Secondary Air Flow Research Articles

STUDY ON EFFECTS OF SECONDARY AIR INJECTION FOR COMPRESSED AIR TRANSPORT IN HORIZONTAL PIPE

The purpose of this research is to investigate effect of compressed secondary air injection and flow resistance in horizontal pipe flow transport system by compressed air. This transport system is very useful for high-density slurry transport because it is easily to separating air from slurry. This paper describe about the mechanism of slurry transporting system using a compressed air in the experimentally. In the experiment, the airliquid two-phase flows have been focused on liquid of low viscosity in long distance pipelines with narrow diameter and discussed the effect of secondary air and relation between air-injection volume and friction loss. As the results of experiments it was shown that the secondary air injection is useful for acceleration of slug velocity in horizontal pipe flow.

Joint Air-Fuel Ratio and Torque Regulation Using Secondary Cylinder Air Flow Actuators

Actuation schemes exist that permit the joint management of air and fuel flow into the cylinders of a spark ignition engine. With the exception of drive by wire systems, to-date, the transient control aspects of these schemes, collectively refered to here as secondary cylinder air flow actuators, has not received any attention from the control community. This paper takes a first step in the analysis of the simultaneous dynamic control of air fuel ratio and torque response using secondary actuators placed before the intake ports of the cylinders, when used in combination with standard fuel injectors and primary throttle regulated by the driver. The emphasis is on basic issues of designing a feedforward scheme to enhance actuator authority for feedback control, and the fundamental multivariable nature of the feedback problem. Enhanced transient air-to-fuel ratio performance improvement is shown to be possible without sacrificing engine torque response with respect to a conventional engine. In addition, this is achieved with overall higher manifold pressure, offering the possibility of reduced pumping losses in the engine, depending on the actual actuation scheme employed.

Hydrodynamic behaviour of solid transport for a closed loop circulating fluidized bed with secondary air injection

The aim of this work was to study the mechanism of solid circulation in a Circulating Fluidized Bed pilot as a function of secondary air flow rate A rectangular column of 7 m height equipped with a U type siphon was used for this purpose The results obtained showed that the solid circulating phenomenon depends on different limiting steps like feeding step (dense bed), siphon circulating capacity and suspension saturation capacity.

Thermal wakes measurement in electronic modules in the presence of heat transfer enhancement devices

This paper reports the thermal wake measurements in electronic modules in the presence of heat transfer enhancement devices. The enhancement devices consist of various sizes and shapes of ribs, secondary air flow injections through cylinders and “film cooling-like” injection devices. The effects of such devices on the thermal wake and the pressure drop characteristics of an array of rectangular modules at different values of Reynolds number in the range 4.0×10 3–1.6×10 4 have been investigated. Generally, it was found that using sizes and shapes of ribs as well as the presence of secondary air flow injection cylinders and film cooling-like injection hole devices tends to results in a significant attenuation in the thermal wake, in particular in the region downstream of the enhancement devices, depending on the location of the active module in the array. A maximum attenuation in the thermal wake of 33%, 30% and 25% for the rectangular, triangular and cylindrical ribs occurs at the sixth row, respectively, when the active module is located just upstream of the rib-enhancement devices. The film cooling-like enhancement devices tend to have higher attenuation in the thermal wake than the rib enhancement devices for the same location of the active module downstream of these devices, but with very much smaller pressure drop.

