The theoretical combustion temperature of coal is in the range of 1000 ... 2300 ° C and depends on a number of factors - combustion conditions, specific calorific value, moisture content and so on. Actual heating in the center of the flame burning in the furnace of the boiler or stove rarely exceeds 1200 degrees. But the owner of the home does not at all have the task of glowing the unit and the pipes white. The main goal is to effectively use the energy of a valuable mineral, getting the right amount of heat for a long period.
Types of coal used for heating
The formation of black fuel in the bowels takes from several hundred thousand to millions of years. The deeper and the ancient deposit, the higher the density and heat of combustion of the coal mass. The energy value of fuel depends on one indicator - the percentage of pure carbon in the composition of the fossil.
We list the types of coal burned in heating furnaces, in order of increasing calorie content:
- Brown coal contains up to 70% carbon. The remaining 30% are volatile substances (bound oxygen, nitrogen, hydrogen) and impurities - sulfur, iron, phosphorus, silicon and aluminum.
- Dense coal is 82% carbon, the rest is impurities and moisture.
- Anthracite is the oldest fuel containing up to 95% carbon.
Reference. This chain lacks the first and last link. First, biomass - plants and trees - forms low-calorie peat, which lies close to the surface and is suitable for briquette production. Natural graphite consisting of pure carbon completes the chain.
Coal solid fuel is divided into types and classes according to the physical properties and size of the fraction. Depending on the origin, the composition of coal varies, which affects its characteristics - ignition and burning temperature, calorific value and ash content. The table below shows the classification of fossil fuels by their volatile matter, moisture and ash content.
After mining, the coal mixture is calibrated - divided into fractions. The larger the pieces, the higher the energy price and the better the burning. We show in the next table how different and how coals of different sizes are designated.
Note. If in addition to the brand of fuel it is necessary to indicate the size of the fraction, the letter index is assigned to the main class designation. Example: GO - gas nut, AP - anthracite - stove. Marking a brown mixture of nuts and small things - BOM.
We do not rank charcoal as a general classification for several reasons:
- fuel is not fossil, it is a product of dry processing (distillation) of wood;
- the use of burnt coal for heating a house is economically unprofitable, it is cheaper to buy ordinary wood;
- This fuel is well suited for the operation of a blacksmith forge, gas generator or burning in a barbecue.
Flash point and other parameters
The process of burning coal is a chemical reaction of carbon oxidation that occurs at a high initial temperature with intense heat. Now it’s simpler: coal fuel cannot ignite like paper, for pre-heating it is necessary to pre-heat up to 370–700 ° С depending on the type of fuel.
Key moment. The efficiency of burning coal in a furnace or in a household solid fuel boiler is characterized not by the maximum temperature, but by the completeness of combustion. Each carbon molecule combines with two particles of oxygen in the air to form carbon dioxide, CO2. The process is reflected in the chemical formula.
If you limit the amount of incoming oxygen (cover the blower, put the TT boiler in smoldering mode), carbon monoxide, combustible CO gas is formed instead of CO2, which is emitted into the chimney, the combustion efficiency will be significantly reduced. To achieve high efficiency, it is necessary to provide favorable conditions:
- Brown coal ignites at a temperature of +370 ° C, stone - 470 ° C, anthracite - 700 degrees. Pre-heating of the heating unit with firewood (sawdust briquettes) is required.
- The air in the firebox is supplied in excess, the safety factor is 1.3-1.5.
- Combustion is supported by the high temperature of the hot layer of coal lying on the grate. It is important to ensure that oxygen passes through the entire thickness of the fuel, as air moves through the ash pan due to natural chimney draft.
Comment. The exceptions are home-made Bubafony stoves and cylindrical top-burning boilers, where air is supplied from top to bottom in the furnace.
The theoretical combustion temperature and specific heat transfer of various types of fuel are shown in the comparative table. It is noticeable that under ideal conditions, any fuel will release a maximum of heat when interacting with the desired amount of air.
In practice, creating such conditions is unrealistic, so air is supplied with some excess. The actual burning temperature of brown coal in a conventional TT boiler lies within 700 ... 800 ° C, of rock and anthracite - 800 ... 1100 degrees.
If you go too far with the amount of oxygen, energy will begin to be spent on heating the air and simply fly out into the pipe, the efficiency of the furnace will drop noticeably. Moreover, the temperature of the fire can reach 1500 ° C. The process resembles an ordinary fire - the flame is large, there is little heat. An example of efficient burning of coal with a retort burner on an automatic boiler is presented in the video:
Coal heating - practical tips
The full burning of coal fuel requires a special approach to the issue. The task is to achieve maximum efficiency of the heat source, not to overheat the coolant and not to cause a fire due to too high a temperature.
We offer to consider our recommendations for the selection of equipment:
- Purely wood-fired boilers and factory-made steel stoves are undesirable to be heated with high-calorie coals - stone and anthracite. Powerful heat transfer and strong heating can deform the walls of the firebox (usually they are made with a thickness of 3 mm).
- For coal heating, TT boilers with water-filled grate are not suitable. Due to the temperature difference, the red-hot sinter layer sticks tightly to the pipes with water, air passage and further cleaning of the unit is very difficult.
- If you have calibrated hard coal with a grain size of 25–50 mm (walnut classification), the best choice is a boiler with automatic fuel supply. The unit is equipped with a retort burner and a fan, which accurately dispenses air injection at the command of the electronics. Duration of continuous work - up to 7 days.
- The ideal option is to buy a mine or a traditional boiler, designed for the use of coal. In the heat generator there are movable grates, rotated by an external handle. The device helps to dump ash from the furnace into the lower chamber.
- Heaters equipped with a fan or smoke exhaust are more convenient and safer than boilers with mechanical controls on the chain. With a critical increase in temperature, the automation will turn off the air supply and the channel will be closed by a damper. The usual blower cover does not fit snugly, oxygen seeps into the chamber, and slow combustion continues.
- Coal burning an open fireplace is useless. You won’t get much heat, just dilute the dirt in the room and an unpleasant odor will appear.
- In order to increase safety, it is very advisable to install an additional heat release valve on the boiler.In case of overheating and boiling, the element dumps part of the coolant from the boiler jacket and at the same time fills it with cold tap water.
Every type of coal needs to be adapted. It is better to fill in unfamiliar fuel in small portions, adjusting the draft with a gate and observing the temperature increase. When calculate all the burning nuances of this brand, fill the firebox by 2/3.
An important point regarding the operation of a brick stove with a stove. In no case do not open the burners after loading a new portion of coal, use the side door. With a lack of oxygen, fuel emits pyrolysis gas, which will escape through the removed burner.
Lastly about burning coal dust
The fine fraction remaining from raw coal is also a full fuel. The problem is loading - most of the dust immediately wakes up in the ash pan. If you load it on top of firewood, the access of oxygen is blocked, and burning deteriorates. In such cases, you can apply 3 methods:
- Dedovsky. Coal dust is mixed with water, cakes are made and dried in the sun.
- Briquetting If you have a lot of dust, it makes sense to make or order a screw press for forming coal briquettes at home.
- Add to the fine fraction of water and load into the firebox in old plastic bags.