Performance of a NiO-based oxygen carrier for chemical looping combustion and reforming in a 120 kW unit

AbstractIn this study the performance of two different Ni-based oxygen carriers in a 120kW chemical looping pilot rig at Vienna University of Technology is presented. A dual circulating fluidized bed (DCFB) system has been designed with the important characteristics of high solid circulation, very low residence times and a high power to solid inventory ratio. For all presented results the pilot rig is fueled with methane at 140kW fuel power. For both oxygen carriers high CH4 conversion and CO2 yield is achieved. Air to fuel ratio and temperature are varied. CH4 conversion at higher air to fuel ratio as well as at higher temperature seems to decrease. This phenomenon is linked to the Ni/NiO ratio of the particle which determines the catalytic activity and thus influences the CH4 conversion and the CO2 yield

Hypertrophic cardiomyopathy is characterized by alterations of the mitochondrial calcium uniporter complex proteins: insights from patients with aortic valve stenosis versus hypertrophic obstructive cardiomyopathy

Introduction: Hypertrophies of the cardiac septum are caused either by aortic valve stenosis (AVS) or by congenital hypertrophic obstructive cardiomyopathy (HOCM). As they induce cardiac remodeling, these cardiac pathologies may promote an arrhythmogenic substrate with associated malignant ventricular arrhythmias and may lead to heart failure. While altered calcium (Ca2+) handling seems to be a key player in the pathogenesis, the role of mitochondrial calcium handling was not investigated in these patients to date.Methods: To investigate this issue, cardiac septal samples were collected from patients undergoing myectomy during cardiac surgery for excessive septal hypertrophy and/or aortic valve replacement, caused by AVS and HOCM. Septal specimens were matched with cardiac tissue obtained from post-mortem controls without cardiac diseases (Ctrl).Results and discussion: Patient characteristics and most of the echocardiographic parameters did not differ between AVS and HOCM. Most notably, the interventricular septum thickness, diastolic (IVSd), was the greatest in HOCM patients. Histological and molecular analyses showed a trend towards higher fibrotic burden in both pathologies, when compared to Ctrl. Most notably, the mitochondrial Ca2+ uniporter (MCU) complex associated proteins were altered in both pathologies of left ventricular hypertrophy (LVH). On the one hand, the expression pattern of the MCU complex subunits MCU and MICU1 were shown to be markedly increased, especially in AVS. On the other hand, PRMT-1, UCP-2, and UCP-3 declined with hypertrophy. These conditions were associated with an increase in the expression patterns of the Ca2+ uptaking ion channel SERCA2a in AVS (p = 0.0013), though not in HOCM, compared to healthy tissue. Our data obtained from human specimen from AVS or HOCM indicates major alterations in the expression of the mitochondrial calcium uniporter complex and associated proteins. Thus, in cardiac septal hypertrophies, besides modifications of cytosolic calcium handling, impaired mitochondrial uptake might be a key player in disease progression

Chemical looping combustion for 100% carbon capture - Design, operation and modeling of a 120kW pilot rig

