An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350ºC and 200ºC, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with CO2 and traces of CH4, CO, and saturated H2O. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Chemical Engineering))--North-West University, Potchefstroom Campus, 2006.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

An investigation was undertaken to determine the feasibility of increasing the hydrogen production rate by coupling the water gas shift (WGS) process to the hybrid sulphur process (HyS). This investigation also involved the technical and economical analysis of the water gas shift and the H2 separation by means of Pressure swing adsorption (PSA) process. A technical analysis of the water gas shift reaction was determined under the operating conditions selected on the basis of some information available in the literature. The high temperature system (HTS) and low temperature system (LTS) reactors were assumed to be operated at temperatures of 350°C and 200°C, respectively. The operating pressure for both reactors was assumed to be 30 atmospheres. The H2 production rate of the partial oxidation (POX) and the WGS processes was 242T/D, which is approximately two times the amount produced by the HyS process alone. The PSA was used for the purification process leading to a hydrogen product with a purity of 99.99%. From the total H2 produced by the POX and the WGS processes only 90 percent of H2 is recovered in the PSA. The unrecovered H2 leaves the PSA as a purge gas together with C02 and traces of CH4, CO, and saturated H20. The estimated capital cost of the WGS plant with PSA is about US$50 million. The production cost is highly dependent on the cost of all of the required raw materials and utilities involved. The production cost obtained was US $1.41/kg H2 based on the input cost of synthesis gas as produced by the POX process. In this case the production cost of synthesis gas based on US $6/GJ for natural gas and US $0/Ton for oxygen was estimated to be US $0.154/kg. By increasing the oxygen and natural gas cost, the corresponding increase in synthesis gas has resulted in an increase in H2 production cost of US $1.84/kg. / Thesis (M.Sc. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2009.

An experimental pressure swing adsorption unit has been constructed and used to investigate the separation of carbon dioxide from carbon dioxide enriched air using both an activated carbon and a type 5A molecular sieve adsorbent. Continuous, cyclic operation was achievedusing a pair of fixed bed adsorbers. At any one time the feed gas entered one bed at a high pressure and part of the purified gas was returned to the other bed at a reduced pressure to provide countercurrent regeneration of the adsorbent. The beds of adsorbent used were each nominally 0.165m diameter and Im. deep. Separations were carried out at approximately ambient temperature using air flow rates in the range 0.15 to 0.95 kg/m2s and inlet carbon dioxide concentrations'in the range 0.1 to 1.5% v/v. Adsorption pressures of 2 to 6.4 bar were examined, the desorption pressure being maintained throughout at essentially 1.0 bar. The period time was varied from 30 to 900 seconds and the revert ratio (i. e. the ratio of the product gas returned for desorption to the total feed rate to the unit) was varied from 0 to 1.0. The carbon dioxide separation efficiency was found to increase markedly as the adsorption pressure and the revert ratio were increased whereas it was relatively insensitive to variations in feed rate and, more particularly, feed concentration. The performance of the molecular sieve adsorbent was found to be very sensitive to the presence of moisture in the feed gas. In contrast the carbon dioxide efficiencies observed with Lhe activated carbon were unaffected by the presence of small amounts (circa 100 ppm) of moisture in the feed. A theoretical model has been proposed for predicting the performance of pressure swing adsorption systems of the type investigated and approximate analytical equations and more precise numerical techniques have been established to represent its solution. The approximate analytical solutions were found to give close agreement with the more precise methods examined under conditions corresponding to low values of a dimensionless period time parameter. The proposed theoretical model incorporates an effective irean mass transfer coefficient to represent the diffusion process within the adsorbent particles. Methods for estimation of the value of this coefficient based on the limiting conditions of a periodic constant surface flux or a periodic constant surface concentration are presented. The experimental performance data were analysed in terms of the proposed analytical solution to give values of the apparent solid phase mass transfer coefficient for comparison with those predicted theoretically. In general the apparent experimental values were consistently less than the predicted values. In addition the relationship between the experimental and predicted coefficients was found to be dependent on both the nature of the adsorbent and a parameter formed by the product of the revert ratio and the adsorption to desorption pressure ratio. Empirical correlating equations which incorporate this dependence are presented.

