The stability of the grid is jeopardized with the large percentage of non-dispatchable renewables like wind power and also with increasing solar power. This creates various problems because these forms of energy are v...The stability of the grid is jeopardized with the large percentage of non-dispatchable renewables like wind power and also with increasing solar power. This creates various problems because these forms of energy are very volatile and difficult to predict. In most countries the in-feed of these sources must not be curtailed. In addition most of the renewables do not provide short circuit capacity and inertia in the same way as classical units and so further worsen the stability of the grid. The growing exploitation of wind and solar might be limited due to grid stability problems. In order to compensate those problems a large amount of reserve capacity is needed and therefore new technologies for electricity storage are required. Hydraulic pumped storage—the classical storage technology—has some disadvantages. These plants are in mountain regions often far away from wind farms. The distance to the wind farms mean additional loading for the already stressed grid and additional transmission losses. To compensate the very volatile wind energy, the pump input power should be varied continuously. This is so far only possible with variable speed units. Up to now double-fed asynchronous motor-generators are used which are rather expensive. In order to provide a solution for the described situation, ANDRITZ HYDRO has developed a new innovative concept of decentralized pump storage plants. Small standardized pump turbines are combined with a synchronous motor-generator and a full size converter which allows speed variation in pump and turbine mode over a wide range. These plants can be built locally close to wind farms and other sources to be balanced, allowing the increase of renewable energy without increasing the transmission line capacity. For the future smart grids this will be a key storage technology. This concept is reliable, innovative and more economic than other storage technologies.展开更多
The understanding of enzymatic saccharification of pretreated lignocellulosic material is of great importance. There are several important commercially available enzymes in the market that are used for this purpose. T...The understanding of enzymatic saccharification of pretreated lignocellulosic material is of great importance. There are several important commercially available enzymes in the market that are used for this purpose. The conditions of pH and temperature performance of any particular enzyme are very well defined and it is clearly indicated by its manufacturer and it depends on the type of enzyme or enzymes in the complex pool. It is well know that commercial cellulases work best at pH around 4.8-5.0 and as a consequence this is widely used in the industry and the literature. In this study it was found that optimum pH of cellulases is different than that recommended by its manufacturer at higher solids load saccharification. The optimum pH changes depending on the consistency or solids loads of the matrix where the enzyme is acting upon. Steam exploded corn stover was tested with cellulases and xylanases at different pH, consistencies and ionic strength. Results showed that the optimum pH at lower consistency （1% w/w） is the same as the one recommended by the manufacturer and in the literature; however at higher consistency the value obtained was higher （pH 5.5 to pH 6.5） instead ofpH 4.8. The difference could represent up to 30-50% higher yields and hence of great importance for the economics of second generation fuel production. An explanation of this behavior could be associated with the Donnan effect theory. This effect indicates that the presence of charged groups in the fiber matrix creates a pH gradient within the slurry. If the charged groups are negatively charged this would create a local or internal pH lower than the surrounding liquid pH. This could explain why by reducing the concentration of H^＋ higher enzymatic conversion yields were observed.展开更多
The first part of this paper summarizes relevant literature information, which rationalizes our selection of chemicals. The second part reports some preliminary screening results. We have investigated a wide range of ...The first part of this paper summarizes relevant literature information, which rationalizes our selection of chemicals. The second part reports some preliminary screening results. We have investigated a wide range of reagents, chosen for their different chemistries and divided into seven classes: (1) reducing agents, (2) reduced sulfur compounds, (3) hydrogen donors, (4) antioxidants and radical scavengers, (5) nucleophiles, (6) chelating agents, and (7) oxidizing bleaching agents. It is noted that some chemical reagents fall into more than one class. The obtained results will be discussed with respect to the effectiveness of each class.展开更多
End windings of generators are excited to vibrations due to electromagnetic forces which can cause severe damage and noise. To avoid this, it is important to predict the natural frequencies and modes of the end windin...End windings of generators are excited to vibrations due to electromagnetic forces which can cause severe damage and noise. To avoid this, it is important to predict the natural frequencies and modes of the end windings with finite elements. Due to the complex structure and unknown boundary conditions, the conventionally calculation of stator end windings has been very difficult and time consuming up to now. This paper describes the development of a full parameterized modeling tool, which allows a quick calculation of natural frequencies during the design phase of the generator. To keep the computing time low, it is important to find a way to get exact calculation results without detailed modeling of all pans. Additionally, special attention was paid to the active part, which has been replaced by spring-damper elements, and the determination of their stiffness via experimental modal analysis combined with finite element calculations.展开更多
The end windings of generators are excited to vibrations due to electromagnetic forces which can cause severe damage （especially in case of resonance） and noise. To avoid this, it is important to predict the natural...The end windings of generators are excited to vibrations due to electromagnetic forces which can cause severe damage （especially in case of resonance） and noise. To avoid this, it is important to predict the natural frequencies and modes of the end windings with finite elements during the design process. Hence, a material model of the complete stator bar is necessary. This paper shows the development of such a material model. The composite structure of a stator bar is quite complex and makes it impossible to provide a quick calculation of the eigenvalues. That is the reason for using a suitable, homogeneously, geometry based solid model. Special attention was paid to the experimental determination of the material characteristics of the orthotropic composite space brackets. The numerical results have been evaluated against measurements. Eigenvalues, Young＇s modulus, and shear modulus have been experimentally investigated.展开更多