Zsfassung in dt. SpracheChemical looping combustion (CLC) ist eine neuartige Technologie mit inhärenter CO2 Abscheidung. Es handelt sich dabei um einen zweistufigen Verbrennungsprozess bei dem Brennstoff und Luft nicht miteinander gemischt werden. Das Reaktorsystem besteht aus zwei separaten Reaktoren, einem Brennstoff-Reaktor und einem Luft-Reaktor.Ein Sauerstoffträger zirkuliert zwischen diesen beiden Reaktoren und transportiert den für die Verbrennung erforderlichen Sauerstoff.In dieser Arbeit wird ein neues Reaktorkonzept, das Dual Circulating Fluidized Bed (DCFB) Reaktorsystem, für chemical looping Prozesse vorgestellt. Dieses Konzept zeichnet sich durch hohe Feststoffzirkulation sowie optimierten Gas-Feststoffkontakt aus und ist für chemical looping combustion und reforming sehr gut einsetzbar. Der Aufbau und die bestimmenden Gleichungen dieses Systems werden am Beispiel der 120kW CLC Versuchsanlage an der Technischen Universität Wien erläutert und diskutiert. Zusätzlich werden das eingesetzte Kühlsystem und verschiedene Hilfsaggregate vorgestellt.Im ersten Betriebsjahr wurden verschiedene Sauerstoffträger in der Versuchsanlage eingesetzt. Ilmenit, ein Mineral mit der chemischen Formel FeTiO3, weist ein großes Potenzial für die Verbrennung von Synthesegasen (CO- und H2-reiche Gase) auf. Für die Verbrennung von CH4 wird allerdings ein katalytisch aktives Material benötigt. Experimente mit zwei verschiedenen Partikeln auf Ni-Basis zeigen, dass mit diesen Partikeln H2 und CO Umsätze erzielt werden, die sehr nah am thermodynamischen Gleichgewicht liegen. Der CH4 Umsatz ist ebenfalls fast vollständig (99%) und die CO2 Ausbeute erreicht Werte bis 95%. Eine weitere Steigerung dieser Werte wird durch eine Erhöhung des Reaktors erwartet. Im Gegensatz zu Ergebnissen von kleineren CLC Versuchsanlagen weisen die Partikel einen niedrigen Oxidationsgrad im gesamten Reaktorsystem auf. Dies scheint sich jedoch nicht negativ auf die Verbrennung auszuwirken.Neben der Auslegung und den Versuchsergebnissen wird in dieser Arbeit ein Ansatz zur Modellierung von zirkulierenden Wirbelschichtanlagen mit reagierendem Feststoff präsentiert. Das Modell konzentriert sich auf die im System auftretenden chemischen Reaktionen (Gas-Feststoffreaktionen) und verwendet ein einfaches hydrodynamisches Modell. Trotz des einfachen Modells können verschiedene Aspekte der CLC Versuchsanlage, wie zum Beispiel der sehr niedrige Oxidationsgrad der Partikel, vorausgesagt werden. Zusätzlich zur Modellierung werden auch die makroskopischen Vorgänge in den Partikeln während der Oxidation und der Reduktion erläutert sowie die Unterschiede zwischen Ergebnissen von Batch- und kontinuierlichen Versuchsanlagen diskutiert.Chemical looping combustion (CLC) is a novel technology with inherent separation of CO2. It is a two-step combustion process in which air and fuel are not mixed during combustion. The reactor system consists of two separate reactors, an air reactor and a fuel reactor. An oxygen carrier circulates between these two reactors and transports the necessary oxygen for combustion.A new reactor concept called the dual circulating fluidized bed (DCFB) reactor system is proposed for chemical looping processes. This concept features high solids circulation as well as optimized gas-solids contact and is highly suitable for chemical looping combustion and reforming. In this thesis, the main set-up of this concept is presented and the governing equations for the design of chemical looping combustors are discussed with the example of the 120kW CLC pilot rig at Vienna University of Technology. Additionally, the cooling system and different auxiliary units of the pilot rig are presented.In the first year of operation, different oxygen carriers have been applied to the pilot rig. Ilmenite, a natural mineral with the chemical formula FeTiO3, shows a high potential for the combustion of syngases (CO- and H2-rich gases). For the combustion of CH4, however, a catalytically active particle is required. Experiments with two different batches of Ni-based particles show H2 and CO conversions close to the thermodynamic maximum. The CH4 conversion is also almost complete (close to 99%) and the CO2 yield reaches values of up to 95%. Even greater improvement of these values is expected for increased reactor heights. Contrary to data reported for smaller continuous chemical looping units, the particles have a low degree of oxidation throughout the reactor system. This, however, does not seem to have a negative influence on combustion efficiency.In addition to the design and operating results of the pilot rig, this work also includes a modeling approach for circulating fluidized bed reactors with reactive solids and their combination in the DCFB system.The model mainly focuses on the chemical reactions taking place in the reactor system (gas-solid reactions) and applies a very simple hydrodynamic model. Despite the simplicity of the model, different aspects of the CLC pilot rig, such as the very low degree of particle oxidation, can be predicted. In the course of modeling, a discussion on the macroscopic progress of particle oxidation and reduction in the air and fuel reactors is included. This part focuses on the comparability as well as the fundamental differences of the results obtained from the two approaches to the investigation of CLC, i.e. batch reactor experiments and continuous looping experiments.<br /

