Application of ESP for gas cleaning in cement industry--with reference to India

Electrostatic precipitators (ESP) are used for gas cleaning in almost every section of cement manufacture. Application of ESP is studied, keeping in view Indian conditions. The characterisation of dust emissions has been done for different units, such as rotary kiln and raw mill, alkali by-pass, clinker cooler, cement and coal mill, in terms of exit gas quantity, temperature, dew point, dust content and particle size. It is seen that all these characteristics have a wide range of variance. The ESP system must effectively deal with these variations. The fundamental analytical expression governing the performance of ESP, i.e. the Deutsch equation, and that for particle migration velocity, were analysed to predict the effect of major operating parameters, namely particle size, temperature and applied voltage. Whereas the migration velocity (and the efficiency) varies directly with the particle size, it is proportional to the square and square root of applied voltage and absolute temperature of the gas, respectively. The increase in efficiency due to temperature is not seen in dc based ESP, perhaps due to more pronounced negative effect on the applied voltage due to the increase in dust resistivity at higher temperatures. The effect of gas and dust characteristics on the collection efficiency of ESP, as seen in the industrial practice, is summarised. Some main process and design improvements effectively dealing with the problem of gas and dust characteristics have been discussed. These are gas conditioning, pulse energization, ESP-fabric filter (FF) combination, improved horizontal flow as well as open top ESP.Generally, gas conditioning entails higher operating and maintenance costs. Pulse energization allows the use of hot gas, besides reducing the dust emission and power consumption. The improved horizontal flow ESP has been successfully used in coal dust cleaning. The open top or vertical flow ESP has a limitation on collection efficiency as it provides for only one electric field.     

Enhancing fine particle separation by hybrid-electrostatic-turbulence coagulation: An experimental and numerical investigation

The electrostatic precipitator(ESP) has low efficiency in removing sub-micron particles. Coagulation technology, as a fine particle pretreatment technology, uses an external effect to agglomerate and grow fine particles, increase the average particle size, and make it easier to remove by subsequent dust removal equipment. However, the coagulation efficiency of a single coagulation technology is limited. Aiming at the particle charging mechanism and coagulation mechanism in the electric/turbulent composite coagulation process of fine particles, this paper uses a combination of numerical simulation and experiment to study the effects of different structural parameters, discharge parameters and flue gas parameters on corona discharge and particle charge. On this basis, the coagulation characteristics of charged particles in the turbulent flow field are studied. The results show that, when the Angle between the tip of the arista electrode is 90°, the corona discharge effect is the best. With the increase of supply voltage and temperature, the charge of particles increases. When the applied positive voltage is 29 kV and negative voltage is ?35 kV, the total coagulation coalescence efficiency of fine particles reaches the maximum. The coagulation efficiency increases with the increase of temperature, but decreases with the increase of inlet flow rate.     

Mercury emissions from coal combustion: modeling and comparison of Hg capture in a fabric filter versus an electrostatic precipitator

Mercury emissions from coal combustion must be reduced, in response to new air quality regulations in the U.S. Although the most mature control technology is adsorption across a dust cake of powdered sorbent in a fabric filter (FF), most particulate control in the U.S. associated with coal combustion takes the form of electrostatic precipitation (ESP). Using recently developed models of mercury adsorption within an ESP and within a growing sorbent bed in a FF, parallel analyses of elemental mercury (Hg(0)) uptake have been conducted. The results show little difference between an ESP and a FF in absolute mercury removal for a low-capacity sorbent, with a high-capacity sorbent achieving better performance in the FF. Comparisons of fractional mercury uptake per-unit-pressure-drop provide a means for incorporating and comparing the impact of the much greater pressure drop of a FF as compared to an ESP. On a per-unit-pressure-drop basis, mercury uptake within an ESP exhibited better performance, particularly for the low-capacity sorbent and high mass loadings of both sorbents.     

