Concerns about climate change have encouraged significant interest in concepts for zero-emission power generation systems. These systems are intended to produce power without releasing CO2 into the atmosphere. One method to achieve this goal is to produce hydrogen from the gasification of fossil or biomass fuels. Using various membrane and reforming technologies, the carbon in the parent fuel can be shifted to CO2 and removed from the fuel stream, followed by direct CO2 sequestration. The hydrogen fuel can be used directly in gas turbines fitted with low-NO x combustors. A second approach to producing zero-emission power is to replace the nitrogen diluent that accompanies conventional combustion in air with either CO2 or H2O. In this concept, CO2 or H2O is added to oxygen to control combustion temperatures in oxygen-fuel reactions. In the absence of nitrogen, the primary combustion products for any hydrocarbon under lean conditions are then simply CO2 and H2O. Thus, merely cooling the exhaust stream condenses the water and produces an exhaust of pure CO2, ready for sequestration. The dilute oxy-fuel combustion strategy can be incorporated in power cycles that are similar to Brayton or Rankine configurations, using CO2 or H2O as the primary diluent respectively. While the relative merits of the various strategies to zero-emission power are the subject of various technical and economic studies, very little work has focused on defining the combustion issues associated with the dilute oxy-fuel option. In this paper, the expected combustion performance of CO2 and H2O diluted systems are compared. Experimental results from a high-pressure oxy-fuel combustor are also presented.
level. The agreement between the experimental results and the ab initio predictions is otherwise excellent, giving credence to the spectral assignments for A12H6 and the mixed dimers. The removal of symmetry results in much richer IR spectra and thus the assignment of new bands to the mixed dimer, say BGaH6, in a mixture of B2H6 and Ga2H6 should be possible based on Table II. In fact the exchange reaction, B2H6 + Ga2H6 -* 2BGaH6, should be experimentally accessible and provide new and interesting information regarding the chemistry of these systems. ConclusionsThe structures of the hexahydrides of boron, aluminum, and gallium are all diborane-like. The d10 electrons in gallane incompletely shield the nucleus, making it a stronger Lewis acid than might be otherwise expected. It was found necessary to split the valence orbitals to obtain a reasonable description of the gallium hydrides. The dissociation energies of diborane, dialane, digallane, and alaborane, gallaborane, and gallalane are remarkably similar when correlation is taken into account, suggesting that the decreased Lewis acidity of alane and gallane are compensated for by their increased hydridic bonds. Alaborane, gallaborane, and gallalane spectra are predicted to be very rich as a consequence of the loss of symmetry and should allow experimental detection of these mixed hexahydrides in the appropriate mixtures of diborane, dialane, and digallane.
The purpose of this article is to provide an overview of the basic technology of coal gasification for the production of syngas and the utilization of that syngas in power generation. The common gasifier types, fixed=moving bed, fluidized bed, entrained flow, and transport, are described, and accompanying typical product syngas compositions are shown for different coal ranks. Substantial variation in product gas composition is observed with changes in gasifier and coal feed type. Fuel contaminants such as sulfur, nitrogen, ash, as well as heavy metals such as mercury, arsenic, and selenium, can be removed to protect the environment and downstream processes. A variety of methods for syngas utilization for power production are discussed, including both present (gas turbine and internal combustion engines) and future technologies, including oxy-fuel, chemical looping, fuel cells, and hybrids. Goals to improve system efficiencies, further reduce NO x emissions, and provide options for CO 2 sequestration require advancements in many aspects of IGCC plants, including the combustion system. Areas for improvements in combustion technology that could minimize these tradeoffs between cost, complexity, and performance are discussed.
An experimental and modeling study has been performed jointly by UTRC and DOE-FETC to determine the effect of humidity in the combustion air on emissions and stability limits of gas turbine premixed flames. This study focuses on developing gas turbine combustor design criteria for the Humid Air Turbine (HAT) cycle. The experiments were conducted at different moisture levels (0%, 5%, 10% and 15% by mass in the air), at a total pressure of 200 psi, pilot levels (0%, 1%, 3% and 5% total fuel), and equivalence ratio (0.4 to 0.8 depending on the moisture levels). The moisture levels were achieved by injecting steam into dry air well upstream of the fuel-air premixing nozzle. Computations were made for comparison to the experiments using GRI Mech 2.11 kinetics and thermodynamic database for modeling the flame chemistry. A Perfectly Stirred Reactor (PSR) network code was used to create a network of PSRs to simulate the flame. Excellent agreement between the measured and modeled NOx (5–10%) was obtained. Trends of added moisture reducing NOx and the effects of equivalence ratio and piloting level were well predicted. The CO predictions were higher by about 30–50%. The CO discrepancies are attributed to in-probe oxidation. The agreement between the data and model predictions over a wide range of conditions indicate the consistency and reliability of the measured data and usefulness of the modeling approach. An analysis of NOx formation revealed that at constant equilibrium temperature, Teq, the presence of steam leads to lower O-atom concentration which reduces “Zeldovich and N2O” NOx while higher OH-atom concentration reduces “Fenimore” NOx.
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