A New Equilibrium Model for the Bazarov Urea Synthesis Process

1989 ◽  
Vol 42 (11) ◽  
pp. 1819 ◽  
Author(s):  
LJ Bagnell ◽  
AM Hodges ◽  
M Linton ◽  
AWH Mau
Keyword(s):  
Equilibrium Model ◽  
Ammonium Hydroxide ◽  
Synthesis Process ◽  
Urea Synthesis ◽  
Synthesis Conditions ◽  
A Value ◽  
Excess Water ◽  
Temperature And Pressure ◽  
Increasing Temperature ◽  
Good Agreement

A new equilibrium model for the high temperature and pressure Bazarov urea synthesis process is presented. By including the formation of ammonium hydroxide as an important equilibrium in the process the model can quantitatively predict the yield of urea under the following range of synthesis conditions: NH3/C02 ratios (L) greater than 2, when no excess water is added, in the temperature range 170-210�C. The model also predicts the observed maximum in urea yield with temperature for a given L> 2. New experimental data for L> 9 are presented that confirm the model's prediction that the yield of urea asymptotically approaches 100% at high L ratios. These data also reveal a pressure dependence for the urea yields which becomes more pronounced with increasing temperature and L ratio. In this region the agreement between theory and experiment is generally within 3% in the pressure range 30-50 MPa. Enthalpies of reaction for the formation of urea from ammonium carbamate and for the formation of ammonium hydroxide under urea synthesis conditions have been derived, and are 26 and -40 kJ mol-1 respectively, the former being in good agreement with a value estimated from literature data.

Au–Ir nanoalloy nucleation during the gas-phase condensation: a comprehensive MD study including different effects

2018 ◽  
Vol 5 (6) ◽  
pp. 1445-1457 ◽  
Author(s):  
Mohsen Abbaspour ◽  
Hamed Akbarzadeh ◽  
Zahra Valizadeh
Keyword(s):  
Gas Phase ◽  
Experimental Results ◽  
Temperature And Pressure ◽  
Increasing Temperature ◽  
Good Agreement

The number of formed clusters and their size increases with the increasing temperature and pressure, which is in good agreement with the experimental results.

scholarly journals Formulasi sistematika knowledge-based engineering untuk penanganan permasalahan proses

2018 ◽  
Vol 7 (1) ◽  
pp. 743
Author(s):  
Surahmad W Widodo ◽  
Yazid Bindar ◽  
P Praharso
Keyword(s):  
Equilibrium Model ◽  
Cfd Simulation ◽  
System Model ◽  
Molar Ratio ◽  
Synthesis Process ◽  
Urea Synthesis ◽  
Heuristic Knowledge ◽  
Process Knowledge ◽  
Knowledge Based System ◽  
Knowledge Based

Urea plant is a petrochemical plant considered as one of strategic industries in Indonesia. Knowledge is important asset for the company that should be managed well in order to give the optimal profit. Without the adequate knowledge to operate the process plant, the process problems tend to be solved by trial-error effort in the field with unknown result and can cause the losses for the company. With the knowledge-based system, the knowledge can be stored, organized can be accessed again to solve the process problem and minimize the trial-error losses in this thesis knowledge-based system formulation for process problem solving in urea synthesis process unit done by study the heuristic knowledge, study the urea synthesis equilibrium model, study the urea tray reactor with CFD simulation and study of development of process knowledge-based system model. Urea reaction equilibrium model used can explain the impact of temperature, NH3/C02 molar ratio and H2O/C02 molar ratio to the urea conversion. Calculation results of conversion and reactor outlet composition show the agreement with the reactor data. Results of CFD simulation show that the new configuration of reactor tray give the better mixing effect of liquid and gas phase than the conventional tray. Heuristic knowledge based on the experience and the knowledge based on process model become the knowledge base for development of knowledge-based system model for process problem solving.Keywords: knowledge-based, process knowledge, heuristic, simulation, CFD, urea reactor AbstrakPabrik pupuk adalah pabrik petrokimia yang termasuk salah satu industri strategis nasional. Pengetahuan merupakan aset penting bagi perusahaan yang harus dikelola sebaik-baiknya agar memberikan manfaat dan keuntungan yang optimal. Tanpa pengetahuan yang cukup dalam mengoperasikan pabrik, maka masalah proses yang dihadapi cenderung diselesaikan dengan percobaan di lapangan yang hasilnya tidak pasti dan mengakibatkan kerugian bagi perusahaan. Dengan sistem berbasis pengetahuan, maka pengetahuan disimpan, terorganisasi dan dapat diakses kembali untuk menyelesaian masalah proses, serta tindakan coba-coba yang menghasi/kan kesalahan dapat diminimalkan. Dalam tesis ini formulasi sistem berbasis pengetahuan untuk penanganan permasalahan proses pada unit reaktor sintesis urea dilakukan dengan melakukan kajian pengetahuan heuristis, kajian model kesetimbangan reaksi sintesis urea, kajian simulasi CFD tray reaktor, serta kajian model pengembangan sistem berbasis pengetahuan proses. Model kesetimbangan yang digunakan dapat menjelaskan pengaruh suhu, rasio NH3/CO2 dan rasio H20/C02 terhadap konversi. Hasil perhitungan untuk konversi dan komposisi keluaran reaktor menunjukkan kesesuaian dengan data rancangan pabrik. Hasil kajian simulasi CFD menunjukkan bahwa dengan konjigurasi tray baru dihasilkan efek pencampuran fasa cair dan gas yang lebih baik daripada dengan tray konvensional. Pengetahuan heuristis dari pengalaman dan pengetahuan berdasarkan model proses menjadi basis pengetahuan yang dikembangkan sebagai model sistem berbasis pengetahuan untuk menyelesaikan masalah proses.Kata Kunci: basis pengetahuan, pengetahuan proses, pengetahuan heuristis, simulasi, CFD, reaktor urea

