Download Report

th
6 International Freiberg Conference on IGCC & XtL Technologies,
Coal Conversion and Syngas,
19-22 May 2014, Dresden/Radebeul, Germany
Evaluation of an automated duplicate-sample Fischer Assay setup
according to ISO/ASTM standards and analysis of the tar fraction
1
Leon Roets1, John R. Bunt1, 2, *, Hein W.J.P. Neomagus1 and Daniel van Niekerk2
Coal Research Group, Unit of Energy Systems, School of Chemical and Minerals Engineering,
North West-University, Potchefstroom, 2520, South Africa.
2
Sasol Technology (Pty) Ltd, Box 1, Sasolburg, 1947, South Africa
* Corresponding author: Tel.: +27 18 299-1376; Fax.: +27 18 299-1535;
e-mail: [email protected]
The ISO 647 standard describes a method for the liquefaction/primary pyrolysis of coal that
quantitatively yields water, gas, tar and char, also known as a Fischer Assay. This method has
several limitations i.e. the versatility of the method is limited by the thermal properties of aluminium (the retort material); the result is operator-dependent due to manual manipulation of the
retort temperature using a gas generated flame. This study evaluates an alternative method,
(referred to as the automated Fischer Assay setup), which operates with a pre-programmed
heating curve using two stainless steel retorts in an electrical oven. Comparison of the methods
indicated a lower tar yield for the automated Fischer Assay method, whilst the water yield
increased and the gas and char yields were within the same ranges. The automated Fischer
Assay experiments were, however, more repeatable when compared to the standard ISO
method. Simulated distillation (simdis) and size-exclusion chromatography (SEC-UV) analyses
of the tar fractions found no significant differences between the tars from the two methods. Gas
chromatography mass spectrometry (GCMS) found the tars of the automated Fischer Assay
method to contain more alkyl-phenolic groups, with a decrease in the mixed compounds (compounds that exhibited both aromatic and aliphatic mass peaks in the mass spectra). It is concluded that the new method is more versatile with regards to the operating temperature control
and the pre-programmed heat curve. Additionally, it provides an alternative means to generate
a Fischer Assay that is not limited by the thermal properties of the retort material. It is noted,
that the goal of the study was not to propose a replacement to the current ISO 647 Fischer
Assay method, but to establish an automated system that can be used in pyrolysis research
(qualitative and quantitative studies). Results showed that this method is adequate for qualitative and quantitative pyrolysis research and can be used as an alternative, less-biased method
for ISO 647.
th
6 International Freiberg Conference on IGCC & XtL Technologies,
Coal Conversion and Syngas,
19-22 May 2014, Dresden/Radebeul, Germany
Oxidative thermal cracking of tar compounds in raw syngas from
fluidized bed gasification of solid fuels.
Piotr Babiński, Grzegorz Łabojko
Institute for Chemical Processing of Coal, 1 Zamkowa, 41-803 Zabrze, Poland
email: [email protected], [email protected]
Tar compounds are unnecessary wastes which must be removed from raw gas from
the gasification of solid fuels in a fluid bed. Modern methods utilize thermal cracking in the
absence of oxygen or oxidizing atmosphere, as well as catalytic steam or autothermal
reforming of tar compounds contained in the raw synthesis gas. System which could be used
as a solution for this purpose is a reactor with a porous barrier. It provides heat for the
endothermic tars’ decomposition reactions by the distribution of oxygen through a porous
barrier. This solution also provides safety increase by reducing the partial pressure of oxygen
in the reactor.
Results presenting thermal and oxygen conversion of tar model compounds (toluene,
α-methylnaphthalene, and their mixtures) in a model gas from coal gasification consisting of
50% CO, 25% H2, 20% CO2, and 5% CH4 are shown. The content of the model compound
was about 15 g/m3 and steam about 100 g/Nm3 in terms of dry gas. The experiments were
conducted in a reactor with a porous barrier used to distribute the O2 within the interior of the
reactor. Research covered a temperature range of 700–1000 °C, residence time of reactants
in the reactor, 1.5 s and 3.0 s, and the addition of oxygen at 5, 10, and 20 % vol. relative to
the amount of process gas. The experiments have shown the increment of aromatic
compounds’ decomposition rates according to increases in temperature reaching levels of
loss of aromatic compounds of over 50 % for 1000°C. The experiments conducted at the
same temperature level (1000 °C) and the same residence time (3.0 s) have shown
decomposition intensification of aromatics with an increase in oxygen addition.
