How and what kind of coal is better to fire a solid fuel boiler

Selecting the proper coal for your solid fuel boiler is an important choice that can have a big impact on the comfort and heating efficiency of your house. With so many different kinds of coal on the market, it’s critical to know the differences and choose the kind that best meets your needs.

For centuries, people have used coal as a fuel source to heat their homes because it is dependable and reasonably priced. But not every coal is made equally. The kind of coal you select can have an impact on heat production, combustion efficiency, and even the environment. Therefore, before choosing, it’s critical to understand the traits of various coal varieties.

The calorific value of the coal, or how much heat it can produce when burned, is one of the most important factors to take into account when choosing coal for your solid fuel boiler. Coals with a higher calorific value generally produce more heat per unit of weight, which improves heating efficiency and may require less fuel.

The amount of ash in the coal is another important consideration. Ash is the residue that remains after coals burn. Lower ash content coals tend to produce less waste and require ash removal less frequently, which makes boiler maintenance easier and cleaner.

Moreover, coal’s burning properties can be greatly influenced by its moisture content. Coal that is wet or has a high moisture content may burn less effectively, producing less heat and possibly more emissions. Consequently, choosing coal with the ideal moisture content is crucial to getting the most out of your solid fuel boiler.

What kind of coal is better to heat a solid fuel boiler?

Following the official recommendations of the manufacturer listed in the boiler’s data sheet (instruction) is worthwhile in order to maximize the boiler’s efficiency, or the best ratio of fuel volume consumed to heat generated, and to prolong its lifespan.

Stone, brown, wood or anthracite: which one to choose

Coal is an organic sedimentary rock that is combustible and is made up of carbon and other residual elements, or impurities.

In Russia, natural coal falls into three primary categories as a valuable energy resource (unified classification per GOST 25543-88):

• brown (sub-bituminous) – the most widespread and cheapest coal with an earthy structure, has a dark brown or black color, burns quickly (smoky flame), emitting an unpleasant smell of burning and a lot of waste;
• stone (bituminous) – hard metallic-black or tar-black coal, contains a small amount of mineral and volatile substances, is characterized by a fairly high calorific value and an acceptable price;
• anthracite – very ancient and expensive coal, it is determined by its gray-black color with metallic or glassy luster, it takes a long time to ignite, but then it burns easily (without smoke and fire, it does not sinter) with increased heat output.

Consumer attributes of various natural coal grades:

Combined grades with intermediate markings, such as DG (long-flame gas coal) and OS (cleaned sintering), are also available for purchase.

The best type, according to the conclusion, is anthracite because it has the highest calorific value. It is best to purchase it exclusively for high-energy fuel boilers, though. The key point is that anthracite reaches its maximum when combustion temperature rises to extremely high levels (2200–2300 °C), which is beyond the capacity of most boilers. In any event, unprofitable: you’ll have to pay too much for inefficient boiler or take a chance on it.

Although less calorific varieties are intended for use in classic boilers (particularly those with steel furnaces), they still extract the maximum amount of useful energy from them.

Hard coal with a long flame is a reasonably adaptable fuel. It emits a lot of heat energy due to the high content of volatile substances, is practically non-sinterable, and is simple to ignite. However, this type is not quite appropriate for long-burning pyrolysis type boilers due to the moisture content.

Because pyrolysis technology significantly lowers the temperature of gases at the chimney outlet, burning raw fuel may cause condensate to build up and create a sticky, difficult-to-remove scale. It is advised to use gas (G or DG) coal to fuel these boilers in order to prevent this.

Overview. It should be kept in mind that only non-toxic coal with a sulfur content of no more than 2% is suitable for use in domestic settings, regardless of the grade selected. If not, an excessive amount of sulfur dioxide gas (SO2) will be released during combustion, contaminating the air and eroding metal surfaces.

Charcoal can be a good environmentally friendly alternative to regular coal because it has a material composition similar to firewood and contains no sulfur (0.03-0.05%).

Charcoal is a high-carbon, flammable substance that is made by distilling wood that has little oxygen.

Since charcoal is not a naturally occurring fossil, it belongs to a separate fuel group that, in accordance with GOST 7657-84, consists of three types:

• A – coal from birch, beech, ash, hornbeam, hornbeam, elm (elm, birch bark), oak and maple;
• B – charcoal from aspen, alder, linden, poplar and willow, A may be added;
• B – coal from pine, spruce, fir, larch, it is possible to add A and B.

