Complete Operation Cycle Research Articles

Global and Local Elastic-Plastic Stress Analysis of Coke Drum Under Thermal-Mechanical Loadings

Coke drums are critical equipment in the petroleum industry. The failure modes of coke drums include excessive bulging deformation and fatigue cracking. The elastic-plastic behavior of a coke drum, subjected to both thermal and mechanical loadings, is analyzed for a complete cycle of operation. The effects of multiple operational cycles and localized hot/cold spots are also investigated. It is found that yielding of the clad layer starts at the very early stage in an operating cycle and permanent deformation is caused in the first operating cycle. Plastic shakedown occurs in the clad layer under combined operating thermal and mechanical loadings. It is also found that both hot and cold spots will cause bulging of the shell and the cold spot can cause more severe deformation than the hot spot.

Heat Transfer and Stress Analysis of Coke Drum for a Complete Operating Cycle

Coke drums experience severe thermal and mechanical loadings during operation, and the reliability and safety of the coke drums are critical to the industry. The objective of this study is to analyze temperature and stress of the coke drum for a complete process cycle. The thermal analysis model of the coke drum is first developed incorporating appropriate boundary conditions. The heat transfer coefficients at the inner surface of the coke drum, which change with the operation stages and the levels of oil filling and water quenching, are determined based on the temperature measurement data at a certain location on the outer surface of the coke drum. The temperature history of the coke drum of a complete cycle is then obtained by finite element heat transfer analysis, and computed temperature data are used for the stress analysis of the coke drum, including both thermal and mechanical loadings. It is found from numerical results that the clad experiences a biaxial stress cycling with maximum value higher than the yield limit of the material, which coincide with the low cycle fatigue failure of the structure.

Investigation of peeling resistance in a bimetallic joint of petrochemical reactors in hydrogen environment

We give an example of the numerical modeling of hydrogen redistribution in constructional elements with protective overlays caused by nonstationary thermal actions. It has been established that variations of the thermal state change hydrogen diffusion in two-layer constructional elements, forming, in this case, nonequilibrium hydrogen supersaturations of local volumes of the melting zone. The degree of danger depends here on the kinetics of thermal processes. We have investigated experimentally the hydrogenation of steel specimens with an anticorrosive layer applied by three methods. Hydrogenation simulated the complete cycle of operation of a reactor for oil hydrocracking. The results of ultrasonic inspections as well as macro- and microcontrol of the melting zone show that there are no defects in the bimetallic joint.

Effect of Aeration Rate on Nutrient Removal from Slaughterhouse Wastewater in Intermittently Aerated Sequencing Batch Reactors

The effect of aeration rate on nutrient removal from slaughterhouse wastewater was examined in two 10-L laboratory-scale sequencing batch reactors (SBRs—SBR1 and SBR2) operated at ambient temperature. The contaminants in the slaughterhouse wastewater had average concentrations of 4,000 mg chemical oxygen demand (COD) L−1, 350 mg total nitrogen (TN) L−1 and 26 mg total phosphorus (TP) L−1. The duration of a complete SBR operation cycle was 8 h and comprised four operational phases: fill (7 min), react (393 min), settle (30 min) and draw/idle (50 min). During the react phase, the reactors were intermittently aerated four times at 50-min intervals, 50 min each time. DO, pH and oxidation–reduction potential (ORP) in the reactors were real-time monitored. Four aeration rates—0.2 L air min−1 in SBR1 for 70 days, 0.4 L air min−1 in SBR1 for 50 days, 0.8 L air min−1 in SBR2 for 120 days and 1.2 L air min−1 in SBR1 for 110 days—were tested. When the aeration rate was 0.2 L air min−1, the SBR was continuously anaerobic. When the aeration rate was 0.4 L air min−1, COD and TP removals were 90% but TN removal was only 34%. When the aeration rates were 0.8 and 1.2 L air min−1, average effluent concentrations were 115 mg COD L−1, 19 mg TN L−1 and 0.7 mg TP L−1, giving COD, TN and TP removals of 97%, 95% and 97%, respectively. It was found that partial nitrification followed by denitrification occurred in the intermittently aerated SBR systems.

