All about pellets: production rules, standards and methods of quality control

From this article you will learn all about pellets: production rules, standards and methods of quality control. To ensure the stable operation of pellet heating boilers, which are often installed in autonomous boiler rooms, "correct" pellets are needed. This English word means small fuel pellets, which are made by pressing from wood flour. The raw material for this fuel is very simple. In its quality can be oshkurennaya and not oshkurennaya wood, waste from sawmills, large or small woodworking enterprises and furniture manufactures.

Manufacturers of such alternative solid fuels have mastered even the production of agropellets from ordinary straw, sunflower husk, corn, buckwheat husk, etc. When transporting pellets and storing them, it is necessary to comply with a number of requirements that are much milder than the rules that apply to liquid and gaseous fuels. Therefore, the popularity of solid-fuel pellet heating boilers is growing significantly among owners of individual suburban housing. When buying such granulated fuel, all consumers are interested in its properties and quality, as this directly affects the performance of all boiler equipment and the percentage of efficiency. The main influence on the quality of pellets is provided by raw materials, the organization of the production cycle, the conditions for storing the final product and delivering it to the consumer.

The essence of pellet production

These small fuel pellets are formed under high pressure equal to 300 atm and under the influence of high temperature. In the process, an interesting substance is extracted from the ground mass, which is called lignin. It ensures the qualitative gluing of individual fragments of the material into granules. The length of one pellet can vary within 10-30 mm. By the diameter of pellets are from 6 to 10 mm. It is not for nothing that they are referred to environmentally friendly solid fuels, since only natural natural materials are used in the process of their production. During the combustion of granular solid fuel, in pellet boilers the maximum amount of carbon dioxide that enters the atmosphere is negligible. The decomposition of wood in natural natural conditions is accompanied by the release of the same volume of carbon dioxide. Pellets - environmentally friendly and very economical fuel for solid fuel fireplaces, stoves, boilers

. What kinds of pellets

exist? According to the existing classification in the world, fuel pellets are divided intothree main groups:

• White pellets - they are also called premium fuel, which is suitable for use in high-tech heating boilers.
• Dark or otherwise industrial pellets, which are somewhat inferior to the first quality group. They use not only the wood itself, but also the bark. Such fuel is suitable for combustion in conventional pellet boilers, but more frequent ash removal is required.
• Agro pellets are considered the cheapest fuel with standard quality. They are burned in large boilers, which are produced precisely for this crude type of solid fuel.

The heat of combustion of white and dark pellets is not different: 17.2 MJ / kg, while in agrophelet it is somewhat lower - 15 MJ / kg. Ash content of premium products is 0.5%, dark - about 0.7% and sometimes even higher, agropellets leave the most ash after combustion - 3% or more.

Excellent flowability of dry fuel pellets is best ensured by their cylindrical shape and special physical and geometric characteristics, among which abrasion, density and bulk density. Due to these qualities, such fuel can be automatically fed through special screw devices that are used in boiler rooms. Automation of the fuel supply to the boiler allows it to maintain its long-term operation without any active human involvement. This is the key to the success of pellets in most European countries.

The main stages of the technological process of production

Pellet production can easily be represented in several separate steps:

• grinding of prepared raw materials;
• drying of shredded finished components;
• re-grinding of already thoroughly dried particles;
• water treatment of raw materials for the purpose of moistening the resulting wood meal;
• pressing of crushed and already moistened raw materials into finished granules;
• cooling pellets and blowing them clean of dust;
• packing of fuel pellets and their packaging.

In order to understand this process well, it is necessary to consider each of the listed stages in more detail.

Wood shredding stage

With the help of special chippers, which are called crushers, grinding of harvested wood raw material to such fractions is provided, the length and width of which is not more than 25 mm, and the thickness is only 2 mm. This crushed material is then dried. Moreover, the smaller the size obtained after the fractions of the fractions, the less electricity they need to dry them.

pellet crusher looks like

additional drying and re-grinding stage. The humidity level of wood raw material that is sent under the press should not exceed 10% with a deviation of 2% in one direction or another. If the raw materials obtained are too wet, additional energy-consuming drying will be required. If parts of the wood used are too dry, they will need to be slightly moistened to achieve a 10% moisture level.

Drying equipment produces drum and tape type. In this case, the last option is more preferable, albeit expensive. The use of belt-type pellet dryers is much safer. Dryers can work on gas or on the same wood waste. There is also a separation of equipment by the type of drying unit used. In its quality are usually: hot air, water vapor or flue gases. Stable work pellet press is possible only when the size of the input fraction of the raw material will not exceed the allowable 4 mm. Well-dried raw materials are repeatedly subjected to grinding in special hammer mills, in particle shavings, or disintegrators.

