Showing papers on "Coal published in 2011"

Catalytic routes for the conversion of biomass into liquid hydrocarbon transportation fuels

Abstract: Concerns about diminishing fossil fuel reserves along with global warming effects caused by increasing levels of CO2 in the atmosphere are driving society toward the search for new renewable sources of energy that can substitute for coal, natural gas and petroleum in the current energy system. Lignocellulosic biomass is abundant, and it has the potential to significantly displace petroleum in the production of fuels for the transportation sector. Ethanol, the main biomass-derived fuel used today, has benefited from production by a well-established technology and by partial compatibility with the current transportation infrastructure, leading to the domination of the world biofuel market. However, ethanol suffers from important limitations as a fuel (e.g., low energy density, high solubility in water) than can be overcome by designing strategies to convert non-edible lignocellulosic biomass into liquid hydrocarbon fuels (LHF) chemically similar to those currently used in internal combustion engines. The present review describes the main routes available to carry out such deep chemical transformation (e.g., gasification, pyrolysis, and aqueous-phase catalytic processing), with particular emphasis on those pathways involving aqueous-phase catalytic reactions. These latter catalytic routes achieve the required transformations in biomass-derived molecules with controlled chemistry and high yields, but require pretreatment/hydrolysis steps to overcome the recalcitrance of lignocellulose. To be economically viable, these aqueous-phase routes should be carried out with a small number of reactors and with minimum utilization of external fossil fuel-based hydrogen sources, as illustrated in the examples presented here.

Aviation gas turbine alternative fuels: A review

Abstract: The development of kerosene-like drop-in alternative aircraft fuels is currently receiving increased attention. Using a range payload approach the need for drop in fuels is justified. The alternative fuels available can be categorised into two groups; depending on whether the product increases supply security of supply or provides a reduced environmental footprint. This paper uncovers this relationship through a review of commercially available process technologies (Transesterfication, Fischer–Tropsch (FT) and hydroprocessing (HRJ)) to produce alternative fuels. The lifecycle assessments available are reviewed to identify what are actually clean fuels or have the potential to be one. A summary of the recent alternative fuel flight test campaigns is given and there results evaluated along with ground based results. A review of combustion characteristics available for the alternative fuels including ignition characteristics are presented to demonstrate the effect the distillation curve has on combustion and how too narrow a distribution of components in the fuel could generate problems with high altitude relight. The effect alternative fuels have on gaseous emissions regulated by the International Civil Aviation Organisation (ICAO) Committee on Aviation Environmental Protection (CAEP) is discussed and shown to be engine hardware dependant. Experimental data, from an Auxiliary Power Unit (APU) engine, are provided showing how, although the Gas to Liquid (GtL) and Coal to Liquid (CtL) FT fuels may not reduce GHG emissions, even with Carbon Capture and Sequestration (CCS), the local air quality around airports will benefit through reduced particulate emissions. Finally the prospects for future fuel development are discussed.

Full cost accounting for the life cycle of coal.

Abstract: Each stage in the life cycle of coal-extraction, transport, processing, and combustion-generates a waste stream and carries multiple hazards for health and the environment. These costs are external to the coal industry and are thus often considered "externalities." We estimate that the life cycle effects of coal and the waste stream generated are costing the U.S. public a third to over one-half of a trillion dollars annually. Many of these so-called externalities are, moreover, cumulative. Accounting for the damages conservatively doubles to triples the price of electricity from coal per kWh generated, making wind, solar, and other forms of nonfossil fuel power generation, along with investments in efficiency and electricity conservation methods, economically competitive. We focus on Appalachia, though coal is mined in other regions of the United States and is burned throughout the world.

Clean liquid fuels from direct coal liquefaction: chemistry, catalysis, technological status and challenges

Abstract: Increased demand for liquid transportation fuels coupled with gradual depletion of oil reserves and volatile petroleum prices have recently renewed interest in coal-to-liquids (CTL) technologies. Large recoverable global coal reserves can provide liquid fuels and significantly reduce dependence on oil imports. Direct coal liquefaction (DCL) converts solid coal (H/C ratio ≈ 0.8) to liquid fuels (H/C ratio ≈ 2) by adding hydrogen at high temperature and pressures in the presence or absence of catalyst. This review provides a comprehensive literature survey of the coal structure, chemistry and catalysis involved in direct liquefaction of coal. This report also touches briefly on the historical development and current status of DCL technologies. Key issues, challenges involved in DCL process and directions for the future research are also addressed.

