A cleaner coal technology has been developed. University of Minnesota scientists reveal colloidal coal-in-water slurries with nano-particles of coal which create a pseudo-fluid fuel that can be used in coal fired plants as well as diesel engines and fuel cells in U.S. Patent Application 20100024282. The organic immiscible phase is preferably dispersed into nanodroplets or nanoparticles that enhance coal heat of combustion.
The coal-in-water slurry can be used as a fuel for not only the reburn and/or main fuel in a low NOx burner, but also has potential applications in gasification processes, gas turbines, and diesel engines. Because of the coal's small particle size, and therefore larger surface area compared to commercially available coal-in-water slurries, a burning efficiency of the coal is near one hundred percent, leaving virtually no coal particles in the ash or the resulting gases.
The colloidal coal-in-water slurry generally includes from about fifty to about seventy two weight percent of coal, with about 20 to about 80 percent of the coal having a particle size of about one micron or less with a mode particle size of about 250 nanometers. The coal-in-water slurry can also include a surfactant system containing one surfactant or mixtures of two or more surfactants, or mixtures of one or more surfactants and an inorganic or organic salt.
The nano-dispersion of coal in water can be used in low NOx burner applications as the main fuel and/or the reburn fuel, in gasification processes as the input fuel either alone, or in combination with organic materials, in gas turbine applications, and in diesel engine applications say a team of researchers lead by University of Minnesota Professor of Chemistry Daniel D. Joseph and with Gustavo Nunez, Maria Briceno and Cebers Gomez.
The nano-dispersion of coal in water is essentially a pseudo-fluid, and optionally other additives may be included. The researchers developed methods making the nano-dispersion of coal in water, which can be used in several applications such as a fuel in boilers, secondary fuel for re-burning applications, as a feed for gasification and Oxycoal units, coal cleaning processes, diesel engines, gas turbines and fuel cells.
The nano-dispersion of coal in water can also contain another water-soluble fuel such as methanol, ethanol, propanol, butanol and glycerol. An organic immiscible phase, such as spent oil engine or lube oil, hydrocarbons as heavy crude oils and bitumen, diesel, biodiesel, petroleum coke and/or biomass, can also be incorporated into the water in the form of nanodroplets or nanoparticles that enhance coal heat of combustion.
Coal comprises a mixture of hydrocarbons and carbohydrates, with small amounts of nitrogen, sulfur, water, and minerals. Coal burns in air with a yellow, smoky flame, leaving ash behind. The energy content of coal depends upon its type. The heat of combustion of brown coal or lignite, for example, is about twenty-five kJ/g, and the heat of combustion of bituminous coal and anthracite is about thirty-two kJ/g. When coal burns, it mainly produces water and carbon dioxide, however it also produces harmful sulfur dioxide, carbon monoxide, hydrocarbons, particulate matter and soot, and oxides of nitrogen (hereinafter "NOx").
Boilers are closed vessels in which water or other fluids are heated. The heated or vaporized fluids exit the boiler for use in various processes or heating applications. In particular, utility boilers, which are typical drum-type boilers, are widely used in power plants, oil refineries, and petrochemical plants for steam generation to drive large turbines, producing electricity. In many instances, these boilers are coal-fired using coal at the burner to produce heated gases used to heat water, thereby generating steam.
Coal is also the cheapest and most abundant fuel on the world. As a consequence, any technology that allows the use of coal in a cleaner way is necessarily very attractive. Clean coal technologies require, among other things, more reactive coal in order to reduce or eliminate particulate matter and soot, carbon monoxide, hydrocarbons and NOx's emissions. More reactive coal implies complete combustion of coal particles and improved access to reactants or adsorbants to coal surface.
Coal comprises a mixture of hydrocarbons and carbohydrates, with small amounts of nitrogen, sulfur, water, and minerals. Coal burns in air with a yellow, smoky flame, leaving ash behind. The energy content of coal depends upon its type. The heat of combustion of brown coal or lignite, for example, is about twenty-five kJ/g, and the heat of combustion of bituminous coal and anthracite is about thirty-two kJ/g. When coal burns, it mainly produces water and carbon dioxide, however it also produces harmful sulfur dioxide, carbon monoxide, hydrocarbons, particulate matter and soot, and oxides of nitrogen (hereinafter "NOx").
Boilers are closed vessels in which water or other fluids are heated. The heated or vaporized fluids exit the boiler for use in various processes or heating applications. In particular, utility boilers, which are typical drum-type boilers, are widely used in power plants, oil refineries, and petrochemical plants for steam generation to drive large turbines, producing electricity. In many instances, these boilers are coal-fired using coal at the burner to produce heated gases used to heat water, thereby generating steam.
Coal is also the cheapest and most abundant fuel on the world. As a consequence, any technology that allows the use of coal in a cleaner way is necessarily very attractive. Clean coal technologies require, among other things, more reactive coal in order to reduce or eliminate particulate matter and soot, carbon monoxide, hydrocarbons and NOx's emissions. More reactive coal implies complete combustion of coal particles and improved access to reactants or adsorbants to coal surface.
However, commercially available coal-in-water slurries are not conducive to gas turbine applications. When the pulverized or micronized coal is combined with the compressed air and burned, the presence of unburned coal particles can damage the turbine blades, resulting in a less efficient process, and significant expense in replacing the turbine blades.
In diesel engines, a diesel engine relies upon compression ignition to burn its fuel. If air is compressed to a high degree, its temperature will increase to a point where fuel will burn upon contact. Following intake, the cylinder is sealed and the air charge is highly compressed to heat it to the temperature required for ignition. As the piston approaches top dead centre (TDC), fuel oil is injected into the cylinder at high pressure, causing the fuel charge to be nebulized.
Owing to the high air temperature in the cylinder, ignition instantly occurs, causing a rapid and considerable increase in cylinder temperature and pressure. The piston is driven downward with great force, pushing on the connecting rod and turning the crankshaft. If commercially available coal-in-water slurries are used as the fuel, the presence of unburned coal particles after combustion of these fuels can cause damage to the cylinders, such as damaging the tolerances between the piston and the cylinder. This in turn may cause damage or failure to the seal of the cylinder, resulting in a lack of pressure to increase the temperature to ignite the fuel, for example.
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