Coal boilers: principle of operation
Coal furnace or boiler is designed to produce heat by burning solid fuel. This heat is used to heat the coolant (water or other liquid antifreeze), which then enters the heating pipes. Coal heating has the highest heat capacity of other solid energy carriers (wood, pellets). It is used for seasonal heating of private homes, as well as for the operation of boilers that heat several rooms. Modern boiler house for heating a residential area more often uses natural gas. Coal heating is popular in small boilers that heat several houses, garages, workshops or other premises.
Note: Burning coal produces carbon monoxide, which varies in temperature around 1300ºC. The efficiency of a classic coal boiler is only 70%. Significant part of the thermal energy is lost due to incomplete combustion of gases. Improved models of boilers for coal heating have efficiency operation above 80 and 90%. They burn the fuel more effectively with less smoke and soot. Such boilers are called pyrolytic boilers.
Pyrolysis boilers
The pyrolysis unit has two combustion chambers. In the first one the coal burns and carbon monoxide is formed, while in the second one the gases themselves burn (they are “afterburning”, i.e. the unburned particles contained in them are oxidized and release heat). No smoke is produced at the outlet of the unit. Thus, the efficiency of coal heating increases, the combustion is more complete and its consumption decreases (and therefore the heating costs). The pyrolytic boilers have the energy consumption efficiency of 90-92%. However, they are demanding fuel humidity (up to 30%).
Long-burning boilers
In addition to pyrolysis devices, for coal heating boilers of long combustion are used. Their efficiency is less than pyrolysis (80-85%), but better than the classic coal boilers. In the boilers of long combustion air is precisely supplied to the flame zone by a special blower. The amount of air, its temperature and rate of flow affect the intensity of fuel combustion and the temperature of the coolant.
Solid fuel boilers of long combustion
Devices of long combustion are demanding to the quality of fuel (coal must be dry). Otherwise soot accumulates on the pipes, which reduces the efficiency and leads to failure of automatics.
Conventional boilers for heating the house with coal have a minimum of automatic controllers. Their work requires a separate room coal boiler room. Pyrolysis units and appliances for long combustion are equipped with automation. It provides control of operation and no carbon monoxide, allowing them to be installed inside households. What kind of automation ensures trouble-free operation of heating units?
About solid fuel long combustion boilers
Automatic coal boilers
In some cases, the use of coal is the most economical. But modern users are accustomed to the convenience, so they are not satisfied with the need for an independent supply of fuel. These and other difficulties will be eliminated if you properly use the advanced features of modern heating systems. Let’s take a closer look at what benefits are able to provide automatic coal boilers, or more precisely, modifications designed for domestic use.
How to increase the duration of autonomous operation of boilers
To reduce the frequency of fuel supply, you can simply load a larger volume of coal into the furnace. But household appliances can not be too large. It is also desirable that combustion occurs gradually. These tasks are solved by means of long combustion systems.
The design of the boiler of this type differs from the classic version. In it, solid fuel is loaded from the top of the furnace in a sufficiently large volume. It is pressed by a special device. As the coal, which is lit at the top, burns, it goes down. A telescopic tube installed in the central part is used to convey the air into the combustion chamber.
As reviews indicate, solid fuel boilers of this type are quite practical. The process of long-term combustion under the oppression pressure is more productive than an open flame. It allows a more rational use of thermal energy. But even in this case, a new supply must be made at least once a day.
Systems of automatic solid fuel supply
Inside a Coal Fired Boiler
Modern automatic coal boiler is designed for a longer period of autonomous operation. Let’s list the main elements of such a system and their functions:
- the screw drive is a device designed to eliminate the manual feed. It is driven by a fairly powerful electric motor and moves, when turned on, the coal from the fuel storage tank into the combustion chamber;
- burner (retort). In its lower part there is an opening to which a screw-type conveyor is connected;
- hopper for coal. As a rule, manufacturers offer to equip boilers with their own devices. But if desired, any homeowner can create his own capacity, corresponding to his needs.
The control and management systems, which are also elements, perform several functions:
- ensure timely supply of solid fuel into the furnace;
- Increase/decrease the rate of fresh air supply to adjust the intensity of combustion;
- turn off the fuel and air supply when the temperature rises above a critical level. In some installations, the combustion area is flooded with water.