Secondary airflow and sediment transport in the lee of a reversing dune

Secondary airflow and sediment transport in the lee of a reversing dune

Secondary airflow and sediment transport in the lee of a reversing dune

Lee-side windspeed and sediment transport were measured over a small (1·2 m) transverse ridge in the Silver Peak dunefield, west-central Nevada, USA, using an intensive array of 25 cup anemometers and seven total flux traps. During crest-transverse and transporting flow conditions (u0·3crest ≈ 8·4 m s−1), windspeed near the surface of the lee slope averaged half (48 per cent) that of crest speeds. Dimensionless speeds in the separation zone ranged from 0·2 to 0·8 that of the outer flow (u12). Along the boundary of the separation cell, windspeed increased by 10 per cent of the crest speed before separation. Equilibrium of upper and lower wake regions was not observed by the documented eight dune heights, suggesting that wake recovery may not occur over closely spaced dunes. Sediment transport measured directly on both the lee slope and interdune surfaces averaged approximately 15 per cent of crest inputs. This suggests that a significant amount (c. 70–95 per cent) of sediment transported over the crest moved as fallout. For this data set, flux was approximately proportional to the cube of the near-surface windspeed (u0·3) and in general there was an order of magnitude difference between flux measured at the crest and that measured within the separation zone. Transport direction in the separation zone was acutely oblique to the incident direction owing to secondary flow deflection. Beyond the interdune, transport direction progressed from oblique to crest-transverse. This indicates that an appreciable amount of sediment may move laterally along the lee slope and interdune corridor under crest-transverse flows. Regarding the grain size and sorting properties of transported sediment, there was no significant difference in mean grain size over the dune, although in general particles were finer and more poorly sorted in the lee. Copyright © 1999 John Wiley & Sons, Ltd.

ACTIVE CONTROL OF PERFORMANCE AND NOx EMISSIONS OF STAGED GASEOUS FUEL BURNER

Closed loop feedback control is implemented in gaseous fuel staged burner to maintain low NO„ emission. The experimental set-up is a swirl-stabilized, diffusion flame, staged combustion gaseous fuel burner. The emissions of NO and carbon dioxide are monitored in real time and controlled as a function of burner load. The control input to the system is the . primary and secondary air flow rate. The NO,, emissions and CO2 concentrations are measured through two analyzers near the burner exit plane. This information is conveyed to a computer control system which invokes an optimization algorithm to maintain the low NO„ emissions in addition to high CO2 concentrations which, for fixed overall air/fuel ratio, entails achievement of high combustion efficiency. The success of the control methodology encourages its application on practical systems.

A study on wood gasification for low-tar gas production

We present results of an experimental study on two-stage wood gasification and attempts to reduce the tar content of the gas. Increasing the wood-chip moisture content resulted in an increase of CO 2 and H 2 but a decrease of the CO concentration without significantly affecting the tar content in the producer gas. For a particular primary air flow rate, an increase in the secondary air flow of the two-stage gasifier resulted in decrease of the tar content and the CO 2 and H 2 concentrations while that of CO increased. A charcoal gasifier and a floating-drum gas-storage system were coupled to a two-stage wood gasifier. The tar content of the product gas was in the range 19–34 mg/Nm 3 for a charcoal gasifier coupled to a two-stage wood gasifier. With a floating-drum gas-storage system and a 3.5 h retention time, the tar content was reduced to 9.24 mg/Nm 3, which is 85% less than that obtained by using the a two-stage wood gasifier alone.

Secondary flow and enhancement of heat transfer in horizontal parallel-plate and convergent channels heating from below

Experimental studies of secondary air flow structure and enhancement of heat transfer in horizontal parallel-plate and convergent channels have been carried out. The bottom wall is horizontal and heated uniformly, while the opposite wall is insulated and inclined with respect to the horizontal plate so as to create a convergence angel of 3° for the convergent channel. The aspect ratio (width to height) and the ratio of channel length to height at the entrance of the channel is 6.67 and 15, respectively. The Reynolds number ranges from 100 to 2000, the buoyancy parameter, Gr/ Re 2, from 2.5 to 907 and Pr of the air flow is 0.7. Flow structure inside the channel is visualized by injecting smoke at the inlet flowing along the bottom wall. The complete processes for the formation of the plumes associated with vortices and their transformation into longitudinal convection rolls due to the lateral extension and combination of the vortices are observed. The number of convection rolls formed is much less than those found in the experiments with water. For the convergent channel,the favorable pressure gradient causes a thinner bottom heated layer which results in much later initiation of secondary flow and fewer the number of plume produced. The interactions between neighboring vortices and plumes are suppressed by the acceleration of mainstream, and results ina stable flow and less pronounced enhancement of heat transfer. Temperature fluctuations at different locations are measured to indicate the flow structure and oscillation of the secondary flow. The effects of the buoyancy parameter and the convergence of the channel on the secondary flow structure and the Nusselt number are presented and discussed.

