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Why coal fired power stations don’t work so well when they are old

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The ageing of coal fired power stations is currently in the news with the likely shutdown on Liddell Power Station in 2022.

Industrial plants and utilities shutting due to old age is actually a bit unusual. coal fired stations 1Most plants and equipment systems that aren’t subject to arduous or corrosive environments can typically have their operational life extended with relatively low levels of maintenance and capital money spent, relative to the cost of their replacement.

They are more commonly finally shut down due to competition from new and more efficient technologies then from old age. Most power station electrical generator and transmission systems would fall into this category.

What does not fall into this category is power plant steel components in high temperature steam and boiler systems. They can be subject to a dangerous ageing mechanism called “high temperature creep cracking.”

Manufactures of power stations rate the life of their plants at 20 years and the high temperature creep failure mechanism in steel pipework and pressure vessels is the reason for this rating.

Power station manufacturers would like us to replace power stations at 20 years, but this rarely occurs. This is because the engineer standards for assessing creep failure mechanisms are very conservative and focus on worst case scenarios.

It is also because there are Non-Destructive Testing (NDT) methods that can assess the level of creep deterioration in steam systems. The biggest limiting factor is the cost and the power plant outage length to carry out these NDT tests.

The most likely place for creep cracking to occur is in the highest operating temperature steel tubing inside a boiler. The image at right is a boiler tube that has been cut open to examine a creep crack failure.coal power stations 2

This type of boiler tube failure can cause unexpected outages but these problems once identified can be manages without major safety risks. Liddell power station is now 45 years old and so is well over twice its rated age.

This means that the locations where creep cracking may lead to the possibility of failure is now much more extensive and so much more difficult and expensive to manage.

One of the worst-case failure scenarios for a power station steam system is a creep failure in one of the large main steam pipes within the turbine building of the power station.

It has been estimated that a main steam pipe rupture would fill a typical turbine building with high temperature steam in under 30 seconds. Anyone in the turbine building would be severely scalded and probably die.

This is not just an academic possibility as 21 people were killed and five injured in a high-pressure steam pipe failure at a Chinese power station in in the city of Dangyang in August of 2016 (Link). The ratio of killed to injured gives an indication of the horrific nature of such an accident.

The probability that this type of failure could occur in Liddell is very small, but it is possible. AGL, the owner of Liddell power station would be aware of these risks and it is likely one of the reasons they want to shut the station down.

Making full assessments of creep fatigue risks would be a huge and expensive exercise that would include scheduling shutdowns, building scaffolding, removing insulation and doing sophisticated NDT testing with lots of complicated prep work on kilometres of pipework.

It is very likely that some cracks and crack risk areas would be found and the required repairs would be very complicated and expensive.  Add this to huge number of other problems that need to be repaired and managed in an aging plant, it is no wonder that AGL is keen to shut down Liddell.

Peter Todd is a reliability engineer and this was an article written for the quarterly publication Asset Reliability which he publishes.  

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  • Malcolm M

    Doesn’t neocon economics trump physics ? Why would the COALition want to listen to a reliability engineer with experience in coal-fired power stations when they know the answer already ?

    • Alastair Leith

      And low appreciation of economics among neocons and neoliberal economists. Matt Carnarvon was airing his ignorance around renewable energy prices and value on QandA recently. So bad I had to switch him off.

      • Malcolm M

        Matt Canavan also recently quoted the the spot power prices in Queensland as over $300/MWh, blaming gaming of the market. It seems he didn’t look up the Aneroid Energy website, which showed that several of Queensland’s coal-fired generators were off-line, including the huge Kogan Creek power station (750 MW). As soon as Kogan Creek fired up again, the prices came back to normal. This in itself is a problem, that with about 10% of the Queensland market in a single generation unit, the market is stressed if it trips. Perhaps if Kogan Creek had been built as two units with half the capacity, its financials would not have stacked up. So in order to achieve economies of scale, it puts the Queensland market at a higher level of risk.

        • Alastair Leith

          Me missed the $14,000 spot prices in SA with no coal or storage! Storage becomes very affordable when generation needs gaps filled.

    • Alastair Leith

      HELE and either bolt on retrofitted CCS or purpose built CCS plants would have even more problems ramping as we start seeing midday duck curve biting into the base-load part of demand curve, mid century in places like SA and WA.

  • Tom

    Great article. Thanks.

  • Chris Drongers

    But doing all that very expensive work would add to GDP. Gains to gdp from investment in solar panels and racks wouldn’t show a commensurate return for years.
    This GDP argument is probably why Trump et al aren’t that concerned about the costs of rebuilding after cyclones.

    • Mark Roest

      I think they’re not concerned with the costs because they plan to phase out the money as soon as it becomes low-profile enough for them to get away with it. that applies double to Puerto Rico.

  • Chris Drongers

    Sorry -DP Fat finger

  • wmh

    Coal miners (and perhaps coal mine owners) are also worried about Black Lung Disease, mine explosions, mine tunnel collapses and sudden catastrophic flooding of shafts.

  • Joe

    They don’t work so well when it is hot weather either. The old girl, ‘Liddell’, went down to 2 working boilers in the February heatwave here in NSW…just at the very moment that The COALition’s ‘Baseload Power’ was most needed. We almost had blackouts but load shedding and household rooftop solar came to the rescue.

  • Rod

    In my short time at a combined cycle gas plant I never even contemplated a main steam pipe failure. I do remember them stripping down a turbine and xray ing every blade on the $5 million turbine for fatigue cracks. With all the mentioned scaffolding and insulation removal it was a huge job.

  • Cooma Doug

    I was lucky enough to avoide the role of APPO….assistant power plant operator. But did do a couple of shifts in the old Wallerawang PS. Problems would come along and we would have to investigate potential steam infrastructure faults. The most dangerous thing we carefully avoided was small invisable super heated steam leaks. It would cut you in half if you walked into the invisable hazzard.
    I was able to get a role in a safer place.

    • Rod

      Yes, in hindsight my $20 a week danger money probably wasn’t enough. And we used to do public tours!

  • Ken Dyer

    Old coal fired power stations are just the same as old locomotives – they just run out of steam.

  • Andy Saunders

    There’s also the creeping cost of replacement of small failed items, and the cost of increasing inspections. This maintenance capex is hard to predict, but eventually the increasing need for it (along with the increasing shutdown times) overpowers the economics of the whole station, even without getting close to catastrophic failure.

  • Bristolboy

    In the UK coal generators are increasingly struggling with staffing issues. Many with experience are seeing the end and transferring to other more buoyant industries where their experience is valued. The next generation of engineers are also avoiding the industry meaning there is no new blood.

    Coal plant operators are therefore stuck with a less dynamic workforce, often with relatively unmotivated staff who are only there for the short term OR they have to pay much higher salaries than other industries.

    Of course, it could be argued that it is more stark in the UK with the government frequently referencing a complete stop to unabated coal from 2025 but I would expect similar trends are present throughout the world including Australia.

    Of course, this may pale into insignificance with the increasing risk of old component failure over time.

  • DogzOwn

    Another worry is outsourcing of maintenance which can deliver under skilled personnel with no experience in coal power. Even bean counters are outsourced, of course they make sure that all boxes are ticked to show maintenance works done whether or not.

  • Chris O’Neill

    The other way of dealing with creep fatigue not mentioned here is to reduce the temperature and pressure of the steam plant, thus reducing efficiency (ratio of kWh out to tonnes of coal in). Of course, this is also a bit of a disaster for CO2 emissions but when the carbon price of CO2 emissions is zero who cares!