Boiler explosion, its causes & effects in Bangladesh PDF

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Boiler explosion, its causes & effects in Bangladesh Introduction: A boiler explosion is a catastrophic failure of a boiler. As seen today, boiler explosions are of two kinds. One kind is a failure of the pressure parts of the steam and water sides. There can be many different causes, such as fa...

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Boiler explosion, its causes & effects in Bangladesh Rahmatullah BD

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Boiler explosion, its causes & effects in Bangladesh

Introduction: A boiler explosion is a catastrophic failure of a boiler. As seen today, boiler explosions are of two kinds. One kind is a failure of the pressure parts of the steam and water sides. There can be many different causes, such as failure of the safety valve, corrosion of critical parts of the boiler, or low water level. Corrosion along the edges of lap joints was a common cause of early boiler explos.The most common boiler hazards that lead to accidents are low water levels, excessive pressure and a failure to purge combustible gases from the firebox before ignition. These hazards can cause serious boiler accidents like explosions or fire. Low water levels in a boiler are caused by improperly functioning low water cut-offs. Water levels that are too low can cause the boiler to buckle or deform, melt down or even explode—all of which can generate severe damage to the boiler and/or to the building. Excessive pressure in a boiler can also lead to explosions. This occurs when pressure is allowed to build in the boiler. Boiler explosions are very dangerous and can completely destroy buildings. Fuel-related accidents, like fires and explosions, are also common and occur when combustible gases are not purged from the firebox. Leaking fuel valves can also cause this kind of accident.

Methodology The methodology for this study included collection of major information from secondary sources, from several official and unofficial websites and much information collected from some journals which are written by some famous environment scientists. All the information in this paper are collected and written by the group members.

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Objectives This article is written under following objectives: 

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Causes of boiler explosions

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Boiler explosions in Bangladesh and their effects

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Principle of Boiler explosion

Boiler Accident Prevention

Causes of boiler explosions The stationary steam engines used to power machinery first came to prominence during the industrial revolution, and in the early days there were many boiler explosions from a variety of causes. One of the first investigators of the problem was William Fairbairn, who helped establish the first insurance company dealing with the losses such explosions could cause. He also established experimentally that the hoop stress in a cylindrical pressure vessel like a boiler was twice the longitudinal stress. Such investigations helped him and others explain the importance of stress concentrations in weakening boilers. There are many causes for boiler explosions such as poor water treatment causing scaling and over heating of the plates, low water level, a stuck safety valve, or even a furnace explosion that in turn, if severe enough, can cause a boiler explosion. Poor operator training resulting in neglect or other mishandling of the boiler has been a frequent cause of explosions since the beginning of the industrial revolution. In the late 19th and early 20th century, the inspection records of various sources in the U.S., UK, and Europe showed that the most frequent cause of boiler explosions was weakening of boilers through simple rusting, by anywhere from 2 to 5 times more than all other causes. Before materials science, inspection standards, and quality control caught up with the rapidly growing boiler manufacturing industry, a significant number of boiler explosions were directly traceable to poor design, workmanship, and undetected flaws in poor quality materials.

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The alarming frequency of boiler failures in the U.S. due to defects in materials and design were attracting the attention of international engineering standards organizations, such as the ASME, which established their first Boiler Testing Code in 1884. The boiler explosion that caused The Grover Shoe Factory Disaster in Brockton, Massachusetts on March 10, 1905 resulted in 58 deaths and 117 injuries, and inspired the state of Massachusetts to published its first boiler laws in 1908. Several written sources provide a concise description of the causes of boiler explosions: "The principal causes of explosions, in fact the only causes, are deficiency of strength in the shell or other parts of the boilers, over-pressure and over-heating. Deficiency of strength in steam boilers may be due to original defects, bad workmanship, deterioration from use or mismanagement."[1] "Cause.-Boiler explosions are always due to the fact that some part of the boiler is, for some reason, too weak to withstand the pressure to which it is subjected. This may be due to one of two causes: Either the boiler is not strong enough to safely carry its proper working pressure, or else the pressure has been allowed to rise above the usual point by the sticking of the safety valves, or some similar cause"[2]

Principle of Boiler explosion Many shell-type boilers carry a large bath of liquid water which is heated to a higher temperature and pressure (enthalpy) than boiling water would be at atmospheric pressure. During normal operation, the liquid water remains in the bottom of the boiler due to gravity, steam bubbles rise through the liquid water and collect at the top for use until saturation pressure is reached, then the boiling stops. If some pressure is released, boiling begins again, and so on. If steam is released normally, say by opening a throttle valve, the bubbling action of the water remains moderate and relatively dry steam can be drawn from the highest point in the vessel.If steam is released more quickly, the more vigorous boiling action that results can throw a fine

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spray of droplets up as "wet steam" which can cause damage to piping, engines, turbines and other equipment downstream. If a large crack or other opening in the boiler vessel allows the internal pressure to drop very suddenly, the heat energy remaining in the water will cause even more of the liquid to flash into steam bubbles, which then rapidly displace the remaining liquid. The potential energy of the escaping steam and water are now transformed into work, just as they would have done in an engine; with enough force to peel back the material around the break, severely distorting the shape of the plate which was formerly held in place by stays, or self-supported by its original cylindrical shape. The rapid release of steam and water can provide a very potent blast, and cause great damage to surrounding property or personnel.

