When specifying a conveyor chain for a corrosive environment, such as wet ash removal at a biomass energy plant, it’s important to consider the wear characteristics of the material and design. Stainless steel pins and bushes that have been welded for extra strength, for example, can dramatically increase service life and prevent costly unscheduled downtime.
Waste-to-energy (WtE) now provides over 11% of the UK’s electricity and is continuing to grow. A wide range of different biomass fuels are burnt but each process has one thing in common – the ash waste must be removed somehow.
There are two typical methods of ash removal. The first is a wet ash removal conveyor, where the ash is dropped into a water bath and scraped out using a scraper conveyor. The other is a dry ash removal conveyor, where the ash is passed through an air-cooled system before being dealt with.
For the purposes of this article, we will look at wet ash removal conveyors only, since they are the more widespread variety. The implementation cost of a dry ash system is considerably more than a wet ash removal system, but wet ash removal conveyors still have their challenges.
The question of corrosion
During the five years I’ve been at FB Chain, I’ve worked with numerous customers in the energy-from-waste (EfW) sector – conveying biomass fuels like crops, wood chip, pellets and waste wood, even household black bin waste and commercial waste.
Before coming to us, many of these biomass plant operators struggled with the corrosive environment and inconsistency of the ash as it came out of the furnace and through the water bath. ‘How do I stop my wet ash chain corroding?’ is one of the most common questions we are asked.
The answer is actually pretty simple – consider the operating environment. Many conveyor designers and operators discuss the load specifications and pitch of the conveyor chain to manage the speed and amount of product they want to convey but fail to factor in the wear characteristics of the chain.
In a corrosive environment, a standard conveyor chain produced from mild steel hardened to increase strength just will not do. We, in the UK and the FB Group as a whole, have been dealing with the waste-to-energy sector since its inception and have learned that a few material changes to the right components can significantly increase the life of wet ash removal chain.
Locating the point of wear
The load bearing components on the chain always wear first. That’s the pin and bush, and potentially the rollers if they are used to take the load and come into contact with the sprocket as the chain is driven. Over time, as the chain moves through the water bath, there will also be corrosion build up in between the pin and bush (and roller), which increases the wear rate of these components.
Visual checks will not pick up pin and bush wear and if left, the chain will stretch to the point of failure. Chain failure in any situation can be catastrophic due to the expensive unplanned downtime it causes.
From mild steel to stainless steel
That’s why we recommend specifying a conveyor chain with stainless steel pins and bushes to massively reduce any potential wear between the surfaces of the pin and bush and increasing the life of the wet ash conveyor chain.
In addition to the material change, we have also found that welding the pin and bush adds up to 30% more strength to the system – again increasing the life of the chain.
So there it is. By considering the corrosive nature of the environment during the specification stage and asking for a chain with corrosion-resistant stainless steel pins and bushes that have been welded for extra strength, you can not only keep your wet ash conveyor chain working for longer but also reduce the risk of costly unscheduled down time.