Are carrier-to-noise algorithms equivalent in all situations?

This paper describes methods to estimate the carrier to noise ratio in GNSS application

A model for enhanced coal bed methane recovery aimed at carbon dioxide storage: The role of sorption, swelling and composition of injected gas

Numerical simulations on the performance of CO2 storage and enhanced coal bed methane (ECBM) recovery in coal beds are presented. For the calculations, aone-dimensional mathematical model is used consisting of mass balances describing gas flow and sorption, and a geomechanical relationship to account for porosity and permeability changes during injection. Important insights are obtained regarding the gas flow dynamics during displacement and the effects of sorption and swelling on the ECBM operation. In particular, initial faster CH4 recovery is obtained when N2 is added to the injected mixture, whereas pure CO2 allows for a more effective displacement in terms of total CH4 recovery. Moreover, it is shown that coal swelling dramatically affects the gas injectivity, as the closing of the fractures associated with it strongly reduces coal's permeability. As a matter of fact, injection of flue gas might represent a useful option to limit this proble

Fixed bed adsorption of CO2/H2 mixtures on activated carbon: experiments and modeling

We present breakthrough experiments in a fixed bed adsorber packed with commercial activated carbon involving feed mixtures of carbon dioxide and hydrogen of different compositions. The experiments are carried out at four different temperatures (25°C, 45°C, 65°C and 100°C) and seven different pressures (1bar, 5bar, 10bar, 15bar, 20bar, 25bar and 35bar). The interpretation of the experimental data is done by describing the adsorption process with a detailed one-dimensional model consisting of mass and heat balances and several constitutive equations, such as an adsorption isotherm and an equation of state. The dynamic model parameters, i.e. mass and heat transfer, are fitted to one single experiment (reference experiment) and the model is then further validated by predicting the remaining experiments. Furthermore, the choice of the isotherm model is discussed. The assessment of the model accuracy is carried out by comparing simulation results and experimental data, and by discussing key features and critical aspects of the model. This study is valuable per se and a necessary step toward the design, development and optimization of a pressure swing adsorption process for the separation of CO2 and H2 for example in the context of a pre-combustion CO2 capture process, such as the integrated gasification combined cycle technolog

Pure and binary adsorption of CO2, H2, and N2 on activated carbon

A new developing field of application for pressure swing adsorption (PSA) processes is the capture of CO2 to mitigate climate change, especially the separation of CO2 and H2 in a pre-combustion context. In this process scheme the conditions of the feed to the separation step, namely a pressure of 3.5 to 4.5MPa and a CO2 fraction of around 40% are favorable for an adsorption based separation process and make PSA a promising technology. Among the commercial adsorbent materials, activated carbon is most suitable for this application. To evaluate the potential, to benchmark new materials, and for process development a sound basis of the activated carbon thermodynamic data is required, namely equilibrium adsorption isotherms of the relevant pure components and mixtures, Henry's constants and isosteric heats. In this work pure adsorption equilibria of CO2, H2 and N2 on commercial activated carbon (AP3-60 from Chemviron, Germany) are measured using a Rubotherm Magnetic Suspension Balance (MSB) (Bochum, Germany) in a wide temperature and pressure range. The data is used to fit the temperature dependent parameters of Langmuir and Sips (Langmuir-Freundlich) isotherms and to determine the Henry's constants as well as isosteric heats. Based on this evaluation different methods to evaluate the data are compared and discussed. With the pure isotherm parameters of the Sips isotherm binary adsorption is predicted using an empirical binary Sips equation and ideal adsorbed solution theory (IAST). The results are compared to binary measurements in the same MSB applying a gravimetric-chromatographic metho

Reliable measurement of near-critical adsorption by gravimetric method

A gravimetric apparatus is used to measure the excess adsorption at high pressure. The equipment consists of a Rubotherm magnetic suspension balance, which allows to measure also the density of the fluid. In order to obtain the excess adsorbed amount, the measured weight has to be corrected with a buoyancy term, for which the density of the adsorbing fluid has to be known at each experimental conditions. Therefore the homogeneity of density in the high-pressure cell plays a fundamental role in determining the accuracy of the measured excess adsorbed amounts. This paper is intended to show the impact of the actual approach to thermostating the unit on the density distribution of the adsorbing fluid inside the high-pressure cell. Namely, by changing the inlet position of the heating fluid, large differences in the measured excess adsorption are produced. The closer to the critical point of the fluid, the stronger are these differences. An optimum configuration for our measuring device has been found and it has been used to study the adsorption of carbon dioxide (CO2) on Filtrasorb 400 activated carbon at supercritical and near-critical condition

Near-critical adsorption of CO2 on 13X zeolite and N2O onsilicagel: lack of evidence of critical phenomena

The excess adsorption of CO2 on 13X zeolite and of N2O on silica gel has been studied at high pressure using a magnetic suspension balance, i.e. a gravimetric method. Recently, a detailed study on the density distribution in the measuring cell of the magnetic suspension balance showed that a proper approach to thermostatting the unit should be used in order to obtain reliable and accurate excess adsorption measurements. This is particularly important in the vicinity of the critical point of the fluid, where the density is strongly dependent on pressure and temperature. In the past, several effects were observed in our laboratory when measuring near-critical adsorption on 13X zeolite and on silica gel, namely critical adsorption and critical depletion. In the present study, these effects have been checked using the balance in the new thermostatting configuration, and the conclusion can be drawn that the accuracy of the measurement is not sufficient to prove that they indeed occur. More accurate adsorption data for the two systems have been measured and reporte