Curvature theory for a two-degree-of-freedom planar linkage

This paper shows that the method of kinematic coefficients can be applied in a straightforward manner to the kinematic analysis of mechanisms with more than one input. For illustrative purposes, the paper presents an example of a two-input linkage or two-degree-of-freedom linkage; namely, the well-known planar five-bar linkage. The two inputs are the side links of the five-bar linkage which are assumed to be cranks. Since the linkage is operated by two driving cranks independently then the linkage can produce a wide variety of motions for the two coupler links. The kinematic coefficients are partial derivatives of the two coupler links with respect to the two input crank angles and separate the geometric effects of the mechanism from the operating speeds. As such they provide geometric insight into the kinematic analysis of a mechanism. A practical application of the five-bar linkage is to position the end-effector of an industrial robotic manipulator, for example, the General Electric model P50 robotic manipulator. The paper then presents closed-form expressions for the radius of curvature and the center of curvature of an arbitrary coupler curve during the complete operating cycle of the linkage. The analytical equations that are developed in the paper can be incorporated, in a straightforward manner, into a spreadsheet that is oriented towards the path curvature of a multi-degree-of-freedom linkage. The author hopes that, based on the results presented here, a variety of useful tools for the kinematic design of planar multi-degree-of-freedom mechanisms will be developed for planar curve generation.

Tunneling and impact ionization in thin-film ZnS:Mn-based electroluminescent structures

The errors in determining the depth of the surface-state levels of the insulator-phosphor cathode interface, the width of the potential barrier, and the probability of electron tunneling from the surface states are analyzed using the numerical simulation of experimental time dependences of the current flowing across the phosphor layer. The time dependences of the above parameters for the complete cycle of operation of electroluminescent emitters are obtained, and the effect of the frequency and amplitude of excitation voltage pulses as well as illumination of emitters in the blue spectral region during the interval between the pulses on these dependences is revealed. The time dependences of the multiplication factor and the number of ionization events per electron in the impact ionization region are determined. The largest value of the impact ionization coefficient is estimated to be ≥2.6 × 104 cm−1.

Irreversible performance of a quantum harmonic heat engine

The unavoidable irreversible loss of power in a heat engine is found to be of quantum origin. Following thermodynamic tradition, a model quantum heat engine operating in an Otto cycle is analysed, where the working medium is composed of an ensemble of harmonic oscillators and changes in volume correspond to changes in the curvature of the potential well. Equations of motion for quantum observables are derived for the complete cycle of operation. These observables are sufficient to determine the state of the system and with it all thermodynamical variables. Once the external controls are set, the engine settles to a limit cycle. Conditions for optimal work, power and entropy production are derived. At high temperatures and quasistatic operating conditions, the efficiency at maximum power coincides with the endoreversible result . The optimal compression ratio varies from in the quasistatic limit where the irreversibility is dominated by heat conductance to in the sudden limit when the irreversibility is dominated by friction. When the engine deviates from adiabatic conditions, the performance is subject to friction. The origin of this friction can be traced to the noncommutability of the kinetic and potential energy of the working medium.

Analysis of multidimensional and two-phase flows in solid rocket motors

A physicomathema tical model describing the processes in the combustion chamber of solid rocket motors (SRMs) is suggested. The model can be used in practical calculations of the parameters of real motors with solid-propellant charges of complex geometry. The model allows the description of two-phase flows (from averaged zero dimensional to three dimensional) for the complete operation cycle of SRMs, including transition to steady-state operating conditions and pressure drop accompanying the propellant burnout. Equations obtained can readily be employed in designing computer codes. Methods for the solution of these equations are discussed. Results of studying the gasdynamics parameters of internal flows are reported. Calculated values are compared with experimental data obtained for a modeled gas flow turning from the head-end to the charge channel. A three-dimensional calculation of flow parameters in a slotted-tube charge of a large-size motor is illustrated by distribution patterns for pressure and velocity. The influence of the redistribution of aluminum in a solidpropellant charge on the combustion efficiency coefficient of the metal, specific impulse, and in-chamber losses is analyzed.

Instantaneous Invariants and Curvature Analysis of a Planar Four-Link Mechanism

This paper shows that the canonical system and the instantaneous invariants for a moving plane, which is connected to the fixed plane by a revolute-revolute crank, are functions of the derivatives of the crank angle. Then closed-form expressions are derived for the curvature ratios of the path generated by an arbitrary point fixed in the moving plane, in terms of the coordinates of the point and the instantaneous invariants of the plane. For illustrative purposes, numerical results are presented for the instantaneous invariants (up to the fourth-order) of the coupler of a specified crank-rocker mechanism, as a function of the input angle. In addition, the paper shows the variation in the first and second curvature ratios of an arbitrary coupler curve during the complete operating cycle of the mechanism. The authors hope that, based on the results presented here, a variety of useful tools for the kinematic design of planar mechanisms, with a rotary input, will be developed for plane rigid body guidance as well as curve generation.

