Centrifugal Compressor Surge Control Systems - Fundamentals of a Good Design

LectureLecture 2: Many facilities employ two or more centrifugal compressors, operated in either series or parallel configurations. An accurately designed surge control system that includes multiple compressors with the associated piping systems is a vital element of a facility’s design and ongoing operational integrity. The design must ensure compressors are not subjected to damaging fast dynamic events leading to large capital costs and significant down time for operators. Examples of such fast dynamic events are those following emergency shutdown (ESD) or fast stop of one or all compressor units in a station. Typical studies are not accurate enough to capture the complex interactions leading to catastrophic events, especially for complicated system arrangements. This paper introduces three methods of surge control analysis that can be conducted to assess the effectiveness of any surge control system design to prevent the compressor from surge. The first method utilizes the perturbation theory to relate the compressor deceleration and the resulting drop in its flow and head to determine the elapsed time that the compressor can stay out of surge before the surge control system brings about enough positive flow to prevent the unit from undergoing deep surge. The second method is simpler, and is based on a dimensionless number, called the inertia number, which combines the salient parameters from the dynamic equation between the fluid energy and that of the compressor rotor inertia to determine, as a first cut check, if the surge control system is adequate. The third method, which is always recommended, and is based on solving the full gas dynamic partial differential equations (PDEs) in spatial and temporal domain, which describe the true dynamic characteristics of the flow through the various piping elements, the compressor itself, to provide much more accurate predictions of surge control system behavior during fast transient events. Comparisons are made to field measurements to provide model validations, and an example application (Case Study) of three units operating in parallel. The first two (Units 6 and 7) were existing in a compressor station, while the third (Unit 8) was an add-on. The addition of Unit 8 meant a number of station layout modifications, which included: re-wheeling of Units 6 and 7 (i.e., change the compressor impellers); adding after gas cooling; and relocating the anti-surge valves downstream of the coolers to allow for both hot (fast stop) and cold recycle (anti-surge) capabilities. Due to the addition of equipment and significant reconfiguration of station piping and valves, a dynamic surge analysis on Units 6, 7, and 8 was required to determine whether the existing anti-surge and fast stop valves were adequately sized and whether the anti-surge valves could be relocated downstream of the gas coolers. A new fast stop recycle system was added along with Unit 8, which also needed to be adequately sized. Further complications arose from the fact that Unit 6’s anti-surge valve configuration differs from that of Unit 7 and that Unit 6 has twin recycle valves jointly serving as anti-surge valves with a single fast stop valve while Unit 7 has a single anti-surge valve and a single fast stop valve

In vitro differentiation of human umbilical cord blood mesenchymal stem cells into functioning hepatocytes

Mesenchymal stem cells (MSCs) were isolated by gradient density centrifugation from umbilical cord blood. Spindle-shaped adherent cells were permitted to grow to 70% confluence in primary culture media which was reached by day 12. Induction of differentiation started by culturing cells with differentiation medium containing FGF-4 and HGF. Under hepatogenic conditions few cuboidal cells appeared in culture on day 7. From day 21 to day 28, most of cells became small and round. The control negative cells cultured in serum free media showed fibroblast-like morphology. Urea production and protein secretion by the differentiated hepatocyte-like cells were detected on day 21 and increased on day 28. Protein was significantly increased in comparison with control by day 28. The cells became positive for AFP at day 7 and positive cells could still be detected at days 21 and 28. The cells in the control group were stained negative for AFP. The cells expressed albumin gene at the 14th day that became markedly increased at the 28th day of culture with HGF and FGF-4. No albumin expression was observed in the 7th day sample and the control. This study demonstrated that UCB-derived MSCs had the ability to differentiate into functioning hepatocyte-like cells starting from the 7th day after culturing under hepatogenic conditions and became well functioning at days 21 and 28. These data indicated that UCB-derived MSCs can be a promising source of cell therapy for intractable liver diseases.Keywords: Umbilical cord blood; Mesenchymal stem cells; Culture; Hepatocytes; HGF; FGF-