Water treatment of raw materials

If the moisture content of raw materials does not reach 8%, then it is very difficult to compress. To obtain the required degree of humidity, it is necessary to pass the dried raw material through the additional humidification device. An excellent option is a faucet with auger, in which hot steam or even water is supplied. Steam is usually used in the processing of wood raw materials, which is obtained from hardwoods. Under the influence of hot steam, the strength of the wood itself is greatly reduced and its plasticity considerably increases. The presses of some manufacturers are designed so that they do not need a preliminary exposure to the raw material. Some not very conscientious producers use steam to process too old and already caked raw materials. At the same time, it will not be possible to get high-quality pellets from "reanimated" raw materials in this way.

Pressing process

The process of pellet formation is carried out by means of special presses, which have structural differences, mainly in the form of the matrix. There are presses for pellets:

• With a round type matrix, which were previously created for use in the food and chemical industries. They also used to produce mixed fodders.
• With a flat type matrix, created for the disposal of solid waste.

Despite significant design differences, these and other presses work on the same principle. In them, the running rollers crush the raw material entering the matrix, ensuring that it inevitably extrudes through the holes provided for this purpose on its surface. The granules that appear from under the matrix are cut with special sharp knives. During the whole process of pressing such equipment it is possible to compact the original raw material three times.

Frictional forces, which under the conditions of the adiabatic thermodynamic process caused by very sharp compression of the raw materials, contribute to a significant rise in temperature in the working compartment of the press up to 100 degrees. Therefore, for processing a ton of raw materials, only 30-50 kW of electric power is consumed per hour. When granulating wood waste, the equipment experiences colossal permanent loads, so it is made of particularly strong materials. Some parts like the matrix are produced from specially hardened wear-resistant alloys.

Cooling of finished pellets and cleaning them from contamination

The pressure and temperature in the work area have a strong influence on the quality of the finished fuel. For this reason, the raw material should not be heated above 120 degrees, as it contributes to the beginning of irreversible processes in its structure, which will drastically reduce all consumer characteristics of the fuel. Therefore, already compressed granules need to be cooled. For this, air conditioning equipment is used, which for one thing and blows dust from the pellets.

Fuel pellet packing and packing

Granulated fuel can be packed and packed in various ways. This allows us to satisfy the needs of all consumers to a large extent. Pellets can be shipped loose in a completely free form or in very voluminous bags, sometimes called "big bags"( can hold 500 to 1200 kg).

In bulk, fuel pellets sent to large CHP plants are shipped. Although it is possible to ship pellets in bulk with high quality. They are purchased for use in boilers of small enterprises or for further sale after packaging in small bags."Big-bags" are polymeric bags, which are equipped with strong slings for mechanization of loading and unloading operations. Pellets, which are stored and transported in bags, absolutely do not lose their flowability and maintain the necessary humidity level. The purchase of pre-packaged fuel pellets naturally costs more than an ordinary consumer.

granules. They transport big bags on special automobile platforms, on which they are loaded with forklift trucks. But bags of 10 - 20 kg, too, are a success, but already with private owners of solid fuel boiler equipment. Owners of pellet boilers, as well as fireplaces that do not have a place for large reserves, acquire them in small packages. Thus, we sell pellets of selected quality.

By what standards do you determine the quality of the finished pellets?

All domestic producers of pellets today use the quality standards that are adopted in most European countries. Foreign producers of solid fuels for pellet boilers should receive certificates of conformity for manufactured products according to the quality standards in force in the European Union. If such a document is not available, this circumstance discourages buyers. The quality standards EN plus and EN-B fix the requirements for both household and industrial pellets according to several criteria. This includes: diameter, length, bulk mass, heat of combustion, humidity, abrasion or dust percentage, hardness, ash content, melting point of ash, content of metals and other chemical elements.

How to choose the right pellet?

When buying pellets, an ordinary citizen should pay attention to the presence of a quality certificate. In addition to this important document, it is necessary to find out the place where the fuel pellets were made. Large producers enter into contracts with regular suppliers of raw materials, under which all production equipment of companies is adjusted. Therefore, pellets will be of better quality. Visual inspection of fuel pellets also helps to determine the suitability of the products for operation in specific pellet boilers. With this control, you need to pay attention to the color of the granules themselves, the shape safety, the amount of dust left, the integrity of the pellets, the absence of odors, etc. You can order highly efficient laboratory fuel pellets for their full compliance with European quality standards. Naturally, the service provided is affordable only to businesses that have installed solid fuel boilers.