99/00600 The integration of low NO x control technologies at the Southern Energy, Inc. Birchwood Power Facility

The Southern Energy, Inc. (SEI) Birchwood Power Facility, a cogeneration unit, represents the first application worldwide of the TFS 2000{trademark} firing system and selective catalytic reduction (SCR). The installation of these state-of-the-art NOx control technologies was necessary to meet strict Commonwealth of Virginia environmental regulations requiring a 0.10 lbs/10{sup 6} Btu (0.043 g/MJ) NOx emission rate based upon a 30-day rolling average. The plant successfully completed all performance and emission testing on September 24, 1996. Commercial operation began November 14, 1996. Stack NOx emission rates are consistently maintained below 0.10 lbs/10{sup 6} Btu. The paper describes the integration of both in-furnace and post-combustion NOx control technologies into the overall boiler design. Operational data depicting boiler outlet NOx, stack NOx and loss on ignition (LOI) are presented across the design load range from 32% to 100% boiler output. The description, arrangement, design parameters and operation of the NOx control equipment are discussed. Novel design features include a split economizer, an air heater suitable for ammonia applications, Dynamic{trademark} classifiers, and a multi-zone secondary air flow control system utilized for the TFS 2000{trademark} firing system.

Simulation of the gas temperature deviation in large-scale tangential coal fired utility boilers

For tangential coal fired boilers, the gas temperature deviation at the exit of the furnace will occur when boiler capacity becomes large. In this paper, the flow, heat transfer and combustion process in a boiler of 300 MWe unit at Shiheng Power Plant, Shandong, China and a boiler of 600 MWe unit at Shidongkou Power Plant, Shanghai are simulated. The causes and decrease ways of the gas temperature deviation are investigated. It is found that the gas temperature deviation results from the after twirl and the platen superheater. Decreasing the diameter of tangential circle formed by secondary air flow can result in the decrease of temperature deviation to a certain extent. Although the after twirl can be decreased by opposing the tangential direction of some secondary air flows, the flow field in the furnace might be disturbed, and the temperature deviation might be increased, if the momentum and the angle of the opposite secondary air flow are not appropriate.

Nitric Oxide Formation in an Iron Oxide Pellet Rotary Kiln Furnace

ABSTRACT A one-dimensional numerical model was developed to simulate the effects of heat and mass transfer on the formation of oxides of nitrogen (NOx) in a rotary kiln furnace for iron oxide pellet induration. The modeled kiln has a length-to-diameter ratio of approximately seven. The principal mechanism of heat transfer is radiation from the flame, which was described by the net radiation method. The well known Zeldovich mechanism was used to predict thermal NOx generation. Temperature fluctuations in the vicinity of the flame were estimated with a clipped Gaussian probability density function. The thermal energy and mass balance model equations were solved numerically. The model is capable of predicting temperature profiles and NOx production rates in agreement with observed plant performance. The model was used to explore the effects of process changes on the total NOx formation in the kiln. It was concluded that the gas temperature as well as the partial pressure of oxygen in the process gases controls the rate of NOx formation. Lowering the temperature of the kiln gases by increasing the secondary air flow rates requires simultaneously decreasing the pellet production rate in order to maintain the pellet temperatures needed for blast furnace conditions.

A hybrid, knowledge-based system as a process control ‘tool’ for improved energy efficiency in alumina calcining furnaces

This paper describes the development and implementation of a hybrid SCADA (Supervisory Control and Data Acquisition) system for the air suspension ‘flash’ alumina calciner at Aluminium de Grece St. Nicholas plant. The system includes two additional modules, an ‘expert system’ based on 10 years of commissioning and operating experience and a dynamic model continuously predicting the quality of the product. It is implemented on an industrial PC under an industrial control software environment and interfaces to the furnace through a programmable logic controller (PLC) system. The system guides the furnace operator to reduce sensible heat losses by operating with a marginal excess air flow rate, to take advantage of the higher energy efficiency at higher production rates and, at the same time, to avoid potentially dangerous operating conditions leading to loss of production and consequential energy losses. It also performs the traditional SCADA functions (data acquisition, maintaining history files for important parameters and display of important operating parameters in both a mimic process diagram and a series of graphs.) In addition to these tasks a simplified dynamic model gives the operator a prediction of the current value of the main product quality parameter, which can only be measured with laboratory equipment. Preliminary results have shown that reduction of secondary air flow rate and reduced downtime achieved by the operator under the guidance of the system can reduce energy consumption by as much as 10%. A similar, or even greater, improvement in energy efficiency can be expected by implementing a similar system to cement calcination kilns based on the same technology.

