Question

1. Exhaust gas at 400 C and 1 bar from i engines flows at the rate of 125 mol s into a waste-heat boiler where saturated steam in generated at a pressure of 1200 kPa. Water enters the boiler at 20 C (Ta) and the exhaust gases are cooled to within 10°C of the steam temperature. The heat capacity of the exhaust gases is C/R-3.341.12x10 T/K. The steam flows into an adiabatic turbine and exhausts at a pressure of 25 kPa. If the turbine efficiency ( ) is 72%. What is W., the power output of the turbine? a. b. What is the thermodynamic efficiency of the boilerturbine combination? c. Determine So for the boiler and for the turbine d. Express Wloe(boiler) and Wlaa(turbine) as fractions of Wid, the ideal work of the process 2. A large steam turbine takes in 5 kg s of steam at 600°C and 12 bar, rejects it at 0.5 bar, and is supposed to produce power of 4 MW. This seems to be a rather large power output. Is it possible and if so, what is its efficiency compared to an adiabatic reversible turbine? A sugar mill in MPK has been disposing of the bagasse (???????, by open-air burning. You, as a new hired chemical engineer, determine that by using dried bagasse as boiler fuel in the mill, you can generate 5 tonhr of surplus steam at 20 bar & 600°C. You propose to your supervisor that the mill invest in a steam-turbine electrical generator assembly to generate electricity that can be sold to EGAT (as SPP). If you purchase a state-of-the-art adiabatic turbine and generator with ? of 0.90. calculate the power of electricity being produced from this power plant in unit of MW. In addition, calculate the temperature of exit steam, fraction of exit steam that is vapor and the rate of entropy generated. If the plant operates 24 hours a day and 320 day per year (the rest if for maintenance) and the price of electricity being sold to EGAT is 2.3 BahtkWh, estimate the revenue of this power plant. Note that the turbine exhaust is open to the atmosphere. In a certain chemical plant a 40% solution of organic salts is being evaporated to an 80% solution (% w/w). The organie salts cause only a very small boiling-point rise, which can be considered negligible. The condenser operates in such a manner that the pressure in the vapor line to the condenser is equivalent to a temperature of 130PF. At the present time, the only steam available for this operation is that which comes directly from the boiler. Since the tubes in the evaporator cannot withstand high pressure, the boiler steam is throttled to 10 psig before entering the evaporator. A manufacturer of turbo expander-turbo compressors suggests improving the steam economy (pound of water evaporated/pound of steam used) by installing one of his machine, shown by the dashed lines in Fig. 4-1. Per pound of feed solution handled, calculate the saving in boiler steam which might be made if the turbo expander-turbo compressor operates with T-8090 (based on isentropic operation) at both ends 3, 4. Turbo expander compressor Condense Throttling valve 400 pso PEvaporator Fig. 4-1

Answer 1