Suction pyrometer, temperatures measured

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 ... 

Special problems arise in measuring local temperature within spray flames. Liquid and solid particles cause deposits and blockage of orifices in instruments. High-temperature conditions, with particles having high emissivity, result in complex radiative heat transfer which affects the accuracy of temperature measurement. In industrial furnaces and gas turbine combustion chambers, suction pyrometers have been used for... 

Figure 4, Comparison of temperatures measured by suction pyrometer and by coated thermocouple...

Temperature proflles in spray flames were similar to those previously measured in gaseous diffusion flames. Measurement of temperature by coated thermocouple was more accurate than measurements by suction pyrometer within the temperature range and particular conditions of the spray flames investigated. Changes in temperature within the flame could be explained in terms of convection, reaction, entrainment, and dilution. 

The measurement system developed, as shown in Figure 5, is introduced into the furnace on level SCCo i so that the ceramic tip is in the gas flow. The key elements of the measurement equipment are a suction pyrometer for the temperature measurement, a wide-range oxygen sensor (BOSCH LSU4) for the fast oxygen measurement, and a thermal conductivity detector (TCD) to measure the transient response of the Helium tracer concentration. For the determination of the transient response of the TCD measurement system itself Helium tracer was injected Just at the inlet of the suction pyrometer. In Figure 7 a typical transient response of the TCD measurement system is shown (curve with index SCCi . 

The measurements on the research facility were carried out at stationary or quasi stationary conditions. The measurements of air flows, gas temperatures, gas composition, and heat output were analysed continously and monitored online. The gas composition was analyzed in the flue gas after the boiler exit with industrial gas analyzers. For the analysis of the hot gas in the reduction zone a suction pyrometer combined with a probe for detection was used. With this probe also short fluctuations could be monitored with extremely short delay. Besides, a hot gas sampling line with different analyzers for measuring the gas in the reburn zone was installed. Table 2 gives on overview over the gas analysis equipment. 

The optimum temperature range for NO, reduction begins above 800 for all fuel combinations tested. However NO, reduction begins to be effective already above 700 °C. A decrease of the reduction potential with increasing temperature cannot be seen within the measured data, although the data of fuel staging with wood chips at wood chip combustion (W/W) indicate a minimum at about 800 °C. If the indicated temperatures are compared it has to be taken into account, that the presented data were measured with thermocouples, while the real gas temperature, measured with the suction pyrometer are up to 100 °C higher. 

Testing can be used to validate new experimental techniques. For example, the optical techniques for measuring temperature discussed in Chapter 5 have been tested against more traditional and well-established techniques such as bare wire thermocouples and suction pyrometers. Some of these optical techniques (e.g., tunable diode lasers discussed in Chapter 14) used more traditional methods such as bare wire thermocouples for calibration. In either case, testing is required to validate new experimental techniques. In many cases, a well known and fully tested configuration with sufficient measurements using proven techniques will be used to demonstrate the validity of a new measurement technique. 

Figure 2.19 shows a custom-made cylindrical muffler on the air outlet of a velocity thermocouple, often called a suction pyrometer (see Chapter 5), used to measure higher temperatures. This type of temperature... 

A suction pyrometer is designed to measure closer to the true gas temperature than a bare thermocouple measures in a hot environment such as a combustion chamber. There are several types of heat transfer fo and... 

At the desired measurement location, gases are extracted from the flame through a sampling tube in the suction pyrometer. A thermocouple is positioned just inside this tube, typically made of a ceramic or high temperature metal, which acts as a radiation shield. In some designs, multiple shields are used (see Figure 5.6). Examples of suction pyrometers are shown in Figure 5.7. 

A variety of optical techniques have been used to measure gas temperatures in combustion applications, particularly in flames. There are potentially some important advantages of optical techniques compared to contact techniques such as suction pyrometers (see Figure 5.7). Optical measurement techniques do not disturb the flow, where thermocouples may have a significant impact on the fluid dynamics. Optical techniques can potentially measure higher temperatures as there are not the materials issues compared to thermocouples. For some optical techniques, temperature profiles can be measured at one point in time without the need to make multiple individual measurements over some length of time. Optical techniques often have a much faster response time compared to contact methods. This is particularly important in turbulent and transient flows. 

A velocity thermocouple (also known as a suction thermocouple or suction pyrometer see Chapter 5) was used to measure the furnace and stack gas temperatures. The furnace draft was measured with an automatic, temperature-compensated, pressure transducer as well as an inclined manometer connected to a pressure tap in the furnace floor. Fuel flow rates were measured using... 

