ME433 Homework 7 solution(4)

# ME433 Homework 7 solution(4) - ME 433 Homework 7 Biofuels...

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ME 433 Homework 7 - Biofuels 1. Located in Kettle Falls, Washington, the Kettle Falls Generating Station began operation in 1983. The 53 MW power plant generates electricity via a Rankine steam cycle fueled by direct combustion of wood waste with a 23% moisture content and 5% ash, as-received. The system has an efficiency of 35% and a capacity factor of 90%. During periods of high demand, the plant supplements its electricity generation with an 8 MW natural gas turbine with a heat rate of 8000 Btu/kWh. The plant consumes the wood waste fuel at a rate of 70 tons per hour at rated power. The plant supplies electrical power to 50,000 homes, each using 9,000 kWh of electricity annually. Assume the natural gas is pure methane (CH 4 ). The wood waste and methane have higher heating values of 14.0 MJ/kg (as-received) and 48.0 MJ/kg, respectively. Neglect transmission losses. The ultimate composition of the dry, ash-free wood waste is given in the table below. Ultimate Composition (wt%) a. How much natural gas is needed to fuel the gas turbine each year (MBtu/y)? b. What is the as-received higher heating value of the wood waste on a dry ash-free basis (MJ/kg daf )? c. How many tons of as-received wood waste are required to fuel the plant each year (T as-recd / y)? C 50% H 6% O 44% 50,000 homes 1 × 9000 kWh home y × MWh 10 3 kWh = 450,000 MWh y 53 MW 1 × 8760 hr y × 0.90 MWh del MWh rated = 417,900 MWh y 450,000 417,900 ( ) MWh y × 10 3 kWh MWh × 8000 Btu thermal kWh e × MBtu 10 6 Btu = 257,000 MBtu y 1 kg as-recd 0.23 kg w 0.05 kg ash = 0.72 kg daf 14 MJ kg as-recd × kg as-recd 0.72 kg daf = 19.4 MJ kg daf 417,900 MWh e y × 3600 MJ MWh × MJ thermal 0.35 MJ e × kg as-recd 14.0 MJ × 2.204 lbm kg × T 2000 lbm = 338,000 T y This study resource was shared via CourseHero.com

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d. How many metric tons of CO 2 are emitted from the power plant annually (Mg CO2 /y)? Include the emissions resulting from the direct combustion of wood waste and the emissions from the natural gas combustion.
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