Diffusion and reaction in a char particle and in the surrounding gas phase. Two limiting models

Sotirchos, Stratis V.; Amundson, Neal R.

doi:10.1021/i100014a009

Cited by 24 publications

(13 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…. These observations agree with the predictions of Sotirchos and Amundson (Sotirehos 1982;Sotirehos and Amundson 1984a;Sotirchos and Amundson 1984b; of the transient combustion behavior of a char particle. When the particle reacts at low conversions it may have low micropore surface area and therefore lie in the unignited branch of the solution locus.…”

Section: Case I: Particles Exhibit Single Ignitionssupporting

confidence: 90%

Pyrolysis and gasification of coal at high temperatures

Zygourakis¹

1989

View full text Add to dashboard Cite

The macropore structure of chars is a major factor in determining their reactivity during tL_e gasification stage. The major objectives of this contract were to (a) quantify by direct measurements the effect of pyrolysis conditions of the macropore structure, and , (b) establish how the macropores affected the reactivity pattern, the ignition behavior and the fragmentation of the char particles during gasification in the regime of strong ditTusional limitations. Results from this project provide much needed information on the factors that affect the quality of the solid products (chars) of coal utilization processes (for example, mild gasification prcx-,esses). The reactivity data will also provide essential parameters for the optimal design of coal gasification processes.

show abstract

Section: Case I: Particles Exhibit Single Ignitionssupporting

confidence: 90%

Pyrolysis and gasification of coal at high temperatures

Zygourakis¹

1989

View full text Add to dashboard Cite

show abstract

“…Another obsexvation is that after reaching a threshold temperature the particles ignite (see Figure 6). This phenomenon has been predicted by previous investigators (Sotirehos andAmundson 1984a, Sotirehos andAmundson 1984b) who solved the coupledmass and heat transfer equa_ons inside a coal particle and in the boundary layer around it. Sotirehos and…”

Section: Methodssupporting

confidence: 77%

Pyrolysis and gasification of coal at high temperatures. Quarterly progress report No. 10, December 15, 1989--March 15, 1990

Zygourakis¹

1990

View full text Add to dashboard Cite

“…Since the char used is very porous, it will further be assumed that the macropores account for almost all the porosity at any level of conversion and that the Knudsen diffusion terms used in the dusty gas model equations can be neglected. Note that our calculations have shown (Sotirchos and Amundson, 1984a) that if the pore-size distribution of the char sample, Table 2, were narrow and unimodal, the initial average pore radius should be about 1,700 A.…”

Section: Resultsmentioning

confidence: 71%

“…That is, we considered that the macropores form a highly interconnected network of pores from which short small pores emanate and that locally we have complete utilization of the internal surface area of each small pore. The last assumption resulted from some calculations (Sotirchos and Amundson, 1984a) that showed that the effectiveness factor of the individual small pores takes values close to unity at temperatures less than 1,600 K, even for large length to diameter ratios. Eventually, as the simulation results will show, the model appears to be valid in the whole temperature range considered since at temperatures higher than 1,600 K the combustion process is controlled by diffusion in the boundary layer; consequently, the intraparticle diffusion and reaction details do not influence quantitatively the solution.…”

Section: Char Pore Structurementioning

confidence: 99%

Dynamic behavior of a porous char particle burning in an oxygen‐containing environment: Part I: Constant particle radius

Sotirchos

Amundson

1984

AIChE Journal

View full text Add to dashboard Cite

The transient combustion of porous char particles is modelled. The model takes into account the reactions of carbon with COz and 0 2 and the oxidation of CO in the gas phase. It reveals strong effects of the intraparticle thermal gradients and of the pore structure evolution scheme on the burning time and predicts an optimum particle size that gives minimum burning time. S. V. SOTIRCHOS and N. R. AMUNDSONUniversity of Houston Houston, TX 77004 SCOPEFormulating mathematical models describing the behavior of a combustion or gasification reactor or even of a cloud of coal dust, we usually include in the analysis submodels simulating the transient combustion or gasification of the individual microsystems, char or coal particles. It is understandable that these submodels must be simple and, if possible, analytically or semianalytically tractable. Unfortunately, the dynamic behavior of the individual subsystems is very complex, a result of the strong interplay between diffusion and reaction. In particular, the combustion of a porous char particle involves not only diffusion of oxygen and carbon dioxide through the surrounding gas phase and the pores of char and reaction of these two species with carbon, but also oxidation of carbon monoxide produced by the heterogeneous reactions in the gas phase. Moreover, because of local depletion of the solid material, the pore structure of the solid changes spatially and temporally, its evolution involving pore growth, coalescence of adjacent pores, as well as initiation of new pores. Therefore, the study of the combustion of a single char particle with the goal of understanding the effect of every assumption and simplification on the solution structure and identifying suitable simple models reproducing to a satisfactory degree most of the quantitative and qualitative features of the solution does not appear to be an easy task.This study aims to investigate the dynamic behavior of porous char particles exposed to an oxidizing environment. As the pseudosteady-state analysis of the problem has shown (Sotirchos and Amundson, 1984b), consideration of intraparticle thermal gradients in the mathematical model has strong quantitative and qualitative effects on the pseudosteady-state behavior of the system. In addition, the solution structure has been found to be very sensitive to the reactivity of the char sample. Since this varies with the pore structure characteristics, different modes of pore structure evolution may lead to significant differences in the predicted burning times. Thus, although the model is fairly general describing the diffusion and reaction process both in the interior of the particle and in the surrounding gas phase, we chiefly focus on the effects of intraparticle thermal gradients and of the evolving pore structure on the transient behavior of the reacting particles. According to the assumptions on which the model is built, the properties of the porous matrix evolve spatially and temporally, but locally they are completely determined by the conversion. In other wo...

show abstract

Diffusion and reaction in a char particle and in the surrounding gas phase. Two limiting models

Cited by 24 publications

References 7 publications

Pyrolysis and gasification of coal at high temperatures

Pyrolysis and gasification of coal at high temperatures

Pyrolysis and gasification of coal at high temperatures. Quarterly progress report No. 10, December 15, 1989--March 15, 1990

Dynamic behavior of a porous char particle burning in an oxygen‐containing environment: Part I: Constant particle radius

Contact Info

Product

Resources

About