May 2017 Dry Cargo International
The growing pressure to reduce CO2 emissions has seen an enormous growth in the transshipment of biomass, writes Les Williams of Dunlop. With the Kyoto Protocol and the EU’s continuing objective to reduce its member’s states’ carbon footprints, more and more countries are making the push towards biofuel. In fact, the EU wants to achieve 63% of heat generation by biomass by 2020. Just in the Port of Amsterdam alone, the boom in biomass volumes means that the port could see handling of biomass products rise from its current 1.5mt (million tonnes) per annum to 6mt by 2020. At the same time, there continues to be a parallel decline in the volume of coal transshipment. As Bob Dylan famously sang, “the times they are a – changing.” For a great many reasons, conveyor systems previously used to carry coal or other cargo such as iron ore cannot simply be used to carry biomass. Adapting existing conveyor systems and building new ones entails enormous investment and very expensive lessons are already being learnt. Here we discuss the impact of handling the biomass boom and its ramifications concerning conveyor systems, maintenance, safety and the critical importance of conveyor belt technology.
WHAT IS BIOMASS?
Biomass is used to meet a variety of energy needs, including generating electricity, heating homes, fuelling vehicles and providing process heat for industrial facilities. To the uninitiated, a commonly held belief is that biomass is simply compressed wood waste that is formed into pellets. Not unsurprisingly, it is not nearly as simple as that. Biomass can be made up of combination of several different resources. Apart from wood and wood waste (of which there are several types), biomass can include agricultural crops and their waste by-products, municipal solid waste, animal wastes, waste from food processing and even aquatic plants and algae. Nowadays, ports often receive shipments that contain a mixture of different biomass pellets. This multitude of different organisms plus other characteristics of biomass provide a wide range of challenges and demands in terms of safety, maintenance and efficiency. These challenges certainly apply to the conveyor belts used to carry biomass. Apart from the usual considerations of adequate tensile strength, tear strength, elongation and cross-rigidity, there are four essential characteristics that biomass-carrying belts must have, all of which have a direct or at least important influence on safety.
RISK OF EXPLOSION
One of the biggest issues is dust emission. In the production process of biomass wood pellets, wood chip and similar renewable resources, the materials are continually broken down. This results in high levels of combustible dust. The dry flammable dust found in biomass can be ignited even by abrasion created within a conveyor system because the source only requires ignition energy as low as 17mJ for the ultimate ignition. This is one of the major factors in biomass dust explosion prevention. Biomass dust can also be highly prone to self-ignition, especially if the material has become damp. A chemical reaction can take place that causes self-heating and what is referred to as ‘off-gassing’ (carbon dioxide, carbon monoxide and methane emissions). In the atmosphere immediately surrounding a biomass conveyor, there should be no more than 35 grammes of dust in a cubic metre of air. Put into perspective, that is approximately the volume of a small tube of popular children’s sweets. This means that conveyor design including dust extraction systems and chutes take on a much greater importance. Strict conformity to Directive 94/9/EC (also known as ‘ATEX 95’ or ‘the ATEX Equipment Directive’) applicable to potentially explosive atmospheres of zones 20, 21 and 22 where combustible dust is present should be a pre-requisite. Dust build-up has to be kept to an absolute minimum, which means almost constant cleaning. When carrying out any form of maintenance or repair, the dust must be completely removed within several meters of the working area to prevent the possibility of ignition. From a conveyor belt point of view, it is absolutely essential that the electrostatic dischargeability (antistatic) properties of the conveyor belt cover rubber (according to DIN EN ISO 284 test methods) do not exceed the maximum resistance value of 300 MΩ. Despite the claims of some manufacturers, not all rubber belts are sufficiently anti-static. The key ingredient in conveyor belt rubber is carbon black, which acts as an electrical conductor. It is widely accepted that premium grade belts will contain an optimum level of high quality carbon black whereas belting designed to compete in the lower price range end of the market will almost invariably contain less carbon black, often with ‘fillers’ used as a substitute to keep prices to a minimum. It is strongly recommended that the belt supplier be asked to provide certification issued by an independent expert body for explosion protection such as DEKRA in Germany, which is the organization that is used by Dunlop Conveyor Belting…
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Dry Cargo International (May 2017)