One suggestion that has been made to conserve energy is that all new electrical power generation plants should be co-generation facilities. In a typical power plant the combustion of coal or natural gas is used to produce steam that is run through a turbine and the only useful energy that results is electricity. In such cases the pressure at the downstream end of the turbine is kept as low as possible to produce the most work (electricity). This is done by having a condenser after the turbine cooled by (frequently river) water or air. Another alternative is a co-generation power plant in which the temperature of the exiting steam is kept higher so that the steam leaving the turbine can be used for heating purposes (as process stream in a chemical plant or for residential heating as in New York City). In a cogeneration plant the useful energy obtained is the sum of the electrical energy and energy that can be used for heating. Calculate the useful energy and overall energy efficiency obtained from: 

a. A standard power generation plant.

b. A co-generation plant.

The following data are available: 

i The heat combustion of the fuel is used to produce steam at 900^◦C and 25 bar from water at 1 bar and 25^◦C. This is accomplished with 80% efficiency (that is 20% of the heating value of the fuel is lost in the process); 

ii The steam turbines are adiabatic and reversible; 

iii The condensed saturated steam leaving the standard power plant is at 45^◦C which sets the pressure at the exit of the turbine and 

iv The steam exit pressure in the co-generation plant is 1 bar, and this steam in then used as a heat transfer fluid until is condensed and its temperature is 40^◦C.