Mathematical Modeling and Simulation of a One-Dimensional Transient Entrained-flow GEE/Texaco Coal Gasifier

Numerous gasifier models of varying complexity have been developed to study the various aspects of gasifier performance. These range from simple one-dimensional (1D) models to rigorous higher order 3D models based on computational fluid dynamics (CFD). Even though high-fidelity CFD models can accurately predict many key aspects of gasifier performance, they are computationally expensive and typically take hours to days to execute even on high-performance computers. Therefore, faster 1D partial differential equation (PDE)-based models are required for use in dynamic simulation studies, control system analysis, and training applications.;In the current study, a 1D transient model of a single-stage downward-firing entrained flow General Electric Energy (GEE)/Texaco-type gasifier has been developed. The model comprises mass, momentum and energy balances for the gas and solid phases. A detailed energy balance across the wall of the gasifier has been incorporated in the model to calculate the wall temperature profile along the gasifier length. This balance considers a detailed radiative transfer model with variable view factors between the various surfaces of the gasifier and with the solid particles. The model considers the initial gasification processes of water evaporation and coal devolatilization. In addition, the key heterogeneous and homogeneous chemical reactions have been modeled. The resulting time-dependent PDE model is solved using the method of lines in Aspen Custom ModelerRTM, whereby the PDEs are discretized in the spatial domain and the resulting differential algebraic equations (DAEs) are then integrated over time using a variable step integrator.;Results from the steady-state model and parametric studies have been presented. These results include the gas, solid, and wall temperature profiles, concentrations profiles of the solid and gas species, effects of the oxygen-to-coal ratio and water-to-coal ratio on temperature, conversion, cold gas efficiency, and species compositions. In addition, the dynamic response of the gasifier to the disturbances commonly encountered in real-life is presented. These disturbances include ramp and step changes in input variables such as coal flow rate, oxygen-to-coal ratio, and water-to-coal ratio among others. The results from the steady-state and dynamic models compare very well with the data from pilot plants, operating plants, and previous studies

Successful term pregnancy after uterine artery embolization for caesarean scar ectopic pregnancy: a case report

The incidence of caesarean scar pregnancy range from 1 in 1800 to 1 in 2500 of all pregnancies. It has been estimated that 6.1% of pregnancies in women with at least one previous Caesarean section and a diagnosis of ectopic pregnancy will be Caesarean scar pregnancy (CSP). There is no consensus on the management of CSP. An invasive intervention such as excision of scar ectopic can reduce recurrence but affects patient’s fertility. Conservative management like administration of methotrexate and uterine artery embolization (UAE) is specially important for young women who want to keep their fertility. This is a case report of a 29-year-old woman who presented with persistent heavy bleeding following failed MTP at 12 weeks of gestation. Ultrasonogarphy was suggestive of Caesarean scar pregnancy and MRI of chronic left adnexal ectopic. Laparotomy also was suggestive of Caesarean scar ectopic. She was managed conservatively with UAE followed by Methotrexate. The procedure was performed successfully, and the patient’s fertility was preserved. Follow up consisted of serial bhCG monitoring which gradually returned to normal levels. She conceived four years after UAE and had an uneventful antenatal period and underwent Elective Cesaraen section at 38 weeks. For those patients with CSP who desire future pregnancy, the comprehensive treatment including UAE can be considered in management

Discrete Breathers in One-Dimensional Diatomic Granular Crystals

We report the experimental observation of discrete breathers in a one-dimensional diatomic granular crystal composed of compressed elastic beads that interact via Hertzian contact. We first characterize their effective linear spectrum both theoretically and experimentally. We then illustrate theoretically and numerically the modulational instability of the lower edge of the optical band. This leads to the dynamical formation of long-lived breather structures, whose families of solutions we compute throughout the linear spectral gap. Finally, we observe experimentally such localized breathing modes with quantitative characteristics that agree with our numerical results.Comment: 5 pages, 4 figure

