Among the extensive family of heat generators that burn various types of biomass, a special place is occupied by solid fuel boilers with automatic fuel supply. They are becoming more and more in demand, since, unlike traditional wood-fired units, they fully satisfy one of the main requirements of users - ease of maintenance and operation. In this article, we will review existing boilers with automated loading and figure out what types of solid fuels they can use for their work.
Types of automatic boilers
The main disadvantage of a solid fuel heat generator is the frequent loading of wood or coal. To eliminate it, it is necessary to automate the fuel supply, but this is not so simple, a device for loading logs has not yet been invented. But if the fuel has a free-flowing structure, then it is much easier to solve the issue, which was done in the corresponding heating units. According to the types of free-flowing biomass burned, they are divided into the following types:
- pellet boilers with automatic fuel supply;
- coal automatic heat generators;
- aggregates operating on chips;
- universal boilers.
Let's consider each of the presented types in more detail.
STORAGE OF COAL
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Pellet boilers
Pellets are a versatile biofuel produced in the form of solid cylindrical granules. It is universal because a variety of waste wood and agricultural products are used as raw materials for its production: sawdust, wood chips, sunflower husks, straw and so on. In turn, a pellet boiler is a perfect fully automated unit that requires human attention no more than 1-2 times a week. In addition to this advantage, the heat generator has others:
- the highest operating efficiency among all solid fuel boilers - up to 90%;
- high degree of automation, including ignition;
- complete absence of inertia and the danger of overheating of the coolant. After the supply of fuel and air to the combustion zone stops, the flame goes out almost immediately;
- environmental friendliness and cleanliness in the furnace room.
Of the shortcomings, only two significant ones should be noted: the high cost of equipment and service, as well as the need to store the granules in a dry room so that they do not become damp and do not crumble.
All the advantages that a pellet boiler has come from the successful design of the fuel supply system and burner. The unit itself is nothing special - a steel or cast iron combustion chamber with a two- or three-way heat exchanger, surrounded by a water jacket. Various sensors are built into the boiler body, which function in conjunction with the controller and transmit information about the presence of draft, temperature, pressure, water level in the boiler block, and so on.
Note. The units of some foreign manufacturers are designed to work with various types of flare burners. Natural gas, diesel or pellet burners can be built into one and the same body - at choice.
Much more interesting is how the automatic supply of fuel to the combustion chamber of a pellet boiler is arranged. Here, the main element is a screw conveyor that moves the pellets to the combustion zone.
Inside the auger, fuel is poured under its own weight from the feed hopper, and is dosed depending on the temperature of the coolant. It is monitored by the controller using an appropriate sensor and regulates the pellet consumption by controlling the electric motor of the auger and the fan - air blower, thereby changing the thermal power of the unit. If the loading hopper is close to emptying, then on the signal of the sensor, the controller informs the homeowner about this, and then stops work.
Many automated pellet feeding systems can be remotely controlled via GSM communication or a mobile application for a smartphone. It depends on whether the controller has the corresponding function.
STORAGE OF COAL
1. Coal quality
Charcoal, obtained by charcoal burning, is considered the best and is appreciated by consumers much higher than coal cooked in special charcoal-burning furnaces.
The quality of charcoal can be determined by external inspection and analysis. Coal analysis, which requires special equipment, is rarely used, and the quality of coal is mostly judged by external examination.
Good charcoal should be mostly black, shiny and slightly bluish in the fracture, hard, ringing on impact, not getting your hands dirty and dry. The dryness of coal mainly depends on the way it is stored, and all other properties depend on the results of charcoal burning and the quality of the raw wood.
In addition, coal should not have foreign impurities, such as: earth, stones, pieces of wood and any other trifles, as a result of careless breaking of a fire and cleaning coal.
It is relatively easy to remove impurities and fines from coal. To do this, it is passed through a roar, which is a box with a bottom made of metal mesh, with holes usually no more than 5-6 cm. Such a roar is prepared 1.5 m long, 1 m wide and about 25 cm high. coal, fines and impurities are sown, and as a result, cleaned coal remains at the bottom of the screen and only a large impurity, which can be easily picked out by hand.
It is difficult to get rid of the moisture content of coal, which it easily acquires, since coal dries poorly in air, and drying in special dryers is expensive and undesirable, in view of the decrease in the strength of coal.
