Operational Experience of a Centrifugal Particle Receiver Prototype

The centrifugal particle receiver “CentRec” is a solar tower receiver development by DLR based on a direct absorption receiver concept especially suitable for high temperature process heat and electricity generation applications. Ceramic particles are used as heat transfer and storage medium for temperatures up to 1000°C. A centrifugal particle receiver system including a CentRec receiver prototype has been tested up to 965°C average receiver outlet temperature in the research platform of DLR’s test facility Juelich Solar Tower, Germany. This paper describes the first test results with a focus on first operational experiences

Structural Optimization of a Line-Focussing Solar Collector With Stationary Absorber Tube

A preliminary study on a line concentrating solar collector with stationary absorber tube has revealed significant cost reduction and performance enhancement compared to state-of-the-art Parabolic Trough Collectors. To decide whether this so called Fixed Focus Parabolic Trough concept is worth continuing, a pre-design of the concentrator structure for such a collector must be investigated. In this paper, the effects of operating conditions represented by wind forces and dead load on the shape accuracy of the concentrator are determined via finite element method (FEM). An optimization procedure written in ANSYS is applied to determine appropriate geometry and dimensions of the structure to obtain best optical performance at lowest material consumption. To maintain a mean focus deviation of the reflected rays from the focal line of less than 6 mm under operating conditions, a specific weight of 14 kg/m2 could be reached. As structural elements of the collector are located between mirror and absorber, ray tracing analysis is performed for one selected conceptual design to estimate the effects of blocking and shading on the optical performance. The ray tracing revealed a reduction of the optical performance due to blocking and shading of 27 % for an incidence angle of 45° compared to 0° incidence angle

Development of Receivers for the DSG Process

The direct steam generation (DSG) in parabolic trough collectors is a promising option for improving the mature SEGS type parabolic trough solar thermal power plant technology. The European DISS and INDITEP projects have proven the feasibility of the DSG process in parabolic trough collectors under real solar conditions at the life size DISS test facility at the Plataforma Solar de Almería (PSA). Because of this successful demonstration the erection of the first DSG demonstration plant is expected for the near future. So far no commercial parabolic trough receivers, also known as heat collecting elements (HCE), are available for the DSG process. These receivers would have to withstand a higher operation pressure since the operation pressure of the receivers is equal to the life steam pressure of the power cycle which can be 100 bar and more. Furthermore the thermal load of the receivers is higher since the heat transfer in the superheating section of a DSG collector loop is worse than that of SEGS type collector loops. To solve this problem SCHOTT Rohrglas has decided to adapt their receivers to the specific needs of the DSG process. In collaboration with the German Aerospace Center (DLR) necessary modifications were identified and integrated into the design of the SCHOTT receiver. Prototypes of the receivers have been manufactured. The paper presents the design of the DSG receivers for the first time

Development of a window cooling for high temperature solar receivers

ANSYS/FLOTRAN had been used to calcualte the air flow in a gap between two quartz glass windows. This was done to design a cooling system for high temperature solar receivers, which are used to convert concentrated sunlight into high temperature heat. The most important thermal influences as radiation exchange between the windows and the absorber as well as the radiation to space of the pressure window had been considered. With a 2D axially symmetric parametric modell the CPU time was small enough to calculate severall varitations. The aim was to find out the best geometry for the cooling window for reaching the lowest possible glass temperatures by an minimum cooling mass flow and by adherence the possible pressure drop of the cooling system. The calculations showed that the best result could be reached by giving a swirl (around the middle axis) to the cooling flow. Therefore a special flange was designed for an uniform distribution and to give the swirl to the cooling flow. After manufactoring of the cooling window, the window was measured on a 3D measurement machine and the geometrie in the CFD modell was aligned to the real geometrie. Further calculations with the “real” gemetrie showed that the pressure drop will be less and the temperatures in the windows will be a little higher then in the design geometrie.The high temperature module was tested together with an gas turbine at the Plataforma Solar de Almeria (PSA) in south Spain. The first evaluation of the measurements showed that the cooling works well. The cooling flow works like CFD calculation predicted. Even the pressure drop was near the simulations

Infrared-Reflective Coating on Fused Silica for a Solar High-Temperature Receiver

