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.
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