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Show 0 10 20 30 40 Radiant Heat Loss from Flame l\ (%) Fig. 14. Relation between radiant heat release from flame and N O emission (7) Fig. 14 is the result of calculations according to equation (4). C N O x } Thermal = 1. 45 x 106 exp (-34,600/RTf) (4) Here, A = 1.45 x 106 frequency factor (ppm) E = 34, 000 activation energy (cal/mol) As explained by Zeldovich's mechanism or expanded Zeldovich's mech-anismQ3,° 0, concentration of formation of thermal N O x is a function of flame temperature, oxygen concentration and staying time and is particularly affected by flame temperature. Accordingly, as evident from equations (2) thru (4) and Fig. 14, lowering of flame temperature is effective for suppression of thermal NOx, and taking a larger radiant heat release from flame7\ becomes adventageous in view of the heat transfer and NOJC suppression. That is to say, our low N O x burners can reduce N O x and save |C»WW«I •*««#1 Fig. 15. Temperature distribution in the furnace (longitudinal section) (straight burner tile) energy by increasing flame surface area Af and flame emissivity 6f in equation (3) through slow combustion. Fig. 15 shows temperature distribution of longitudinal section in the furnace of the conventional burner and Model E low N O x burner burning butane as their fuel. In the low N O x burner, the maximum flame temperature is 80°C lower than the conventional burner, and flame temperature becomes uniform. Besides, N O x is also reduced by about a fourth. Fig. 16 shows the total radiant heat flux obtained at that time and its distribution. At the flame existing region (of up to 2. 6 = L/D), the low NOx burner shows higher total radiant heat flux than the conventional burner. The reason for a larger radiant heat flux in spite of a lower flame temperature is the higher flame emissivity. It is thought that higher flame emissivity of the low N O x burner is attributed to a high luminous flame emissivity. To confirm this, the ratio (fc L/£c) of flame emissivity of the low N O x burner (g L ) and the conventional burner (g c) and the ratio (6f/6g) of flame emissivity (£f) of each burner 11- 8 - |