A series of tests were conducted in the furnace to compare CARS temperature measurements with those acquired with a suction pyrometer [84]. A suction pyrometer is an intrusive probe to measure gas temperature in a flame. The principle of the device is to insert the water cooled probe to the measurement point and draw furnace gases over a thermocouple located at the tip of the probe in an enclosure shielded from flame radiation. The gases are drawn at sufficient velocity to enhance the convective heat transfer to the thermocouple bead. Typically, the flow rate of furnace gases through the probe tip is increased until the thermocouple temperature no longer increases. At this point the thermocouple is assumed to measure the true gas temperature. The disturbance by such a measurement technique can be considerable in the near burner region where chemical reactions are occurring and there is heat release. 

Table 13.2 shows the comparison between the temperatures measured with the CARS and suction pyrometer techniques as measured in the flame about 1.0 m from the burner. This point was chosen to have a minimal effect on the flow field by the suchon pyrometer. 

Typical mean temperature variation with time at the test point. The duration of the suction pyrometer measurement is also shown. 

Several existing instruments, including suction pyrometers, IR spectrometers, and acoustic pyrometers are already in regular use for combustion gas temperature measurement. However, conventional sensors are often subject to errors due to disturbances caused by the presence of the probe, ill-defined spatial resolution, and slow response time. Tunable Diode Laser (TDL) absorption spectroscopy seeks to overcome limitations sometimes associated with these traditional instruments. This technique is of particular interest for industrial combustion applications since it provides the following features ... 

Measurements were made at the flue of the pilot furnace with the TDL and with Air Liquide s Integrated Sampling Probe that incorporates a suction pyrometer. The TDL measurements are made over a pathlength of 30 cm. During these tests, the temperatures measured by the TDL and suction pyrometer matched to within less than 1°F when averaged over a two minute period. Matching occurred both with and without particles added to the flowstream in the test furnace (2590°F and 2507°F, respectively). 

MMBtu/hr. Figure 14.16 shows the LTS-100 temperature and water concentration measured on Level 2 over a period of five minutes. The suction pyrometer traverse was performed along the LTS-100 line-of-sight immediately after the LTS-100 data were acquired. The suction pyrometer data. Figure 14.17, consists of the minimum and maximum temperature readings that occurred in a two minute period at each of the 10 stations across the furnace. 

While furnaces typically do not have many access ports, a variety of probes can be inserted through ports that are available to measure key process variables that can provide feedback used to fine-tune burner settings. For example, suction pyrometers, such as those described in Section 27.5, can be inserted in the furnace or flue gas duct to measure true gas temperatures as thermocouples are usually placed at locations where significant radiation losses can occur thereby biasing... 

In-flame temperature measurement provides useful insight into estimation of radiative heat release from flames, kinetics of the reaction, soot formation, and NO formation. In oxy-burner testing, thermocouple and suction pyrometer are extensively used to take point measurements within the flame. Recently, laser-based advanced diagnostic methods have been developed to map 2-D temperature field of the flame within the furnace [17]. 

A suction pyrometer provides a more accurate measurement of the local flame temperature. Here, a thermocouple bead is shielded within a tube and thus the radiant exchanges with the surroundings are minimized. Combustion gases are made to flow over the thermocouple bead at higher velocities (using a suction mechanism) so that only convective effects are dominant. Since radiative corrections are not needed, suction p3u-ometer measurements usually provide better results than thermocouples. Figure 27.25 shows a schematic of the hitemational Flame Research Foxmdation (IFRF) suction pyrometer. 

Stack gas temperature measurements are taken to provide a basis for furnace continuous emission monitoring (CEM) and also to setup safety interlocks for emergency shutdown. Hence, accurate measurement of stack gas temperature is crucial to the operation of the furnace. The measurement location must be chosen in such a way that the bulk of the flue gases are sampled and the radiation from refractory tiles is minimal. A suction pyrometer is preferred to a thermocouple for stack gas measurement. Although not recommended, if an unshielded thermocouple is used, it must be corrected for radiative losses from the bead otherwise, the measurement would result in errors up to the order of 200°F to 400°F. 

Suction pyrometers can be used to obtain more accurate measurements of the flue gas temperature. A suction pyrometer recesses the thermocouple in an extractive probe to shield it from radiation exchange with the rest of the vessel. Flue gas is rapidly educted into the extractive probe to maximize the convective heat transfer of the flue gases to the thermocouple (while minimizing radiative exchange with the rest of vessel). 

The solids outlet temperature was measured with a fixed thermocouple. Temperatures of the outside shell wall (the skin) were measured with a contact thermometer and with colour chalk. A shielded velocity thermocouple (suction pyrometer) was used for measurement of gas temperatures at the cold and hot ends of the kiln. Gas samples were taken from the cold (gas outlet) end of the kiln using a long sampling tube to minimize inclusion of false air from the kiln seals at the cold end. The sampled gas was analysed on line for oxygen to determine the total amoiint of excess combustion and false air sucked in from the hot end of the kiln. 

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