The above mentioned elements are used in different brands of boilers.
Here are other variants of the fuel feeding device, except for the auger mechanism considered above:
- conveyor. This device is installed in the lower part of the bunker at an angle to the horizontal. It is a wide, flexible belt with fixed, rigid ribs. This solution allows to handle coal in different fractions, up to the size of individual pieces of up to 1416 cm. It is poured through a special manhole, mounted in the upper lid of the boiler. According to consumer reviews, this technique is unpretentious, high reliability. Solid fuel boilers of this type are produced by several domestic manufacturers using inexpensive component parts. Repair will also not be too expensive. The disadvantage of this design is the placement of the coolant only in the side walls, which somewhat reduces the efficiency of the technique;
- it is possible to free the upper part of the furnace to place there an effective heat exchange system not only by means of auger drive. The same result is obtained with the use of a special grate. It is created in the form of a drum with blades. As it rotates, it adds the right amount of coal to the furnace.
Features of modern household boiler equipment
All listed solid fuel combustion devices are designed for autonomous operation from a few days to a couple of weeks. Of course, in such long intervals the absence of the owner of the house cannot be ruled out. To ensure safe operation of the equipment during the heating period, and do not provoke stressful situations for the owners, you can provide appropriate additional equipment.
It is made with the help of specialized electronic and software blocks. They are capable of transmitting information using cell phone communication channels or the Internet. The owner can not only get important information promptly. If necessary, it will not be difficult to give him a remote command to change the mode of operation of the boiler. This raises the temperature to the right level before the owners return home and lowers it during their absence to save fuel.
The following convenient addition can be used, if it is supposed to alternate different types of raw materials for heating:
- Pellets, according to the statements of experts and ordinary users, are well suited for solid fuel boilers for long combustion. Their standard size and small weight of individual elements allow the use of not too powerful electric motors in fuel supply systems;
- if it is possible to use wood chips, you will need to install special devices, chopping the raw material, stirring it in the storage hopper. This will increase the load on the actuators, so more powerful units will be needed.
Universal long combustion boilers will work fully not only on coal. Slightly overestimated initial investment in this case will pay off later, as the user can choose the most economical fuel option without additional costs for changes in the design of heating equipment.
In some cases, the use of coal is the most economical. But modern users are accustomed to convenience, so they are not satisfied with the need to supply fuel independently. These and other difficulties will be eliminated if properly used.
Automatic long combustion coal boiler
Autonomous heating is very popular among owners of private houses.
There are different types of heating equipment, one of the most popular is a solid fuel heating boiler.
About types of solid fuel boilers, automation of their work and selection criteria will be discussed in the article.
Types of solid fuel boilers
Solid fuel units are used at industrial sites or in private homes, where there is no main source of hot water and heat. They are quite effective and easy to use, and can also serve as an additional source of heat.
- Traditional solid fuel boilers.
- Solid fuel boilers.
- Top combustion boilers.
- Solid fuel boilers with electric heaters.
Solid fuel units are used at industrial objects or in private houses, where there is no main source of hot water and heat. They are quite efficient and easy to use, and can act as an additional heat source.
Traditional solid fuel boilers have a very simple principle of operation: the fuel (coal, wood and other types) is placed on the grate in the furnace of the unit, followed by ignition. The generated heat is taken by the heat exchanger, which is connected to the heating system. As the heat transfer medium can be used normal distilled water (condensate).
SZL seies coal fired chain grate boiler. 3D animation version
For more information about heating systems for baths, click here.
On the choice of material for underfloor heating and technology of its installation, read the article
Advantages of traditional solid fuel boilers:
Disadvantages of traditional solid fuel boilers:
- Lack of automation and protection. The temperature of the coolant is regulated manually by the air damper.
- Requires constant monitoring of unit operation and fuel loading.
- Low efficiency.
Solid fuel boilers for long combustion. is a traditional solid fuel units, only in their principle of combustion of fuel has some differences:
- Fuel is placed in layers, and combustion begins with the top layer.
