Combustion Modification Techniques Research Articles

Trends in pulp and paper mill emissions of SO2 and NOx, 1980-2010

Sulfur dioxide (SO2) and oxides of nitrogen (NOx) emissions from U.S. pulp and paper mills have been estimated from industry-wide surveys conducted every five years, beginning in 1980 and continuing through 2010. Between 1980 and 2010, total SO2 emissions declined by over 70%, while paper and paperboard production rose 35%. NOx emissions peaked in 1995, but fell by almost 40% over the next 15 years. Paper and paperboard production only declined 7% over the same period. These downward emission trends resulted from several factors, including reductions in oil and coal use, declining oil and coal sulfur content, increased use of add-on SO2 and NOx control systems on boilers, growing use of combustion modification techniques to minimize emissions, improvements in energy efficiency, and declining pulp, paper, and paperboard production over the past 15 years.

Flue gas Hg measurements from coal-fired boilers equipped with wet scrubbers

The U.S. EPA has indicated they are considering additional SO2 and NOx emission reductions, and EPA is under a consent agreement to propose mercury reduction regulations by 2004 for the utility industry. The boiler manufacturers and the utility industry have developed improved combustion modification techniques to reduce NOx emissions. These advanced combustion modification techniques, plus selective catalytic reduction (SCR), offer the potential to reduce NOx emissions at reduced cost. Wet and dry FGD systems have been shown to reduce SO2 emissions by up to 95%. CONSOL has shown that conventional wet FGD and ESP systems can remove an average of 67±6% of the inlet mercury. These data show that utility boilers equipped with ESP-scrubber combinations are removing two-thirds of the mercury in the as-fired coal at no added cost. The mercury speciation data show that 80 to 95% of the oxidised mercury, as determined by the Ontario Hydro method, is removed by the scrubber. The average mercury material balance closure at the six plants was 103±8%. The mercury removed from the scrubber reported to the scrubber by-product. Standard leachate testing conducted on fixated and unfixated scrubber by-product from one test showed no mercury leaching. Mercury volatility was evaluated by heating the scrubber by-product 140°F for eleven weeks. After eleven weeks, no loss of mercury was reported. Based on these findings, there may be combinations of environmental control systems that can achieve significant SO2, NOx, and mercury reductions at lower cost than the conventional approach of three add-on processes FGD for SO2 control, selective catalytic reduction for NOx control, and carbon injection for mercury control.

Combustion Modifications of Batch Annealing Furnaces and Ammonia Combustion Ovens for NOX Abatement in Steel Plants.

NOX control employing several combustion modification techniques is studied in batch annealing furnaces and ammonia combustion ovens in steel plants. The fuels of the annealing furnace and ammonia oven are by-product fuel gases and ammonia vapor, respectively, which are generated in the same steelworks. Study of the emission characteristics of the annealing furnace show that delayed combustion can effectively reduce NOX emissions. Delayed combustion is accomplished by air-staging in burners, off-symmetric mixing of fuel and air, and air-biasing in the furnace, and these modification can operations achieve 60%, 40%, and 26% of NOX reductions, respectively. For the ammonia oven, NOX emission from combustion of ammonia vapor is remarkably reduced by staging the air injected into the oven, adjusting the total air rate, and adding by-product fuel gases to the combustion system.

Emissions of Organic Hazardous Air Pollutants from the Combustion of Pulverized Coal in a Small-Scale Combustor

The article gives results of a characterization of emissions of 76 organic hazardous air pollutants (HAPs) in flue gases from the combustion of pulverized coal in a small-scale down-fired combustor. The combustor was operated under different conditions to simulate baseline, high excess air firing, and nitrogen oxide (NOx) controls by combustion modifications. Samples were extracted near the combustor exit, upstream of any pollution control equipment. Data collected indicate that relatively low levels of organic HAPs are present in the flue gases for any of the combustion conditions; however, several compounds were present that have not been reported in previous studies. To the extent that these small-scale tests accurately simulate full-scale units, estimates based on these experiments indicate that the total HAP emissions from a large utility power plant are not likely to increase significantly due to installation of combustion modification techniques for NOx control.

MHD emissions and their controls

The characteristics of emissions and control techniques for MHD power generation are surveyed. The most impressive advantage of MHD generation is its built-in sulfur removal capability. No flue gas scrubbing system available can remove SO2 as effectively as the potassium seed reaction in the MHD process can. If uncontrolled, MHD could generate ten times the NOx produced by conventional coal combustion. It appears that these emissions will be controlled through several combustion modification techniques, including initial fuel-rich combustion, downstream adjustment of the fuel-air mixture to make it air-rich, and regulation of exhaust gas cooling rates in downstream components. (2 diagrams, 1 drawing, 2 photos, 6 references)

Combustion modifications for the control of NO x emissions

A theoretical evaluation of combustion modification techniques for the control of nitric oxide emissions from radiant dominated industrial and utility

Nitrogen Oxide Emissions from Stationary Sources

When fossil fuels are burned with air, some of the oxygen and nitrogen present combine to form nitrogen oxides. Their concentrations depends upon variables such as flame temperature, oxygen concentration and nitrogen content in fuels.Because of the absence of practically available techniques for removing nitrogen oxides from flue gases, the efforts are focused to the combustion modification techniques for eliminating the nitrogen oxide emissions. The present status of their development, such as two stage combustion, flue gas recirculation, off-stoichiometric combustion and etc., are described in this paper.Some problems for the determination of nitrogen oxides in flue gases are also described here.