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Show INTRODUCTION Heavy residual oil is the fuel of choice for industrial and utility boiler owners where natural gas and coal are not continuously available. Residual oil is an inexpensive liquid fuel with significantly lower operating costs than coal. Many regions within the United States have been designated Ozone Non-Attainment areas under the Clean Air Act Amendment and are under increasing pressure to reduce N O x emissions. N O x emissions reductions can be obtained by (1) switching to an alternate fuel with less propensity for N O x production, (2) installation of flue gas treatment systems such as S C R and S N C R , and (3) installation of low N O x burner equipment. The first option is not possible where natural gas or diesel oil are unavailable, such as in the Northeast United States. The second option, S C R or S N C R , is costly and prohibitive to many industrial boiler owners w h o m may choose to leave the United States where environmental restrictions are less stringent. The most cost effective option to reduce N O x emissions from residual oil is the installation of low N O x burner equipment of which the atomizer is an integral part. Many boiler owners find themselves very near to compliance levels of N O x emissions and would like to achieve compliance through the most cost effective method. Coen has offered a low N O x atomizer program where the typically uniform and symmetrical spray pattern shape of the atomizer is modified for rich-lean staging yielding significant reductions in both fuel and thermal N O x production. This paper summarizes the results of several of these N O x reduction studies in both field-erected and package water tube boilers. Multiple Venturi MV Atomizer: The multiple venturi atomizer is an inside mix, twin fluid atomizer used for the combustion of liquid fuels from light oil up to heavy asphalt or pitch which require heating prior to atomization (see Figure 1). Liquid fuel passes through the central fuel tube, surrounded by the steam tube, until reaching the multiple venturi mixer where a two-phase mixture is produced. This mixture is forced through a nozzle body to increase its momentum prior to exiting through a plain-jet cap. The cap design of the M V allows great flexibility for flame shaping through the cap drilling pattern. Four different sizes of the M V atomizer are used to achieve capacity ranges from 1 to 40 gallons per minute fuel flow. BACKGROUND N O x is the term typically used to refer to N O , and N O 2 formed as by combustion. It is estimated that the majority of global N O x is naturally occurring. Significant natural sources are lightning, forest fires, and bacterial action. O f the anthropogenic sources, approximately 5 5 % are from stationary sources, and the remainder from mobile sources. Although man-made N O x sources are a small portion of the global N O x , they tend to be concentrated in urban areas resulting in excessive production of ozone. O f the N O x formed during combustion in industrial boilers, 9 5 + % will be emitted as N O , and less than 5 % will be N O 2 . The N O , however, is readily converted to N O 2 in the presence of atmospheric radiation. N O 2 is a reddish-brown gas, toxic, and corrosive. The two sources of nitrogen for the formation of NOx are atmospheric N2 (forms thermal NOx), and nitrogen atoms organically bound to the fuel being fired (forms fuel N O x ) . The thermal and fuel N O x formation mechanism are outlined below. |
