| OCR Text |
Show processes of N O x formation are complete in the vertical tube furnace. After condensation of the combustion water, gas analysis was performed for N O x (NO and N02), C02 , 02, S02, C O and N 20. Oxides of nitrogen were measured by means of a chemiluminescence gas analyser. Switching between modes enabled measurements of both N O and total-NOx, and the amounts of N 0 2 were calculated by subtraction of N O from total-NOx. Other species were measured by infrared gas analysers, whereas oxygen was measured in a paramagnetic gas analyser. The furnace wall temperature was set at 900 °C. Although the actual flame temperatures are higher, a parallel study 12 has demonstrated that negligible amounts of thermal-NO are formed in the vertical furnace at the experimental conditions reported. Three equivalence ratios were investigated, namely fuel-lean (cp = 0.833), stoichiometric (cp = 1.00) and fuel-rich (cp = 1.20). The impact of increasing amounts of sulphur on N O x was assessed by feeding a stream of 2 % vol. S 0 2 gas (balance N2) into the combustion chamber through the atomiser. The flow rates of S 0 2 were calculated so that the mass fraction of fuel-S was increased by 0.5, 1.0, 1.5 and 2.0 % (maximum 1.5 % in the case of Orimulsion). Since nitrogen is added as a balance for sulphur dioxide, oxygen was also introduced to preserve the equivalence ratio with decreasing flow rates of atomisation air. The effect of sulphur on Orimulsion was investigated at fuel-lean conditions only as the formation of large amounts of particulates made gas analysis unfeasible at the other equivalence ratios. Property Density @ 15 °C, kg/I Viscosity® 100 °C, cSt Gross calorific value, MJ/kg Net calorific value, MJ/kg Nitrogen, ppmw Sulphur, % by weight Carbon, % by weight Hydrogen, % by weight C/H ratio Water content, % by weight Ash content, % by weight Asphaltene content, % by weight Conradson residue, % by weight M1 0.9627 4.73 42.58 40.69 3,231 3.59 85.21 8.68 - - ~ - 0.76 G1 0.9114 8.30 44.36 42.94 1,300 1.74 85.43 11.71 6.47 - 0.0017 - 0.18 G2 0.8869 10.10 44.70 43.37 600 1.10 85.16 11.83 6.45 - 0.0014 - 0.20 Orimulsion ~ - - 30.40 4,000 2.90 61.40 6.50 - 29.8 0.22 7.90 11.85 Table 1: Partial specifications of the fuels used in this study Experimental results a. Baseline emissions of oxides of nitrogen The emissions of nitrogenous compounds without added sulphur were measured in order to establish a baseline to assess the effect of increased amounts of sulphur. Measured baseline emissions are plotted versus overall the equivalence ratio in the vertical tube furnace in Figures 2 (NO), 3 (N02) and 4 (total N O x). 7 |
