Technical specifications of the solid fuel boiler

Efficiency coefficient (EC) of a solid fuel boiler [%] - is determined as the ratio of the amount of heat transferred to the water to the amount of heat obtained during fuel combustion. The efficiency of the boiler is an indicator of its effectiveness and shows the degree of perfection of its design.

The efficiency coefficient of a steel solid fuel boiler is 75-80%, and for a coal boiler with a smaller heat exchange surface area - 67-75%.

The passport indicates the efficiency coefficient of the boiler obtained under optimal conditions: the combustion chamber and heat exchange surfaces are clean, the optimal amount of air is supplied for combustion, and the temperature regime of the water circuit is not less than 65°C at the inlet and 90°C at the outlet.

Factors that reduce the efficiency coefficient of a solid fuel boiler:

1 Excessive or insufficient air supply to the boiler combustion chamber. It is considered that the optimal excess air coefficient in the combustion chamber is 1.3, which means that 30% more air than necessary for fuel combustion should be supplied to the combustion chamber. Exceeding this coefficient will lead to excessive air supply and loss of useful energy for its heating, and reducing the coefficient will lead to incomplete fuel combustion in the combustion chamber. With optimal air supply, the flame should have a straw color.

2 Scale on the heat exchange surfaces on the side of the heated water and soot on the side of the combustion chamber. Therefore, it is essential to prepare the feed water and periodically clean the heat exchange surfaces of the boiler.

3 Incomplete fuel combustion due to uneven burning, falling through the grate, or burning with insufficient oxygen, which leads to excessive soot formation.

4 High heat losses from the boiler casing to the surrounding environment. This factor is influenced only by the quality and thickness of the insulation material placed between the heat exchange surfaces.

Nominal thermal power of a solid fuel boiler [kW] - the amount of heat generated by the boiler in one hour when burning the main type of fuel, for solid fuel boilers - anthracite coal.

The power values specified in the technical characteristics are obtained when burning anthracite during the time of one load combustion at maximum power. For example, if the time of one load combustion is 4 hours, then in the first and last hour of operation, the boiler can provide 80% of its power, and for two hours, work with a power of 120%, while the nominal power equal to 100% is indicated in the technical characteristics.

The power of the boiler depends very much on the type of fuel used. Therefore, if other types of fuel are planned to be used during the operation of the boiler, different from the main one, then correction factors relative to anthracite coal should be applied when calculating the required power of the boiler:

0.95 - bituminous coal
0.85 - brown coal
0.80 - peat briquettes
0.80 - dry wood (two years of drying, moisture 15-20%)
0.30 - raw firewood (humidity 70-80%)

Minimum water temperature at the boiler inlet [°C] - the minimum water temperature at which steam from the flue gases does not condense on the heat exchange surfaces.

The combustion products are a dangerous corrosive environment for a solid fuel boiler. During operation, working with water temperature below 65°C at the inlet should be avoided, except for the short firing phase.

The cast iron boiler heat exchange surfaces are more resistant to corrosion, allowing for a water inlet temperature of 55°C, while for steel boilers, the inlet temperature should not be lower than 65°C.

For more information on protecting solid fuel boilers from low temperatures, see the section on connection schemes for solid fuel boilers.

Nominal water pressure in the boiler [MPa] - the maximum excess water pressure at which safe and long-term operation of the solid fuel boiler is ensured.

When connecting the boiler to a heating system with a closed expansion tank, the system pressure rises during heating. At maximum temperature mode, the pressure in the boiler should not exceed the nominal value.

The working water pressure in the boiler circuit should be at least 1 bar and not exceed the pressure specified in the boiler passport.

The boiler test pressure is usually not less than 1.25 times the nominal pressure.

Draft pressure difference in the flue gas duct at the boiler connection point [Pa] - the draught in the flue pipe. Supply of air to the furnace is possible only at a pressure in the flue pipe below atmospheric pressure.

The pressure difference in the flue pipe is determined by the difference in density of the hot gases inside the flue pipe and the cooler air outside.

The minimum pressure difference in the flue gas duct shows how much pressure in the flue pipe at the boiler connection point should be below atmospheric. The excess pressure difference is regulated by a damper installed at the flue gas outlet of the boiler.

Temperature of the flue gases [°C] in a solid fuel boiler depends on the operating mode and type of fuel. Under normal conditions, the temperature can vary from 150°C at minimum power to 280°C at nominal loads. With a disturbed draft, the temperature of the exhaust gases can vary in the range from 70 to 600°C.

Burning time of a single fuel load [hours] - for solid fuel boilers operating at nominal power, it is no more than 4 hours when burning coal or coke, and no more than 2 hours when burning firewood.

When operating at lower power, the burning time can be increased by no more than 2-3 times, but this significantly reduces the boiler efficiency, and the low power mode does not contribute to long-term boiler operation.

Remember! The optimal operating mode for a solid fuel boiler is operation at nominal power.