Reduction In Gas Volume Research Articles

CFD Investigation on Movement Features of Hydrogen Bubble under Microgravity Environment

A designed cryogenic upper stage adopted liquid hydrogen and liquid oxygen (LH2/LO2) as an aerospace propellant. During a zero-gravity coast period in space, the wall heat leakage into the delivery tube could induce liquid propellant evaporation and two-phase flow phenomenon, so that a bubble discharge operation must be employed prior to engine restart. In this study, a CFD approach was utilized to numerically study the bubble discharge behaviors inside the LH2 delivery tube of the upper stage. The bubble motion properties under two different schemes, including positive acceleration effect and circulation flow operation, were analyzed and discussed. The results showed that the boiled hydrogen bubbles could increase to the size of the tube inner diameter and distribute randomly within the entire tube volume, and that, in order for the bubble to spill upward under the acceleration effect, a higher acceleration level than the needed value of acquiring liquid–vapor separation inside the propellant tank should be provided. When creating an acceleration level of 10−3 g0, most of the bubbles could spill upward within 700 s. Significantly, the bubbles could not be completely expelled in the created acceleration condition since a number of small bubbles always stagnate in the bulk liquid region. In the circulation flow operation, the gas volume reduction was mainly attributed to two mechanisms: the vapor condensation effect; and bubble discharge effect. For the case with a circulation flow rate of 0.2 kg/s, a complete bubble discharge purpose was reached within 820 s, while a large bubble stagnation in the spherical distributor occupied a remarkable proportion of the total time. In addition, both the liquid flow rate and liquid subcooling exert important effects on bubble performance. When applying a high circulation flow, the gas volume reduction is mainly due to the inertial effect of liquid flow, but the bubble stagnation in the spherical distributor still affects the total discharge time. The liquid subcooling influence on the gas volume reduction is more significant in smaller circulation flow cases. Generally, the present study provides valuable conclusions on bubble motions inside a LH2 delivery tube in microgravity, and the results could be beneficial to the sequence design of engine restart for the cryogenic upper stage.

Gas Lift Operations Require Accurate Predictions of Downhole Annulus Pressure

This article, written by JPT Technology Editor Judy Feder, contains highlights of paper SPE 190929, “Gas Lift Annulus Pressure,” by Kenneth Decker, SPE, retired, and Robert P. Sutton, SPE, consultant, prepared for the 2018 SPE Artificial Lift Conference and Exhibition—Americas, The Woodlands, Texas, USA, 28–30 August. The paper has not been peer reviewed. Downhole annulus pressure is required for any gas lift design. This paper presents several methods of determining annulus pressure at depth and helps determine which method is most appropriate for specific conditions. It also provides advice on the accuracy of a combination of different critical properties and compressibility correlations, offers an alternative design technique to account for changing annulus temperature during unloading, and provides guidelines for modeling changes in annulus pressure during unloading. Introduction While many methods of computing gas pressure in a flowing environment are available, what is needed in the case of gas lift is the static annulus pressure at depth. Historically, the method of using average temperature and pressure to compute compressibility factors and assuming linear well-temperature gradients made gas lift design relatively simple. The small errors were tolerable and within the normal design safety mar-gins of operating systems with surface pressures of less than 1,500 psi. When surface injection pressures exceed 1,500 psi, calculations become more important. Computers are now used to calculate downhole annulus pressure, and the designer must trust the number that appears on the computer screen. That trust may not be warranted, depending on the method of calculation. The small errors that creep into computer calculations increase linearly as surface injection pressure increases. Additionally, the choice of which correlation to use to model the critical properties of the gas and which compressibility factor correlation to use also affect the accuracy of the calculation. As a gas lift well transitions from a geothermal to a flowing temperature profile during unloading and lifting, the annulus pressure at depth decreases despite surface injection pressure remaining unchanged. The change in annulus pressure is governed by the volume of gas present in the annulus. Reduction in gas volume decreases pressure. Traditional design techniques ignore this reality and substitute a simplified analogy of valve performance that incurs errors and misconceptions about how the annulus pressure changes during unloading. A more-detailed discussion of these issues and proposed questions for program developers is presented in the complete paper. Annulus Pressure Calculation Methods Methods of determining downhole annulus pressure include monographs, density equations used to full depth with average pressure and temperature, and density equations used in small depth increments with average temperature and pressure within the increment. An examination of one of these monographs is shown in Fig. 1. The choice of which method to use comes with limitations on the accuracy of the predicted pressure at depth.

