Performance evaluation of a tidal current turbine with bidirectional symmetrical foils

As one might expect, tidal currents in terms of ebb and flood tides are approximately bidirectional. A Horizontal Axial Tidal Turbine (HATT) with unidirectional foils has to be able to face the current directions in order to maximize current energy harvesting. There are two regular solutions to keep a HATT always facing the direction of the flow, which are transferred from wind turbine applications. One is to yaw the turbine around the supporting structure with a yaw mechanism. The other is to reverse the blade pitch angle through 180° with a pitch-adjusting mechanism. The above solutions are not cost-effective in marine applications due to the harsh marine environment and high cost of installation and maintenance. In order to avoid the above disadvantages, a turbine with bidirectional foils is presented in this paper. A bare turbine with bidirectional foils is characterized in that it has nearly the same energy conversion capability in both tidal current directions without using the yaw or pitch mechanism. Considering the working conditions of the bidirectional turbine in which the turbine is installed on a mono-pile, the effect of the mono-pile on the turbine’s performance is evaluated in this paper, especially when the turbine is downstream of the mono-pile. The paper was focused on the evaluation of the hydrodynamic performance of the bidirectional turbine. The hydrodynamic performance of the bare bidirectional turbine without any supporting structure was evaluated based on a steady-state computational fluid dynamics (CFD) model and model tests. Performance comparison has been made between the turbine with bidirectional foils and the turbine with NACA foils. The effect of the mono-pile on the performance of the bidirectional turbine was studied by using the steady-state and the transient CFD model. The steady-state CFD model was used to evaluate the effect of the mono-pile clearance, which is the distance between the mono-pile and the turbine on the performance of the turbine. The transient CFD model was used to determine the time-dependent characteristics of the turbine, such as time-dependent power and drag coefficients. The results show that the bare bidirectional turbine has nearly the same energy conversion capability in both tidal current directions. The performance of the bidirectional turbine is inferior to the turbine with NACA foils. At the designed tip speed ratio, the power coefficient of the turbine with NACA foils is 0.4498, which increases by 1.6% compared to the 0.4338 of the bidirectional turbine. The turbine’s performance decreases due to the introduction of the mono-pile, and the closer the turbine is to the mono-pile, the greater effect on the turbine’s performance the mono-pile has. At the designed clearance of 1.5 DS, the presence of a mono-pile decreases the peak Cp value by 1.82% and 3.17% to a value of 0.4156 and 0.4004 for the turbine located in the mono-pile upstream and downstream, respectively. The mono-pile can result in the fluctuation of the turbine’s performance. This fluctuation will detrimentally harm the life of the turbine as it will lead to increased wear and fatigue issues

Chemical Looping Combustion and Chemical Looping with Oxygen Uncoupling Experiments in a Batch Reactor Using Spray-Dried CaMn1–xMxO3−δ (M = Ti, Fe, Mg) Particles as Oxygen Carriers

Chemical looping combustion and chemical looping with oxygen uncoupling (CLOU) with oxygen carrier particles consisting of CaMn1-xMxO3-delta (M = Ti, Fe, Mg) has been studied by consecutive oxidation and reduction experiments in a fluidized-bed batch reactor. The examined particles were produced by spray drying, and all did show a significant release of gas-phase oxygen to the inert atmosphere at 900 and 1000 degrees C. All particles also provided very high reactivity with syngas and methane. Some of the examined particles showed unfavorable fluidization characteristics, i.e., they formed dust during operation or showed agglomeration or defluidization tendencies. The crushing strength of the particles that formed dust was typically <1.2 N. The desired perovskite structure was detected in all samples by X-ray diffractometry. The materials that included iron and titanium had these elements incorporated in the perovskite structure, substituting manganese. When magnesium had been included, it was not incorporated into the crystal structure; instead, it was present as a separate phase of MgO. In addition to a perovskite phase, most samples also contained small amounts of marokite (CaMn2O4). Particles doped with MgO calcined at 1300 degrees C showed good fluidization behavior, as well as particularly high reactivity with fuel

Deactivation of a Pd/Pt Bimetallic Oxidation Catalyst Used in a Biogas-Powered Euro VI Heavy-Duty Engine Installation