Association of macrophage migration inhibitory factor promoter polymorphism -173G/C with susceptibility to childhood asthma

Abstract Introduction: macrophage migration inhibitory factor (miF) is a proinflammatory cytokine that plays an important role in the pathogenesis of asthma. Polymorphisms associated with inflammatory diseases exist in the promoter region of miF, which alter its expression. We aimed to study the association of MIF promoter polymorphism -173G/C with childhood asthma. (p = 0.019, OR = 3.12,. Material and methods: in this case-control study, we recruited 60 pediatric patients with bronchial asthma and 90 age-and sex-matched healthy controls. MIF-173G/C was genotyped using polymerase chain reaction-restriction fragment length polymorphism (PCr-rFlP). Results: Genotype distribution between cases and healthy controls was statistically evaluated. Our results revealed that the frequency of the MIF-173C allele was significantly higher in children with asthma than in the control group (p = 0.002, odds ratio [OR] = 3.61, 95% confidence interval [CI] = 1.63-7.97). The frequency of the MIF-173CC genotype was higher in the asthmatic children than in the controls (p = 0.028, OR = 6.24, 95% CI = 1.24-31.29). Comparing carriage of the MIF-173C allele in pediatric patients with asthma with that observed in healthy controls (GC + CC vs. GG) revealed a positive association with the disease Conclusions: These results suggest that MIF-173G/C polymorphism confers an increased risk of susceptibility to the development of childhood asthma in an Egyptian population

Vaccination with DNA plasmids expressing Gn coupled to C3d or alphavirus replicons expressing Gn protects mice against rift valley fever virus

Background: Rift Valley fever (RVF) is an arthropod-borne viral zoonosis. Rift Valley fever virus (RVFV) is an important biological threat with the potential to spread to new susceptible areas. In addition, it is a potential biowarfare agent. Methodology/Principal Findings: We developed two potential vaccines, DNA plasmids and alphavirus replicons, expressing the Gn glycoprotein of RVFV alone or fused to three copies of complement protein, C3d. Each vaccine was administered to mice in an all DNA, all replicon, or a DNA prime/replicon boost strategy and both the humoral and cellular responses were assessed. DNA plasmids expressing Gn-C3d and alphavirus replicons expressing Gn elicited high titer neutralizing antibodies that were similar to titers elicited by the live-attenuated MP12 virus. Mice vaccinated with an inactivated form of MP12 did elicit high titer antibodies, but these antibodies were unable to neutralize RVFV infection. However, only vaccine strategies incorporating alphavirus replicons elicited cellular responses to Gn. Both vaccines strategies completely prevented weight loss and morbidity and protected against lethal RVFV challenge. Passive transfer of antisera from vaccinated mice into naïve mice showed that both DNA plasmids expressing Gn-C3d and alphavirus replicons expressing Gn elicited antibodies that protected mice as well as sera from mice immunized with MP12. Conclusion/Significance: These results show that both DNA plasmids expressing Gn-C3d and alphavirus replicons expressing Gn administered alone or in a DNA prime/replicon boost strategy are effective RVFV vaccines. These vaccine strategies provide safer alternatives to using live-attenuated RVFV vaccines for human use. © 2010 Bhardwaj et al