Influence of operating temperature on performance of electrostatic precipitator for pulverized coal combustion boiler

Electrostatic precipitator (ESP) is a major dust collection device used in pulverized coal combustion boilers in Japan. Although the collection efficiency of ESP is over 99%, the performance of ESP is affected by dust properties, especially the electric resistivity of the dust. In Japan, many different kinds of coal are used in pulverized coal combustion boilers. The property of coal ash formed in pulverized coal combustion is different for different coals. It is very important to develop high performance ESPs for different kinds of coal ash. In general, the low temperature ESP operated at about 423 K has been used for a long time, but the electric resistivity of some kinds of coal ash is higher than suitable for the ESP in this temperature range. A high temperature ESP operated at 623 K was developed about 20 years ago and an advanced low temperature ESP operated at 373 K has been used recently for control of the electric resistivity of coal ash.In this paper, we report on the influence of operating temperature from 363 K to 623 K on performance of ESP for a pulverized coal combustion boiler. The influence of coal ash properties including electric resistivity, alkali metal concentration, and operating condition on collection efficiency of an ESP is estimated.     

Study of high-pressure air curtain and combined dedusting of gas water spray in multilevel ore pass based on CFD-DEM

In order to solve the problem of dust pollution caused by ore unloading in ore pass, this paper, taking Li Lou Mining as a case study, conducted the wind speed variation law in the fluid domain and the impact of the collision between the ore in the unloading process on the fluid to determine the key dust control point based on the CFD-DEM coupling software. By Fluent software, the air curtain dust-proof efficiency under the action of unloading airflow is analyzed, and the relationship between the dust-control wind speed and the impinging airflow is known. And an experimental model of gas water spray is established to analyze the effect of spray dust removal. By analyzing the impact airflow and dust migration caused by ore unloading and the effect of air curtain dust control through numerical simulation, it can be seen that when the ore discharging quantity M_o = 4000 kg, the dust production is mainly concentrated in the fourth middle section. By high-pressure air shield assisting dust removal, dust diffusion can be better controlled when the ratio of impact wind speed of ore pass wellhead (denoted as λ) to high-pressure air curtain wind speed (denoted as ζ) is at least 1:8. When the dust removal effect is optimal, the ratio δ of the water supply amount q_l and the gas supply amount Q_g is determined by the gas water spray dust control experimental platform.     

Simulation analysis and engineering application of distribution characteristics about multi-stage atomization field for cutting dust in fully mechanized mining face

To improve the dust suppression efficiency of the external spray systems of shearers, a dust reduction method consisting of shearer external multi-stage atomization and dust removal fan was proposed. Computational fluid dynamics-based numerical simulation was combined with atomization experiments to analyze the migration and distribution of the cutting dust and multi-stage atomization field under airflow at the 2307 fully mechanized mining face of the Tangkou mine. The results show that with adding dust removal fan and multi-stage atomization points, the peak area of wind speed appeared on both sides of the shearer, and the wind speed was greater than 2.7 m/s, the dust concentration on the downside side of the shearer decreased, the spray coverage area increased significantly, and the droplet concentration at the shearer drum was the largest, exceeding 0.05 kg/m³. According to the research results, the multi-stage atomization arrangement of single-fluid water nozzles of shearer was put forward, and the field application was carried out. Compared with the engineering application results of the single-stage atomization dust suppression system, the total dust reduction rate of the synergistic effect of multi-stage atomization external spray with dust removal fan for the shearer is 87.12%, which is 38.59% higher than that of the conventional single-stage atomization dust suppression system.     

无人机静电喷雾治理开放性粉尘的数值模拟

将静电喷雾技术与无人机技术相结合用于治理开放性粉尘,使用Fluent对粉尘的扩散模型进行数值模拟。模拟得出无人机工作高7m,喷雾压力为0.2MPa时,无人机静电喷雾的平均降尘效率能达到85.87%,并在自然风速为1m/s、空气相对湿度为70%时,局部区域的降尘效率高达95.93%。本文提出的无人机静电喷雾控制开放性粉尘技术降尘效果较好,对沉降重金属污染粉尘技术发展有重要意义。     

The investigation of parameters affecting boron removal by electrocoagulation method

Boron removal from wastewaters by electrocoagulation using aluminum electrode material was investigated in this paper. Several working parameters, such as pH, current density, boron concentration and type and concentration of supporting electrolyte were studied in an attempt to achieve a higher removal capacity. The experiments were carried out by keeping the pH of solution constant and optimum pH of solution was determined 8.0 for the aluminum electrode. Although energy consumption increased with decreasing boron concentration, which conductivity of these solutions were low, boron removal efficiency was higher at 100 mg/L than that of 1000 mg/L. Current density was an important parameter affecting removal efficiency. Boron removal efficiency and energy consumption increased with increasing current density from 1.2 to 6.0 mA/cm2. The types of different supporting electrolyte were experimented in order to investigate to this parameter effect on boron removal. The highest boron removal efficiency, 97%, was found by CaCl2. Added CaCl2 increased more the conductivity of solution according to other supporting electrolytes, but decreased energy consumption. The results showed to have a high effectiveness of the electrocoagulation method in removing boron from aqueous solutions.     

