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Efficiency measurements at Vessingfoss power stationParr, Leif Ragnar Rundquist January 2007 (has links)
A measurement of the hydraulic turbine efficiency at the Vessingfoss hydro power station by the thermodynamic method has been attempted, but has not given the desired results. Two problems have been encountered. The high pressure side temperature measurements show an abnormal scatter resulting in standard deviations of sy=0.05ºC. The reason for the scatter may be temperature layers in the reservoir lake Nesjø. This theory has been investigated, but needs further work. The other problem has been the mechanical strength of the low pressure side collector probes. Two different collectors have been tried, and both have broken down. The second attempt was made with a collector design based on wire rope, which failed because the turnbuckles were under-dimensioned. With proper dimensions, this solution is interesting in the future, as it was easy to install and may contribute to lose collector weight. The relative turbine efficiency has been calculated based on pressures and levels measured during the thermodynamic test. An uncertainty analysis of the result has been carried out. The head loss has been calculated based on technical drawings of the penstock and loss coefficients from the literature.
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Biomass gasification integration in recuperative gas turbine cycles and recuperative fuel cell integrated gas turbine cycles : -Løver, Kristian Aase January 2007 (has links)
A multi-reactor, multi-temperature, waste-heat driven biomass thermochemical converter is proposed and simulated in the process simulation tool Aspen Plus. The thermochemical converter is in Aspen Plus integrated with a gas turbine power cycle and a combined fuel cell/gas turbine power cycle. Both power cycles are recuperative, and supply the thermochemical converter with waste heat. For result comparison, the power cycles are also integrated with a reference conventional single-reactor thermochemical converter, utilizing partial oxidation to drive the conversion process. Exergy analysis is used for assessment of the simulation results. In stand-alone simulation, the proposed thermochemical shows high performance. Cold gas efficiency is 108.0% and syngas HHV is 14.5 MJ/kg on dry basis. When integrated with the gas turbine power cycle, the proposed converter fails to improve thermal efficiency of the integrated cycle significantly, compared to reference converter. Thermal efficiency is 41.8% and 40.7%, on a biomass HHV basis, with the proposed and the reference converter respectively. This is despite superior cold gas efficiency for the proposed converter, and the gas turbine cycle is found not to be able to properly take advantage of the high chemical energy in the syngas of the proposed converter. When integrated with the combined fuel cell/gas turbine power cycle, the proposed converter significantly improves the thermal efficiency of the integrated cycle, compared to the reference converter. Thermal efficiency is 56.0% and 51.2%, on a biomass HHV basis, with the proposed and the reference converter respectively. The fuel cell is found to be able to take advantage of the high chemical energy in the syngas of the proposed converter, which is the main cause of increase in thermal efficiency. Operation of the proposed thermochemical converter is found to be feasible at a wide range of operating conditions, although low operating temperatures in the converter may cause problems at very high carbon conversion ratios.
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Contribution of humidity and pressure to PEMFC performance and durabilitySørli, Jan Gregor Høydahl January 2008 (has links)
In this work, a 23-1 designed experiment has been performed to evaluate the effect of selected operating conditions on PEMFC performance and durability. Relative humidity, clamping pressure and back pressure were studied at two levels for Gore MEAs and GDLs. Two replicated experiments were performed. An ON/OFF test cycle was used to accelerate degradation. Total duration of the tests, after a break in procedure suggested by Gore, was ten days. In addition to sampling of voltage and current response and ohmic resistance, effluents were manually sampled from both electrodes every 24 hours and analyzed. Experiments with low humidification levels showed inferior durability. The combination of high relative humidity (100 %), high clamping pressure (10 barg) and high back pressure (1.5barg) result in the best performance and the lowest degradation rate. Results indicate that relative humidity is important both for performance and durability. Generally, fluoride emission rates (FER) showed an increasing trend with time. Higher rates were observed at the cathode. For the experiment with low relative humidity (25 %), low clamping pressure (5 barg) and high back pressure (1.5 barg) FER was significantly higher compared to the other experiments. For all tests the sulfur emission rates (SER) are initial high. Rates are higher at the anode. For the experiment with high relative humidity, low clamping pressure and no back pressure, the SER was significantly higher than for the other experiments. The sustained high levels of sulfur are probably a result of sulfuric acid residue from production of the MEA and/or GDL. High humidification of gases appears to more effectively wash out the sulfur.
