Producing pellets – how the growing demand is causing strain on equipment
23 May 2017
The global market for pellets is thriving, thanks to a growing demand for pellets used as biofuel for heating in residential use and furnaces and boilers in industrial applications. However, equipment and machinery used for the high load and high-pressure production of pellets faces a reduced lifespan due to the inadequacy of existing industrial grease products.
Global wood pellet production was estimated to be 28 million tonnes in 2015, the majority of which was split between heating and industrial use. This is according to market research firm Hawkins Wright, whose report also shows that the EU accounts for 77 per cent of the global demand for pellets. The same report also shows that in the industrial wood pellet sector, the UK accounts for 46 per cent of demand, closely followed by Sweden, Denmark and Belgium.
This is not surprising, considering the push towards renewable biofuels and biomass, which offers a carbon efficient method of energy production. Popular biofuels include short-rotation crops grown specifically for fuel such as coppice, willow and poplar among others, as well as agricultural by-products such as straw, feedstock in the form of grain husks, waste wood and animal waste such as slurry and chicken litter.
The materials used to create pellets also means that it can be produced and distributed locally, from local wood and biomass materials, to produce an affordable fuel.
With their low moisture content, pellets produce virtually no smoke while burning and are considered by several governments as an environmentally friendlier alternative to coal. The drive towards sustainable energy sources such as these is a welcome move, but what is less encouraging for plant engineers, facilities managers and business leaders is the toll that pellet production takes on equipment and machinery.
Although pellets are simpler and more convenient than chopped wood, their production involves compressing crushed, chopped and liquid organic material at high pressures and temperatures and under very high loads.
What many plant managers do not realise is that the rate at which material is fed into the pellet-making machine can affect the overall quality. By maintaining a steady and consistent feed-rate into the machines, managers can reduce their plant’s energy consumption. In addition to this, pellet-production equipment can quickly begin to wear out and even break down if not maintained properly.
Poor lubrication causes breakdowns
The biggest cause of breakdowns in applications is poor lubrication. Often this is where the grease is unable to withstand the high pressure and temperatures. This is exacerbated by contamination from wood dust and dirt that mixes with grease to become a powerful abrasive, causing wear, corrosion and part failure.
In some environments, the need to replace grease is unavoidable and so it is vital that maintenance engineers take the necessary precautions to ensure it is done properly. When working with materials that result in many abrasive granules such as wood-dust, poor maintenance can result in costly breakages.
The biggest mistake made when changing grease, is not cleaning the systems before refilling them with fresh grease. This commonly forgotten stage immediately results in heavy contaminants, such as acidic deposits, breaking down the grease thickener and resulting in oil separation and oil loss.
The lubricating properties of grease are in the oil and so as these deposits form on the system’s metal surfaces, what remains has little or no value as a lubricant and will further damage the machinery.
As the global market for pellets and alternative energy becomes a feasible fuel source, the demands placed on industrial equipment will only increase. When calculating operating and maintenance costs, engineers and facilities managers should pay close attention to the properties of their chosen grease.
Selecting the proper lubricant will not only have a positive impact on the production and quality of the wood pellets, but also the life and reliability of the plant’s equipment, reducing the chances of unexpected downtime.
Calm under pressure
Having serviced the EU and the Nordic pellet industry in particular, for over a decade, NCH Europe has developed K Nate HV, a new grease designed for heavy loading applications such as pellet production, construction, mining and the steel industries. The high viscosity base-oil ensures that a strong film of lubricant protects materials against abrasive wear, allowing the grease to remain in place under extreme operational pressure and elevated temperatures.
The use of a calcium-sulphonate thickener provides excellent anti-corrosion resistance to the product for comprehensive protection in harsh environments. K Nate HV uses a potent blend of extreme pressure agents that react to heat at heavy loads, providing effective use up to 220 degrees.
This is important because once grease is heated beyond its dropping point, it is unlikely to retain its original structure and so will no longer work to provide satisfactory lubrication. Spot temperatures reaching 1000 degrees can lead to components being flash-welded together causing equipment to fail.
To tackle contamination, K Nate HV incorporates special polymers that coat the contaminating particle. This stops it from wearing down and abrading surfaces, ultimately elongating the life of the equipment and subsequent return on investment.
This high-performing grease has also been designed to resist oxidation to provide further protection to machine parts. Water and steam in outdoor and indoor environments wash away grease, leaving surfaces unprotected and prone to corrosion. Using a water-resistant grease limits water-washout and contains corrosive inhibitors to prevent rust.
All of this means that where normal greases last around 300-500 hours between changes, we have tested K Nate HV to last many times more than this. A high interval time between changes also reduces downtime and means engineers spend less time removing and replacing grease.
Mark Burnett is vice president of the Lubricants & Fuel Additives Innovation Platform at NCH Europe