CO emissions of fuel oil boilers used in domestic heating

To assess the CO emissions of fuel oil boilers, tests have been performed on a boiler in transient and steady state regimes. The tests were performed so that the output power (about 370 kW) was kept constant in steady state regime (same water flow rate and inlet and outlet temperatures). On the other hand, the oxygen content of the flue gas in the chimney was kept
constant (around 3%). Classical gas analysers were used to measure the CO2, O2, CO and NOx
concentrations in the flue gas.
The two main parameters investigated are the nozzle capacity and the corresponding fuel
injection pressure to keep the same burner consumption. Four nozzles whose capacity ranges
from 30 to 45 kg/h (at a fuel supply pressure of 20 bar) were fitted on the burner equipping
the fuel oil boiler. All the nozzles used are spill return and 45° spray angle type.
The tests performed showed that in steady-state regime, the CO emissions are very low
compared to the limits established by the European standard (110 mg/kWh of energy
consumption). A comparison with calculated CO emissions shows also that the values
obtained in equilibrium conditions are too high. On the other hand, in the transient regime
(start-up regime for a cycling boiler), the CO emissions are not negligible and increase
significantly if a high capacity nozzle is fitted on the fuel oil burner.
In short, the paper demonstrates that in order to increase the boiler thermal efficiency and thus
to reduce CO2 emissions (for the same output power), one has to avoid the CO emissions in
the transient regime. When performing a replacement of the burner nozzle, a low capacity
nozzle associated with an adjustment of a high fuel injection pressure is recommended, since
a reduction of CO emissions in the starting-up regime is achieved and, on the other hand, the
thermal efficiency and the pollutants emissions of the fuel oil boiler in steady state regime are
not affected.