Effect of Burner Operation on the Catalyst Tube Lifetime of a Steam Methane Reformer: A Numerical Study

In this paper, the catalyst tube lifetime of a practical steam methane reformer is analyzed numerically. The effect of burner operating mode on the flow development, hydrogen yield, and catalyst tube lifetime is discussed, with the aim of improving the reformer performance. The results of this study reveal that using the periodic boundary conditions, the temperatures and hydrogen yields obtained are much lower than the experimental values and the pressures are much lower than those using the real model. This results in overestimating the catalyst tube lifetime and underestimating the reformer operation risk. The catalyst tubes in the downstream area have longer lifetimes, while those in the upstream area have shorter lifetimes. Turning the upstream burners off is more efficient to the catalyst tube lifetime, while turning off the central groups of burners is less efficient. The main drawback of turning off burners is the decrease of hydrogen yield.

EXTENSION OF THE RESOURCE OF THE BURNER SWIRL BLADES OF THE BOILER TPP-312

Numerical research of high-temperature corrosion of steel blades of the swirler of a pulverized coal burner of the TPP-312 boiler in real conditions of its operation is carried out. Data on the dynamics of oxidation of the blade surface for two steels and different operating conditions of the burners were obtained. The results of the calculation allow a reasonable assessment of the service life of the blades of the burner device. Corrosion rate calculations were performed based on the results of computer simulation of pulverized coal combustion in the boiler volume with subsequent determination of the temperature field on the blade surface. The corrosion dynamics was determined using the experimental oxidation constants of steel given in the literature. Data were obtained for two types of low-carbon steel, two different modes of burner operation, for the number of blades 8 and 24, and for different distances of burner blades from the embrasure of the boiler furnace, a total of 16 different variants were calculated. Calculations have shown that with increasing the distance of the blades from the embrasure of the furnace, corrosion is significantly reduced. The highest corrosion, which in its absolute value is comparable to the thickness of the blade, occurs for the disconnected burner with blades from Art. 3. The lowest corrosion occurs for the working burner with blades made from steel 20 (reduction of corrosion by 4 times), and for the disconnected burner this dependence is much smaller (reduction of corrosion by 30… 40%). References 6, Figures 5

Development of a High Pressure Dry Coal Feed System for a 100 kWt Oxy-Coal Reactor

A design concept to feed dry coal from a hopper to a 100 kWt pressurized oxy-coal (POC) reactor using CO2 at 2 MPa was developed using transient computational fluid dynamics (CFD) simulations and bench-scale measurements. The feed system was required to maintain a steady flow of gas and solids at a coal flowrate of approximately 3.8 g/s and a CO2-to-coal mass ratio in the range 1–2. A 5.08-cm diameter vertical coal hopper feeding into a 0.635-cm diameter horizontal pipe was used to represent key elements of the feed system. A fluidized bed concept was found capable of providing the desired coal flowrate and CO2-to-coal flow ratio. Use of separate fluidization and dilution flows allowed the coal flowrate and CO2-to-coal flow ratio to be controlled independently. The amount of coal transported from the hopper was dependent on the net CO2 flow in the hopper but independent of the CO2 dilution flow. Pipe exit coal flowrates were found to fluctuate at levels acceptable for steady burner operation. Tests from a bench-scale apparatus using Pittsburgh 8 coal with a median particle diameter of 50 µm and moisture content of 6% confirmed the feasibility of the fluidization design. However, for a given CO2 fluidization flowrate, experimental coal flowrates were lower than predicted coal flow, in part due to simplifying assumptions of dry, spherical coal particles and smooth piping in the simulations.

Influence of Surroundings on Radiant Tube Lifetime in Indirect-Fired Vertical Strip Annealing Furnaces

The effects of surrounding radiation—emanating from radiation exchange with neighboring partners in indirect-fired vertical strip annealing furnaces, such as the other radiant tubes, the passing strip, and the enclosing furnace chamber—on the radiant tube lifetime were studied. In-house developed and validated numerical models were used to calculate the thermomechanical behavior, especially creep deformations and the corresponding stresses as lifetime indicating parameters. Different setups of recirculating P-type radiant tubes were investigated, including a reference case of an isolated tube. The investigations could be broadly classified into the study of the effects of different tube arrangements, burner operations (synchronous/asynchronous on/off firing), and changes of strip parameters (width/temperature). Results showed higher creep deformation of the central radiant tube in the setup with three tubes arranged horizontally in a row compared to three tubes stacked in a vertical column, even though the respective characteristic temperature values in a firing cycle were similar. Furthermore, the cases with asynchronous burner firing resulted in lower creep rates than other cases, where the burners were operating in synchronous on/off firing modes. In addition, the change of strip width had a higher impact on radiant tube lifetime compared to locally changing strip temperatures across the furnace. Alternating temperatures, caused by burner operation or process changes, such as change of strip’s speed or cross-section, and local temperature gradients were observed to be the main factors influencing the tube’s service life.