Acknowledgement
The results presented in this paper were obtained from research work co-financed by the
National Centre of Research and Development in the task of Research No. 3 Strategic
Research Programme – Advanced technologies for obtaining energy. "Development of coal
gasification technology for high-efficiency production of fuels and energy”
th
6 International Freiberg Conference on IGCC & XtL Technologies,
Coal Conversion and Syngas,
19-22 May 2014, Dresden/Radebeul, Germany
INTEGRATED PROCESS OF COAL PYROLYSIS WITH STEAM
REFORMING OF METHANE FOR IMPROVING TAR YIELD
Haoquan Hu, Chan Dong, Lijun Jin, Yang Li, Liang Zou
State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of
Technology, Dalian, CHINA
email: [email protected]
A new process of integrated coal pyrolysis with steam reforming of methane (SRM) process
(CP-SRM) was put forward to improve the yield of tar. Two Chinese lignites were used to confirm the validity of the integrated process. The effects of pyrolysis temperature (550-750 oC) and
pyrolysis atmosphere (H2, N2, SRM) on tar yield and tar compositions were investigated. The
results, see Figure 1, show that CP-SRM has the highest tar yield at the investigated temperature range and the optimum temperature for integrated process is 650 oC. The integrated process achieved lower CO and H2 yields than SRM, but higher CH4 yield than that from pyrolysis
in N2. Meanwhile, the CP-SRM process can improve tar quality, especially the content of phenol, naphthalene and their C1-C3 alkyl-substituted derivatives.
16
XL-SRM
XL-H2
XL-N2
Ytar(wt. %, daf)
(a)
14
12
10
8
6
550
600
650
o
700
750
Temperature( C)
Figure 1: Tar yields of Xilinguole lignite (XL) pyrolysis in different atmospheres at 550-750 oC
th
6 International Freiberg Conference on IGCC & XtL Technologies,
Coal Conversion and Syngas,
19-22 May 2014, Dresden/Radebeul, Germany
“Dusty” vs. “Clean” Tar Reforming of Biomass Gasification Gas –
An Operational Point of View
Winnie L. Eriksen1*, Rasmus M. Nielsen1, Jørgen Madsen1, Bodil Voss1, Klas J. Andersson1, P.
E. Højlund Nielsen1
1
Haldor Topsoe A/S, Kgs. Lyngby, Denmark
*email: [email protected]
Gasification of biomass and other alternative carbon sources is a hot subject, as it offers the
potential to produce carbon-neutral or renewable fuels, contrary to the traditional coal gasification. However, one problem with the biomass gasification is the presence of tars in the exit gas,
which can foul process lines and equipment. Developing gas cleaning technologies downstream
biomass gasifiers is the main focus of biomass gasification technologies. Tar reforming may be
applied as part of a promising gas cleaning solution for the emerging biomass-to-chemicals and
biomass-based CHP technologies.
Besides removing the tars from the process stream, it is also important to ensure a good thermal utilization of the hot exit synthesis gas from the gasifier. The removal of tars from sulfurand dust-filled exit gas from the biomass gasifier is crucial for the process and may be met by
“dusty” or “clean” high-temperature tar steam reforming (tar reforming), converting the harmful
components to useful synthesis gas. The pros and cons of these reforming approaches will be
discussed for different, pressurized or near-atmospheric, gasification applications.
In “clean” tar reforming, dust is removed upstream the tar reformer, preferentially at temperatures in the vicinity of the gasifier exit temperature to minimize loss of exergy, however, requiring a high-temperature filter (700-850°C), which is not commercially available today. In contrast,
in the “dusty” tar reforming process, residual dust is removed downstream the tar reformer at
lower temperatures (150-300°C). In the “clean” tar reformer, pelletized catalysts, featuring a
very high content of active material, can be used leading to a more compact design, whereas in
the “dusty” tar reformer, monolithic catalysts, which are less prone to dust accumulation, are
used.
