Energy-efficient electrochemically-driven CO2 capture systems for biogas upgrading

Biogas encompassing mainly CO2/CH4 mixture has gained increased attention as a renewable energy source over the last years, mainly due to its contributions to greenhouse gas (GHG) abatement. However, this gaseous stream has been undervalued owing to its high CO2 content. Capturing endogenous CO2 from biogas broadens its utilisation as a substitute for natural gas. High energy consumption of traditional CO2 capture technologies has led to an opportunity to develop an alternative technique for large-scale carbon capture. Employing an anion exchange membrane (AEM)-based electrochemical cell for CO2 removal from gas mixtures is a new strategy based on the pH-gradient generated during redox reactions. This technology offers significant practical advantages owing to near-ambient temperature and pressure operating conditions. To open avenues for development research on the electrochemically-driven CO2 capture technique, key principles and features of all major methods for CO2 capture in the literature were summarised as part of this thesis. While to date the (AEM)-based electrochemical cells have received eminent fame for their application in CO2 capture, there are still major enhancement researches required to enhance the technology maturity and reduce costs. In this thesis, the aim was to determine the viability of this CO2 capture system as an alternative to conventional technologies for biogas upgrading. In this context, the main research chapters are summarised as follows: Firstly, a CO2 absorption column was integrated with an alkaline water electrolyser for biogas upgrading. After scrubbing CO2 in an aqueous absorption column, the resulting bicarbonate solution was fed through the cathode of an anion exchange membrane (AEM)-based electrolyser. With bicarbonate being the dominant anion, it migrates proportionally to the electron flow to the anode from where it is released together with anodic oxygen (O2). The proposed system allows electrochemically-assisted scrubbing and stripping of CO2 without the addition of chemicals. Coulombic efficiency calculations showed that the theoretical electron/carbon ratio of 1 (1 e/ 1 HCO3-) can be achieved by using a pH of 9 while using a traditional pH of around 13 results in more electrons and hence more energy requirement for electrochemical CO2 removal. As predicted from electrochemical stoichiometry, the system optimisation demonstrated that operating the integrated system at pH=9 results in the lowest energy requirement, even though the CO2 absorption rate in the absorbent pH= 13 was about three times higher than that at pH= 9. Results of this study suggest that integrated (AEM)-based alkaline water electrolyser and CO2 absorption column offer a low energy approach for the capture and removal of CO2 from biogas (0.25 to 0.92 kWh/kg CO2). This could potentially reduce the energy demand for CO2 separation from biogas by about 50% compared to the most energy-efficient technologies that are currently available. Recovery of absorbed CO2 on the anode side of the alkaline membrane diminishes the O2 content in the anodic gas stream. Given this high purity electrolytic O2 has a growing industrial interest in diverse applications such as biological wastewater treatment processes we designed and developed an innovative three-chamber electrochemical cell configuration capable of capturing CO2 and recovering it in an intermediate chamber enabling concomitant anodic high-purity oxygen generation. Our prototype successfully demonstrated that CO2 recovery can be separated from the anodic O2 gas stream by adding a cation exchange membrane (CEM) to the cell. A concise model was also developed to accurately predict the polarisation characteristic of the designed electrochemical cell by considering the numerical coefficient for the Tafel equation and ohmic losses. Next to the regeneration of spent alkaline solution for CO2 removal from biogas using an alkaline water electrolyser, the generated high-purity electrolytic O2 from the three-chamber electrochemical cell can be used as a valuable by-product in various industrial processes to improve the energy efficiency of the system. Our strategy to cut down the cost of electrochemically-driven CO2 removal was the effective utilisation of high-purity O2 in the aeration process of a wastewater treatment plant. The high-purity electrolytic O2 can be used to substitute the air in the conventional activated sludge process. To determine the benefit of switching from air to oxygen-enriched air or pure oxygen, an analytical model was derived to simulate the dynamic behaviour of a single bubble rising in stagnant water. This study explored the influence of operation parameters such as bubble diameter, and bubble release depth on gas-liquid mass transfer. The predicted results suggested that replacing air with high-purity oxygen in the aeration process of the conventional activated sludge can offset up to 30% of the energy required for water electrolysis. A greater advantage could be obtained by using the generated high-purity oxygen in the aeration system of industries with higher dissolved oxygen requirements such as the aquaculture industry. Finally, co-mixing electrolytic H2 generated during electrochemical biogas upgrading and CH4 may not be desirable and present some challenges such as the increased probability of ignition and material degradability. In this scenario, electrolytic H2 could be recycled from the cathode to the anode side to replace the kinetically sluggish oxygen evolution reaction (OER). The technical and economic aspect of the H2 recycling cell to generate the pH gradient required for capturing and stripping CO2 was explored. The experimental results showed that the H2 recycling cell enables CO2 capture with a minimum electrochemical work of 0.19 kWh/kg CO2, which is 30% lower than the alkaline water electrolyser system where anodic OER limits the energy efficiency of the process. The main conclusion drawn from this study is that the electrochemical-driven CO2 capture systems have the potential to reduce energy costs associated with the regeneration of spent alkaline absorbents in biogas upgrading systems

