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Show 2 Like carbon dioxide and water vapor, trace concentrations of hazardous air pollutants, such as the carcinogen formaldehyde, are natural products of combustion in industrial burners. This realization provides a new motivation for a coupled attack on the chemical kinetics and fluid mechanics of combustion that exploits the advent of more powerful computers and advances in combustion chemistry. That realization also provides an incentive for industry to work with government to seek methodologies that prevent emission of these pollutants while also continuing today's energyefficient processing. The success of this cooperative initiative will enable the continued use of process gas to fuel petroleum industry combustion sources while also reducing toxic emissions to acceptable health-risk levels to the general population through new burner configurations and operating methodologies that comply with scientifically well-founded regulations. Assessment Track. The objectives of this program are met by proceeding along three parallel tracks, or phases, that run concurrently. Phase I, referred to as the assessment track, seeks to provide a systematic exposition of both the air toxic production of current burners and the concomitant flame structures that result in those emissions. The purposes of this track are to (1) measure the air toxic emissions from each of today's burner technologies, and (2) determine why each of those technologies produces the level of emissions found. The air toxic emission assessment is accomplished by performing extractive sampling and analysis on several burner technologies. Determination of the reasons why the burners exhibit those emissions is made by correlating the emissions with flame and flow field structure measurements. Both types of assessment (toxic emissions and flame structure) are made for generic~ full-scale burners (2 mmBtuIhr) designed in collaboration with and provided by the major burner suppliers to the petroleum industry. Burner technologies that will be analyzed in the assessment track include a conventional diffusion flame burner ("CDFB," natura1-draf~ non-staged) typical of a large fraction of current installations; a 10w-NOx diffusion flame burner ("LOFB," natural-draft, fuel-staged) typical of new installations; a conventional premixed flame burner ("CPFB"), again typical of current installations; and a surface-stabilized premixed flame burner ("SPFB"), a candidate technology for future installations. The participants will assess these burners according to a test matrix designed to encompass a majority of refmery process conditions. Four basic fuels will be employed in the testing: natural gas and three varieties of refinery fuel gas (high, moderate and low hydrogen). Natural gas is included both because of its importance as a petroleum industry fuel component and to provide technical leveraging of the results with parallel work sponsored by the Gas Research Institute. The three varieties of refinery fuel gas are representative of the broad spectrum of gases in use at U. S. refineries. In addition to the four basic fuels, the test matrix includes three levels of excess air, two heat extraction conditions, and provision for fuel spikes. These conditions simulate petroleum industry practice from process heaters to pyrolysis units, low excess air to high. Mechanism Track. Phase II of the program, referred to as the mechanism track, seeks to establish the chemical mechanisms by which air toxic species form or circumvent destruction in burner flames. These mechanisms are investigated by means of detailed chemical kinetic modeling. Species up to and including four carbon atoms (including the toxics formaldehyde and butadiene) are already included in the composite mechanism with fully detailed kinetic reactions. Detailed submechanisms for larger species such as benzene~ ethyl benzene, toluene, and xylene are being developed and incorporated. High molecular weight air toxics, including the polycyclic aromatic hydrocarbons (PAHs) naphthalene, anthracene, and benzo(a)pyrene, will be modeled using a semiempirical approach and incorporated into the composite mechanism. Class groupings will be formed of toxics that exhibit similar trends with variations in operating conditions in order to facilitate tracking of multiple species by focusing on only a few canonical species. |