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A Recipe for a Very Large Fire

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A Recipe for a Very Large Fire Learning From Losses Turbine Generators: a Recipe For a Very Large Fire What’s the “main ingredient” in a turbine generator fi re? A few hundred gallons (several hundred liters) of relatively low fl ash point mineral oil. ut it under pressure and confi ne it Fires involving turbine generators in within piping, seals or removable- non-utility facilities like paper mills Popening covers. Then, provide an and combined cycle power plants also available “hot” surface—hot enough to were reported. Here’s an example of ignite mineral oil…nearby steam pip- what can happen when oil is released ing or a turbine casing will do the job. in a spray pattern: Now, wait until a fl ange leaks, a pipe breaks, a seal fails or a cover is left off A fi re at a process pulp mill began an opening—and you have a “recipe” when pressurized oil from a leaking for one of the largest fi res you could control-oil system pipe sprayed onto ever imagine. And, if the oil is released hot steam piping. The control-oil line in a spray, it could be even larger. serviced a 37.5-MW steam turbine driving an AC generator. The fi re was Has this recipe for disaster been tested? further fed by the oil that continued to It sure has. During a recent 15-year fl ow, then spread to nearby cable trays. period, 17 large turbine building fi res The fi re caused extensive damage to resulted in more than US$400 million critical power cables in the turbine- in gross loss. Lost generating capac- generator basement. The resulting loss ity was in excess of 20 million MWh, to boilers and other equipment led to which is roughly the equivalent of a a total mill shutdown for more than mid-sized investor-owned utility in the four days. The gross loss was more United States. The average loss was than US$13 million, a large portion US$24 million and the average outage of which was lost business. was more than 24 weeks. 8 Record ■ Vol. 81, No. 4, 2004 Lack of automatic fi re protection in the In this example, the ignited oil fl owed In this second example, oil leaking fi re area allowed the fi re to spread. For- downward, engulfi ng a large area: from a fl ange of an oil-return line tunately, manual fi re fi ghting, which is ignited inside a gas turbine generator usually delayed due to smoke and heat, Following repairs to a boiler feed pump compartment at a cogeneration facil- was able to prevent even more damage. hydraulic servomotor, the servomotor ity for a dehydration plant. Lock nuts cover was left off to check for leak- for the fl ange bolts had not been used Operators also can initiate these types age as the oil line was re-pressurized. and the bolts loosened. The fi re was of events. Some of the routine mainte- A fi tting beneath the cover separated, extinguished by the gaseous suppres- Turbine Generators: nance involves working on pressurized and the oil began to fl ow out instead sion system protecting the enclosure, systems—shifting and cleaning strain- of down the guardian pipe as it would limiting damage to US$20,000. ers, for instance. If the mechanic loses normally. The ignited oil found a 9-ft.2 concentration and forgets where he or (0.8-m2) fl oor opening and spread along The bottom line is there is a high likeli- she is in the procedure, an oil release open cable trays below. The fi re burned hood of a fi re wherever there is mineral is possible. This example illustrates until all oil was consumed. Damage oil under pressure and hot surfaces human error: included walls, I-beams and supports, around to ignite it. If one of the myriad exterior metal panel walls, cable trays mechanical joints does not fail, opera- A 620-MW generator driven by a and cables, and the feed pump. Gross tor error could instigate the oil release. four-fl ow tandem compound steam loss was more than US$35 million. So, the best option is to lower thethe turbine at a utility generating station severity of the fi re by ensuring the best sustained a lube-oil fi re. The cause But, despite these losses, there is some protection scheme is installed, tested of the fi re was failure to shut off, or good news. With proper protection in and maintained as recommended by bypass, the oil fl ow to the fi lters of place, damage can be minimized as your local FM Global engineer. Your the hydrogen-seal oil system while evidenced by these two examples: business cannot afford the alternative. an employee was changing or cleaning the fi lters. Five bolts had been loosened In the fi rst example, a hot surface ig- on the second fi lter