Customer who possesses varying grades of wood charcoal:

* In certain circumstances, it is permissible to increase the moisture content of coal of grades B and C to 15–25%, given that the actual mass of the fuel is recalculated to account for the extra 5–6% of moisture content.

The best charcoal to use for boiler firing is hardwood, type A. It is visually easy to distinguish: it looks like stone because of its blue-black color and obvious glossy cast, but if you break the edge, you can see the fibrous structure.

Compared to fossil fuels, wood fuel burns longer and distributes heat more evenly while emitting little to no smoke or odor. However, the high cost of production—one ton of product requires eight to twelve meters of firewood—affects the price and poses a serious drawback for a lot of people.

An estimate of the cost for various grades of natural and charcoal

Purchasing wood fuel is roughly two to three times more expensive than even reasonably priced anthracite. Thus, if this kind of decision still needs to be made, you can attempt to lower your heating expenses by starting a small-scale home business, which is particularly successful when there is inexpensive firewood available.

Application for burning charcoal briquettes

Briquettes of coal: Partially burned coal that is formed by pressing the tiniest coal fractions (dust, chips).

Briquettes are advantageous to use because they burn for a long time, are simple to ignite, and take up less room in the furnace because of their compact shape. However, the heat energy output is not less than that of anthracite. The price is the only real drawback; it is 25–35% more expensive than bulk material.

Installing a set of automatics can help solid fuel boilers operate more efficiently and economically.

How to heat with coal dust?

It’s challenging to stoke with coal dust because the dust typically either turns to ash or sinters into stone. In this case, a unique method is required:

• a special burner – will allow to create a homogeneous dust-air mass, which under pressure will be dosed into the combustion zone;
• home version of briquettes – the formation of whole pieces will ensure easy sintering, dust will not concentrate in the air and fall into the ashtray.

Both pure dust and a mixture of sawdust are used to make these handcrafted bars. For the first version, the dust is simply moistened to the consistency of lumpy dough and frozen in molds; for the second, coal and wood waste are mixed 50/50, water is added, and roughly equal blanks are molded before being dried.

It is preferable to light a solid fuel boiler after the wood has burned for 15 to 20 minutes using pre-made briquettes. Then, as is customary, the briquettes are positioned in the middle of the furnace, the fan can be turned on during the ignition process, and the draught is opened to the maximum, and you are left to wait for the water to heat up to 85 to 90 degrees Celsius.

Reference: It is officially forbidden to use furnace dust without installing a special burner coal boiler. These are sensible safety precautions because flammable particles can start to build up in suspension in environments with restricted air flow, and at a certain concentration, this can cause an explosion.

Coarseness classes (fractions) of fuel

Classifications of natural coal’s coarseness (fractions) based on GOST 19242-73:

Following the grade designation, the class letter is assigned: brown fine, or BM, and lean coarse, or TK. Several letters are used to indicate different coal classes when mixing them by fraction: long-flame nut with fines and pith (DOMSH), anthracite fist with fines (AKM).

Coal (DK, GK, and DKO) is used to heat standard boilers; however, only fine fraction (DOM, GOM, AOM, and t. д) can be used in automatic boilers.

How to properly fire a boiler with coal: instructions on how to ensure a long burning time

Prior to operating the boiler, it is essential to examine it for damage and cracks, measure the intensity of the draft, and ensure that the electronic components are functioning properly after connecting it to the network. It is then advised to clean and dry the combustion chamber and ash pan, and to begin heating the boiler with coal.

According to experts, boilers should be fired using a fuel that is more flammable but has a lower efficiency before gradually adding coal over the course of two runs:

1. Put crumpled paper on the grate, place wood chips or kindling on top of it.
2. Close the furnace door, evenly light paper and other things from all sides.
3. Open the ash pan shutter and wait for the fine fuel to ignite.
4. Pour fine coal directly over the flame in a thin layer of 10-15 cm.
5. After 15-30 minutes, put coarse coal up to the upper edge of the door.
6. leave the under-blower half ajar (only a slit if it smokes).

By adding fuel on a regular basis, you can now enjoy a comfortable temperature in the room. The ash pan shutter needs to be closed before refueling.

As you can see, starting the boiler is simple. However, to ensure that it burns for an extended period of time, doesn’t use "extra" coal, and is generally efficient, you will need to manage its operation:

• Ruffle the burned coal before storing it again to prevent mass sintering, and if the crust has already formed – break it with a poker;
• dilute insufficiently calorific (low quality) fuel with small layers of wood to prevent the layers of coal from coking each other;
• Organize the thermal insulation of the house and install a thermostat in each room, which will avoid boiler recycling and save up to 20-25% of coal in the end;
• to ignite the paper use the power of natural air circulation, even if the automatics controls the blowing (so the chimney will have time to warm up);
• completely clean the chimney and all internal components at least 2 times a year, otherwise in a few years the accumulation of soot will lead to a drop in efficiency by 25-30%.

