Numerical Simulation of the Effects of Oil Gun Location and Oil Feed Rate on Coal Ignition and Burner Wall Temperature in a Tiny Oil Ignition Burner

To solve the overheating problem of tiny oil ignition burners’ walls during the firing-up process in a 330 MWe tangentially pulverized coal-fired boiler, a numerical model of a tiny oil ignition burner was carefully built considering combustion, gas–solid flow, and heat transfer. Then, the burner location and oil feed rate were optimized based on the model to prevent the burner’s walls from overheating. The effects of the oil gun extension distance (100, 200, 300, 400, 500 mm) and oil feed rate (160, 140, 120, 100, 80, 70, 60 kg/h) on coal ignition performance and burner wall temperature were carefully investigated. The simulation results showed good agreement with the measured results. The results indicated that decreasing the oil gun distance within the burner diminished the flame length of the co-combustion of oil and pulverized coal, thus lowering the burner wall temperature. Decreasing the oil feed rate appropriately could also reduce the burner wall temperature without influencing the ignition performance. Considering both ignition performance and burner wall temperature, an extension of 400 mm of the oil gun location and an oil feed rate of 160 kg/h were successfully applied to the actual operation without adverse effects. Moreover, it is suggested to move the temperature monitor points from the burner upper wall to the burner side wall.

Investigation of the direct-flow jets vortex motion in the M-shaped boiler invert furnace

For advanced ultra-supercritical parameters (A-USC) of steam, the design of an M-shaped boiler is proposed, designed to operate in a 500 MW unit on a lean coal (grade TR). The boiler profile is selected from the condition of minimizing the length of the main steamlines made of expensive nickel-alloy steel. With regard to this boiler, a scheme has been developed for pulverized coal combustion in an invert furnace using direct-flow burners and nozzles. Research has been carried out on the physical model of the furnace in the implementation of this combustion scheme: a qualitative study of the trajectories of the burner jets, jets of secondary and tertiary air obtained by their hot spark visualization; quantitative determination of the main characteristics of burner jets and their weight gain. The studies have shown the high efficiency of the recommended scheme of the furnace-burner device: a staged supply of the oxidizer along the flame length and along the furnace height is organized; the dynamic pressure of jets on the furnace wall tubes is excluded; vortex furnace aerodynamics should provide a high degree of burnout of coal dust particles; air jets evenly fill the horizontal section of the furnace; the ejection capacity of turbulent jets is much higher than for a flat submerged jet.

Experimental investigations on two-sided upward flame spreading over thin flax fabric under the influence of restricted distance

Up to 2021, most previous work focused on upward flame spread over thin solid fuel completely attached to objects or with both sides freely exposed to the air, but did not take the restricted distance (distance between fuel and objects) effects into account. In this paper, the restricted distance effects on upward flame spread over thin solid fuels were investigated using 0.65 mm thick, 120 cm tall and 6.0 cm wide flax fabric sheets under various restricted distances of 1.0–3.5 cm. The essential parameters were monitored and analyzed simultaneously, including flame length, pyrolysis spread rate, surface temperature and ignition time. The main conclusions drawn are as follows: when the restricted distance is no more than 1.5 cm, the flame length on the unrestricted side is larger than that on the restricted side, whereas the variation exhibits the opposite trend when the restricted distance is beyond 1.5 cm. As the restricted distance increases from 1.0 to 3.5 cm, the flame length and flame spread rate first increase and then decrease, reaching a maximum value at 3.0 cm restricted distance, whereas the ignition time shows the opposite trend. The decrease rate of the surface temperature with the distance from the pyrolysis front first drops and then rises as the restricted distance increases, which qualitatively characterizes that the heat flux received by the virgin surface first increases and then decreases with restricted distance. The non-monotonic trends of heat flux received by the virgin surface and consequently the flame spread rate as a function of restricted distance are due to the combined restricted distance effects of the chimney effect, wall radiation and restricting oxygen supply. The results of this paper are not only helpful in better understanding the upward flame spread over a thin flax fabric under restricted distance, but also provide some basic data for fire prevention of thin solid fuels.

Rotating co-flow jets with horizontal lip and shape transition

Purpose Control over large-scale coherent structures and stream-wise vortices lead to enhanced entrainment/conservation of the jet which is desirable for most free jet applications such as design of combustion chamber in jet engines and flame length elongation of welding torch used for metal cutting. Design/methodology/approach A co-flow nozzle with lip thickness of 2 mm, between the primary (inner) and secondary (outer) flow, is selected. Three nozzle combinations are used, i.e. C–C (circle–circle), C–E (circle–ellipse) and C–S (circle–square) for acquiring comparative data. For these nozzle combinations, inner nozzle exit plane is kept as a circle, whereas the outer nozzle exit planes are varied to circle, ellipse and square. The exit plane area of outer nozzle for the nozzle combinations has equivalent diameter, De. The nozzles are fabricated in a way that the outer nozzle can be rotated along the longitudinal axis, keeping the inner nozzle intact. Findings The C–C nozzle combination is effective in low Mach number regime in decaying the jet, when the rotational component is introduced. Around 30% reduction in the jet core length is observed for the C–C nozzle combinations without any lip. The C–E nozzle shows sedative result in decaying or preserving the jet. The C–S nozzle combination shows interesting phenomenon, whereby the low subsonic case tends to conserve the jet by 15% and the higher subsonic case tends to decay the jet by 10%. Originality/value The developed nozzle systems show both conservative and destructive effect on the jet, which is desirable for the mentioned applications.

Influence of DC Electric Field on the Propane-Air Diffusion Flames and NOx Formation

The aim of this research is to investigate the effects of a direct current (DC) electric field on the combustion behavior of a co-flow propane diffusion flame. The flame length and NOx emission were observed and measured. The electric field enhances the combustion process of propane diffusion flame by causing the movement of ions and molecules in the flame, resulting in a change in the shape of the flame. The flame heights decrease with an increase in the applied voltage and polarity, a more dominant effect to be observed with a positive DC electric field. However, for the applied negative polarity, the inner-cone of the propane diffusion flame is shifted by the electric field. Drastic reduction in the NOx emission is observed with an increase in the applied DC voltage and polarity. In the existing system, the reduction percentage of NOx is within the range of 55 to 78%.

Experimental and statistical ANOVA analysis on combustion stability of CH4/O2/CO2 in a partially-premixed gas turbine combustor

The application of the oxy-fuel combustion technique could tackle the combustion process's environmental issues. Experiments were conducted on partially premixed air- and oxy-methane combustion flames stabilized over a novel perforated burner in the present work. The burner has a premixing ratio of 7.0. In oxy-fuel combustion, the experiments were performed at oxygen fractions (OF%: volumetric percentage of O2 in the oxidizer mixture) of 29%, 32%, and 36% and over a range of operating conditions necessary for a stable flame. The results of oxy-combustion flames were compared with the corresponding air-combustion flames at the same operating conditions. Two sets of statistical analyses were performed for further confirmation of the experimental results. The first set investigated the operating parameters' effect, including OF and oxidizer Reynolds number (Re), on the upper flammability limits (UFL). Simultaneously, the second set studied the impact of OF and equivalence ratio on flame length. The experimental results revealed that the flammability limits get wider as the OF increases due to the resulting flame speed rise with O2-enrichment. The statistical analysis is conducted by ANOVA technique, which carries innovation and confirms that OF and Re significantly impacted the UFL. The visual flame length of oxy-flames was longer than its correspondents of air-flames due to the reduction of flame speed associated with the negative influence of CO2 dilution in oxy-flames. The statistical analysis showed a significant effect of OF and equivalence ratio on the visible flame appearance.