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CO2 Capture from Coal fired Power PlantsDugstad, Tore, Jensen, Esben Tonning January 2008 (has links)
Coal is the most common fossil resource for power production worldwide and generates 40% of the worlds total electricity production. Even though coal is considered a pollutive resource, the great amounts and the increasing power demand leads to extensive use even in new developed power plants. To cover the world's future energy demand and at the same time limit our effect on global warming, coal fired power plants with CO2 capture is probably a necessity. An Integrated Gasification Combined Cycle (IGCC) Power Plant is a utilization of coal which gives incentives for CO2 capture. Coal is partially combusted in a reaction with steam and pure oxygen. The oxygen is produced in an air separation process and the steam is generated in the Power Island. Out of the gasifier comes a mixture of mainly H2 and CO. In a shift reactor the CO and additional steam are converted to CO2 and more H2. Carbon dioxide is separated from the hydrogen in a physical absorption process and compressed for storage. Hydrogen diluted with nitrogen from the air separation process is used as fuel in a combined cycle similar to NGCC. A complete IGCC Power Plant is described in this report. The air separation unit is modeled as a Linde two column process. Ambient air is compressed and cooled to dew point before it is separated into oxygen and nitrogen in a cryogenic distillation process. Out of the island oxygen is at a purity level of 95.6% and the nitrogen has a purity of 99.6%. The production cost of oxygen is 0.238 kWh per kilogram of oxygen delivered at 25°C and 1.4bar. The oxygen is then compressed to a gasification pressure of 42bar. In the gasification unit the oxygen together with steam is used to gasify the coal. On molar basis the coal composition is 73.5% C, 22.8% H2, 3.1% O2, 0.3% N2 and 0.3% S. The gasification temperature is at 1571°C and out of the unit comes syngas consisting of 66.9% CO, 31.1% H2, 1.4% H2O, 0.3% N2, 0.2% H2S and 0.1% CO2. The syngas is cooled and fed to a water gas shift reactor. Here the carbon monoxide is reacted with steam forming carbon dioxide and additional hydrogen. The gas composition of the gas out of the shift reactor is on dry basis 58.2% H2, 39.0% CO2, 2.4% CO, 0.2% N2 and 0.1% H2S. Both the gasification process and shift reactor is exothermal and there is no need of external heating. This leads to an exothermal heat loss, but parts of this heat is recovered. The gasifier has a Cold Gas Efficiency (CGE) of 84.0%. With a partial pressure of CO2 at 15.7 bar the carbon dioxide is easily removed by physical absorption. After separation the solvent is regenerated by expansion and CO2 is pressurized to 110bar to be stored. This process is not modeled, but for the scrubbing part an energy consumption of 0.08kWh per kilogram CO2 removed is assumed. For the compression of CO2, it is calculated with an energy consumption of 0.11kWh per kilogram CO2 removed. Removal of H2S and other pollutive unwanted substances is also removed in the CO2 scrubber. Between the CO2 removal and the combustion chamber is the H2 rich fuel gas is diluted with nitrogen from the air separation unit. This is done to increase the mass flow through the turbine. The amount of nitrogen available is decided by the amount of oxygen produced to the gasification process. Almost all the nitrogen produced may be utilized as diluter except from a few percent used in the coal feeding procedure to the gasifier. The diluted fuel gas has a composition of 50.4% H2, 46.1% N2, 2.1% CO and 1.4% CO2. In the Power Island a combined cycle with a gas turbine able to handle large H2 amounts is used. The use of steam in the gasifier and shift reactor are integrated in the heat recovery steam generator (HRSG) in the steam cycle. The heat removed from the syngas cooler is also recovered in the HRSG. The overall efficiency of the IGCC plant modeled is 36.8%. This includes oxygen and nitrogen production and compression, production of high pressure steam used in the Gasification Island, coal feeding costs, CO2 removal and compression and pressure losses through the processes. Other losses are not implemented and will probably reduce the efficiency.