Machining Characteristics of Inconel 718 by Sinking-EDM and Wire-EDM

Inconel 718 superalloy has wide applications in several industries due to its excellent mechanical properties. However, it is very difficult to machine using conventional cutting and grinding because of its high strength at elevated temperatures. Electrical discharge machining (EDM) is an alternative competitive process to machine Inconel alloys by electrical erosion. However, machinability and surface characteristics of EDMed Inconel surfaces are poorly understood. This study focuses on the machining characteristics of Inconel 718 by Wire-EDM and Sinking-EDM with a new Cu-SiC electrode, respectively. Material removal efficiency, surface roughness, surface topography, surface alloying, and electrode wear have been characterized. It is found that the high toughness of Inconel 718 would be the major contributing factor to the absence of microcracks on the EDMed surface. The new fabricated Cu-SiC electrode for Sinking-EDM has better performance in terms of material removal rate (MRR), surface roughness, and electrode wear. The higher melting temperature and fine microstructure of SiC contribute to the lower electrode wear of the new Cu-SiC electrode than the traditional Cu electrode.     

Packing of fine particles in an electrical field

A numerical model based on the Discrete Element Method (DEM) is developed to study the packing of fine particles in an electrical field related to the dust collection in an electrostatic precipitator (ESP). The particles are deposited to form a dust cake mainly under the electrical and van der Waals forces. It is shown that for the packing formed by mono-sized charged particles, increasing either particle size or applied electrical field strength increases packing density until reaching a limit corresponding to the density of random loose packing obtained under gravity. The corresponding structural changes are analyzed in terms of coordination number, radial distribution function and other topological and metric properties generated from the Voronoi tessellation. It is shown that these properties are similar to those for the packing under gravity. Such structural similarities result from the similar changes in the competition of the cohesive forces and the driving force in the packing. In particular, it is shown that by replacing the gravity with the electrical field force, the previous correlation between packing density and the ratio of the cohesive force to the packing-driven force can be applied to the packing of fine particles in ESP.     

Gas-liquid dual phase inhibition method for explosion accident of wet Al dust collection system based on KH2PO4

Metal dust has explosion risk in wet dust removal system. In this study, a gas–liquid dual phase explosion hydrogen inhibition method (EHIM) is proposed. The inhibitory effect of KH₂PO₄ on Al dust explosion in a dust removal pipe (gas phase) and Al dust hydrogen generation in a wet dust collector (liquid) is discussed separately and collectively. Adding 70% KH₂PO₄ totally inhibits the formation of Al dust explosion flames while inhibiting Al–water reaction in the wet dust collector at the same time. Inside the dust removal pipe, KH₂PO₄ acts in the initial stage of Al dust combustion and works as a pyrolysis endothermic coolant under 220℃–380℃; inside the aqueous solution of the dust collector, it generates AlPO₄ with water and creates a film over the surface of the Al particles, which isolates water from Al, thus blocking Al–water reaction. Our new method offers a novel way of protecting the safety of wet dust removal systems.     

Experimental Evaluation of Trilateration-Based Outdoor Localization with LoRaWAN

Long Range Wide Area Network (LoRaWAN) in the Internet of Things (IoT) domain has been the subject of interest for researchers. There is an increasing demand to localize these IoT devices using LoRaWAN due to the quickly growing number of IoT devices. LoRaWAN is well suited to support localization applications in IoTs due to its low power consumption and long range. Multiple approaches have been proposed to solve the localization problem using LoRaWAN. The Expected Signal Power (ESP) based trilateration algorithm has the significant potential for localization because ESP can identify the signal’s energy below the noise floor with no additional hardware requirements and ease of implementation. This research article offers the technical evaluation of the trilateration technique, its efficiency, and its limitations for the localization using LoRa ESP in a large outdoor populated campus environment. Additionally, experimental evaluations are conducted to determine the effects of frequency hopping, outlier removal, and increasing the number of gateways on localization accuracy. Results obtained from the experiment show the importance of calculating the path loss exponent for every frequency to circumvent the high localization error because of the frequency hopping, thus improving the localization performance without the need of using only a single frequency.     

