Furnaces temperature profiles

Figure 21-10 Reduction of interference by using a matrix modifier, (a) Graphite furnace temperature profile for analysis of Mn in seawater, (b) Absorbance profile when 10 xL of 0.5 M reagent-grade NaCl is subjected to the temperature profile in panel a. Absorbance is monitored at the Mn wavelength of 279.5 nm with a bandwidth of 0.5 nm. (c) Reduced absorbance from 10 nl of 0.5 M NaCl plus 10 of 50 wt% NH4NO3 matrix modifier. [From M. N. Quigley and F. Vernon, "Matrix Modification Experiment lor Electrothermal Atomic Absorption Spectrophotometry." J. Chem. Ed. 1996, 73. 980.]...

Improved glass quality resulting from improved furnace temperature profile, lower volatilization, and better batch line control and... 

Figure 6. Drop-tube furnace temperature profiles.

A shortcut method for estimating furnace gas exit temperature is offered by the graph of figures 2.20 and 5.3, adapted by coauthor Shannon from radiant tube data, and extrapolated above 1800 F (1255 C). Also refer to Estimating Furnace temperature profile for calculating heating curves in chapter 8. 

To reduce fuel cost and improve productivity, an engineer must be able to adjust furnace gas temperatures to change the furnace temperature profile. In a longitudinally fired furnace, shortening the flame will raise the temperature near the burner wall. This can be accomplished by spinning the combustion air and/or fuel, which in turn spins the poc. The resultant increase in heat transfer near the burner wall will reduce the flue gas exit temperature, raising the % available heat. 

Graphite furnace temperature profile for analysis of Mn in seawater. ib) Absorbance profile when 10 jjiL of 0.5 M reagent grade NaCl are subjected to the temperature profile. Absorbance is monitored at the Mn wavelength of 279.5 nm with a bandwidth of 0.5 nm. 

Laser Raman diagnostic teclmiques offer remote, nonintnisive, nonperturbing measurements with high spatial and temporal resolution [158], This is particularly advantageous in the area of combustion chemistry. Physical probes for temperature and concentration measurements can be debatable in many combustion systems, such as furnaces, internal combustors etc., since they may disturb the medium or, even worse, not withstand the hostile enviromnents [159]. Laser Raman techniques are employed since two of the dominant molecules associated with air-fed combustion are O2 and N2. Flomonuclear diatomic molecules unable to have a nuclear coordinate-dependent dipole moment caimot be diagnosed by infrared spectroscopy. Other combustion species include CFl, CO2, FI2O and FI2 [160]. These molecules are probed by Raman spectroscopy to detenuine the temperature profile and species concentration m various combustion processes. 

FIG. 23-43 Reactors for solids, (a) Temperature profiles in a rotary cement lain, (h) A multiple hearth reactor, (c) Vertical lain for lime burning, 55 ton/d. (d) Five-stage fluidized bed lime burner, 4 by 14 m, 100 ton/d. (e) A fluidized bed for roasting iron sulfides. (/) Conditions in a vertical moving bed (blast furnace) for reduction of iron oxides, (g) A mechanical salt cake furnace. To convert ton/d to kg/h, multiply by 907. 

The growth rate is quite sensitive to the axial temperature profile. An axial temperature profile that increases along the reactor because it improves the deposition uniformity is commonly used in industry. The temperature of each successive zone in the furnace (defined by the furnace elements in Figure E14.5a) can be adjusted by voltage applied to variac heaters. The zone temperatures are assumed constant within each zone, T-,j = 1,..., ntv where ntz is the number of temperature zones to be used,... 

An example of an incredibly complex multiphase chemical reactor is iron ore refining in a blast furnace. As sketched in Figure 12-22, it involves gas, liquid, and solid phases in countercurrent flows with complex temperature profiles and heat generation and removal processes. 

A conventional flow apparatus shown in Figure 1 was used. It consisted of gas-flow controlling devices, tubular reactor in an electric furnace, Liebig condenser, liquid trap, etc. The temperature profile along the longitudinal axis of the reactor was measured by a thermocouple. The reaction zone is defined here as the part of the reactor above 350°C. The reaction temperature means the highest temperature in the reaction zone. 

The flue gas at the NH3 injection location can be assumed to have the following composition (vol) NO = 200 ppm, CO = 100 ppm (peak 500 ppm), O2 = 3.0%, CO2 = 12.0%, H2O = 15.0%. The pressure is atmospheric. The residence time can be estimated from Fig. 16.12, assuming that there is about 0.5 s from the rebum fuel injector level to the rebum overfire air ports below the wing walls. An estimated temperature profile for the furnace indicates that the temperature can be assumed to be constant, around 950°C, from the upper OFA level until the flue gas reaches the wing wall. Mixing of NH3 with the flue gas is assumed to be instantaneous. 

Figure 21-10 shows a temperature profile for a furnace atomic absorption experiment. Explain the purpose of each different part of the heating profde. 

Figure 1730. Kilns and hearth furnaces Walas, 1959). (a) Temperature profiles in a rotary cement kiln, (b) Space velocities in rotary kilns, (c) Continuous lime kiln for production of approximately 55tons/24hr. (d) Stirred salt cake furnace operating at 1000°F, 11-18 ft dia, 6-10 tons salt/24 hr. (e) Multiple-hearth reactor one with 9 trays, 16 ft dia and 35 ft high roasts 1250 lb/hr iron pyrite. (f) Siements-Martin furnace and heat regenerators a hearth 13 ft wide and 40 ft long makes 10 tons/hr of steel with a residence time of 10 hr.

The ampul is fired in a furnace at 800°C. for about 20 hours. The crystals formed vary in size (1-4 mm. in largest dimension), number, and position, depending on the temperature profile of the... 

For the reformer we assume that the outer wall temperature profile of the reformer tubes decouples the heat-transfer equations of the furnace from those for the reformer tubes themselves. The profile is correct when the heat flux from the furnace to the reformer tube walls equals the heat flux from the tube walls to the reacting mixture. We must carry out sequential approximating iterations to find the outer wall temperature profile Tt,o that converges to the specific conditions by using the difference of fluxes to obtain a new temperature profile T) o for the outer wall and the sequence of calculations is then repeated. In other words, a T) o profile is assumed to be known and the flux Q from the furnace is computed from the equations (7.136) and (7.137), giving rise to a new Tt o-This profile is compared with the old temperature profile. We iterate until the temperature profiles become stationary, i.e., until convergence. 

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