Ultrasonic studies on interionic interactions of some alkali metal halides in aqueous d-glucose solution at varying molalities and temperatures

The  present experimental investigation was carried out in order to explore the possible molecular interionic interactions of alkali metal halides namely, sodium chloride, potassium chloride, potassium bromide and potassium iodide in aqueous D-glucose solution at 303.15, 308.15K and 313.15 K. Experimental values of density (ρ), viscosity (η) and ultrasonic velocities (U) were carried out on the liquid ternary mixtures of water +D-glucose + alkali metal halides The binary solvent mixture of water + D-glucose was prepared under molality(m) basis say, at two fixed   molalities (0.2 and 0.4mol.kg-1). Alkali metal halides (NaCl, KCl, KBr and KI) were added under different molalities with these binary solvent mixtures. The related and relevant parameters correlated to our present study such as adiabatic compressibility (b), molal hydration number (nH), apparent molal compressibility (jk), apparent molal volume (jv), limiting apparent molal compressibility ( ), limiting apparent molal volume ( ) and their associated constants (SK, SV), partial transfer volume (∆ ) from water to aqueous solution were determined. In order to stress more on the viscometric data to substantiate its importance, the viscosity B-coefficient has been meticulously evaluated, The present investigation has exploited the possible molecular associations such as ion-ion, ion-solvent, solute-solvent, solute-solute etc., which are identified and eventually discussed about the behaviour of solutes (alkali metal halides) in the solvent mixture

Does Conservation Agriculture Matters in Swazis’ Economy? Evidence from Maize Producing Farmers in Ngwempisi Rural Development Area of Swaziland

The purpose of the study was to determine the economic impact of conservation agriculture on maize production in the Ngwempisi Rural Development Area of Swaziland. Data were obtained from maize farmers distributed equally among farmers practicing conservation agriculture and conventional agriculture. Data obtained were analyzed by the use of descriptive analysis as well as budgeting technique of analysis. Results showed that maize farmers operating under conservation agriculture obtained higher profit level with an average gross margin of about E 3609 compared with an average gross margin of about E161 obtained for maize farmers who operated under conventional agriculture. Majority of farmers practicing conservation agriculture were males with an average age of about 48 years. It was recommended that famers who are currently not practicing conservation agriculture should adopt the method. Key words: Conservation agriculture, production, input costs, Swazilan

The Primacy of As-Built Drawings in the Management of Underground Utility Operations: A New Zealand Study

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Constrained RS coding for Low Peak to Average Power Ratio in FBMC -- OQAM Systems

Multi-carrier modulation techniques have now become a standard in many communication protocols. Filter bank based multi-carrier (FBMC) generation techniques have been discussed in the literature as a means for overcoming the shortcomings of IFFT/FFT based OFDM system. The Peak to Average Power Ratio (PAPR) is a problem faced by all multi-carrier techniques. This paper discusses the methods for reducing PAPR in a FBMC system while maintaining acceptable Bit Error Rate (BER). A new PAPR minimizing scheme called Constrained Reed Solomon (CRS) coding is proposed. The hybrid techniques using coding and companding are tested for different channel models and is found to yield promising results.Comment: 6 pages,6 Figures, Journal of Electrical and Electronics Engineerin

Contested staring: issues and the use of mutual gaze as an on-line measure of social presence

Despite many of the current social presence measures relying heavily on subjective post-test questionnaires, some researchers have identified the value of using on-line, behavioural measures. Gaze, and specifically mutual gaze, is known to be related to social perceptions of an interlocutor, as well as facilitating task performance during an interaction [1, 2, 17]. Second Life allows for the investigation of task- based interaction in a highly controllable social environment, whilst simultaneously allowing measurement of eye movements (using a head-mounted eye-tracker). A paradigm for measuring eye movements of a user during interaction with an avatar or agent is presented. The potential for using this paradigm to investigate the use of mutual gaze as an on- line measure of social presence is discussed