Abstract
A study of reducing nitrogen oxide (NO) emission by using different fuel oil/hydrogen-rich refinery gas ratios (FO/RG) of the volumetric flow rate in a 130-ton/hr, full-scale, mediumpressure boiler was carried out. The influence of the FO/RG ratio on boiler outlet temperature, flue -gas flow rate and temperature, and O2 concentration in the excess air was also investigated. Test results show that by adjusting the FO/RG volumetric flow rate ratio from 5:1 to 1.8:1, fuel cost was reduced by as much as $33 million NT (~$1.1 million US) per year. Concentration of NO was lowered from 167 to 152 ppm, reducing NO emission a total of 72 tons per year. The air pollution fee was cut as much as $860,000 NT (~$27,000 US) each year. Hence, changing the FO/RG ratio of the volumetric flow rate can not only save fuel costs, but can also greatly reduce NO emission and air pollution fees. Results of this study can help to develop boilers that operate more economically and efficiently.
Highlights
To control the emission of NOx effectively, we must first understand its formation mechanism
Based on Zeldovichs Mechanism, the formation of thermal NOx is mainly initiated by free radicals as nitrogen, oxygen and OH which come from the destruction of gaseous molecules under the heat released during combustion at high temperature (>1,300°C) (Kokkinos, 1994; Sloss et al, 1992)
To find out the impact of fuel oil/hydrogen-rich refinery gas ratios (FO/refinery gas (RG)), two different volumetric flow-rate ratios were applied in this study with fullscale plant measurement: one with the FO/RG volumetric flow-rate ratio at 5:1 and the other at 1.8:1
Summary
To control the emission of NOx effectively, we must first understand its formation mechanism. Based on Zeldovichs Mechanism, the formation of thermal NOx is mainly initiated by free radicals as nitrogen, oxygen and OH which come from the destruction of gaseous molecules under the heat released during combustion at high temperature (>1,300°C) (Kokkinos, 1994; Sloss et al, 1992). Those active substances react further with other gaseous molecules to form NOx. Fuel NOx mainly comes out of the combustion of nitrogen molecules contained in the fuel under oxidized conditions.
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