Showing papers on "Coal published in 2009"

The Economic Effects of Climate Change

Abstract: Greenhouse gas emissions are fundamental both to the world’s energy system and to its food production. The production of CO2, the predominant gas implicated in climate change, is intrinsic to fossil fuel combustion; specifically, thermal energy is generated by breaking the chemical bonds in the carbohydrates oil, coal, and natural gas and oxidizing the components to CO2 and H2O. One cannot have cheap energy without carbon dioxide emissions. Similarly, methane (CH4) emissions, an important greenhouse gas in its own right, are necessary to prevent the build-up of hydrogen in anaerobic digestion and decomposition. One cannot have beef, mutton, dairy, or rice without methane emissions. Climate change is the mother of all externalities: larger, more complex, and more uncertain than any other environmental problem. The sources of greenhouse gas emissions are more diffuse than any other environmental problem. Every company, every farm, every household emits some greenhouse gases. The effects are similarly pervasive. Weather affects agriculture, energy use, health, and many aspects of nature—which in turn affects everything and everyone. The causes and consequences of climate change are very diverse, and those in low-income countries who contribute least to climate change are most vulnerable to its effects. Climate change is also a long-term problem. Some greenhouse gases have an atmospheric life-time measured in tens of thousands of years. The quantities of emissions involved are enormous. In 2000, carbon dioxide emissions alone (and excluding land use change) were 24 billion metric tons of carbon dioxide (tCO2).

An overview on oxyfuel coal combustion—State of the art research and technology development

Abstract: Oxyfuel combustion is seen as one of the major options for CO2 capture for future clean coal technologies. The paper provides an overview on research activities and technology development through a fundamental research underpinning the Australia/Japan Oxyfuel Feasibility Project. Studies on oxyfuel combustion on a pilot-scale furnace and a laboratory scale drop tube furnace are presented and compared with computational fluid dynamics (CFD) predictions. The research has made several contributions to current knowledge, including; comprehensive assessment on oxyfuel combustion in a pilot-scale oxyfuel furnace, modifying the design criterion for an oxy retrofit by matching heat transfer, a new 4-grey gas model which accurately predicts emissivity of the gases in oxy-fired furnaces has been developed for furnace modelling, the first measurements of coal reactivity comparisons in air and oxyfuel at laboratory and pilot-scale; and predictions of observed delays in flame ignition in oxy-firing.

Carbon capture and sequestration.