Effect of coal dust on the air-methane mixture combustion in the Swiss-roll burner

The 2-D numerical model has been developed to simulate the combustion of lean coal-methane-air mixture in ?Swiss-roll? burner and investigate the effect of coal particles content and mixture feed rate on the stable burner operation. Five homogeneous and three heterogeneous chemical reactions are considered. The Eulerian model for gas phase and the discrete particle model (Lagrangian) for particle phase taking into account the radiation are used in this study. Simulations are performed for the two turns ?Swiss roll? burner with heat insulated outer wall, channel width of 6 mm and inner wall thickness of 2 mm. It is shown that the presence of coal particles in a lean methane-air mixture expands the range of stable operation of the "Swiss-roll" burner. It is found that an increase in the content of coal particles reduces the combustion time of the particles by in-creasing the combustion temperature, changes the shape of the reaction zone, and shifts it to the burner inlet.

Effect of ring formation on burner flame stability in lime kilns

Ring formation in lime kilns is a common problem in pulp mills. Unstable burner operation that causes wide temperature variations within the kiln has been shown to be a main contributor. As rings grow thicker and longer, they are expected to affect the burner flame pattern, alter the temperature distribution, and further aggravate the problem. This study systematically examines the effect of rings on burner operation as a function of primary air and ring characteristics, using a laboratory mock kiln. The results show that primary air greatly affects the burner flame pattern and stability. Without a ring, the flame is brighter and shorter, with an increase in primary air (PA) up to 17%, and blows out at 20% PA or higher. In the presence of a ring, the flame becomes unstable and blows out when the ring is placed near the burner, but it is more stable when the ring is placed away from the burner. Thick and long rings destabilize the flame more than thin and short rings.

Spray Characteristics Measured in a New FLOX® Based Low Emission Combustor for Liquid Fuels Using Laser and Optical Diagnostics

A liquid fuel combustor based on the FLOX® burner concept has been developed for application in a Micro Gas Turbine (MGT) Range Extender (REX) for next generation cars. The characterization of this combustor was performed at the High Pressure Optical Test rig (HIPOT) at DLR Stuttgart. The operability limits of the burner were mapped out for full load conditions at 3.5 bars by varying global lambda (λG) from 1.25–2.00 and bulk jet velocity (vBulk) from 80–140 m/s. Exhaust gas measurements show NOx and CO levels below 5 and 10 ppm respectively (corrected for reference 15% O2) at λG = 1.89. Optical and laser diagnostic measurement techniques have been employed to characterize the spray flames. The flames at stable burner operation points (BOPs) show a predominantly jet like flame shape irrespective of λG and vBulk. Droplets in the size range 2–40 μm have been measured close to the nozzle exit plane. Velocities conditioned on the droplet size show large droplets d > 15 μm transitioning from negative slip velocity at the exit plane to positive slip velocity at downstream location. The positive slip velocities and slow evaporation of large droplets lead to droplets travelling further into the combustion chamber and hence resulting in long flames. A comprehensive data set for the spray characteristic of the new liquid FLOX® burner is made available.

Demonstration Plant and Combustion System for an Oxy-Fuel Gas Turbine Cycle

A semi-closed oxy-fuel retrofit gas turbine demonstration plant (DEMOXYT) is described and preliminary results of the oxy-fuel burner under relevant conditions are presented. The plant consists of a 100 kWel radial turbine with a pressure ratio of 4.25, featuring a recuperator, to which a specific oxy-fuel burner has been designed and constructed, and a condensing scrubber in the flue gas recirculation loop. An overview and salient thermodynamic data of the plant are provided, as well as important parameters governing its limits of operation. Results from combustion experiments obtained in a pressurized oxyfuel combustor are presented in terms of a burner operation map for 4.2 bar. The combustion testing results describe the stability maps of the burner and the influence of excess oxygen and total oxygen concentration in the reactants on the formation of CO. It was found that excess oxygen values below about 5% could result in excessive CO concentrations in the undiluted product gases of the flame, but that CO formation was relatively independent of the oxygen concentration in the reactants.

Effects of Diluents on Lifted Turbulent Methane and Ethylene Jet Flames

The effects of diluents on the liftoff of turbulent, partially premixed methane and ethylene jet flames for potential impact in industrial burner operation for multifuel operation have been investigated. Both fuel jets were diluted with nitrogen and argon in separate experiments, and the flame liftoff heights were compared for a variety of flow conditions. Methane flames have been shown to liftoff at lower jet velocities and reach blowout conditions much more rapidly than ethylene flames. Diluting ethylene and methane jets with nitrogen and argon, independently, resulted in varying trends for each fuel. At low dilution levels (∼5% by mole fraction), methane flames were lifted to similar heights, regardless of the diluent type; however, at higher dilution levels (∼10% by mole fraction) the argon diluent produced a flame which stabilized farther downstream. Ethylene jet flames proved to vary less in liftoff heights with respect to diluent type. Significant soot reduction with dilution is witnessed for both ethylene and methane flames, in that flame luminosity alteration occurs at the flame base at increasing levels of argon and nitrogen dilution. The increasing dilution levels also decreased the liftoff velocity of the fuel. Analysis showed little variance among liftoff heights in ethylene flames for the various inert diluents, while methane flames proved to be more sensitive to diluent type. This sensitivity is attributed to the more narrow limits of flammability of methane in comparison to ethylene, as well as the much higher flame speed of ethylene flames.