Nitrogen is usually available from the cryogenic air separation unit, so it can conveniently be employed in the IGCC process. The use of a diluent to lower flame temperature, such as nitrogen or steam, is currently the preferred method for minimizing NOx generation from a syngas-fired turbine. Finally, coal gasification-derived syngas will likely contain higher concentrations of H 2S than natural gas, which may impact post-combustion NOx control technologies. This very fast flame speed of the hydrogen component of the syngas prevents the use of the lean-premix technology. The latter means that the syngas should have a stable flame at leaner conditions than natural gas, while the former indicates that the kinetics (chemical reaction speed) of H 2 combustion are much quicker than that of natural gas. When compared to natural gas, the H 2 component of syngas exhibits a higher flame speed and broader flammability limits. Furthermore, whereas the combustible composition of natural gas is primarily methane (CH 4), the syngas combustible components are carbon monoxide (CO) and hydrogen (H 2), with an H 2/CO ratio generally ranging from 0.6 to 0.8 2. This yields a significant flow rate increase compared with natural gas (~14% more), resulting from the need to maintain a specified heat input to the combustor. An oxygen-blown, entrained-flow IGCC plant will typically produce syngas with a heating value ranging from 250 to 400 Btu/ft 3 (HHV basis), which is considerably lower than the 1000 Btu/ft 3 for natural gas. Gasification-derived syngas differs from natural gas in terms of calorific value, gas composition, flammability characteristics, and contaminants. Differences between syngas and natural gas composition and combustion characteristics are the source of the problem. The so-called Lean-Premix Technology 1, which permits the latter to achieve emissions as low as 9 ppm (at 15% O 2), is not applicable to IGCC gas turbines. Following is a review of both combustion-based and post-combustion NOx control methods used for NOx emissions control.Īvailable combustion-based NOx control options for syngas-fired turbines are more limited than those available for natural gas-fired turbines.
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However, known methods for controlling NOx formation keep these levels to a minimum and result in NOx emissions substantially below those associated with other coal-fired electrical production technologies, as seen in the following figure.Īlthough NOx emissions from operating IGCC power plants are quite low as shown above, stricter regulations may require control to levels as low as 3 ppm in the heat recovery steam generator (HRSG) stack gas.
In coal gasification-based processes, NOx can be formed downstream by the combustion of syngas with air in electricity-producing gas turbines. Since both NH 3 and HCN are water soluble, this is a straightforward process. Small levels of ammonia (NH 3) and hydrogen cyanide (HCN) are produced, however, and must be removed during the syngas cooling process. The feedstock flexibility of gasification allows for a wide variation in the nitrogen content of coal.ĭuring gasification, most of the nitrogen in the coal is converted into harmless nitrogen gas (N 2) which makes up a large portion of the atmosphere. The nitrogen found in coal typically takes the form of aromatic structures such as pyridines and pyrroles.
Atmospheric nitrogen-containing particles decrease visibility.NOx can deteriorate water quality by overloading the water with nutrients causing an overabundance of algae.Along with sulfur oxides (SOx), NOx contributes to the formation of acid rain and causes a wide range of environmental concerns.Respiratory problems may result from exposure to NO 2 by itself, but also of concern is NOx reacting to form airborne nitrate particles or acid aerosols which have similar effects.NOx is a main constituent in the formation of ground-level ozone which causes severe respiratory problems.The environmental effects of releasing too much NOx into the atmosphere are listed below. NOx refers to both nitric oxide (NO) and nitrogen dioxide (NO 2). Interagency Working Group Initial Report.FECM Extramural R&D Final Technical Reports.Solicitations and Funding Opportunities.Strategic Systems Analysis and Engineering.
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