The global market for membrane separation technologies is forecast to reach $16 billion by the year 2017 due to wide adoption of the membrane technology across various end-use markets. With the growth in demand for high quality products, stringent regulations, environmental concerns, and exhausting natural resources, membrane separation technologies are forecast to witness significant growth over the long term (Global Industry Analysts Inc., 2011). The future of membrane technology promises to be equally exciting as new membrane materials, processes and innovations make their way to the marketplace. The current trend in membrane gas separation industry is, however, to develop robust membranes, which exhibit superior separation performance, and are reliable and durable for particular applications. Process simulation allows the investigation of operating and design variables in the process, and in new process configurations. An optimal operating condition and/or process configuration could possibly yield a better separation performance as well as cost savings. Moreover, with the development of new process concepts, new membrane applications will emerge. The thesis addresses developing models that can be used to help in the design and operation of CO2 capture processes. A mathematical model for the dynamic performance of gas separation with high flux, asymmetric hollow fiber membranes was developed considering the permeate pressure build-up inside the fiber bore and cross flow pattern with respect to the membrane skin. The solution technique is advantageous since it requires minimal computational effort and provides improved solution stability. The model predictions and the robustness of the numerical technique were validated with experimental data for several membrane systems with different flow configurations. The model and solution technique were applied to investigate the performance of several membrane module configurations for air separation and methane recovery from biogas (landfill gas or digester gas). Recycle ratio plays a crucial role, and optimum recycle ratios vital for the retentate recycle to permeate and permeate recycle to feed operation were found. From the concept of two recycle operations, complexities involved in the design and operation of continuous membrane column were simplified. Membrane permselectivity required for a targeted separation to produce pipeline quality natural gas by methane-selective or nitrogen-selective membranes was calculated. The study demonstrates that the new solution technique can conveniently handle the high-flux hollow fiber membrane problems with different module configurations. A section of the study was aimed at rectifying some commonly believed perceptions about pressure build-up in hollow fiber membranes. It is a general intuition that operating at higher pressures permeates more gases, and therefore sometimes the membrane module is tested or characterized at lower pressures to save gas consumption. It is also perceived that higher pressure build-up occurs at higher feed pressures, and membrane performance deteriorates at higher feed pressures. The apparent and intrinsic permeances of H2 and N2 for asymmetric cellulose acetate-based hollow fiber membranes were evaluated from pure gas permeation experiments and numerical analysis, respectively. It was shown that though the pressure build-up increases as feed pressure increases, the effect of pressure build-up on membrane performance is actually minimized at higher feed pressures. Membrane performs close to its actual separation properties if it is operated at high feed pressures, under which conditions the effect of pressure build-up on the membrane performance is minimized. The pressure build-up effect was further investigated by calculating the average loss and percentage loss in the driving force due to pressure build-up, and it was found that percentage loss in driving force is less at high feed pressures than that at low feed pressures. It is true that unsteady state cyclic permeation process can potentially compete with the most selective polymers available to date, both in terms selectivity and productivity. A novel process mode of gas separation by means of cyclic pressure-vacuum swings for feed pressurization and permeate evacuation using a single pump was evaluated for CO2 separation from flue gas. Unlike transient permeation processes reported in the literature which were based on the differences in sorption uptake rates or desorption falloff rates, this process was based on the selective permeability of the membrane for separations. The process was analyzed to elucidate the working principle, and a parametric study was carried out to evaluate the effects of design and operating parameters on the separation performance. It was shown that improved separation efficiency (i.e., product purity and throughput) better than that of conventional steady-state permeation could be obtained by means of pressure-vacuum swing permeation. The effectiveness of membrane processes and feasibility of hybrid processes combining membrane permeation and conventional amine absorption process were investigated for post-combustion CO2 capture. Traditional MEA process uses a substantial amount of energy at the stripper reboiler when CO2 concentration increases. Several single stage and multi-stage membrane process configurations were simulated for a target design specification aiming at possible application in enhanced oil recovery. It was shown that membrane processes offer the lowest energy penalty for post-combustion CO2 capture and likely to expand as more and more CO2 selective membranes are developed. Membrane processes can save up to 20~45% energy compared to the stand-alone MEA capture processes. A comparison of energy perspective for the CO2 capture processes studied was drawn, and it was shown that the energy requirements of the hybrid processes are less than conventional MEA processes. The total energy penalty of the hybrid processes decreases as more and more CO2 is removed by the membranes.

