Pyrometer, temperatures measured

Temperature measurements ranging from 760 to 1760°C are made using iron—constantan or chromel—alumel thermocouples and optical or surface pyrometers. Temperature measuring devices are placed in multiple locations and protected to allow replacement without incinerator shutdown (see Temperature measurement). 

Absorption ratio and pyrometer temperature measurements. Time histories (L) (Lighter Traces 30 second average. Darker Traces 30 minute moving average) (Reprinted from Teichert, H., Fernholz, T, and Ebert, V., "Simultaneous In Situ Measurement of CO, H2O, and Gas Temperatures in a Full-Sized Coal-Fired Power Plant by Near-Infrared Diode Lasers," Applied Optics 42,2043-51,2003. With permission.) and temperature versus absorption rate (R). 

Control Devices. Control devices have advanced from manual control to sophisticated computet-assisted operation. Radiation pyrometers in conjunction with thermocouples monitor furnace temperatures at several locations (see Temperature measurement). Batch tilting is usually automatically controlled. Combustion air and fuel are metered and controlled for optimum efficiency. For regeneration-type units, furnace reversal also operates on a timed program. Data acquisition and digital display of operating parameters are part of a supervisory control system. The grouping of display information at the control center is typical of modem furnaces. 

The deterrnination of surface temperature and temperature patterns can be made noninvasively using infrared pyrometers (91) or infrared cameras (92) (see Infrared technology and raman spectroscopy). Such cameras have been bulky and expensive. A practical portable camera has become available for monitoring surface temperatures (93). An appropriately designed window, transparent to infrared radiation but reflecting microwaves, as well as appropriate optics, is needed for this measurement to be carried out during heating (see Temperature measurement). 

The problem of emissivity from real materials has stimulated the study of pyrometers that measure radiation at two different wavelengths. The principle of the two-color pyrometer is that the energy radiated from a source of one wavelength increases with temperature at a rate different from that radiated at another wavelength. Thus temperature can be deduced from the ratio of the intensities at the two wavelengths, regardless of emissivity. Two-color pyrometers are not widely used. 

The temperature in the hottest part of the kiln is closely controlled using automatic equipment and a radiation pyrometer and generally is kept at about 1100—1150°C (see Temperature measurement). Time of passage is about four hours, varying with the kiln mix being used. The rate of oxidation increases with temperature. However, the maximum temperature is limited by the tendency of the calcine to become sticky and form rings or balls in the kiln, by... 

Measurement of the hotness or coldness of a body or fluid is commonplace in the process industries. Temperature-measuring devices utilize systems with properties that vaiy with temperature in a simple, reproducible manner and thus can be cahbrated against known references (sometimes called secondaiy thermometers). The three dominant measurement devices used in automatic control are thermocouples, resistance thermometers, and pyrometers and are applicable over different temperature regimes. 

Total Radiation Pyrometers In total radiation pyrometers, the thermal radiation is detec ted over a large range of wavelengths from the objec t at high temperature. The detector is normally a thermopile, which is built by connec ting several thermocouples in series to increase the temperature measurement range. The pyrometer is calibrated for black bodies, so the indicated temperature Tp should be converted for non-black body temperature. 

Because indirect-heat calciners frequently require close-fitting gas seals, it is customaiy to support aU parts on a selFcontained frame, for sizes up to approximately 2 m in diameter. The furnace can employ elec tric heating elements or oil and/or gas burners as the heat source for the process. The hardware would be zoned down the length of the furnace to match the heat requirements of the process. Process control is normaUy by shell temperature, measured by thermocouples or radiation pyrometers. When a special gas atmosphere must be maintained inside the cyhnder, positive rotaiy gas se s, with one or more pressurized and purged annular chambers, are employed. The diaphragm-type seal ABB Raymond (Bartlett-Snow TM) is suitable for pressures up to 5 cm of water, with no detectable leakage. 

Boslough, M.B., and Ahrens, T.J. (1989), A Sensitive Time-Resolved Radiation Pyrometer for Shock-Temperature Measurements above 1500 K, Rev. Sci. Instrum. 60,3711-3716. 

The value of k is determined experimentally by gas temperature measurement. The measurement error of a simple pyrometer can be 250 to 300 K, due to re-radiation to water-cooled surroundings, and the values given below are based on measurement by a Land multi-shielded high-velocity suction pyrometer. Typical values for normal excess air at or near full boiler load are ... 

