Motive steam work, calculation

Calculating work available from motive steam... 

Most of the turbines you will encounter in your work are called topping, or extraction, turbines. The idea of such a turbine is to extract much of the potential work from the motive steam, and then use the exhaust steam to reboil towers. Typically, the energy content of the exhaust steam is only 10 to 20 percent less than that of the motive steam. That is the calculation we just did with the Mollier diagram. The rest of the energy of the steam may then be used as the steam condensers, to reboil towers. This sounds pretty efficient. It is the basis for the new cogeneration projects you may have heard about. Of course, this system was used by the British Navy in the nineteenth century. 

Calculating Work Available from Motive Steam... 

Divide your answer by 2500 Btu/hp. This is the fraction of a horsepower that each pound of steam can produce. However, as turbines are not 100 percent efficient, multiply the calculated horsepower by 0.90 to account for internal turbine inefficiencies called -windage losses. Incidentally, the reciprocal of the calculated horsepower per pound of steam is called the water rate, which is the pounds of motive steam needed to generate 1 horsepower worth of shaft work. 

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