Dipl. Ing. Matthias Mayerhofer Technische Universität München ...
Dipl. Ing. Matthias Mayerhofer Technische Universität München ...
Dipl. Ing. Matthias Mayerhofer Technische Universität München ...
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4 Introduction<br />
1.3 Structure of the work<br />
Chapter two includes a general overview regarding biomass gasification, why it is worth research<br />
and what are the potentials for the future. Also, the main gasifiers are being mentioned along with<br />
the advantages and disadvantages of each technology. The reason why a fluidized bed was used<br />
during the experiment is also explained. The basic and most commonly used gas cleaning methods<br />
are presented and the step of the procedure in which that they can be applied. Hot gas cleaning is<br />
the most appropriate one and it is explained why it is the most profitable. It is essential to state also<br />
the main types of gas impurities and which are the ones that are most prominent to damage the<br />
engine in downstream applications. Sulfur is considered as very dangerous species so the commonly<br />
used chemical solutions for its depletion are mentioned. As tar decomposition is the main<br />
focus of this thesis there is a whole analytical part in this chapter regarding higher hydrocarbons.<br />
Which of them are defined as tar and with which mechanisms they can be catalytically destructed.<br />
The tar removal methods are presented in details, along with comments for the advantages and<br />
disadvantages of every one of them. Of course, the operating parameters such as the temperature<br />
and pressure at which the gasification is realized play an important role to the final quantity of the<br />
produced tar. As for catalysts, the chemical mechanisms with which they act are explained.<br />
In chapter three, the main catalyst, Nickel based, that has been widely tested for the past 20 years<br />
is presented here. The most important promoters and supports that have been tested and their<br />
effectiveness are explained. This part is very important for their comparison with the iron based<br />
catalysts as the pretreatment and the basic structure of these two kinds of catalysts is similar. The<br />
advantages and disadvantages of this catalyst have been described by many writers. The basic<br />
problem of this type of catalyst is its rapid deactivation, so all the possible deactivation reasons are<br />
mentioned in detail at this point. Eventually, there are methods to overcome the deactivation of the<br />
nickel catalysts, especially regarding sulfur poisoning but they are not adequate. It is concluded<br />
that because of the strong inconveniences of nickel based catalysts it is essential to focus and<br />
research on a different type that could be more appropriate to achieve the desired result.<br />
In chapter four, the work is focusing on the presentation and description of the iron based catalysts.<br />
It is evident that they don’t easily deactivate as the nickel based ones, but according to most experimental<br />
researches made they don’t have such high potential in tar destruction. The reason why<br />
there are so promising is the fact that they can be used in situ, mixed with the bed material, so<br />
there is no need for the construction of catalytic test rig. As a result, there should be a lot of research<br />
done not only regarding the operating conditions of the gasifier and catalyst bed, but also in<br />
the structure and the composition of the catalysts. As the main experiment that were conducted in<br />
this work involved iron based catalysts, an analytical presentation of the measurements that take<br />
place before and after the use of the catalyst for its evaluation is made. It is evident that depending<br />
on the pretreatment the results obtained can be better or worse.<br />
In chapter five, a theoretical review is done regarding precious metal catalysts. The results from<br />
prior investigations are presented, their potentials for the future along with their advantages and<br />
disadvantages.<br />
In chapter six, the experimental facility is described. The basic procedure that was followed is explained<br />
in details according to the literature investigation, and it is justified why it was chosen.<br />
In chapter seven, the final results of all the experiments are presented. It was agreed to conduct a<br />
series of experiments involving iron based, nickel based and precious metals catalysts in order to<br />
jump into conclusions for their potentials and to compare their results. Also, it was important to<br />
investigate not only the impact of the catalyst on the tar destruction but also on the composition of<br />
the product gas and how this changed with the use of different catalysts. The yield of the product<br />
gas varies depending on different operating parameters and the catalyst used. With this general<br />
overview, it easier to understand which type of catalyst is more appropriate in different downstream<br />
applications and why.