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ME 200 L32ME 200 L32Utility Power Generation

Self Study Assignment 8.2Today’s Class 8.3 Today’s Class 8.3

Kim See’s Office ME Gatewood Wing Room 2172 Examination 3 grades are available Blackboard and Examinations

can be picked up all of this week from Gatewood Room 2172

Exams not picked up this week may be recycled!Exams not picked up this week may be recycled!

https://engineering.purdue.edu/ME200/ThermoMentor© Program

Spring 2014 MWF 1030-1120 AMJ. P. Gore

gore@purdue.eduGatewood Wing 3166, 765 494 0061

Office Hours: MWF 1130-1230TAs: Robert Kapaku rkapaku@purdue.edu

Dong Han han193@purdue.edu

2

Outline• Rankine Cycle (with Improved Performance) – Will introduce base-line Rankine Cycle while Will introduce base-line Rankine Cycle while

introducing Superheating and Open feed water heatingintroducing Superheating and Open feed water heating

– Reheating- will mention but leave for you to explore

– Supercritical- will mention but leave for you to explore

– Closed feed water heating- will mention but leave for you to explore

– Multiple feed water heating- will mention but leave for you to explore

Regenerative Vapor Power Cycle Using an Open Feed-Water Heater

►See T-s diagram: Open feed-water heater and high pressure pump move the material to 7. So heat transfer to the cycle takes place from state 7 to state 1, rather than from state a to state 1- increasing the average temperature of heat addition & Carnot

Tavg(a-1)

Tavg(7-1)

Regenerative Vapor Power Cycle Using an Open Feed-Water Heater

►Follow a unit of mass as it moves through the cycle. The unit of mass is denoted in parentheses by (1).

►(1) enters turbine at state 1 and expands to state 2 where a fraction (y) is extracted into the open feed-water heater.►Remaining (1-y) expands through the second turbine stage to state 3, is condensed to state 4, and then pumped to state 5 where it enters the open feed-water heater.

(1) (1-y)(y)

Regenerative Vapor Power Cycle Using Open Feed-Water Heater

►(y) and (1-y) entering the feed-water heater at states 2 and 5, respectively, mix, giving a single stream at state 6 and recovering the unit mass (1).►Unit mass (1) at 6 is pumped to state 7 and fed to the steam generator and boiled and superheated to state 1 by external heat addition

(1)

(1-y)

(y)

►With fraction y known, mass and energy rate balances applied to control volumes around the other components yield the following expressions, each on the basis of a unit of mass entering the first turbine stage.

Mass, Energy, Entropy Balance Equations

►Applying steady-state mass, energy and entropy balances to the feed-water heater, the fraction of the total flow y is

► For the pumps

► For the steam generator

► For the condenser

► For the turbine stages

Mass, Energy, Entropy Balance Equations

Apply second law to all components as a classexercise.

Cogeneration Systems

►Are integrated systems that simultaneously yield two valuable products, electricity and steam (or hot water) from a single fuel input.►Typically provide cost savings relative to producing power and steam (or hot water) in separate systems.►Are widely deployed in industrial plants, refineries, food processing plants, and other facilities requiring process steam, hot water, and electricity. ►Can be based on vapor power plants, gas turbine power plants, internal combustion engines, and fuel cells.

Cogeneration Systems

►An application of cogeneration based on vapor power plants is district heating – providing steam or hot water for space heating together with electricity for domestic, commercial, and industrial use.

Steam exported to the community

Electricity provided to the community

Cogeneration Systems►Exporting useful steam to the community limits the electricity that also can be provided from a given fuel input, however.►For instance, to produce saturated vapor at 100oC (1 atm) for export to the community water circulating through the power plant will condense at a higher temperature and thus at a higher pressure.►In such an operating mode thermal efficiency is less than when condensation occurs at a pressure below 1 atm, as in a plant fully dedicated to power production.

T > 100oCp > 1 atm