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Geothermal: Classroom Activities

Exploring the Emissions from a Geothermal Plant and a Fossil Fuel Burning Plant


Goal

To compare the emissions from burning fossil fuels to those from a geothermal plant.

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Background Information

Geothermal power plants use steam from hot water to produce electricity. They release mostly water in the form of steam and very few harmful emissions or greenhouse gases. In contrast, coal is a sedimentary rock that consists mostly of combustible material in the form of carbon. The emissions of gaseous pollutants and soot from burning coal for heat or power are far greater than those from using stream.

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Activity Overview

In this simple activity, students compare a porcelain plate held above a source of steam from boiling water to one that is held above a burning fossil fuel, such as a paraffin candle or a piece of coal. Their observations will reveal which of the two sources is the cleaner form of energy. If you have a very sensitive balance you can measure and record the loss of mass of the fuel source. You may prefer to perform this investigation as a demonstration because of the risks involved in burning combustible fuels.

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Materials and Equipment

: combustible fossil fuel sources (e.g. candles, Bunsen burners, charcoal, wood, coal, barbecue igniter, Sterno candles), matches, small tins for burning materials, hotplate, tea pot, water, oven mitts, tongs, porcelain tile, sensitive balance, watch.

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Activity

  1. Have your students examine the assortment of fossil fuel sources.
  2. If you have Bunsen burners, use them for the combustion of wood, charcoal, or coal. Alternatively you can use a barbecue igniter, Sterno candles, or matches. The Bunsen burner can also be tested because methane (propane or butane) is a fossil fuel.
  3. If you have a sensitive mass balance, ask students to weigh the samples before combustion.
  4. Have students ignite each of the samples in turn. Each sample should be allowed to burn for the same length of time following ignition. Have students use tongs to hold a clean porcelain tile above the sample to collect any particles released during combustion.
  5. Ask students to rank their samples in terms of their emissions from cleanest to the dirtiest. If you have a sensitive mass balance you can weigh the samples after combustion. Results will vary depending on the samples that are tested. Typically, propane is the cleanest, followed by oil, followed by wood, followed by coal as the least clean.
  6. Have students observe the steam flowing from the kettle. Hold the mirror in the steam to collect the emissions. Ask students to observe the residue on the glass and record its description. Students will observe only colorless condensation on the mirror.
  7. Have students discuss their results as a class. Ask them the following:
    1. Explain your results.
      Explanations will vary but students should recognize that their experiment collected some of the particulates that form during the combustion of organic materials. When a gas is combusted then particles are not common. In contrast, coal produces soot and ash. Burning wood also produces smoke particles which are minute pieces of ash that rise into the air. However, burning coal also releases sulfur dioxide, nitrogen oxides, carbon dioxide, and traces of mercury. Coal burning power stations carefully scrub the air before passing it as exhaust into the atmosphere.
    2. Describe the merits of the various fuels burned?
      Answers will vary depending on the materials they use. Student's answers should prioritize the merits of cleaner sources of fuel, while considering their energy yield.

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