Bubbling fluidized bed methanation study with resolving the mesoscale structure effects

AbstractTo elucidate the influence of the changes in the mesoscale structure caused by microscale chemical reactions on the macroscale properties, continuity equations, simplified momentum equations, and pressure‐drop balance equation were introduced into the conventional reactor model to accurately analyze the mesoscale phenomenon in the fluidized bed methanation system, thereby avoiding the limitation due to the use of empirical correlations to describe the mesoscale structure. The reduction of gas volume and the variations of composition and physical properties due to methanation reactions were considered in this model, and the effects of these changes on the mesoscopic flow structures and the macroscopic properties of the entire reactor were further investigated. Several experiments of fluidized bed methanation were also carried out to verify the effectiveness of the proposed reactor model. The results showed that the suggested model can successfully predict the hydrodynamics and reaction behaviors under various operating conditions.

Effects of initial static bed height on fractional conversion and bed pressure drop in tapered-in and tapered-out fluidized bed reactors

In this article, a standard 2D Two-Fluid Model (TFM) closed by the kinetic theory of granular flow (KTGF) has been applied to simulate the behavior of tapered-in and tapered-out fluidized bed reactors. In this regard, two types of chemical reactions with gas volume reduction and increase were considered to investigate the effects of initial static bed height on the fractional conversion and bed pressure drop. To validate the CFD model predictions, the results of hydrodynamic simulations concerning bed pressure drop and bed expansion ratio were compared against experimental data reported in the literature and excellent agreement was observed. The obtained simulation results clearly indicate that there is an appropriate static bed height in a tapered-in reactor in which the fractional conversion becomes maximum at this height; whereas variations of static bed height in a tapered-out reactor have insignificant influences on the fractional conversion. Moreover, it was found that the residence time, temperature, and intensity of turbulence of the gas phase are three important factors affecting the fractional conversion in tapered fluidized bed reactors. In addition, it was observed that increasing the static bed height increases the bed pressure drop for both the tapered-in and tapered-out fluidized bed reactors.

Study of Combustion Characteristics of Ethanol at Different Dilution With the Carrier Gas

With the ever-rising concern of global warming, carbon capture is gaining the reputation of one of the most challenging fields of research. A very promising technology to capture CO2 is oxy-combustion. Oxy-combustion offers several advantages over conventional combustion technologies, such as flue–gas volume reduction, high combustion efficiency, low fuel consumption, and significant reduction in NOx emissions. Liquid fuel is available and it is the most widely used source of energy in the world. Easy handling and transporting, less storage volume and higher flame temperature are some of the features of liquid fuel which give it an upper hand over other sources. In this study, an experimental work on oxygen enriched combustion of ethanol in a vertical reactor by Lacas et al. (2005, “Experimental Study of Air Dilution in Oxy-Liquid Fuel Flames,” Proc. Combust. Inst., 30(2), pp. 2037–2045) has been modeled numerically. Nonpremixed model using probability density function (PDF) has been incorporated to simulate the combustion process of ethanol droplets. Predicted combustion characteristics are found to be in good compliance with the experimental data. In addition to this, effects of dilution of carbon dioxide in oxygen on the flame properties have also been presented. Combustion of ethanol in oxygen–carbon dioxide environment has been compared with that of the conventional air environment.

Pressure Fluctuation Analysis of the Defluidization Caused by a Reaction Involving Gas-Volume Reduction in a Fluidized Catalyst Bed

Severe defluidization occurs when a reaction that is accompanied by a decrease in gas volume is performed in a fluidized catalyst bed. Defluidization occurs because the gas velocity in the emulsion phase decreases to less than the minimum fluidization velocity. Because numerous useful industrial reactions involve a decrease in gas volume, the development of a method for rapid detection of defluidization is important for maintaining good fluidization. In this study, the inside of a column was visually observed during CO2 hydrogenation in a fluidized bed. When the reaction rate was low, good fluidization was always observed. However, defluidization, such as channeling, occurred occasionally when the reaction rate was increased. These reaction conditions were classified as the defluidization region in this study. The time-change characteristics for the frequency of pressure drop fluctuations were studied using continuous wavelet transfer (CWT). Additionally, the autocorrelation function was used to determine the dominant frequency. Using these functions, the decrease in the dominant frequency and the periodicity of the pressure fluctuations were detected in the defluidization region, even when the bed was observed to be satisfactorily fluidized. On the other hand, the prediction of defluidization itself several seconds before it occurred proved difficult.