The global market for membrane separation technologies is forecast to reach $16 billion by the year 2017 due to wide adoption of the membrane technology across various end-use markets. With the growth in demand for high quality products, stringent regulations, environmental concerns, and exhausting natural resources, membrane separation technologies are forecast to witness significant growth over the long term (Global Industry Analysts Inc., 2011). The future of membrane technology promises to be equally exciting as new membrane materials, processes and innovations make their way to the marketplace. The current trend in membrane gas separation industry is, however, to develop robust membranes, which exhibit superior separation performance, and are reliable and durable for particular applications. Process simulation allows the investigation of operating and design variables in the process, and in new process configurations. An optimal operating condition and/or process configuration could possibly yield a better separation performance as well as cost savings. Moreover, with the development of new process concepts, new membrane applications will emerge. The thesis addresses developing models that can be used to help in the design and operation of CO2 capture processes. A mathematical model for the dynamic performance of gas separation with high flux, asymmetric hollow fiber membranes was developed considering the permeate pressure build-up inside the fiber bore and cross flow pattern with respect to the membrane skin. The solution technique is advantageous since it requires minimal computational effort and provides improved solution stability. The model predictions and the robustness of the numerical technique were validated with experimental data for several membrane systems with different flow configurations. The model and solution technique were applied to investigate the performance of several membrane module configurations for air separation and methane recovery from biogas (landfill gas or digester gas). Recycle ratio plays a crucial role, and optimum recycle ratios vital for the retentate recycle to permeate and permeate recycle to feed operation were found. From the concept of two recycle operations, complexities involved in the design and operation of continuous membrane column were simplified. Membrane permselectivity required for a targeted separation to produce pipeline quality natural gas by methane-selective or nitrogen-selective membranes was calculated. The study demonstrates that the new solution technique can conveniently handle the high-flux hollow fiber membrane problems with different module configurations. A section of the study was aimed at rectifying some commonly believed perceptions about pressure build-up in hollow fiber membranes. It is a general intuition that operating at higher pressures permeates more gases, and therefore sometimes the membrane module is tested or characterized at lower pressures to save gas consumption. It is also perceived that higher pressure build-up occurs at higher feed pressures, and membrane performance deteriorates at higher feed pressures. The apparent and intrinsic permeances of H2 and N2 for asymmetric cellulose acetate-based hollow fiber membranes were evaluated from pure gas permeation experiments and numerical analysis, respectively. It was shown that though the pressure build-up increases as feed pressure increases, the effect of pressure build-up on membrane performance is actually minimized at higher feed pressures. Membrane performs close to its actual separation properties if it is operated at high feed pressures, under which conditions the effect of pressure build-up on the membrane performance is minimized. The pressure build-up effect was further investigated by calculating the average loss and percentage loss in the driving force due to pressure build-up, and it was found that percentage loss in driving force is less at high feed pressures than that at low feed pressures. It is true that unsteady state cyclic permeation process can potentially compete with the most selective polymers available to date, both in terms selectivity and productivity. A novel process mode of gas separation by means of cyclic pressure-vacuum swings for feed pressurization and permeate evacuation using a single pump was evaluated for CO2 separation from flue gas. Unlike transient permeation processes reported in the literature which were based on the differences in sorption uptake rates or desorption falloff rates, this process was based on the selective permeability of the membrane for separations. The process was analyzed to elucidate the working principle, and a parametric study was carried out to evaluate the effects of design and operating parameters on the separation performance. It was shown that improved separation efficiency (i.e., product purity and throughput) better than that of conventional steady-state permeation could be obtained by means of pressure-vacuum swing permeation. The effectiveness of membrane processes and feasibility of hybrid processes combining membrane permeation and conventional amine absorption process were investigated for post-combustion CO2 capture. Traditional MEA process uses a substantial amount of energy at the stripper reboiler when CO2 concentration increases. Several single stage and multi-stage membrane process configurations were simulated for a target design specification aiming at possible application in enhanced oil recovery. It was shown that membrane processes offer the lowest energy penalty for post-combustion CO2 capture and likely to expand as more and more CO2 selective membranes are developed. Membrane processes can save up to 20~45% energy compared to the stand-alone MEA capture processes. A comparison of energy perspective for the CO2 capture processes studied was drawn, and it was shown that the energy requirements of the hybrid processes are less than conventional MEA processes. The total energy penalty of the hybrid processes decreases as more and more CO2 is removed by the membranes.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2004. / Bibliography: leaves 98-100.

