Low NOx Combustion of Paraho Shale Oil in a 45 MW Utility Boiler

Combustion tests of crude Paraho shale oil (0.7 percent sulfur and 2 percent nitrogen) were conducted in a 45 MW boiler equipped with six frontface mounted burners each rated at 85 million Btu/hr. Shale oil was blended in various proportions with low sulfur oil and natural gas so that the sulfur content of the fuel did not exceed 0.5 percent. The fuel piping system was modified to allow blending the fuels in the furnace, and this blending technique was called dual fuel combustion. NOx emissions were compared using tank blending and dual fuel combustion, and it was found that significant levels of NOx reduction were obtained using dual fuel combustion. This result was confirmed during further testing of the two blending methods at various combustion stoichiometries using both conventional and steam-atomized low NOx burners. The maximum reductions in NOx emissions occurred during fuel-rich combustion of shale oil in the bottom row of burners followed by combustion of a low-nitrogen fuel in the top row of burners.