Heat of pyrolysis

Some publications give amounts of pyrolysis heat (H) per mass of volatiles others include numbers for estimating H. The heats appear to vary greatly from author(s) to author(s) for trials under similar conditions, but one trend is obvious heat of pyrolysis decreases as temperature increases. 

Temperature rci Sample Mass (a) Duration (h) Solid Residue <%) Heat of Pyrolysis fj/g) Source... 

Pyrolysis Increment x Heat of Pyrolysis = Heat Release... 

Figure 4 shows the results. Above 200"C, the dashed line reflects heats of pyrolysis according to Equation 2 and Figure 3, while the more realistic, full line is based on heats which approach zero at 300 C. According to the figure, heat release peaks between 130 and 230 C. Since heat dissipates out of self-heating materials in proportion to temperatures above ambient, and at 230"C the dissipation should exceed the dissipation at 130 C by a factor of two, the most rapid pyrolytic self-heating can be expected between 120 and 170 C. 

Figure 3. Heat of pyrolysis H per mass of volatiles at various pyrolysis temperatures, calculated with Equation 2.

Figure 5. Rate of heat evolution in wood and cotton. Experiments 70 C included heat of pyrolysis 80 C the material was moist, 130"C it was ovendry between 80" and 130 C, moisture contents are mentioned in %, unless the material was ovendry. 1 — Bowes (28) wood raspings heat values extrapolated from measurements at 190-335 C. 2 — Eriksson and...

Design practices stem from standard fire test procedures in which the temperature history of the test furnace is regarded as an index of the destructive potential of a fire. Thus, the practice of describing the expected effects and damage mechanism is based on temperature histories. This standard design practice is convenient but lacks accuracy in terms of structural performance. The severity of a fire should address the expected intensity of the heat flux that will impact the structure and the duration of heat penetration. A simple analysis of the expect nature of an unwanted fire can be based on the heats of combustion and pyrolysis of the principal contents in the facility. The heat of combustion will identify the destructive nature of the fire, while the heat of pyrolysis will identify the severity of the fire within the compartment itself and will also identify the destructive potential of the fire in adjacent spaces. 

Solid degradation in milligram scale (using TG, DSC, and MDSC for heat of pyrolysis and specific heat)... 

L is the latent heat of pyrolysis, which can be determined from DSC tests or by considering the energy balance at the peak MLR in the cone calorimeter tests... 

Because of the difficulties in accurately measuring the heat of pyrolysis in DSC, manifested by the fact that the measurements at University of Ulster are only about half the values in another study in [8], the values determined in the cone calorimeter, which are also close to those reported in [8], are used in the present analysis. 

DSC/MDSC can be used to determine the thermal and transport properties as well as the heat of melting and pyrolysis. The measurement of heat of pyrolysis is very challenging and needs more investigation. 

Heat transfer at a wall is related to the Reynolds number, generally to the power 0.7. Thus, there is great interest in secnring a low viscosity when the heat of pyrolysis is to be supplied. Dissolving the feed in oil is a possible procedure. 

Table III. Heats of Pyrolysis for Green River Oil Shale and Devonian Shale (Unit cal/g)...

The heat of pyrolysis (in an inert atmosphere) can be calculated by integrating the area under the differential thermal analysis curve and comparing it with the value obtained for a reference substance according to the following equation... 

The model uses material properties and models of these properties, such as thermal conductivity, permeability, diffusivity, specific heats, heat of pyrolysis, final sample radius and so on. The appendix gives an overview of the data used in the simulations. 

In earlier work a sensitivity analysis of simulations of dry wood shows an 8% reduction in time of pyrolysis at 1 mm reduction of the final charcoal radius [I], This was shown to be in the same range as the influence from an exothermic heat of pyrolysis (150 kJ/kg). In this paper the inclusion of an axial convective flow is shown to influence the time of pyrolysis in the same range, a reduction of 6% (evaluated from Figure 2a where the times of conversion of Case 1 and Case 3 are estimated to 750 and 708 seconds respectively). For wood with a moisture content above the fibre saturation point the axial liquid permeability is shown to dominate the influence on the conversion time. 

The test begins by slowly introducing the solid fuel feed into the bed via the screw feeder. The bed temperature immediately drops because of the sensible heat required to heat the solid to the reaction temperature plus the heat of pyrolysis. The solid feed rate is carefully adjusted so that the bed temperature does not drop below the desired 1400-1500°F range. The reaction system is allowed to come to a new steady-state condition with a constant splids feed rate, and the feed rate of the solids is determined by weight difference. 

Research described in this paper focuses on the second step of the gasification process, and details the effects of temperature and residence time on product gas formation. Cellulose is used as a feedstock for pyrolytic volatiles formation. Earlier papers (JS.M) have discussed the effect of steam on cellulose pyrolysis kinetics. Two recent papers (1, 1 6) presented early results on pelletized red alder wood pyrolysis/gasification in steam. Future papers will discuss results using other woody materials, crop residues, and manures (17,1 ). Research to date indicates that all biomass materials produce qualitatively similar results in the gasification reactor described in the following section of this paper. Effects of pressure on the heat of pyrolysis of cellulose are also discussed as a prelude to future papers detailing the more general effects of pressure on reaction rates and product slates. 

Figure VIII presents the results of three measurements of the heat of pyrolysis of cellulose at different pressures. At elevated pressures, the pyrolysis reaction becomes exothermic, and char production increases from about 12% by weight of the cellulose feedstock at 1 bar to 16% at 6 bars. Future research is expected to refine this initial data and extend it over a broader range of pressures.

Table V. Variation of Heat of Pyrolysis With Pressure ...

Determination of the Heat of Pyrolysis The value of the heat of pyrolysis was calculated from the following two equations ... 

Estimation of Required Heat of Pyrolysis for Different Compounds Polyethylene (PE) is usually referred as (C2H4) , or... 

---