- As the fuel burns, the combustion zone moves from top to bottom.
- Air is blown directly into the hearth, without affecting the lower layers of fuel.
Top combustion boilers have an oblong shape and a high furnace. This shape allows stacking of fuel in many layers. The principle of work of the top combustion boilers can be compared with the combustion of a match. If you point a lit match downwards, it will burn in 10 seconds, and holding it with the flame upwards, the time of complete combustion increases by 4 times.
There are units with additional electric heater. It is used when cleaning or loading the boiler. This is a kind of emergency heating.
For example, a solid fuel household boiler Warmos-TT (Evan), burns wood and coal, is equipped with automatic temperature control and an additional electric heater for 2 kW. Similar models: EKO-EL (Wirbel), Smoke and Mix (Zota).
Modern Solid Fuel Boilers
Traditional solid fuel boilers are from the last century, and using old models has become inefficient.
With the development of innovative technologies modern solid fuel boilers create a serious competition to the newest automated gas boilers. What has changed in the traditional units? Increased efficiency of solid fuel boilers.
Traditional solid fuel units are not characterized by the efficiency of fuel combustion, to correct this new technologies have been developed:
- Pyrolysis boiler is a unit that burns pyrolysis gas obtained from the thermal treatment of solid fuel. Such units have high efficiency rates (up to 92%).
- A pellet boiler is a unit that burns special pellets (pellets). The efficiency of such units reaches 95%.
- Modern solid fuel boilers for long combustion are equipped with additional fans and the system of primary air preheating.There is also a mixing of secondary air (re-incineration of volatile gases of already burned fuel). This ensures more complete combustion of fuel, and reduces heat loss. Smoke dampers are installed to regulate the secondary air supply. Due to this, the efficiency of solid fuel boilers increases significantly and varies from 70-90%.
Automation of automatic coal-fired long combustion boiler
Traditional solid fuel units are inconvenient because they require constant monitoring, frequent fuel loading, and manual adjustment of the fluid temperature.
Now all these processes are fully or partially automated.
Fuel loading
In order to increase the combustion time, fuel was burnt in layers from top to bottom, instead of the opposite way round. Coal can be loaded once every seven days. With the development of technology the size of the furnace was increased.
For the pelletized type of fuel an automatic system of its loading has been developed, but in this case it is necessary to equip a special hopper and install in it an automatic conveyor.
Automatic temperature control
Automatic temperature control is carried out by means of a special air damper. Opening the damper increases the intensity of combustion, while closing it decreases it.
Temperature sensors are installed on the mowing line of the coolant supply and with the help of the thermostat the temperature is automatically regulated. To reduce the range of deviation from the set temperature, a room temperature sensor is installed.
Pyrolysis (gas generator) boilers can be automated in the same way as gas-fired units. This is due to the fact that the intensity of pyrolysis gas emission can be regulated.
Protection of solid fuel boilers
An automatic protection system will ensure safe and trouble-free operation of the solid fuel unit:
- The heating system should be installed in such a way that natural circulation of the coolant is possible.
- Modern solid fuel boilers are energy dependent. For their uninterrupted operation it is necessary to install a backup power supply (batteries).
- If the coolant does not circulate properly, it will overheat to critical temperatures. This process will be accompanied by an increase in pressure in the heating system. To avoid such situations there is a cooling circuit.
Choice of coal
Coal, lignite, coking coal and anthracites are the main types of solid fuel. However, the quality of coal can be determined by its characteristics:
- Calorific value is the amount of heat released during combustion of fuel. The unit of measurement is kilocalories (Kcal). Lignite. 4500 kcal/kg, coking coal. 8700 kcal/kg, anthracites. 8600 kcal/kg.
Coking coal is not designed for use in conventional boilers, because the combustion produces high temperature.
- The ash content of fuel is the non-combustible. It is expressed in percents: high quality coal. 25% of ash content, low quality. 40% and more.
- Fuel moisture is the moisture in the coal. A distinction is made between surface and internal moisture. The greater the internal moisture content, the less heat is released during combustion. The internal humidity is determined by special instruments, while the external humidity can be determined “by eye”.
