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76-464: Construction of Duvha Power Station started in November 1975 and the last unit came into operation in 1984. In 1993 Duvha became the first power station in the world to be retrofitted with pulse jet fabric filter plants on three of its six units. These plants contribute largely to the reduction of air pollution by removing 99.99% of the fly ash , which otherwise would be released into the air through

152-415: A collection efficiency of more than 99% for very fine particulates. Dust-laden gases enter the baghouse and pass through fabric bags that act as filters. The bags can be of woven or felted cotton, synthetic, or glass-fiber material in either a tube or envelope shape. Dust collectors that use liquid are known as wet scrubbers . In these systems, the scrubbing liquid (usually water) comes into contact with

228-479: A combination of forces, such as centrifugal, gravitational, and inertial. These forces move the dust to an area where the forces exerted by the gas stream are minimal. The separated dust is moved by gravity into a hopper, where it is temporarily stored. The three primary types of inertial separators are: Neither settling chambers nor baffle chambers are commonly used in the minerals processing industry. However, their principles of operation are often incorporated into

304-405: A dead air space and settle. Baffle chambers are used as precleaners. Centrifugal collectors use cyclonic action to separate dust particles from the gas stream. In a typical cyclone, the dust gas stream enters at an angle and is spun rapidly. The centrifugal force created by the circular flow throws the dust particles toward the wall of the cyclone. After striking the wall, these particles fall into

380-418: A dust collector. There are two main kinds of industrial fans: Centrifugal fans consist of a wheel or a rotor mounted on a shaft that rotates in a scroll-shaped housing. Air enters at the eye of the rotor, makes a right-angle turn, and is forced through the blades of the rotor by centrifugal force into the scroll-shaped housing. The centrifugal force imparts static pressure to the air. The diverging shape of

456-457: A dust layer just over one particle thick can reduce the sparking voltage by 50%. The most marked effects of back corona on the current-voltage characteristics are: The Figure below and to the left shows the variation in resistivity with changing gas temperature for six different industrial dusts along with three coal-fired fly ashes. The Figure on the right illustrates resistivity values measured for various chemical compounds that were prepared in

532-836: A fan and some form of dust collector. They are suitable for isolated, portable, or frequently moved dust-producing operations, such as bins and silos or remote belt-conveyor transfer points. Advantages of unit collectors include small space requirements, the return of collected dust to main material flow, and low initial cost. However, their dust-holding and storage capacities, servicing facilities, and maintenance periods have been sacrificed. A number of designs are available, with capacities ranging from 200 to 2,000 ft /min (90 to 900 L/s). There are two main types of unit collectors: Fabric collectors are frequently used in minerals processing operations because they provide high collection efficiency and uninterrupted exhaust airflow between cleaning cycles. Cyclone collectors are used when coarser dust

608-415: A function of temperature in accordance with IEEE Standard 548. This test is conducted in an air environment containing a specified moisture concentration. The test is run as a function of ascending or descending temperature, or both. Data is acquired using an average ash layer electric field of 4 kV/cm. Since relatively low applied voltage is used and no sulfuric acid vapor is present in the test environment,

684-399: A gas stream containing dust particles. Greater contact of the gas and liquid streams yields higher dust removal efficiency. There is a large variety of wet scrubbers; however, all have one of three basic configurations of gas-humidification, gas-liquid contact or gas-liquid separation - Regardless of the contact mechanism used, as much liquid and dust as possible must be removed. Once contact

760-463: A high resistivity dust in the precipitator. Higher voltages can be required in order for corona generation to begin. These higher voltages can be problematic for the TR-Set controls. The problem lies in onset of corona causing large amounts of current to surge through the (low resistivity) dust layer. The controls sense this surge as a spark. As precipitators are operated in spark-limiting mode, power

836-414: A hopper located underneath. Cyclone separators are found in all types of power and industrial applications, including pulp and paper plants, cement plants, steel mills, petroleum coke plants, metallurgical plants, saw mills and other kinds of facilities that process dust. Single-cyclone separators create a dual vortex to separate coarse from fine dust. The main vortex spirals downward and carries most of

