OCR Text |
Show The considerable spread in the staged fuel NO. emissions from 10 ppm to almost 30 ppm was due to variations in fuel fraction (amount of staged fuel), the shape of secondary combustion zone, and steamer load. Higher fuel fractions generally resulted in lower NO. emissions because the primary burner was operating at the highest excess air and lowest NO. emissions condition. Carbon monoxide emissions were generally well below 50 ppm (corrected to 30/0 oxygen). The RSB with fuel staging consistently achieved sub-20 ppm NO. emissions and sub-50 ppm CO emissions (corrected to 30/0 O2) at 30/0 stack oxygen. By adding a secondary combustion zone to the existing lean premixed surface combustion burner, NOx emissions and stack oxygen levels were Simultaneously reduced. Although we were not able to demonstrate sub-9 ppm NO. performance as we had hoped, modifications were proposed to further reduce NO. emissions to the sub-9 ppm levels. These concepts were tested in the 3 MMBtu/hr test boiler at the Alzeta combustion laboratory . Our work also showed that the secondary fuel distribution is critical to the emissions performance of the burner. Proper distribution results in low NO. and CO emissions and a tight flame envelope with little chance of flame impingement. Improper distribution can result in flame impingement, excessive CO formation or even sooting. FGR Simulation The 50,000 Iblhr oil field steamer also provided the opportunity to verify the laboratory FGR tests at industrial boiler scale. Oil field steaming operations create "casing" gas which must be combusted. The volatile gas (typically up to 500/0 methane) together with significant amounts of hydrogen sulfide (up to 50/0) and carbon dioxide (balance) collect in the production well casings. If the gas is not removed, the "gas jacket" in the well casing can cut off crude oil production. Therefore, casing gas must be continually extracted from the well casing and destroyed by burning in the steamers. Because of the large amount of inert CO2 in the casing gas, firing the RSB on caSing gas simulates FGR operation. In fact, by measuring the flow of caSing gas to the burner, the amount of inert gas flowing to the burner can be determined and equated to an equivalent FGR rate. A limited amount of casing gas was available, so the oil field burner was reconfigured to fire at 1/4 of its normal capacity. This was 10 |