Considering non-power generation uses of coal in the United States
Introduction
The outlook for the coal industry has changed drastically this decade; in 2015, global coal consumption fell for the first time in over 30 years [1]. In the U.S., the situation is more dire, with domestic coal production peaking in 2008, and current production, even with a slight rebound in 2017, is below 1980 production levels [2] (Fig. 1). The cause of this diminishing production can be attributed to several factors: price competition with natural gas in the power sector, increased environmental regulation and pressure, increasing penetration of renewables, and stagnating electricity demand.
The landscape for global energy use and production is currently undergoing a shift. Improvements in technology have led to better recovery of energy sources such as natural gas and oil, while dramatic advancements in renewable energy has made these sources both more affordable and more accessible. The overall impact of these factors has aided in countries transitioning away from fossil fuels—especially coal.
Still, coal can be utilized in ways that go beyond traditional combustion, such as a feedstock for industrial use, or be converted into gas (Fig. 2).
Natural gas is the primary competition for coal in the U.S. power sector, due to the increase in natural gas production, and associated decline in production costs. The onset of unconventional shale gas production in the U.S. due to technological innovation such as horizontal drilling and hydraulic fracturing, has allowed the U.S. to become an exporter of liquefied natural gas (LNG)—something unheard of a decade ago [4,5]. This is further amplified by environmental policies, which support the switching to cleaner fuels [3]. This is expected to be magnified on a global scale as well, with current forecasts expecting natural gas to surpass coal in 2030, becoming the second-most utilized energy source [6].
Global short-term demand for coal for power generation is expected to be flat; by 2023, under some scenarios, coal's share of the world's energy mix will fall from 27% to 25% [9]. Regionally, demand for coal for power generation in Europe and North America will likely continue to decline, while developing countries—mainly India and Southeast Asia—will account for the bulk of the demand growth [7].
The shift away from coal-fired power generation is also supported by current policies which aim to lower global greenhouse gas and pollutant emissions. Natural gas is considered by some to be a “bridge” fuel for economies attempting to lower their emissions, as its combustion produces roughly half the amount of CO2 emissions associated with coal [8].
Renewable energies such as wind, solar, hydropower are also experiencing dramatic growth, largely due to price decreases, and many governments have policy mechanisms in place that promote fuel-switching to these sources for power generation.
There are other factors placing downward pressure on coal combustion. For example, China, the world's largest producer and consumer of coal, is currently taking aggressive steps to limit smog and particulate pollution. The government's 13th 5-year plan, which has placed emphasis on reducing consumption of, and pollution from, coal-fired generation through increased renewable generation, has expedited the closure of small coal mines, while supporting further use of low-emission coal technology. Nevertheless, the transformation has not reached local levels, and in 2018, China saw an increase in coal-fired power generation [9] and coal mining [10] in the country. Certain provinces—encouraged by economic stimulus [11] measures—have turned back to smokestack industries to prime local economies, and support employment in coal industry dependent regions.
For areas in the U.S. that are historically dependent on coal production, as well as many mining companies, these changes in energy production and consumption are having serious economic and policy implications [12] . Thus, it is timely to explore possible alternatives uses for coal, outside of combustion. This review focuses on the U.S. domestic use of coal in the industrial, manufacturing, and chemicals sectors, where it may provide alternatives as a source of feedstock and other materials.
Coal can be divided into four categories based on the amount of carbon the material contains—often referred to as rank. Coal consists of carbon, volatile matter, and minerals; coal with higher-rank have higher energy content, or heating value. The focus area of this paper includes bituminous (thermal), subbituminous, and lignite coal.
The U.S. coal market has historically played a small role in the global coal market [13], as vast domestic resources have largely been dedicated to the domestic power sector. Many coal-fired power plants opened between the mid-1970's and mid-1990's, stemming from policies aimed at decreasing oil consumption following the OPEC oil embargoes. During this time, domestic coal production transitioned from the Appalachian region in Eastern U.S. to the Powder River Basin in the West, due to lower production costs. Coal in Eastern mines tend to be bituminous with a high BTU content and a range of sulfur contents, these seams are smaller and farther from the surface, requiring underground mining techniques; in contrast, Mines in the Western U.S. are generally sub-bituminous coal with low sulfur and low BTU content. However, these seams tend to be thick and close to the surface, making their extraction costs low. Currently, coal mines West of the Mississippi river account for about 61% of total U.S. coal production [2] (Fig. 3).
