By applying a parallel reaction model the activation energies of different types fuel such as DB, sorghum, LARM, LAPC, HARM, HAPC, and TXL can be determined (as Table 3.5).

3.7 IGNITION

3.9.1 Ignition temperature

TGA analysis can also be used to determine the ignition temperature of a fuel when experiments are performed in an air environment. Each fuel was first analyzed in a nitrogen environment and then analyzed again in an air environment. The TGA traces of the two fuels began similarly, but upon ignition, the fuel would oxidize if air was present. Ignition caused the two TGA traces to

deviate. The temperature at which this deviation occurred was defined as the ignition temperature (Fig. 3.18). For the mass loss traces obtained during testing, ignition is defined as the point at which the difference between the moisture normalized traces begin to deviate by more than 5% of the average value at that point and continue to deviate thereafter (Lawrence, 2007):

(m%)N2 — (m%)air

(m%)N2 + (m%)air
2

This is best illustrated graphically as in Figure 3.18.

The ignition behavior of the biomass fuels was analyzed with similar independent variables as those used to analyze the activation energy behavior (Table 3.6). Figure 3.18 gives the temperature [K] at which ignition of the fuel sample is said to have occurred according to the definition.

The results show that the fixed carbon content of the fuel, particle size, and coal: FB blend ratio had very little effect on the ignition temperature of the fuel. The fixed carbon content for all the fuels tested is given in Table 3.7.

*Computed from HHVdaf & VMdaf *HHVvm + FCdaf *HVfc where HVfc & 32765 kJ/kg of carbon (Chapter 4, Annamalai and Puri, 2007).

Boie basedHHVVM in kJ/kg ofVM released & [35160 YC + 116225 YH — 11090 YO + 6280 YN + 10465 YSFC * HVfc]/VM], where VM, FC… Yc, Yh. .. are either in mass fractions as received or %.

The type of FB used also had little effect on the ignition behavior of the fuel. The overall average ignition temperature for those fuels, which had coal present, is 566 K with a standard deviation of only 2.9%. The only appreciable difference in ignition point temperature is for those fuels that were pure biomass. For the pure biomass fuels, no matter the particle size, the average ignition temperature is 747 K with a standard deviation of 2.7%, probably due to lower quality of volatiles from biomass fuels.

It can be seen from Table 3.8 that coal volatiles are of high quality compared to volatiles from biomass.