Standardisation of von Willebrand Factor in Therapeutic Concentrates: Calibration of the 1st International Standard for von Willebrand Factor Concentrate (00/514)

2002 ◽  
Vol 88 (09) ◽  
pp. 380-386 ◽  
Author(s):  
Dawn Sands ◽  
Andrew Chang ◽  
Claudine Mazurier ◽  
Anthony Hubbard
Keyword(s):  
Von Willebrand Factor ◽  
International Study ◽  
Expert Committee ◽  
International Standard ◽  
A Value ◽  
Significant Difference ◽  
Factor Concentrate ◽  
Von Willebrand ◽  
Willebrand Factor ◽  
Good Agreement

SummaryAn international study involving 26 laboratories assayed two candidate von Willebrand Factor (VWF) concentrates (B and C) for VWF:Antigen (VWF:Ag), VWF:Ristocetin Cofactor (VWF:RCo) and VWF:Collagen binding (VWF:CB) relative to the 4th International Standard Factor VIII/VWF Plasma (4th IS Plasma) (97/586). Estimates of VWF:Ag showed good agreement between different methods, for both candidates, and the overall combined means were 11.01 IU/ml with inter-laboratory variability (GCV) of 10.9% for candidate B and 14.01 IU/ml (GCV 11.8%) for candidate C. Estimates of VWF:RCo showed no significant difference between methods for both candidates and gave overall means of 9.38 IU/ml (GCV 23.7%) for candidate B and 10.19 IU/ml (GCV 24.4%) for candidate C. Prior to the calibration of the candidates for VWF:CB it was necessary to calibrate the 4th IS Plasma relative to local frozen normal plasma pools; there was good agreement between different collagen reagents and an overall mean of 0.83 IU per ampoule (GCV 11.8%) was assigned. In contrast, estimates of VWF:CB in both candidates showed large differences between collagen reagents with inter-laboratory GCV’s of 40%. Candidate B (00/514) was established as the 1st International Standard von Willebrand Factor Concentrate by the WHO Expert Committee on Biological Standardisation in November 2001 with assigned values for VWF:Ag (11.0 IU/ampoule) and VWF:RCo (9.4 IU/ampoule). Large inter-laboratory variability of estimates precluded the assignment of a value for VWF:CB.

scholarly journals Lead Recovery from Solid Residues of Copper Industry Using Triethylenetetramine Solution

Minerals ◽  
2021 ◽  
Vol 11 (5) ◽  
pp. 546
Author(s):  
Mateusz Ciszewski ◽  
Andrzej Chmielarz ◽  
Zbigniew Szołomicki ◽  
Michał Drzazga ◽  
Katarzyna Leszczyńska-Sejda
Keyword(s):  
Lead Extraction ◽  
Pressure Leaching ◽  
Base Metals ◽  
Lead Carbonate ◽  
Pure Lead ◽  
Industrial Processing ◽  
High Temperature And Pressure ◽  
Lead Recovery ◽  
Temperature And Pressure ◽  
Increasing Temperature

