Behind the Grid — Coal

Posted: May 27, 2020 at 7:00 am

The world continues to seek new methods to generate and store electricity. There is no perfect solution. Challenges include reliability, renewability, and greenhouse gas emissions. This series seeks to explore those questions. This month, we look at coal.


Coal Power

(Published, 06/01/2020, Ruralite)

coalCoal is among the oldest and most-used fuels known to civilization. It is found and mined in nearly every nation in the world and has long been coveted as a powerful source of heat and light. Beginning in the 1880s, coal became the fuel of choice for generating electricity. Its abundance and low cost have made it the most common resource for electricity generation for over 100 years. But those days have come to an end.

How is coal formed?

Coal formation begins with dead and decaying plants. Sometimes, that plant matter gets covered beneath water and mud. As the plant matter gets buried deeper and deeper, there is less and less oxygen and eventually the decay stops. This partially-decayed matter is called peat. The peat gets compressed by weight from above and heat from below which slowly pressure-cooks it into coal.

Why is coal so full of energy?

Plants store energy in chemical bonds called carbohydrates. Usually, that energy is released slowly as plants decay. But in the case of coal, that energy is trapped and compressed. Not all coal is the same. Some forms are far more energy-dense than others. Different types of coal are found in different places depending on their geologic history. Lignite has the least energy, bituminous is in the middle and anthracite coal is the most energy-dense.

How is coal used to make electricity?

In a modern power plant, processed coal is milled to a fine powder, which increases the surface area and allows it to burn more quickly. The powdered coal is blown into a chamber and burned at high temperatures. Water is stored in tubes above the chamber and the heat boils the water into steam.

This high-pressure steam goes into a turbine containing thousands of propeller-like blades. The steam pushes these blades causing the turbine shaft to rotate at high speed. A generator is mounted to the end of the turbine shaft. After passing through the turbine, the steam is condensed and returned to the boiler to be heated again.

What is the environmental impact of coal?

Coal is composed almost entirely of carbon. Burning it emits large amounts of carbon dioxide (a greenhouse gas) into the atmosphere. Burning coal also releases traces of sulfur, mercury, lead, arsenic, and other particulates into the air.

Surface mining of coal impacts the environment and ecosystem in many negative ways. And subsurface coal mining causes lung damage and is a dangerous environment for workers.

Is there a future for "Clean Coal"?

Clean coal usually means capturing carbon emissions from burning coal and injecting them into the earth. There is some merit to the concept but even the best system would still produce carbon and it is an expensive technology. It should also be noted that coal is a finite resource that will eventually be depleted.

Coal can be found in nearly every country in the world. Only about 70 countries have enough to be economically recovered. There are an estimated 1.1 trillion metric tons of proven coal reserves worldwide. The ample supply is one of the reasons it remains in such high use.

Top 12 Known Coal Reserves:

22.3% — United States
15.5% — Russia
14.0% — Australia
13.1% — China
9.50% — India
3.50% — Germany
3.30% — Ukraine
3.10% — South Africa
2.50% — Poland
2.50% — Kazakhstan
2.20% — Indonesia
1.10% — Turkey

Source: Worldometer


Natural Gas

(Published, 05/01/2020, Ruralite)

several gasometersMore electricity is generated by natural gas than any other energy resource in the United States. For over 100 years, coal had been the top source. Is natural gas an ideal solution or just a short-term fit?

What is natural gas?

Natural gas is a fossil fuel formed from decomposed plant and animal matter. The primary ingredient is methane gas (CH4) with several other trace gases and impurities that must be processed, removed, and used separately. Byproducts of natural gas refining include propane and butane gas. Natural gas is mined via underground petroleum wells, gas wells, or through hydraulic fracturing (fracking).

How is it used to generate electricity?

Generating electricity is the process of converting one form of energy to another. In the case of natural gas, it is burned in a turbine which causes a generator to spin. Modern (combined-cycle) turbines are then able to capture the hot exhaust from the turbine to boil water and that high-pressure steam is then used to spin the turbines of electric generators. This means the fuel was essentially used twice, resulting in a highly efficient use of its energy.

What are the challenges and problems with natural gas?

First, natural gas is a finite resource. Like all fossil fuels, it must be mined from the earth and those sources will eventually be depleted. Estimates on when that happens vary greatly from 50 years to 250 years. New finds, new extraction methods and fluctuations in demand heavily impact those estimates.

Extracting natural gas through drilling or fracking directly impacts water, land, and air quality. The US Geological Survey connects fracking to earthquakes but other government organizations do not recognize this claim. Mining and burning natural gas produces pollutants and greenhouse gases including CO2 exhaust, escaped methane, and several others.

Considering the drawbacks, why has natural gas grown to be the top source for generating electricity?

Methane (the main component of natual gas) is among the most energy dense fuels on earth. Burning it releases massive amounts of heat. It is also lighter and easier to transport than coal or petroleum. Among fossil fuels, natural gas is the cleanest. It produces 40% less CO2 than coal. Coal also creates a lot of ash and natural gas does not. It is also very versatile and once it is processed, it can be used at an electrical generation plant or used directly to heat homes, as vehicle fuel or in various industrial applications.