Citation. In order to maximize resource efficiency, frugal owners sort their ash waste using a metal grate measuring 5 to 6 mm. Any large pieces of coal that remain after burning are returned to the boiler along with a fresh batch of coal. As a result, fuel consumption is typically decreased by 10% to 15%.

What to do if the coal in the boiler burns badly?

Although there are many reasons why coal burns poorly or does not burn at all, the following are some of the more frequent ones:

• draught reduction due to clogging of the chimney and grate;
• use of unsuitable grade or simply low-quality coal;
• too large boiler output, which does not correspond to the area of the house;
• loading of a large volume of coarse coal, without preliminary stoking;
• Failure of the automatic forced air supply system;
• breach of structural integrity (flame often goes out + smoke).

The latter options will necessitate the services of a boiler repair specialist; however, the remaining faults can be resolved with appropriate operation and cleaning.

Consumption rates and rules for calculating the required volume of fuel

Technical standards state that 2 kg of coal is needed to produce 10 kW of heat energy. With this information, the following formula can be used to determine the required volume:

Μ ̅=X/fuel heating capacity (5 kW/kg in this example)

• where М _х – fuel consumption for a limited period of time (day, month, season);
• Х – heat losses during the heating period, determined by the formula:

X = S×D×24×0,7×70

• where S – heated area of the house, including all living and domestic premises;
• D – duration (number of days) of the heating period;
• 24 – the burning time (number of hours) of the boiler per day;
• 0,7 – The average efficiency of coal-fired boilers;
• 70 – average heat loss per hour (for a standard house in a temperate climate).

Using an area of 100 m 2 and an average heating period of 6 months (175 days), we can calculate the heat loss as follows: X = 100×175×24×0,7×70 = 20 580 kW per season, or 117 kW per day. For the same duration, the coal consumption will be M1 = 20,580/5 = 4,116 kg and M2 = 177/5 = 23 kg, meaning that approximately 4.5 tons of coal will need to be bought.

Aid. Primitively, you can follow the "live" experience of other coal boiler owners: one bucket of fuel burns for every degree Celsius that the outside temperature rises above + 1 °C per day; two to three buckets are needed for every degree Celsius that the outside temperature falls below -15 °C; and in particularly icy winters, 20 °C or lower requires loading up to ten buckets* per day.

* An average hard coal bucket (12 liters) can hold approximately 18 kg of coal.

Selecting the appropriate kind of coal for your solid fuel boiler is essential for effective heating and reducing the negative effects on the environment. The composition, burning qualities, and suitability of various types of coal for use in boilers differ. Making an informed choice can be aided by your understanding of these distinctions.

First, think about the coal’s quality. Anthracite, a high-quality coal, burns cleaner and generates less ash when burned than bituminous coal, a low-quality coal. Anthracite is the best fuel for boilers because it burns hotter and longer. However, because bituminous coal has a higher ash content, it might need to be cleaned more frequently.

Next, determine which types of coal are available and how much they cost in your area. Despite its high efficiency, anthracite can be more expensive and harder to find in some places. Despite being more widely available and less expensive, bituminous coal may need more upkeep and emit more pollutants.

The environment should be taken into account when selecting coal for your boiler. Particulate matter and sulfur dioxide are two of the many pollutants released into the atmosphere during the burning of coal. Mitigating the environmental impact can be achieved by selecting coal varieties that burn cleaner and by putting in place appropriate emission control measures.

Last but not least, when choosing coal for your solid fuel boiler, seek professional advice or go by the manufacturer’s recommendations. They can offer insightful information based on the features of your boiler, the amount of heat you need, and regional laws. To guarantee effective operation and increase the boiler’s lifespan, regular maintenance and appropriate coal selection are crucial.

Selecting the appropriate kind of coal for your solid fuel boiler is essential for effective heating and reducing the negative effects on the environment. The way that different coals burn has an impact on emissions and heat output. Anthracite coal is perfect for long-lasting warmth with little ash buildup because it burns cleanly and consistently produces heat. Although bituminous coal is less expensive, it can produce more ash and smoke, necessitating more frequent cleaning. You can make an informed choice for heating your home that strikes a balance between cost-effectiveness, efficiency, and environmental responsibility by being aware of the characteristics of each type of coal and taking local regulations, availability, and cost into account.

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