In concentrating solar power, high-temperature solar receivers can provide heat to highly efficient cycles for electricity or chemical production. Excessive heating of the fused-silica window and the resulting recrystallization are major problems of high-temperature receivers using windows. Excessive window temperatures can be avoided by applying an infrared-reflective solar-transparent coating on the fused-silica window inside. Both glass temperatures and receiver losses can be reduced. An ideal coating reflects part of the thermal spectrum (λ>2.5 µm) of the hot absorber (1100°C) back onto it without reducing solar transmittance. The examined transparent conductive oxides (TCO) involve a high solar absorptance, inhibiting their use in high-concentration solar systems. Although conventional dielectric interference filters have a low solar absorption, the reflection of solar radiation which comes from various directions is too high. It was found that only rugate filters fulfill the requirements for operation under high-flux solar radiation with different incident angles. A thermodynamic qualification simulation of the rugate coating on a window of a flat-plate receiver showed a reduction of almost 175 K in mean window temperature and 11% in receiver losses compared to an uncoated window. Finally, a first 25-µm thick rugate filter was manufactured and optically characterized. The issue of this paper is to share the work done on the choice of filter type, filter design, thermodynamic evaluation, and deposition experiments

Development of a tube receiver for a solar-hybrid microturbine system

Solar-hybrid microturbine systems with cogeneration offer new possibilities for the generation of electricity and heat or air conditioning. The solar receiver is an important component of such a system. For a prototype system demo project a tube receiver for a 100kWe microturbine system is currently under development. The receiver is designed for air preheating up to 800°C at a pressure of 4.5 barabs. The challenge of the design is to find the right compromise between high efficiency, low pressure drop, high durability and low cost. The receiver consists of multiple metallic tubes, arranged in a cavity and connected in parallel. For the design the knowledge of local flux density, fluid and material temperature is required. A finite-element program coupled with a ray tracer was used for the layout. The final receiver design is described, which was optimized with respect to efficiency, material temperatures and pressure drop. Expected performance data for nominal load and off-design conditions will be presented, including the expected annual receiver and system performance. In addition, several possibilities for future improvements will be outlined

Effects of vertically ribbed surface roughness on the forced convective heat losses in central receiver systems

External receiver configurations are directly exposed to ambient wind. Therefore, a precise determination of the convective losses is a key factor in the prediction and evaluation of the efficiency of the solar absorbers. Based on several studies, the forced convective losses of external receivers are modeled using correlations for a roughened cylinder in a cross-flow of air. However at high wind velocities, the thermal efficiency measured during the Solar Two experiment was considerably lower than the efficiency predicted by these correlations. A detailed review of the available literature on the convective losses of external receivers has been made. Three CFD models of different level of detail have been developed to analyze the influence of the actual shape of the receiver and tower configuration, of the receiver shape and of the absorber panels on the forced convective heat transfer coefficients. The heat transfer coefficients deduced from the correlations have been compared to the results of the CFD simulations. In a final step the influence of both modeling approaches on the thermal efficiency of an external tubular receiver has been studied in a thermal FE model of the Solar Two receiver

Optimierung der Struktur eines linienfokussierenden Kollektors mit ortsfestem Absorber

ls neuer Ansatz für linienfokussierende Kollektoren wurde im DLR ein Konzentrator mit ortsfestem Absorberrohr entwickelt[1][2], der die Vorteile von Linearen Fresnel- und Parabolrinnenkollektoren vereint. Dieser Kollektor ist durch eine Segmentierung der Spiegelfläche gekennzeichnet, wodurch erreicht wird, dass Schwerpunkt und Brennlinie koinzidieren. In der hier vorgestellten Konzeptstudie wird ein FEM Modell des Kollektors hinsichtlich der optischen Performance und des Gewichts unter Betriebsbedingungen (Verformung durch Eigengewicht und Windlasten) untersucht und optimiert

Rectal surgery - risk factors for postoperative complications and influence of protective loop ileostomy on morbidity and course of therapy