CFD Simulation of Hydrodynamics and Methanation Reactions in a Fluidized-Bed Reactor for the Production of Synthetic Natural Gas

Numerical investigations of hydrodynamics and kinetic reactions in a fluidized bed methanation reactor are carried out by coupling methanation kinetics with the two-fluid flow model. The gas–solid reacting flow models are implemented within OpenFOAM software. The grid resolution is investigated using two-dimensional and three-dimensional (2D and 3D) meshes. The bed height is reasonably predicted with the Gidaspow and Syamlal models. Simulated results are compared against experimental data in the literature. The simulated axial species concentrations agree well with the measured results at the end of the bed. The effects of different operating parameters are evaluated using the established models. The increase in the gas inlet velocity results in more dilute solid concentration and larger bed expansion. The weak bed expansion results from the methanation reaction with gas volume reduction. The methane concentration is increased when increasing catalyst inventory in the reactor. The addition of water into t...

An emulsion phase condensation model to describe the defluidization behavior for reactions involving gas-volume reduction

The fluidization quality decreases drastically when the reactions involving a gas volume decrease were carried out in a fluidized bed reactor. The model to describe the defluidization behavior for reactions involving gas-volume reduction is highly required to choose proper operation parameters. Herein a phase condensation model is proposed to describe the fluidization and the transfer behavior of the chemical reactions involving a gas volume decrease when they are carried out in a fluidized bed reactor. The phase condensation model concerns an emulsion phase domain. The mass transfer between bubbles and the modeling domain, the governing equations for the hydrodynamics and mass transport, the Brinkman equation, together with the kinetic sub-model are incorporated in the model. The simulation result captures the spatial distribution of reactant concentration and gas velocity which is onion-shaped for the CO2 hydrogenation reaction. The fluidization quality can be predicted by the phase condensation model. The result indicates that lower temperature and higher inert gas content in the feed gas are favorable for good fluidization. A phase diagram of fluidization quality is obtained using temperature and expansion factor as indices. The phase condensation model renders the precise prediction which compares well with published experimental data.

Prevention of Defluidization by Recycling Unreacted Gas for Reactions Involving Gas Volume Reduction in a Fluidized Bed

Prevention of Defluidization by Recycling Unreacted Gas for Reactions Involving Gas Volume Reduction in a Fluidized Bed

Prevention of defluidization by gas dilution for reactions involving gas–volume reduction

In industrial fluidized bed processes, the system often involved a change in volumetric flow. Defluidization occurs when reactions involving a decrease in gas volume are carried out in a fluidized catalyst bed. This is due to decrease in gas velocity below the minimum fluidization velocity in the emulsion phase. One method to improve fluidization quality is to supply an inert gas with reactant gases: similar effect can be obtained by supplying an excessive amount of one of the reactants. In the present study, the effect of a diluted reactant gas on fluidization quality is quantitatively analyzed by performing CO2 hydrogenation in a fluidized catalyst bed. Stable operation can be established by operating the fluidized bed to avoid the conditions contained in the defluidization zone using two parameters that influence fluidization quality.

In vitro ruminal fermentation of Pennisetum purpureum CT-115 supplemented with four tropical browse legume species

An in vitro gas production experiment was completed to determine effects of four tropical browse legumes ( i.e., Acacia cornigera, AC; Albizia lebbekoides, AL; Enterolobium cyclocarpum, EC; Leucaena leucocephala, LL) at 0.15 or 0.30 of total substrate on microbial fermentation of the tropical grass Pennisetum purpureum CT-115 (PP). Two incubation runs with four bottles per treatment were completed, using two bottles for gas production measurements up to 96 h and two bottles for microbial purine bases (PB) concentration analysis after 24 h. Inclusion of AC, EC and LL linearly increased ( P<0.05) gas production from PP alone at an initial stage of fermentation (5 h) because of their higher fermentation rate versus PP. However, whereas the linear increase in gas production was maintained at mid fermentation ( i.e., 24 h) with AC, there was no effect with LL and a linear reduction in gas volume at 24 and 96 h with EC, possibly because of its saponin content. Gas production with AL was linearly reduced at 24 and 96 h ( P<0.01). There were no differences in microbial concentrations, either estimated from a partitioning factor or PB analysis, but PB concentration in the solid residue increased three-fold when LL were included. Differences among legume species in chemical composition, and in the nature of their secondary compounds, are responsible for the fermentation pattern of mixed substrates.

Compactness factors for rolled, stacked-screen regenerative heat exchangers

The objective for the current research was to determine how the heat transfer and pressure drop characteristics changed in a stacked, wire-screen regenerative heat exchanger (regenerator), if the screens which were used to construct the matrix were rolled to decrease their thickness. More of the rolled screens would fit into a regenerator with a reduction in gas volume in the regenerator. During the course of the research, an improved method for determining the heat transfer characteristics of a porous medium regenerator was developed. The results show that the compactness factor ( j H/ f) was adversely affected by rolling. Flattening the screens by 15%, 30%, or 50%, did not improve the heat transfer rate to the matrix, but it did increase the total pressure drop. Rolling the screens caused a decrease in both wetted surface area and pore size. The heat transfer which is proportioned to the wetted surface area was reduced. The pressure drop, which is strongly dependent on pore size, increased. Rolling the screens also reduced the effectiveness of the regenerator.

