Air Injection Scheme Research Articles

Numerical and chemical kinetic analysis to evaluate the effect of steam dilution and pressure on combustion of n-dodecane in a swirling flow environment

In the present study, numerical analysis on the effect of steam dilution and high pressure on liquid fuel swirl combustion is carried out using a turbulent non-premixed combustion model. Tangential air injection scheme is adopted in a conical combustor. High recirculation is achieved inside the combustor due to the swirl pattern produced by the tangential air inlets. n-Dodecane, which is a major component of kerosene and Jet-A fuel, is selected as fuel in the present study. The thermal intensity of 5.37 MW/m3 with 21.1 kW thermal input is considered for the computational study. The chamber pressure is varied from 1 to 20 atm, keeping the momentum of inlet airflow constant. Steam added in the oxidizer as a diluent is varied from 0 to 20% by mass. Computational Fluid Dynamics (CFD) analysis using RANS (Reynolds Averaged Navier-Stokes) equations is performed to understand the flow characteristics and study the effect of steam dilution and pressure on NO formation. Realizable k-ε turbulence model is used in the present study to capture the flow behavior due to the swirling motion. Spray characteristics are modelled using the Discrete Phase Model. The chemical representation is realized using scalar conservation concept with β-PDF model. Detailed chemical kinetic analysis with ignition delay characteristics, rate of species production, reaction behavior and sensitivity analysis is carried out. It is observed that the ignition delay decreases rapidly with pressure and very slowly with steam dilution. Effect of pressure and dilution on the OH concentration and olefins are discussed. Peak flame temperature and NO formation decreased with the steam addition. Emission characteristics are presented in the paper.

Distributed combustion mode in a can-type gas turbine combustor – A numerical and experimental study

A novel combustor design assisted with increased hot air jet momentum is used to enhance the internal recirculation. Geometric modifications are incorporated in terms of altered air injection scheme to improve the mixing and internal recirculation of hot combustion products. The combustor operates with liquefied petroleum gas in a distributed combustion mode, and thermal intensities vary in the range of 20–40 MWm−3atm−1. Numerical calculations of the reacting flow field show the presence of large recirculation zones, and they are quantified using reactant dilution ratio, Rdil. It is greater than 2.5 for the most part of the combustor, thereby creating a sufficiently heated and diluted environment for sustaining the distributed combustion at high thermal intensities. OH* chemiluminescence studies are carried out for the first time to observe the combustion zone structure for the conventional and distributed combustion regime in a gas turbine combustor. The distribution of OH* becomes increasingly uniform with reduced maximum OH* intensity in this combustion mode. The measured NOx is less than 8 ppm, and CO emission is below 25 ppm for all the operating conditions (ϕ = 0.2–1). Acoustic emissions drop significantly, as the combustor switches its operation to a distributed combustion mode. The novelty of this study lies in the application of this combustion mode in a gas turbine engine. This article also sheds light on the importance of the internal recirculation of combustion products, to achieve a distributed combustion mode in a generic can combustor at gas turbine relevant conditions.

A novel air injection scheme to achieve MILD combustion in a can-type gas turbine combustor

This article presents the design and development of a can-type gas turbine combustor operating in flameless combustion mode with liquid fuels. The combustor operates with kerosene and thermal intensities varying from 5.1 to 7.5 MW/m3. A novel air-injection scheme is proposed, in which air is supplied from different injection holes namely, swirl air near fuel injection, primary, secondary and dilution air in the downstream. These air injection holes are arranged in a way to help create strong recirculation of hot combustion products leading to increased mixing and dilution of incoming fresh reactants. Direction, orientation and mass fraction of swirl, primary, secondary and dilution air are optimized through a series of reacting flow simulations aimed at maximizing the reactant dilution ratio, a key parameter to achieve flameless combustion. It is observed that if the momentum of the air is increased beyond a critical value, the combustor switches its operation into flameless mode due to increased mixing and dilution of fresh reactants with hot combustion products. Combustion occurs in a well-distributed reaction regime within the combustor volume. Measured NOx emissions are less than 5 ppm and acoustic emissions are significantly reduced during the combustor operation in flameless combustion mode.

