Furnace Conditions

Specifications for acceptable CAB furnaces (with the use of 5 g/m uniform flux load) are  

Many production sites work with flux loads of 3 g/m. As flux coating goes down, furnace atmospheric conditions become more critical. Most CAB furnace manufacturers produce furnaces which routinely operate in the 20-50 ppm oxygen and dew point levels of -45 to -50 °C (i.e., 92-67 ppm H2O). A low dew point will keep the formation of hydrogen fluoride to a minimum [97]. 

A suitable treatment for the furnace exhaust (i.e. dry scrubber) is required. 

Controlled atmosphere brazing using non-corrosive potassium fluoroaluminate flux is the dominant process for making all aluminium heat exchangers. 

There are several factors determining the success of aluminium brazing  

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Sulfuric acid loss is approximately 1.84% H2SO4 for each percentage of R2O2. Oleum consumption is increased to consume the water that is formed. The metal sulfates are more stable than metal fluorides under furnace conditions and are discharged from the process with the residue. 

Orga.nic Carbon. Organic materials interfere with plant operation because these compounds react with sulfuric acid under furnace conditions to form sulfur dioxide. There is a reducing atmosphere in the furnace which may reduce sulfur dioxide to elemental sulfur, which results in sulfur deposits in the gas handling system. 

The burden support and permeabiUty function of coke is enhanced by the coke degrading in size as tittle as possible as it progresses downward through the blast furnace. This means that, in addition to minimum breakage as the coke is transported from coke plant to blast furnace, the coke should be as resistant as possible to all of the blast furnace conditions that act to degrade the coke. 

Pruszkowska et al. [135] described a simple and direct method for the determination of cadmium in coastal water utilizing a platform graphite furnace and Zeeman background correction. The furnace conditions are summarised in Table 5.1. These workers obtained a detection limit of 0.013 pg/1 in 12 pi samples, or about 0.16 pg cadmium in the coastal seawater sample. The characteristic integrated amount was 0.35 pg cadmium per 0.0044 A s. A matrix modifier containing di-ammonium hydrogen phosphate and nitric acid was used. Concentrations of cadmium in coastal seawater were calculated directly from a calibration curve. Standards contained sodium chloride and the same matrix modifier as the samples. No interference from the matrix was observed. 

Ca- and Mg-oxides (lime, periclase [MgO]) may occur as small crystals embedded within the glass or they may be located on its surface depending on temperature and furnace conditions where the minerals formed. Low-temperature minerals such as anhydrite (CaS04) may form on the surface of the fly ash grains after they have left the high-temperature zones in the furnace (Linton et al. 1977 Soroczak et al 1987 Ainsworth et al. 1993 Fishman et al. 1999). 

Adequate control of the chemistry in the front end furnace can significantly effect the lifetime and efficiency of the downstream catalyst beds in a sulfur plant. Inadequate removal of Ce+ hydrocarbons from the acid gas feed can result in catalyst fouling by polymeric materials formed under furnace conditions. Toluenes, ethylbenzenes and xylenes have been shown to be particularly troublesome in this regard. Oxygen breakthrough into the catalyst beds can also shorten the effective lifetime of the Alumina catalyst by sulfation i.e. 

Modem installations often impose furnace conditions so severe that refractories other than lire-clay are needed. High aluminum and silicon carbide refractories are typical of tlie.se. The heal conductivities of the super-refractories are larger than those of lire-clay brick, and such construction should be backed up with high temperature insulation. Silicon carbide blocks are the most refractory and have the quality of resisting clinker adhesion heitcr than ordinary fire-brick. Their fusion temperature is about 4000 F (2204 C)... 

Using palladium-magnesium nitrate mixtures as chemical modifiers, Hinds and Jackson [114] effectively delayed the atomisation of lead until atomic absorption spectrometer furnace conditions were nearly isothermal. This technique was used to determine lead in soil slurries. Zhang et al. [115] investigated the application of low-pressure electrothermal atomic absorption spectrometry to the determination of lead in soils. 