when the seal rup- nited lube oil leaking from a hydraulic tured, releasing lubricating oil at 70 to governor for a steam turbine driving a 90 psi (5 to 6 bar). The lubricating oil generator in the powerhouse of a paper spewed out of this opening, contacted mill. Employees manually activated hot piping and ignited. During the inci- an open-head waterspray system. The dent, the plant’s other turbine generator waterspray and portable extinguishers was tripped and off-site power secured. put out the fi re. The employees were This caused the operating electric able to coast down the turbine with- fi re pump to shut down. out bearing damage and the fi re was extinguished without property damage. Extensive damage occurred to the The turbine generator was down for generator, the two LP-turbine sections, six hours. The waterspray system had steam pipes, oil piping and isophase recently been installed—as recom- bus bars. The roof over the turbine mended by FM Global. generator sagged over a 10,000-ft.2 (930-m2) area, pulling the walls inward approximately 5 ft. (1.5 m). The gross loss was in excess of US$44 million. Record ■ Vol. 81, No. 4, 2004 9 Neeww RResearchesearch Electrifi es Industry Q: What weighs more than a locomotive and spins at 3,600 rpm? A: The rotor in a large steam turbine generator. he tremendous forces created by this furiously spinning To avoid this, oil is pumped continually to the bearings mass are borne by a series of large bearings. A continu- of the turbine, generator, exciter and boiler-feed pumps. Tous fl ow of lubricating oil is forced into these bearings To ensure oil fl ow and prevent damage, even if the main under high pressure. As the turbine shaft accelerates, it is pump fails, turbine lubrication systems also are equipped forced up onto a thin fi lm of oil—about the thickness of a with a battery-powered backup pump. human hair. Much of the world’s energy is produced by turbines that A large oil reservoir—containing up to 20,000 gal. depend on this type of lubrication system to keep them (80,000 L) of oil—is required to maintain this high- running smoothly and effi ciently. A break anywhere in this pressure fl ow. Should this oil fl ow be cut off for any oil supply network spells trouble, not only for the turbine, reason, the spinning rotor shaft would soon make metal- but also can pose a serious fi re hazard. to-metal contact with the inner bearing surfaces—and that could result in catastrophic damage and lengthy downtime. 10 Record ■ Vol. 81, No. 4, 2004 Oil Fires–a Clear and Present Danger and turbines were out of service from one to seven weeks, with an average downtime of less than two weeks. While Inadequate fi re protection systems and a lack of proper this still represents a substantial loss, it is far less than those emergency protocols can lead to serious damage and for under-protected facilities. extended outages in the event of a lube-oil fi re. In a recent 15-year period, FM Global found fi re protection defi ciencies And, these losses do not take into account the additional for lube-oil systems were a major factor in 17 large turbine costs of business interruption and the possible penalties building fi res. The property damage alone (not including imposed by contractual obligations such as service guaran- business interruption losses) totaled more than US$400 tees, fuel-purchasing arrangements and the many other million. Lost generating capacity was in excess of 20 million factors that an increasingly deregulated power industry MWh (assumes a base-loaded station with a capacity factor faces. Why do these losses continue to occur? One key of 86 percent), which is equivalent to the annual generating factor is the lack of defi nitive research into the specifi c capacity of a mid-sized investor-owned utility. fi re threats faced by the power generation industry. Until last winter, no research organization had ever done full- The average property loss from these incidents was more scale fi re tests of actual turbine-hall fi re scenarios. than US$26 million. The turbines involved were out of service from 10 days to 48 weeks, with an average down- time of more than 24 weeks. In addition, three turbines Blazing a New Trail were retired following two large fi res. By contrast, in six To help refi ne its knowledge of the fi re hazards faced turbine-building fi res where recommended protection was by power producers, FM Global conducted an ambitious installed, the average property damage was US$700,000 fi rst-of-its-kind test program earlier this year at the compa- ny’s new Research Campus in West Glocester, R.I., USA.
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