91Ó°ÊÓ

Energy may be produced from solid waste in two ways: (1) generate methane from anaerobic decomposition of the waste and burn it (landfill-gas-to-energy, or LFGTE) or(2) burn the waste directly (waste-to-energy, or WTE). The heat generated by either method can be used to produce steam, which impinges on a turbine rotor connected to a generator to produce electricity. LFGTE produces about 215 k Wh electricity/ton of waste, and WTE produces roughly 600 kWh/ton of waste. The average output of a large power plant is 1 GW, which is enough to supply the annual residential energy consumption of a city of roughly 800,000 people. (a) The current rate of municipal solid-waste generation in the United States is approximately 413 million tons per year. If all of it were used for energy recovery, how many \(1 \mathrm{GW}\) power plants could LFGTE supply? How many if WTE is used? A useful source of information regarding LFGTE is the U.S. EPA Landfill Methane Outreach Program, http://www.epa.gov//mop/; the Waste-to-Energy Research and Technology Council at Columbia University provides useful information on WTE, http://www.seas.columbia.edu/earth/wtert/; and information on natural gas can be obtained from the U.S. Energy Information Administration, http:// www.eia.doe.gov/oil_gas/natural_gas/info_glance/natural_gas.html.

Step by step solution

01

Calculate the Total Energy Production for LFGTE and WTE

First, calculate the total potential energy production if all the municipal solid waste was subjected to each of the two methods. For LFGTE, this would be \(413 \times 10^{6} \, \text{tons} \times 215 \, \text{kWh/ton}\) to get a value in kilowatt hours. For WTE, the analogous calculation is \(413 \times 10^{6} \, \text{tons} \times 600 \, \text{kWh/ton}\).

02

Convert Energy Yield to GW

Next, convert the energy yield from kWh to gigawatt hours (GWh) so it can be compared to the power plant output. Since 1 GWh is equivalent to \(1 \times 10^{6} \, \text{kWh}\), divide the energy yield from Step 1 by \(10^{6}\) to get a figure in GWh.

03

Calculate Number of Power Plants

Finally, since a power plant operates continuously over the course of a year, calculate the number of power plants that can be supplied by dividing the annual energy yields for LFGTE and WTE (calculated in GWh per year) by the output of a single power plant (1 GW continuously over a year corresponds to \(1 \, \text{GW} \times 24 \, \text{hours/day} \times 365 \, \text{days/year} = 8760 \, \text{GWh/year}\). Thus, divide the figures obtained in Step 2 by 8760.

Unlock Step-by-Step Solutions & Ace Your Exams!

• Full Textbook Solutions

  Get detailed explanations and key concepts

• Unlimited Al creation

  Al flashcards, explanations, exams and more...

• Ads-free access

  To over 500 millions flashcards

• Money-back guarantee

  We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91Ó°ÊÓ!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Landfill-Gas-to-Energy (LFGTE)

Harnessing energy from the waste that fills our landfills is a method recognized for both its waste management and renewable energy benefits. Landfill-Gas-to-Energy (LFGTE) technologies capitalize on the natural decomposition of organic materials found in municipal solid waste (MSW). As waste breaks down anaerobically—without oxygen—it releases methane-rich biogas, a potent greenhouse gas.

LFGTE systems collect this gas through a series of wells and pipes networked throughout the landfill. Once collected, the biogas is processed to remove impurities and then used as fuel to generate electricity. This process creates about 215 kilowatt-hours (kWh) of electricity for every ton of waste processed, reducing methane emissions and generating a source of renewable energy.

Incorporating the exercise improvement advice, to better understand this, imagine a scenario where your city collects all of its waste in a single year and channels it through an LFGTE system. The conversion of this waste to energy could help power homes, businesses, and infrastructure, minimizing the dependency on fossil fuels and mitigating the impacts of waste on the environment.

Waste-to-Energy (WTE)

An alternative to LFGTE is the Waste-to-Energy (WTE) process which involves burning municipal solid waste directly to produce electricity. WTE technology is a form of thermal treatment where waste materials are used as a combustible fuel. More efficient than LFGTE in electricity production, WTE can generate approximately 600 kilowatt-hours (kWh) per ton of waste.

The WTE process begins with the incineration of waste, where the heat generated from burning turns water into steam. This steam then drives turbines which are connected to generators, ultimately producing electricity. Modern WTE plants are equipped with sophisticated pollution control systems to minimize environmental impact, capturing emissions and managing ash residue.

When conceptualizing the energy potential from WTE, consider that every ton of solid waste can yield enough energy to keep a 60-watt light bulb lit for over a month continuously. This potential represents not just a sustainable disposal method for our growing waste but also a significant source of renewable energy.

Municipal Solid Waste Energy Potential

The amount of energy that can be obtained from municipal solid waste (MSW) is astounding. In the United States alone, approximately 413 million tons of MSW are produced annually. Considering the energy conversion rates of both LFGTE and WTE technologies, this waste could be a key player in meeting national energy demands.

To contextualize the municipal solid waste energy potential using the exercise as an example, it would be helpful to comprehend that if all the MSW generated annually were converted into energy through LFGTE or WTE, it could supply several 1 gigawatt (GW) power plants. Such a comparison illustrates the significant role that waste can play in the broader spectrum of energy production, highlighting the importance of exploring and investing in technologies that enable waste to become a resource rather than remain a disposal problem.

Power Plant Energy Production

Power plants are the industrial engines that produce electricity for public consumption. The average output of a large power plant is around 1 gigawatt (GW), which is sufficient to supply an entire city's residential energy requirements for a year. Energy from waste, whether through LFGTE or WTE, can contribute meaningfully to this process.

In using the given exercise as a standpoint, multiply the number of hours in a year (24 hours/day * 365 days/year = 8760 hours/year) by 1 GW to understand the total output of a power plant annually. With this, we can interpret how waste-derived energy can be quantified to match the scale of power plants' capabilities. By converting trash to treasure, waste energy recovery can effectively bolster the energy grid, reducing reliance on non-renewable resources and providing cleaner, more sustainable energy options for future generations.