The reactor design and comparison of Fenton, electro-Fenton and photoelectro-Fenton processes for mineralization of benzene sulfonic acid (BSA)

A new approach for promoting ferric reduction efficiency using a different electrochemical cell and the photoelectro-Fenton process has been developed. The use of UVA light and electric current as electron donors can efficiently initiate the Fenton reaction. Benzene sulfonic acid (BSA) was the target compound in this study. The parameters investigated to evaluate the reactor design include the electrode working area, electrode distance, energy consumption. Furthermore, the study also contains the intermediates and the mineralization efficiency of electrolysis, Fenton, electro-Fenton and photoelectro-Fenton process. Oxalic acid, the major intermediate of aromatic compound degradation, can complex with ferric ions. Meanwhile, a double cathode reactor could increase the current efficiency by 7%, which would translate to greater ferrous production and a higher degradation rate. Although the current efficiency of an electrode distance 5.5 cm device is 19% higher than 3.0 cm, results show that after 2 h of electrolysis the electronic expense using an electrode gap of 5.5 cm is much higher than 3.0 cm. The final TOC removal efficiency was 46, 64 and 72% using the Fenton, electro-Fenton and photoelectron-Fenton processes, respectively.     

Droplet breakup in electrostatic spray based on multiple physical fields

A droplet breakup model was proposed for simulating electrostatic spray in multiple physical fields. The static electricity, laminar flow and droplet atomization in COMSOL Multiphysics were coupled completely, and a two-dimensional simulation model was established. The process of droplet breakup and movement of electrostatic spray was revealed under the action of electric field, gravity field and air field. The electric field distribution under the needle ring electrode configuration was studied. The effects of different electrostatic voltage, needle ring distance and ring electrode diameter on droplet breakup characteristics, distribution uniformity and charge characteristics were analyzed. When the electrostatic voltage is -6 ～ -7 kV, the needle ring distance is 4 mm, and the ring electrode diameter is 30 mm, the electrostatic spray effect is better, and the density standard deviation is as low as 0.04528 /mm², 0.0559 /mm² and 0.06016 /mm², respectively. Electrostatic spray has the characteristics of refining droplets, improving the uniformity of droplets distribution and controlling spray morphology, which provides a strong basis for the application of electrostatic spray in surface film preparation, dust removal, fuel injection and other practical engineering fields.     

Performance evaluation of two-stage electrostatic air filter with low-ozone emission corona charger

The ozone emitted from indoor air cleaners with corona chargers is harmful to the human respiratory system. In this study, a functional treatment of the discharge electrode surface was attempted to reduce the level of ozone generation from the corona discharge. The ozone emission level and charger performance were evaluated by measuring the particle removal efficiency and the pressure drop characteristics with the dust loading on the filter. Ozone production from the low-ozone discharge electrode was reduced by approximately 60% compared to conventional discharge electrode, but the corona initiating voltage and discharge current were equivalent to those of the conventional electrode. The particle removal efficiency of a low-grade filter assisted by the corona charger increased to a high-grade filter without a charger. The replacement time for the low-grade filter with the charger was approximately three times longer than that of a high-grade filter.     

Evaluation of primary and secondary fugitive dust suppression methods using enclosed water spraying systems at bulk solids handling

To suppress effectively fugitive dust emissions using water spraying systems at bulk solids handling an optimal design of these devices is necessary. The dust suppression mechanism for example at conveyor belt hand over points can be subdivided in a primary and a secondary dust minimization effect. In this case the moistening of the bulk solids is a primary dust minimization effect and the airborne dust capture is a secondary dust minimization effect. In this work the evaluation of both dust minimization effects is carried out. As a first step an experimental investigation of the total and the secondary dust suppression efficiency took place. A model of two separators which are acting in series got used to compare the measured efficiencies and to calculate the primary dust suppression efficiency. The secondary dust suppression effect showed low performance compared to the primary dust suppression efficiency. So it has to be clarified if the streaming situation and the dust concentration situation at the position where the nozzle operates can get improved. Therefore enquiries at different positions in the middle and aside a concentrated particle flow got carried out.The results provide an informative basis how water spraying systems can get improved to suppress fugitive dust emissions at bulk solids handling.     

