Effect of Heating Rate

In slow heating experiments, slow removal of the volatiles from the bed of biomass allows for secondary reactions between 

6 Elliott M.A., Editor, Chemistry of Coal Utilization, 2nd Supplementary Volume, Wiley-Interscience, 1981, P.700. 

Sjostrom and Bjornbom, Royal Institute of Technology, Stockholm, Sweden - http //www.lib.kth.se/Sammanfattningar/zanzi010607.pdf 

For samples approximately 2 mm thick, most DMAs return thermal lag errors of about 1°C for each l°C/min of heating rate. This was established in a roimd robin survey carried out by the NPL [11]. This is easy to check. Three 7 determinations should be made at heating rates of say 1°, 3° and 5°C/min. A new sample should be used each time. The measured 7 temperature is recorded against heating rate and a plot extrapolating back to 0°C/min should be constructed. The value at 0°C/min is the true 7 and the slope of the line is the thermal lag error as a function of heating rate. 

Therefore a 1 or 2°C/min test will provide more accurate temperature information, but will of course take longer. If tests are only made for comparative purposes the temperature error is largely insignificant. Thicker samples are not preferred as they will cause larger thermal lag errors. 

The onset times for the traces with time as the x-axis were artificially lined up. The onset of the melting endotherm for slower heating rates would normally be much later, since it would take a longer time for the furnace to reach the melting temperature. For the reference temperature as the ordinate, the higher temperature onset for faster heating rates is caused by the heat transfer lag from the sample interior to the thermocouple junction. During the limited amount of time needed for 

The intensity at peak maximum for the faster heating rates is greater than that for the slower heating rates, since for DTA the reference temperature increase is more rapid, while at the same time the sample strives to remain at the melting temperature. For faster heating rates in power-compensated DSC, the sample chamber temperature deviates more quickly from the rising setpoint, so the device compensates with more heat dissipation per unit time to the sample side. 

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Fig. 2. Effect of heating rate on a desorption peak at a fixed pumping speed. Hyperbolic heating schedule, l/To = 9.95 X 10-1 K-1 S/V = 4.8 sec-1 E — 80 kcal mole-1 x = 1. Reproduced from Hansen and Mimeault (30), with permission.

Fig. 29. Effect of heating rate and particle size on the dehydration of whevellite. A 8 °C/min, B 2 C/min. Solid line powdered material (150 mesh), dotted line single crystal...

Fig. 31. Effect of heating rate on the weight curve for palygorskite. Solid line 6 °C/min, dotted line 0.5 °C/ min...

The effect of heating rate on evolution of volatiles is most clearly evidenced in the case of woody biomass, which has been shown to have a volatile yield of greater than 90% when small particles are rapidly heated to 1200°C and to have a volatile yield of only 65% when large particles are slowly heated to 500°C in the commercial charcoal-making process. 

Figure 5. Effect of heating rate on longitudinal shrinkage of redwood...

Figure 3.30 Effect of heating rate on shape of melting (indium) endotherm in a heat-flux DSC. The temperature scale on the lower figure represents reference temperature. If sample temperature were used, the peak shape would be deformed since temperature does not change linearly with time during the endotherm.

Figure 6A. The effect of heating rate on the integral thermogram of a hardwood kraft pulp. All curves are for pulp BBC. Rate of heating from left to right 5°, 10°, 20°, 40 and 80°C/min.

Figure 5. The effect of heating rate on devolatilization rate of Wyoming coal hydropyrolysis.

Table III. Effect of Heating Rates on the Cumulative Weight Loss (Final Temperature 500°C)...

Table I summarises the average data observed for two major carbonization parameters, the mass yield and the fixed carbon content of charcoal. A highly significant effect of temperature was observed, as well as a significant effect of the residence time and a significant interaction between these two factors. The effect of heating rate was not significant.

Figure 10.26 Effects of heating rates on TG curves of powdered polyvinyl chloride (PVC). Experimental conditions 5mg in dry N2 gas with a flow rate of 20 ml min. (Reproduced with permission from T. Hatakeyama and F.X. Quinn, Thermal Analysis Fundamentals and Applications to Polymer Science, 2nd ed., John Wiley Sons Ltd, Chichester. 1999 John Wiley Sons Ltd.)...

FIGURE 1.8 The effect of heating rate on signal sensitivity (see text for explanation of symbols). (Reproduced from Coleman, N.J. and Craig, D.Q.M., Int. J. Pharm. 135, 13, 1996.)... 

The effect of heating rate on the DSC heat flow signal will be considered in more detail in Subsection 2.4.2. However, it is useful to consider this parameter in terms of calibration protocols. Figure 2.1 shows the onset temperature of the melting peak of indium at seven different heating rates. As the heating rate increases, the thermal lag between the furnace and the sample increases. From Figure 2.1 it can... 

FIGURE 2.10 Effect of heating rate on the DSC data for 2.78 mg of indium in an aluminum general pan. Nitrogen purge gas at 25 ml/min. 

Van Dooren, A. A. 1982. Effects of heating rates and particle sizes on DSC peaks. Anal. Proc. 554-555. 

Hinds, G. P. "Effect of Heating Rate on the Retorting of Oil Shale," presented at 71st Annual Meeting of AIChE, Nov. 1978. 

Fig. 24. Resolution of dual peaks Effect of heating rate ( — b) and exit speed (SE). Two components, with the same initial concentration, evolve according to first-order kinetics with i/1 1 = 3.54 X 1013 sec 1, E jJ — 80 kcal/mole i>(3) = 4.17 x 1013...

The effect of heating rate change on the procedural decomposition temperatures of a sample has been widely studied. Perhaps the only other parameter that has been studied more is that of the effect of atmosphere on the TG curve. For a single-stage endothermic reaction, Simons and Newkirk (1) have pointed out the following changes for T and Tf, as a function of fast (F) and slow (S) heating rates. For the initial procedural decomposition temperature, T-... 

The effect of heating rate on the TG curve of a sample has been discussed by numerous authors. Mention should be made of the investigations or reviews by Duval (3, 4, 11), Newkirk (12), Redfern and co-workers (6, 8), Simmons and Wendlandt (13), DeVries and Geliings (14), HerbeU (15), and... 

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