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912-437: A multistage baghouse, or a chemically treated wet scrubber or stripping tower. Smaller dust collection systems use a single-stage vacuum unit to create suction and perform air filtration , where the waste material is drawn into an impeller and deposited into a container such as a bag, barrel, or canister. Air is recirculated into the shop after passing through a filter to trap smaller particulate. Larger systems utilize

988-456: A predetermined interval. Cleaning a precipitator can usually be done without interrupting the airflow. The following factors affect the efficiency of electrostatic precipitators: Precipitator performance is very sensitive to two particulate properties: 1) electrical resistivity; and 2) particle size distribution . These properties can be measured economically and accurately in the laboratory, using standard tests. Resistivity can be determined as

1064-430: A primary and secondary separation/filtration system. In many cases the heat or moisture content of dust can negatively affect the filter media of a baghouse or cartridge dust collector. A cyclone separator or dryer may be placed before these units to reduce heat or moisture content before reaching the filters. Furthermore, some units may have third and fourth stage filtration. All separation and filtration systems used within

1140-426: A single, large collector. Dust collectors vary widely in design, operation, effectiveness, space requirements, construction, and capital, operating, and maintenance costs. Each type has advantages and disadvantages. However, the selection of a dust collector should be based on the following general factors: The fan and motor system supplies mechanical energy to move contaminated air from the dust-producing source to

1216-544: A total installed capacity of 3,600 MW operating with a turbine efficiency of 37.6%. The station is a twin sister to Tutuka Power Station . In April 2017 General Electric filed a court application accusing Eskom of rigging the tender to install a new boiler at the station so that Dongfang Electric would get the contact even though their bid was R1 billion (US$ 76 million) more than the General Electric bid. Dust collector#Reverse jet A dust collector

1292-449: A two-stage system, which separates larger particles from fine dust using a pre-collection device, such as a cyclone or baffled canister, before drawing the air through the impeller. Air from these units can then be exhausted outdoors or filtered and recirculated back into the work space. Dust collection systems are often part of a larger air quality management program that also includes large airborne particle filtration units mounted to

1368-428: Is a filterless device that removes fine particles, such as dust and smoke, from a flowing gas using the force of an induced electrostatic charge minimally impeding the flow of gases through the unit. In contrast to wet scrubbers , which apply energy directly to the flowing fluid medium, an ESP applies energy only to the particulate matter being collected and therefore is very efficient in its consumption of energy (in

1444-518: Is a function of a particle's chemical composition as well as flue gas operating conditions such as temperature and moisture. Particles can have high, moderate (normal), or low resistivity. Bulk resistivity is defined using a more general version of Ohm’s Law, as given in Equation ( 1 ) below: A better way of displaying this would be to solve for resistivity as a function of applied voltage and current, as given in Equation ( 2 ) below: Resistivity

1520-432: Is a system used to enhance the quality of air released from industrial and commercial processes by collecting dust and other impurities from air or gas. Designed to handle high-volume dust loads, a dust collector system consists of a blower, dust filter, a filter-cleaning system, and a dust receptacle or dust removal system. It is distinguished from air purifiers , which use disposable filters to remove dust. The father of

1596-407: Is as precleaners for more efficient collect. Advantages: 1) simple construction and low cost 2) maintenance free 3) collects particles without need of water. Disadvantages: 1) low efficiency 2) large space required. Baffle chambers use a fixed baffle plate that causes the conveying gas stream to make a sudden change of direction. Large-diameter particles do not follow the gas stream but continue into

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1672-523: Is funded by royalties paid by commercial firms after commercialization occurs. Research Corporation has provided vital funding to many scientific projects: Goddard 's rocketry experiments, Lawrence 's cyclotron , production methods for vitamins A and B 1 , among many others. Research Corporation set territories for manufacturers of this technology, which included Western Precipitation (Los Angeles), Lodge-Cottrell (England), Lurgi Apparatebau-Gesellschaft (Germany), and Japanese Cottrell Corp. (Japan), and