Coal combustion-generated aerosols: Formation and properties

Abstract: Coal combustion for power generation is a major source of particulate air pollution. Understanding of the formation mechanisms and properties of coal combustion aerosols is critical to both the development of particulate control technologies and the assessment of their impacts on human health. This paper presents an overview of the current understanding of the mechanisms of ash particle formation in major coal-based power generation processes such as pulverized coal combustion, fluidized bed combustion and coal gasification, and a summary of the aerosol properties that are important for elucidating particle formation and evaluating their health effects. Principal particle formation mechanisms, including mineral coalescence, particle fragmentation, and vaporization-condensation, are reviewed. The complex nature of the formation mechanisms of submicron aerosols is emphasized. Evidence is provided for some solid-to-particle processes that are suspected to contribute to the formation of the submicron aerosols. Physicochemical properties such as particle size, composition and morphology are discussed. Of particular interest is the trimodality of the ash aerosol size distribution. Size-resolved elemental composition data are used to identify particle modes and to uncover their formation mechanisms. The formation of the additional central particle mode is attributed to heterogeneous condensation of vaporized species on existing fine residual ash particles. Future research topics associated with ash aerosol formation and properties are discussed.

Making Fischer-Tropsch fuels and electricity from coal and biomass: Performance and cost analysis

Abstract: Major challenges posed by crude-oil-derived transportation fuels are high current and prospective oil prices, insecurity of liquid fuel supplies, and climate change risks from the accumulation of fossil fuel CO2 and other greenhouse gases in the atmosphere. One option for addressing these challenges simultaneously involves producing ultraclean synthetic fuels from coal and lignocellulosic biomass with CO2 capture and storage. Detailed process simulations, lifecycle greenhouse gas emissions analyses, and cost analyses carried out in a comprehensive analytical framework are presented for 16 alternative system configurations that involve gasification-based coproduction of Fischer−Tropsch liquid (FTL) fuels and electricity from coal and/or biomass, with and without capture and storage of byproduct CO2. Systematic comparisons are made to cellulosic ethanol as an alternative low GHG-emitting liquid fuel and to alternative options for decarbonizing stand-alone fossil-fuel power plants. The analysis indicates tha...

Solar-driven gasification of carbonaceous feedstock-a review

Abstract: Given the future importance of solid carbonaceous feedstocks such as coal, coke, biomass, bitumen, and carbon-containing wastes for the power and chemical industries, gasification technologies for their thermochemical conversion into fluid fuels are developing rapidly. Solar-driven gasification, in which concentrated solar radiation is supplied as the energy source of high-temperature process heat to the endothermic reactions, offers an attractive alternative to conventional autothermal processes. It has the potential to produce high-quality synthesis gas with higher output per unit of feedstock and lower specific CO2 emissions, as the calorific value of the feedstock is upgraded through the solar energy input by an amount equal to the enthalpy change of the reaction. The elimination of an air separation unit further facilitates economic competitiveness. Ultimately, solar-driven gasification is an efficient means of storing intermittent solar energy in a transportable and dispatchable chemical form. This review article develops some of the underlying science, examines the thermodynamics and kinetics of the pertinent reactions, and describes the latest advances in solar thermochemical reactor technology.

Arsenic hazards in coal fly ash and its fate in Indian scenario

Abstract: Fly ash (FA) generated as a waste produced from thermal power plants globally has started gaining as a potentially significant anthropogenic source of arsenic (As). In India electricity generation is predominantly dependent upon coal-based thermal power plants and are being producing huge amount of FA. Coal contains many toxic metals, arsenic is one of those, which is significantly toxic for aquatic and terrestrial life including human being. Coal used in Indian thermal power plants is mainly bituminous and sub-bituminous and which on combustion generate over 40% of FA. Generated FA is being disposed to open ash pond in thin slurry form. More than 65,000 acre of land in India is occupied for storage of this massively generated quantity of FA. Dumping of FA in open ash pond causes serious adverse environmental impacts owing to its elevated trace element contents, in particular the As which causes ecological problems. Although, the As problem in our country is not new, in recent years the occurrence of As contamination cases of agricultural soil, ground water as well as human health has resulted a great concern for its mitigation. Very recently India has been charged for being a “dumping hub for As”. Utilization of FA in India is still infancy (more than 38%) as compared to developed countries (more than 70%). In India FA is used particularly in cement production, brick industry, as road base, as amendments in the restoration ecology and forestry. This review emphasized on the concentration of As in FA, its fate and behaviour as hazardous element on human health, environment quality and on mitigation strategies to accomplish environmental management.

