This is a review of our analytical and experimental studies on flame sensing, efficiency improvement and control, and flue emission. In addition, we report on new insights gained by an analysis of flue gas enthalpies dependence on firing rate and flue gas volume, and how this was used to predict and verify efficiencies of boilers fired with different fuels. Other results:

-- Geiger-Müller-type UV tubes can detect the UV emission of flames of hydrocarbons, CO, H2, methanol, and sulfur with air, in addition to H2-Cl2 flames.
-- Low or medium Btu fuel gases may lead to boiler efficiencies that are not at all low. For example, CO is more “efficient” than CH4 or H2 on both lower or higher heating value bases.
-- Using cold outdoor air for combustion leads to lower boiler efficiencies.
-- The influence on NOx generation of over 10 different parameters on one combustor is analyzed.

In addition to reporting on spectral flame measurements, the effects of reducing firing rate or steam pressure setting, and emulsifying fuel-oil with water on efficiency are discussed.