Air staging application effects on overall steam boiler operation

This paper presents the results of calculation system of main processes in power steam boiler, before and after application of air staging. Modified air injection scheme was implemented during 2015 on the power steam boiler within unit 1 of TPP Kostolac B. Measurements performed on site showed that applied reconstruction led to a permanent loss of the steam boiler power. This study was performed in order to define the cause of such an occurrence and to consider the possibility for regaining the designed steam parameters along with keeping NO concentration in prescribed limits. This paper x discusses the influence of repositioning the air injection location on processes within the furnace. Furthermore, the influence of the redistribution of injected air-flow along the furnace height on important boiler operation parameters has been analyzed. Analysis showed that, with appropriate dosing of air along the height of the existing furnace, it is possible to achieve the optimum of the boiler's operation parameters. Results of research showed that air staging throughout the furnace height in best test case additionally reduces NO concentration (195-225 mg/Nm3) and increases the power of x considered boiler (828.8-751.1 MW) with an insignificant decrease of the boiler's efficiency (86.27-86.77%). Furthermore, the designed temperatures of superheated (540-498?C) and reheated (540-518?C) steam have been reached again, whereby the safety of the boiler's operation has been significantly increased. Results of this study improve the present explanation of the processes occurred in the furnace with applied primary measures. They also give directions on defining the most influential parameters on considered processes with the final purpose to increase the efficiency and availability of the entire plant.

Investigation of the formation process of a low-permeability unsaturated zone by air injection method in a slope

Slope drainage is crucial to landslide mitigation, yet current drainage technologies still encounter difficulties in achieving fast drainage. Based on the permeability characteristics of unsaturated soil with low water content, this study presents a new drainage measure, known as the air injection method, by injecting compressed air into the soil to form a low-permeability unsaturated zone for slope drainage. A series of physical model tests and numerical simulations are performed to study the formation process of the unsaturated zone by the air injection method. The study shows that the formation process undergoes four phases according to the variations in groundwater level in the slope and the features of the air–water flow in the unsaturated zone at different injection pressures. Additionally, numerical analyses indicate that the two-phase flow in the development of the unsaturated zone gradually transitions from a water-flow- to an air-flow-dominant zone. Furthermore, the expansion of the unsaturated zone by air injection is asymmetrical along the injection point, but tends to align with the downstream slope direction owing to the influence of groundwater flow. The findings are important for the establishment of the theoretical foundation of the air injection method, and the optimization of the air injection scheme. The proposed method and results obtained through laboratory investigation and numerical simulation provide a fresh perspective on slope drainage.

Longitudinal pulsed detonation instability in a rotating detonation combustor

The peculiar phenomenon of longitudinal pulsed detonation (LPD) in a rotating detonation combustor (RDC) is studied using hydrogen–air mixtures, by utilizing: (i) two air injection schemes having different inlet areas, and (ii) a convergent nozzle assembly with different spacers that affixes to the RDC exit. By varying the air injection pressure ratio and the backpressure, the regime of occurrence and the mechanism of this pulsed detonation instability are investigated. Immense evidence to suggest that LPD is caused by a peculiar detonation initiation mechanism enabled by a reflected shock wave from the RDC exit is discovered through an ensemble axial pressure profile analysis. Distance–time plots show that a single cycle of the pulsed detonation has two components: a fast-moving axial forward decaying detonation wave (with 75% of the ideal detonation speed) and a slower reflected detached shock wave (with 30% of the ideal speed). When the weak reflected wave comes in contact with the fresh reactants at the RDC headwall, another strong axial detonation is produced, thereby continuing the cycle without external ignition. LPD is also found to have three diverse facets, namely, inception, sustenance and operating frequency. For similar backpressures, the two air injection schemes have completely different operating regimes, leading to the inference that while backpressure is necessary for the onset of the pulsed detonation instability, by virtue of enabling reflected shock waves from the exit, lower air injection pressure ratio dictates the sustenance of the instability. A narrow band of injection pressure ratios, between 1.4 and 1.85, under back-pressurized RDC operation has high proclivity to produce sustained periodic longitudinal pulsed detonations in the combustor. Above this range, stable rotating detonation is preferred, and below this range, the operation is distinguished by the mixed presence of both rotating and pulsed detonations for a given test point, finally breaking down into chaotic instability for lower pressure ratios. The frequency of the pulsed detonation operation is found to depend on the initial combustor pressure and equivalence ratio, with higher frequency observed with an increase in backpressure and equivalence ratio.

