HW 20 - STEAM PLANT TOUR (36 Points)

HW 20 - STEAM PLANT TOUR (36 points)

YORK REFRIGERATION UNIT (8 points) 1. What working fluid is used in this unit? If the working fluid in this unit vaporizes at 40 °F, what is its pressure (psia) at this temperature? If the working fluid in this unit condenses at 85 °F, what is its pressure (psia) at this temperature? Use this information to calculate the pressure difference across the compressor (psia)? 2. Chilled water enters the evaporator at 53 °F and exits at 42 °F. Calculate the mass flow rate (lbm/hr) of water if the unit is operating at its rated cooling capacity of 1200 tons? NOTE: One ton of air conditioning capacity is capable of melting one ton of ice in 24 hours. One ton is also 12,000 Btu/hr. AIR COMPRESSOR (8 points) 3. Where and why are heat exchangers deployed in this device? 4. What thermodynamic/mechanical principles are used to remove moisture in outlet air? 5. Given a capacity of 373 standard cubic feet per minute (measured at inlet conditions), and an increase in pressure from atmospheric to 100 psig, estimate the air compressor power if compression is polytropic and isentropic. How does this compare with the motor that is rated as 75 hp? FEEDWATER PUMP (6 points) 6. What is a VFD and why is there one on this device> 7. Calculate the power required (hp) to run the feedwater pump. From the snapshot on the next page we know that the water enters the pump at 14.3 psig, and leaves at 218 psig. Mass flow of water/steam in the system is shown in the diagram on the following page. For the sake of simplicity, assume the water enters the pump as saturated liquid (even though it is slightly compressed) WOOD BOILER (14 points) Use the data on the next sheet to calculate questions 7-10 8. What device does water go through just before it enters the boiler? Why is this used? 9. Calculate the boiler duty (the rate of heat transfer to the working fluid in the boiler). You know the pressure and temperature of the liquid coming in to the boiler. You know the pressure of steam leaving the boiler. For the sake of estimation, assume the water leaving the boiler is saturated steam at the pressure shown in the diagram. 10. The maximum boiler capacity is around 57.5 x 106 Btu/hr. Approximately what fraction of boiler capacity is the plant running during this snapshot? 11. If dry fuel has a heating value of 7500 BTU/lbm and the fuel has 30% moisture by mass, what was the mass flow rate of fuel on this particular day? Assume 100% of the fuel energy goes in to heating the water. 12. What is the purpose of the air preheater? How does it work? Snapshot of UI Steam System Performance 2/15/13

Feedwater inlet pressure 218 psig Boiler outslet pressure is 136 psig Massflow of water/steam in the system is 38,482 pph (which is lbm/hr)

Economizer feedwater inlet temp 233 °F Economizer feedwater outlet temp 269 °F Economizer inlet flue temp 488 °F Economizer outlet flue temp 390 °F

Air PreHeater inlet flue temp 390 °F Air Pre-Heater outlet flue temp 362 °F Combustion air inlet temp 81 °F Combustion air outlet temp 210 °F