[填空题]
At a steam power plant, steam enginesl;e53prad6uvc/ep uz pw;d ;6 work in pairs, the output of heaxm1h/:yll4uo t from one being the approximate heat input of the second. The operating temperatures of ux/:mol1y 4h lthe first are 670$^{\circ}\,C$ and 440$^{\circ}\,C$, and of the second 430$^{\circ}\,C$ and 290$^{\circ}\,C$. If the heat of combustion of coal is $ 2.8\times10^{7 }\,J/kg$ at what rate must coal be burned if the plant is to put out 1100 MW of power? Assume the efficiency of the engines is 60% of the ideal (Carnot) efficiency. $kg/s$
