Zugl.: Hamburg, Techn. Univ., Diss., 2007

Zugl.: Dresden, Techn. Univ., Diss., 2008

Originally presented as the author's Thesis--Technische Universität Hamburg, 2007. / Includes bibliographical references.

Für die künftige Versorgung des Mobilitätssektors mit nachhaltig erzeugtem Wasserstoff wird die Konversion von Biomasse als eine bedeutende Herstellungsoption angesehen. In dieser Studie werden Verfahren und Technologien für die Erzeugung von Wasserstoff auf Basis von Biomasse evaluiert. Dies umfasst sowohl thermo-chemische Verfahren - wie z. B. die Vergasung von Biomasse oder die Dampfreformierung biogener Sekundärenergieträger (z. B. Biogas) - als auch biochemische Verfahren, wie die Vergärung von Biomasse zu Wasserstoff oder die Photolyse von Wasser. Nach einer grundlegenden Klassifizierung aller geeigneten Optionen werden drei Verfahren, die für eine kurz- bis mittelfristige Realisierung in einer Demonstrationsanlage am geeignetsten erscheinen, ausgewählt. Für diese werden anschließend Anlagen- und Bereitstellungskonzepte entworfen und einer Detailanalyse unterzogen. Zwei der detailliert untersuchten Anlagenkonzepte basieren auf der allothermen Wirbelschichtvergasung (Konzepte 1 und 2) und ein drittes auf der Dampfreformierung von Biogas (Konzept 3).

Thermal co-processing of coal and biomass has been increasingly focused for its environmental and economic benefits. In the present work, the experimental and kinetic study on co-pyrolysis and co-gasification of Rhenish brown coal (HKN) and wheat straw (WS) was made. The pyrolysis behavior, especially for co-pyrolysis, was investigated in a thermogravimetric analyzer (TGA) and a small fixed bed reactor (LPA). In TGA, the mass loss and reaction rate of single and blend samples were studied under various experimental conditions, and their effects on synergy effects. The synergy effects on products yield and properties of chars were studied in LPA. The kinetics of pyrolysis was obtained based on data from TGA by using the Coats-Redfern method. For gasification with CO2, a small fixed bed reactor (quartz glass reactor), equipped with an online GC to monitor the gas composition, was used. The effects of processing conditions on gasification behavior and synergy effects for mixed chars and co-pyrolysis chars were investigated. The volume reaction model (VRM), shrinking core model (SCM) and random pore model (RPM), were applied to fit the experimental data. The model best fitting the experiments was used to calculate the kinetic parameters. The reaction orders of gasification reactions with single chars are also investigated. The pyrolysis study showed that a small amount of wheat straw added to the brown coal promoted the decomposition better and showed more significant synergy effects. The synergy effects varied with increasing heating rates and pressures, especially at 40 bar. The kinetic parameters were inconsistent with experimental behavior during co-pyrolysis, since the reaction was also affected by heat transfer, contact time, particles distribution and so on. The gasification study on single chars showed that Rhenish brown coal chars had higher reactivity; chars pyrolyzed at higher temperatures showed lower reactivity; and higher gasification temperatures and CO2 partial pressures led to higher reactivity. For co-gasification process, there was no significant synergy effect for mixed chars. However, negative synergy effects (reactivity decreased compared to the calculated values based on rule of mixing) were observed for co-pyrolysis chars, caused by properties change by co-pyrolysis process. For kinetics, the reaction orders of chars ranged from 0.3 to 0.7. Only random pore model fitted most experiments at low and high temperatures. Synergy effects were also observed in kinetic parameters. The values of activation energy E and pre-exponential factor A for mixed chars and co-pyrolysis chars were lower than expected. The negative synergy effects showed the pre-exponential factor A had more effects. However, the higher reactivity of mixed chars than co-pyrolysis chars showed that the reaction was affected more by activation energy E. Therefore, only investigating E or A value was not enough. In addition, a marked compensation effect between activation energies and pre-exponential factors was found in the present study. The isokinetic temperature for the present study was 856 °C. This was close to the temperature at which the gasification reaction transforms from the chemical controlled zone to the diffusion controlled zone for most chars.