PRELIMINARY PERFORMANCE TESTS OF A PULSED JET PLEATED PAPER CARTRIDGE FILTER SYSTEM

A pulsed jet pleated paper cartridge filter system was tested for particle removal efficiency and operating stability using agricultural limestone as the test dust. The test system consisted of 6 pleated paper filter units arranged in parallel, each unit having an effective filtration area of 18.1 square meters. The system was operated at constant pressure drops of 6.25, 7.50 and 8.75 kPa (2.5, 3.0 and 3.5 inches of water), with face velocities of 0.78 to 1.04 m/ min (2.5 to 3.4 feet per minute) and dust loadings ranging from 0.5 g/ m to 2.5 g/ m³. Penetration through the media appeared to be relatively independent of dust loading, and efficiencies were in the 99.95 + % range. Slightly lower efficiencies were found for particles having diameters of 0.3 to 1.0 micrometers. A measure of the redeposition of dust pulsed from the filter was required to describe the effects on the pulse rate caused by changes in system flow and pulsing set point. Increased redeposition was found to occur with increasing flow rate, causing an increase in the pulse rate required to maintain operation of the system at a pulsing set point. Overall, the reverse pulse jet pleated paper cartridge filter system displayed extremely high particle removal efficiency in a compact unit that operated with low differential pressure.     

Enhanced collection of fine particles in a cyclone using ultrasonic vapor with surfactants

Using water vapor to improve the efficiency of dust removal in gas cyclones was recently proposed. However, some dust particles are not hydrophilic which can reduce the effectiveness of the vapor. This paper investigates using surfactants to overcome such a difficulty. In particular, surfactants are added to the water solution which is atomized into vapor and added in a cyclone dust collector. The effects of surfactant type and quantity on the removal efficiency of the cyclone are studied by a series of experiments. Three surfactants are used to change the wettability of the two types of fine particles to be collected: molecular sieve dust and white carbon black. The particles in the cyclone are found to form agglomerates, which are measured by using a laser particle size analyzer and scanning electron microscopy. The results show that the addition of surfactants can greatly enhance the agglomeration and thus improve the collection efficiency, especially for particles approximately two microns in size. This indicates that using the atomized vapor with containing surfactants is an effective way to enhance the collection of fine particles in a cyclone separator.     

Slotted electrodes for the improvement of machining performances in EDM drilling

In electrical discharge machining (EDM), poor debris removal may occur under certain conditions. This leads to debris accumulation and degrades machining efficiency. In this study, the rotation and retracting movements of slotted electrodes were coordinated during EDM to realize a pumping effect for expelling debris in the gap between the electrodes and workpieces. The study compared the performance of different slotted electrodes with that of a regular cylindrical (RC) electrode. Moreover, a computational fluid dynamics module was adopted to simulate the effects of the RC and slotted electrodes on debris removal capability in EDM under different conditions. The experimental results demonstrated that among all slotted electrodes, the deep slotted electrode engendered the most-favorable debris removal capability. The deep slotted electrode saved machining time by shortening the electrode jump time or even obviating electrode jumping. This increased the material removal rates by 120%–153% during EDM drilling.     

EDM with an Air-Assisted Multi-Hole Rotating Tool

In the present research work, an extensive experimental study of air-assisted rotary electrical discharge machining (AAEDM) of high chromium, high carbon die steel has been made. Investigations have been performed to study the process factor effect namely pulse-on time, discharge current, duty cycle, tool rotation, and air pressure on material removal rate (MRR) and electrode wear ratio (EWR). A comparative analysis of solid rotary tool electrode electrical discharge machining (REDM) and AAEDM has been presented. It was found that a high MRR and low EWR occurred in AAEDM as compared to the REDM process, under the same processing conditions. Use of a multi-hole tool provided better circulation of dielectric in the discharge gap, thus it improved the flushing efficiency of the process. The results showed that the application of compressed air has a favorable influence on MRR and EWR.