In summary, the operating temperatures of the first steam engine are 680 degrees Celsius and 430 degrees Celsius, while the operating temperatures of the second steam engine are 415 degrees Celsius and 280 degrees Celsius. If the heat of combustion of coal is 2.8 E8 J/kg, at what rate must coal be burned in order to produce 900 MW of power at the plant? Assume the efficiency of the engines is 65 percent of the ideal (Carnot) efficiency.
The first engine spits out some work, which is part of the electricity generated. It also spits out waste heat, which is used to power the second engine. I thought the first engine's work was used to power the second engine; in fact, it's the waste heat.