Question 1. A steam turbine is divided into two sections, H.P and L.P with a reheater interposed in between the two sections. The steam on its way to the turbine at 30 bar and 500 oC passes through a reheater where it gives up heat at constant pressure to heat flowing from the H.P turbine to the L.P section. The steam then enters the H.P turbine at 30 bar and 380oC. The steam leaves the H.P turbine at 7 bar and the L.P turbine at 0.07 bar. Assuming no pressure losses between two sections of the turbine and an internal efficiency of 80% for both sections, determine the steam condition at entrance to the L.P section and the thermal efficiency of the plant.
Question 2. A steam power plant equipped with regenerative as well as reheat arrangement is supplied with steam to the H.P turbine at 80 bar and 470oC. For feed heating, part of the steam is extracted at 7 bar and the remainder of the steam is reheated to 350 oC in a reheater and then expanded in L.P turbine down to 0.035 bar. Determine the following: -
(a) Amount of steam bled off for feed heating
(b) Amount of steam in L.P turbine
(c) Heat supplied in boiler and reheater
(d) Output of the turbine
(e) Cycle efficiency
Question 3. In a steam power plant generating 250MW of electrical power, boiler supplies steam at a pressure of 150 bar and 550oC. The condenser pressure is 0.05 bar. The turbine, mechanical and generator efficiencies are 88, 98 and 99% respectively. The fuel is diesel having calorific value of 44.8 MJ/Kg. The boiler efficiency is 90%. The feed water enters the boiler at 160oC.
The risers of the furnace are 50m high while the downcomers are outside the furnace producing natural circulation. The quality of steam at the top of the risers is 10% and a minimum exit velocity of mixture leaving and entering the drum is 1.5 m/s.
The dimensions of the riser tubes is 60mm OD and 3mm wall thickness. Dimensions of the downcomers are 150mm and 6mm thick.
Assuming no pressure drop amd heat loss in risers calculate
(a) The generation of rate of steam
(b) the rate of fuel flow required
(c) Evaporation rate
(d) Pressure head developed due to natural circulation
(e) Circulation ratio
(f) Number of risers
(g) Number of downcomers