Questions and Answers - Strobile Energy

Questions and Answers

1. What are the advantages of wood pellets in comparison to other fuels?
The main conventional methods of premises heating include the usage of natural gas, coal, firewood and mazut. The use of wood pellets is relatively a cheaper way to heat premises in comparison to the natural gas. The amount of savings depends on the country and region, the presence of gas counter, the volumes of consumption, the quality and calorific value of both kinds of fuels, and room area. In contrast to the high quality wood pellets, the use of coal has such disadvantage as presence of high amount of waste – ashes, which is prone to spontaneous combustion. Moreover, the burning of coal releases poisonous saturated and unsaturated hydrocarbons, as well as a large amount of carbon monoxide CO, which pollutes the atmosphere and harm human health. Mazut pollutes the environment in the same way – by releasing a lot of sulfur. The use of mazut as a source of energy has huge disadvantages, connected with the initial preparation for the usage – while transferring the mazut it is obligatory to comply with temperature conditions, violation of which threatens to ignition. The use of firewood is a relatively cheaper way of heating, but it has several disadvantages. First, the firewood has high humidity – 30-50% in comparison with 5-9% in wood pellets, which are easier to ignite. Secondly, high-quality wood pellets are debarked and, thus, the product has low ash content in comparison with the firewood, where the value of ashes and sand components are rarely controlled. Finally, compared to firewood or wood briquettes, pellets allow to accurately control the temperature of the room – raising or lowering the supply of pellets, providing an opportunity to save fuel. Pellet boiler thermostat can reduce supply of pellets if the room is already warmed to the desired temperature.

2. How many pellets are required for heating the building of 200 m2?
     

About 1.0-1.5 tons of pellets per month. This meaning, however, is very rough.
The quantity of pellets required to heat a building depends on the following factors:
1) Heat loss coefficient for the room. In modern buildings it can be around 70 W / m2 per hour;
2) Outdoors atmosphere temperature and the duration of the heating season. The higher temperature outside is, the fewer pellets it is necessary to use and vice versa. For example, let’s imagine that we use pellets during cold winter months – that is, 30 days;
3) Duration of heating during the day. In autumn we can heat the room only during the cold nights, while in winter – we do not turn off the heating for about 16 hours. For calculations we use time ratio during which we heat the room to the time of the day: 16/24 = 0.67.
4) Boiler efficiency coefficient. Some new models of boilers declare ratio at 100%, but it is more realistic to count 85-90%. For convenience we consider it to be 90%.
5) Calorific value of pellets – pellets producers often manipulate with this coefficient. Unfortunately, this coefficient can be determined only by using the proper fuel yourself. Usually it varies from 5,0 to 5,4 kWh / kg.

 During winter month it is possible to have the following losses while heating the building of 200 m2:

In this case the quantity of pellets necessary to heat 200 m2 building is:

        or      

3. How important is the quality of pellets?
        Depending on what parameters of the standard are deteriorated, the use of poor quality pellets may educe the efficiency of the boiler, leads to the boilers clogging because of the high ash content or even breakage due to the formation of “plates” on the grate. There are about 20 pellet quality parameters, the main ones among them are: ash content, moisture, calorific value and sand component. Moisture or water content parameter should not exceed 10%. If the manufacturer does not dry raw materials in a proper way, pellets lose heat and calorific ability. As a result it is necessary to spend more time and energy just to ignite boiler. Pellets calorific value and ash content depend fluently on the raw materials used for producing them. If the manufacturer uses bark or imperfectly debarked wood, pellets ash content exceeds the standard rate of 0.5-0.7% and will significantly waste the boiler. The most dangerous, however,it is not the quantity of ash, but its quality. Ash should be velvety, soft and in small amount- in this case the boiler will work for a long time, and it will require relatively less ash cleaning. If the raw materials used for producing pellets contains sand, stones or other objects – burning pellets will lead to the formation of “stone plates”, which can fully clog the grate and spoil boiler. In this case the repair of boiler can be very expensive, and usually guarantee does not cover the costs, appeared from the use of poor quality pellets.

4. Are there any standards of pellets quality?
           Pellets manufacturing is often associated with the choice between quantity and quality. It is very important that in order to increase the volume of production and sales the manufacturer do not neglect the control of incoming raw materials, technological process and physical, chemical and mechanical features of the final product. The first standards for pellets were founded in Germany (DIN 51731) and Austria (ONORM 7135) and did not have unique standards for performance. For example, DIN standards did not include abrasion and ONORM 7135 had different quality parameters limits. With time, the national standards for pellets were introduced in countries where this type of fuel became popular -for example, in Sweden SS 187120, in the UK – BSI, in Holland – NTA. In 2010, the European Biomass Association ENplus implemented a system based on the standard EN 14961-2 with the intention to replace all national standards of European countries and to introduce a single unified standard. Producers should receive the proof of conformity to this standard only by passing the procedure of external audit made by laboratories officially accredited in the European Pellets Union. For now, this standard (EN 14961-2), in our opinion, is the most respectable.

 5. How to choose the quality pellets?

           Nowadays there are numerous ways of manipulation with pellets quality parameters. In our practice, we have met, for instance, the following: the mismatch between the mentioned in technical card product characteristics and the real quality of product, obvious deception concerning the origin of raw materials and country of origin, or unauthorized use of the European quality certificates. The quality of pellets can not be determined only by simple visual inspection. Often people mistakenly believe that color shows quality of product – the lighter pellets, the higher quality. Thus, manufacturers often use additives in the raw materials to “lighten” the pelelt. The origin and composition of additives is often not clear, but it certainly leads to poor calorific value of the final product. Previous receipt of samples is also a field for manipulations – supplier provides high quality products as a model that does not guarantee the conformity of the sample set to the future product delivered by this manufacturer.
         Nevertheless, some recommendations on the selection process of pellets exist. First, you must understand that any description on the package does not guarantee quality. Quality must be checked by personal use or by the advice of those who have already tried the product. The best way is to burn 15-30 kg of the product in own heating system and verify the quality. Such amount of product should not spoil the boiler while burning low quality fuel, but will give the opportunity to evaluate the product. Secondly, product visual observance has to be conscious – pellets color depends on the type of wood (whiter color for silver fir, pink color for pine, golden for beech and deep dark for oak and chestnut). Of course, black (dark)pellets often indicate the presence of bark. Thirdly, wooden pellets should smell like wood. The use of chemically treated wood or additives kills the smell of wood. Finally, the fourth, is to cooperate with suppliers and manufacturers who value their reputation and have their own brand, which stands for product quality.