The aim of this work is to assess the influence of mowing and grazing with different frequency and fertilization on species composition, fodder value and bimas production. The experiment was carried out at the village of Hrazany, district of Písek in 2017. The ecological conditions of grasslands, terms and intensity of use, biomass production, botanical composition and species diversity were monitored on these parcels. The data obtained was used to calculate the Hill's Diversity Index, calculate the pasture load, and calculate the yield in dry matter. Non-fertilized plots reach the lowest yields. Most grasses are located on the soil fertilized with urine. The smallest disturbance and shortcomings appear on the pasture with the finch pasture. The values were statistically processed.

This work presents a methodology for detecting islanding in distributed generation systems - DG - which use internal combustion engines as primary sources and synchronous generators connected directly to grid. The proposed method considers the characteristics of this type of DG, and is based on the analyses of the injected power and voltage level to disable or enable the under/over frequency protection. The proposed protection scheme considers the frequency as the main electrical signal, and has three stages: the first stage is disabled when power injected oscillations are detected, in the others cases, the stage is enabled; the second stage is normally disabled, it will be enabled when a balanced voltage is detected after a unbalanced voltage condition and the third stage is normally enabled and is used to detect large frequency deviations. The proposed protection was tested over diferentes events, islanding with different load and generation levels, temporary short-circuit and islanding during short-circuit. The results show the efficiency and reliability in detecting islanding, presenting no false detections. / Esse trabalho apresenta uma metodologia para detecção de ilhamento e proteção de sistemas de Geração Distribuída - GD - as quais utilizam motores de combustão interna como fontes primárias e possuem alternadores síncronos conectados diretamente na rede elétrica. A metodologia proposta leva em consideração as características desse tipo de GD, e baseia-se na análise da potência gerada e nos níveis de tensão para bloquear ou habilitar proteção de sub e sobre-frequência. O esquema de proteção proposto utiliza a frequência como grandeza elétrica principal, e possui três estágios: o primeiro é bloqueado quando oscilações na potência injetada na rede pela GD forem detectadas, nos outros casos, o estágio permanece ativo; o segundo estágio está normalmente bloqueado, sendo desbloqueado quando as tensões sofrerem desequilíbrios e passarem a apresentar tensões de linha equilibradas e o terceiro estágio atua sem bloqueios para grandes desvios de frequência. A metodologia proposta foi testada para diferentes cenários, como ilhamento em diferentes níveis de geração e carga, curtos-circuitos momentâneos e curtos-circuitos seguidos de ilhamento. A metodologia mostrou-se eficiente e confiável na detecção de ilhamento, não apresentando atuações indevidas.

Power grids constitute an essential infrastructure providing and distributing electrical energy. The grid structure is currently subject to rapid changes due to the integration of renewable energy sources. In this development one is confronted with several challenges and opportunities as, for instance, the reduction of inertial masses in the system, the strongly increasing decentralisation of generators, and the fluctuating power feed-in by generators relying on renewable energy sources. In this thesis, models are studied that describe the non-linear power-grid dynamics in the presence of fluctuating power feed-in from renewable energy sources, primarily wind turbines. Realistic features of wind-power feed-in are captured by using real data measured at a research platform located in the North Sea. This approach is applied to test systems provided by the Institute of Electrical and Electronics Engineers (IEEE), in which one conventional generator is replaced by a wind turbine. It is found that so-called dead ends and other weakly coupled network parts are particularly prone to power fluctuations and perturbations. In contrast to previous studies, the often pronounced heterogeneities of the power grid elements are taken into account when solving the non-linear power-flow and swing equations. Also reactances between locations of power generation and power feed-in are considered, which causes the link topology in the power grid to correspond to a full graph, where all nodes are effectively connected. Both the grid heterogeneities and the additional generator reactances have a decisive impact on power grid stability. Some structures considered as particularly stable in simplified models are prone to perturbations when utilising the more realistic model and vice versa. By the analysis of various quantities characterising functional grid operation, it is shown that a reliable assessment of power grid stability requires the consideration of heterogeneities and generator reactances.