Rift Valley Fever – epidemiological update and risk of introduction into Europe

Rift Valley fever (RVF) is a vector-borne disease transmitted by a broad spectrum of mosquito species, especially Aedes and Culex genus, to animals (domestic and wild ruminants and camels) and humans. Rift Valley fever is endemic in sub-Saharan Africa and in the Arabian Peninsula, with periodic epidemics characterised by 5–15 years of inter-epizootic periods. In the last two decades, RVF was notified in new African regions (e.g. Sahel), RVF epidemics occurred more frequently and low-level enzootic virus circulation has been demonstrated in livestock in various areas. Recent outbreaks in a French overseas department and some seropositive cases detected in Turkey, Tunisia and Libya raised the attention of the EU for a possible incursion into neighbouring countries. The movement of live animals is the most important pathway for RVF spread from the African endemic areas to North Africa and the Middle East. The movement of infected animals and infected vectors when shipped by flights, containers or road transport is considered as other plausible pathways of introduction into Europe. The overall risk of introduction of RVF into EU through the movement of infected animals is very low in all the EU regions and in all MSs (less than one epidemic every 500 years), given the strict EU animal import policy. The same level of risk of introduction in all the EU regions was estimated also considering the movement of infected vectors, with the highest level for Belgium, Greece, Malta, the Netherlands (one epidemic every 228–700 years), mainly linked to the number of connections by air and sea transports with African RVF infected countries. Although the EU territory does not seem to be directly exposed to an imminent risk of RVFV introduction, the risk of further spread into countries neighbouring the EU and the risks of possible introduction of infected vectors, suggest that EU authorities need to strengthen their surveillance and response capacities, as well as the collaboration with North African and Middle Eastern countries.info:eu-repo/semantics/publishedVersio

Rift Valley fever virus (Bunyaviridae: Phlebovirus): an update on pathogenesis, molecular epidemiology, vectors, diagnostics and prevention

Rift Valley fever (RVF) virus is an arbovirus in the Bunyaviridae family that, from phylogenetic analysis, appears to have first emerged in the mid-19th century and was only identified at the begininning of the 1930s in the Rift Valley region of Kenya. Despite being an arbovirus with a relatively simple but temporally and geographically stable genome, this zoonotic virus has already demonstrated a real capacity for emerging in new territories, as exemplified by the outbreaks in Egypt (1977), Western Africa (1988) and the Arabian Peninsula (2000), or for re-emerging after long periods of silence as observed very recently in Kenya and South Africa. The presence of competent vectors in countries previously free of RVF, the high viral titres in viraemic animals and the global changes in climate, travel and trade all contribute to make this virus a threat that must not be neglected as the consequences of RVF are dramatic, both for human and animal health. In this review, we present the latest advances in RVF virus research. In spite of this renewed interest, aspects of the epidemiology of RVF virus are still not fully understood and safe, effective vaccines are still not freely available for protecting humans and livestock against the dramatic consequences of this virus

High-velocity impact welding

Bibliography: p. 203-211

Lecture 12: Dynamic Instabilities in Industrial Compression Systems with Centrifugal Compressors

Lecturepg. 118-132Compression systems involving centrifugal compressors are designed and operated in a manner to eliminate or minimize the potential for compressor surge, which is a dynamic instability that is detrimental to the integrity of the unit. Compressor surge can occur when the compression systems are subjected to rapid transients such as those caused by and emergency shutdown (ESD) or a power failure. Compression systems, like other second-order dynamic systems, are prone to instabilities. These depend on compressor head-flow characteristics of the compressor units as well as the dynamic characteristics of the machinery train and associated piping systems. Parameters such as gas volume capacitance in the recycle path, compressor power train inertia and the recycle valve capacity, anti-surge valve prestroke and stroke time, and check valve dynamic characteristics are crucial in determining the conditions for dynamic instabilities to occur. Anti-surge control protocols also contribute to potential compressor instabilities particularly when the compressor is operating close to the surge control line. This paper gives an overview concept of the principle of static and dynamic stabilities in a simple compression system involving centrifugal compressors, capacitance, gas inertia, and flow throttling. For a more complex compression system design, involving complex piping geometries akin to those employed in industrial compression system, techniques and methods of determining whether a certain design or an operating mode will lead to instabilities are also formulated and solved. This investigation lead to the notion of a dimensionless inertia number with a threshold value below which a given design is prone to instability during an ESD operation. Data are drawn from over a dozen compressor station of various designs employing different compressor models and drive types, e.g., electric motors or gas turbines. An example is presented to illustrate the concept of instabilities