Reformer temperature measurements

Temperature measurements at high temperatures need special considerations, in particular when the purpose is to determine heat transfer parameters. 

Reliable catalyst temperatures inside the bed ean be measured by thermocouples loaded individually to avoid disturbing the flow pattern as would be the case if a central thermopocket is used. Radial temperatures can be measured using thermocouples plaeed on a bracket pointing directly against the flow direction to avoid disturbance from false heat conduction. 

In fired reformers, outside tube-wall temperatures must be measured carefully [19] [131]. Apart from their impact on tube life, they are key variables in the evaluation of heat transfer coefficients. Measurements may be carried out using commercial IR cameras with different wavelengths, but in a pilot plant such measurements are best carried out using Pt/Rh thermocouples attached on the cold side of the tubes. In an industrial plant thermocouples must be embedded, but a gold cup pyrometer [131] can be used locally to obtain accurate measurements. 

A tool to measure tube-wall temperatures is Ihe IR camera. It interprets the radiation emitted from a tube surface as coming from a black body and converts it to a temperature. Provided the tube is clean, it typically has an emissivity in die order of 0.8-0.9 and it will hence reflect some of die radiation coming from the warmer furnace walls and flames. The instrument will consequendy interpret a measined temperature higher than it actually is. The IR camera has filters so that only radiation at a certain wavelength pl is measured and the equation to correct the 

Fpx is a view factor, which can here be set to unity, since the measured temperature is the one on the front. The furnace temperature varies significantly on the furnaee wall, so an average value recorded by the IR camera is used. In a pilot plant the correction is small if the measurements are made on the eold side of the tube, whereas in an industrial reformer the measured temperatures are those on the hot side along the furnace and larger eorreetions result. 

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Even the process of experimental setup and measurement can be an issue. In a fixed bed laboratory reactor at reforming temperatures (near 800°C), the following sequence of reactions is thought to take place. Very near the... 

Reuse et al. [68] combined endothermic methanol steam reforming with exothermic methanol combustion. The reactor consisted of a stack of 40 foils, 20 dedicated to each reaction (see Figure 2.77). The total length of the foils was 78 mm and their thickness was 200 pm. The foils carried 34 S-shaped channels each with a length of 30 mm, a depth of 100 pm and a width of 310 pm. A special plate in the center of the stack allowed for temperature measurements. The plates were made of FeCrAlloy and an a-alumina film 5 pm thick was generated on their surface by temperature treatment at 1000 °C for 5 h to improve the adherence of the catalyst coatings (see Section 2.10.7). 

Aicher et al. [72] measured the temperature profile in their autothermal diesel reformer reactor (see Figure 4.4). Temperatures up to 900 °C were detected upstream of the catalyst honeycomb, while the reformate temperature never exceeded 700 °C at the reactor exit... 

The catalyst activity in the model can be a function of tube length, but t3 ically is specified as uniform along the length. Measured data fi om an industrial reformer is essentially never available to allow the calculation of the activity profile. Even in reformers with in-the-tube temperature measurements, this information is usually insufficient to determine activity as a function of length. Process gas composition is required as a function of length to establish the activity profile. Clearly, such information can only be obtained in a laboratory environment. 

Temperature Distribution Measurement The temperature distribution in fuel cells can be of critical importance to the kinetics, electrolyte conductivity, material compatibility issues (high-temperature fuel cells), internal reformation process (high-temperature fuel cells), and other kinetic and transport phenomena known to be functionally dependent on temperature. Since the SOFC is dominated by the electrolyte resistance, which is a strong function of temperature, the current distribution in these systems closely follows the temperature profile. Several techniques can be used to measure the temperature distribution in a fuel cell. An embedded thermistor or thermocouple can be used when carefully placed. Additionally, infrared temperature measurement is a fascinating way to observe real-time temperature variation in a fuel cell. Infrared scanners can be used to look at temperature distribution in a specially modified single fuel cell and have been useful to see the phase change processes from ice to liquid in a low-temperature fuel cell [31]. 

The extent to which anode polarization affects the catalytic properties of the Ni surface for the methane-steam reforming reaction via NEMCA is of considerable practical interest. In a recent investigation62 a 70 wt% Ni-YSZ cermet was used at temperatures 800° to 900°C with low steam to methane ratios, i.e., 0.2 to 0.35. At 900°C the anode characteristics were i<>=0.2 mA/cm2, Oa=2 and ac=1.5. Under these conditions spontaneously generated currents were of the order of 60 mA/cm2 and catalyst overpotentials were as high as 250 mV. It was found that the rate of CH4 consumption due to the reforming reaction increases with increasing catalyst potential, i.e., the reaction exhibits overall electrophobic NEMCA behaviour with a 0.13. Measured A and p values were of the order of 12 and 2 respectively.62 These results show that NEMCA can play an important role in anode performance even when the anode-solid electrolyte interface is non-polarizable (high Io values) as is the case in fuel cell applications. 

A similar study reports the results of adding 100 ppm thiophene to As in the Palm et al. study,the catalyst is not described rather, it is identified only as a commercial naphtha reforming catalyst, presumably Pt-based. In their reactor, the reformate from the ATR step passes through separate high and low temperature shift reactors before being analyzed. Thus, it was not possible to determine the effect of sulfur on the reforming step alone, nor was any post-reaction characterization of the catalyst reported, for example to determine coke or sulfur content. Figure 16 shows the observed deactivation, as measured by a decrease in H2 and CO concentrations. 

Regardless of how fast a chemical reaction takes place, it usually reaches an equilibrium position at which there appears to be no further change, because the reactants are being reformed from the products at the same rate at which they are reacting to form the products. This position of equilibrium commonly is characterized at a given temperature by a constant K,., called the equilibrium constant (see Chapter 16). The equilibrium constant commonly is measured at several different temperatures for a given reaction, because these values of are related to the Kelvin temperature (T) at which they are measured the relationship is... 

Complete denaturation of DNA leads to separation of the two complementary strands. If a solution of denatured DNA is cooled quickly, the denatured strands remain separated. However, if the temperature is held for some time just below Tm (a process known as annealing), the native double-stranded structure can be reformed. An important tool for studying DNA has been the measurement of the kinetics of reassociation of separated strands of relatively short DNA fragments.72 556 557... 

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