Blow-by gas volume reduction of water cooled gasoline engine for motorcycle

Blow-by gas volume reduction of water cooled gasoline engine for motorcycle

Countermeasure Against Explosion of Gas Insulated Porcelain Bushing

In order to investigate countermeasures against the explosion of gas-insulated porcelain bushings, full-scale explosion tests using actual porcelain bushing shells were conducted. Suitable countermeasures are gas volume reduction, gas pressure reduction, and elastic lining methods. The effectiveness of each was demonstrated by the full-scale explosion tests. An equation on the scattering distance of fragments of the porcelain shell was derived from the test results. A prototype explosion-proof gas-insulated porcelain bushing was developed, and its mechanical and electrical performance were confirmed. >

Countermeasure against explosion of gas insulated porcelain bushing

In order to investigate countermeasures against the explosion of gas-insulated porcelain bushings, full-scale explosion tests using actual porcelain bushing shells were conducted. Suitable countermeasures are gas volume reduction, gas pressure reduction, and elastic lining methods. The effectiveness of each was demonstrated by the full-scale explosion tests. An equation on the scattering distance of fragments of the porcelain shell was derived from the test results. A prototype explosion-proof gas-insulated porcelain bushing was developed, and its mechanical and electrical performance were confirmed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Effect of pneumococcal lobar pneumonia on canine lung mechanics.

We produced left lower lobe (LLL) pneumococcal pneumonia in seven dogs and measured lung volumes and pulmonary mechanics before (day 1) and 48 h after (day 3) development of the infection. Compared with seven control dogs, total lung capacity (TLC) and functional residual capacity (FRC) decreased 550 and 140 ml, respectively, representing a 15% reduction from the initial value in both cases. Compliance measured during tidal breathing decreased by 30%, and even when corrected for the smaller FRC on day 3, specific compliance (CLsp) was reduced. At autopsy, the infected LLL had an excess weight of 89 g, and its 50% reduction in gas volume accounted for the decrease in TLC from day 1 to day 3. Compared with control dogs, there were no changes in the deflation pressure-volume curves of the noninfected lung of the pneumonia dogs. These results indicate that the reduction in TLC in bacterial lobar pneumonia was small and resulted from the reduced gas volume of the infected lobe. Assuming that the increased weight gain in the LLL represented 89 ml of exudate that filled alveoli, we propose that bacterial pneumonia reduced gas volume at FRC by filling alveoli with inflammatory exudate and further decreased TLC by preventing these alveoli from inflating. The reduced CLsp suggested nonventilation of air spaces in addition to those that were liquid filled and was consistent with nonventilation of the entire LLL.

A Computer Program for Gas Volume Reduction Tables

A Computer Program for Gas Volume Reduction Tables

Measurement Problems in Gas Plant Operations

Introduction In September, 1962, the gas processing plant owned by Edmonton Liquid Gas, located on the southern outskirts of the City of Edmonton, started processinggas delivered to it by Northwestern Utilities for the removal of hydrocarbonliquids. The plant was originally designed to handle 50 MMcf/D of gas coming toEdmonton from the Pembina field and another 20 MMcf/D from the Texaco plant atBonnie Glen. These gas streams were to remain segregated, so two separateabsorption towers were required for processing. The Pembina unit was to operateat 650 psig and the Bonnie Glen at 450 psig. The residue gas was to be returnedto the Northwestern Utilities transmission line system. The reduction in gasvolume through the extraction of approximately 48,000 gal/D of liquid productswas estimated at 3.6% of the inlet gas volume. Payment was to be made for thisreduction on a therm basis. Normally, gas plants of this nature are either subsidiaries of production ortransmission companies or part of an integrated system. As such, anydiscrepancies in a plant balance between the gas shrinkage and the extractedproducts are of no great consequence and can be taken care of in the accountingprocedures. However, in this case with separate ownership of the two companies, metering becomes a major problem to determine an accurate value of the productsextracted or used. The measurement in the reduction of gas volume cannot beused because the inherent inaccuracies in gas orifice metering are too greatfor this purpose. Measurement of the liquid products with positive displacementmeters would be the basis for billing. Gas measurement would be done only forthe purpose of obtaining plant balances. Prior to the selection and installation of the gas measurement equipment, asurvey was made of gas plants operating under similar circumstances in bothCanada and U.S.to determine their experiences and practices.