Darwin exhibit in at the American Museum of Natural History.
Environmental Impacts of Coal Consumption and Transportation Using more coal to produce hydrogen will have a number of environmental consequences. Coal mining itself causes numerous environmental issues, ranging from widespread land disturbance, soil erosion, dust, biodiversity impacts, waste piles, and so forth, to subsidence and abandoned mine workings.
Once coal has been extracted, it needs to be moved from the mine to the power plant or other place of use. The main pollutants resulting from conventional combustion of coal are sulfur oxides SOxnitrogen oxides NOxparticulates, CO2, and mercury Hg.
SOx is dealt with through lower-sulfur-content coal as well as Chapter 11 summary chem gas desulfurization FGD. Approximately 30 percent of U. Potentially the most significant future issue for coal combustion is CO2 emissions, since on a net energy basis coal combustion produces 80 percent more CO2 than the combustion of natural gas does, and 20 percent more than does residual fuel oil, which is the most widely used other fuel for power generation EIA , Table B1.
Likewise, the CO2 emissions associated with making hydrogen from coal will be larger than those for making hydrogen from natural gas. Using currently available technology, the CO2 emissions are about 19 kg CO2 per kilogram of hydrogen produced, compared with approximately 10 kg CO2 per kilogram of hydrogen manufactured from natural gas.
Since the s, the U. To the extent that new emission control technologies can be applied to existing plants and that new generating technologies can be used, further progress is expected in overall emissions reductions Ness et al.
Current Coal Technologies Conventional coal-fired power generation uses a combustion boiler that heats water to make steam, which is used to drive an expansion steam turbine and generator.
Overall efficiencies are typically in the 36 to 40 percent range. Although a staple for power generation for decades, this conventional combustion technique is not suitable for making hydrogen. Hydrogen-making technologies employ a conversion process rather than a combustion process.
Clean Coal Technologies Clean coal technologies use alternative ways of converting coal so as to reduce plant emissions and increase plant thermal efficiency, leading to an overall cost of electricity that is lower than the cost for electricity from conventional plants.
The goal is to attain thermal efficiencies in the 55 to 60 percent range higher heating value [HHV] Ness et al. With the exception of the IGCC systems, all of the others rely on increasingly sophisticated emissions control systems; IGCC uses a different conversion system to reduce emissions at the outset.
It is this gasification technology that is best suited to making hydrogen from coal. Gasification Technology Gasification systems typically involve partial oxidation of the coal with oxygen and steam in a high-temperature and elevated-pressure reactor.
The short-duration reaction proceeds in a highly reducing atmosphere that creates a synthesis gas, a mix of predominantly CO and H2 with some steam and CO2.
This syngas can be further shifted to increase H2 yield. Both can penetrate the lungs and are known to cause long-term damage resulting in respiratory and bronchial diseases. Page Share Cite Suggested Citation: The National Academies Press. The use of high temperature and pressure and oxygen minimizes NOx production.
The slag and ash that is drawn off from the bottom of the reactor encapsulate heavy metals in an inert, vitreous material, which currently is used for road fill. The high temperature also eliminates any production of organic materials, and more than 90 percent of the mercury is removed in syngas processing.
Syngas produced from current gasification plants is used in a variety of applications, often with multiple applications from a single facility. These applications include syngas used as feedstock for chemicals and fertilizers, syngas converted to hydrogen used for hydro-processing in refineries, production, generation of electricity by burning the syngas in a gas turbine, and additional heat recovery steam generation using a combined cycle configuration.
There are currently at least operating gasification plants running on a variety of feedstocks. These include residual oils from refining crude oil, petroleum coke, and to a lesser extent, coal.
The syngas that is generated has typically been used for subsequent chemicals manufacture; making power from IGCC systems is a more recent innovation, successfully demonstrated in the mids and commercially operated since the mids.
Gasification is, therefore, a well-proven commercial process technology, and several companies offer licenses for its use. Oxygen-Blown Versus Air-Blown Gasification Gasification plants exist that use either air-blown or oxygen-blown designs.
Air-blown designs save the capital cost and operating expense of air separation units, but the dilution of the combustion products with nitrogen makes the separation of CO2, in particular, a much more expensive exercise.1 A B A A n n n Mole fraction of componentA x + = = Chapter 11 – Properties of Solutions.
Solution Composition. A. Molarity 1. liters of. solution moles solute. Vitamin C is an electron donor (reducing agent or antioxidant), and probably all of its biochemical and molecular functions can be accounted for by this function.
The potentially protective role of vitamin C as an antioxidant is discussed in the antioxidants chapter of this report.
Ascorbate. This appendix discusses in more detail the technologies that can be used to produce hydrogen and which are addressed in Chapter 8. Cost analyses for them are presented in Chapter 5. In this appendix, the committee addresses the following technologies: (1) reforming of natural gas to hydrogen, (2.
This chapter focuses on high performance liquid chromatography (HPLC), which is an instrumental analytical method that gained increased acceptance mainly because it met two basic factors: (1) the need for a wide range of rapid analyses for nutrients, and (2) .
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