Contents
Not everywhere firewood or coal is an affordable fuel, but waste from the woodworking industry or agriculture can be found, perhaps, everywhere. It has long been noticed that they burn, maybe a little worse, but it is quite possible to heat them. Just pouring sawdust or straw is very inconvenient. Therefore, they came up with the idea of processing and pressing them into briquettes or granules. For fuel pellets – pellets – there are even special boilers. With good fuel, they are serviced (ashed out) once a month. The best news is that it is quite possible to make pellets with your own hands. This will require a lot of equipment, but the basis is a granulator (extruder or pelletizer). Nothing without him.
What are pellets and what types are there?
Pellets are fuel pellets that are made from woodworking industry waste, some crop residues (straw, sunflower husks, buckwheat, etc.) and even chicken manure. The technology of their production is such that no additives and binders are required. That is, it is absolutely safe and XNUMX% natural fuel, which is also made from waste.
Since the raw materials for fuel pellets can be different, the characteristics of the fuel are also different. Pellets are divided into three categories:
- White. This is a premium fuel with the highest performance (and price). Named for its characteristic color – light yellow, almost white. But the color is secondary, the characteristics are primary and the main one is a very low ash content. After the combustion of white ash pellets, no more than 0,5% of the fuel volume remains. It will be very rare to clean the boiler. White fuel pellets are obtained from chips without bark and other foreign inclusions. As a rule, this is a carpentry or furniture production.
- Grey. Raw materials for this type of pellets may contain a certain percentage of bark, needles and some other impurities. But the ash content should not be more than 1,5%.
- Industrial or dark pellets. This type of fuel pellets is made from straw or cake in its pure form or with the addition of wood waste. The ash content of this type of fuel is much higher than those described above, however, it cannot be higher than 5%.
White and gray pellets are used for individual heating. They are also called “first class” or first-cash. They have a diameter of 6-8 mm, a density of approximately 600 kg / m3, the amount of generated heat is about 4,7 kW/h. They are burned in special boilers, which are called pellet boilers. Usually this equipment is very demanding on the quality of fuel. In addition to low ash content, requirements are also imposed on the integrity of the granules, and on the absence of a dusty fraction. Otherwise, the burner of the pellet boiler is clogged, the boiler is turned off. Industrial pellets are also burned in special furnaces, but they have a completely different structure and much larger volumes.
In principle, any pellets can be poured into solid fuel boilers, only they are usually used at the smoldering stage. When the oven is already preheated, a certain amount of pellets is added.
Production technology
For any owner, the idea of turning waste into fuel, or even making money from it, is attractive. In principle, it is realistic to make pellets with your own hands, but you should not expect industrial quality from them. It is unlikely that it will be possible to make an imported pellet boiler work on home-made pellets, but a home-made or solid fuel unit does an excellent job with them.
Wood pellet production technology consists of several successive stages:
- Large crushing of raw materials. Fragments should be no more than 1,25 cm3. This is preparation for better drying. For this operation, a crusher is needed.
- Drying in a drying chamber. The raw material is brought to a moisture content of 8-12%. There are different types of chambers, some use direct heating (hot air from the furnace is supplied to the drying chamber), in others the heat exchanger is heated, and from it the air in the dryer is heated. The second option is less effective, but in this case the possibility of soot getting into the raw material is excluded. Even a small amount of soot can stain wood chips. As a result, the quality of the pellets can be referred to as “white” (if the appropriate raw materials were used), and in terms of color – to gray.
- Fine crushing. Dried wood is fed into crushers (usually hammer type). At the output, wood fragments are larger than 1,5 mm for white and gray pellets, and 4 mm for industrial ones.
- Hydration. Wood fibers with low moisture will not be able to stick together. That’s why they are hydrated. If pine, spruce waste is used, water is injected. Hardwood raw materials – oak, birch, beech – are processed with hot steam.
- Pressing. Presses of various designs work here. The raw material is pressed through a matrix (flat or round), which form cylinders of a given size.
- Cooling. Under the influence of high pressure, the pellets are heated up to 70-90°C. In this state, they crumble easily, so they are left to cool.
- Finished granules are screened (from the remnants of non-sticky particles) and packaged.
As you can see, the process is multi-stage and requires a fairly large amount of equipment. Nevertheless, with the availability of cheap or free raw materials, it is profitable to produce pellets with your own hands.
Features of the production of pellets from straw
Making straw pellets is easier. It initially goes dry, because there is no drying stage. If there is wet straw, it is dried under natural conditions in the sun, and then crushed and mixed with dry, thereby achieving the required moisture content of the feedstock before pressing.
It is also easier to grind. This requires a straw cutter, which immediately cuts the raw material into fragments of the required length. So grinding also takes place in one go. After bringing the mass to the required moisture content, it is pressed through a press. And here everything is simpler: since the raw material is softer, less effort is required. Less powerful equipment means lower costs. In this case, the productivity of the line can be high.
As you can see, straw pellet production requires less equipment and less time and energy.
Homemade granulators
Although a lot of equipment is required for the production of pellets, the main device is a granulator. With its help, pellets are formed from raw materials. There are several models of granulators:
- Screw. The structure is similar to a household meat grinder. The same screw shaft and matrix – a grate through which the raw material is forced. They can be used for soft raw materials such as straw. Wood, even well chopped, he “does not pull” – there is not enough effort. In principle, with sufficient strength of the parts, you can put a more powerful motor.
Schematic diagram of a screw extruder (granulator) - With a flat matrix. There is a metal circle in which holes of the required diameter are made (usually 3-4 mm). There are toothed rollers that push the raw material through the holes, forming granules.
The device of the main node of the granulator with a flat matrix - With a round matrix. The idea is the same, only the matrix is made in the form of a ring, respectively, the rollers are located in a different plane. This option has greater productivity, but do-it-yourself granulators of this type are rarely made.
The device of the granulator with a cylindrical matrix
The simplest screw extruder. It is often made for pressing compound feed, but can also be used to make fuel pellets from soft raw materials. If you need to make equipment for the production of pellets, this is the easiest option. Provided that you know how to handle a lathe and a welding machine.
Homemade screw granulator
As in any equipment of this type, the screw granulator has a matrix. In this case, it looks like a meat grinder mesh, only it is made of a much thicker plate. The second important node is the screw shaft. All these details can be done by hand. How – it is useless to describe in words, see the video.
Making a matrix for the finished screw.
The screw and the matrix are “packed” into a housing or sleeve. How to do it, see the next video.
After assembling the main assembly, it is necessary to install a motor with a gearbox, a hopper into which chopped straw will be fed. You can run.
How to make a flat die granulator
First you need to figure out how it works. Everything is well shown in the video.
In the next video, quite detailed explanations on the manufacturing process of the matrix and rollers.