1748-424: Is generated, as in woodworking, metal grinding, or machining. The following points should be considered when selecting a unit collector: Use of unit collectors may not be appropriate if the dust-producing operations are located in an area where central exhaust systems would be practical. Dust removal and servicing requirements are expensive for many unit collectors and are more likely to be neglected than those for

1824-513: Is increased electrical sparking. When the sparking rate exceeds the "set spark rate limit," the automatic controllers limit the operating voltage of the field. This causes reduced particle charging and reduced migration velocities toward the collection electrode. High resistivity can generally be reduced by doing the following: Thin dust layers and high-resistivity dust especially favor the formation of back corona craters. Severe back corona has been observed with dust layers as thin as 0.1 mm, but

1900-683: Is made, dust particulates and water droplets combine to form agglomerates. As the agglomerates grow larger, they settle into a collector. Spray-tower scrubber wet scrubbers may be categorized by pressure drop as follows: Due to the large number of commercial scrubbers available, it is not possible to describe each individual type here. However, the following sections provide examples of typical scrubbers in each category. Electrostatic precipitators use electrostatic forces to separate dust particles from exhaust gases. A number of high-voltage, direct-current discharge electrodes are placed between grounded collecting electrodes. The contaminated gases flow through

1976-429: Is terminated and the corona generation cycle re-initiates. Thus, lower power (current) readings are noted with relatively high voltage readings. The same thing is believed to occur in laboratory measurements. Parallel plate geometry is used in laboratory measurements without corona generation. A stainless steel cup holds the sample. Another stainless steel electrode weight sits on top of the sample (direct contact with

2052-413: Is the determination of dew point by measurement of the current between adjacent electrodes mounted on a glass surface. A sharp rise in current signals the formation of a moisture film on the glass. This method has been used effectively for determining the marked rise in dew point, which occurs when small amounts of sulfuric acid vapor are added to an atmosphere (commercial Dewpoint Meters are available on

2128-409: Is the electrical resistance of a dust sample 1.0 cm in cross-sectional area, 1.0 cm thick, and is recorded in units of ohm-cm. A method for measuring resistivity will be described in this article. The table below, gives value ranges for low, normal, and high resistivity. Resistance affects electrical conditions in the dust layer by a potential electric field (voltage drop) being formed across

2204-436: Is the high-voltage, single-stage precipitator, which is widely used in minerals processing operations. The low-voltage, two-stage precipitator is generally used for filtration in air-conditioning systems. The majority of electrostatic precipitators installed are the plate type. Particles are collected on flat, parallel surfaces that are 8 to 12 in. (20 to 30 cm) apart, with a series of discharge electrodes spaced along

2280-411: The dust must be captured or extracted . This is accomplished with devices such as capture hoods to catch dust at its source of origin. Many times, the machine producing the dust will have a port to which a duct can be directly attached. Second, the dust must be conveyed . This is done via a ducting system, properly sized and manifolded to maintain a consistent minimum air velocity required to keep

2356-494: The "charged particles" heading toward the collection electrode. Disruptions of the normal corona process greatly reduce the ESP's collection efficiency, which in severe cases, may fall below 50% . When back corona is present, the dust particles build up on the electrodes forming a layer of insulation. Often this can not be repaired without bringing the unit offline. The third, and generally most common problem with high resistivity dust

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2432-436: The air, improving the operating environment and preventing buildup of flammable oil fog accumulations. Collected oil is returned to the gear lubricating system. Tubular precipitators consist of cylindrical collection electrodes with discharge electrodes located on the axis of the cylinder. The contaminated gases flow around the discharge electrode and up through the inside of the cylinders. The charged particles are collected on

