Modern people who are concerned about the impact that they are having on the environment are turning more and more often to the clean burning and fuel efficient biomass stoves, which burn fuel like wood pellets at a very high heat, allowing a small stove to heat a room very well. These pellets cost less than other sources of fuel, and burn very cleanly, which is much better than coal can do.
Wood pellets are relatively small, shaped almost like a gel capsule type of pill. They are shiny, which adds to the pill illusion and makes them look almost like small, varnished pieces of wood. In reality, wood pellets are not single pieces of wood, but are rather many pieces that have been compressed together to create the small pellets that you see when you buy wood pellets for your biomass stove at home.
Wood pellets are actually recycled material. They are created out of the sawdust that is left over after the process of sawmilling and after other wood production activities. The sawdust left over after transformative activities with wood is collected and sold to the facilities that produce the wood pellets, which has become a very sizeable industry in Europe as the price of fossil fuels continues to rise.
The sawdust collected in this way is compressed into a super dense pellet, but not until the wood material has been prepared. This is done by sending the wood material through what is known in the industry as a hammer mill. The hammer mill creates a uniform mass that is almost dough-like, and the wood is then fed through to a press.
The press compresses the wood pellets through a die, which is designed with an appropriately sized hole, usually as small as 6 mm in diameter. The extreme pressure of the press compresses the wood and causes the temperature of the wood to rise very much as well. This temperature rise causes the lignin of the wood to form a sort of natural glue which holds the pellets together as the wood cools again.
The regulations on wood pellets specify that they are supposed to have less than a 10% water content to increase the efficiency of the burn, and that they must be uniform in density. For the most part, wood pellets must be dense enough that they do not float when placed in water, but sink to the bottom instead. The pellets must be structurally sound and must not crumble or break easily, and they must have a low dist content and ash content.
Although different kinds of woods look different when they are used for things like planks or furniture, the processing in the hammer mill causes a different effect. The hammer mill breaks down the fibers of the wood so that it looks almost entirely uniform. Although pretty much any kind of wood can be used in the processing of wood pellets, the pellets look very uniform. The breaking down of the fibers early in the process means that the finished pellets do not have much distinction no matter what the type of wood used.
The different kinds of woods used for pellets must be accounted for in the processing because of the different properties of various woods. This is done with good instruments on the pellet press, meaning that the differences in the feed material can easily be compensated for by regulating the press with external controls.
An important fact to know about wood pellets is that the regulations on the pellets mean that in addition to the content restrictions mentioned above, the pellets may also not be created out of recycled wood, which may have been exposed to contaminants. Wood pellets must also remain free of other external contaminants so that they burn clean and do not pose a risk to the environment or to the homes in which they are burned. For this reason, materials like particle board, painted or treated wood, coated panels, and other recycled wood products are particularly unsuited for use in wood pellets.
Because of the low emissions of the wood pellets and the regulations that prevent excessive pollution from being released when the wood pellets are burned for fuel, this fuel source is one of the cleanest available today. Further developments are being made to make burning wood pellets even more efficient and even safer, making them an attractive heating alternative in many places including home heating systems and more.
Wood pellets have become the standard source of fuel for many homes across the world. Countries like Sweden pioneered the usage of this carbon-neutral fuel while now it is a rage in homes in the UK as well as US. There are several criteria and norms of quality that get followed while assessing the relative quality of the pellets.
DIN 51731
This is essentially a European standard of establishing the overall quality of wood pellets. While on the whole this is a holistic method of identifying the condition of the pellets it fails to take into account an essential factor like abrasion. In addition to this it also does not include any assessment of the process of manufacture to be done. Thus in essence the standard is lacking because of the absence of certain parameters.
Norm M 7135
This is traditionally originated from Austria. There are far more criteria included in this method of assessing the wood pellets. Factors like abrasion which are absent in the DIN 51731 are included in the Norm M 7135. The overall stability as well as hardness quotient of the pellets is ascertained before it is given this quality check. Using a Lignotester the wood pellets are stressed in order to ascertain their abrasiveness. The dust that is an outcome of this exercise is then evaluated for abrasion standards. If there is a lesser fraction of dust obtained it indicates a much more solid set of wood pellets which in turn yields a lower abrasion count.
How inspection is carried out
The institute of DINPlus is responsible for certifying and assessing the norms of quality in the wood pellets. The certification process is carried out by the certification members who strictly follow all the standards as laid down by the DIN Certco. There are several controls which get placed to secure high quality of the wood pellets. One additional guarantee seal is provided by the PVD or the Pellet Association Germany and the seal is called the GGuaranty seal. This seal has the same stringent set of criteria as recommended by DINPlus.
What criteria are ascertained?
There are many criteria associated with the wood pellets which are assessed before a seal of approval is provided. Aspects like the diameter of the pellets, the length, density, heating value, humidity, sulphur, chlorine, ash, nitrogen content as well as the levels of abrasion and press aid all are taken into account before assessment begins. It is to be noted that all quality checks are considered only till the point when the wood pellets are loaded. After that these aspects are not taken into account.
ONorm 7136
This is another norm which takes into account the quality of wood pellets during and after transportation. For example the pellets can actually go through plenty of wear and tear during the process of transportation. Therefore this standard emphasizes the quality of the bunker, supplier, as well as transportation vehicle too. Aspects like scales on board, quality of suction mechanisms as well as insulation from humidity levels are all calibrated. Thus this norm aims to establish a superior quality level during the transportation of wood pellets.
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