The United States produces more natural gas than any other nation. 90% of domestic consumption is produced here and the US is also a major exporter. That makes it easier and more cost-stable for electric generating stations to depend on a fuel that is not connected to any foreign entities.

Of all natural gas processed in the United States, approximately 35% is used to generate electricity and 65% is used as “end-use” fuel. Meaning, people burn it to heat their homes, desalinate water, or power machinery.

Energy Density of Fossil Fuels:

Natural Gas — 54
Propane — 50
Gasoline — 46
Diesel — 45
Crude Oil — 42
Coal — 26

Values listed in MJ/kg


Hydropower

(Published, 04/01/2020, Ruralite)

hydroelectric damHydroelectric power is among the earliest and simplest ways to generate electricity. It is a renewable resource taking advantage of the natural water cycle. The flow of water through a dam generates electricity year-round. There are three main types of hydroelectric facilities including: impoundment, diversion, and pumped storage hydropower.

Water flows from a higher to a lower elevation. This constant running flow of water spins turbines and generators to convert this motion into electricity. The water then exits the turbine and is returned below the dam.

Hydropower works well in some areas and not in others. It is advantageous if the body of water (river) is either large or swift. The northwest has high capacity for hydropower as many powerful rivers in the Columbia drainage basin begin with high elevations and then flow swiftly into the Pacific ocean.

There are over 300 hydro projects in the Northwest including: four on the Lower Snake, fourteen on the Columbia (3 in Canada, 11 in the US), one on the Clearwater.

Hydroelectric power is cost-stable. The rivers that flow through dams are a sustainable resource and are not affected by market volatility.

The power generated at a dam is “firm.” Meaning, that it can be called upon when needed and left off when not needed. This is crucial to utilities and consumers. It is also crucial to non-firm sources like wind and solar which need firm sources to back them up when the wind isn’t blowing or when sunlight is not present. Water can be stored behind a dam to be released when needed. In this way, reservoirs act as giant batteries; the weight of the water is potential energy.

There are also many ancillary benefits to hydroelectric dams including flood control, irrigation, transportation of goods, and recreation.

The hydroelectric process produces zero greenhouse gas or other emissions into the atmosphere. Dams alter the natural flow of rivers so there is a significant environmental impact to the environment. Although many dams are built with fish passage, many are not. Slow-moving water in reservoirs can get warmer than swift-moving water. This also has a significant impact on the environment.

  • Industrialization of the northwest has many environmental impacts. Hydropower sales provide financial support to help mitigate those impacts - regardless of whether the impact is related to dams.
  • The Federal government recently released a Draft Environmental Impact Statement (DEIS), which provides a comprehensive analysis of the Northwest’s federally-operated hydro system. Agencies were tasked with specifically examining the lower Snake River dams, their impact on salmon, and what purpose they serve for our region. Visit the Northwest River Partners website for more information.

Wind Power

(Published, 03/01/2020, Ruralite)

Operation & Design

wind turbinesAs wind blows across propeller blades, it pushes them causing a turbine to spin. That spinning action generates electricity. Most wind turbines are built onto masts of 280-330 feet tall. This height puts the propeller blades in optimal position to take advantage of greater wind speeds. The blades themselves average 120 feet in length.

Renewable Resource

Wind is a renewable resource. It is created as air naturally moves from areas of high pressure to areas of low pressure. Generally, this is caused by the uneven heating of the Earth’s surface by the Sun.

Emissions and Environmental Impact

Wind turbines do not produce any emissions. They have been known to endanger flying birds and bats. The whirring blades produce some noise as well that may affect people and wildlife. Although, these same criticisms could be said for highways, skyscrapers or industrial sites.

Operating and Maintenance Costs

Wind turbines obviously don’t require fuel so they cost very little to operate. As with anything, maintenance costs increase as they age. Modern wind turbines are still a relatively new technology. Some estimates suggest they can operate for over 30 years, though there are many deployed turbines that lasted less than 20 years. Turbines can be repaired and most of the metal structure can be recycled but the fiberglass blades deteriorate over time and must be placed in landfills. Efforts are being made to find ways to recycle the material used in the blades.

Location

Most wind turbines are placed in flat, grassy, rural areas. Some locations are better than others. It is more economical to place wind turbines near existing electrical infrastructure. Wind turbines can also be located offshore, distributed throughout a grid or even built completely off-grid.

Reliability

Wind is unpredictable and intermittent. In order to generate electricity, turbines require a minimum wind speed of about 6-9 miles per hour (this is known as the cut-in speed). The optimum range for wind speed is around 20 miles per hour and the maximum safe speed is about 45 mph (cut-out speed).