Respiratory motion correction of PET using MR-constrained PET-PET registration

BACKGROUND: Respiratory motion in positron emission tomography (PET) is an unavoidable source of error in the measurement of tracer uptake, lesion position and lesion size. The introduction of PET-MR dual modality scanners opens a new avenue for addressing this issue. Motion models offer a way to estimate motion using a reduced number of parameters. This can be beneficial for estimating motion from PET, which can otherwise be difficult due to the high level of noise of the data. METHOD: We propose a novel technique that makes use of a respiratory motion model, formed from initial MR scan data. The motion model is used to constrain PET-PET registrations between a reference PET gate and the gates to be corrected. For evaluation, PET with added FDG-avid lesions was simulated from real, segmented, ultrashort echo time MR data obtained from four volunteers. Respiratory motion was included in the simulations using motion fields derived from real dynamic 3D MR volumes obtained from the same volunteers. RESULTS: Performance was compared to an MR-derived motion model driven method (which requires constant use of the MR scanner) and to unconstrained PET-PET registration of the PET gates. Without motion correction, a median drop in uncorrected lesion [Formula: see text] intensity to [Formula: see text] and an increase in median head-foot lesion width, specified by a minimum bounding box, to [Formula: see text] was observed relative to the corresponding measures in motion-free simulations. The proposed method corrected these values to [Formula: see text] ([Formula: see text] ) and [Formula: see text] ([Formula: see text] ) respectively, with notably improved performance close to the diaphragm and in the liver. Median lesion displacement across all lesions was observed to be [Formula: see text] without motion correction, which was reduced to [Formula: see text] ([Formula: see text] ) with motion correction. DISCUSSION: This paper presents a novel technique for respiratory motion correction of PET data in PET-MR imaging. After an initial 30 second MR scan, the proposed technique does not require use of the MR scanner for motion correction purposes, making it suitable for MR-intensive studies or sequential PET-MR. The accuracy of the proposed technique was similar to both comparative methods, but robustness was improved compared to the PET-PET technique, particularly in regions with higher noise such as the liver

Operating experience with chemical looping combustion in a 120 kW dual circulating fluidized bed (DCFB) unit

AbstractIn this study, first operating experience with a 120 kW chemical looping pilot rig is presented. The dual circulating fluidized bed reactor system and its auxiliary units are discussed. Two different oxygen carries, i.e. ilmenite, which is a natural iron titanium ore and a designed Ni-based particle, are tested in the CLC unit. The pilot rig is fueled with H2, CO and CH4 respectively at a fuel power of 65–145 kW. High solids circulation, very low solids residence time and low solids inventory are observed during operation. Due to the scalability of the design concept, these characteristics should be quite similar to those of commercial CLC power plants. Ilmenite shows a high potential for the combustion of H2 rich gases (e.g. from coal gasification with steam). The H2 conversion is quite high but there is still a high potential for further improvement. The Ni-based oxygen carrier achieves the thermodynamic maximum H2 and CO conversion and also very high CH4 conversion. A variation of the air/fuel ratio and the reaction temperature indicates that the Ni/NiO ratio of the particle has a high influence on the performance of the chemical looping combustor

The incidence of lumbar ligamentum flavum midline gaps

Lumbar epidural anesthesia and analgesia has gained increasing importance in perioperative pain therapy for abdominal and lower limb surgery. The loss-of-resistance technique, used to identify the epidural space, is thought to rely on the penetration of the ligamentum flavum. However, the exact morphology of the ligamentum flavum at different vertebral levels remains controversial. Therefore, in this study, we directly investigated the incidence of lumbar ligamentum flavum midline gaps in embalmed cadavers. Vertebral column specimens were obtained from 45 human cadavers. On each dissected level, ligamentum flavum midline gaps were recorded. The incidence of midline gaps per number of viable specimens at the following levels was: L1-2 = 10 of 45 (22.2%), L2-3 = 5 of 44 (11.4%), L3-4 = 5 of 45 (11.1%), L4-5 = 4 of 43 (9.3%), L5/S1 = 0 of 33 (0%). In conclusion, the present study determined the frequency of lumbar ligamentum flavum midline gaps. Gaps in the lumbar ligamentum flavum are most frequent between L1 and L2 but are more rare below this level. When using the midline approach, the ligamentum flavum may not impede entering the epidural space in all patients. IMPLICATIONS: The ligamentum flavum is a crucial anatomical landmark for the safe performance of epidural anesthesia. However, the present study demonstrates some failure of the lumbar ligamentum flavum as a landmark. This may mean that, using a midline approach, one cannot always rely on the ligamentum flavum as a perceptible barrier to epidural needle advancemen