Transient Stability Enhancement of Wind Farms Using Power Electronics and FACTS Controllers

Nowadays, it is well-understood that the burning of fossil fuels in electric power station has a significant influence on the global climate due to greenhouse gases. In many countries, the use of cost-effective and reliable low-carbon electricity energy sources is becoming an important energy policy. Among different kinds of clean energy resources- such as solar power, hydro-power, ocean wave power and so on, wind power is the fastest-growing form of renewable energy at the present time. Moreover, adjustable speed generator wind turbines (ASGWT) has key advantages over the fixed-speed generator wind turbines (FSGWT) in terms of less mechanical stress, improved power quality, high system efficiency, and reduced acoustic noise. One important class of ASGWT is the doubly-fed induction generator (DFIG), which has gained a significant attention of the electric power industry due to their advantages over the other class of ASGWT, i.e. fully rated converter-based wind turbines. Because of increased integration of DFIG-based wind farms into electric power grids, it is necessary to transmit the generated power from wind farms to the existing grids via transmission networks without congestion. Series capacitive compensation of DFIG-based wind farm is an economical way to increase the power transfer capability of the transmission line connecting wind farm to the grid. For example, a study performed by ABB reveals that increasing the power transfer capability of an existing transmission line from 1300 MW to 2000 MW using series compensation is 90% less than the cost of building a new transmission line. However, a factor hindering the extensive use of series capacitive compensation is the potential risk of sub- synchronous resonance (SSR). The SSR is a condition where the wind farm exchanges energy with the electric network, to which it is connected, at one or more natural frequencies of the electric or mechanical part of the combined system, comprising the wind farm and the network, and the frequency of the exchanged energy is below the fundamental frequency of the system. This phenomenon may cause severe damage in the wind farm, if not prevented. Therefore, this dissertation deals with the SSR phenomena in a capacitive series compensated wind farm. A DFIG-based wind farm, which is connected to a series compensated transmission line, is considered as a case study. The small-signal stability analysis of the system is presented, and the eigenvalues of the system are obtained. Using both modal analysis and time-domain simulation, it is shown that the system is potentially unstable due to the SSR mode. Then, three different possibilities for the addition of SSR damping controller (SSRDC) are investigated. The SSRDC can be added to (1) gate-controlled series capacitor (GCSC), (2) thyristor-controlled series capacitor (TCSC), or (3) DFIG rotor-side converter (RSC) and grid-side converter (GSC) controllers. The first and second cases are related to the series flexible AC transmission systems (FACTS) family, and the third case uses the DFIG back-to-back converters to damp the SSR. The SSRDC is designed using residue-based analysis and root locus diagrams. Using residue-based analysis, the optimal input control signal (ICS) to the SSRDC is identified that can damp the SSR mode without destabilizing other modes, and using root-locus analysis, the required gain for the SSRDC is determined. Moreover, two methods are discussed in order to estimate the optimum input signal to the SSRDC, without measuring it directly. In this dissertation, MATLAB/Simulink is used as a tool for modeling and design of the SSRDC, and PSCAD/EMTDC is used to perform time-domain simulation in order to verify the design process

THE EFFECT OF GASTRIC GAS EMPTYING ON THE RESIDUAL GASTRIC VOLUME IN MECHANICALLY-VENTILATED INTENSIVE CARE UNIT PATIENTS FED THROUGH NASOGASTRIC TUBES: A RANDOMIZED, SINGLE-BLIND, CLINICAL TRIAL

Objective: Increased gastric residual volume is a complication of enteral nutrition intolerance that leads to gastrointestinal complications such as nausea, vomiting, and aspiration pneumonia. The present study was conducted to determine the effect of gastric gas emptying on the residual gastric volume in mechanically-ventilated patients fed through nasogastric tubes.Methods: This randomized, single-blind, clinical trial was conducted on two groups of patients in the intensive care unit (ICU) of Kamyab Hospital of Mashhad. A total of 64 patients were randomly divided into a case and a control group. In the case group, the gastric gases accumulated through the nasogastric tube were emptied by applying palm pressure on the epigastric region. The control group did not undergo this intervention but received the routine care provided in the ward. Data were collected using a demographic questionnaire and a form containing records of the patients' residual gastric volume and disease-related information. The residual gastric volume was measured and compared in the two groups before and after the intervention. Data were analyzed in SPSS-19 using the Chi-square test, the independent t-test, and the repeated measures ANOVA at the significance level of 5%.Results: The residual gastric volume did not differ significantly between the two groups before the intervention (p=0.14); after the intervention; however, a significant reduction was observed in the case group compared to the controls (p=0.007).Conclusion: Gastric gas emptying helps reduce the residual gastric volume in mechanically-ventilated patients fed through nasogastric tubes. Further studies are recommended to further ensure the benefits of this method