Cold flow velocity measurements in recovery boilers: Part I: Interaction of primary and secondary air flows

AbstractCold air flow velocities were measured in a commercial recovery boiler during shutdown periods, using hot‐wire anemometers, modified to indicate direction. Five tests were carried out using different primary and secondary air configurations. The conditions tested included arrangements recommended by others to improve gas flow uniformity, as well as unrealistic extremes to be used in the evaluation of computational fluid dynamic models. The measurements demonstrated the inherent unsteadiness of recovery boiler flows and confirmed that balanced air flows through opposed walls result in a central region of high velocity upward flow. Interlacing of the secondary air significantly reduced the peak velocity and flattened the upward velocity profile at the liquor gun level.

Development of a New Aerosol Generating Cell with an Ultrasonic Nebulizer.

A new efficient cell was developed to generate a large quantity of aerosol using an ultrasonic nebulizer. The currently used conventional pail-type cell cannot generate such a large quantity of aerosol because a large portion of the mist is lost by agglomeration and subsequent liquefaction onto the cell wall and liquid surface. The newly developed cell is a chimney-type cell characterized by the attachment of a vertical cylinder at its center and a partition to separate the cell into upper and lower compartments, each of which is supplied with a carrier air flow. The mist emanating from the fluid surface is carried upward through the vertical cylinder by a laminar primary airflow. The secondary airflow served to sheath the primary airflow containing the mist and to prevent the impact and adhesion of the mist on the surrounding wall. The nebulizing rate of TiO2 suspension was found to be three times higher with the chimney-type than with the pail-type. No differences were found between the two types in terms of particle diameters, particle size distribution, and the electron microscopic images of the aerosol. It was concluded that a commercially available ultrasonic nebulizer equipped with the chimney-type cell allowed generation of a large quantity of aerosol for use in inhalation animal experiments.

Hydrodynamics of a circulating fluidized bed operated with different secondary air injection devices

A cold model of a circulating fluidized bed combustor having a 0.120 m i.d. and 5.75 m high riser, was operated by splitting the total gas flow rate in a primary air stream fed through the bottom distributor and a secondary air stream laterally injected at a fixed level along the riser. Two different feeding devices were used: in one case the injection of secondary air stream occurred over the whole circumference of the riser through a slot; in the other the injection occurred through four opposite ports. Solids used were 89 μm Ballotini. Overall superficial gas velocity was fixed at 6 m/s. Solids mass flux was alternatively equal to 35 and 55 kg/(s m 2). The ratio between secondary and primary air flow rates was kept at a value of 1. An isokinetic probe was used to measure radial profiles of upward and downward solids mass fluxes and those of tracer gas concentration. A stream of CO 2 was mixed with the secondary air stream before the injection and used as tracer gas. For each set of operating conditions, axial profile of voidage and radial profiles of solids mass flux and CO 2 concentration were measured along the riser. Results confirm that lateral air stream remarkably affects the hydrodynamics in the regions below and above the gas inlet. They also show that the mechanism of interaction between the secondary air stream and the gas-solids suspension rising from the primary zone completely changed when the injection device was changed. Solids and tracer gas distribution along the riser were noticeably different.

