Power from waste |
Wear protection improves reliability and extends life of EfW plants
Changing attitudes and regulations are making EfW (energy from waste) plants rethink their operational strategies to enhance efficiency and longevity
Martin Trenk Head Engineer for Boiler Coatings and EfW Applications, Castolin Eutectic
Thermal power plants must have a consistent power output if they are to achieve a steady baseload role in the power generation mix. This, however, is a particular challenge for EfW plants, which use a fuel – municipal waste – that does not always yield the same amount of energy per tonne. The last thing an operator needs, while closely monitoring the boiler temperature and turbine speed, is an unplanned stoppage. Yet, planned and unplanned stoppages remain frequent at EfW plants to replace worn parts, or to mitigate emissions. And as the European Union tightens its rules around burning municipal waste, EfW operators must ensure their plants are efficient and help support their nations’ power infrastructure.
Castolin Eutectic is playing a major role in addressing these issues, building on more than a century’s experience of innovation focused on improving the lifespan and efficiency of industrial facilities.
Unpredictable abrasion and wear in waste handling
Most EfW plants burn mixed municipal waste – food, paper, textiles, wood and plastic – that
would otherwise be sent to landfill. There are also more abrasive materials like metal, glass and electronic waste. Because the different materials present yield widely different amounts of energy, the waste must be mixed well before incineration, to achieve a stable boiler temperature. However, this causes significant wear on the hoppers the waste is delivered into, the crusher rotors that mix and break it up, and the systems that convey it to the incinerator.
The wear on fuel handling parts is also unpredictable because the fuel loads are not uniformly abrasive – the composition of the waste varies depending on the habits of people in the feeder municipalities. However well mixed the waste is, some loads will contain more glass, metal and hard plastic, and some will contain less. All these factors have historically posed an economic conundrum for EfW plant builders, owners and operators.
The case for up-front investment in harder wearing parts would be more obvious if the plant only handled the most abrasive materials: it would be unable to operate for long without them. Because not all the fuel is significantly abrasive, it can be tempting to gamble on less hardwearing parts.
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At the same time, a planned stoppage in six months’ time can become an unplanned stoppage tomorrow. This brings up the challenges of quickly and safely shutting the incinerator and turbine, and later ramping back up to a stable boiler temperature. A typical example illustrating the difference wear protection can make is provided by fuel crusher rotors, and their casings, which need to be rewelded on a yearly basis because of high wear. An effective solution is to refurbish the rotor using welding wire to rebuild it to its original dimensions. This increases the lifetime of the crusher significantly, resulting in a life 2 to 10 times that without wear protection. The ideal welding wire will provide excellent wear resistance while preventing health and safety risk. For example, the absence of chromium and nickel in Castolin Eutectic’s EnDOTec SafeHard 600 meets the strictest European Exposure Occupational Limits (EOL), while carbon and carbide content boosts wear resistance by providing toughness and hardness. The abrasive fuel in EfW plants also creates wear issues for hydraulic garbage grabs. This results in more waste falling back into the bunker
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