Modeling-based optimization of a fixed-bed industrial reactor for oxidative dehydrogenation of propane

An industrial scale propylene production via oxidative dehydrogenation of propane (ODHP) in multi-tubular reactors was modeled. Multi-tubular fixed-bed reactor used for ODHP process, employing 10000 of small diameter tubes immersed in a shell through a proper coolant flows. Herein, a theory-based pseudo-homogeneous model to describe the operation of a fixed bed reactor for the ODHP to correspondence olefin over V2O5/γ-Al2O3 catalyst was presented. Steady state one dimensional model has been developed to identify the operation parameters and to describe the propane and oxygen conversions, gas process and coolant temperatures, as well as other parameters affecting the reactor performance such as pressure. Furthermore, the applied model showed that a double-bed multitubular reactor with intermediate air injection scheme was superior to a single-bed design due to the increasing of propylene selectivity while operating under lower oxygen partial pressures resulting in propane conversion of about 37.3%. The optimized length of the reactor needed to reach 100% conversion of the oxygen was theoretically determined. For the single-bed reactor the optimized length of 11.96m including 0.5m of inert section at the entrance region and for the double-bed reactor design the optimized lengths of 5.72m for the first and 7.32m for the second reactor were calculated. Ultimately, the use of a distributed oxygen feed with limited number of injection points indicated a significant improvement on the reactor performance in terms of propane conversion and propylene selectivity. Besides, this concept could overcome the reactor runaway temperature problem and enabled operations at the wider range of conditions to obtain enhanced propylene production in an industrial scale reactor.

Investigation of rotating detonation combustor operation with H2-Air mixtures

The operating range and wave speed performance of a Rotating Detonation Combustor (RDC) is characterized for hydrogen-air mixtures for three fuel injection schemes and two air injection schemes. The fuel injection scheme is altered by changing the total number of injection orifices and the individual orifice area, while maintaining the same fuel mass flux across the three schemes. The operability, performance and combustion-induced pressure rise due to the addition of a back-pressurizing convergent nozzle is also characterized. While the operating range is largely unaffected by changes in the length-to-diameter ratio of the fuel injector orifices, higher length-to-diameter ratios correspond to a lower number of transitional RDC operation where there is a sudden abatement of the continuously propagating detonation wave, once established inside the combustor. Increased air injection area diminishes the operability, while producing high stochasticity in the performance of the RDC. The length-to-diameter ratio of the fuel orifices has a significant impact on the number of detonation waves that can exist in the chamber. For the highest length-to-diameter ratio of the fuel orifices, and at the highest air flow rates, the RDC supports multiple detonation waves inside the chamber. Without the convergent nozzle attachment, 80% of Chapman–Jouguet (C–J) detonation speed is achieved for all three fuel injection schemes. C–J detonation wave speed is achieved in the annulus when the RDC is back-pressurized using the nozzle. The ratio of reactant fill-height to the detonation cell-width tapers at the lean and rich operating conditions, while peaking at an equivalence ratio of around 1.2. The detonation-induced static pressure rise produced in the RDC is found to be dependent on the air flow rate and the equivalence ratio of the reactants.