Protective Effect of Crocin on Ovarian Ischemia-Reperfusion Injury in Rats

Background & Aims: Ischemia-reperfusion (I-R) injury of the ovary may lead to ovarian injury. In this study, we investigated the protective effect of the crocin on ovarian I-R injury. Materials & Methods: Thirty-six male Sprague-Dawley rats were divided into 6 groups: sham surgery, ischemia, I-R, I-R+normal saline (NS), I-R+low dose crocin (20 mg/kg crocin), and I-R+ high dose crocin (80 mg/kg crocin). Neurological function, biochemical and histological evaluation was done 72 hours after ischemia. Results: The plasma levels of malondialdehyde (MDA) and Total Antioxidative Capacity (TAC) in the ischemia, I-R, and I-R+ NS groups increased and decreased significantly compared to the crocin groups, respectively (p<0.01, p<0.05, respectively). Catalase activity in the high dose crocin group was higher than the ischemia, I-R, and I-R+ NS groups (p<0.01). The mean scores of edema, congestion, hemorrhage, and follicular degeneration were significantly lower than in the crocin groups than in the ischemia, I-R, and I-R+NS groups (p<0.05). Conclusion: Findings suggest that crocin may protect ovary from ischemia-reperfusion injury

Effect of Evidence-Based Education on Nursing Students' Self-Efficacy

Background & Objective: Clinical efficacy plays an important role in clinical knowledge and skill application. One of the ways to increase self-efficacy is using experience, and results of clinical research. The aim of the present study was to evaluate the impact of evidence-based education on nursing students' self-efficacy. Methods: This experimental study was conducted on 48 nursing students in their 3rd semester in Urmia University of Medical Sciences, Iran. The study subjects were selected using convenience sampling and randomly divided into 2 groups of intervention and control (n = 24). Considering the students' training in the orthopedic ward, the intervention group participants were divided into 8 groups. Students in the intervention group were trained in evidence-based education in 2 sessions each lasting 2 hours. Self-efficacy was evaluated before and after training in the control and intervention groups using the generalized self-efficacy (GSE) scale. Data were analyzed using SPSS software, and chi-square, t-test, Mann-Whitney test, and Wilcoxon test. Data were analyzed using confidence interval of 95 ± 2%. Results: Of the students, 33.3% were female and 66.7% male. Mann-Whitney test showed the self-efficacy of the intervention group students to be significantly higher than control group students (P < 0.001). No significant differences were observed in the control group. Conclusion: Evidence-based education causes greater improvement in self-efficacy in comparison to conventional methods. Therefore, the use of this method is recommended in clinical education. Keywords Evidence-based education Efficacy Nursing student

DRUJ instability after distal radius fracture: A comparison between cases with and without ulnar styloid fracture

AbstractBackgroundBecause of the importance of the DRUJ in upper extremity function and the prevalence of distal radius fractures, either with or without ulnar styloid fracture, this study was designed to assess the relationship between ulnar styloid fracture and the incidence of DRUJ instability after treatment of distal radius fractures treated with ORIF (volar plate).Methods112 patients suffering from type two and three distal radius fractures (Fernandez classification), were evaluated. Depending on the presence of ulnar styloid avulsion fracture, patients were divided into two groups: 86 cases with isolated radial fracture and 26 cases with a distal radius fracture accompanied by ulnar styloid fracture. All patients underwent distal radius fracture ORIF. CT scanning was done both immediately after surgery and 3 months post-op. DRUJ stability was examined using the modified radioulnar line method and the incidence of DRUJ instability was compared between the two groups.ResultsImmediate instability was seen in 11 patients. Three of these patients had concomitant ulnar styloid fracture and were excluded for further fixation. Three months later, another 9 cases were diagnosed with DRUJ instability, 2 of whom had concomitant ulnar styloid fracture and the other 7 suffered from isolated distal radius fracture. Chi-square test revealed no significant difference (p < 0.05). There were no cases of delayed union or non-union distal radius fracture.ConclusionOur study demonstrated that untreated stable or minimally displaced ulnar styloid fracture accompanied by distal radius fracture, has no adverse effect on DRUJ stability following ORIF of the radius

Priprava mikrokuglica s antigenom leptospira od biološki razgradivih alginatnih polimera.