Coal to gas: the influence of methane leakage

Abstract: Carbon dioxide (CO2) emissions from fossil fuel combustion may be reduced by using natural gas rather than coal to produce energy. Gas produces approximately half the amount of CO2 per unit of primary energy compared with coal. Here we consider a scenario where a fraction of coal usage is replaced by natural gas (i.e., methane, CH4) over a given time period, and where a percentage of the gas production is assumed to leak into the atmosphere. The additional CH4 from leakage adds to the radiative forcing of the climate system, offsetting the reduction in CO2 forcing that accompanies the transition from coal to gas. We also consider the effects of: methane leakage from coal mining; changes in radiative forcing due to changes in the emissions of sulfur dioxide and carbonaceous aerosols; and differences in the efficiency of electricity production between coal- and gas-fired power generation. On balance, these factors more than offset the reduction in warming due to reduced CO2 emissions. When gas replaces coal there is additional warming out to 2,050 with an assumed leakage rate of 0%, and out to 2,140 if the leakage rate is as high as 10%. The overall effects on global-mean temperature over the 21st century, however, are small.

Chemical Looping Combustion of Biomass/Coal with Natural Iron Ore as Oxygen Carrier in a Continuous Reactor

Abstract: Chemical looping combustion (CLC) is a new innovative technology with inherent separation of CO2 without energy penalty. Experiments on chemical looping combustion of biomass/coal were conducted in a 1 kWth continuous reactor, and an Australia iron ore was selected as oxygen carrier. Both biomass/coal mixture and biomass were used as fuels. The effect of temperature on gas composition of both the fuel reactor and the air reactor, conversion efficiency of carbonaceous gases, carbon capture efficiency, and oxide oxygen fraction was investigated. An increase in the fuel reactor temperature produced a higher CO2 concentration in the fuel reactor for biomass/coal mixture, whereas it produced a lower one for pure biomass. CO concentration in the fuel reactor increased in both fuel conditions. Due to the poor oxygen transport capacity and the thermodynamic constraint of the iron ore conversion from Fe2O3 to Fe3O4, a higher temperature would contribute to decreasing the conversion efficiency of carbonaceous gases...

Steam gasification of various feedstocks at a dual fluidised bed gasifier: Impacts of operation conditions and bed materials

Abstract: Gasification of biomass is an attractive technology for combined heat and power production as well as for synthesis processes such as production of liquid and gaseous biofuels. Dual fluidised bed (DFB) technology offers the advantage of a nearly nitrogen-free product gas mainly consisting of H2, CO, CO2 and CH4. The DFB steam gasification process has been developed at Vienna University of Technology over the last 15 years using cold flow models, laboratory units, mathematical modelling and simulation. The main findings of the experimental work at a 100-kW pilot scale unit are presented. Different fuels (wood pellets, wood chips, lignite, coal, etc.) and different bed materials (natural minerals such as olivine, limestones, calcites, etc. as well as modified olivines) have been tested and the influence on tar content as well as gas composition was measured and compared among the different components. Moreover, the influence of operating parameters such as fuel moisture content, steam/fuel ratio and gasification temperature on the product gas has been investigated. DFB steam gasification of solid biomass coupled with CO2 capture, the so-called absorption enhanced reforming (AER) process, is highlighted. The experiments in pilot scale led to commercial realisation of this technology in demonstration scale. Summarising, the DFB system offers excellent fuel flexibility to be used in advanced power cycles as well as in polygeneration applications.

Inferring absorbing organic carbon content from AERONET data

Abstract: Black carbon, light-absorbing organic carbon (of- ten called "brown carbon") and mineral dust are the ma- jor light-absorbing aerosols. Currently the sources and formation of brown carbon aerosol in particular are not well understood. In this study we estimated the amount of light-absorbing organic carbon and black carbon from AERONET measurements. We find that the columnar ab- sorbing organic carbon (brown carbon) levels in biomass burning regions of South America and Africa are relatively high (about 15-20 mg m 2 during biomass burning season), while the concentrations are significantly lower in urban ar- eas in US and Europe. However, we estimated significant ab- sorbing organic carbon amounts from the data of megacities of newly industrialized countries, particularly in India and China, showing also clear seasonality with peak values up to 30-35 mg m 2 during the coldest season, likely caused by the coal and biofuel burning used for heating. We also com- pared our retrievals with the modeled organic carbon by the global Oslo CTM for several sites. Model values are higher in biomass burning regions than AERONET-based retrievals, while the opposite is true in urban areas in India and China.