Industrial processing of mineral ores and concentrates generates large amounts of solid residues, which can be landfilled or further processed to recover selected elements depending on its economical profitability. Pressure leaching is a technology enabling high recovery of base metals like copper and zinc, transferring others like lead and iron to the solid residue. High temperature and pressure of such leaching leads to formation of sparingly soluble lead jarosite (plumbojarosite). The load of lead landfilled as solid residues resulting from such operation is so big that its recovery is perspective and crucial for waste-limiting technologies. This paper is devoted to lead extraction from pressure leaching residues using triethylenetetramine solution and then its precipitation as a commercial lead carbonate. The highest obtained recovery of lead was 91.3%. Additionally, presented technology allows to manage and recycle amine solution and reuse solid products. Produced pure lead carbonate can be directly added to smelting, not increasing temperature within the furnace.

Temperature Dependence of Hole Impact Ionization Coefficient in 4H-SiC Photodiodes

2009 ◽  
Vol 615-617 ◽  
pp. 311-314 ◽  
Author(s):  
W.S. Loh ◽  
J.P.R. David ◽  
B.K. Ng ◽  
Stanislav I. Soloviev ◽  
Peter M. Sandvik ◽  
...  
Keyword(s):  
Phonon Scattering ◽  
Impact Ionization ◽  
Positive Temperature Coefficient ◽  
Positive Temperature ◽  
Different Temperatures ◽  
Ionization Coefficients ◽  
Increasing Temperature ◽  
The Impact ◽  
Good Agreement ◽  
Ionization Rates

Hole initiated multiplication characteristics of 4H-SiC Separate Absorption and Multiplication Avalanche Photodiodes (SAM-APDs) with a n- multiplication layer of 2.7 µm were obtained using 325nm excitation at temperatures ranging from 300 to 450K. The breakdown voltages increased by 200mV/K over the investigated temperature range, which indicates a positive temperature coefficient. Local ionization coefficients, including the extracted temperature dependencies, were derived in the form of the Chynoweth expression and were used to predict the hole multiplication characteristics at different temperatures. Good agreement was obtained between the measured and the modeled multiplication using these ionization coefficients. The impact ionization coefficients decreased with increasing temperature, corresponding to an increase in breakdown voltage. This result agrees well with the multiplication characteristics and can be attributed to phonon scattering enhanced carrier cooling which has suppressed the ionization process at high temperatures. Hence, a much higher electric field is required to achieve the same ionization rates.

Heat-flow experiments in liquid 4He with a variable cylindrical geometry

1987 ◽  
Vol 174 ◽  
pp. 209-231 ◽  
Author(s):  
H. Gao ◽  
G. Metcalfe ◽  
T. Jung ◽  
R. P. Behringer
Keyword(s):  
Cylindrical Geometry ◽  
Small Scale ◽  
Onset Of Convection ◽  
Aspect Ratios ◽  
A Value ◽  
Prandtl Numbers ◽  
Convection Rolls ◽  
Flow Experiments ◽  
Increasing Function ◽  
Good Agreement

This paper first describes an apparatus for measuring the Nusselt number N versus the Rayleigh number R of convecting normal liquid 4He layers. The most important feature of the apparatus is its ability to provide layers of different heights d, and hence different aspect ratios [Gcy ]. The horizontal cross-section of each layer is circular, and [Gcy ] is defined by [Gcy ] = D/2d where D is the diameter of the layer. We report results for 2.4 [les ] [Gcy ] [les ] 16 and for Prandtl numbers Pr spanning 0.5 [lsim ] Pr [lsim ] 0.9 These results are presented in terms of the slope N1 = RcdN/dR evaluated just above the onset of convection at Rc. We find that N1 is only a slowly increasing function of [Gcy ] in the range 6 [lsim ] [Gcy ] [lsim ] 16, and that it has a value there which is quite close to 0.72. This value of N1 is in good agreement with variational calcuations by Ahlers et al. (1981) pertinent to parallel convection rolls in cylindrical geometry. Particularly for [Gcy ] [lsim ] 6, we find additional small-scale structure in N1 associated with changes in the number of convection rolls with changing [Gcy ]. An additional test of the linearzied hydrodynamics is given by measurements of Rc. We find good agreement between theory and our data for Rc.

