Radiant Tube Burner Research Articles

97/04081 Transient heat transfer analysis in vacuum furnaces heated by radiant tube burners

This paper presents a CFD-DEM study of gas-solid flow in the raceway region in an ironmaking blast furnace (BF). In the simulation, 120,000 spherical particles are packed into a full-scale 2D slot BF geometry. Gas is injected into the geometry via tuyeres, generating raceways in different sizes and shapes under different conditions. It is observed that the raceway characteristics are much more complex under the full-scale BF than those observed under the laboratory scale in the literature. Three kinds of raceways can be identified: anti-clockwise circulating raceway, clockwise circulating raceway, and plumelike raceway. The results are analysed in terms of solid flow patterns, and flow and force structures of particles. The simulation has a good agreement with the observed in physical experiments in terms of two contrary circulating gas vortexes located upon and below tuyeres during raceway formation. Moreover, it is also indicated that operational variables have significant effect on one of the gas vortexes, which becomes the main circulating gas flow stream and determines the gas circulating direction.

Transient heat transfer analysis in vacuum furnaces heated by radiant tube burners

To develop the method to analyze transient characteristics of the combined radiative and conductive heat transfer in the industrial furnaces, heat transfer in vacuum furnaces is numerically analyzed. The vacuum furnace is heated by several radiant tube burners and enclosed with thermal insulation walls. Object materials to be heated are placed at the central region of the furnace. A three-dimensional computer program for general purpose is developed to solve radiative heat transfer within enclosure including the transient conductive heat transfer within the insulation walls surrounding the system. The Monte Carlo method is used for the radiative heat exchange calculation. The results of the numerical simulation are compared with the results of experiment. The simulated results fit very well with the experimental ones, which shows the validity of the present simulation method.

Ignition Process and Delay of Sprays Injected into a Hot-Air Stream.

A portion of the heat accumulation-type radiant-tube burner, which has a pair of gas burners with a honeycomb regenerator on both ends, was utilized as a test rig for spray ignition. The effects of various parameters on the ignition process were examined by perpendicularly injecting a liquid fuel (gas oil) into the hot-air stream immediately after cutting off the city-gas supply to the burners. If a cavity is embedded in the wall confronting the injection nozzle, only the jet portion of the spray is exposed to the hot stream and ignited, while the tip portion chills in the cavity. With no cavity, on the other hand, ignition takes place in the tip portion just before impinging on the wall, or the secondary spray generated by the impingement is ignited within the wall boundary layer. The data for both cases and our former shock-tube data were compared with those of other researchers and examined. As a result, the reason why ignition delay data were so widely different from researcher to researcher was elucidated to some extent.

95/01795 The use of silicon carbide cermic in high performance radiant tube Burners and low NO x open flame burners

95/01795 The use of silicon carbide cermic in high performance radiant tube Burners and low NO x open flame burners

Experimental study on the radiant tube burner with self-biased fuel nozzle

Full scale combustion tests for a conventional fuel nozzle and a self-biased one were carried out using a two-stage radiant tube burner as the basis. Compared with the conventional nozzle, more than 40% reduction in NOx emission was achieved with the self-biased nozzle. Under the same furnace temperature, the peak temperature was lowered and the temperature uniformity on the radiant tube was enhanced with the self-biased nozzle. The optimal design criteria for the self-biased nozzle were derived.

RADIATIVE HEAT TRANSFER AUGMENTATION IN GAS-FIRED RADIANT TUBE BURNERS BY POROUS INSERTS: EFFECT OF INSERT GEOMETRY

This article presents the results of an experimental investigation of heat transfer augmentation by porous media in a natural gas-fired radiant tube burner. The results show that significant heat transfer augmentation is possible with the use of porous ceramic inserts in both premixed and nonpremixed gas-fired radiant tube burners. Furthermore, this work has shown that geometry variations in the porous insert configuration can appreciably alter both heat transfer rates and mixing and chemical reaction rates in these systems. In the case of nonpremixed flames, the effect of variation of insert geometry is more than simple heat transfer augmentation via gas enthalpy conversion to thermal radiation by the porous medium. There is also a significant alteration of the reactive gas mixing (and therefore chemical reaction and heat release) rates along the length of the tube. The basic mechanisms that control the mixing rate and heat release distribution in these systems are still unknown. Nevertheless, it appears...

Strength Evaluation of Reaction‐Bonded Silicon Carbide Radiant Tubes after Long‐Term Exposure to Combustion and Endothermic Gas Ambients

The strengths of reaction‐bonded silicon carbide radiant tubes were examined after a 14‐month campaign at 800°–950°C in an industrial heat‐treating furnace. The inner tube of the single‐ended radiant tube (SER) burner system was exposed to a combustion gas environment, and the outer tube was exposed to both a combustion gas (inner surface) and an endothermic gas (outer surface) environment. Diametral compression testing of C‐rings and O‐rings was employed to assess the effect of exposure on the strengths where failure initiated from the outer and inner surfaces of the tubes, respectively. Comparisons of strengths obtained on exposed versus as‐received tubes revealed that exposure to the combustion ambient yields an apparent moderate strengthening, with a concurrent increase in strength variability. No significant difference in strength distribution was observed for tubes exposed to combustion versus endothermic gas ambients. Failure most often originated at silicon‐rich regions remaining from silicon infiltration of macroporosity in the slip cast tubes during reaction sintering. Specimens sectioned from the outer tube exhibited unexpectedly high strengths (based on predictions from Weibull statistics) compared to those sectioned from the smaller inner tube after the same exposure. These results indicate that the larger tubes have flaws with characteristics different from those present in smaller tubes, and underscore the need to use data from the same material, with the same flaw populations, in making predictions of the effect of component size on strength distributions and reliability in service.

Radiative heat transfer augmentation of natural gas flames in radiant tube burners with porous ceramic inserts

Experiments were conducted using porous ceramic inserts to enhance the radiative heat transfer from natural gas flames in a straight-through radiant tube burner. The performance of the radiant tube burner with partially stabilized zirconia and silicon carbide inserts is compared to a baseline case of no inserts at three levels of combustion air preheat. Spectral intensities, temperatures within the radiant tube burner, tube wall temperatures, and exhaust temperatures were measured to determine the effectiveness of the enhanced heat transfer due to the inserts. Exhaust emission constituents were also measured to determine the effect that the inserts have on exhaust products. NO x emissions are reduced by up to 30% with the inserts. The silicon carbide inserts have higher spectral intensities and total radiative energy transfer than partially stabilized zirconia inserts. Both inserts have enhanced radiant heat transfer compared to the no-insert configuration, with the radiative enhancement due to inserts as great as five times that of the no-insert configuration. The net result is increased tube wall temperatures and decreased exhaust temperatures with the ceramic inserts.

Noise of Radiant Tube Burner and its Control

Noise of radiant tube burner has been recently regarded as public nuisance.At first, noise nature and cause of noise emission were examined by sound level meter.As a result, it was found that it is low frequency with 50 to 500Hz and sound pressure level is 110 to 120dB at 50cm apart from exhaust gas outlet, and the cause chiefly came from resonance which occurs along longitudinal direction of tube.Secondly, experiments were made on silencers to control the noise. As a result, it turned out that multistage expansions type and resonator type silencers are effective and the former can reduce the noise to 90∼100dB by insertion loss of 20dB and the latter can to 85∼95dB by insertion loss of 25dB.