Transporting coal is determined by several factors that often make its transport more costly than production. These factors include distance, availability of transport mode, supply source options, and the competition between coal and substitutes. Rail is the main mode of transport in the U.S [15]. Yet, rail shipments of coal can often be delayed, as intermodal transport (i.e. passenger trains) are given priority, adversely impacting power plants that rely on this coal [16]. Shipments of coal through any modality in the U.S. have been on the downturn, and 2017 marked the 4th consecutive year of decline [17].
In 2017, the U.S. mining industry employed 53,051 people [2]. While this is a 2% increase compared to 2016 employment [2], this is below the 66,000 employed by the sector in 2015 [18], and dramatically lower than jobs numbers in the clean energy sector. As the energy mix continues to shift, coal will find it even harder to reclaim its share of the electricity market, likely leaving its production and the communities that have been historically reliant on the coal mining industry, stranded.
As domestic consumption of coal has fallen, coal mines have looked to international markets for growth opportunities. The U.S. has historically not been a significant exporter to the global coal market; however, in the past decade, coal exports have increased, so that the U.S. is considered a net exporter [19]. In 2017, the U.S. exported 97 million short tons (MMst) of coal, a 61% increase compared to 2016 [20]. Europe is the largest consumer of U.S. coal, although India, South Korea, and Japan are also top recipients of U.S. coal exports. In the U.S., the Appalachian mines in the East have an advantage due to their proximity to port facilities for sales to international markets. Currently, the Norfolk, Virginia port sees the most coal exports. In contrast, coal mines in the Western U.S. are around 1000 miles from ports on the West Coast where all the coal ports are currently at capacity. This has led to several proposals to build new or expand current ports on the West Coast in Washington and California. Most of these attempts have run into political problems, and it is unlikely these will begin construction, creating a level of uncertainty around the future of coal exports.
As noted, it is possible to utilize coal for uses other than power generation; it can be processed to produce fuels, liquids, chemicals, and materials. The purpose of this paper to explore some of these non-power generation uses of coal, and the possible impacts theses uses may have on the U.S. chemicals and manufacturing sectors. The paper addresses whether coal can be considered as a raw material for producing other value-added materials.
The remainder of this paper is organized as follows. Section 2 briefly considers the recovery of Rare Earths from coal and coal byproducts, while Section 3 consider coal combustion byproducts. Section 4 covers a range of topics from chemicals to materials. Section 5 concludes.
Section snippets
Rare earth elements and coal ash
Coal and coal combustion byproducts can serve as inputs across industries, lending credibility to coal's use beyond conventional power generation. Rare Earth Elements (REE's) are 17 strategic elements, considered so because they are necessary in technologies such as catalysts, cell phones, hard drives, hybrid engines, lasers, and magnets, as well as other applications [21]. REE's are typically found in the earth's crust and mined from ore; their extraction is difficult-a multistep process that
Gasification of coal
Coal can be biologically converted to methane gas in such a manner that is efficient in energy usage and emissions [30], which is especially attractive as this process can be performed on coal seams that would be too costly for traditional mining [31]. Coal has been known to host large communities of anaerobic bacteria and archaea [32] when extracted from coal beds and given nutrients contained in yeast extract and peptone, these bacteria and archaea can produce continuous amounts of methane [33
Coal-to-liquids and coal-to-chemicals
Following coal's conversion to syngas, it may be processed into liquid fuels through either the Fischer-Tropsch process or hydrogenation. Coal-to-liquids (CTL) via Fischer-Tropsch is commonly used to synthesize diesel, naphtha, LNG, though gasoline and kerosene can be further refined through additional steps [38].
The CTL process is advantageous as it produces non-petroleum-based alternatives for vehicle fuels. For countries with large coal reserves, such as the U.S. and China, CTL represents a
Conclusion
While there are technically feasible products for coal beyond combustion, the majority of them have significant environmental impacts and high costs. One viable use of coal that goes beyond combustion is for the extraction of REE's, which are considered critical for the deployment of clean technology. This is especially true as the current tensions between China, a main global REE supplier, and the U.S. have heightened. The gasification process holds potential for alternative fuels and energy
Declaration of competing interest
We the undersigned declare that this manuscript is original, has not been published before and is not currently being considered for publication elsewhere.
We would like to draw the attention of the Editor to the following publications of one or more of us that refer to aspects of the manuscript presently being submitted. Where relevant copies of such publications are attached.
We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no
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