Hospitals are big users of electricity, heating and cooling. Standby power is essential for hospital as...

 

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Hospitals are big users of electricity, heating and cooling. Standby power is essential for hospital as any interruption to electricity supply could risk loss of life. Therefore, onsite power generation is a consideration for all hospitals. An engineer is designing a cogeneration system as shown in the diagram below for a hospital. 20 kg/s of steam exits the boiler at 10 MPa and 500 C. The steam can be throttled to 500 kPa by an expansion valve and then enters the process heater. Some steam can also be extracted from the turbine at 500 kPa into the process heater. The minimum pressure for the cogeneration system is 10 kPa. The steam exits both the process heater and condenser as saturated liquid. (a) Mixing chamber Boiler Expansion valve 10 Pump II Process heater Pump I Turbine Condenser (b) 11 94 10 1,2,3 Figure: (a) Schematic diagram and (b) T-s diagram of the cogeneration system. (a) Calculate the maximum net power (MW) that can be produced. (b) Calculate the maximum rate of process heat (MW) that can be supplied. (c) The engineer estimates 35 MW of process heat will be required during normal operation. 20 % of steam can be extracted before it enters the turbine. Calculate the percentage of steam that should be extracted from the turbine to produce process heat. Hospitals are big users of electricity, heating and cooling. Standby power is essential for hospital as any interruption to electricity supply could risk loss of life. Therefore, onsite power generation is a consideration for all hospitals. An engineer is designing a cogeneration system as shown in the diagram below for a hospital. 20 kg/s of steam exits the boiler at 10 MPa and 500 C. The steam can be throttled to 500 kPa by an expansion valve and then enters the process heater. Some steam can also be extracted from the turbine at 500 kPa into the process heater. The minimum pressure for the cogeneration system is 10 kPa. The steam exits both the process heater and condenser as saturated liquid. (a) Mixing chamber Boiler Expansion valve 10 Pump II Process heater Pump I Turbine Condenser (b) 11 94 10 1,2,3 Figure: (a) Schematic diagram and (b) T-s diagram of the cogeneration system. (a) Calculate the maximum net power (MW) that can be produced. (b) Calculate the maximum rate of process heat (MW) that can be supplied. (c) The engineer estimates 35 MW of process heat will be required during normal operation. 20 % of steam can be extracted before it enters the turbine. Calculate the percentage of steam that should be extracted from the turbine to produce process heat.