Abstract: ![Figure][1] CREDIT: U.S. DEPARTMENT OF ENERGY Overwhelming scientific evidence shows that CO2 emissions from fossil fuels have caused the climate to change, and a dramatic reduction of these emissions is essential to reduce the risk of future devastating effects. On the other hand, access to energy is the basis of much of the current and future prosperity of the world. Eighty percent of this energy is derived from fossil fuel. The world has abundant fossil fuel reserves, particularly coal. The United States possesses one-quarter of the known coal supply, and the United States, Russia, China, and India account for two-thirds of the reserves. Coal accounts for roughly 25% of the world energy supply and 40% of the carbon emissions.[*][2] It is highly unlikely that any of these countries will turn their back on coal any time soon, and for this reason, the capture and storage of CO2 emissions from fossil fuel power plants must be aggressively pursued. This special issue of Science discusses the potential role of carbon capture and sequestration (CCS) in reducing CO2 emissions. The scale of CCS needed to make a significant dent in worldwide carbon emissions is staggering. Roughly 6 billion metric tons of coal are used each year, producing 18 billion tons of CO2. In contrast, we now sequester a few million metric tons of CO2 per year. At geological storage densities of CO2 (∼0.6 kg/m3), underground sequestration will require a storage volume of 30,000 km3/year. This may be sufficient storage capacity, but more testing is required to demonstrate such capacity and integrity. We should pursue a range of options for new coal-fired power plants (such as coal gasification, burning coal in an oxygen atmosphere, or postcombustion capture) to determine the most cost-effective approach to burn fuel and reduce the total amount of CO2 emitted. No matter which technology ultimately proves best for new plants, we will still need to retrofit existing plants and new plants that will be built before CCS is routinely deployed. Each new 1-gigawatt coal plant is a billion-dollar investment and, once built, will be used for decades. ![Figure][1] CREDIT: DOE/NREL Estimates of CCS costs vary considerably, but experience with other pollution control technologies such as the scrubbing of SO2 and NOx show that costs can be considerably lower than initial estimates. Furthermore, new ideas are now being explored, such as more efficient, lower-temperature catalytic conversion of coal to hydrogen and methane, CO2 capture based on phase separation, and polygeneration (production of variable mixtures of electricity, methane, liquid fuel, and ammonia). In the natural world, sequestration of CO2 occurs through photosynthesis, calcification of CO2 by phytoplankton, and mineralization in ground root systems. Can we enhance natural processes (“reforestation plus”) or draw inspiration from nature as a starting point for artificial capture? Similarly, nature provides proof that the energy penalty for releasing adsorbed CO2 in postcombustion capture can be decreased: Through carbonic anhydrases, our blood captures CO2 created by cell metabolism and releases it in the lungs with no enthalpic energy penalty. Public support of CCS R&D is essential, and for this reason, $3.4 billion of American Recovery and Reinvestment Act money is being invested by the U.S. Department of Energy (DOE) in CCS R&D. The DOE is also supporting the testing of CO2 sequestration in seven different U.S. geologic formations. To accelerate global dissemination of CCS technology and expertise, international collaborations are essential. The G-8 leaders called for at least 20 CCS projects by 2010. In July, I announced a new U.S.–China Clean Energy Research Center that will facilitate joint research in several areas, including CCS. Intellectual property developed jointly will be shared between our countries. There are many hurdles to making CCS a reality, but none appear insurmountable. The DOE goal is to support R&D, as well as pilot CCS projects so that widespread deployment of CCS can begin in 8 to 10 years. This is an aggressive goal, but the climate problem compels us to act with fierce urgency. [1]: pending:yes [2]: #fn-1

Particle imaging of ignition and devolatilization of pulverized coal during oxy-fuel combustion

Abstract: Oxy-fuel combustion of coal is a promising technology for cost-effective power production with carbon capture and sequestration that has ancillary benefits of emission reductions and lower flue gas cleanup costs. To fully understand the results of pilot-scale tests of oxy-fuel combustion and to accurately predict scale-up performance through CFD modeling, fundamental data are needed concerning coal and coal char combustion properties under these unconventional conditions. In the work reported here, the ignition and devolatilization characteristics of both a high-volatile bituminous coal and a Powder River Basin subbituminous coal were analyzed in detail through single-particle imaging at a gas temperature of 1700 K over a range of 12–36 vol % O 2 in both N 2 and CO 2 diluent gases. The bituminous coal images show large, hot soot cloud radiation whose size and shape vary with oxygen concentration and, to a lesser extent, with the use of N 2 versus CO 2 diluent gas. Subbituminous coal images show cooler, smaller emission signals during devolatilization that have the same characteristic size as the coal particles introduced into the flow (nominally 100 μm). The measurements also demonstrate that the use of CO 2 diluent retards the onset of ignition and increases the duration of devolatilization, once initiated. For a given diluent gas, a higher oxygen concentration yields shorter ignition delay and devolatilization times. The effect of CO 2 on coal particle ignition is explained by its higher molar specific heat and its tendency to reduce the local radical pool. The effect of O 2 on coal particle ignition results from its effect on the local mixture reactivity. CO 2 decreases the rate of devolatilization because of the lower mass diffusivity of volatiles in CO 2 mixtures, whereas higher O 2 concentrations increase the mass flux of oxygen to the volatiles flame and thereby increase the rate of devolatilization.