- Fuel labeling: A. anthracite, D. long-flame (easy to ignite), SS. weakly melted coal and T. lean coal are representatives of not the most efficient types of coal.
- Coal fraction (see “Fraction of charcoal”). table).
Alternate Heating Systems Coal Gun 130:Filling The Bunker and The Hopper
The passport of each unit specifies the requirements for fuel. Failure to meet these requirements could result in machine breakdown.
Selection criteria for a solid fuel boiler
The main criteria for selecting a long-burning coal boiler for the house:
- Energy dependence.
- Fuel availability.
- EFFICIENCY.
- Dimensions and weight.
- Presence and functions of automation system.
- Sufficient power.
- Auxiliary electric heater.
- Price.
If there is no access to the central gas supply, the coal boiler with automatic fuel supply can be a worthy alternative and completely replace the gas analogue.
Construction of the simplest solid fuel boiler with their own hands
These are all the basic elements that actually make up an ordinary stove. Its construction will not cause you much trouble: just take a suitable metal box or barrel with thick walls, cut a door in it for fuel supply and equip this device with a chimney. and an elementary stove-burzhuyka ready. During the construction of the stove must pay attention to quality insulation of its surfaces from flammable materials, since the iron of such boilers can heat up almost to redness.
complicated is the construction of a brick oven. Before building it, it is imperative to create a furnace design. In addition, the large weight of the brick oven requires a solid foundation. Therefore, such stoves should be designed and built at the stage of construction of the house. Creating a brick Russian stove. it is almost an art, and here you can hardly install with your own hands. Consequently. the installation of such a stove, or at least the development of its project is best left to a specialist. Otherwise, the stove, not built according to the proper design, may not have sufficient draft or smoke, poisoning the surrounding space.
Adding a water heating system
Solid fuel boilers, combined with water heating systems, are more complicated. In this case, in addition to the increased requirements for the materials of manufacture, a competent engineering calculation is also necessary.
The schematic diagram of a solid fuel boiler with water heating system is shown on the picture.
In order to build such a boiler, it is necessary to observe several basic fundamental points.
First of all, such a solid fuel boiler must have a rigid and durable structure. There is no way to manage with a simple metal barrel, like in the elementary campfire stove. To create a combustion chamber in such a boiler must be made of a solid metal sheet with a wall thickness of not less than a centimeter. Connect the cut blanks for the boiler must be welded.
In order to create a home boiler, the area of the bottom should be about one and a half square meters.
Increased demands are placed on the heat exchanger unit. It is made of steel pipes with a wall thickness of 3-4 millimeters. Note that in a good heat exchanger tube diameter decreases as the coolant heats up, so you will not just insert sections of pipe in the boiler, and purchase specially made parts.
An important issue is the organization of the coolant circulation. It can be natural or forced. In the second case you can place a solid fuel heating boiler in any part of your house, for example in the basement, and the water will be heated by circulating pumps delivered to radiators located throughout the house. Also such heating systems can have several circuits, so that each circuit can be equipped with its own individual pump.
In order to control the operation of such a heating system it is necessary to integrate control devices. You will need two temperature sensors: one will be installed at the inlet to the heat exchange zone, and the second is installed at the outlet. Pumps that ensure circulation of the heating medium can also have a stepped capacity control.
Heat transfer fluid circulation systems in systems with solid fuel boilers can be open and closed. In the second case, the liquid circulating in the system will circulate in a closed circle and. therefore used for one purpose only. the transfer of heat to inhabited rooms. And when creating systems with an open loop heated water from the water supply can be used not only for heating but also for domestic purposes, such as washing.
Creating a horizontal solid fuel boiler from prefabricated elements
To create a simple solid fuel boiler for the heating system you can also use prefabricated elements. The picture shows such boiler, made on the basis of a metal barrel. At the initial stage, one of the covers is cut off from the barrel. Inside the barrel in the front of it is a combustion chamber, formed from thick metal sheets. The hot air after the combustion of fuel enters the heat exchange section located in the back of the boiler drum and then exits through the chimney system. In order to build such a boiler you need to have welding skills, in another way all the components of the boiler can not be connected.