Toward a model for airflow on the lee side of aeolian dunes

ABSTRACTThe interaction between dunes and the primary wind results in a complex pattern of secondary airflow on the lee side of dunes. From 15 dunes studied during transverse flow conditions at Padre Island in Texas, White Sands in New Mexico, and the Algodones in California, distinct flow regions can generally be recognized, with the overall flow structure comparing favourably to that proposed for subaqueous bedforms. Downwind of dunes with flow separation is a back‐flow eddy that extends about four dune‐brink heights downwind from the brink of the dune. Beyond the separation cell, the velocity profiles can be divided into regions based upon segments separated by ‘kinks’ in the velocity profiles. The interior is an area above the dunes of relative high wind speed but low velocity gradient. Beneath the interior is the wake, which consists of two layers. The upper wake exhibits an uppermost portion where the flow decelerates while the remainder exhibits accelerating flow, so that the overall velocity gradient decreases downwind. The lower wake exhibits low velocity gradients and wind speeds that accelerate downwind at all heights, but primarily near the top of the layer, thereby causing the velocity gradient to increase downwind. At about eight dune heights downwind, the upper and lower wakes equilibrate to a single profile with the kink between them no longer apparent. The lowest recognizable region is the internal boundary layer. It is recognized by a relatively steep velocity gradient below the wake, and never exceeds a few tens of centimetres in height for our data set. Because of acceleration and increasing shear stress within this layer, interdune flats are at least potentially erosional. Overall, the wake and internal boundary layer show a downward transfer of momentum from upper regions so that the flow recovers. Where flow separation does not occur, simple flow expansion down the lee‐face causes flow deceleration.

95/06307 Effect of secondary superficial air velocity on the elutriation rate of fine particles in a cold-model two-stage swirl-flow fluidized-bed combustor

The elutriation rate of fine particles were measured in a cold model Two-Stage Swirl-Flow Fluidized Bed Combustor(TSSF-FBC). The range of secondary air flow rate was varied from 0.1 m/s to 0.35 m/s while the primary air flow rate was kept to a constant value of 1 m/s. It was found that the elutriation rate of fine particles slightly increased with the secondary superficial air velocity. When the secondary superficial air velocity exceeded over 0.3 m/s, however, the elutriation rate rapidly increased. The elutriation rate of fine particles was strongly dependent upon the swirl intensity. It was exponentially decreased as the swirl intensity increased. The elutriation rate constant increased with the secondary superficial air velocity, and the critical particle diameters were in range of . Under the experimental conditions, the elutriation rate constant of fine particles can be correlated with secondary excess air velocity() and as follows;

Combustion-Driven Oscillation in a Furnace with Multispud-Type Gas Burners. 4th Report. The Effects of Position of Secondary Air Guide Sleeve and Openness of Secondary Air Guide Vane on Combustion Oscillation Condition.

In the preceeding papers, "the resonance factor", which predicts the degree of combustion oscillation, was proposed, and applied to both the furnace with a single burner and that with multiple burners. It was found that the combustion oscillation occurred in the region of low primary and secondary air flow rates in both furnaces and that the region of combustion oscillation was affected by the openness of secondary air vane and the burner arrangement in a furnace under a fixed flame holder condition. If the operational conditions of the practical burners are not within this region, the furnace will not oscillate at all. This study's objective is to clarify the effects of the position of the secondary air guide sleeve and the openness of the secondary air guide vane on the combustion oscillation region in a multiburner furnace, since the combustion oscillation condition varies with position and strength of the heat release zone is a furnace and thus is governed by the configurations of flame holder which is composed of an impeller, air guide sleeves and air guide vanes. Futhermore, a procedure of burner operation while avoiding combustion oscillation is demonstrated.

The Shrouding of Highly Loaded, Aerovalved, Pulse, Pressure-Gain Combustors

Abstract The provision of a shrouding duct for an aerovalved pulse combustor is, for some applications, essential in that it permits the combustor to both entrain a secondary airflow and operate with a single air inlet and with a single outlet. Results are summarised representing extensive testing of pulse-combustor shroud ducts showing that the geometrical configuration of a shroud duct is relatively critical to performance. A stagnation pressure gain of 4% of the compressor absolute delivery pressure has been demonstrated on a small, low pressure ratio, gas turbine employing a shrouded, aerovalved, pulse combustor. The loadings of shrouded pulse-combustors are compared with loadings of steady-flow combustors. It is shown that when the core pulse combustor is of the single inlet type, shrouded pulse-combustors have relatively low volumetric loadings although it appears to be possible to ameliorate this by substituting a multiple-inlet pulse-combustor for one of the single inlet type.