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International trade with electric powerÅrdal, Frode January 2009 (has links)
In 2003 the European Commission introduced the Directive 2003/54/EC and Regulation 1228/2003/EC which increased the focus on the liberalization of the European electricity market. The international electricity trade has increased and created new challenges related to cross-border transmission and compensation mechanisms. The focus of the report has been to discuss the development of the electricity market in Europe, and the status of international exchange. The report also discusses the concept of cross-border trade and transit, and investigates a proposed ITC model and whether correct investment incentives are given. Price data from the main power exchanges in Europe indicate that the market is experiencing increasingly integration and efficiency. There has also been a trend towards market based congestion management methods. Regional markets have successfully developed in Spain and Portugal (the Iberian market) and between France, Belgium and The Netherlands (the Trilateral Market Coupling, TLC). Further plans for regional coupling are also underway (see chapter 5. The most common definition of transit is the one adopted by ETSO (Association of European Transmission System Operators), where transit is defined as the minimum between exports and imports. This definition could create opportunities for market participants to manipulate transit income (discussed in chapter 5.3). The Inter-TSO compensation (ITC) model used in this report is based on the With-and-Without transit algorithm. The model only focuses on costs and load flow, and do not include market incentives or evaluation of benefits. The model bases the compensation calculation on the transit term, which can lead to misguided identification of network responsibility. Two scenarios were compared with a base case scenario in order to identify possible investment incentives. The first scenario included a situation where one of the cross-border lines in the network was constrained. Results from this simulation indicate that the transmission system operators involved would experience increased ITC payment, and therefore not receive investment incentives. The TSOs involved would benefit from the bottleneck in form of increased revenue (assuming Cost-Of-Service regulation). In the second scenario an extra cross-border line was implemented, and the situation was compared to the base case. The results from this simulation show that the TSOs involved would receive a positive effect in form of reduced ITC cost. The ITC mechanism would in this case be in line with the European Commission’s Regulation 1228/2003/EC, and give the involved TSOs correct investment incentives. The lack of correlated results in these two cases indicates that the ITC mechanism (in this case modeled by the WWT algorithm) cannot be regarded as relevant from an investment incentive perspective (more information found in chapter 7.3).
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Fixed Speed Electric Motor Drives for LNG Refrigeration Compressors. : Back-to-Back Starting Methods and Grid Consequences.Breistein, Hallvard January 2009 (has links)
Experimental studies as well as simulations have been performed on the Back-to-Back starting schemes low frequency-, partial frequency-, and soft -start-up. A Back-to-Back configuration of two synchronous machines has been established in the laboratory, upon which parameter estimation and start-up experiments have been performed. Extensive parameter estimation was conducted in order to replicate the laboratory machines in the simulation model as accurately as possible. This was done in order to verify the validity of the simulation model. Studies into the effects of inductance interconnecting the machines were made in the laboratory and in the simulation model. Effects of resistance and inertia were studied in the simulation model. It is concluded that the simulation model appears to be as reliable as is its input parameters. Discrepancies were found in line voltages, due to faulty implementation of field current replication. Full scale simulations using Motorformer parameters were performed in the simulation model, featuring low frequency- and soft -staring. The effects of an interconnecting cable were studied. It is concluded that low frequency starting appears to be most reliable and least violent starting method. However, it might be limited by the availability of a turbine. This is not the case for soft starting, which has a lower starting capability and is more violent to the motor damper- and field windings. Low frequency startig is the recommended starting method of the ones studied. Dynamic short circuit simulations were done on a fixed speed LNG-facility. The fixed speed alternative appears to be more stable when responding to a short circuit. This is because the motors contribute to upholding the voltage during a fault by delivering reactive power to the short circuit, and because the motors do not loose all torque as is the case for LCI drives when the voltage dip exceeds 20$%$. Further work is needed in up-scaling the experiments. A sophisticated simulation model should be established and its validity tested on the up-scaled experiments. Preliminary custom design of machines should be initiated depending on what starting scheme is chosen. Custom machine parameters should then be used in full scale simulation using the more sophisticated model.