2508-575: The ceiling of shop spaces and mask systems to be worn by workers. Air filtration units are designed to process large volumes of air to remove fine particles (2 to 10 micrometres ) suspended in the air. Masks are available in a variety of forms, from simple cotton face masks to elaborate respirators with tanked air — the need for which is determined by the environment in which the worker is operating. In industry, round or rectangular ducts are used to prevent buildup of dust in processing equipment . Inertial separators separate dust from gas streams using

2584-449: The centerline of two adjacent plates. The contaminated gases pass through the passage between the plates, and the particles become charged and adhere to the collection plates. Collected particles are usually removed by rapping the plates and deposited in bins or hoppers at the base of the precipitator. The most basic precipitator contains a row of thin vertical wires, and followed by a stack of large flat metal plates oriented vertically, with

2660-514: The coarser dust particles. The inner vortex, created near the bottom of the cyclone, spirals upward and carries finer dust particles. Multiple-cyclone separators consist of a number of small-diameter cyclones, operating in parallel and having a common gas inlet and outlet, as shown in the figure, and operate on the same principle as single cyclone separators—creating an outer downward vortex and an ascending inner vortex. Multiple-cyclone separators remove more dust than single cyclone separators because

2736-448: The collection area. The secondary air flow protects the separator from particulate abrasion and allows the separator to be installed horizontally because gravity is not depended upon to move the separated particulate downward. Commonly known as baghouses , fabric collectors use filtration to separate dust particulates from dusty gases. They are one of the most efficient and cost-effective types of dust collectors available, and can achieve

2812-478: The collection electrode. On the other hand, particles with low resistivity easily become charged and readily release their charge to the grounded collection plate. Both extremes in resistivity impede the efficient functioning of ESPs. ESPs work best under normal resistivity conditions. Resistivity, which is a characteristic of particles in an electric field, is a measure of a particle's resistance to transferring charge (both accepting and giving up charges). Resistivity

2888-498: The collection electrode. The particles take on the charge of the collection electrode, bounce off the plates, and become re-entrained in the gas stream. Thus, attractive and repulsive electrical forces that are normally at work at normal and higher resistivities are lacking, and the binding forces to the plate are considerably lessened. Examples of low-resistivity dusts are unburned carbon in fly ash and carbon black. If these conductive particles are coarse, they can be removed upstream of

2964-434: The collection electrode. These particles slowly leak their charge to grounded plates and are retained on the collection plates by intermolecular adhesive and cohesive forces. This allows a particulate layer to be built up and then dislodged from the plates by rapping. Within the range of normal dust resistivity (between 10 and 2 × 10 ohm-cm), fly ash is collected more easily than dust having either low or high resistivity. If

3040-544: The curve downward at temperatures below 500 °F (260 °C). These films usually differ both physically and chemically from the interiors of the particles owing to adsorption phenomena. Theoretical calculations indicate that moisture films only a few molecules thick are adequate to provide the desired surface conductivity. Surface conduction on particles is closely related to surface-leakage currents occurring on electrical insulators, which have been extensively studied. An interesting practical application of surface-leakage

3116-491: The design of more efficient dust collectors. A settling chamber (or stiveroom ) consists of a large box installed in the ductwork. The increase of cross section area at the chamber reduces the speed of the dust-filled airstream and heavier particles settle out. Settling chambers are simple in design and can be manufactured from almost any material. However, they are seldom used as primary dust collectors because of their large space requirements and low efficiency. A practical use

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3192-482: The device to the collection of sulphuric acid mist and lead oxide fumes emitted from various acid-making and smelting activities. Wine-producing vineyards in northern California were being adversely affected by the lead emissions. At the time of Cottrell's invention, the theoretical basis for operation was not understood. The operational theory was developed later in Germany, with the work of Walter Deutsch and

3268-471: The dew point to prevent corrosion problems in the ESP or downstream equipment. The figure to the right shows the effect of temperature and moisture on the resistivity of a cement dust. As the percentage of moisture in the gas stream increases from 6 to 20%, the resistivity of the dust dramatically decreases. Also, raising or lowering the temperature can decrease cement dust resistivity for all the moisture percentages represented. The presence of SO 3 in

