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Development of a predictive method to analyze the effect of sustainable gases on soot Soot measurements in rich-premixed/diffusion flames using Laser Induced Incandescence (LII) Research performed at DNV GL Gas Consultancy & Services Groningen Pieter Visser, Martijn van Essen, Sander Gersen & Howard Levinsky Contact: [email protected] Measurement results Equivalence ratio at 30 ppb soot [-] Introduction 18 • The diminishing natural gas reserves, increasing diversity of supply and desire to introduce sustainable gases have resulted in an increasing trend towards the use of “new” gases in the Netherlands. • It was observed that the soot fraction increased with the primary equivalence ratio (Figure 4) • These gases may have different tendencies to soot than traditionally distributed gases. • Figure 3 shows that the soot fraction measured at a constant equivalence ratio for methane and the binary hydrocarbon mixtures scales with the propane equivalent number. Consequences: Soot formation due to new gases in end user equipment may cause soot deposition resulting in clogging and safety issues, while in equipment dependent on soot, soot formation may diminish. Goal: Development of a model that predicts soot formation in new gases. 1 • LII signal[a.u.] • Soot particles are heated to 4000K using laser pulses (λ=1064nm) the subsequent emission (incandescence signal) is a measure for the soot concentration (soot volume fraction). Gating and optical filters are used to reduce interferences (e.g. C2 emission and PAH fluorescence). The peak of the LII signal is proportional to the average soot particle diameter (dp) and the number of soot particles (Np) as follows: 0.8 LII signal 0.6 Laser pulse Gating 0.4 0.2 0 0 LII signal ~Np·dp3 200 400 Time [ns] Figure 1: Example of LII signal decay and gating Soot fraction [ppb] Laser Induced Incandescence • The addition of inert gases and hydrogen to methane reduces the soot fraction in the flame. In contrast, higher hydrocarbons have the opposite effect. • 120 100 60 40 20 0 • The measurements were performed at the highest soot fraction in the flame by positioning the burner on the vertical axis. The overall reproducibility of the measurements was better than 10%. Partly premixed diffusion flame Power meter Diaphragm Lens Burner Nd:YAG Foto diode Glass beads laser Attenuator Filter PC ICCD camera Air Air Fuel Figure 2: Experimental setup LII (left) and the experimental burner (right) 10 15 Equivalence ratio [-] 14 12 10 8 6 4 0 5 10 Propane equivalent number[-] • For mixtures of propane in methane the addition of inert gases decreases the soot fraction at a constant equivalence ratio (Figure 4). • The addition of approximately 5% hydrogen to mixtures with a fixed propane fraction in methane decreases the soot fraction while a small increase is observed upon the addition of approximately 10% and 20% hydrogen. This effect deviates from the addition of hydrogen to methane. The influence of hydrogen on soot formation is a topic of study in literature and is at present poorly understood. 20 Figure 4: Measured soot fractions in diffusion flames of 3- and 4component mixtures as function of the equivalence ratio Model A statistical model is developed to characterize gases for their soot tendencies. This model predicts the equivalence ratio at which a soot fraction of 30 ppb is expected (here ϕ30ppb). Both the binary and multi-component mixtures have been used as input for the model. Based on a linear fit of the soot fraction versus the equivalence ratio for each mixture the measured ϕ30ppb is determined. An excellent agreement was found between the measurements and the model as shown in Figure 5. Predicted ϕ at 30 ppb soot [-] • The flame height was kept constant for each individual gas mixture during the LII measurements while varying the equivalence ratios. 5 16 20 Conclusion y = 0.9691x + 0.3219 R² = 0.9691 15 • A model was developed to determine the soot tendency of gases with different compositions. 10 • The model can be used to characterize gaseous fuels for soot formation. 5 0 5 10 15 Measured ϕ at 30 ppb soot [-] Figure 5: Predicted versus the measured values of ϕ30ppb 15 Figure 3: Equivalence ratio at a soot fraction of 30 ppb as a function of the propane equivalent number for different hydrocarbons pseudo ELG 6.6% C3 & 12.8% N2 4.7% C2 & 4.9% C3 9.4% C3H8 9.3% C3 & 10.9% H2 9.3% C3 & 20.7% CO2 80 Measurements and experimental setup • A coflow diffusion burner was used to produce the partly premixed flames fueled with 2, 3 and 4 component mixtures of C2H6, C3H8, C4H10, N2, CO2 and H2 in CH4. CH4 pseudo DLG 0.9% CO2, 3.8% C3 & 14.0% N2 3.8% C2, 5.9% H2 & 11.0% N2 9.3% C3 & 5.3% H2 9.3% C3 & 20.8% H2 CH4 C2H6 C3H8 C4H10 20