Furnace Conditions Corresponding to Characteristic Stages of Burning Behavior... 

N.I. Dowling, J.B. Hyne and D.M. Brown, Kinetics of the Reaction between Hydrogen and Sulfur under High-Temperature Clause Furnace Conditions". Ind. Eng. Chem. Res., 29 2327-32 (1990). 

Allow a 10 to 25 percent factor of safety to ensure adequate pressure during all boiler loads and furnace conditions. Using a 20 percent factor of safety for this fan, the total actual pressure loss is 8.95 + 8.95(0.20) = 10.74 inH20 (2.7 kPa). Round this off to 11.0 inH20 (2.7 kPa) for fan-selection purposes. 

Element Analytical wavelength (nm) AAS Spectral bandpass (nm) Flame conditions8 ETA Graphite furnace conditions ... 

K. M. Bryden K. W. Ragland (1997) Combustion of a Single Log under Furnace Conditions, Developments in Thermochemical Biomass Conversion, (Ed by A.V. Bridgwater D. B. G. Boocock), pp.1331-1345, Blackie Academic and Professional. 

Flameless atomic absorption spectroscopy using the heated graphite furnace is a sensitive method for analyzing environ-mental samples for trace metals. High salt concentrations cause interference problems that are not totally correctable by optimizing furnace conditions and/or using background correctors. We determined that samples with identical ratios of major cations have trace metal absorbances directly related to their Na and trace metal concentrations. Equations and curves based on the Na concentration, similar to standard addition curves, can be calculated to overcome the trace element interference problem. Concentrations of Pb, Cd, Cu, and Fe in sea water can be simply (ind accurately determined from the Na concentration, the sample absorbance vs. a pure standard, and the appropriate curve. 

Couples Purposely Insufficiently Immersed-— It is frequently desirable purposely to immerse the couple to an insufficient depth. In many processes the furnace is operated at such a high temperature that a thermocouple or protecting tube cannot withstand the severe conditions to which it may be subjected. In this case the couple may be immersed only part way through the furnace wall, or to a distance flush with the inner wall of the furnace. The temperatures indicated by couples installed in this manner are always lower than those of the furnace interior, but they bear a fairly definite relation to the temperature of the furnace, and hence the method is satisfactory for temperature control and reproduction of furnace conditions from day to day. 

TABLE 5.10. Rotary Furnace Conditions and Capacities for Different Grain Sizes"... 

Typical furnace conditions are stage 1— nitrogen atmosphere, 1350 °C (reduction) stage 2— hydrogen atmosphere, 1650 °C (carburization). 

In order for sintering tests to accurately predict actual behavior it is necessary that tests be conducted with ash produced under representative furnace conditions (time-temperature history). Fouling behavior is often greatly influenced by sodium reactions. Sodium which vaporizes in the furnace can condense in downstream convection sections thereby concentrating on flyash surfaces. Particle surface reactions are primarily responsible for convection deposit bonding. 

It must be stressed that this study was designed to examine the specific economic points under discussion. It was not practical to optimize the cases in other respects. In particular, no attempt was made to optimize cracking severity, cracking furnace conditions, or energy recovery. Thus, the cases are definitely conservative in their reported earnings potential. 

Temperature dependence of NO readings for Enerac 2000 inconel probe at reducing furnace conditions. 

See color insert following page 424.) Immediate information on current furnace conditions appears on monitors of furnace camera system. Operators can take corrective action when necessary. 

The process burner test facility will have a limited number of types of furnaces available. It will never have an identical furnace into which the burners will be installed. The flue gas recirculation patterns and heat sinks will be significantly different. It is often the case that the burner will still behave slightly differently in the field than in the test furnace due to these reasons and others. Due to these reasons it can be a challenge to extrapolate the test results to the actual furnace conditions and predict how the burner performance may change as a function of these differences. 

A purge airflow of 25 to 30% should be maintziined during light-off so that a highly air-rich furnace condition exists. 

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