3344-464: The dust collector was Wilhelm Beth  [ de ] from Lübeck . In 1921, he patented three filter designs that he had pioneered to remove dust from air. Dust collectors are used in many processes to either recover valuable granular solid or powder from process streams, or to remove granular solid pollutants from exhaust gases prior to venting to the atmosphere. Dust collection is an online process for collecting any process-generated dust from

3420-449: The dust in suspension for conveyance to the collection device. A duct of the wrong size can lead to material settling in the duct system and clogging it. Finally, the dust is collected . This is done via a variety of means, depending on the application and the dust being handled. It can be as simple as a basic pass-through filter, a cyclonic separator , or an impingement baffle. It can also be as complex as an electrostatic precipitator ,

3496-591: The dust layer). As voltage is increased from small amounts (e.g. 20 V), no current is measured. Then, a threshold voltage level is reached. At this level, current surges through the sample... so much so that the voltage supply unit can trip off. After removal of the unburned combustibles during the above-mentioned annealing procedure, the descending temperature mode curve shows the typical inverted “V” shape one might expect. Particles that have low resistivity are difficult to collect because they are easily charged (very conductive) and rapidly lose their charge on arrival at

3572-536: The form of electricity). The first use of corona discharge to remove particles from an aerosol was by Hohlfeld in 1824. However, it was not commercialized until almost a century later. In 1907 Frederick Gardner Cottrell , a professor of chemistry at the University of California, Berkeley , applied for a patent on a device for charging particles and then collecting them through electrostatic attraction—the first electrostatic precipitator. Cottrell first applied

3648-463: The formation of the Lurgi company. Cottrell used proceeds from his invention to fund scientific research through the creation of a foundation called Research Corporation in 1912, to which he assigned the patents. The intent of the organization was to bring inventions made by educators (such as Cottrell) into the commercial world for the benefit of society at large. The operation of Research Corporation

3724-410: The gas stream has been shown to favor the electrostatic precipitation process when problems with high resistivity occur. Most of the sulfur content in the coal burned for combustion sources converts to SO 2 . However, approximately 1% of the sulfur converts to SO 3 . The amount of SO 3 in the flue gas normally increases with increasing sulfur content of the coal. The resistivity of

3800-476: The gas stream. The electrical conductivity of a bulk layer of particles depends on both surface and volume factors. Volume conduction, or the motions of electrical charges through the interiors of particles, depends mainly on the composition and temperature of the particles. In the higher temperature regions, above 500 °F (260 °C), volume conduction controls the conduction mechanism. Volume conduction also involves ancillary factors, such as compression of

3876-404: The gas that is trapped within the dust layer. The dust layer breaks down electrically, producing small holes or craters from which back corona discharges occur. Positive gas ions are generated within the dust layer and are accelerated toward the "negatively charged" discharge electrode. The positive ions reduce some of the negative charges on the dust layer and neutralize some of the negative ions on

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3952-429: The grounded walls of the cylinder. The collected dust is removed from the bottom of the cylinder. Tubular precipitators are often used for mist or fog collection or for adhesive, sticky, radioactive, or extremely toxic materials. The four main components of all electrostatic precipitators are: The collected material on the electrodes is removed by rapping or vibrating the collecting electrodes either continuously or at

4028-412: The individual cyclones have a greater length and smaller diameter. Secondary-air-flow separators use a secondary air flow, injected into the cyclone to accomplish several things. The secondary air flow increases the speed of the cyclonic action making the separator more efficient; it intercepts the particulate before it reaches the interior walls of the unit; and it forces the separated particulate toward

4104-409: The laboratory. Results for Fly Ash A (in the figure to the left) were acquired in the ascending temperature mode. These data are typical for a moderate to high combustibles content ash. Data for Fly Ash B are from the same sample, acquired during the descending temperature mode. The differences between the ascending and descending temperature modes are due to the presence of unburned combustibles in