The normal moisture content of coal is considered to be 8-15%; it is obtained by the absorption of moisture in the air by coal. From rain, the moisture content of coal can be over 80%, and such coal wetting is not allowed, since consumers do not take such coal.
Given the above ability of coal to easily absorb water, its storage should be directed primarily towards protection from water.
2.
Coal storage location
A place for storing coal is chosen somewhat elevated and in such a way that in the rainy season and during spring floods, the water does not wet the coals from below. When there is no such place near the charcoal burning or coal dispatch point, it must be artificially increased by flooring from poles, slats and even an embankment of compacted earth.
3.
Coal storage
The creation of subsequent storage conditions for coal should be directed towards protecting it from water falling from above. This is achieved in two ways: 1) the construction of special coal heaps and 2) the construction of coal sheds and sheds.
Coal heaps.
In the forest or where coal burning is carried out temporarily, and when the shelf life of coal is assumed to be short, coal storage facilities are made the most simple, not requiring significant expenditures of money. Such a simple coal storage is a coal heap, which is arranged as follows.
Coal is poured onto a previously prepared place in a dense heap, with a height of 2% to 5 m. The walls (sides) of the heap are made as steep as possible, and it must be shaped so that it facilitates the rapid flow of water falling onto the heap. The top of the pile is sprinkled with coal fines, and then the top surface (the head of the pile) is covered with slabs or bark.
In winter, when the coal is being transported along the sled route, the coal heaps can only be covered with pine needles, which quite well protects the coal from snow. In the summer, it is possible to leave them without a tire and be limited to filling the heaps with small coal.
Sometimes, to create the steepest walls of the piles, the place designated for dumping coal is surrounded by a fence, 1% -2 m high and well fixed. In this case, covering the top of the heap, the material is positioned in such a way that the incoming water can drain off the fence. Coal sheds and sheds.
In places of central charcoal burning, where large accumulations of coal occur, which is exported only after significant periods of time, in warehouses where coal arrives from different places
and
stored for a long time, coal storages are built more thoroughly, in the form of sheds or sheds.
Typically, coal sheds are built in such a way that they can be easily converted into a shed and back.
Such a shed is built on pillars dug every 4.5 m into the ground, to a depth of 30 to 150 cm.
If the soil is weak for a larger shed, the pillars break in deeper. The upper link can be ordinary. The roof of the shed is made with a tattered or plank roof, and its walls are taken only with poles that can be easily disassembled. If the shed is being built on a dry elevated house, then the floor is not made. The usual dimensions of the shed: length 18-35 m, width 8, height along the tie 3 m and from the tie to the ridge of the roof 3 m ...
P. TOC o "1-3" hz Foreword 3 Forest and its waste ……………………………………………………………………… .. - Charcoal and its consumers ………………………………………… 4 Conditions for obtaining charcoal ………………………………………… 5 I. Preparation of wood raw materials for charcoal burning…
Automatic boilers for coal and wood chips
The device and principle of operation of these units is not much different from pellet ones.The screw conveyor in the same way supplies coal to the furnace at the command of the control unit, air injection and ignition also work. The difference is in the design of the auger itself, for coal it is made more massive, respectively, the power of the electric motor is increased. In addition, a coal-fired solid fuel boiler with automatic fuel supply requires fuel of a certain quality and moisture content. This is due to the design features of the retort burner used in such heat generators.
Heating units burning wood chips have one additional function in the feeder - wood chipping. After all, the length of the chips can be different and it is impossible to foresee a screw for it. To make the size of the chips the same, a rotary chopping knife is built into the feed pipe between the hopper and the auger. Both the conveyor and the knife are driven by one powerful electric motor. Such products are offered by many European manufacturers, for example, the Austrian automatic solid fuel wood chip boiler FROLING.
A little about universal units. Their convenience is that in case of a shortage of any type of bulk fuel, you can switch to ordinary firewood at any time. For this, the design provides for an additional combustion chamber for laying wood logs. Of course, the efficiency in this case is significantly reduced (from 90 to 80%), since the heater operates in the mode of a simple solid fuel boiler. One more circumstance should be noted: each manufacturer of automatic boilers is trying to expand the range of fuel burned by modernizing the supply system. Therefore, in addition to pellets, some products can use coal dust, eco peas and even seed husks. An example of this is the Polish universal boilers DEFRO DUO UNI.
