Solid fuel boilers are a source of air pollutant emissions. The combustion of 100 tons of coal from the Donets Basin (for heating a typical school building) releases a large amount of toxic chemicals into the atmosphere, including:
- 4,000 - 7,000 kg of solid ash particles (sulfates, nitrates, ammonia, sodium chloride, carbon);
- 5040 kg of sulfur oxides (SO2, SO3);
- 220-250 kg of nitrogen oxides (NOx);
- 20-40 kg of carbon monoxide (CO).
Pollutants produced by coal combustion can cause a variety of human health problems, including:
- Cardiovascular problems;
- Respiratory ailments, such as asthma, bronchitis, otitis media; lower respiratory tract infections;
- Chronic lung diseases in children;
- Lung cancer in women and low birth weight in newborns;
- Urinary tract cancer.
Emissions from burning coal are particularly dangerous for young children under the age of 12 whose immune system does not generate an adequate response to these pollutants.
Levels of emissions largely depend on the boiler efficiency, the temperature of combustion and the temperature of the flue gases leaving the combustion zone. The efficiency of any boiler is calculated by the following formula:
q1 + q2 + q3 + q4 + q5 = 100%, where:
q1 = thermal energy transferred to the heat carrier fluid circulating in the heating system;
q2 = heat loss due to excess air, which should be no more than 10-15%;
q3 = heat loss as a result of chemical underburning due to a low percentage of excess air (must be no less than 20-30%);
q4= heat loss due to mechanical underburning of fuel;
q5 = heat loss to the environment, heat loss due to a high temperature of the flue gases.
We can offer two possible ways to modernize existing coal-fired boilers:
Option 1. Increasing boiler efficiency by controlling the volume of air. Installing a forced draft fan with a control system and a cyclone to catch unburned coal particles (ash).
Option 2. Improving boiler efficiency by reuse of the flue gas temperature. Installing economizers to remove valuable thermal energy from the flue gas.
Figure 2 shows an economizer connected to a solid fuel boiler.
Figure 3. Circulation Boiler