Field scale numerical modeling of low temperature air injection with propane for heavy-oil recovery from naturally fractured reservoirs

The alternatives for EOR in heavy oil deep fractured reservoirs are limited. Air injection is one of the options but running it in the high temperature mode, namely in-situ combustion, has technical limitations (poor areal distribution of injected air) because of highly heterogeneous characteristics of fractured reservoirs. This may also create a problem from safety point of view, i.e., there is a risk that oxygen is not completely consumed in reservoir reaching production wells quickly without fully consumed. Air, however, can be used as a pressurizing agent to recover matrix oil in the low temperature oxidation mode (LTO) even though it may result in oxidation of oil that forms asphaltenes. Our recent lab results showed that injecting a mixture of air–propane instead of pure air might reduce these negative effects. This enhanced diffusion of air and propane into matrix may also add to recovery. Hence, those lab results opened the window to think of air injection (LTO mode) as a way to produce some of the oil left in the matrix in addition to its pressurizing effect.In the present study, a single porosity numerical simulation model, with explicit representation of fractures, was developed to analyze the injection of a mixture of gases in a naturally fractured reservoir, involving the use of air in the LTO mode. A sector model of a hypothetical fractured heavy oil reservoir was created and several air–gas injection cases such as pure air, propane–air–propane and air–propane–air cycles were analyzed. The runs were performed using the diffusion data obtained from our previous experimental studies. Different scenarios of huff-and-puff options (cycle type and duration) were tested. Attention was paid to oxygen consumption in the matrix, while fracture to matrix oxygen transfer was mainly due to voidage replacement of oil by air, and some through diffusion of air into matrix during the injection and shut off periods of each cycle.The results obtained considering various shut in times and injection rates scenarios as well as safety aspects, showed benefits in the use of air in the LTO mode mixed with propane. This optimized air injection scheme could be considered as an alternative to develop naturally fractured heavy oil fields.

Possibility of air-filled rubber membrane for reducing hull exciting pressure induced by propeller cavitation

To mitigate hull excitation induced by the propeller cavity, our previous work proposed a single-nozzle air injection scheme based on the principle of acoustic destructive interference. Although inefficient energy consumption in a conventional air-carpet system could be reduced significantly, the proposed method was still hindered by the continuous usage of an air compressor and maintenance of the nozzle exposed to sea water.In this study, we take advantage of the acoustic properties of rubber-like materials, which are similar to that of water. Accordingly, a rubber layer existing at the water-to-air interface appears to be transparent in the propagation of acoustic waves. More specifically, a rubber membrane filled with air could be anticipated to act only the role of air-packing without influencing the desired acoustic phenomenon, i.e., destructive interference. Hence, the purpose of this work is to provide analytical evidence to prove that an air-filled rubber membrane is capable of replacing the previous effort of air-injection. A design strategy for tuning the frequency of maximum destructive interference to an exciting frequency is also presented, which can be accomplished by adjusting the rubber membrane size. Finally, two experimental demonstrations conducted in a water tunnel verified the suggested scheme.

Fixed‐Bed Multi‐Tubular Reactors for Oxidative Dehydrogenation in Ethylene Process

AbstractAn industrial‐scale reactor for ethylene production was modeled using the oxidative dehydrogenation of ethane (ODHE) in a multi‐tubular reactor system, examining a variety of parameters affecting reactor performance. The model showed that a double‐bed multi‐tubular reactor with intermediate air injection scheme was superior to a single‐bed design, due to the increased ethylene selectivity while operating under lower oxygen partial pressures. The optimized reactor length for 100 % oxygen conversion was theoretically determined for both reactor designs. The use of a distributed oxygen feed with a limited number of injection points indicated a significant improvement on the reactor performance in terms of ethane conversion and ethylene selectivity. This concept also overcame the reactor runaway temperature problem and enabled operations over a wider range of conditions to obtain enhanced ethylene production.

