18. If a coal-burning electrical generating plant burns 2 tons of coal to generate 6000 kWh of electricity, calculate the efficiency of the plant as the ratio of electricity output to fuel energy input (refer to Table 3.4). 19. If a 1000-MW power plant is shut down for one day, what will be the loss in rev- enues if the utility could sell its electricity at 12"/kWh? 20. If 60% of U.S. petroleum use goes for transportation, and 1% of this goes for buses, how much oil could be saved per year if all buses were electrified (assuming the electrical energy was generated from nonpetroleum resources)? What is this in MBPD? 21. Suppose you left a 100-W light bulb on continuously for one month. If the elec- tricity generation and transmission efficiency is 30%, how much chemical energy (in joules) was wasted at the power plant for this oversight? If the fuel consumption for one meal in Cambodia using a kerosene wick stove is 6 MJ (1 MJ = 1,000,000 joules), how many equivalent meals could be cooked with this wasted energy? 22. Refer to Problem 25 of Chapter 2. Using the conversions of Table 3.4, to how many
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According to Table 3.4, the energy content of coal is 24 million joules (MJ) per kilogram (kg). We need to convert tons to kg and then find the total energy input. 1 ton = 1000 kg 2 tons = 2000 kg Energy input = (2000 kg) * (24 MJ/kg) = 48000 MJ Now, we need to Show more…
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An electrical power plant has an overall efficiency of $15 \%$. The plant is to deliver $150 \mathrm{MW}$ of electrical power to a city, and its turbines use coal as fuel. The burning coal produces steam at $190^{\circ} \mathrm{C}$, which drives the turbines. The steam is condensed into water at $25^{\circ} \mathrm{C}$ by passing through coils that are in contact with river water. (a) How many metric tons of coal does the plant consume each day $\left(1\right.$ metric ton $\left.=1 \times 10^{\circ} \mathrm{kg}\right) ?$ (b) What is the total cost of the fuel per year if the delivery price is $\$ 8$ per metric ton? (c) If the river water is delivered at $20^{\circ} \mathrm{C}$, at what minimum rate must it flow over the cooling coils so that its temperature doesn't exceed $25^{\circ} \mathrm{C}_{?}^{\circ}$ (Note: The heat of combustion of coal is $7.8 \times 10^{3} \mathrm{cal} / \mathrm{g}$.)
A UK-based utility company is considering adapting a coal fired power station so that it can burn a combination of wood grown in plantations in the UK and North America and waste wood such as broken pallets and wood from demolition sites. a. Explain in around 100 words why burning wood has advantages over coal in respect of greenhouse gas emissions. (4 marks) b. If the heat of combustion of the wood is 9.8 MJ kg−1 and the power station will generate electricity with an efficiency of 31% when burning wood, calculate how much electricity can be produced (in units of MW) if the station burns 10 tonnes of wood per hour. Give your final answer to 1 decimal place. (6 marks) c. How much wood would need to be burned per hour to maintain an output of 500 MW from the power? Give your answer to 2 significant figures. (2 marks) d. The wood is to be stored under cover and the plant operators wish to keep two weeks supply of wood on site. If the bulk density of the wood is 300 kg m−3, calculate the minimum volume of storage that will be required for the 500 MW plant.
Krishna G.
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