Thermal co-processing of coal and biomass has been increasingly focused for its environmental and economic benefits. In the present work, the experimental and kinetic study on co-pyrolysis and co-gasification of Rhenish brown coal (HKN) and wheat straw (WS) was made. The pyrolysis behavior, especially for co-pyrolysis, was investigated in a thermogravimetric analyzer (TGA) and a small fixed bed reactor (LPA). In TGA, the mass loss and reaction rate of single and blend samples were studied under various experimental conditions, and their effects on synergy effects. The synergy effects on products yield and properties of chars were studied in LPA. The kinetics of pyrolysis was obtained based on data from TGA by using the Coats-Redfern method. For gasification with CO2, a small fixed bed reactor (quartz glass reactor), equipped with an online GC to monitor the gas composition, was used. The effects of processing conditions on gasification behavior and synergy effects for mixed chars and co-pyrolysis chars were investigated. The volume reaction model (VRM), shrinking core model (SCM) and random pore model (RPM), were applied to fit the experimental data. The model best fitting the experiments was used to calculate the kinetic parameters. The reaction orders of gasification reactions with single chars are also investigated. The pyrolysis study showed that a small amount of wheat straw added to the brown coal promoted the decomposition better and showed more significant synergy effects. The synergy effects varied with increasing heating rates and pressures, especially at 40 bar. The kinetic parameters were inconsistent with experimental behavior during co-pyrolysis, since the reaction was also affected by heat transfer, contact time, particles distribution and so on. The gasification study on single chars showed that Rhenish brown coal chars had higher reactivity; chars pyrolyzed at higher temperatures showed lower reactivity; and higher gasification temperatures and CO2 partial pressures led to higher reactivity. For co-gasification process, there was no significant synergy effect for mixed chars. However, negative synergy effects (reactivity decreased compared to the calculated values based on rule of mixing) were observed for co-pyrolysis chars, caused by properties change by co-pyrolysis process. For kinetics, the reaction orders of chars ranged from 0.3 to 0.7. Only random pore model fitted most experiments at low and high temperatures. Synergy effects were also observed in kinetic parameters. The values of activation energy E and pre-exponential factor A for mixed chars and co-pyrolysis chars were lower than expected. The negative synergy effects showed the pre-exponential factor A had more effects. However, the higher reactivity of mixed chars than co-pyrolysis chars showed that the reaction was affected more by activation energy E. Therefore, only investigating E or A value was not enough. In addition, a marked compensation effect between activation energies and pre-exponential factors was found in the present study. The isokinetic temperature for the present study was 856 °C. This was close to the temperature at which the gasification reaction transforms from the chemical controlled zone to the diffusion controlled zone for most chars.

The present study mainly focus on two parts: one was the optimization of FactSage calculation, compared with HT-XRD measurements on mineral matter behaviors during the heating of coal and blend ashes from 500 °C to 1000 °C in reducing atmosphere. The aim was to obtain the optimized input parameters and options for FactSage calculation, and the outputs should be as close as possible to HT-XRD results. The other was the application of FactSage on ash melting behaviors. Since the maximum temperature of HT-XRD measurement in laboratory was 1000 °C in reducing atmosphere, the optimized FactSage was applied to investigate the ash melting behaviors in temperature range between 600 °C and 1600 °C for coal, biomass and their blends. The FactSage calculation was optimized by investigations of several input parameters and options including the mass ratio of reactant gas amount to ash sample, solution species and compound solid species. The results obtained from the optimized calculation were much better to fit the mineral transformations measured by HT-XRD. However, there were still some differences between the results from optimized FactSage calculations and HT-XRD measurements. This is mainly due to the amorphous substances which occurred as solid phases and liquid slag in FactSage outputs but cannot be detected by HT-XRD. Besides, several factors, such as the diffusion, particle size distribution and so on, affect the actual measurements greatly but been neglected in thermodynamic calculations, which enhance the distinctions. In addition, the effects of atmosphere were investigated and the differences of mineral matter behaviors were mainly embodied in sulphur-rich minerals, iron-rich minerals and amorphous substance. For application of FactSage on ash melting behaviors, AFTs tests for coal, biomass and their blends were adopted, and the results were well investigated by ash chemical components analyzed by XRF and also equilibrium phases calculated by FactSage. Hemispheric temperature and flowing temperature were mainly dependent on the high melting point substances at high temperature, such as free CaO in HKN and SWC, SiO2 in WS and KOL. The sintering temperature was largely affected by alkali oxides, which could combine with other oxides to form low melting point substances. For blended ashes, AFTs of the blended ash of HKN and WS shown a V shape with WS addition mass ratio rising, and the minimum values of AFTs appeared at 50 wt.% WS addition. AFTs of KOL changed in a small scale when mixed with WS, due to their similar ash composition (high in SiO2). As the SWC ash contents is much less than HKN and KOL, it did not affect the AFTs much when blended with coals. Moreover, the biomass addition affection on the blended ashes AFTs were also well illustrated by the liquid phases mass fraction and also the mineral matter transformations calculated by FactSage.