4180-417: The layer as negatively charged particles arrive at its surface and leak their electrical charges to the collection plate. At the metal surface of the electrically grounded collection plate, the voltage is zero, whereas at the outer surface of the dust layer, where new particles and ions are arriving, the electrostatic voltage caused by the gas ions can be quite high. The strength of this electric field depends on

4256-472: The loss of electrical attraction forces. The table below summarizes the characteristics associated with low, normal and high resistivity dusts. The moisture content of the flue gas stream also affects particle resistivity. Increasing the moisture content of the gas stream by spraying water or injecting steam into the duct work preceding the ESP lowers the resistivity. In both temperature adjustment and moisture conditioning, one must maintain gas conditions above

4332-465: The market). The following discussion of normal, high, and low resistance applies to ESPs operated in a dry state; resistance is not a problem in the operation of wet ESPs because of the moisture concentration in the ESP. The relationship between moisture content and resistance is explained later in this work. As stated above, ESPs work best under normal resistivity conditions. Particles with normal resistivity do not rapidly lose their charge on arrival at

4408-403: The necessary energy to drive the fan. Motors are selected to provide sufficient power to operate fans over the full range of process conditions (temperature and flow rate). Dust collectors can be configured into one of five common types: Important parameters in specifying dust collectors include airflow the velocity of the air stream created by the vacuum producer; system power, the power of

4484-415: The particle layer, particle size and shape, and surface properties. Volume conduction is represented in the figures as a straight-line at temperatures above 500 °F (260 °C). At temperatures below about 450 °F (230 °C), electrical charges begin to flow across surface moisture and chemical films adsorbed onto the particles. Surface conduction begins to lower the resistivity values and bend

4560-530: The particles in the air stream. The ionized particles, due to the electrostatic force , are diverted towards the grounded plates. Particles build up on the collection plates and are removed from the air stream. A two-stage design (separate charging section ahead of the collecting section) has the benefit of minimizing ozone production, which would adversely affect the health of personnel working in enclosed spaces. For shipboard engine rooms where gearboxes generate an oil mist , two-stage ESP's are used to clean

4636-505: The passage formed by the discharge and collecting electrodes. Electrostatic precipitators operate on the same principle as home "Ionic" air purifiers. The airborne particles receive a negative charge as they pass through the ionized field between the electrodes. These charged particles are then attracted to a grounded or positively charged electrode and adhere to it. Unlike central collectors, unit collectors control contamination at its source. They are small and self-contained, consisting of

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4712-439: The plate, making them difficult to remove and causing trapping problems. In low resistance dust layers, the corona current is readily passed to the grounded collection electrode. Therefore, a relatively weak electric field, of several thousand volts, is maintained across the dust layer. Collected dust particles with low resistance do not adhere strongly enough to the collection plate. They are easily dislodged and become retained in

4788-423: The plates typically spaced about 1 cm to 18 cm apart, depending on the application. The air stream flows horizontally through the spaces between the wires, and then passes through the stack of plates. A negative voltage of several thousand volts is applied between wire and plate. If the applied voltage is high enough, an electric corona discharge ionizes the air around the electrodes, which then ionizes

4864-417: The precipitator by using a device such as a cyclone mechanical collector . The addition of liquid ammonia ( NH 3 ) into the gas stream as a conditioning agent has found wide use in recent years. It is theorized that ammonia reacts with H 2 SO 4 contained in the flue gas to form an ammonium sulfate compound that increases the cohesivity of the dust. This additional cohesivity makes up for

4940-463: The quality of air in the workplace environment. Fume and smoke collectors are used to remove sub-micrometer-size particulates from the air. They effectively reduce or eliminate particulate matter and gas streams from many industrial processes such as welding , rubber and plastic processing, high speed machining with coolants, tempering , and quenching . Dust collection systems work on the basic formula of capture , convey and collect . First,