Backward Traveling Rotating Stall Waves in Centrifugal Compressors

Rotating stall waves that travel against the direction of rotor rotation are reported for the first time and a new, low-order analytical approach to model centrifugal compressor stability is introduced. The model is capable of dealing with unsteady radially swirling flows and the dynamic effects of impeller-diffuser component interaction as it occurs in centrifugal compression systems. A simple coupling criterion is developed from first principles to explain the interaction mechanism important for system stability. The model findings together with experimental data explain the mechanism for first-ever observed backward traveling rotating stall in centrifugal compressors with vaned diffusers. Based on the low-order model predictions, an air injection scheme between the impeller and the vaned diffuser is designed for the NASA Glenn CC3 high-speed centrifugal compressor. The steady air injection experiments show an increase of 25% in surge-margin with an injection mass flow of 0.5% of the compressor mass flow. In addition, it is experimentally demonstrated that this injection scheme is robust to impeller tip-clearance effects and that a reduced number of injectors can be applied for similar gains in surge-margin. The results presented in this paper firmly establish the connection between the experimentally observed dynamic phenomena in the NASA CC3 centrifugal compressor and a first principles based coupling criterion. In addition, guidelines are given for the design of centrifugal compressors with enhanced stability. Winner of the “Best Paper Award,” Turbomachinery Committee

A hot-flow model analysis of the MSW incinerator

A hot-flow model incinerator was constructed to simulate the combustion chamber of mass-burn municipal solid waste (MSW) incinerator. Experiments using the reduced scale simplified model were designed to reproduce the physical processes. The Current study focuses on the gas phase mixing and the subsequent oxidative destruction of incomplete combustion products. Excessive carbon monoxide is generated by operating the gas burner under fuel-rich conditions, and is supplied into the furnace chamber as a hot gas stream, where fresh air is provided by the secondary air injection. Mixing is quantified by measuring the local gas concentrations (CO and O2) and temperatures since the destruction rate of CO is controlled by oxygen availability and chemical kinetic rates. The degree of mixing is monitored while the design alternatives of the secondary air injection pattern are systematically adjusted. This effect of the secondary air injection schemes on the degree of mixing are observed, and the measurements of temperature fluctuation with fine-wire thermocouples are performed for the quantitative evaluation of mixing. The results agree well with the plausible scenario of mixing and provide a better understanding of the mixing process. The hot flow accompanying chemical reactions in the model incinerator is also analysed numerically using the computational fluid dynamics codes to bolster the understanding of the experimental results. The modelling results compare reasonably well with experimental data. This comparison helps to cross-check the results. © 1997 John Wiley & Sons, Ltd.

A hot‐flow model analysis of the MSW incinerator

A hot-flow model incinerator was constructed to simulate the combustion chamber of mass-burn municipal solid waste (MSW) incinerator. Experiments using the reduced scale simplified model were designed to reproduce the physical processes. The Current study focuses on the gas phase mixing and the subsequent oxidative destruction of incomplete combustion products. Excessive carbon monoxide is generated by operating the gas burner under fuel-rich conditions, and is supplied into the furnace chamber as a hot gas stream, where fresh air is provided by the secondary air injection. Mixing is quantified by measuring the local gas concentrations (CO and O2) and temperatures since the destruction rate of CO is controlled by oxygen availability and chemical kinetic rates. The degree of mixing is monitored while the design alternatives of the secondary air injection pattern are systematically adjusted. This effect of the secondary air injection schemes on the degree of mixing are observed, and the measurements of temperature fluctuation with fine-wire thermocouples are performed for the quantitative evaluation of mixing. The results agree well with the plausible scenario of mixing and provide a better understanding of the mixing process. The hot flow accompanying chemical reactions in the model incinerator is also analysed numerically using the computational fluid dynamics codes to bolster the understanding of the experimental results. The modelling results compare reasonably well with experimental data. This comparison helps to cross-check the results. © 1997 John Wiley & Sons, Ltd.