The reduction of anthropogenic greenhouse gas emissions is crucial to avoid further warming of the planet. We investigated how effluent gases from a biogas powered Euro VI heavy-duty engine impact the performance of a bimetallic (palladium and platinum) oxidation catalyst. Using synthetic gas mixtures, the oxidation of NO, CO, and CH4\ua0before and after exposure to biogas exhaust for 900 h was studied. The catalyst lost most of its activity for methane oxidation, and the activity loss was most severe for the inlet part of the aged catalyst. Here, a clear sintering of Pt and Pd was observed, and higher concentrations of catalyst poisons such as sulfur and phosphorus were detected. The sintering and poisoning resulted in less available active sites and hence lower activity for methane oxidation

Innovative Oxygen Carriers for Chemical-looping Combustion

Chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) are combustion technologies where carbon dioxide is inherently obtained in pure form without any gas separation step. In the processes, fuel is introduced to the fuel reactor and combustion air is introduced to the air reactor. Circulating metal oxide particles transport oxygen from the air to the fuel reactor, and high purity CO2 can be obtained after steam condensation. Some metal oxides have the ability to release oxygen to the gas phase, or so-called uncoupling properties, which may facilitate fuel conversion. The metal oxide, named oxygen carrier, is the cornerstone of the CLC process. Prior to this work, NiO was the benchmark oxygen carrier for gaseous fuels, like natural gas. However, the high cost, toxicity and thermodynamic limitation of Ni would likely make it difficult to up-scale a process using this type of oxygen carrier. Thus, the focus in this work is on oxygen carriers based on cheaper and more environmentally benign materials, i.e. combined manganese oxides and CuO-based oxygen carriers. Both of these types of oxygen carriers have the propensity to release gas phase oxygen in the fuel reactor, something which was deemed highly beneficial. The main focus is on the combined materials, and this work presents the first major screening of these types of oxygen carriers. All oxygen carriers were manufactured by the commercial spray-drying method and examined in a batch fluidized reactor system with respect to parameters important for chemical-looping. Several combined manganese oxide systems were investigated in this work, with the main focus on three rather promising systems: i) calcium manganites, ii) manganese-silica and iii) manganese with magnesium. For the first system, Ca-Mn-X-O (X= Fe, Ti and Mg), all materials had perovskite structure and performed very well. Clear oxygen uncoupling ability and full conversion of CH4 were achieved in the batch testing. Adjusting the production parameters, i.e. calcination temperature, calcination time and milling time, the physical properties of the oxygen carrier can be enhanced. The oxygen carrier with molar composition CaMn0.775Mg0.1Ti0.125O3-δ was produced by a wide range of Mn- and Ti-sources available commercially at tonnage scales. All materials showed similar oxygen uncoupling behaviour and had the perovskite structure. This shows that this type of oxygen carrier not only can be produced with cheap raw materials, but is simple to produce independent of the material source. Although the oxygen carriers based on Mn-Si-O had limited oxygen release at lower temperatures, there was a remarkable increase in release at temperatures above 950C for particles with less than 45 wt% SiO2. Similarly, the ability to convert CH4 for these particles increased with temperature, and over 90% combustion could be achieved at temperatures at and above 950\ub0C. The third promising system investigated was a combination of Mn and Mg oxides. In this system, the uncoupling reactions were more pronounced at 900\ub0C for the material with a molar ratio of Mn/Mg of one. Also, the methane conversion for some samples studied was high, making this material yet another interesting alternative. CuO-based materials with different support materials have a seemingly fast release rate of oxygen, approaching equilibrium at 900\ub0C. Most investigated materials had the ability to fully convert CH4 at 925\ub0C at the experimental conditions. Some CuO-support combinations did not perform so well, for instance the Cu36FAl24 sample due to formation of Cu0.95Fe1.05AlO4. Several very promising oxygen carriers have been developed in this work. Some of them have been successfully tested in continuous operation at 120 kW scale. Further, the work has led to the development of calcium manganites ready to be up-scaled to large scale application. In addition to this, several other promising systems have been developed, which may not be ready for upscaling, but have great potential when optimized further