GC-MS Experiments. GC-MS pyrolyses were carried out using a Porapak Q column 6-ft (flow rate 35 mL/min) attached to a Finnigan 4000 quadrupole GC-MS. The sample was placed in a stainless steel tube 10 cm long connected to a 4 way valve. One of the outlets was attached to a Porapak Q column interfaced with the M.S. The stainless steel tube containing a portion of Au colloid film was placed in a furnace connected to a Variac provided with a digitial quartz pyrometer to measure the temperature. Three pyrolyses were performed at 100, 200 and 350°C with the Au-acetone film. 

Fig. 3.1 Modified domestic household microwave oven. Inlets for temperature measurement by IR pyrometer (left side) and for attaching reflux condensers (top) are visible. A magnetic stirrer is situated below the instrument.

The other limit is the problem of temperature measurements. Classical temperature sensors could be avoided in relation to power level. Hence, temperature measurements will be distorted by strong electric currents induced inside the metallic wires insuring connection of temperature sensor. The technological solution is the optical fiber thermometers [35-39]. However, measurements are limited below 250 °C. For higher values, surface temperature can be estimated by infrared camera or pyrometer [38, 40], However, due to volumic character of microwave heating, surface temperatures are often inferior to core temperatures. 

Fig. 1. Typical a.c. plasma systems used for hydrogenation of semiconductor samples. A. In this aparatus, hydrogen is pumped through the quartz tube (Q) and a plasma excited by inductive coupling of 13.56 MHz r.f. power with a copper coil (c2). The sample rests on a graphite block (b) that is heated by 440 KHz power coupled by a second coil (cl). A pyrometer (P) measures the sample temperature. B. In this system, a high frequency oscillator is used for plasma excitation while the sample is heated in a tube furnace (Pearton et al., 1987).

The temperature measurement devices which do not contact the hot surfaces, for example, optical -, radiation pyrometers, and infrared techniques, are not typical for high-pressure application. 

The methods of temperature measurement of graphite filaments are also subject to criticism. Temperature must be measured by an optical pyrometer. Duval (19) admits a possible error of 50° C. due to uncertainty in the calculated emissive power of a dull graphite surface (60). Furthermore, the temperature range of investigation cannot be extended far below 1000° C. without making arbitrary extrapolations of temperature vs. voltage curves. 

In deflagration, the limiting temperature is the adiabatic flame temperature. Figure 11 (41) presents some temperature measurements made with an optical pyrometer on the exit wall of the same ceramic combustion chamber for which pressure loss data were presented in Figure 5. Temperatures w ithin 500° F. of the adiabatic flame temperature were obtained. 

Pyrometer, optical -role m temperature measurement [TEMPERATURE MEASUREMENT] (Vol 23)... 

All boiler temperatures were measured just prior to and after the collection of the coal samples and their respective fly ashes, since it was physically impractical to collect the samples and measure the temperatures at the same times. In all cases, the temperatures remained essentially constant. An optical pyrometer was used to measure flame temperatures, and water-cooled jacketed thermocouples were used to monitor the boiler temperatures. The wall effects on the temperature measurements were minimized by insertion of the thermocouple into the boiler until temperatures remained constant with distance upon further insertion of the thermocouple into the boiler. 

For maximum sensitivity, the wavelength of the infrared pyrometer should also be selected based on where the spectral radiancy changes most rapidly. For example, in the temperature range depicted in Figure 8.3, a frequency of 1.5 x 10u Hz (2 /im) will permit more precise temperature measurement than a frequency of 0.4 x 1014 Hz (7.5 /im). 

Fig. 13.7. D/3 emission from Ta and W as a function of surface temperature measured by a pyrometer. Above 1300 K, D/j emission from the Ta surface increases linearly with the surface temperature...

The ITS-90 scale extends from 0.65 K to the highest temperature measurable with the Planck radiation law (—6000 K). Several defining ranges and subranges are used, and some of these overlap. Below —25 K, the measurements are based on vapor pressure or gas thermometry. Between 13.8 K and 1235 K, Tg is determined with a platinum resistance thermometer, and this is by far the most important standard thermometer used in physical chemistry. Above 1235 K, an optical pyrometer is the standard measrrremerrt instmment. The procedtrres used for different ranges are sttmmarized below. 

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