Many companies need to generate heat to meet the requirements of their production systems. This heat is produced in the form of liquid fluid or steam through combustion boilers using different fuels such as diesel oil or natural gas.
The efficiency of a heat-generating unit (boiler, furnace or dryer) indicates the percentage of useful power that is effectively used in the production process compared to the total power supplied by the fuel consumed.
This efficiency decreases due to various heat losses during the transfer of heat from the boiler to the point of use, along with other factors that must be monitored in order to achieve the highest possible performance while minimising energy costs related to fuel consumption.
Energy Saving and Efficiency Measures
Combustion control (Savings of up to 6%)
Boiler combustion should be optimised in order to release the maximum amount of energy from the fuel. To achieve this, an analysis of the flue gases emitted through the boiler chimney should be carried out.
The most determining factor for proper combustion is the excess air level, which must be adjusted until complete combustion is achieved.
Depending on the flue gas analysis, if efficiency is low, the boiler combustion chamber should be cleaned of ash and unburned residues, and the airflow supplied to the burner should be adjusted.
Minimisation of blowdown in steam boilers (Savings of around 1%)
Steam boilers must be periodically blown down in order to keep the concentration of dissolved solids (carbonates dissolved in the water) within acceptable limits. These solids increase as steam is generated.
Blowdown should be kept to the minimum necessary level, as excessive blowdown leads to higher water consumption and, consequently, greater energy losses.
There are different methods for calculating the optimal blowdown rate depending on factors such as boiler type, operating pressure, and water treatment and quality.
Recovery of residual heat from exhaust gases (Savings between 5% and 20%)
The flue gases released after combustion have a very high temperature (above 200 °C), which in some cases can be utilised to preheat combustion air through a heat recovery unit, or to preheat feedwater by means of an economiser.
Both measures contribute to improving overall equipment efficiency.
Minimising heat losses through walls (Savings above 2%)
All heat generated during combustion should be directed to the production process; therefore, heat losses through furnace walls or piping must be minimised by ensuring proper insulation.
A thermographic analysis should be carried out to assess whether the insulation condition is adequate or deficient.
Reinjection of condensate in steam boilers (Savings above 5%)
Condensed steam generated during the process should be returned to the boiler in order to reuse the residual heat it still contains, thereby reducing the thermal energy required to generate new steam.
Fuel switching (Savings between 10% and 40%)
Switching to a cheaper fuel is not strictly an energy efficiency measure, but rather an economic one. For example, as of January 2012, fuel prices ranked from lowest to highest cost for the same energy input were: biomass, natural gas, diesel oil, propane and electricity.