Innovative Oxygen Carriers for Chemical-looping Combustion

Chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) are combustion technologies where carbon dioxide is inherently obtained in pure form without any gas separation step. In the processes, fuel is introduced to the fuel reactor and combustion air is introduced to the air reactor. Circulating metal oxide particles transport oxygen from the air to the fuel reactor, and high purity CO2 can be obtained after steam condensation. Some metal oxides have the ability to release oxygen to the gas phase, or so-called uncoupling properties, which may facilitate fuel conversion. The metal oxide, named oxygen carrier, is the cornerstone of the CLC process. Prior to this work, NiO was the benchmark oxygen carrier for gaseous fuels, like natural gas. However, the high cost, toxicity and thermodynamic limitation of Ni would likely make it difficult to up-scale a process using this type of oxygen carrier. Thus, the focus in this work is on oxygen carriers based on cheaper and more environmentally benign materials, i.e. combined manganese oxides and CuO-based oxygen carriers. Both of these types of oxygen carriers have the propensity to release gas phase oxygen in the fuel reactor, something which was deemed highly beneficial. The main focus is on the combined materials, and this work presents the first major screening of these types of oxygen carriers. All oxygen carriers were manufactured by the commercial spray-drying method and examined in a batch fluidized reactor system with respect to parameters important for chemical-looping. Several combined manganese oxide systems were investigated in this work, with the main focus on three rather promising systems: i) calcium manganites, ii) manganese-silica and iii) manganese with magnesium. For the first system, Ca-Mn-X-O (X= Fe, Ti and Mg), all materials had perovskite structure and performed very well. Clear oxygen uncoupling ability and full conversion of CH4 were achieved in the batch testing. Adjusting the production parameters, i.e. calcination temperature, calcination time and milling time, the physical properties of the oxygen carrier can be enhanced. The oxygen carrier with molar composition CaMn0.775Mg0.1Ti0.125O3-δ was produced by a wide range of Mn- and Ti-sources available commercially at tonnage scales. All materials showed similar oxygen uncoupling behaviour and had the perovskite structure. This shows that this type of oxygen carrier not only can be produced with cheap raw materials, but is simple to produce independent of the material source. Although the oxygen carriers based on Mn-Si-O had limited oxygen release at lower temperatures, there was a remarkable increase in release at temperatures above 950C for particles with less than 45 wt% SiO2. Similarly, the ability to convert CH4 for these particles increased with temperature, and over 90% combustion could be achieved at temperatures at and above 950\ub0C. The third promising system investigated was a combination of Mn and Mg oxides. In this system, the uncoupling reactions were more pronounced at 900\ub0C for the material with a molar ratio of Mn/Mg of one. Also, the methane conversion for some samples studied was high, making this material yet another interesting alternative. CuO-based materials with different support materials have a seemingly fast release rate of oxygen, approaching equilibrium at 900\ub0C. Most investigated materials had the ability to fully convert CH4 at 925\ub0C at the experimental conditions. Some CuO-support combinations did not perform so well, for instance the Cu36FAl24 sample due to formation of Cu0.95Fe1.05AlO4. Several very promising oxygen carriers have been developed in this work. Some of them have been successfully tested in continuous operation at 120 kW scale. Further, the work has led to the development of calcium manganites ready to be up-scaled to large scale application. In addition to this, several other promising systems have been developed, which may not be ready for upscaling, but have great potential when optimized further

Controlling selectivity in direct conversion of methane into formaldehyde/methanol over iron molybdate via periodic operation conditions

The partial oxidation of methane over a Fe 2 (MoO 3 )4 powder catalyst was studied under transient inlet gas conditions. The preparation of the Fe 2 (MoO 4 ) 3 catalyst was performed using a hydrothermal synthesis route. Analytical-grade Fe(NO 3 ) 3 .9H 2 O and (NH 4 ) 6 Mo 7 O 24 .7H 2 O were dissolved separately in distilled water. The molybdate solution was then added dropwise to the iron nitrate solution under continuous stirring to form a homogeneous solution, which was pH-adjusted to 3 by adding NH 3 .H 2 O and HNO 3 . The solution was transferred to a Teflon lined autoclave, sealed, and kept at 140\ub0C for 12 h. The formed precipitate was then washed several times with distilled water and ethanol. At the lowest temperature, only CO can be observed, while at the higher temperatures, also HCHO and CO 2 are formed

Experimental investigation of binary and ternary combined manganese oxides for chemical-looping with oxygen uncoupling (CLOU)