Over the past 13 years, ANDRITZ Hydro has developed an in-house tool based on the SPH-ALE method for applications in flow simulations in hydraulic turbines. The initial motivation is related to the challenging simulat...Over the past 13 years, ANDRITZ Hydro has developed an in-house tool based on the SPH-ALE method for applications in flow simulations in hydraulic turbines. The initial motivation is related to the challenging simulation of free surface flows in Pelton turbines, where highly dynamic water jets interact with rotating buckets, creating thin water jets traveling inside the housing and possibly causing disturbances on the runner. The present paper proposes an overview of industrial applications allowed by the developed tool, including design evaluation of Pelton runners and casings, transient operation of Pelton units and free surface flows in hydraulic structures.展开更多
文摘The stability of the grid is jeopardized with the large percentage of non-dispatchable renewables like wind power and also with increasing solar power. This creates various problems because these forms of energy are very volatile and difficult to predict. In most countries the in-feed of these sources must not be curtailed. In addition most of the renewables do not provide short circuit capacity and inertia in the same way as classical units and so further worsen the stability of the grid. The growing exploitation of wind and solar might be limited due to grid stability problems. In order to compensate those problems a large amount of reserve capacity is needed and therefore new technologies for electricity storage are required. Hydraulic pumped storage—the classical storage technology—has some disadvantages. These plants are in mountain regions often far away from wind farms. The distance to the wind farms mean additional loading for the already stressed grid and additional transmission losses. To compensate the very volatile wind energy, the pump input power should be varied continuously. This is so far only possible with variable speed units. Up to now double-fed asynchronous motor-generators are used which are rather expensive. In order to provide a solution for the described situation, ANDRITZ HYDRO has developed a new innovative concept of decentralized pump storage plants. Small standardized pump turbines are combined with a synchronous motor-generator and a full size converter which allows speed variation in pump and turbine mode over a wide range. These plants can be built locally close to wind farms and other sources to be balanced, allowing the increase of renewable energy without increasing the transmission line capacity. For the future smart grids this will be a key storage technology. This concept is reliable, innovative and more economic than other storage technologies.
文摘The understanding of enzymatic saccharification of pretreated lignocellulosic material is of great importance. There are several important commercially available enzymes in the market that are used for this purpose. The conditions of pH and temperature performance of any particular enzyme are very well defined and it is clearly indicated by its manufacturer and it depends on the type of enzyme or enzymes in the complex pool. It is well know that commercial cellulases work best at pH around 4.8-5.0 and as a consequence this is widely used in the industry and the literature. In this study it was found that optimum pH of cellulases is different than that recommended by its manufacturer at higher solids load saccharification. The optimum pH changes depending on the consistency or solids loads of the matrix where the enzyme is acting upon. Steam exploded corn stover was tested with cellulases and xylanases at different pH, consistencies and ionic strength. Results showed that the optimum pH at lower consistency （1% w/w） is the same as the one recommended by the manufacturer and in the literature; however at higher consistency the value obtained was higher （pH 5.5 to pH 6.5） instead ofpH 4.8. The difference could represent up to 30-50% higher yields and hence of great importance for the economics of second generation fuel production. An explanation of this behavior could be associated with the Donnan effect theory. This effect indicates that the presence of charged groups in the fiber matrix creates a pH gradient within the slurry. If the charged groups are negatively charged this would create a local or internal pH lower than the surrounding liquid pH. This could explain why by reducing the concentration of H^＋ higher enzymatic conversion yields were observed.
文摘The first part of this paper summarizes relevant literature information, which rationalizes our selection of chemicals. The second part reports some preliminary screening results. We have investigated a wide range of reagents, chosen for their different chemistries and divided into seven classes: (1) reducing agents, (2) reduced sulfur compounds, (3) hydrogen donors, (4) antioxidants and radical scavengers, (5) nucleophiles, (6) chelating agents, and (7) oxidizing bleaching agents. It is noted that some chemical reagents fall into more than one class. The obtained results will be discussed with respect to the effectiveness of each class.
文摘End windings of generators are excited to vibrations due to electromagnetic forces which can cause severe damage and noise. To avoid this, it is important to predict the natural frequencies and modes of the end windings with finite elements. Due to the complex structure and unknown boundary conditions, the conventionally calculation of stator end windings has been very difficult and time consuming up to now. This paper describes the development of a full parameterized modeling tool, which allows a quick calculation of natural frequencies during the design phase of the generator. To keep the computing time low, it is important to find a way to get exact calculation results without detailed modeling of all pans. Additionally, special attention was paid to the active part, which has been replaced by spring-damper elements, and the determination of their stiffness via experimental modal analysis combined with finite element calculations.
文摘The end windings of generators are excited to vibrations due to electromagnetic forces which can cause severe damage （especially in case of resonance） and noise. To avoid this, it is important to predict the natural frequencies and modes of the end windings with finite elements during the design process. Hence, a material model of the complete stator bar is necessary. This paper shows the development of such a material model. The composite structure of a stator bar is quite complex and makes it impossible to provide a quick calculation of the eigenvalues. That is the reason for using a suitable, homogeneously, geometry based solid model. Special attention was paid to the experimental determination of the material characteristics of the orthotropic composite space brackets. The numerical results have been evaluated against measurements. Eigenvalues, Young＇s modulus, and shear modulus have been experimentally investigated.
文摘Over the past 13 years, ANDRITZ Hydro has developed an in-house tool based on the SPH-ALE method for applications in flow simulations in hydraulic turbines. The initial motivation is related to the challenging simulation of free surface flows in Pelton turbines, where highly dynamic water jets interact with rotating buckets, creating thin water jets traveling inside the housing and possibly causing disturbances on the runner. The present paper proposes an overview of industrial applications allowed by the developed tool, including design evaluation of Pelton runners and casings, transient operation of Pelton units and free surface flows in hydraulic structures.