The rapidly expanding steam bubbles can also perform work by throwing large "slugs" of water inside the boiler in the direction of the opening, and at astonishing velocity. A fast-moving mass of water carries a great deal of kinetic energy (from the expanding steam), and in collision with the shell of the boiler results in a violent destructive effect. This can greatly enlarge the original rupture, or tear the shell in two.[3]

Many plumbers and steamfitters are aware of this phenomenon, which is called "water hammer". A few ounce "slug" of water passing through a steam line at high velocity and striking a 90 degree elbow can instantly fracture a fitting that is otherwise capable of handling several times the normal static pressure. It can then be understood that a few hundred, or even a few thousand pounds of water moving at the same velocity inside a boiler shell can easily blow out a tube sheet, collapse a firebox, even toss the entire boiler a surprising distance through reaction as the water exits the boiler, like the recoil of a heavy cannon firing a ball.

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Several accounts of the SL-1 experimental reactor accident vividly describe the incredibly powerful effect of water hammer on a pressure vessel: "The expansion caused by this heating process caused water hammer as water was accelerated upwards toward the reactor vessel head, producing approximately 10,000 pounds per square inch (69,000 kPa) of pressure on the head of the reactor vessel when water struck the head at 160 feet per second (50 m/s)" "This extreme form of water hammer propelled control rods, shield plugs, and the entire reactor vessel upward. A later investigation concluded that the 26,000-pound (12,000 kg) vessel had jumped 9 feet 1 inch (2.77 m) and the upper control rod drive mechanisms had struck the ceiling of the reactor building prior to settling back into its original location"

Boiler explosions in Bangladesh and their effects We are writing about two most destructive boiler explosions in our country for the recent time: KONABARI, Bangladesh - A boiler explosion at a Bangladeshi garment plant in July 3, 2017 near the city of Dhaka killed 10 people and injured dozens, emergency workers said on Tuesday, the latest industrial tragedy to hit one of the world’s biggest garment producers. The blast, late on Monday, occurred at a plant operated by local Bangladeshi firm Multifabs while maintenance work was going on, company and fire brigade officials said. The explosion at the boiler, located in a tin-roofed shed, partially damaged a nearby three-storey factory building. “I heard a big bang when I was having tea outside,” factory driver Hafiz Mostafa said, as dozens thronged the factory site and firefighters moved rubble in search of missing persons. “I saw windows, doors, glasses, machinery and a section of the wall of the building go flying.”

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Families scoured the scene for missing people. The plant had been shut for 10 days for Eid holidays at the end of the Muslim holy month of Ramadan and was being readied to resume operations on Tuesday, when the accident occurred.

“We’re looking for my brother. We checked all the hospitals, but have not found him,” said Nazim Uddin, whose brother Ershad Ullah worked as an electrician at the plant for the last decade. [5]

FIG: Boiler explosion in Multifabs Firm, Karnabari, Bangladesh.

TONGI, Bangladesh ( September 10, 2016) — A boiler explosion in a cigarette packaging factory outside Dhaka enveloped the five-story building in flames early Saturday, killing at least 23 people, fire officials said.

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The blaze was the latest in a series of industrial disasters over the last several years in Bangladesh. At least 50 people were injured in Saturday’s fire, said Mozammel Hoque, a deputy director of the fire service. The cause of the explosion was unclear, he added. The blast occurred at 6 a.m. at the Tampaco Foils factory in an industrial park in Tongi. The factory makes, among many other things, foil for cigarette packs for British American Tobacco and snack-food packaging for Nestlé. By Saturday evening, firefighters had not yet completely extinguished the blaze. They tried to rescue anyone still trapped inside. “There’s definitely still people inside,” Mr. Hoque said around noon on Saturday. “So far, we’ve only been finding dead bodies, no one who was still alive.” [6]

FIG: A boiler explosion in Tongi, Bangladesh.

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Boiler Accident Prevention Routine maintenance can generally be done by the boiler operator to avoid these devastating accidents. But there are circumstances when a trained professional is needed. These include: 

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Leaking safety and/or safety relief valves Contaminated feed water Steam leaks (in steam boilers) High stack temperatures (exceeding 177° C) Insufficient heat for the building Condensation dripping down the stack or out of the front of the boiler Constant resetting of controllers and safety devices Ongoing routine maintenance and inspection is the best way to prevent a boiler accident. Use a checklist when inspecting a boiler to ensure you’re inspecting it thoroughly.

Conclusion Boiler explosion causes long outage and loss of generation. It can cause loss of life and property. NFPA has collected data on explosion and has large number of standards which guide to prevent explosion. Evaluating the cause, documenting it for corrective and preventive action is essential. Explosions in boilers are not uncommon. Irrespective of the type of fuel being fired, boilers have experienced explosions. Remember that an explosion analysis is not a fault finding mission, but a fact finding one for prevention of the cause in future. Never officially put on record any of your findings before the chief of the plant at the highest level agrees with you. There are many areas to be taken care by the plant owner and you as a fact finding man have to be helping him in all. However it is very important to record all the facts for your analysis and corrective / preventive action. Which able to lead to minimize the damage and saving of lives.

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References 1.Roper, Stephen (1899). Roper's Engineer's Handy Book (15th edition) Philadelphia: David McKay (p.207–208)

2.The Colliery Engineers Company (1900) Locomotive Boilers (I.C.S. Reference Library #59) Statione's Hall, London: International Textbook Company 3. The Colliery Engineers Company (1900) Locomotive Boilers (I.C.S. Reference Library #59) Stationer's Hall, London: International Textbook Company (sec.12,p.76) 4. Milo D. Koretsky, “Engineering and Chemical Thermodynamics”, John Wiley & Sons, 5.https://www.reuters.com/article/us-bangladesh-blast/blast-in-bangladesh-garment-factory-kills10-investigation-underway-idUSKBN19P0A0

6.https://www.nytimes.com/2016/09/11/world/asia/boiler-explosion-at-bangladesh-factory-killsat-least-23.html?mcubz=3

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