Some binary and ternary combined manganese oxides of Mn with one or two additional metals or metalloids of Fe, Si, Ca and Mg were investigated as oxygen carriers for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). More specifically the following systems were investigated: (1) MnyMgOx, (2) CaMnO3-(Fe0.25Mn0.75)2O3, (3) CaMnO3-(Fe0.67Mn0.33)2O3, (4) CaMnO3-MnMgOx, (5) MnMgOx-(Fe0.25Mn0.75)2O3 and (6) Mn2SiOx-Fe2SiOx. The general trend was that the binary systems, where two metals are used in the formulation showed the most promising results in terms of oxygen uncoupling and reactivity. However, there are several ternary combinations which show a combination of high oxygen uncoupling, reactivity with methane and reasonable strength. A pseudo first-order effective rate constant was evaluated for the investigated particles. The measured rates are lower than for benchmark nickel oxide and calcium manganites, but higher than for ilmenite. The ternary System 6, Mn2SiOx-Fe2SiOx was investigated in more depth, including solid fuel experiments to determine the rate of oxygen release. At 850 and 900 °C (Mn0.5Fe0.5)2SiOx had the highest average reactivity, with a maximum average yield of 91.5% at 850 °C. On the other hand, at higher temperatures, the particles with the highest Mn content showed best behavior, i.e. (Mn0.67Fe0.33)2SiOx. Reactivity experiments with char in the FB reactor with this OC showed that the oxygen capacity for CLOU was high, 3.5 wt% at 950 °C, with a maximum release rate of 0.2 g O2/kg OC,s. The low rate of uncoupling means that the experiments with gaseous fuel were likely dominated by the direct gas-solid reaction, and not CLOU. X-ray powder diffraction suggests that the main reaction path is via (MnxFe1- x)2O3 to (MnxFe1- x)3O4, although the reaction between Mn7SiO12 to MnSiO3 cannot be ruled out as a possible route of oxygen transfer. This was supported by thermodynamic calculations of this multi-component system

Development of CaMn0.775Mg0.1Ti0.1Ti0.125O3-delta oxygen carriers produced from different Mn and Ti sources

Perovskite CaMa(0.775)Mg(0.1)Ti(0.125)O(3-delta) has attracted great interest as an oxygen carrier. To apply this material to a commercial scale chemical-looping unit, one key challenge is to find raw materials which are cheap and available in large quantities for production. Considering the content and price, Mn- and Ti-oxides are likely the raw materials having the major effect. Twelve Mn-oxide sources and four different TiO2 powders were evaluated for production of CaMa(0.775)Mg(0.1)Ti(0.125)O(3-delta) in this work. Particles with perovskite structure were successfully spray dried. All oxygen carriers showed oxygen uncoupling characteristics and most of them had a high reactivity, i.e. over 90% methane conversion already at 950 degrees C with a bed mass corresponding to 57 kg/MW, when examined in a batch fluidized-bed system at 900-1050 degrees C. Furthermore bulk density, crushing strength and resistance against attrition were studied. Although the attrition index varied, materials with good attrition resistance were identified. The rates of reaction were analyzed using two pseudo-first order apparent rate constants. The rates varied in a wide range, and are generally lower than with optimized Ni-based materials, but higher than with ilmenite. Still, the added oxygen uncoupling likely has a large positive effect at high degrees of solid conversion, something not seen with Ni-based materials

Examination of Perovskite Structure CaMnO 3-δ with MgO Addition as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Using Methane and Syngas

Perovskite structure oxygen carriers with the general formula CaMn x Mg 1-x O 3-δ were spray-dried and examined in a batch fluidized bed reactor. The CLOU behavior, reactivity towards methane, and syngas were investigated at temperature 900\ub0C to 1050\ub0C. All particles showed CLOU behavior at these temperatures. For experiments with methane, a bed mass corresponding to 57 kg/MW was used in the reactor, and the average CH 4 to CO 2 conversion was above 97% for most materials. Full syngas conversion was achieved for all materials utilizing a bed mass corresponding to 178 kg/MW. SEM/EDX and XRD confirmed the presence of MgO in the fresh and used samples, indicating that the Mg cation is not incorporated into the perovskite structure and the active compound is likely pure CaMnO 3-δ . The very high reactivity with fuel gases, comparable to that of baseline oxygen carriers of NiO, makes these perovskite particles highly interesting for commercial CLC application. Contrary to NiO, oxygen carriers based on CaMnO 3-δ have no thermodynamic limitations for methane oxidation to CO 2 and H 2 O, not to mention that the materials are environmentally friendly and can utilize much cheaper raw materials for production. The physical properties, crystalline phases, and morphology information were also determined in this work. \ua9 2013 Dazheng Jing et al