Considering Thermoeconomics Figure P7.140 provides steady-state operati...

Considering Thermoeconomics

Figure P7.140 provides steady-state operating data for a coal gasification system fueling a cogeneration system that produces power and process steam. The numbers given for each of the seven streams, in MW, represent rates of exergy flow. The unit cost based on exergy of stream 1 is c₁ = 1.08 cents per kW · h. On the advice of a cost engineer, the unit costs based on exergy of the process steam (stream 4) and power (stream 5) are assumed to be equal, and no cost is associated with combustion air and water (stream 7). The costs of owning and operating the gasification and cogeneration systems are $3600/h and $1800/h, respectively. These figures include expenses related to discharge of ash (stream 3) and flue gas (stream 6) to the surroundings. Determine the

(a) rate of exergy destruction, in MW, for each system.

(b) exergetic efficiency for each system and for an overall system formed by the two systems.

(c) unit cost based on exergy, in cents/kW · h, for each of streams 2, 4, and 5.

(d) cost rate, in $/h, associated with each of streams 1, 2, 4 and 5.