Calculate the net work output of the overall system if 1.2 x 107 joules of heat is released per kg of waste.
In a powerplant, 1500 kg of wastes must be utilzed per hour. Wastes is burned in an industrial boiler to turn 1 kg/s of preheated H2O to pressurized steam (44 atm, 450 °C).
The outgoing high-pressure steam, with 70 m/s speed, then drives a high-pressure turbine. The steam outlet of the high-pressure turbine is then used in a heat exchanger under 10 atm, 250 °C to preheat the H2O feed to the boiler. From an underground reservoir, this H2O is pumped at a low velocity (1 atm, 25 °C).
After preheating the H2O, the steam from the heat exchanger is used to drive a low-pressure turbine. Lastly, the steam from this low pressure turbine leaves at 10 m/s (at 1 atm and 100 °C) via an exhaust 10 m above the pump inlet.
The boiler is insulated, there are inevitably heat losses. As such, 25% of the heat from the burning of wastes is lost from the boiler.
Take note of the following data:
| T (deg C) | P (atm) | H (kJ/kg) | phase |
| 25 | 1 | 104.93 | liquid |
| 100 | 1 | 2675.53 | steam |
| 250 | 10 | 2942.73 | steam |
| 450 | 44 | 3324.63 | steam |
Calculate the net work output of the overall system if 1.2 x 107 joules of heat is released per kg of waste.
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