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33-459: 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

66-415: 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

99-479: 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

132-405: 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

165-418: 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

198-836: 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

231-399: 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

264-414: 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

297-437: 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

330-430: 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

363-426: 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

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396-536: 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

429-449: 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

462-432: 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

495-407: 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

528-424: 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

561-683: 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

594-411: 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

627-575: 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

660-514: 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

693-448: 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

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726-491: 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

759-464: 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

792-449: 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 ,

825-412: 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

858-403: 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

891-505: 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

924-463: 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,

957-472: 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

990-508: 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

1023-520: 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

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1056-442: 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

1089-404: 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. Wet scrubber Too Many Requests If you report this error to

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