Install such a boiler in the room can be installed on a base, laid out of bricks, or on metal supports.
Providing a continuous power supply to the boiler
The created in this way boiler can be upgraded by adding to it a continuous feeding system running on pellets. It is a container. hopper, in which pellets are poured from the top. In the lower part is mounted a screw device, familiar to us from the usual meat grinders, which has an electric power supply with stepped regulation of power. Rotating, the auger moves the pellets into the combustion chamber, while the speed of rotation of the auger controls the intensity of combustion of fuel, and therefore the temperature of heating.
Instructions for making it with your own hands
Pyrolysis boiler principle of operation
When assembling a self-made device, you should take into account. The enlarged afterburning chamber and the use of a shelf in it allow to reduce the number of tubes in the heat exchanger. On the top of the boiler it is necessary to provide hatches for cleaning the heat exchanger pipes. The water supply is connected in the upper part, the return is connected to the side in the lower part.
The chimney is welded on the side in the upper part. According to a previously prepared drawing make blanks for the body, the holes for the tubes of the heat exchanger can be cut with an electric jigsaw or an angle grinder. Then it is necessary to weld all metal parts of the device.
For the heat exchanger pipes you can use a pipe with a diameter of 76 cm, cut it into equal pieces and weld them to both sides of the unit. Next, weld the outer casing, attaching it to the inner part using spacers.
Cut openings for the afterburning chamber doors, for ash and for the charging chamber. The door for the stoking chamber can be made with two handles, which will provide a tighter fit. Seal the doors and handles of the direct draught flap with vitrified clay or asbestos rope.
The afterburning chamber and the bottom of the gasification chamber shall be made of fireclay bricks. Install a removable hatch for cleaning the chimney pan. Next you need to install a fan, an expansion vessel and connect the heating system.
Boiler connection diagram to the chimney
Connect an uninterrupted power supply for stable operation of the fan. Boiler body should be primed, covered with thermal insulation and a protective thermal shield. Such a unit can run on coal, wood, or any other solid fuel.
The fuel loading mechanism is of two types:
Boilers with automatic fuel supply have a main part and a special hopper, in which the fuel is loaded. As a rule, one load of coal, pallets or waste is enough for 3-5 days of continuous boiler operation. Automatic fuel supply is carried out with the help of an auger or piston. This system allows you to save a lot of fuel and spend less time on the heating process.
Manual loading. This is undoubtedly the traditional type of solid fuel equipment. This kind of loading assumes that the fuel will be loaded with your own hands. Such equipment can run on any type of fuel from coal to briquettes and toa.
In heating and industrial boilers of different capacities, there are several possible ways of feeding coal into the boiler, depending on its power and type of furnace. Feeding of coal into the boiler can be carried out in the following ways:
Manual feeding of coal into the boiler
This method of fuel supply is mostly used in coal-fired boiler-houses with installed small boilers, up to 0.8-1.0 MW, Energia, Universal, HP types, steel KVr boilers with manual grate furnace. Coal is delivered to the boiler room by the stoker on a cart from the fuel warehouse, poured in front of the boiler furnace and manually, using a shovel, is thrown into the furnace of the boiler. This is the most labor-intensive way to organize coal supply to the boiler, but at the same time it is the easiest, most reliable and cheapest.
Coal supply to the boiler by fuel conveyors
Feeding of fuel to the boiler by fuel conveyors is carried out in mechanized solid fuel boilers with mechanical furnaces of more than 1 MW. Conveyors can be belt type TL and scraper type LSU and TS.
The scraper conveyor belt transports coal through closed steel sections by gripping it with scrapers. It is assembled of separate, interconnecting sections of straight and rotary type. Using various combinations of sections, the conveyor belt moves the coal from the fuel bunker through the entire boiler house to the furnace bunker of each boiler.
The belt conveyor transports the coal in the same way, only the fuel moves with the moving flexible rubber belt.
Coal feeding into the SKIP boiler
Skip hoist is most often installed in modular boiler plants. Coal from the fuel bunker is poured into the skip bucket and lifted and discharged into the boiler fuel bunker. Each boiler house requires an individual SKIP.
