Steam turbine generators are extensively made use of throughout the world as a common resource of energy production for utilities and populations.
Fires in steam turbines are not constant, yet when they happen they could be unsafe for responders to deal with, difficult for power plant operators to manage, and also pricey for the utility and the public they serve.
Therefore steam turbine fire protection is paramount.
Water mist systems have the firefighting capacity to make managing a steam turbine fire much less complex. This article presents the idea of turbine fire security utilising high-pressure water mist as well as exactly how these systems could integrate with a power plant’s procedure.
What Do Steam Turbines Do and How Can They Ignite?
A standard steam turbine operates using superheated steam to spin a rotor shaft. The power given to the shaft could be used for various work outputs like running big compressors and pumps. The most common usage is electrical power generation– producing electricity by affixing a generator to the end of the steam turbine shaft.
Steam turbines vary in size from 5 kilowatts to over 1500 megawatts. These are huge, hefty machines rotating at 3,600 RPM for 60 Hz power production and also 3,000 RPM for 50 Hz.
There are a number of subsystems supporting turbine operation, however the lubrication (lube) oil system is the main fire problem.
Lube oils have temperature flash factors varying from 190 °C to 260 °C. The flash point of lube oil is high enough that in numerous applications it would certainly not be simple to ignite from one spark.
Yet since how the lube oil is made use of for steam turbines, the fires that do occur are very difficult to control and also tough to extinguish out.
Lube oil is made use of to lubricate bearings along the high-speed turbine shaft. Pumped via steel pipelines from a storage tank and also pump skid in a recirculating system, lube oil systems can contain up to thousands of litres of oil.
If, for any reason, lube oil flow is reduced or cut off completely, the high speed-spinning shaft will cause the inner bearing race to make metal-to-metal contact with the shaft surface areas.
Bearing failure or shaft damage could cause catastrophic damage to the steam turbine, so the flow of high quality lube oil must be provided to the steam turbine shaft at all times it is operation.
The presence of lube oil presents a fire hazard though. If a pipe breaks, a seal fails, or any other type of lube oil system failure is experienced, the pressurised oil can saturate the insulation material and start a smouldering fire or sometimes also spray into the hot surfaces, firing up and causing a liquid spray fire.
Oil leaks will trigger pool fires by collecting on flat surface areas, or cause vertical surface fires by moving down structures sustained within the turbine.
Not all fires happen at the turbine– fires could additionally come from the lube oil skid. Lube oil skids consist of the lube oil bulk holding tank, system pumps with seals, oil filters, and also an oil colder.
Many turbines have secondary oil systems utilised to operate control valves on the turbine, which have the exact same fire hazards.
How To Mitigate Fire Using Water Mist Systems
Water mist systems are also utilised in power generation applications for combustion type turbines and also diesel generators.
These machines experience comparable fires to steam generators. Water mist styles for combustion type turbines and also generators are usually overall water flooding systems fit to the dimension of those machines.
Steam turbines provide a very large difference in difficulty for installations of water mist systems; they are set up in huge areas with high ceilings, frequently going beyond the listings of a lot of complete flooding water mist systems.
For steam turbines fire protection, closed loop local applications of water mist system layouts are the only available option.
3 firefighting systems of water mist have actually been developed:
1. Ultra-rapid evaporative
2. Local oxygen variation, and
3. Induction heat barring of the fire to un-burnt gases.
A Recent Steam Turbine Fire
As reported by the East Bay Times on 30th January, 2017 a steam turbine at the Delta Energy Centre in Pittsburg CA was shut down following an explosion and resulting fire from the leaking lube oil.
– PITTSBURG – The Delta Energy Centre power plant was shut down on Sunday after an explosion and fire destroyed the steam turbine generator.
At 3:43 p.m., calls came in to the Contra Costa Fire District line of a fire involving the hydrogen cooling system of the steam turbine at the Delta Energy Centre power plant at 1200 Arcy Lane in Pittsburg.
Firefighters arrived on scene to find a lubrication oil fire that was slowly starting to dwindle after power plant staff purged the hydrogen and carbon dioxide from the system, which starved the fire of flammable gas. The fire took approximately two hours to fight and no injuries were reported.
“One end of the generator was destroyed in the fire, mostly because of the initial explosion of the hydrogen gas,” fire marshal Robert Marshall said. “There was concern about the gear lubrication oil going into a storm drain near there, but we were able to boom that and no oil made it down to the river.”
The Delta Energy Centre is an 880-megawatt, natural gas-fired, “combined-cycle” plant, which uses both gas and steam to generate electricity.
The plant uses three gas turbines to generate electricity and each are equipped with a heat recovery system that delivers steam to an additional steam turbine, which generates 70 percent more electricity, on average.
Calpine has said that the damage was isolated to the steam turbine’s generator and that the rest of the plant, as well as the neighbouring communities, was not directly impacted.
Calpine is still assessing the accident and was not able to comment on the cause of the explosion nor the extent of the damage.
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No reports of any water mist fire protection systems were present, however as reported the cost of reduced power generation and damage would moat likely be severe and possibly reduced had an adequate water mist system be installed.
High pressure water mist systems have the essential firefighting efficiency & qualities. As more designers, engineers as well as plant operators familiarise the abilities of water mist systems, a greater number of these installations will take place.