Temperature exhaust gas

Exhaust gas temperature sensor Catalytic substrate Heat insulator... 

The precious metals possess much higher specific catalytic activity than do the base metals. In addition, base metal catalysts sinter upon exposure to the exhaust gas temperatures found in engine exhaust, thereby losing the catalytic performance needed for low temperature operation. Also, the base metals deactivate because of reactions with sulfur compounds at the low temperature end of auto exhaust. As a result, a base metal automobile exhaust... 

Multipressure Steam Generators—These are beeoming inereasingly popular. With a single pressure boiler, there is a limit to the heat reeovery beeause the exhaust gas temperature eannot be redueed below the steam saturation temperature. This problem is avoided by the use of multipressure levels. 

Pinch Point—This is defined as the differenee between the exhaust gas temperature leaving the evaporator seetion and the saturation temperature of the steam. Ideally, the lower the pineh point, the more heat reeovered, but this ealls for more surfaee area and, eonsequently, inereases the baek-pressure and eost. Also, exeessively low pineh points ean mean inadequate steam produetion if the exhaust gas is low in energy (low mass flow or low exhaust gas temperature). General guidelines eall for a pineh point of 15-40°F (8-22 °C). The final ehoiee is obviously based on eeonomie eonsiderations. 

Off-Design Performance—This is an important eonsideration for waste heat reeovery boilers. Gas turbine performanee is affeeted by load, ambient eonditions, and gas turbine health (fouling, ete.). This ean affeet the exhaust gas temperature and the air flow rate. Adequate eonsiderations must be given to bow steam flows (low pressure and high pressure) and superheat temperatures vary with ehanges in the gas turbine operation. 

Gas turbine power adjustments in a utility application require that the mechanical speed must remain constant due to unacceptable consequences of frequency fluctuations. The control is obtained by IGV adjustments to reduce the flow at off-design loads and to maintain the high exhaust gas temperature. 

The interval between more thorough inspections will depend on the operating conditions of the gas turbine. Manufacturers generally provide guidelines for determining inspection intervals based on exhaust gas temperatures, type and quality of fuel utilized, and number of starts. 

Enclosed flares are composed of multiple gas burner heads placed at ground level in a staeklike enclosure that is usually refractory or ceramic lined. Many flares are equipped with automatic damper controls that regulate the supply of combustion air depending on temperature which is monitored upstream of the mixing, but inside the staek. This class of flare is becoming the standard in the industry due to its ability to more effectively eontrol emissions. Requirements on emissions includes carbon monoxide limits and minimal residence time and temperature. Exhaust gas temperatures may vary from 1,000 to 2,000 F. 

Exhaust gas temperature at anticipated ambient and at various loads... 

Due to the amount of water vapor produced when natural gas is burned, it is important not to allow the exhaust gas temperature to fall below 80°C, otherwise the water dewpoint will be reached. Not only the economizer but also the ductwork and chimney must be considered and provision incorporated for drainage. 

The reactions that have a strong heat effect are the oxidation reactions, which may increase the exhaust gas temperature by hundreds of degrees. 

SCR systems at stationary diesel engines profit from the high exhaust gas temperatures of about 350-400 C, caused by the usually constant high load operation conditions of the diesel engine. In this temperature window nearly all known SCR catalysts are very active. Moreover, weight and size of the exhaust gas catalyst are usually not strictly limited, which results in a good NO, reduction efficiency (DeNOJ. However, DeNO, is not the only criterion for an SCR catalyst. Further requirements are excellent selectivities regarding NO and urea/ammonia as well as low ammonia slip, which is an undesired secondary emission of the SCR process. Therefore, all SCR catalysts exhibit surface acidity, which is necessary to store ammonia on the catalyst surface and, thus, to prevent ammonia slip. 

Below 200°C, reliable urea thermohydrolysis is very hard to achieve, therefore urea dosage is usually stopped in real-world urea-SCR systems in this temperature regime. Another serious problem connected with the urea injection at low temperatures is the formation of white to yellowish deposits, which are observed when urea solution is injected at very low exhaust gas temperatures or if the urea spray forms a thick film at the walls of the SCR system. The analysis of these deposits [26] showed that they mainly consist of urea and some biuret at low temperatures and of cyanuric acid and some biuret at higher exhaust gas temperatures around 350°C. From laboratory investigations of the urea decomposition, it is known that biuret is easily formed from 150 to 190°C [27], whereas the formation of cyanuric acid is predominant from 200 to 300°C, according to the following reactions [12] ... 

The authors concluded that for the production of hydrogen-rich gas, diesel fuel could be reformed by exhaust gas at temperatures typical of exhaust gas temperatures (from 200 to 700°C). 

Exhaust gas temperature measurements are made with a fine-wire R-type thermocouple connected to an Omega model 660 digital readout. Gas samples are extracted using a 6.4-millimeter (0.25-inch) O.D. water-cooled stainless-steel suction probe and then filtered, dried, and analyzed for CO, CO2, O2, UHC, and NOj . Instrumentation includes a Beckman model 864 NDIR CO2 analyzer, Beckman model 867 NDIR CO analyzer, Siemens OXYMAT 5E paramagnetic O2 analyzer, Siemens FIDAMAT 5E-E FID total hydrocarbon analyzer, and a Beckman model 955 Chemiluminescent NO/NOj, analyzer. Certified span gases are used for instrument calibration. PC-based data acquisition is available during experimentation. All of the emissions data reported here were obtained approximately 24 pipe diameters downstream of the fuel injector and represent average exhaust concentrations. 

To carry out measurements in exhaust gases, the 16-pin holder is mounted in a specially designed tube [Figure 2.19(a) [128], which was improved recently [52]. The exhaust gases are cooled while passing through the tube, which makes it possible to make measurements with the sensor chip at a constant temperature that is somewhat below the exhaust gas temperature. 

Table 8 Exhaust Gas Temperature and Composition (%voL, dry basis) at Different Diesel Engine Operating Conditions ...

The fuel-gas regulator can now be opened, because we are no longer constrained by the exhaust-gas temperature. 

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