What are the factors that affect boiler thermal efficiency?

Factors that affect boiler thermal efficiency can be categorized into several main groups. Here is a clear and structured list of these factors:

1. Combustion Efficiency:
   • Chemical Incomplete Combustion: The more severe the chemical incomplete combustion is, the lower the boiler's thermal efficiency. This relates to the amount of unburned fuel in the exhaust gases.
   • Mechanical Incomplete Combustion: Similarly, the more severe the mechanical incomplete combustion (i.e., the more particulate matter in the smoke), the lower the thermal efficiency.
2. Heat Losses:
   • Exhaust Gas Temperature (Flue Gas Losses): Higher exhaust gas temperatures result in lower thermal efficiency. This loss is due to the heat carried away by the flue gases.
   • Radiation and Convection Losses (Heat Dissipation): Stronger heat dissipation through the boiler walls leads to lower thermal efficiency. Boilers with lower heat dissipation properties are preferred.
   • Ash and Slag Physical Heat Losses: Ash and slag carrying heat away from the combustion chamber can also contribute to heat losses.
3. Operational Parameters:
   • Excess Air Coefficient: A higher excess air coefficient (the ratio of actual air supplied to the theoretical air required for complete combustion) results in lower thermal efficiency. Excess air leads to increased heat losses through the exhaust gases.
   • Use of Heat: The way, time, and temperature of heat utilization also impact the boiler's thermal efficiency.
4. Maintenance and Design:
   • Leakage and Deposits: Leakage of air and deposits on the heat transfer surfaces (such as ash and slag) can reduce the boiler's thermal efficiency.
   • Boiler Design: The overall design and efficiency of the boiler system, including its insulation, heat exchangers, and combustion chamber, play a role in determining its thermal efficiency.

To improve boiler thermal efficiency, measures such as ensuring complete combustion, maintaining appropriate excess air coefficients, reducing heat losses through insulation and efficient heat transfer surfaces, and regular maintenance to minimize leakage and deposits can be taken.