Flow injection on-line sorbent extraction pre-concentration for graphite furnace atomic absorption spectrometry

Flow injection (FI) techniques were used to develop an efficient on-line sorbent extraction pre-concentration system for graphite furnace atomic absorption spectrometry with lead as a model trace element. Bonded silica with octadecyl functional groups (C18) was used as sorbent in a 15-µl conically shaped micro-column. The lead diethyldithiocarbamate chelate was formed on-line, loaded on to the column for 60 s, washed with de-ionised water and eluted with ethanol into a collector with a volume of 75 µl, made from 0.35 mm i.d. polytetrafluoroethylene tubing. The collected eluate was introduced into the graphite tube by an air flow on initiation of the FI system for pre-concentration of the next sample. The reproducibility of FI peak gradients was exploited through precise timing of the collection of the eluate fraction so that end sections of the eluate bolus containing lower analyte concentrations were discarded. A 26-fold enhancement in peak area compared with 50 µl direct introduction was obtained with 60-s pre-concentration while achieving a precision of 1.9% relative standard deviation for 0.1 µg l–1 of Pb (n= 11), and a detection limit of 0.003 µg l–1(3σ). The complete cycle of operation was 150 s which conveniently fitted into the time interval between successive graphite furnace firings. Determination of Pb in sea water samples showed that the interfering matrix had been almost completely removed during the pre-concentration, and determinations were made without using chemical modifiers. Results obtained for National Research Council of Canada Standard Reference Materials CASS 1, CASS 2 [Seawater (Coastal)] and NASS 1 [Seawater (Open Ocean)] using matrix-matched standards and for the SLRS 1 Riverine Water using simple aqueous standards agreed well with certified values.

Thermal boundary layer thickness in the cylinder of a spark-ignition engine

The thicknesses of the thermal boundary layers in the cylinder of a spark-ignition engine were measured throughout the complete operating cycle. The engine used for these experiments was a special visualization engine with a square cross-section ‘cylinder’ and two quartz glass walls. Measurements of thickness were taken at different locations, speeds and loads, from schlieren photographs. The results show that the layers on the cylinder wall reach a maximum thickness of about 2 mm at the end of expansion. On the cylinder head and piston top, the layers are two to three times thicker. Reducing engine speed resulted in thicker layers, while changing load showed no significant effects on thickness. It is shown that on the cylinder wall, the thermal boundary layer thickness depends on thermal diffusivity and the time available for the layer to develop. The growth of this layer was correlated with an expression in the form δ T √( αt) ∞ Re 0.2.

Non-linear detector response in gas and liquid chromatography — quantification with a laboratory automation system

A Laboratory Automation System (Hewlett-Packard 3354 B) minimizes systematic errors in quantification problems when detector responses are not linear. The calibration curves for the various products are stored and results are calculated by linear segmental interpolation. The complete operating cycle is controlled by the System.

Analysis of a High-Speed Solenoid-Actuated Mechanism

The mechanism which is considered in this paper is a high-speed, solenoid-driven, impact printing mechanism. The purpose of the analysis is to construct a mathematical model of the mechanism from which the dynamics of the mechanism can be studied during a complete printing cycle. The basic approach taken is to construct a lumped parameter model of the mechanical system. Motion equations are written which are solved simultaneously with equations governing the electromagnetic system. Elements of the mechanical system which are described include viscoelastic buffers between impacting parts. Dead space or intermittent contact between parts is another aspect of the problem which is defined. The relationship between core flux and impressed current is established through an experimentally measured magnetization curve. Equations governing both the rise and fall of the magnetic flux are developed since a complete cycle of operation is under study. The resulting set of equations is nonlinear in nature and impractical to solve by hand. However, a systematic solution to the equations is readily obtained by numerical integration on a digital computer.

The tetrode power transistor

Power transistor circuits are characterized by the fact that the collector current must swing over a wide range of values during any complete cycle of operation. One disadvantage of present-day alloyed junction power transistors is that the current gain decreases with increasing collector current. This causes distortion in linear applications and makes temperature stabilization in switching circuits more difficult. Power transistors having emitter areas large enough to handle currents in the amperes range can be made as tetrodes by use of an annular ring geometry. Experimental results show that the gain characteristics can be altered by applying a bias voltage or a portion of the signal voltage transversely across the base. The gain characteristic can be made flatter for improved fidelity in audio applications, or even reversed to give increasing gain with collector current for certain switching applications. Practical circuitry utilizing the improved gain characteristics of power tetrodes has been developed, and the annular geometry permits the fabrication of tetrodes using conventional alloying techniques.