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Power Production from Low Temperature Heat SourcesMidtsjø, Alexander January 2009 (has links)
As part of the energy recovery part of the ROMA (Resource Optimization and recovery in the Materials industry) project, a laboratory prototype power production system is being built and completed in 2009. The laboratory prototype is based on a new technology for power production from low to medium temperature heat sources (the off gas from electrolysis cells in the aluminum industry) where CO2 is used as a working medium in a trans-critical Rankine cycle. The laboratory rig consists of the power cycle with a prototype expander as the core unit, an air loop to provide the heat, and an ethylene glycol loop to provide condensation of the working fluid in the power cycle. As a preparation to the assembling and instrumentation of the prototype rig, a simulation and an uncertainty analysis were conducted for the prototype rig in the autumn of 2008. This report focuses on the continuation of that work by an experimental investigation of the individual loops and the components of the prototype rig. The emphasis of this investigation has been put on the air loop and the expander unit of the power cycle. This is basically because these are of great importance to the performance of the power production prototype rig. The air loop was thoroughly tested, and from the investigations it was discovered that there was an unfavorable temperature distribution of the air going into the air-to-CO2 heat exchanger. This is the heat exchanger where heat is provided to the power cycle. The source for this temperature maldistribution was identified, and solutions were investigated to improve on the problem without results. The reduced performance of the air loop was incorporated in a new simulation of the power cycle in order to quantify the consequences for the optimization of the power cycle. The simulation was carried out for warm air temperature of 80 °C. The new calculations showed a reduction in maximum net work output of 27 % compared to the original simulation. The optimal conditions for the power cycle were also changed as a consequence of the reduced air loop performance. The investigation of the expander unit revealed that the expander isentropic efficiency was a strong function of the pressure difference across the expander, and a weak function of the expander inlet pressure. It also revealed that overall the isentropic efficiency was much less than the value of 80 % which was used in the original simulation. A new simulation of the power cycle was carried out where the expander isentropic efficiency was incorporated as a function of the pressure difference across the expander. This function was based on the data from the expander testing. The simulation showed a reduction in maximum net work output from 225 W to about 60 W, for warm air temperature of 80 °C. The new expander characteristics also affected the optimization of the power cycle. The simulation results and the results from the prototype investigation will be important in the optimization and control procedures of the assembled prototype power production system.
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Hydro power scheduling in multi-owner river systemsBusuttil, Marie January 2010 (has links)
1. Initial problem formulation 2. Iterative approach building for one reservoir 3. Testing for two cascaded reservoirs 4. Testing for four cascaded reservoirs 5. Further work
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Decision support from monitoring of hydro power stations : An approach to the vision of monitoring systems giving decision support in operation of hydro power stationsMikkelsen, Joar Hylland January 2009 (has links)
This report is the results of the work on a master thesis concerning intelligent monitoring of hydro power stations. In the report two different types of computer software is investigated to find out whether they are suitable to make out a monitoring system capable of giving the user information about faults and unwanted operating conditions at an early stage. It is also investigated whether the software has proven the capability to detect faults and unwanted operating conditions. The different advantages and disadvantages of the two software products are commented and the two software products are compared. This report shows that the two software products are quite different. The software from Volve is software meant to construct an expert system capable of recognising faults from previous cases of faults. The software from SKF is software that gives intelligent machine diagnostics from analysis of vibration measurements in addition to measuring and trending of other variables. It also gives the user tools for analysing the root cause of faults influencing the bearing system of different industry machinery. This means that the software from SKF demands some involvement from the user to produce the best and most precise results. The expert system developed from the Volve software on the other hand is meant to present only results and advice to the user. The results from tests and simulations of the expert system developed by the Volve software are very limited. It is not possible to conclude which of the two software products is better before more tests of the Volve system is performed. In addition to the investigation of these two monitoring software products two different types of sensors are investigated. The sensors that are investigated are smoke sensors and sensors for detection of ultrasonic sound. Both types are commonly used in monitoring of industry processes similar to those in hydro power stations. These two sensors are capable of giving additional information to the monitoring system making it possible to detect faults that it is difficult to detect today. This is because the two sensor types perform measurements that the normal measuring equipment of today is incapable of. This will increase the information flow to the monitoring systems of hydro power stations making it possible to perform better and more precise monitoring.
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Wave Energy Conversion : Simulation Verification and Linearization of Direct Drive Wave Energy Converter with Variable DC-link Voltage ControlDitlefsen, Arne Marius January 2009 (has links)
Lowering the cost of wave energy conversion is an essential task for it to succeed as a future energy resource. In this work a converter, assumed cheaper than the regular back to back converter setting, have been investigated for a electric direct drive point absorber. Both experimental work and simulations are used in the analysis. In the experimental work, a permanent magnet generator with a 6-pulse diode rectifier, a DC-link and a DC/DC converter equivalent, was used. Steady state, dynamic and transient measurements were preformed and a simulation model was compared to the measurements. Good results were obtained and deviations were in general small, mostly +-3% for voltage and current measurements and +-8% for torque measurements. Based on transient measurements and simulations a general linearization of the system was made in order to obtain useful information about the system. A step up converter was used in the simulation and it demonstrated stable passive loading control. By using the information obtained by the linearization, the performance of the simulation model was improved by decreasing the DC-link capacitance. The modified simulation model had significant less torque ripple than the initial. The linearization model also can been used to identify time delay represented by the power take off unit in a wave energy converter. This will be done for a commercial size wave energy converter summer 2009.
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