Leptospirosis is a worldwide zoonosis caused by pathogenic Leptospira spp. Although the currently available whole cell leptospiral vaccines can induce protection against Leptospirosis, further study for a new generation of vaccine that can stimulate long-term immunity is needed. Biodegradable microspheres as antigen delivery systems have been extensively investigated for decades, especially those based on hydrophilic polymers, such as alginate and chitosan, which have excellent biocompatibility, non-toxicity and biodegradability. The aim of this study was to prepare and characterize alginate microspheres as an antigen delivery system for immunization against leptospirosis. Alginate microspheres containing Leptospiral antigen (LA) were prepared by an emulsification method and characterized for shape, size distribution, loading efficiency (LE), loading capacity (LC) and release profie. The effects of some parameters (such as concentration of alginate and emulsifiers and stirring rate) on microspheres characteristics were investigated. The optimal condition parameters for the preparation of LA loaded alginate microspheres were estimated. The optimum concentrations were obtained for alginate and emulsifiers, 3.5 % (w/v), span 80 (0.2 % w/v) and tween 80 (3.75 % w/v), respectively. Moreover, appropriate homogenizing rate was obtained at 500 rparticle size of the microspheres as 200 μm, loading efficiency 97 % and loading capacity 8 %. A suitable release profile was observed for in vitro release test of LA from alginate microspheres over an extended period of time (192 hours). These results make the alginate microspheres particularly interesting for an LA delivery system.pm. Our results showed the mean particle size of the microspheres as 200 μm, loading effiiency 97 % and loading capacity 8 %. A suitable release profile was observed for in vitro release test of LA from alginate microspheres over an extended period of time (192 hours). These results make the alginate microspheres particularly interesting for an LA delivery system.Leptospiroza je zoonoza prouzročena patogenim vrstama roda Leptospira, a proširena je diljem svijeta. Iako današnja cjepiva protiv leptospiroze, proizvedena od cijelih bakterijskih stanica, mogu pružiti zaštitu od leptospiroze, potrebna su daljnja istraživanja nove generacije cjepiva koja će moći potaknuti tvorbu dugotrajne imunosti. Biološki razgradive mikrokuglice istražuju se desecima godina kao mogućnost sporog otpuštanja antigena, a posebice su zanimljive one od hidrofilnih polimera kao što je alginat i kitosan, koji imaju izvrsnu biološku kompatibilnost, nisu toksični, a biološki su razgradivi. Svrha ovog rada bila je pripraviti alginatne mikrokuglice i odrediti njihova svojstva pogodna za otpuštanje antigena u postupku imunizacije protiv leptospiroze. Alginatne mikrokuglice s antigenom leptospira bile su pripravljene postupkom emulgacije te im je bio određen oblik, opseg distribucije, učinkovitost ugradnje antigena u mikrokuglice, kapacitet ugradnje i profil otpuštanja antigena. Istraženi su učinci nekih pokazatelja (kao što je koncentracija alginata i emulgatora te omjer miješanja) na obilježja mikrokuglica. Procijenjeni su optimalni uvjeti za pripravu alginatnih mikrokuglica na koje je vezan antigen leptospira. Optimalna koncentracija za alginat bila je 3,5 % (w/v), a emulgator span 80 (0,2 % w/v) i tween 80 (3,75 % w/v). Odgovarajuća homogenizacija postignuta je na 500 okretaja. Rezultati su pokazali da je srednja veličina mikrokuglica bila 200 μm, učinkovitost ugradnje antigena 97 %, a kapacitet 8 %. In vitro je ustanovljeno da se antigen leptospira oslobađao s alginatnih mikrokuglica tijekom 192 sata. Ti rezultati pokazuju da alginatne kuglice mogu biti od posebnog interesa za oslobađanje antigena leptospira u organizmu

Protective effect of lutein on spinal cord ischemia-reperfusion injury in rats

Objective(s): Paraplegia is deterioration in motor or sensory function of the lower limbs that can occur after modification of a thoracoabdominal aortic aneurysm. The purpose of this survey was to determine the protective action of lutein on spinal cord ischemia-reperfusion (I-R) damage. Materials and Methods: Thirty-five male rats were distributed into five groups: intact, sham, dimethyl sulfoxide (I-R+DMSO), low dose lutein (I-R+0.2 mg/kg lutein), and high dose lutein (I-R + 0.4 mg/kg lutein). Thirty minutes before surgery, a single dose lutein or DMSO was administered to rats of experimental groups. Next, the abdominal aorta was clamped exactly under the left renal artery and proximal to the abdominal aortic bifurcation for 60 min. All animals were evaluated by neurological function and histological and biochemical examinations at 72 hr after I-R.Results: The mean motor deficit index (MDI) scores in lutein groups were lower compared with the DMSO group (