Demand

Consumers want electricity to be available at any time. So, utilities seek ‘firm’ sources of generation that can be ramped up or down to meet demand. Wind is a non-firm resource (wind cannot be made on demand) so it only works when tied to another system to fill in when wind generation can’t meet consumer demand.

  • The output of a wind turbine depends on the turbine’s size and the wind’s speed through the rotor. An average onshore wind turbine has a capacity of 2–3 Megawatts
  • Modern wind turbines are nearly 300 feet tall - about the same height as the Statue of Liberty

Landfill Gas

(Published, 02/01/2020, Ruralite)

coffin butteLandfill gas (also called biogas) is produced by decomposing solid waste. That gas can be captured and used to operate electric generators. The process isn’t perfect but it’s an effective way to turn pollutants into useful fuel and ultimately, into electricity.

When waste is buried at a landfill, gases begin forming within around six months and may continue to be produced for many years into the future. As long as humans create waste, biogas will be produced, as it is the natural consequence of decomposition. It is composed primarily of methane (CH4) and carbon dioxide (CO2). Both of those are considered greenhouse gases. Methane is the same energy-dense material found in Natural Gas. Landfills are the third-largest source of methane in the United States.

At some municipal landfills, biogas simply vents through the ground into the atmosphere. Most landfills use a system to tap and “flare” the gas off in small bursts of flame. Flaring does help limit greenhouse gas emissions but fails to make use of potential chemical energy.
Many modern landfills have begun capturing the gas to power boilers, dryers, or electric generators.

A standard landfill gas capture system consists of vertical wells drilled into each acre of buried waste. These wellheads can capture 60% - 80% of the gas being produced and channel it into tanks where impurities are removed. This process has the added benefit of reducing odor and other hazards associated with emissions. The gas can then be used generators that have been built specifically to burn methane gas.

Many landfill gas operations have an up-time of 95%, meaning they can reliably and predictably produce power whenever needed. The facilities are fairly small compared to other electrical generation sources. In 2018, landfill gas produced less than 1% of the electricity in the United States, but these plants are able to turn a pollutant into a much cleaner energy source.

Visit the U.S. Energy Information Administration website for more information.

  • Methane can be captured from landfills, sewage treatment plants, paper mills, and food processing plants
  • The Coffin Butte Landfill Gas Generation Project is located near Corvallis, Oregon. They began operations in 1995 as a way for electric cooperatives to offer a renewable power subscription to their customers
  • Five large engines have been converted to operate on methane instead of diesel to make electricity
  • Coffin Butte landfill maintains over 300 gas wells and the generation facility produces 5.66 megawatts of power — enough to provide electricity to around 4,000 homes
  • The facility is owned and operated by PNGC Power and Clearwater Power customers have access to this renewable resource. Visit the PNGC Power website to learn more about coffin buttes.

Nuclear & Small Modular Nuclear

(Published, 01/01/2020, Ruralite)

small modular nuclear reactorMost nuclear power plants use uranium fission to create heat. The heat turns water into steam and the steam then drives turbine generators to make electricity. About 20% of electrical generation in the United States comes from nuclear power. It is the largest contributor of non-greenhouse-gas-emitting electric generation.

Nuclear power is extremely reliable. Often running 24/7 at over 90% capacity for 18-24 months without refueling. It is also scalable, able to meet peak demands for power. Uranium is a fairly common element (about as plentiful as tin) and is found all over the world. However, it requires a great deal of refinement to be turned into a useful fuel.

A Northwest company called NuScale Power is currently working on a technology known as Small Modular Nuclear Reactors (SMRs). These nuclear power plants are designed to be cleaner, safer, and more cost-competitive. Their compact design allows them to be built and assembled in a U.S. factory, then shipped to a prepared site for deployment. SMRs are about one-third the size of traditional reactors and their size and simplicity could reduce the time it takes to construct a new nuclear power plant. These factors make SMRs more flexibile for different scales of production or as demand changes over short periods of time. The U.S. Department of Energy supports the design, certification, and commercialization of small modular reactors (SMRs). The greatest concern over nuclear power regards used fuel. Used fuel (often called ‘spent’ fuel) remains radioactive for many thousands of years and must be contained or else it poses a serious environmental threat. Most nuclear waste in the U.S. is stored in large, water-cooled pools on-site at power plants. A safer but more expensive option for storage are large containers called dry casks. Great strides have been made in reusing old fuel but these methods are not currently considered economical.  Visit the Department of Energy website for more information on nuclear power. 

  • The City of Idaho Falls along with other small utilities in Idaho and Utah support purchasing power from SMRs in the future.
  • The first city in the U.S. to receive electricity from a nuclear power plant was Arco, Idaho in 1955.
  • This rendering (above) is a Small Modular Nuclear Reactor (SMR) which incorporates all of the components for steam generation and heat exchange into a single integrated unit called the NuScale Power Module™ (NPM). Each NPM operates independently within a multi-module configuration. Up to 12 modules can be monitored and operated from a single control. Each module can output 60 Megawatts of electricity, which would power about 30,000 homes.