The Free Energy Simulation Approach to Grain Boundary Segregation In Cu-Ni

1990 ◽  
Vol 209 ◽  
Author(s):  
H. Y. Wang ◽  
R. Najafabadi ◽  
D. J. Srolovitz ◽  
R. Lesar
Keyword(s):  
Monte Carlo ◽  
Free Energy ◽  
Grain Boundary ◽  
Chemical Potential ◽  
Boundary Segregation ◽  
Configurational Entropy ◽  
Accurate Method ◽  
Increasing Temperature ◽  
Atomic Coordinates ◽  
Good Agreement

ABSTRACTA new, accurate method for determining equilibrium segregation to defects in solids is employed to examine the segregation of Cu to grain boundaries in Cu-Ni alloys. The results are in very good agreement with the ones given by Monte Carlo. This method is based upon a point approximation for the configurational entropy, an Einstein model for vibrational contributions to the free energy. To achieve the equilibrium state of a defect in an alloy the free energy is minimized with respect to atomic coordinates and composition of each site at constant chemical potential. One of the main advantages this new method enjoys over other methods such as Monte Carlo, is the efficiency with which the atomic structure of a defect, segregation and thermodynamic properties can be determined. The grain boundary free energy can either increase or decrease with increasing temperature due to the competition between energetic and configurational entropy terms. In general, the grain boundary free energy increases with temperature when the segregation is strongest.

Influence of Temperature on Hydraulic Conductivity in Compacted Bentonite

1997 ◽  
Vol 506 ◽  
Author(s):  
W. J. Cho ◽  
J. O. Lee ◽  
K. S. Chun
Keyword(s):  
Hydraulic Conductivity ◽  
Influence Of Temperature ◽  
Temperature Range ◽  
Compacted Bentonite ◽  
Influence Of Temperature On ◽  
Water Saturated ◽  
Increasing Temperature ◽  
Good Agreement

ABSTRACTThe hydraulic conductivities in water saturated bentonites at different densities were measured within temperature range of 20 to 80 °C. The results show that the hydraulic conductivities increase with increasing temperature. The hydraulic conductivities of bentonites at the temperature of 80 °C increase up to about 3 times as high as those at 20 °C. The measured values are in good agreement with those predicted. The change in viscosity of water with temperature contributes greatly to increase of hydraulic conductivity.

scholarly journals Oxidized BPL Carbons

1993 ◽  
Vol 10 (1-4) ◽  
pp. 75-84 ◽  
Author(s):  
S.S. Barton ◽  
M.J.B. Evans ◽  
J.A.F. Macdonald
Keyword(s):  
Nitric Acid ◽  
Surface Area ◽  
Water Adsorption ◽  
Adsorption Properties ◽  
Bet Surface Area ◽  
Adsorption Sites ◽  
A Value ◽  
Nitrogen Desorption ◽  
Oxidized Carbon ◽  
Increasing Temperature

A series of oxidized carbons has been prepared by treatment of the carbon with concentrated nitric acid at various temperatures, and the surface and adsorption properties of the prepared carbons studied. Water adsorption was modelled using a recently derived equation capable of predicting a value for the primary adsorption sites on the surface of a microporous carbon while fitting the experimentally determined isotherm at high relative pressures. The concentration of primary sites was seen to increase with increasing temperature of oxidation. The very highly oxidized carbon samples were found to have a significantly lower BET surface area determined from nitrogen desorption at 77 K and higher apparent density measured from mercury displacement.

Device Modeling of a-Si:H Alloy Solar Cells: Calibration Procedure for Determination of Model Input Parameters

1998 ◽  
Vol 507 ◽  
Author(s):  
M. Zeman ◽  
R.A.C.M.M. Van Swaaij ◽  
E. Schroten ◽  
L.L.A. Vosteen ◽  
J.W. Metselaar
Keyword(s):  
Solar Cell ◽  
Material Properties ◽  
Calibration Procedure ◽  
Model Parameters ◽  
Model Input ◽  
A Value ◽  
Input Parameters ◽  
Simulated Material ◽  
Good Agreement

ABSTRACTA calibration procedure for determining the model input parameters of standard a-Si:H layers, which comprise a single junction a-Si:H solar cell, is presented. The calibration procedure consists of: i) deposition of the separate layers, ii) measurement of the material properties, iii) fitting the model parameters to match the measured properties, iv) simulation of test devices and comparison with experimental results. The inverse modeling procedure was used to extract values of the most influential model parameters by fitting the simulated material properties to the measured ones. In case of doped layers the extracted values of the characteristic energies of exponentially decaying tail states are much higher than the values reported in literature. Using the extracted values of model parameters a good agreement between the measured and calculated characteristics of a reference solar cell was reached. The presented procedure could not solve directly an important issue concerning a value of the mobility gap in a-Si:H alloys.

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