Prediction of competitive adsorption on coal by a lattice DFTmodel

Adsorption is one of the main mechanisms involved in the ECBM process, a technology where CO2(or flue gas, i.e. a CO2/N2mixture) is injected into a deep coal bed, with the aim of storing CO2by simultaneously recovering CH4. A detailed understanding of the microscopic adsorption process is therefore needed, as the latter controls the displacement process. A lattice DFT model, previously extended to mixtures, has been applied to predict the competitive adsorption behavior of CO2, CH4and N2and of their mixtures in slit-shaped pores of 1.2 and 8nm width. In particular, the effect of temperature, bulk composition and density on the resulting lattice pore profiles and on the lattice excess adsorption isotherms has been investigated. Important insights could be obtained; when approaching near critical conditions in the mesopores, a characteristic peak in the excess adsorption isotherm of CO2appears. The same effect could be observed neither for the other gases nor in the micropores. Moreover, in the case of mixtures, a depletion of the less adsorbed species close to the adsorbent surface is observed, which eventually results in negative lattice excess adsorption at high bulk densitie

Competitive adsorption equilibria of CO2 and CH4 on a dry coal

Gases like CO2 and CH4 are able to adsorb on the coal surface, but also to dissolve into its structure causing the coal to swell. In this work, the binary adsorption of CO2 and CH4 on a dry coal (Sulcis Coal Province, Italy) and its swelling behavior are investigated. The competitive adsorption measurements are performed at 45 °C and up to 190bar for pure CO2, CH4 and four mixtures of molar feed compositions of 20.0, 40.0, 60.0 and 80.0% CO2 using a gravimetric-chromatographic technique. The results show that carbon dioxide adsorbs more favorably than methane leading to an enrichment of the fluid phase in CH4. Coal swelling is determined using a high-pressure view cell, by exposing a coal disc to CO2, CH4 and He at 45 and 60 °C and up to 140bar. For CO2 and CH4 a maximum swelling of about 4 and 2% is found, whereas He shows negligible swelling. The presented adsorption and swelling data are then discussed in terms of fundamental, thermodynamic aspects of adsorption and properties which are crucial for an ECBM operation, i.e. the CO2 storage capacity and the dynamics of the replacement of CH4 by CO

Lo studio internazionale multicentrico dell'Organizzazione Mondiale della Sanità sui disturbi psichici nella medicina generale: risultati relativi all'area di Verona

Objectives - To present the results obtained from a cross-sectional evaluation of a sample of primary care attenders selected in Verona in the framework of the World Health Organization International Multicentre Study on Psychological Problems in Primary Care Settings. Methods - Among consecutive attenders at 16 primary care clinics in Verona during the period April 1991/February 1992, a random sample, stratified on the basis of GHQ-12 scores, was selected for a thorough evaluation of psychological status, physical status and disability in occupational and other daily activities. All patients with psychopathological symptoms at baseline assessment and a 20% random sample of those without psychopathological symptoms were interviewed again after 3 and 12 months (data not presented here). Results - Overall, 1,656 subjects were approached at the primary care clinics and 1,625 met inclusion criteria. The screening procedure was completed by 1,558 subjects and the second-stage evaluation by 250. Psychiatric disorders according to ICD-10 criteria were diagnosed in 12.4% of consecutive primary care attenders; of these, about one-third (4.5% of consecutive primary care attenders) satisfied ICD-10 diagnostic criteria for two or more disorders. Current Depressive Episode (4.7%) and Generalized Anxiety Disorder (3.7%) were the most common diagnoses. In addition, 11.2% of consecutive primary care attenders had ‘sub-threshold' psychiatric disorders (i.e., they suffered from symptoms in at least two different areas among those listed in ICD-10, but they did not satisfy diagnostic criteria for well-defined disorders). Psychiatric disorders were more common among females and those aged 24-44 years. Only 20.6% of the subjects with psychiatric disorders contacted the general practitioner for their psychological symptoms, 5.7% complained of symptoms which might have had a psychological origin, whereas in about 70% of the cases the psychiatric disorder was concealed behind the presentation of somatic symptoms, pains in various parts of the body or chronic physical illness. Sixty-two percent of the subjects with psychiatric disorders rated their health status as fair or poor, as compared to 52.0% of those with chronic physical illness and 31.3% of those without such disorders. According to the general practitioner, 40.1% of the subjects with psychiatric disorders and 45.3% of those with chronic physical illness had a fair or poor health status, compared to 14.4% of those without such disorders. Disability in occupational and other daily activities was reported by 52.5% of the subjects with psychiatric disorders (in 40.1% of the cases disability was moderate or severe), 44.4% of those with chronic physical illness (in 26.8% of the cases disability was moderate or severe), and 15.0% of the subjects without such disorders (in 9.1% of the cases disability was moderate or severe). According to the interviewer, disability was identified in 48.4% of the subjects with psychiatric disorders, 39.0% of those with chronic physical illness, and 27.6% of the subjects without such disorders. Sixty per cent of the subjects with psychiatric disorders suffered from concurrent chronic physical illness; these subjects had a poorer health status and higher disability levels than those with psychiatric disorders only. Conclusions - Psychiatric disorders among primary care attenders are frequent and represents a major public health problem, since they entail severe functional limitations for the patients and high costs for the society. Thus, appropriate programs for their recognition and treatment are neede