Coal feeding into the boiler by a grab
The grabber is a bucket which takes the fuel with the help of a crane-beam moves it through the boiler room from the coal dump into the fuel bunkers.
Coal is fed to the boiler from the furnace hopper in mechanical furnaces
From the furnace bunker, the coal is also fed into the boiler by different means, depending on the type of fine-tuning device.
In the furnaces of HSPM the coal is fed into the boiler furnace when the sector feeder is opened and is moved to the grate with the help of a shuddering bar, which performs reciprocating motion. Opening of the sector feeder and moving of the spreader bar is controlled by the furnace automatics.
In TLPH furnaces the coal supply to the grate bed of the boiler is carried out by gravity, as the grate bed moves, the burning layer of fuel is shifted and fresh portions of coal are poured from the hopper. Coal supply to the boiler is regulated by manual handwheels and an adjustment plate.
In TLZM, THZM and WP RCK furnaces coal supply into the boiler is carried out with the help of a mechanical coal scraper ZP or PMZ. From the furnace hopper the spreader with the rotating rotor blades scatters the coal on the grate bed. Regulation of coal supply in such furnaces is carried out by the boiler automatics.
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Fuel for boilers of long combustion
Certain grades of soft coal with low slagging. Long flame coal with T fraction of 25 mm is preferable. At exhibitions, the work of automatic boilers for long combustion is demonstrated on this type of “black” fuel. In this case, you get a beautiful flame with big and long tongues.
However, as soon as a potential buyer tries to find out the brand of coal, company representatives assure that the boiler runs on Polish coal, which is called ECO-pea. And assure: the boiler on our coal will also work beautifully, and most importantly effectively and economically.
In practice, this is not the case:
- the boiler is bought and installed;
- they buy affordable coal on the local market without emphasis on its quality;
- And you do not get the expected fire “as at the exhibition”.
The explanation is simple. This boiler is not designed to work on any coal. In Poland, coal is sold in sorting bags, already sifted/sifted with an indication of the calorific value and the desired fraction, which is suitable for a particular type of boiler. “Sort” coal will cost more (by 20-30%) than what is sold on the local market. However, Polish coal burns with a bright flame, has a high efficiency and excellent calorific value.
Barin” coal boiler with automatic feeding
In the solid fuel boiler “Barin” the automatic feeding is organized in a slightly different way. Here, the hopper is located above the boiler, and the coal is pulled down by gravity into the combustion chamber. The system of breakers prevents it from drifting on the walls of the fuel reservoir.
After passing through the shaft connecting the furnace and the hopper, surrounded by a water jacket, the coal falls onto the water-filled grates, where it is burned. The design of the pit makes it possible to pre-dry the fuel, for more efficient combustion in the furnace of the boiler “Barin”. The hollow grates are filled with thermal fluid to both increase the heat transfer area and prevent the coal from sticking to their surface. Directly under these is the first compartment of the ash pan, in which mainly fine ash accumulates.
Picture 3: Automatic solid fuel boiler “Barin”
The burnt coal is pushed into the second compartment of the ash-pan with the help of the shurring mechanism. In the way of flue gases, still containing unburned particles of fuel, there is a chamber of secondary afterburning, lined with fireclay bricks. High-temperature afterburning of gases, after which they pass through a tubular heat exchanger system and are released into the environment through the chimney.
The boiler is controlled and monitored by an automatic control system. It keeps the combustion process at the required level, controls temperature and pressure, and performs many other functions. The task of the owner is just to set the required parameters once, and then only to add coal into the bunker and periodically clean the ash-pan.
In the table below some technical characteristics of the automatic boiler “Barin” are resulted:
| Hopper volume, m³ | 0.17 | 0.192 | 0.262 | 0.328 | 0.8 |
| EFFICIENCY FACTOR, % | 80 | 85 | |||
| Flow rate, kg/h | 5,1 | 8,5 | 10,4 | 13 | 20 |
| Price, | 98 500 | 155 000 | 175 000 | 185 000 | 290 000 |
in detail about the device, work, advantages and disadvantages of automatic heating boiler on coal “Barin” you can learn from a special review on our website kotlydlyadoma.dedicated to this model.