5016-414: The resistance and thickness of the dust layer. In high-resistance dust layers, the dust is not sufficiently conductive, so electrical charges have difficulty moving through the dust layer. Consequently, electrical charges accumulate on and beneath the dust layer surface, creating a strong electric field. Voltages can be greater than 10,000 volts. Dust particles with high resistance are held too strongly to

5092-429: The sample. Between the two test modes, the samples are equilibrated in dry air for 14 hours (overnight) at 850 °F (450 °C). This overnight annealing process typically removes between 60% and 90% of any unburned combustibles present in the samples. Exactly how carbon works as a charge carrier is not fully understood, but it is known to significantly reduce the resistivity of a dust. Carbon can act, at first, like

5168-472: The scroll also converts a portion of the velocity pressure into static pressure. There are three main types of centrifugal fans: Axial-flow fans are used in systems that have low resistance levels. These fans move the air parallel to the fan's axis of rotation. The screw-like action of the propellers moves the air in a straight-through parallel path, causing a helical flow pattern. The three main kinds of axial fans are: Electric motors are used to supply

5244-508: The source point on a continuous basis. Dust collectors may be of single unit construction, or a collection of devices used to separate particulate matter from the process air. They are often used as an air pollution control device to maintain or improve air quality. Mist collectors remove particulate matter in the form of fine liquid droplets from the air. They are often used for the collection of metal working fluids, and coolant or oil mists. Mist collectors are often used to improve or maintain

5320-526: The station's chimneys. On 8 January 2003, Unit 2 generator exploded while being returned to service after a malfunction. On 9 February 2011 another unit failed catastrophically while performing over speed testing. The units are over speed rated at 3600 rpm and the last recorded speed before failure was 4250 rpm. It was the first power station in South Africa to have a black power station manager, Ehud Matya. The station consists of six 600 MW units with

5396-420: The surface of the dust layer, the voltage difference between the discharge and collection electrodes decreases. The migration velocities of small particles are especially affected by the reduced electric field strength. Another problem that occurs with high resistivity dust layers is called back corona. This occurs when the potential drop across the dust layer is so great that corona discharges begin to appear in

5472-442: The system motor, usually specified in horsepower; storage capacity for dust and particles, and minimum particle size filtered by the unit. Other considerations when choosing a dust collection system include the temperature, moisture content, and the possibility of combustion of the dust being collected. Systems for fine removal may only contain a single filtration system (such as a filter bag or cartridge). However, most units utilize

5548-411: The unit should be specified. A baghouse is an air pollution abatement device used to trap particulate by filtering gas streams through large fabric bags. They are typically made of glass fibers or fabric. A cyclone separator is an apparatus for the separation, by centrifugal means, of fine particles suspended in air or gas. Electrostatic precipitator An electrostatic precipitator ( ESP )

5624-589: The values obtained indicate the maximum ash resistivity. In an ESP, where particle charging and discharging are key functions, resistivity is an important factor that significantly affects collection efficiency. While resistivity is an important phenomenon in the inter-electrode region where most particle charging takes place, it has a particularly important effect on the dust layer at the collection electrode where discharging occurs. Particles that exhibit high resistivity are difficult to charge. But once charged, they do not readily give up their acquired charge on arrival at

5700-411: The voltage drop across the dust layer becomes too high, several adverse effects can occur. First, the high voltage drop reduces the voltage difference between the discharge electrode and collection electrode, and thereby reduces the electrostatic field strength used to drive the gas ion-charged particles over to the collected dust layer. As the dust layer builds up, and the electrical charges accumulate on

5776-512: Was a clearinghouse for any process improvements. However, anti-trust concerns forced Research Corporation to eliminate territory restrictions in 1946. Electrophoresis is the term used for migration of gas-suspended charged particles in a direct-current electrostatic field . Traditional CRT television sets tend to accumulate dust on the screen because of this phenomenon (a CRT is a direct-current machine operating at about 15 kilovolts). There are two main types of precipitators: Described below

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