Biochar as a Fuel: 1. Properties and Grindability of Biochars Produced from the Pyrolysis of Mallee Wood under Slow-Heating Conditions

Abstract: Biomass as a fuel suffers from its bulky, fibrous, high moisture content and low-energy-density nature, leading to key issues including high transport cost and poor biomass grindability. This study investigates the possibility to pretreat biomass to produce biochar as a solid biofuel to address these issues. Biochars were produced from the pyrolysis of centimeter-sized particles of Western Australia (WA) mallee wood in a fixed-bed reactor at 300 to 500 °C and a heating rate of 10 °C/min. The data show that, at pyrolysis temperatures ≥320 °C, biochar as a fuel has similar fuel H/C and O/C ratios compared to Collie coal that is the only coal being mined in WA. Converting biomass to biochar leads to a substantial increase in fuel mass energy density from ∼10 GJ/ton of green biomass to ∼28 GJ/ton of biochars prepared from pyrolysis at 320 °C, in comparison to 26 GJ/ton for Collie coal. However, there is little improvement in fuel volumetric energy density, which is around 7−9 GJ/m3 in comparison to 17 GJ/m3 o...

Low-Rank Coal Drying Technologies—Current Status and New Developments

Abstract: Despite their vast reserves, low-rank coals are considered undesirable because their high moisture content entails high transportation costs, potential safety hazards in transportation and storage, and the low thermal efficiency obtained in combustion of such coals. Their high moisture content, greater tendency to combust spontaneously, high degree of weathering, and the dusting characteristics restrict widespread use of such coals. The price of coal sold to utilities depends upon the heating value of the coal. Thus, removal of moisture from low-rank coals (LRC) is an important operation. Furthermore, LRC can be used cost effectively for pyrolysis, gasification, and liquefaction processes. This article provides an overview the diverse processes—both those that utilize conventional drying technologies and those that is not yet commercialized and hence in need of R&D. Relative merits and limitations of the various technologies and the current state of their development are presented. Drying characteristics ...

Review of Mid- to High-Temperature Sulfur Sorbents for Desulfurization of Biomass- and Coal-derived Syngas

Abstract: This review examines state-of-the-art mid- and high-temperature sulfur sorbents that remove hydrogen sulfide (H2S) from syngas generated from coal gasification and may be applicable for use with biomass-derived syngas. Biomass feedstocks contain low percentages of protein-derived sulfur that is converted primarily to H2S, as well as small amounts of carbonyl sulfide (COS) and organosulfur compounds during pyrolysis and gasification. These sulfur species must be removed from the raw syngas before it is used for downstream fuel synthesis or power generation. Several types of sorbents based on zinc, copper, iron, calcium, manganese, and ceria have been developed over the last two decades that are capable of removing H2S from dry coal-derived syngas at mid- to high-temperature ranges. Further improvement is necessary to develop materials more suitable for desulfurization of biomass-derived syngas because of its hydrocarbon, tar, and potentially high steam content, which presents different challenges as compar...

Emissions inventory of PM2.5 trace elements across the United States.

Abstract: This paper presents the first National Emissions Inventory (NEI) of fine particulate matter (PM2.5) that includes the full suite of PM2.5 trace elements (atomic number > 10) measured at ambient monitoring sites across the U.S. PM2.5 emissions in the NEI were organized and aggregated into a set of 84 source categories for which chemical speciation profiles are available (e.g., Unpaved Road Dust Agricultural Soil, Wildfires). Emission estimates for ten metals classified as Hazardous Air Pollutants (HAP) were refined using data from a recent HAP NEI. All emissions were spatially gridded, and U.S. emissions maps for dozens of trace elements (e.g., Fe, Ti) are presented for the first time. Nationally, the trace elements emitted in the highest quantities are silicon (3.8 x 10(5) ton/yr), aluminum (1.4 x 10(5) ton/yr), and calcium (1.3 x 10(5) ton/yr). Our chemical characterization of the PM2.5 inventory shows that most of the previously unspeciated emissions are comprised of crustal elements, potassium, sodium, chlorine, and metal-bound oxygen. This work also reveals that the largest PM2.5 sources lacking specific speciation data are off-road diesel-powered mobile equipment, road construction dust, marine vessels, gasoline-powered boats, and railroad locomotives.

