for the operational heat. Premise 3 – for process input, the escape steam condition is saturated with title equals 1. Premise 4 – for process output, the escape condensate condition is no steam title. Premise 5 – although every CHP plant has a steam conditioning valve for turbo-generation by-pass, in regular conditions it is considered closed, with flow equals zero. Premise 6 – there is no loss of mass in the flow through each turbine. Premise 7 – the process for a biomass cogeneration system is simplified as having one single stream. Premise 8 – the lost energy due to loss of mass in the stream through the process is derived from the specific enthalpy of steam on the process input. 2) Work – Electrical / Mechanical The work is the most simple parameter to measure in power 5 plants because it is directly available in one single metering device per stream. The generated electricity can be measured by power meters. In order to comply with regulatory standards that are common to many countries, power meters are used so for gross energy metering as for energy export metering in power plants. The auxiliary systems electricity consumption can be measured using so power meters as protection relays. The usual cogeneration auxiliary systems to have measured consumption are: - Boiler Auxiliary Substation; - Power house Auxiliary Substation; - Bagasse conveyor system Auxiliary Substation; - Cooling towers Auxiliary Substation; and - Water utility Auxiliary Substation. The mechanical work from machines like boiler feedwater pumps or milling turbines can be measured by instantaneous power lecture available on its controller. This way, the accumulated kWh in a period of one hour can be measured and transmitted via a device communication port from each power meter, protection relay or controller, to the established database server. 3) Heat The heat measurement is obtained by indirect mean. It is done after lecture and handle over temperature, pressure and flow data from input and output points on the process stream. After measured and integrated in the time base, the values of these parameters are then used for operational heat calculation through the same equations as stated above. Referring to the PFD of Fig. 1, the ideal place for the instruments that would permit to better measure steam and condensate enthalpy, that represents heat, is the line right before the process input and the line right after it. However, the most usual place to have temperature, pressure and flow transmitters that permit to calculate escape steam enthalpy are installed on the pipes between turbine escapes and low pressure steam header. It means that the escape steam enthalpy entering the process is a sum of the ones escaping from the steam turbines as detailed in (7). (7) where: = Turbine generator mass flow, in kg/s. h ES = Escape steam specific enthalpy, in kJ/kg, as derived from steam temperature and pressure. = Turbine machine mass flow, in kg/s. After calculating the average value per second, a one hour time based average can be then obtained. The condensed water enthalpy from the process is quite complex to obtain. The usual place for temperature and pressure transmitters is the escape condensate tank right before condensate pumps that will push it back to the boiler deaerator. The usual place for escape condensate flow transmitter is the line right after the same condensate pumps to deaerator. Therefore, the escape condensate transferred heat can be calculated as detailed in (8). (8) where: = Escape condensate from process output mass flow, in kg/s. h CE = Escape steam specific enthalpy, in kJ/kg, as derived from condensate temperature and pressure. The steam losses heat can be calculated as detailed in (9). (9) where: = Turbine generator mass flow, in kg/s. = Turbine machine mass flow, in kg/s. = Escape condensate from process output mass flow, in kg/s. h ES = Escape steam specific enthalpy, in kJ/kg, as derived from steam temperature and pressure. It is important to notice that the heat loss is derived from the mass loss considered as escape steam enthalpy condition. There are some other important considerations to be done at this point. The here stated places for temperature, pressure and flow transmitters are not general rule. For each cogeneration in which the proposed methodology is applied, the measurement points must be verified as well as eventual adaptations to the stated equations must be made. In order to minimize that risk, the parameters defined in this methodology are as general as possible in order to attend most of the applications. Moreover, some of the instruments usually found in cogeneration plants are not transmitters, what requires manual measurement procedures. For a totally automatic measurement system implementation, verifications and eventual instrument changes must be done. Far from being a technical issue, this requirement is just a matter of instrumentation cost which is perfectly possible to meet by the owner. 4) Fuel The transferred fuel energy measurement is a challenging Download 328.84 Kb. Do'stlaringiz bilan baham: |
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