Im Rahmen der Rektumkarzinomchirurgie erfolgt die Protektion der Anastomosen leitliniengerecht über die Anlage eines temporären Deviationsstomas in Ausführung als doppelläufiges Ileostoma oder doppelläufiges Kolostoma. Im klinischen Alltag entsteht der Eindruck, dass die Ileostomaanlage und -rückverlegung mit nicht unerheblicher Morbidität verbunden sind und zu Verzögerungen in der postoperativen Chemotherapie führen. Dehydratation ist in der Literatur als häufigste Komplikation der Ileostomie beschrieben. Ziel der Datenanalyse war einerseits die Erfassung der Morbidität von Rektumresektionen als Primäroperation unter besonderer Beachtung der Anastomoseninsuffizienzen. Andererseits sollte die Verweildauer der Ileostomie, die Rückverlegungsrate und die Morbidität, insbesondere die Dehydratation, in Abhängigkeit von verschiedenen therapierelevanten Parametern untersucht werden. Es erfolgte die retrospektive, statistische Analyse von demografischen, tumor- und therapierelevanten Daten von Patienten, die sich im Zeitraum vom 1.1.2013 bis zum 31.12.2016 in den DRK Kliniken Berlin | Westend einer Rektumresektion aufgrund eines Rektumkarzinoms unterzogen. Die Auswertung erfolgte über deskriptive Statistik und bivariate Korrelationen (Pearson, Kendall Tau-b, Chi²-Test). Anastomoseninsuffizienzen traten in 15,3% der Fälle auf. Als statistisch signifikante Einflussgröße auf das Auftreten einer Anastomoseninsuffizienz konnte der präoperative Hb Wert ermittelt werden (p = 0,02). Die Ileostomarückverlegungsrate betrug 87,1 %, die mediane Verweildauer der Ileostomata betrug 119 Tage (8-634 d). Mit steigendem Patientenalter sank die Ileostomaverweildauer (p < 0,01) ebenso wie die Durchführungsrate einer indizierten postoperativen Chemotherapie. Mit Indikation und Durchführung der postoperativen Chemotherapie, T- und N-Stadium sowie UICC Stadium korrelierte die Stomaverweildauer (alle p < 0,01). Die Rate an persistierenden Ileostomata betrug 13%. Ein hohes Patientenalter, T-, M- und UICC Klassifikation, R-Status und lange stationäre Verweildauer im Primäraufenthalt konnten als Risikofaktoren für die Persistenz des Ileostomas identifiziert werden. Die Morbidität nach Ileostomarückverlegung betrug 16,4 %, (11 Wundkomplikationen, 2 Anastomosenstenosen), die Re-Operationsrate betrug 11,4 %. Zusammenfassend kann festgestellt werden, dass die protektive Ileostomie im Rahmen der Rektumkarzinomchirurgie ein sicheres Verfahren mit geringer Rate an Major-Komplikationen und moderater Re-Operationsrate nach Ileostomarückverlegung darstellt. Die Stomaverweildauer hing im Wesentlichen vom Patientenalter und vom lokalen Tumorstadium sowie der Durchführung einer postoperativen Chemotherapie ab. Die Dehydratation durch hohen Flüssigkeitsverlust während der Ileostomaverweildauer betraf 4,8 % der Fälle und stellte somit ein moderates Risiko für die Patienten dar.Protection of an anastomosis in colorectal surgery is accomplished in accordance with consensus guidelines through the construction of a loop ileostomy or colostomy. Everyday clinical experience shows that the construction and reversal of an ileostomy can be associated with significant morbidity, which can delay beginning an adjuvant chemotherapy. Dehydration is listed in the literature as one of the most common such complications for the ileostomy. The goal of the data analysis was, on the one hand, to quantify the morbidity associated with resection of the rectum as a primary operation, especially regarding anastomotic leakage. On the other hand, we also examined the length of time until reversal of the ileostomy, the reversal rate and the morbidity, especially that of dehydration, dependent upon various clinically relevant parameters. The study is a retrospective statistical analysis of data relevant to the tumor, the demographics and the treatment of patients undergoing resection of the rectum due to rectal cancer at DRK-Kliniken Berlin Westend between January 1, 2013 and December 31, 2016. The evaluation of data was carried out through descriptive statistics and bivariate correlation (Pearson, Kendall’s Tau-b, Chi2). Anastomotic leakage occurred in 15,3% of the cases. The preoperative haemoglobin level was determined to be a statistically significant factor (p=0.02) for the occurrence of anastomotic leakage. The rate of ileostomy reversal was 87.1%, the median length of time until reversal was 119 days (8-634 days). With increasing age, the length of time until ileostomy reversal decreased (p<0.01), as well as the rate of patients receiving an adjuvant chemotherapy. The length of time until ileostomy reversal correlated with the indication for and carrying out of an adjuvant chemotherapy, the T and N status as well as the UICC classification (p<0.01 for each). The rate of patients keeping an ileostomy was 13%. The risk factors for keeping ileostomies were identified to be high patient age, T and M status, UICC classification, R status and length of hospital stay for the primary operation. The morbidity after reversal of the ileostomy was 16.4% (11 wound complications, 2 cases of anastomotic stricture) and the rate of revisional surgery was 11.4 %. In conclusion, it can be determined that in colorectal surgery the construction of a protective ileostomy is a safe procedure with a low rate of major complications and a moderate rate of revisional surgery after ileostomy reversal. The length of time until reversal depends essentially upon the patient age, tumor stage and adjuvant chemotherapy. Dehydration on account of fluid loss while carrying an ileostomy occurred in 4.8% of the cases, and, therefore, represents a moderate risk for patients