Effects of CO2 and H2O Mixture on Intensified Gasification of Residual Carbon in Partially

This dissertation explores the effects of CO2 and H2O mixture on intensified gasification of residual carbon in partially. It discusses the research and studies through theoretical and experimental analyses of the processes of gasification. The study established that a molecule of carbon dioxide could go through a pore whose size is not less than 1.5 nm whereas a molecule of steam required a pore size that is large than 0.6 nm. The researchers of this study thus made a conclusion that the two dimensionless parameters relied on the carbon active sites form the results obtained from the various chemisorption tests they conducted and hence they were able to validate the Langmuir-Hinshelwood model.

Dissertation 1
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Dissertation 2
Effects of CO2 and H2O Mixture on Intensified Gasification of Residual Carbon in Partially
Gasification is a very fundamental technology when it comes to uncontaminated and energy-
saving use of coal, coke, petroleum as well as other fuels in solid form. The technology has been
in the large-scale industry for a long time owing to its high efficiency, almost zero carbon
dioxide pollution as well as high productivity in the industries in which it is being applied.
Research and studies through theoretical and experimental analyses of the processes of
gasification have picked on gasification rate as an important factor that is used in controlling
gasification behaviors. Such conclusions based on the findings were mainly arrived at based on
the relatively slow kinetics of char-steam reactions and char-CO2 reactions under the different
gasification conditions. This thus makes it important to steer off a proper comprehension of the
kinetics of gasification of char-steam as well as that of char-CO2 (Overend, 2012, p.820).
Numerous reaction models have been developed by various scholars of char-CO2 and char-steam
in that order in order to estimate the rates of their reactions. Still, there have also been elaborate
and extensive studies made on char-CO2 gasification and char steam gasification kinetics. The
main disadvantage with the reaction models that have been developed in the previous studies by
researchers is their inability to be applied in systems in which there are simultaneous reactions of
char-steam and char-CO2 having a sole gasifying agent (Puigjaner, 2011, p.315). Under real
gasification conditions, a reaction is carried out between the chars and with the mixtures of
gasifying agent and CO2.
A research was thus carried out by the scholars to investigate the reactivities of gasification of
metallurgical coke in a steam and CO2 mixture unfortunately it became quite a challenge to

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perform an analysis on the intrinsic chair-steam-CO2 reaction since the sizes of the particles that
were used in the sample were quite large ranging between 3 mm and 6 mm. This led to the
impact of internal diffusion. Other researcher has also done studies on the mechanisms of
gasification of coal char exposed to conditions of a mixture of CO2 and steam and made
proposals on empirical approaches that could be used to elaborate the impacts of the degree of
change of carbon on the rate of gasification (Shelton, 2012, p.177).
A recent study was developed by some researchers recently to come out to examine the relations
in char-CO2-steam reaction with the aid of Langmuir-Hinshelwood model. This model is pegged
on the philosophy of desorption and absorption. It was established from the research that char-
CO2-steam reaction mainly occurs at the common active sites. The findings also illustrated that
hot vapor and CO2 were in a competition for the active sites of the chars. However, the same
research was done by some other researchers who proposed an opposite view over the findings
(Puigjaner, 2011, p.247). These researchers, in the perception, argued that the char-CO2 reaction
and the char-CO2 reaction went on at separate and different active sites and thus the entire rate of
gasification should be determined by adding the gasification rate of the char-CO2 reaction and
the rate of char-steam reaction.
Still, these researchers identified that the mechanism of reaction of lignite gasification was in
line with the different reactive site mechanism of reaction under relatively reduced pressures of
gasification but was greater than mechanism of a reaction in the common reactive site in case the
pressures of gasification was increased (Shelton, 2012, p.258). On another hand, another scholar
found out that the entire rate of gasification is not equivalent to the some of the char-CO2
reaction and the rate of char-steam reaction rates and that there was no proof of competition for
the active site between the two gasifying agents. A Langmuir-Hinshelwood model that had two

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parameters with no dimension was then proposed by the researchers to examine the rate of char-
steam and char-CO2 gasification and thus could further be used in the estimation of the
interactions more accurately in comparison to other models (Cooper, 2013, p.312). The
mechanisms of the two proposed parameters, however, remained unclear.
A modified kinetic model that was based on the concept of active sites was thus proposed and
developed in a study to be used in evaluating the interaction in char-steam and char-CO2
gasification (Yan, 2016, p.269). The model was confirmed to be reliable by char-steam and char-
CO2 gasification experiments that used carbonaceous materials with the aid of
Thermogravimetric Analyzer. Still, chemisorption of CO2 and steam was also carried out in that
study in a Thermogravimetric Analyzer so as to take the measurement of the quantities of
chemisorption in order to study the relationship between the kinetic parameters the proposed
model that has been modified and the quantities of chemisorption. That work would offer not
only a scientific basis for the gasification industry but also a theoretical basis on which
simulation could be performed (Zaborsky, 2012, p.178).
In the experiment, the chars were gasified using a mixture of steam and CO2 to enable defining
the mechanism of the reaction of the char-steam-CO2. There is two mechanism of interaction in a
char-steam-CO2 reaction which has been accepted by scholars. The first mechanism makes an
assumption that the char-steam-CO2 relations may take place at separate active sites and use such
an assumption the overall rate of reaction is determined from the sum of the rate of the two
reactions (Basu, 2013, p.256). The second mechanism makes an assuming that the two reactions
take place at the common active sites. What this means is that there is a competition for the very
active sites by the two gasifying agents. Th overall rate of reaction is that found to be slower than
the total sum of the rates of reactions of the two reactions.

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The study established that a molecule of carbon dioxide could go through a pore whose size is
not less than 1.5 nm whereas a molecule of steam required a pore size that is large than 0.6 nm.
As such, there was a phenomenon in which a few of the active sites were in pores whose sizes
were smaller than 1.5 nm and thus were filled with molecules of steam only. The researchers of
this study thus made a conclusion that the two dimensionless parameters relied on the carbon
active sites form the results obtained from the various chemisorption tests they conducted and
hence they were able to validate the Langmuir-Hinshelwood model (Prakash, 2011, p.222).

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References
Basu, P., 2013. Biomass Gasification, Pyrolysis, and Torrefaction: Practical Design and Theory.
4th ed. Oxford: Academic Press.
Cooper, B., 2013. The Science and Technology of Coal and Coal Utilization. 4th ed. New York:
Springer Science & Business Media.
Overend, R.P., 2012. Fundamentals of Thermochemical Biomass Conversion. 7th ed. London:
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Prakash, G.K.S., 2011. Beyond Oil and Gas: The Methanol Economy. 2nd ed. Moscow: John
Wiley & Sons.
Puigjaner, L., 2011. Syngas from Waste: Emerging Technologies. 3rd ed. New York: Springer
Science & Business Media.
Shelton, S.P., 2012. Environmental Technologies and Trends: International and Policy
Perspectives. 5th ed. London: Springer Science & Business Media.
Yan, X.L., 2016. Nuclear Hydrogen Production Handbook. 5th ed. Beijing: CRC Press.
Zaborsky, O.R., 2012. Biomass Conversion Processes for Energy and Fuels. 4th ed. Paris:
Springer Science & Business Media.