Thermogravimetric studies of the behavior of wheat straw with added coal during combustion.

Abstract: The combustion behavior of biomass and biomass–coal blends under typical heating conditions was investigated. Thermogravimetric analyses were performed on bituminite coal, aspen strawdust and wheat straw used alone and blended with different coal weight ratios. The behavior of biomass fuels in the burning process (different rates of volatilization, char burning and heat production) was analyzed, and the effects of a cold molding procedure for wheat straw on the burning properties were investigated. In addition, the kinetic parameters for the thermal conversion of each fuel were determined. Cold molding led to easier firing, and 5% coal was identified as the ideal ratio to achieve similar heat release characteristics to strawdust. Such a mixed pellet fuel with burning characteristics similar to aspen wood can be produced to take advantage of the wide design basis for wood-fired boilers.

Underground Coal Gasification: A Brief Review of Current Status

Abstract: Coal gasification is a promising option for the future use of coal. Similarly to gasification in industrial reactors, underground coal gasification (UCG) produces syngas, which can be used for power generation or for the production of liquid hydrocarbon fuels and other valuable chemical products. As compared with conventional mining and surface gasification, UCG promises lower capital/operating costs and also has other advantages, such as no human labor underground. In addition, UCG has the potential to be linked with carbon capture and sequestration. The increasing demand for energy, depletion of oil and gas resources, and threat of global climate change lead to growing interest in UCG throughout the world. In this article, we review the current status of this technology, focusing on recent developments in various countries.

Role of adsorption and swelling on the dynamics of gas injection in coal

Abstract: [1] An experimental technique is presented to perform gas injection experiments on coal cores confined by an external hydrostatic pressure, which makes use of the so-called transient step method. The experiments are intended to improve the knowledge on the different mechanisms acting during CO2 storage in coal seams, in particular, those related to permeability. Helium, nitrogen, and carbon dioxide have been injected at pressure ranging from 10 to 80 bars and at confining pressures varying between 60 and 140 bars. The experiments with helium have been used to study the mechanical compliance of the coal core, whereas those with the adsorbing N2 and CO2 to study the effects of adsorption and swelling on the flow dynamics. The obtained experimental transient steps were successfully described using a mathematical model, consisting of mass balances accounting for gas flow and adsorption, and mechanical constitutive equations for the description of porosity and permeability changes during injection. A semiempirical relationship between permeability and operating pressures is validated, and the corresponding parameters have been evaluated. Results showed increase in permeability with decreasing effective pressure on the sample and, when an adsorbing gas was injected, a reduction in permeability caused by swelling, with CO2 having a stronger effect compared to N2.

Low-Grade Coals: A Review of Some Prospective Upgrading Technologies†

Abstract: Low-grade coals are usually those that are low in specific energy because of high moisture content and/or ash content or produce high emissions of concern. These are commonly lignites or sub-bituminous coals. There is a growing need of using these low-grade coals because of higher quest for power generation. In general, the direct use of the low-grade coals results in higher costs of reducing emissions or in lower efficiency and, consequently, higher greenhouse gas emissions. In the present carbon-constrained environment, there is a need of upgrading these coals in terms of moisture, ash, and/or other trace elements. There are a number of upgrading technologies. The current paper reviews these technologies mainly categorized as drying for reducing moisture and cleaning the coal for reducing mineral content of coal and related harmful constituents, such as sulfur and mercury. The earliest upgrading of high-moisture lignite involved drying and manufacturing of briquettes. Drying technologies consist of both...