high fire
High fire is the maximum combustion rate the burner is designed for. It represents the maximum fuel input and heat output at which the burner can safely operate in a specific application.
small fire
Low fire is the minimum amount of fuel input required to keep the burner from flameout. This is similar to a car: if the vehicle takes less gasoline while idling, the engine will stall.
modulation
Burner trim is used to vary the gas input and thus the heat output of the process to match heat load requirements and maintain the desired temperature. The modulating control adjusts the burner in a continuously variable manner between high and low fire,
Regulation ratio
The turndown ratio is defined as the ratio of the maximum fuel input rate to the minimum fuel input rate of the regulated burner. It is used to help determine how low the boiler can be adjusted before shutting off. For example, a gas burner might have a turndown ratio of 5:1. This means the burner can be modulated to less than 20% of its full rated input.
port loading
The term "port load" refers to the amount of gas-air mixture that passes through the burner to produce a stable flame. Burner port loading is expressed as Btu per square inch of port area. Port loading can be changed by changing orifice size or gas pressure (manifold pressure). For most applications using natural gas, port loads between 25,000 Btu and 30,000 Btu per square inch of port area provide a stable flame.
Burner type
Depending on how the combustion air is supplied, gas burners can be mechanical or non-mechanical. Burner classification can be very confusing as there is no standard definition, the following represents some of the more common industry terms.
non-mechanical burner
Non-mechanical or "atmospheric burners" rely on atmospheric pressure to supply the required combustion air. The atmospheric burner has a venturi that draws primary air into the burner and mixes the air and gas before ignition