The long-term stability of our “dusty” tar reforming monoliths has been demonstrated at the
biomass gasification plant in Skive, Denmark. We will present the outstanding durability observed in the specific case and that “dusty” tar reforming is a ready-to-go technology. In parallel,
we have operated our “clean” tar reforming solution at Gas Technology Institute in Chicago
during a wood-to-gasoline project. We will present results from the operations of the pressurized
clean tar reformer.
th
6 International Freiberg Conference on IGCC & XtL Technologies,
Coal Conversion and Syngas,
19-22 May 2014, Dresden/Radebeul, Germany
Options to reach Syngas Quality Requirements by Catalytic Reforming of Tars and Methane from FB-gasification of Biomass
C.Hamel1, S. Kaluza1, C. Unger1
1
Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT, Germany
Email: [email protected]
Despite intensified research efforts during the past years, many technical challenges remain for
large scale gasification and downstream syngas utilization. With the choice of fluidized bed
processes, a reasonable compromise seems possible, regarding efficiency on the one hand and
moderate tar levels in the effluent gas on the other. In the past, it was already shown, that it is
feasible to attain gas qualities clean enough to be used in gas engines by a combination of
primary measures such as specific choice of (partly) active bed materials and downstream catalysts. In recent years, interest in the substantial use of syngas has grown and hence allothermal
gasification with its advantageous gas composition is gaining attention. These processes are
operated at temperatures about 50 – 100 K lower than autothermal ones. In combination with
H2S present in the gas, the activity of common, non-precious metal catalysts no longer suffices
for ultra-low tar levels. Additionally, the small economic benefits of biomass CHP gasification in
comparison to co-combustion in power plants limited the choice of catalysts to low cost ones.
With the goal of substantial gas utilization, precious metal catalysts come into focus again, due
to their increased activity at low temperatures, their better tolerance to sulphur and also their
higher resistance to carbon formation combined with oxidative reactivation stability.
To ensure a high operating temperature for the conversion, catalysts in large scale applications
are placed directly downstream of the reactor and thus face a considerable amount of particles
transported with the syngas. Therefore, for most of the samples studied within this project,
monoliths were preferred as catalyst supports. The catalysts were tested in a lab scale test rig
at Fraunhofer UMSICHT. As for the used test gas, a composition close to the effluent gas of
allothermal steam gasifiers was mixed using mass flow controllers and two separate evaporators for aromatic hydrocarbons and water. Naphthalene and benzene were chosen as model
tar substances, first, because of their high abundance in real syngas mixtures and second, as
they are known for being difficult to reform. The concentrations of benzene and naphthalene
were 5000 and 2500 mg/scm, respectively. The gas is fed to a quartz glass reactor placed
inside a three zone vertical split-tube furnace and is heated up in a first section filled with bulk
SiC material. The second section contains the catalyst and is separated by a quartz glass frit. A
thermocouple close before the frit is used to measure the gas inlet temperature. Before and
after the reactor, the gas can be analysed by means of an online mass spectrometer with direct
inlet, resulting in the advantage of a complete and quasi-continuous composition measurement.
During the research and development project, a large variety of catalysts were tested and
compared regarding their performance for reforming model tar compounds in sulphur free simulated syngas. The test temperatures ranged from 700 to 900 °C and the tests were carried out
at ambient pressure. Differences in performance could be found with respect to the used active
metal of the catalyst and to the preparation method. With H2S added, further tests were carried
out with a reduced number of selected catalysts. As expected, precious metal catalysts showed
better results than catalysts with nickel as active component, especially in presence of sulphur.
Within the last part of the project, which is the basis for this contribution, detailed tests about the
influences of different precious metal components were performed.. Additionally, the conditions
are further altered to match real syngas as good as possible to see whether the application in a
large scale system is feasible. Therefore, alternating loads of sulphur and long term stability
tests are also part of this project step.