رسائل ماجيستير
English
2017
Oxy- Combustion Of Fossil Fuel In A Swirl Stabilized Non-premixed Combustor
Esmail M. A. Mokheimer , محمد راغب شكيل
كلية الهندسة-جامعة الملك فهد للبترول والمعادن · السعودية
Oxyfuel combustion, involving combustion of fossil fuel with pure oxygen is a promising technology to reduce the CO2 emissions by capturing and sequestering the CO2 produced by fossil fuel combustion. In the present study, oxy-combustion of methane at stoichiometry is examined experimentally and numerically.Experiments were carried out in a non-premixed combustor to study the flame stability and the flame length variation with varying CO2 composition in the oxidizer mixture at stoichiometry. The firing rate of the combustor was varied between 2.5-4.5 MW/m3-bar. The fuel used was 100% CH4 and 20/80% H2/CH4 mixture. When the combustor was operated under gas turbine conditions (≥3.5 MW/m3-bar), the flame transitions exhibited tri-modal regime below which the flame transitions exhibited bimodal regime. Weak flames at the nozzle exit were generally observed to precede the Attached flame → Lifted flame transition. The predicted flame length, using empirical equations based on the Near-field concept gave a good match within 5% of our experimentally observed flame length.The temperature along the radius of the combustor was measured for validation of numerical models to have further insight into the Oxy-combustion dynamics of methane in a cost-effective way. A numerical model was developed to model the oxyfuel combustion. The developed model gave an insight into the flow dynamics, temperature distribution and the emissions from the combustor.With increase in CO2 percentage in the oxidizer stream the maximum temperature was found to decrease, but the CO emissions were found to increase. At stoichiometry, for energy level of 4 MW/m3-bar, increasing the CO2 composition in the O2/CO2 oxidizer from 0 to 40% led to a temperature reduction of 15.5% from 3292 K to 2782 K. For the same change in CO2 composition, CO emission increased by 650%, from 682 ppm to 4958 ppm. However, for 40% CO2 in the O2/CO2 oxidizer, the CO emission was reduced to 0.3 ppm by bringing down the equivalence ratio from 1 to 0.98. The decrease is attributed to excess O2 which helps in oxidation of CO. At stoichiometry, for 40% CO2 in the O2/CO2 oxidizer, the increase in the energy level of the combustor from 4 to 5 MW/m3-bar, was found to decrease the CO emissions by 51 % from 4598 ppm to 2428 ppm, due to high temperatures inside the combustor which resulted in efficient burning. Based on the numerical study a new combustor head was designed which improved the swirl flow inside the combustor.